More Quantum Strangeness: Particles Separated From Their Properties

Dupple sends word of new quantum mechanical research in which a neutron is sent along a different path from one of its characteristics. First, a neutron beam is split into two parts in a neutron interferometer. Then the spins of the two beams are shifted into different directions: The upper neutron beam has a spin parallel to the neutrons’ trajectory, the spin of the lower beam points into the opposite direction. After the two beams have been recombined, only those neutrons are chosen which have a spin parallel to their direction of motion. All the others are just ignored. ... These neutrons, which are found to have a spin parallel to its direction of motion, must clearly have travelled along the upper path — only there do the neutrons have this spin state. This can be shown in the experiment. If the lower beam is sent through a filter which absorbs some of the neutrons, then the number of the neutrons with spin parallel to their trajectory stays the same. If the upper beam is sent through a filter, than the number of these neutrons is reduced.

Things get tricky when the system is used to measure where the neutron spin is located: the spin can be slightly changed using a magnetic field. When the two beams are recombined appropriately, they can amplify or cancel each other. This is exactly what can be seen in the measurement, if the magnetic field is applied at the lower beam – but that is the path which the neutrons considered in the experiment are actually never supposed to take. A magnetic field applied to the upper beam, on the other hand, does not have any effect.

Comments

Quantum mechanics is real, like it or not.

[Animats]

That's a nice result. It's in accord with theory. It doesn't match human intuition based on large-scale objects, but it's the way the universe really works. The theory in this area is well understood; Feynman's "QED" has a good overview.

Ever since the double-slit experiment, it's been clear that this stuff is real. Over the last few decades, more of the weirder predictions of quantum electrodynamic theory have been confirmed experimentally. This is another predicted event confirmed. Nice work.

Re:Quantum mechanics is real, like it or not.

[geekoid]

"but it's the way the universe really works. "
at the quantum level. The macro universe is also how the universe really works.

Re:Quantum mechanics is real, like it or not.

[Beck_Neard]

It's the way the Universe works at every level, as far as we know. It doesn't just apply to atoms and electrons, but to rocks, people, and planets. Quantum effects occur at the macroscale. Two important examples are lasers and superfluids.

I know some people are going to say, "But doesn't relativity take over at the scale of galaxies and such? And isn't relativity incompatible with QM" And the answer is: no, they definitely aren't incompatible. In fact most proposals for unified theories have been based on quantizing gravity. It's just that the naive way of combining these two theories (modelling gravity as a traditional QFT) doesn't work.

Re:Quantum mechanics is real, like it or not.

[Anonymous Coward]

This comment is worthless. Are you suggesting some fundamental disagreement between QM and "macroscopic" reality? Because you're mistaken unless you're talking about the very subtle issues surrounding the convergence of a very complicated sum related to the inclusion of general relativistic effects into QFT. If that's your concern, you REALLY have not added anything to that very complicated subject.

If on the other hand, you think there is some "fundamental" disagreement with your popular science understanding of "Schrodinger's cat" or "many worlds," let me assure you that you need to have at least an undergraduate level understanding of quantum information theory before you should jump into this 80-year-old debate.

As a third option, you might be arguing that QM leads precisely to classical mechanics in the appropriate limit. This is indeed true. Quantum is how the world works, at both the macroscopic and microscopic scale. Somehow that's not what you said, though.

Re:Quantum mechanics is real, like it or not.

[bill_mcgonigle]

The macro universe is also how the universe really works.

Only when it doesn't disagree with the quantum result.

People used to think that the Earth was the center of the universe, then some allowed that maybe the Sun might be the center of the universe, but really it was always about, and still is, the "me" being the center of the universe.

The approximations of reality that we sense with our ape-minds is really useful, but far from anything True(tm) or objective. What we feel to be "intuitive" is just a collection of rubrics that happen to work well to keep higher order animals alive. That we can even explore QED is a freaking miracle.

"Oh, but those entangled particles must be separate entities because they look like they are separate in our perception of space" is one of those. "But I have a ruler!"

Re:Quantum mechanics is real, like it or not.

[Anonymous Coward]

The macro universe is also how the universe really works.

At the human scale, "macro" is a subset of quantum mechanics, in the same way that Newtonian mechanics is a subset of GR in the boring limit of conditions. Quantum mechanics can reproduce classical physics on the larger scale. On the cosmological scale, there are some open questions, and there are things that GR predicts that might conflict with quantum mechanics, but typically strong field examples in GR aren't things we can directly observe yet.

Re:Quantum mechanics is real, like it or not.

[kakaburra]

It's in accord with theory.

Care to explain how? AFAICS this is a new phenomenon.

Re:Quantum mechanics is real, like it or not.

[Anonymous Coward]

"Oh, but those entangled particles must be separate entities because they look like they are separate in our perception of space"

You know that's exactly what science is about. Everything we have known about entities have told us one entity is at one place in space. If it is in two separate places it's two separate entities. Now if some experiment shows this might not be the case it's a "strange" result. Even when in this case I believe it was the expected result. This is actually easier to "get" than many much more mundane things where "common sense" goes agains reseched results. Take an average person and start flipping a coin. Wait until you have flipped, say 5 heads in a row. Now ask if the next one will be heads or tails. Your average person will be almost sure a tails is due, because there have been so many heads already.

Re:Quantum mechanics is real, like it or not.

[Buchenskjoll]

It doesn't just apply to atoms and electrons, but to rocks, people, and planets.

Are you saying I can enter two slits at the same time?

Re:Quantum mechanics is real, like it or not.

[Tyler Durden]

Only if you're really really lucky.

Re:Quantum mechanics is real, like it or not.

[Beck_Neard]

From the point of view of an electron, what is it like to pass through both slits at the same time?

Re:Quantum mechanics is real, like it or not.

[Anonymous Coward]

Dunno. Why don't you ask both of it?

(Captcha: spooky)

Re: Quantum mechanics is real, like it or not.

[Anonymous Coward]

You gave two hands, figure it out.... lmao

Strange?

[jandersen]

I'm getting a little bit tired of the never ending fascination with QM 'weirdness', because it seems to me that it tries to see everything as 'weird' simply because it is 'quantum', with the danger that that it makes people blind to what might be explainable by more intuitive means.

In this case I think we see an illustration of the fact that the notion of a particle as a mathematical point in space - something with zero dimensions - is an abstraction; an approximation that works well enough because we can't in that much detail any way, and it makes the equations so much easier. We have always known, somewhere, that this is not true - things like the mysterious wavefunction that mysteriously collapses as soon as we measure it is a big hint, I would say. As explanations go, that one has always sounded a bit strained - hopefully we will be able to handle the maths of a better model in the not too remote future.

A more likely scenario, in my view, is that what we call particles is something more distributed in space, and that somewhere in that 'distributed particle' we can explain how a particle can travel through several paths at once. I mean, it isn't even an altogether new observation - the famous electron diffraction experiment shows something similar.

Re:Strange?

[Rockoon]

In this case I think we see an illustration of the fact that the notion of a particle as a mathematical point in space - something with zero dimensions - is an abstraction; an approximation that works well enough because we can't in that much detail any way, and it makes the equations so much easier.

All that we ever really measure after all is interactions (not exactly the same as 'forces' but 'force' is the macroscopic equivalent.) Both the notion of particles as either something with zero dimensions, something with many dimensions, or perturbations in some theoretical 'field' is an abstraction.

Take the leptons such as the electrons. In our observations we frequently take several interaction measurements of 'an electron' that together happen to be consistent with a mathematical description of a 'distinct thing' but that doesnt make it so - all we actually witness are the interactions, and in actuality its the interactions many times removed that we are witnessing but thats another topic.

'Electron' is just a label to help describe some interactions that we observe. There is a difference between knowing somethings name and knowing what that somethings is. The most truthful statement that can be made is that the universe appears to preserve some quantities in between interactions. We have given names to these quantities (charge, mass, spin, momentum, ...) as well as names to the sets of these quantities (electron, up quark, ..) that appear to be linked in some fashion.

Richard Feynman cared about the interactions. He didnt bother with the notions of what particles actually are, or even what the quantities preserved actually are (or why they are preserved.). In one interview he notes, when talking about inertia, that there is a difference between knowing something and knowing the name of something. We have a word for a phenomenon we observe called inertia, but we havent a clue why it is so.

Particles are just labels.

Re:Strange?

[jrumney]

The only thing that is strange is the confusing terminology that is counter to its standard meaning. "spinning in parallel to its trajectory." and spinning in the opposite direction is somehow not parallel with the trajectory... yep, you lost me there, you boffins must be so much smarter than us mere engineers.

Re:Strange?

[Livius]

I continue to find quantum weirdness very cool and very weird, but I find too often that it's acquired a quasi-celebrity status and people stop thinking as soon as they hear 'quantum'. Quantum weirdness is not the only way for things to be cool and/or weird.

None of the experiments with photons, for example, demonstrate quantum weirdness - they all demonstrate special relativity weirdness, which is completely different. (Remember that the photon, in its own frame of reference, always travels zero distance in zero time.)

The fact that particles not moving at the speed of light have similar weirdness is a whole other kind of weirdness. And it's cool.

Re:Strange?

[DamnOregonian]

Well, it's a label to describe an indivisible quanta of an interaction that we observe.
The electrical field wasn't always believed to have a discrete resolution (the electron).

Re:Strange?

[JoeSilva]

Solitons, or at least soliton-like equations. That's my bet.

Einstein was working in that direction but the math for non-linear equations was not up to it back then and even now it's not clear exactly what set of non-linear equations, in three space dimensions + time + whatever else, gives Solitons that behave exactly like the observations. Also from what I have read he was not taking into account the strong and weak nuclear forces. Plus back then quarks were unknown?

Perhaps string theory is another sort of approximation that makes the math easier, but it might be too approximate to fit the observations. Time will tell but smells to me going from a zero dimensional particles to a one dimensional strings, vibrating in N dimensions, is the wrong approach. Feels to me better to take on that three spatial dimensions etc and find what works.

In a way it feels to me not unlike Wolfram's explorations into cellular automata, emergent behavior that we can not predict, only catalog and compare. That's discreet math but hey, not a bad analogy?

There has been some explorations into continuous automata, which looks like another sort of approximation, maybe more relevant to soliton-like phenomena.

I have not studied any of this deeply, just an intuitive feel.

Some references for the curious:

http://en.wikipedia.org/wiki/S...
http://en.wikipedia.org/wiki/C...
http://en.wikipedia.org/wiki/C...
http://www.applet-magic.com/pa...

Re:Strange?

[Sanians]

I once read an explanation of the dual slit experiment that made a hell of a lot of sense to me. Granted, I don't know much about this shit and so how much sense it makes to me isn't a terribly useful metric, but here it is:

Basically, IIRC, the experiment was set up so that they could allow single electrons through the slits at once and they observed that if they recorded their positions over time, they still obtained the diffraction pattern that was seen when many electrons were present, and so the electrons must be traveling as waves and interfering with themselves, but they assumed that because what they recorded on their film was individual points, that the electrons must also be points as well, and that the electrons were mysteriously turning into whatever they set their experiment up to observe.

Anyway, the page I was reading at the time proposed that the simple explanation of this is that electrons simply are waves, and that the result of a wave collapsing just happens to be a point despite the fact that everyone wants to imagine that it would be something far more mushy. Thus, it isn't that the particle is a wave or a point simultaneously, or that it chooses which to be depending on how it feels or what form we choose to set up our experiment to detect. It simply always is a wave, and when that wave collapses because it hits something, the end result of that collapse is that only a single point is affected.

No idea where the web site is unfortunately. I found it by searching for "physics bullshit" about ten years ago. It may have even been on Geocities.

In any event, I get the feeling that most advanced physics is bullshit, if not simply because it is, then because by the time it reaches an average person like me, it's been filtered through so many douches that are only interested in the magical properties of it that all factual knowledge has been mutilated. So I just end up with nonsense, like people telling me about something they call a "hypersphere" which they explain is like a hypercube, where each end of the cube is connected to another end, and so if you're inside the cube you can go on forever in any direction and not leave the cube. ...except it's a sphere so it doesn't have those pesky corners. Then I try to imagine this, and fail to come to any conclusion other than that the person talking to me has never tried to imagine how such a thing might fit together geometrically and simply made it up because they believe anything is possible and a sphere sounds much more elegant than a cube.

Too many people are willing to throw out logic when thinking about advanced physics. Yes, I get that it doesn't work the way we might assume, but there's a difference between "works like I think it works" and "is logical," the latter meaning something like "what I'm proposing isn't inconsistent with itself."

Like the twin paradox. People say it's solved because one twin accelerates and the other doesn't, but since when do the equations about space and time dilation give a fuck who accelerates and who doesn't? I only see variables for speed, none for acceleration. For that matter, what if we make them both accelerate in opposite directions? Which twin is older than which then? One must be older than the other because there is speed between them. I suppose there must be some truth to relativity if we can put a bunch of scientists on a plane with an atomic clock and have them calculate how far off it will be when it lands, but by the time that truth gets to me in the form of anything I might read about the twin paradox, it's a pile of nonsense.

Re:Strange?

[Anonymous Coward]

People say it's solved because one twin accelerates and the other doesn't, but since when do the equations about space and time dilation give a fuck who accelerates and who doesn't?

Special relativity involves integrating over a function of velocity as a function of time to get the proper time, any changes in velocity will enter there. Also, general relativity explicitly deals with acceleration. If both accelerate in opposite directions, they would both age the same, and this can be checked with the special relativity or general relativity view of acceleration.

The problem is most of physics is not only described, but reasoned with in math. Non-math descriptions might help form pictures, or inspire physicists to come up with new ideas, but it comes back to being rigorously checked and reasoned with math. If a person learned up through calculus, a lot of the stuff can be followed along with, and there would be no middle man to checking the reasoning. The attempts to drop the math sometimes makes things a lot more confusing, as I've seen pages and pages written on some topics trying to form broken analogies for something that takes half a dozen lines of math to show it is straightforward and works only one way given the premises. But without that math, language and expression gets too loose and non-precise, and you get endless arguments just as you would if contracts were written like text messages.

Re:Strange?

[Sanians]

If both accelerate in opposite directions, they would both age the same, and this can be checked with the special relativity or general relativity view of acceleration.

...and this is exactly what I'm talking about: Your explanation is no explanation either. If both twins see identical effects on space and time, then when they accelerate away from each other to come to a speed of 0.9 * c relative to their starting point, then each sees the other moving away at 1.8 c, but relativity tells us that can't happen.

For relativity's explanation of "the twin that goes away and comes back experiences time more slowly" to make sense, you essentially have to cherry-pick the simple case where everyone starts out in a stationary universe so that you can say "well, duh, obviously the twin that left and came back should experience time more slowly." Otherwise it's the case that someone passing us by may actually be experiencing time faster than us since they're "more at rest" than we are and we're the ones who are actually moving and therefore experiencing time more slowly. (...and yes, I know that relativity tells us that "more at rest" doesn't exist.) It's just a clusterfuck of contradiction and I don't get why everyone who tries to explain it tries to use something as painfully simplistic as "they would both age the same" to explain it. Anyone who can understand the twin paradox can obviously understand that that isn't a resolution of it, and that just makes me think that everyone who claims to understand relativity better than me (and believe me, I don't understand relativity at all) is just lying about it and they don't understand shit.

Re:Strange?

[Anonymous Coward]

If both twins see identical effects on space and time, then when they accelerate away from each other to come to a speed of 0.9 * c relative to their starting point, then each sees the other moving away at 1.8 c, but relativity tells us that can't happen.

Relativity has no problem with that situation, just that they would not see each other moving at 0.995c instead of 1.8c.

, you essentially have to cherry-pick the simple case where everyone starts out in a stationary universe so that you can say "well, duh, obviously the twin that left and came back should experience time more slowly.

No, you can do the calculation for both people moving at different rates. There are specifically examples around that don't involve a stationary start too, to illustrate that the special relativity account works even in cases where the acceleration doesn't matter (e.g. A passing B, then B catching up with A, or cases where both accelerate at different times). Also, if that is the only example you seen worked out, it isn't a case of cherry picking, but because you've probably only looked at things that superficially treat the topic (or possibly ones that cover math in enough detail to work it out for any other case...). Textbooks that cover relativity will typically give several such examples, and not just go with a simple one. Just picking the simplest example and not going into detail is an issue with writing on many topics...

"they would both age the same" to explain it

That wasn't an explanation, that was just the answer to what would happen in such a situation according to relativity. As said, this comes down to a calculation of the proper time for both. The calculation is straightforward for anyone with calculus background. If you don't have a calculus background, then to have that method explained, you're down to trusting someone's answer from that method or to trusting someones likely broken analogy. For some simple cases, geometric explanations can be made without the math, assuming you understand what a spacetime digram is and what Lorentz boosts do to such diagrams (both of which are explained in a lot of places). Both the math and geometric approaches are explained elsewhere (even tersely on Wikipedia) and a text based comment is not an efficient way to convey either, so there is no reason to awkwardly and potentially incorrectly do so.

More fundamentally, if someone assumes that everything can be explained to them without much of any background (e.g. in math) and with minimal effort, and that anything that can't is BS, they are going to struggle with a lot more topics than just physics. While it is great that so many things can be broken down into things that connect to the day-to-day intuition, the world and human intuition doesn't work that way in general, so there will be times non-trivial amount of effort is needed to understand something.

Re:Strange?

[euanc]

I found this Wired.com article quite interesting: "Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?" It postulates pilot waves which carry particles but have different properties (e.g. wave properties).

This is compiler optimization error

[sinij]

This is optimization error in the compiler of our simulated universe.

Re:This is compiler optimization error

[NotInHere]

Gonna love a linus rant on this...

Re:This is compiler optimization error

[Anonymous Coward]

Or a feature, where magnets have no effect on upper-beam parallel spinning neutrons. Certainly an edge-case ;)
What does it all mean Basil?

Re:This is compiler optimization error

[wonkey_monkey]

We do not break user spacetime!

Can we dumb it down some more?

[enharmonix]

I'm not exactly sure I followed what happened, and I read the dumbed down version. I don't see how this isn't an extreme case of superposition, but I'm not clear on what they did. They split a stream of neutrons into an upper beam with spin going forward and a lower beam with spin going backward. They did stuff to the lower beam that didn't happen to the upper beam? And it keeps mentioning recombining the beams but I didn't quite catch what profound result that had. Can somebody who follows this please explain it?

Re:Can we dumb it down some more?

[Anonymous Coward]

Here's a super dumbed down version of what I read it to say.

You take a garden hose and spray water out the end. You have a plate or something at the opening of the hose that splits the water into two streams. While the streams are separated. To make it easier to tell the two apart, we add blue dye to the "top" stream.

After the area where the dye is added, the streams are recombined. You see there's just as much dyed water as there is undyed water.

You then take some sort of mesh screen or something and put it in path of the undyed water. You now notice when the streams are combined, there is twice as much dyed water as there is undied.

Then toss is something about when you magnetize the undyed stream, the undyed water reacts in some fashion, but when you do the same to the dyed water, it doesn't happen....

Re:Can we dumb it down some more?

[parallel_prankster]

This is what I understood. They first split the beams into upper and lower paths and filtered out the neutrons from the lower path using their spin state . They double checked this by using limiting/filtering neutrons on one of the paths each time and measuring the number of neutrons after re-combining and filtering out the lower path. This way they made sure that the neutrons coming out after re-combining and filtering must have taken the upper path. Then they applied magnetic field on both paths. But it seems like the neutrons which supposedly could only have come from the upper path had been affected by magnetic field from the lower path. This implies as if their "positions/mass" took one path while their spin took another?

Re:Can we dumb it down some more?

[Anonymous Coward]

They saw the neutron is affected by a field on the lower path, but that lower path is not ever supposed to be taken by the neutron, but it is obviously taken.

My guess is that physcists in 2014 are still under the impression that particles travel. They don't. Energy waves travel. Particles are just from an observable moment in time when energy levels in their respecting field creates a particle.

Re:Can we dumb it down some more?

[mx b]

It's hard to say without the actual paper, but I think I follow what they did.

I interpreted it to mean parallel (forward or back actually), vs the lower beam being opposite (so perpendicular to the field). If they applied a stronger magnetic field to the top, when the two beams recombined and filtered parallel, they got exactly what the expected -- same amount of neutrons as top beam, nothing weird. When they applied a stronger field on the lower beam, and recombined and filtered parallel, then they got amplification/cancellation of neutron spins.

If I understood correctly, this seems an intuitive result. Applying stronger field on the upper beam doesn't do anything other than make sure the neutrons stay aligned, so no numbers changed. If they applied a stronger parallel field to the perpendicular lower beam, then the field is strong enough now to perturb the neutron spins -- some of those spins will become aligned (though not necessarily all -- you can take a look at ferromagnetism and spin domains for an example). So when you recombine with the upper beam, ta-da!! Either there will be more (amplification) as you add up all the parallel from the top + the parallel from the bottom, or you will get cancellation, as the upper ones are parallel (say to the right, for sake of argument), and the lower ones are more often aligned antiparallel (still parallel, so they pass the filter, but pointing left instead of right) so the parallel/anti-parallel spins cancel out and make it look like there's less of them.

Again, it doesn't seem like quantum "weirdness" or a "paradox", just keeping track of what's going on.

It could be more deep than that, since the article is a summary and does not provide data, experimental method, etc., but that's my first thought.

Re:Can we dumb it down some more?

[multimediavt]

You're not the only one. I've studied particle physics for some time now and that summary was gibberish! I will go read the paper and see if it is any easier to follow. The broken and horribly constructed English isn't helping either!

Re:Can we dumb it down some more?

[multimediavt]

The abstract from the Nature Communications article is easier to read and understand what they've accomplished:

From its very beginning, quantum theory has been revealing extraordinary and counter-intuitive phenomena, such as wave-particle duality, Schrodinger cats and quantum non-locality. Another paradoxical phenomenon found within the framework of quantum mechanics is the ‘quantum Cheshire Cat’: if a quantum system is subject to a certain pre- and post-selection, it can behave as if a particle and its property are spatially separated. It has been suggested to employ weak measurements in order to explore the Cheshire Cat’s nature. Here we report an experiment in which we send neutrons through a perfect silicon crystal interferometer and perform weak measurements to probe the location of the particle and its magnetic moment. The experimental results suggest that the system behaves as if the neutrons go through one beam path, while their magnetic moment travels along the other.

Re:Can we dumb it down some more?

[steelfood]

Then they applied magnetic field on both paths.

They applied the magnetic field to each path separately. They saw no change when the magnetic field was applied to the upper path, but they saw a change when it was applied to the lower path.

The way you state it, it's a bit confusing as to what they actually did with the magnetic field.

Re:Can we dumb it down some more?

[sillybilly]

I think its the other way around, the dyed water has a ferromagnetic molecule whose color is sensitive to the applied magnetic field, but the distilled water lacks such a complex additive, and is not sensitive.

Re:Can we dumb it down some more?

[sillybilly]

Why combine the beams to see which path the neutrons took? Why not measure them individually? Because then you don't get the self-interference effects of the electron double-slit experiment. If you block either hole, it's easy to see that each electron wave-packet went through the other one. But if you keep both holes open, each wave-packet electron goes through both holes, and arrives at the screen in a self-diffraction pattern, with highs and lows in probability or abundance amplitudes. I.e., the modeling of the electron as a "particle", as a dot, as something limited in extent in space, is not correct, it does spread out, though I don't know if it spreads out to a mile, if that's the distance between the holes, or across the galaxy, it may be like a sound wave only spreads out to openings on a wall within a limited range, and the range, or amplitude of the unparticleness spread all over the place is limited to the nearby neighborhood, and not halfway across the globe, let alone the galaxy. But soundwaves get absorbed as thermal friction, while electrons live in an undecaying medium, and don't have a half life. So how far do the electrons spread out, halfway across the galaxy? With sound waves, in absence of decay, absence of friction, or light waves in absence of absorbance, there is an inverse square drop in amplitude vs. distance, and I assume this be the case with all waves, as the surface of a sphere is inverse square, it's where the term comes from, and such a rule represents conservation of something when it goes from a 1 cm radius to a 10 cm radius, if spherical, its amplitude as a wave drops as inverse square, but when confined to a reflecting waveguide, the aplitude is constant. Electron microscopy probably shows that electrons behave like other waves of sound, light, etc., and something is conserved, and they follow the inverse square law in a sphere, and a consant law if you can make a waveguide. So the electron self diffracts, and maybe these guys didn't have a neutron-screen to observe the diffraction effects, but a single neutron probe somewhere, so when they were expecting an increase in something, they measured a decrease, as the patterns get a little more complicated with diffraction, based on path length. They need a neutron "display screen", and even if they can't get 800x600 SVGA pixels, maybe 24x24 would be nice. That's a lot of neutron detectors. So even 2x2=4, 3x3=9 or 10x10=100 is better than just 1.

Re:Can we dumb it down some more?

[EmperorArthur]

Here's a question. What would happen if the beams traveled different distances? AKA, one beam took longer to reach the recombinator than the other. I can guess, but I have no clue about Quantum Mechanics.

Re:Can we dumb it down some more?

[multimediavt]

Here's a question. What would happen if the beams traveled different distances? AKA, one beam took longer to reach the recombinator than the other. I can guess, but I have no clue about Quantum Mechanics.

So, go read more about the subject in your free time. There are s of freely available publications that cover the topic. I am not certain that the experiment would yield anything based on your hypothesis, not even the results being discussed. The most quantum experiments are predicated on a very specific set of conditions and why it hasn't been done before, accurately.

Reading too fast...

[Anonymous Coward]

Who else read "interferometer" as interocitor and had an MTS3K flashback?

Limits of Measurement

[mx b]

I have never been a fan of the quantum "weirdness" either. Everyone gets caught up in the Copenhagen interpretation and Schroedingers' cat and all, and ignores a simpler explanation. I think you may be on the right track with zero dimensions not being realistic -- and I believe that is the hypothesis of string theory actually, to model objects as 1d strings instead of 0d points -- but even that I think is overlooking something easier.

The Heisenburg uncertainty principle illustrates the true nature, I think. We cannot measure position and momentum simultaneously. Why? Because on the scale of electrons, those electrons are very small and lightweight and can get jumbled around. We have to do something to measure speed. For cars, we can measure speed by bouncing light ways off them (radar guns). But try a light beam on an electron -- at that size, the electron can feel the full force of the electric field of the light wave, and gets moved out of the way. A car is so huge compared to a beam of light, that we don't affect a car when we measure its speed, but we DO affect the electron. So either we can use the light to find where it was (and knock it around so we're not sure what speed it was going), or we can use the light waves to get an accurate reading of how fast it was going, but now we've knocked the electron somewhere so we're less sure where it is now.

Particles can't really be two places at once. But since we're knocking things around with our light beam, we can't say for sure where it is now -- so we instead talk in terms of probabilities of where the electron is, rather than saying matter-of-factly where it is. This is what quantum mechanics does, it calculates probabilities that the electron is in a certain place, probability it was going a certain speed, etc.

The double slit experiment mentioned by another poster shows this is the correct interpretation too. As you can see from the photos on Wikipedia, when single particles are allowed thru, we see only single points on the detector. It is only when a flood of electrons are allowed that we see an interference pattern similar to that of a wave. Seems pretty weird!! But is it really? In actuality, as our detector reads electrons, it is knocking them around a little (think of billiard balls bouncing around, off of the detector). As electrons build up, the electric field also builds up in the area between the slits and detector. That electric field is so small that our instruments can't really detect it -- but it IS strong enough to again, knock around electrons. That slight push from the build-up electrons onto the electrons coming thru the slit means they get pushed away from the center, away from the build up, and then they settle down at the outer fringes of the build up. Naturally that means there's some gaps at play here, and so we observe it to be a wave interference pattern. This all happens so fast that it seems instantaneous too. But nothing particularly magical going on -- just the rules of forces mean that electrons get knocked around A LOT, even for imperceptible forces on the human scale (or scale of our equipment).

Other physicists have argued for this interpretation. I know, [citation needed], but I'm drawing a blank who. I want to say Ed Witten but not sure. In any case, I know there have been proponents of this interpretation rather than the "weird" Copenhagen interpretation. But hey, people couldn't make TV shows about how quantum strangeness leads to time traveling thru the multiverse if we did away with it.

Re:Limits of Measurement

[sconeu]

Your explanation of Heisenberg with the inability to observe is incorrect. That's a RESULT of Heisenberg.

Heisenberg's Principle comes out of the wave/particle duality. To localize a particle, you have to add waves of differing frequency to its wave function (ala Fourier). The more you localize it, the more waves of higher frequency you add. Momentum is derived from the wave frequency. Therefore, when you localize a particle, you are increasing the uncertainty of the momentum (by adding more and more higher frequency waves).

This is the argument that Heisenberg used (yes, I've read his book).

Re:Limits of Measurement

[sconeu]

Follow up to my own post.

The fact that you cannot measure the momentum and location of a particle exactly is NOT a limitation imposed by measuring apparatus. The fact is that a quantum particle HAS no exact momentum and location, as a result of its wave function.

Re:Limits of Measurement

[Anonymous Coward]

What you're describing is incorrect. The particle *actually* behaves as if it is two places at once - including things like interfering with itself.

However, if you want an interpretation that seems more "intuitively correct" than the Copenhagen interpretation, I like Cramer's transactional interpretation of quantum mechanics. It avoids any "magic" and sticks with a single universe; it does, however, introduce zero mass transaction particles going at the speed of light backwards in time. Assuming relativity as true, this is fine, because at the speed of light time is compressed into nothing, so going backwards or forwards makes no real difference (as there is no change.)

Re:Limits of Measurement

[Anonymous Coward]

Particles can't really be two places at once.

There is no spoon. And there also aren't any particles, there are only fields.
What we call electrons for example are just disturbances in the electron field. And these disturbances don't have to be "local", so one disturbance can be at several places at once.
We cannot even be certain where an individual electron is (even with precise measurement), since we cannot tell one electron apart from the other. The statistics tell us that they behave more like bits of information that like unique physical objects.

Re:Limits of Measurement

[TheCarp]

> I have never been a fan of the quantum "weirdness" either. Everyone gets caught up in the Copenhagen
> interpretation and Schroedingers' cat and all, and ignores a simpler explanation.

Ignores? I am a lay observer but I have yet to see one that actually explains.

> when single particles are allowed thru, we see only single points on the detector.
> It is only when a flood of electrons are allowed that we see an interference pattern similar to that of a wave.

Wrong. when single particles are allowed through a single path yes. However, if multiple paths are available even a single particle interferes with itself. Take enough samples of a single particle going through with multiple paths, and you get an interference pattern: http://en.wikipedia.org/wiki/D...

The problem with the simple explanations is, we already know they are wrong. Between the double slit and the bell inequality, classical theories are pretty sunk. I would love to see a simpler model that actually predicts things like single particle interference and the violation of the bell inequality!

Re:Limits of Measurement

[mx b]

Heisenberg's Principle comes out of the wave/particle duality. To localize a particle, you have to add waves of differing frequency to its wave function (ala Fourier). The more you localize it, the more waves of higher frequency you add. Momentum is derived from the wave frequency. Therefore, when you localize a particle, you are increasing the uncertainty of the momentum (by adding more and more higher frequency waves).

I understand the mathematics involved in Fourier analysis, but that is the mathematics -- is the electron ACTUALLY doing that, or was that simply a mathematical/logical proof that correlates highly with what we see?

Follow up to my own post.

The fact that you cannot measure the momentum and location of a particle exactly is NOT a limitation imposed by measuring apparatus. The fact is that a quantum particle HAS no exact momentum and location, as a result of its wave function.

Is there an experiment or theorem that shows specifically that it cannot be because of the apparatus? It has been a while since I've taken quantum mechanics, so maybe I am forgetting a theorem or something.

But my thought is: Until we measure something, I'm not sure how anyone can really say whether an object has or does not have a certain property. I understand this is basically superposition from quantum mechanics, and that quantum mechanics predicts things correctly -- but none of the mathematical arguments strictly imply that we have the correct conceptual framework of what the mathematics means. All of this mathematical physics has its root in formulas that were derived based on data collected in labs, so most definitely any mathematical argument invoking these formulas is at the mercy of our experimental data's precision/accuracy.

Re:Limits of Measurement

[Anonymous Coward]

Particles can't really be two places at once.

And here you are completely wrong. Finiteness of the universe disagrees.

The double slit experiment mentioned by another poster shows this is the correct interpretation too. As you can see from the photos on Wikipedia, when single particles are allowed thru, we see only single points on the detector. It is only when a flood of electrons are allowed that we see an interference pattern similar to that of a wave

You are wrong again. Stop. Double slit experiment has been duplicated using *individual photons*. Yes, one photon fired at detector at a time. ONE. No more, just ONE. After waiting sufficiently long, interference pattern was produced on the detector. The photon appears to have interfered with itself.

http://www.animations.physics....

Re:Limits of Measurement

[mx b]

What you're describing is incorrect. The particle *actually* behaves as if it is two places at once - including things like interfering with itself.

I recall in classical electromagnetism class having to calculate the effects of the electric field of an object ON ITSELF as the particle was moving. I do not think strictly speaking it has to be a "weird" quantum effect if we had to do similar things in classical calculations. Are you aware of an argument on why it *must* be in two places at once, rather than simply seeming that way because of its interactions while moving (or interactions with nearby particles, which move and therefore change the potential on the original).

However, if you want an interpretation that seems more "intuitively correct" than the Copenhagen interpretation, I like Cramer's transactional interpretation of quantum mechanics. It avoids any "magic" and sticks with a single universe; it does, however, introduce zero mass transaction particles going at the speed of light backwards in time. Assuming relativity as true, this is fine, because at the speed of light time is compressed into nothing, so going backwards or forwards makes no real difference (as there is no change.)

Aha! Thank you for the link, this might have been what I was thinking of. The advanced/retarded waves were what I was thinking of in the electromagnetic response above.

Re:Limits of Measurement

[geekoid]

Reading both your post is like watching dogs try to explain airplanes.

Re:Limits of Measurement

[mx b]

Wrong. when single particles are allowed through a single path yes. However, if multiple paths are available even a single particle interferes with itself. Take enough samples of a single particle going through with multiple paths, and you get an interference pattern: http://en.wikipedia.org/wiki/D...

I perhaps wasn't as careful with my language as I should have been. But even the article you link to says that you release more than one particle. It is one at a time, not perhaps the "flood" I stated (though I was thinking of a large number of electrons more so than time frame). But it is *more than one* particle, so I am not sure how this can be called "self-interference" with a single particle when other particles have already gone thru the apparatus.

If we could carefully release a SINGLE electron, and when we looked for it on the other side got multiple hits as if there were many electrons (or single electron in multiple places), then that would sound like interference. But since we get a single dot from one electron, then we release another and get another dot, and only over time see the interference, it sounds to me more like there is interference between the electron build up and the new electron than a "self" interference. The conditions in the apparatus are different than when the experiment started!

Re:Limits of Measurement

[Zalbik]

Particles can't really be two places at once. But since we're knocking things around with our light beam, we can't say for sure where it is now -- so we instead talk in terms of probabilities of where the electron is, rather than saying matter-of-factly where it is. This is what quantum mechanics does, it calculates probabilities that the electron is in a certain place, probability it was going a certain speed, etc.

As others have mentioned, you are missing a couple of fundamental points of the double-slit experiement.

1) The pattern observed has nothing to do with the photons being hard to measure (classically photons are sent through the slits),
The pattern produced is exactly the interference pattern expected if light were actually a wave. The peaks and troughs of the two waves cancel each other out which results in the dark bands. Dual peaks or dual troughs reinforce each other, resulting in bright bands.

2) If this was a result of electric field build up and the "detector knocking particles around a bit", then it should also happen for a single slit (it doesn't). It also should not occur for photons (electrically neutral), but it does.

3) "when single particles are allowed thru, we see only single points on the detector"

This is incorrect, and the weirdest thing about the experiment. If two slits are opened, and particles are sent through one at a time, there is still the same interference pattern created. Individual particles behave as if they do not have a fixed location, but only a probability of existing at a specific location.

Heisenberg's principle is a result of quantum mechanics and wave-particle duality, not the cause.

Re:Limits of Measurement

[Khashishi]

IAAPhysicist. Parent isn't correct. I advise you to not worry too much about what is "real" and accept that physics looks for simple models which match our experiences. You need to think abstractly, and assume less. For example, everyone grows up with some intuition of what an object is, and then project that notion into realms where they don't apply. The letters on this webpage, for example.... These are black objects which move up and down when you scroll the page. Or, is it really the white spaces between the letters which are the real objects, and the black is just void? Actually both are wrong, and the "reality" is that your monitor is doing certain things, depending on how deep you want to look.

When physicists talk about a particle, they are talking about the smallest step in the amplitude of the fluctuation in some field or combination of fields. A fluctuation doesn't have to be purely one kind of field; for example, a phonon is made out of collective motions of atoms, and polaritons are sort of some mix of photon and phonon. These could be considered particles (but not fundamental particles). This isn't the only way to think about a particle (since it's all just a model anyways), but it is more accurate than billiard balls.

Heisenburg uncertainty principle exists because you are trying to pinpoint a fluctuation in fields which occupy all space.

Parent's description of the double slit experiment is fully wrong. Electrons do not interfere with some build up of electrons. Electrons interfere with themselves, because the fluctuation (which is the electron) exists in the full region between the source and screen. The interference pattern is the same no matter how slowly (in terms of electron rate) you fire the electrons, so build up is not a concern. A similar interference pattern exists in photons and neutrons as well, which aren't charged.

Re:Limits of Measurement

[Anonymous Coward]

(classically photons are sent through the slits)

I'd also like to add that the same interference pattern has also been observed with molecules as large as buckyballs. Not quite as easy to jostle around as a single particle, those.

Re:Limits of Measurement

[mx b]

And here you are completely wrong. Finiteness of the universe disagrees.

I am not sure what "finiteness of the universe" means in this context. Could you elaborate why that immediately says particles must be in two places at once?

You are wrong again. Stop. Double slit experiment has been duplicated using *individual photons*. Yes, one photon fired at detector at a time. ONE. No more, just ONE. After waiting sufficiently long, interference pattern was produced on the detector. The photon appears to have interfered with itself.

The photon does appear to interfere with itself, but only after sufficient time. Is it really interfering with ITSELF? The experiment description on the page you link to says that photon is absorbed by an atom to knock off an electron, which starts an avalanche, and we read the resulting current as a detection. Now, the original photon has been absorbed, however, anytime an electron accelerates it releases radiation (brehmsstralung). So it actually sounds like the photon is causing (a) a current to form, and (b) extra photons to be emitted by the electrons as they bounce around. The new photons scatter in random directions to be sure, but some of them must make it back into the apparatus, bounce around, and come back to the detector, producing a new pattern. Eventually this will settle down as the electrons and photons lose energy over time, but it happens long enough to produce a pattern.

So I don't really see how the original photon interfered with itself; it appears that multiple photons were generated and recorded, and as energy is lost, these waves overlap differently and produce a pattern.

This is my interpretation and I am glad to say I am wrong if provided with some evidence that shows we can rule this possibility out.

Re:Limits of Measurement

[Anonymous Coward]

One interpretation, of many.
http://en.wikipedia.org/wiki/I...
I prefer the Ensemble interpretation myself.

Re: Limits of Measurement

[LoadingEllipsis]

Interference is also noticed in The Double Slit Experiment with single photons and other particles spaced seconds apart. They do interact with themselves. It really is weird.

Re:Limits of Measurement

[tonywestonuk]

mx+b - I used to think, as you did. Then I read this. - http://quantumtantra.com/bell2... - and then I still didn't believe it. So, as a computer programmer, I tried to make a program that would mock what was happening. My theory was if I could model it in code, then it wasn't spookiness. Well, after trying for a few days, I couldn't do it. I realised the *only* way I could make my program work, would be to make the emulated particles in my program communicate with each other..... which means one of two things 1) Entangled particles have some way of Faster than light communication with each other.... (I still think this is impossible!) or 2) The universe we live in is just so weird, that nothing actually exists as we know it. Its only our observation that makes things real. everything is somehow influenced by everything else. That space and time and thought... aren't the separate things they appear (As Wesley Said)..... thinking this way, two entangled particles don't need to communicate - they behave like they do, because they can only ever behave this way in the observational field we project, and that they inteact within..... this observational field isn't something that only intelligent beings can produce - but more, any particle can be an observer of other particles if it is able to receive information about those particles. This I believe to be more the truth. Have you seen a speckle pattern made by a laser as it hits a wall?..... have you notice when you move, the speckle patten moves? How does the speckle patten know where you are, in order to move? It doesn't. You are just effecting it, by your observation of it. A different observer, sees the speckle patten differently. I think, somehow, something similar to this is going on. However, the observed quantum behaviour is caused by every observer of the event, causing it to show a particular result.

Re:Limits of Measurement

[sillybilly]

There are wavepacket objects that can be knocked around. I forget, but I think the word is soliton, or something similar, a single wave-hump, or a wavehump plus some fast decaying amplitude fluctuations a couple wavelengths away, that travels, as if it were a particle. In order to understand quantum "particles" I think they need to delve into the math of ping pong-ing macroscopic single hump wave "particles" around - how they interact with each other, how to get a bounce out of each. Another thing that acts weird, as if it were a particle, but it's distributed, is a macroscopic vortex. Once you build up the intuition about these macroscopic "particles" that are simply a phenomenon of their medium - be it two vortices or two wave humps in macroscopic air or water, or quantum particles in the "ether" of vacuum - (I'm gonna leave this sentence hanging like this.) The math is really complicated with interacting vortices that bounce off each other, or wave solitons that bounce off each other, and conserve the terms of momentum, mv, energy, mv2, and I think angular momentum. What else?

A neutron having a magnetic moment means it has internal charge separation, and the sum of the internal charges is zero, but the "currents" of different charges are separated, such as the positive charges are flow in a small radius donut in the center, and the negative charges in a large radius donut around the small donut, or even if in the same donut (as in a copper donut wire you have both the positive and negative flowing in the same donut) at least at a different speeds relative to each other. If there are acually two donuts, not just one, then these two internal donuts may not be in the same plane, but say vertical to each other, and then the vector sum of the magnetic moments may act a bit more weird, if you can shift the relative plane of each donut differently with an externally applied magnetic field. It would be nice to know which ones are the magnetic field generators in a neutron relative to the lab's velocity taken as zero. In a copper wire we know it's the negative charge that flows, and the positive sits still. Is there a way to tell which one sits still inside a neutron, or what the speeds are? I think artifacts of such considerations might shed light on the devil is in the details of how they performed the experiment and what they actually measured and what actually happened, and it may turn out not to be a separation of the property of the wave from the wave, but some measurement artifact misunderstanding. And by the way I don't believe in the uncertainty principle, you could probably come up with a Schroedinger wave equation or Heisenberg particle matrix for macroscopic vortices or wave solitons, and then could take it to lower scales. Also Dirac's electron-positron pair rising out of pure vacuum is like a vortex and antivortex, or soliton and antisoliton arising out of the "ether" or medium of pure vacuum. And by the way some strange behavior of this "ether" might be deduced in how light travels in the Michelson Moreley experiment, and by the beding of starlight by gravity during a solar eclipse. By the way does light bend equally based on how its polarized vs. the gravitational field vector? A recent issue with a supernova explosion nearby showing two different neutrino peaks followed by a light peak that then stayed on continuously, brought up the idea that the difference in neutrinos might be polarization, as in birefringence in an anisotropic medium - which by the way splits a beam into two, not a spread spectrum like the prizm does with the rainbow. So this concept of ether was killed dead and deemed superfluous, but as all quantum phenomena are wave phenomena, and we can best understand waves by assuming a uniform medium that has properties x, y, z, w, etc., (gimme 19 parameters and I can fit an elephant with a mathematical curve, give me 20 and I can fit the tail too with high accuracy.) The less parameters you need the better, and if you can beat the 26 parameter string theory, with say explaining as much a

Re:Limits of Measurement

[JesseMcDonald]

The electrons are being run through the experiment one at a time, so they can't be interfering with each other. There is no "electron build up"; even if you tore the apparatus down and rebuilt it from scratch each time, guaranteeing that there was no leftover state from previous experiments, you'd still get the same results.

You only get one discrete "hit" per electron, but the location varies according to some statistical distribution—and that distribution, measured over a series of single-electron experiments, matches what one would expect for interfering wave patterns.

Re:Limits of Measurement

[Anonymous Coward]

The photon does appear to interfere with itself, but only after sufficient time. Is it really interfering with ITSELF? The experiment description on the page you link to says that photon is absorbed by an atom to knock off an electron, which starts an avalanche, and we read the resulting current as a detection. Now, the original photon has been absorbed, however, anytime an electron accelerates it releases radiation (brehmsstralung). So it actually sounds like the photon is causing (a) a current to form, and (b) extra photons to be emitted by the electrons as they bounce around. The new photons scatter in random directions to be sure, but some of them must make it back into the apparatus, bounce around, and come back to the detector, producing a new pattern. Eventually this will settle down as the electrons and photons lose energy over time, but it happens long enough to produce a pattern.

So I don't really see how the original photon interfered with itself; it appears that multiple photons were generated and recorded, and as energy is lost, these waves overlap differently and produce a pattern.

This is my interpretation and I am glad to say I am wrong if provided with some evidence that shows we can rule this possibility out.

No, the photon goes out of the emitter. The photon goes through double slits. The photon hits detector. The photon-to-electron conversion happens in the detector. There is no photons emitted out of the detected that "bounce around". If it were, there would clearly be a noise floor, never mind other abnormalities (like detectors not actually working!)

1. ONE photon emitted
2. photon detected at spot A
3. time passes - nothing detected
4. ONE photon emitted
5. photon detected at spot B
6. wait
7. repeat for a while
8. see interference pattern!

Cover 1 slit. Repeat the experiment with 1 photon. *No* interference pattern produced.

No photons arrive in the "dark spot" of the interference pattern. The interference pattern is highly sensitive to the *source position* of the photons - that's from basic basic experiments you can do yourself with many photons (so like a laser pointer and 2 slits).

Interfering with itself, or however you call it, the experiment is reality whether you like it or not. Physics is a science about measurement, not theories. If a theory does not match reality, it is thrown out the door.

Hint: interference pattern is highly sensitive to the wavelength of the photons. They are not measuring thermal photons, or microwave photons, but specific frequency (energy) photons. So like lasers, not like light bulb.

Re:Limits of Measurement

[fahrbot-bot]

Your explanation of Heisenberg with the inability to observe is incorrect. That's a RESULT of Heisenberg.

Cause and Effect? I'm pretty sure Heisenburg simply describes the effect, not causes it :-)

Re:Limits of Measurement

[sillybilly]

By the way, I forgot to add, that it amazes me how every galaxy is flat, or most of them are, and I can't really picture gravity keeping together a centrifugal balanced spherical galaxy, there is no way to have the rotations, and if there is, there'd be a lot of collisions. Like in outer space conquest by humans most of the space stations will have to get in line with the general flow of things, and stay in the flat orbit plane of the Sun, but just like Earth satellites, it's possible to go North-South as opposed to East-West in a geosynchronous orbit, as long as you don't collide. So why are galaxies flat? Why not just random spherically distributed debris going round and round, like we assume in the particle model description of how an electron goes round the atom, and the probability of finding it at any point. I don't like probabilities, I'm willing to trade for a 100 parameter deterministic theory describing quantum mechanics accurately compared to the few parameter probabilistic Schroedinger equation description, which is not as useful to me. Any takers on that deal? So anyway, how do we know neutrons are spherical? Are there such measurements? We have atomic force microscopy to show that molecular surface features are indeed spherical-elliptical, and not flat disk-like, like galaxies. Also the uniform bond angles in methane show that there is spherical uniformity in an atom. But it may turn out that neutrons are weird, and flat-like wave-soliton mixes, just like most debris around planets orbits as a spherical moon, but Saturn is different, it has a ring, that Maxwell conceptually derived, in his dream, not to be uniform continuity, but made up of debris. And so it is, we see it in the Voyager pictures.

Re:Limits of Measurement

[DrJimbo]

I understand the mathematics involved in Fourier analysis, but that is the mathematics -- is the electron ACTUALLY doing that, or was that simply a mathematical/logical proof that correlates highly with what we see?

ISTM your question is meaningless. The best we have to offer on what the electron is ACTUALLY doing is with mathematics that correlates highly with what we see. I don't know what it means for there to be an actuality beyond that.

Even your question/remarks on the "correct conceptual framework" seems to miss the mark. The best we have there is the simplest mathematics that correlates highly with what we see.

All of this mathematical physics has its root in formulas that were derived based on data collected in labs, ..

Actually, a very big part of the theory is predicting new and unexpected results that have not been seen in the lab yet. Another big part is when the same mathematics can describe different phenomenon that were previously thought to be unrelated. Lee Smolin provides an excellent description of how this all works in his book The Trouble with Physics. I highly recommend it.

Re:Limits of Measurement

[Anonymous Coward]

So why are galaxies flat?

It is an unstable equilibrium, as soon as there is a concentration of mass somewhere, stars and gas on orbits away from that will be pulled more toward the concentration of mass. You can think of just two stars orbiting some evenly distributed mass in the center, those two stars would pull on each other and cause a tilt in their orbits to equalize in the long run. The only reason it isn't completely flat is there are still a lot of interactions between individual stars and it takes interactions to adjust the tilts of orbits too, so it is more of a random process. If you have enough stars, you get something more like elliptical galaxies which are less flat.

Re:Limits of Measurement

[sillybilly]

Also, I seen a youtube video of a weird fluid, which under oscillations that resupplied the energy lost to friction, it grew tentacles, standing waves on its surface. Then you can ping ping these waves around.

Re:Limits of Measurement

[Anonymous Coward]

The Vedas describe everything manifest in the universe to be vibration.

Why can't the entire universe be pixelated / voxelated like Haramein describes in The Resonance Project:
https://www.facebook.com/TheResonanceProject

This undoes any "weirdness". It's our equations that are too simplified, and intellectual people always trying to mold the existence into their limited beliefs.

Re:Limits of Measurement

[sillybilly]

Hidden variables are the simplest way to kill a probabilistic model of reality. Like every time I think of quantum theory, I think of the randomness of Brownian motion, how 900 trillion molecules are smacking the pollen under the microscope from the left, 900 million plust 53 from the right, and that 53 is heavy enough to make it move. But luckily, by the time we found the random Brownian motion of lifeless particles, we already had the Maxwell-Boltzmann kinetic theory of gases, and its statistical rules, and the parameters, the rules, are not many in that model, but the actors are - 900 trillion of them at the same time. There may be a deterministic description to quantum theory, but you may have to come up with 900 trillion actors obeying simple rules, to accurately measure and describe at what localize point an electron wave function will decide to collapse on a screen from a double slit experiment. We have no way to measure 900 trillion different velocities and motions of things we don't even know what they are or whether they exist. By the way even into the 20th century there were prominent scientists, like Ostwald who denied the existence of atoms, and maintained that matter is continuous, and ascribed its success to just mere luck, and it will be a matter of time before we find something to disprove it as a valid theory, just like we abandoned phlogiston, caloric, vis viva, etc., but it's hard to hold such a view in face of an atomic force microscope today. We think atoms are real and Brownian motion is from 900 gazillion atoms smashing into each other at the same time. What stuff is there in vacuum, in emptiness, that acts like that? Vacuum, or complete physical void and emptiness, is definitely not empty, as far as I can tell. If it were, it would have a dielectric permittivity of zero, and the speed of light would be infinite.

Re:Limits of Measurement

[sillybilly]

And the speed of gravity may indeed be infinite, if it propagates through a medium that's empty, even empty of electromagnetic vacuum. Does that sentence even make sense? It's like saying vacuum has mass per unit volume, that retards gravity, like, if you put electrically charged obstacles in the way of light, such as a zirconia crystal of a fake diamond ring, it will slow light down, so putting a lot of sand or earth or metal in the way of gravity slows it down too? Or does gravity penetrate mass unimpeded to the mass right behind it. We know an electric field propagates only with the speed of light, and speed of light is impeded by electric charges in abundance in the way.

Re:Limits of Measurement

[sillybilly]

As in is there a way to create absolute vacuum, pump out the electromagnetic field, or ether, or whatever you wanna call it? In the days of Toricelli they used to wonder whether absolute metaphysical void is philosophically possible, and the 760mm Hg mercury tube was their prime example of messing with such vacuum, and how it wants to suck on things, nature abhores emptiness, til someone came around and said no, it does not, what we got is atmospheric pressure pushing down on mercury, and vacuum not pushing down on it, and if you take your Toricelli tube up the mountain side, it will abhor the metaphysical void differently.

Re:Limits of Measurement

[yndrd1984]

Technically, Bell's Theorem only rules out local hidden variables.

Re:Limits of Measurement

[sillybilly]

Elliptical galaxies must have a lot of collisions as stars go about in perpendicular planes to each other. As there has to be a centrifugal force keeping the stuff from falling together right away, like in a vortex the spinning sets up a delay, and keep things from collapsing into each other, in the ellipsoid's vertical plane too, not just everything going about orderly in a horizontal plane.

Re: Limits of Measurement

[Anonymous Coward]

A couple of years back, I spent several solid days trying to work out what the double slit experiment was really all about and why everybody was so excited about QM. Here's one place were my inquiries ran into a block:

How do you emit and detect a single particle in the double slit experiment?

CAN you emit and detect a single particle?

What is the engineering behind such a pair of devices? How do they work?

I'm pretty good with Google, but I couldn't find at the time any explanation of how such machines would operate. (Though, I did discover that there isn't even a concrete "double slit" involved; it's all about prisms and beam splitters, which was at dramatic variance with the old highschool double slit experiment I worked through in my teens.)

From what I could gather, in these high level experiments, the single particle is a theoretical single particle created from mathematical averages. You shoot out a few thousand of them, and call them "one".

I can, however, see emitting a single particle as being more practically doable than actually detecting a single particle.

Generally, for a detector to register a "ping", certain energetic tipping points in the detection machine need to be reached in order for a state change to happen, and then to be read further up the device chain so that a light blinks or a needle jumps, you need a cascade and some input energy. How does that trigger reliably with the instance of a single particle?

I am perfectly willing to concede that the scientists working on these experiments are considerably better informed and equipped than I am, and I am happy to grant that Quantum Weirdness may well be a legitimate phenomenon. However, I consider it responsible to also try to do at least some of the hard thinking myself so that I don't take it all on faith, but in my efforts to bring myself up to par and understand what the scientists understand, I have found such simple nuts and bolts questions to create real obstacles to my understanding.

The single photon Emitter/Detector seems like science fiction, and if it isn't, I could find nothing which explains why it isn't.

Re:Limits of Measurement

[Anonymous Coward]

"Fact" nothing. Pilot wave theory disagrees with you.

Re:Limits of Measurement

[Anonymous Coward]

The Copenhagen interpretation says things are in simultaneous states. That's the orthodox view.

Fortunately it *is* possible to have hidden variable theories, though it's been getting little or no attention for the past 100 years.

Re:Limits of Measurement

[Anonymous Coward]

> I have never been a fan of the quantum "weirdness" either. Everyone gets caught up in the Copenhagen
> interpretation and Schroedingers' cat and all, and ignores a simpler explanation.

Ignores? I am a lay observer but I have yet to see one that actually explains.

> when single particles are allowed thru, we see only single points on the detector.
> It is only when a flood of electrons are allowed that we see an interference pattern similar to that of a wave.

Wrong. when single particles are allowed through a single path yes. However, if multiple paths are available even a single particle interferes with itself. Take enough samples of a single particle going through with multiple paths, and you get an interference pattern: http://en.wikipedia.org/wiki/D...

The problem with the simple explanations is, we already know they are wrong. Between the double slit and the bell inequality, classical theories are pretty sunk. I would love to see a simpler model that actually predicts things like single particle interference and the violation of the bell inequality!

Sorry, but you're wrong: http://en.wikipedia.org/wiki/Pilot_wave

It's not a classical explanation, but it's a deterministic explanation that does away with the inexplicable weirdness.

Re:Limits of Measurement

[DamnOregonian]

Multiple electrons sent serially.

The interference pattern emerges in spite of a conga line of electrically unconnected electrons, sent one at a time at a double-slit interface to the detector. Leptons, not bosons. Things with *rest mass*. Volume. Real shit, not just light, is *actually* a wave-function.

It's the most fucking bizarre thing in the Universe that I'm aware of, and upon learning of the single-electron version of the experiment, I finally realized that what we perceive of the universe isn't anything close to what it really is. We are little circles in a flat universe trying to perceive spheres passing through our planes of perception, or something that our evolved senses have similarly not equipped us to grok.

Re:Limits of Measurement

[DamnOregonian]

Just to up the ante on the weirdness: http://en.wikipedia.org/wiki/D...
The interference pattern can be destroyed, seemingly retroactively (if one doesn't accept superposition). Not many people are willing to accept particles with wave-functions measurable with interferometry (up to buckyballs, I believe) will go back in time and and alter their flight characteristics. The Universe really is quantum. And fucking weird.

Re:Limits of Measurement

[DamnOregonian]

Net angular momentum. Writing software to model simple square-distance fall-off force attraction across many particles will yield a flattened, or progressively more ovoid distribution, depending on the net angular momentum, if angular momentum is conserved.

I did it in high school, give it a shot.

Re:Limits of Measurement

[Anonymous Coward]

Seems pretty weird!! But is it really? In actuality, as our detector reads electrons, it is knocking them around a little (think of billiard balls bouncing around, off of the detector). As electrons build up, the electric field also builds up in the area between the slits and detector.

That's a cute armchair theory. Unfortunately for you, we still see the same interference pattern with single neutrons, which have no electric charge. Also, if it were true, we'd also have to see interference patterns with only one slit, but we don't.

If you think a simple double slit experiment is weird, try the same thing with delayed choice. Again the predictions of QM are weird, but experiments prove them correct.

QM and QED are extremely accurate theories: whenever they predict something weird which cannot be explained with classical models (like your electric field buildup theory), experiments show each time again that they correctly predict the result.

No classical theory can correctly predict the quantum weirdness. There are only two ways to explain it.

One is to do away with reality. This means that there are no particles, just fluctuations in fields that sometimes behave like particles. These fluctuations can spread out in space, so particles seemingly exist in multiple spaces, and even interfere with themselves.

The other is to keep reality, but do away with locality. This means you keep distinct particles, which exist for real, but they somehow influence each other faster than light. The pilot wave theory is an example of this (point-like particles, that interact with each other's pilot waves.

Most people (myself included) favor the first one, since it seems less complicated and more elegant. But both are mathematically equivalent, so you can pick and choose.

Re:Limits of Measurement

[dotancohen]

Double slit experiment has been duplicated using *individual photons*. Yes, one photon fired at detector at a time. ONE. No more, just ONE. After waiting sufficiently long, interference pattern was produced on the detector. The photon appears to have interfered with itself.

I too, er, interfere, with myself when I'm alone after waiting sufficiently long.

Re:Limits of Measurement

[Anonymous Coward]

Or try a delayed choice quantum eraser for something even weirder.

Re: Limits of Measurement

[Anonymous Coward]

You didn't try hard enough.

Single photon detectors:
- Photographic plate or CCD: single photons show up as dots.
- Photomultiplier tube: a single photon hitting it causes an avalanche of electrons to be released, which can be measured as a single voltage spike (with amplitude proportional to the photon's energy).

Single photon emitter:
- Traditionally they just start with a normal light source, and dim it (with filters) until the intensity is about the energy of a single photon (which is actually difficult to setup). Since light is quantized, everything coming through has to be in photons. How we know it's transmitting single photons? Easy, they cause single dots or single spikes on the detectors.
- Nowadays they have far better single photon sources, like these or some based on quantum dots.

Re:Limits of Measurement

[Anonymous Coward]

In actuality, as our detector reads electrons, it is knocking them around a little (think of billiard balls bouncing around, off of the detector). As electrons build up, the electric field also builds up in the area between the slits and detector. That electric field is so small that our instruments can't really detect it -- but it IS strong enough to again, knock around electrons.

In actuality, this is at odds with experimental evidence. The electrons don't build up. You can wait as long as you like between firing electrons, eliminating any non-steady-state behaviour you can suggest, and the diffraction pattern still occurs. We have a mathematical model for the process which doesn't require these assumptions of yours. It works. In principle you can fire single electrons at different targets in different places in the world, and sum them, and still get the diffraction pattern. You can't explain that with hand-waving about electronic build-up in the detectors.

I want to say Ed Witten but not sure

You wish. Nobody who understands the maths would suggest this "interpretation", because it's at odds with the maths, and therefore not an interpretation, but a new theory, which happens to be at odds with experimental evidence.

Re:Limits of Measurement

[Anonymous Coward]

Because HVTs are the Gods of the Gaps of pseudo-science. Local hidden variable theories are ruled out, except for some possible loopholes, and as each loophole gets closed someone springs up with another loophole. So yes it's "possible" to have HVTs but only if they obey more and more highly specific constraints. Nobody has come up with a working one yet. They have not been getting "little or no attention for the past 100 years", in fact every QM 101 student and new-age semi-educated crackpot has a secret dream that HVTs will explain it all. It's a naive hope. The mapping from QM theory to what's "actually" happening is basically irrelevant, and your concept of this is forever biased by your physical and statistical intuitions, which all turn out to be wrong at the quantum scale.

Copenhagen isn't the orthodox view, BTW. That's a lie they teach QM 101 students so the rest of us can spot them in the wild. Many-worlds is the orthodox view.

Re:Limits of Measurement

[Anonymous Coward]

Pilot wave theory is wrong.

Re:Limits of Measurement

[Anonymous Coward]

And only ones that assume counterfactual definiteness or are not superdetermined.

Re:Limits of Measurement

[Anonymous Coward]

Science does not tell us what the world is...it merely tells us how we can describe it.

Re:Limits of Measurement

[Anonymous Coward]

Individual particles do not create interference patterns, they create isolated points of impact. The interference pattern describes the collection of impacts. No information is provided to determine where individual impacts will occur, only where they cannot occur (regions described as constructive interference)..

Re:Limits of Measurement

[grep -v '.*' *]

IAALawyer: I don't like your still hard-to-understand description. We passed a law to make PI exactly 3, right? Well, let's pass one that makes a particle that sits exactly THERE with absolutely no movement. Case closed.

So, where do I go pick up my Nobel prize?


PS - I am NOT really a lawyer, but I stayed at a Holiday Inn last night.

Re:Limits of Measurement

[Anonymous Coward]

"Assuming relativity as true, this is fine, because at the speed of light time is compressed into nothing, so going backwards or forwards makes no real difference (as there is no change."

If there realy was no difference and no change then there would be no reason fora anything massless to move backwards, or in any other direction along time.
Since massless particles clearly interact with time time for them cannot be nothing.

Re: Limits of Measurement

[Anonymous Coward]

Awesome!

Thank-you.

Re:Limits of Measurement

[TapeCutter]

is the electron ACTUALLY doing that, or was that simply a mathematical/logical proof that correlates highly with what we see?

Ummm. physics has been all about testing for discrepancies between the two for at least a century now. There's a nobel prize waiting for anyone who can show an electron not behaving itself in accordance with the standard model.

Re:Limits of Measurement

[jcdr]

I lost a opportunity to moderate you insightful (you already got a 4 anyway) to take a chance to say thank you very much for your explanation. Your second paragraph is just so clear and simple. I think that I have understand a new aspect of the physic in a minute. Great.

Sometimes a simple phrase open a mind so quickly that I wonder how fast we can progress is we got the chance to read a lot of them...

Re:Limits of Measurement

[Melipone]

I wish I could vote this comment up - you've hit the nail on the head.

Re:Limits of Measurement

[Anonymous Coward]

GR gives that an elastic body can have an index of refraction, although it is very close to one, and GR also gives that the speed of gravity in vacuum is c. This has been partially confirmed by observations in the solar system and by decaying orbits of pulsars (although there is a paper or two that disputes the former).

Re:Limits of Measurement

[DahGhostfacedFiddlah]

I hate this point of view - the one that says our math is everything, and there's no objective reality underneath driving it all. The math absolutely has to match observations, but describing physics without trying to understand what's ACTUALLY happening is like describing a baseball game purely in terms of Newtonian interactions. You'll understand individual phenomena very well, but you'll never understand the model well enough to make accurate predictions.

Re:Limits of Measurement

[DahGhostfacedFiddlah]

I like to think of an electrons a droplet of water (well, droplet of EM-field) with some very exotic properties.

• 
  It tends to stick together, but can be pulled apart.
• 
  When an electron is pulled apart (forced through a double-slit, for instance), it's strongly self-attracted, and tries to spring back into an electron-sized droplet very quickly

I think there's a very good reason electrons bound to an atom act like an "electron cloud". It's not that the electron appears and jumps randomly, it's actually everywhere.

Re:Limits of Measurement

[Tyler Durden]

Electrons interfere with themselves, because the fluctuation (which is the electron) exists in the full region between the source and screen. The interference pattern is the same no matter how slowly (in terms of electron rate) you fire the electrons, so build up is not a concern.

And this is an important point. I'm not a physicist, but one thing that helped me understand this better is to consider firing a single electron (for example) at the two slits one at the time. It could be at the rate of one per minute, one hour or whatever.

Every electron that makes it through to the screen behind the two slits will hit it at a single point. Nothing unusual there. However, if you make a histogram on the screen based on how frequently each spot gets hit by an electron you'll see the interference pattern you'd expect from a wave being split in two from the two slits. So each electron is a wave that travels through both slits, not one or the other.

Re:Limits of Measurement

[DamnOregonian]

Of course you can't have a perfect void, but it's quite a stretch to go from "vacuum has a refractive index" to "if it didn't, light speed would be infinite". You're basically saying General and Special Relativity are wrong, as Lorentz Invariance and the Speed of Light (the number, nothing itself to do with light) being the upper bound of velocity that not just the Universe, but Time itself can sustain. At c, time increments by 0. I'm also not including -t (>c) tachyons in that generalization, but they still follow the same rules, just on the other side of the center line.

Re:Limits of Measurement

[DamnOregonian]

I get what you're saying, and even agree with the general point, however, QED for the last half century has been pretty much on a roll of confirming that the math is as close to reality as we can get. There are pretty strong proofs for a lot of bizarre mathematical concepts (wave-function collapse of things larger than bosons, non-locality in entanglement). It appears that the Universe is in fact some kind of bizarre mathematical model, perhaps that we perceive through our limited Einsteinian relativistic space-time. I think this is what leads people to really want to find some kind of String Theory variant to explain it *what it really is* beyond what we can factually test, with the unfortunate side effect of being nearly factually untestable themselves. QM pretty much conclusively shows that whatever "it really is" is not bound by our universal laws of Space Time, but it also concludes that we can only observe it following those laws; so while quantum superposition and entanglement may be real, and there's no fucking way they can happen in 3+1 relativistic space, that's ok, because we'll never observe them directly happening, just the weird slice of the picture we get from our limited view- in short, for us, the math *is* reality, until we're no longer limited by the laws of our relativistic universe.

Re:Limits of Measurement

[Khashishi]

This isn't a perfect analogy, but think of a kink in the carpet. You can push it around, like a object, but you can't make it disappear without taking out some slack in the carpet. Now if we define this kink as a particle, it IS a particle. Using this definition, the particle doesn't have a precise position, nor a rigid shape. But a quantum particle isn't at all like a classical big object, which still has a precise position although it is extended over space. The difference is that a quantum particle appears to be a point particle whenever you look at it, located randomly on a screen in a region where the screen intersects the quantum particle wavefunction. That is, the wavefunction can be so large that the particle basically should cover the whole screen, but we only see a single dot on the screen somewhere. By 'appears to be a point', I mean that the particle collapses onto the resolution of the screen, no matter how high resolution the screen has, to the limits which we can make screens, and a single particle won't excite two neighboring screen pixels at once. Unfortunately, I don't think there's any way to understand this classically.

Re:Limits of Measurement

[DrJimbo]

In addition to what DamnOregonian said, there is another problem with this quest to know what is ACTUALLY happening. For almost all people who voice this desire, "what is ACTUALLY happening" means a model That matches their intuition based on the non-relativistic 3+1 dimensional, classical world of their senses. This ain't gonna happen.

Maybe you misunderstand what the models in theoretical physics actually do. You say we will never understand the models well enough to make accurate predictions. While this may be true of some string theories, but that is a recent phenomenon and a strong deviation from the past. In general physics theories must make disprovable predictions or they are not taken seriously -- they are not physics, just metaphysics.

Whether you like it or not, the underlying theories of the Universe do not match our classical, non-relativistic intuition. But we can still model what happens and make predictions with these models. And people do develop intuitions based on these extremely non-classical models. Almost all progress in physics and math is based on a combination of intuition and turning a crank on complicated mathematical formalisms. Intuition is used for leaping ahead to a possible conclusion which is followed by the grunt work of turning the crank to make sure the intuitive leap was correct. Intuitive leaps are not always correct.

Re:Limits of Measurement

[BranMan]

"This is the argument that Heisenberg used (yes, I've read his book)."

Fine. But did you read it in the original Klingon?

Re:Limits of Measurement

[david_thornley]

What do you mean by "what's ACTUALLY happening"? We've got darn few ways to observe things that happen on this scale, and elementary particles and their combinations behave considerably differently from the scale of the universe we're most familiar with. Electrons behave very differently from charged baseballs, and trying to explain electrons in terminology suitable for baseballs is not productive.

In the meantime, there's quantum phenomena that we inherently can't observe directly. We can measure the spin state of an electron once, getting a binary answer, and then we can't get any more information about what the spin was. We can't simultaneously know the position and momentum of a particle beyond a certain precision. In the two-slit experiment, we can't know which slit an electron goes through without changing the results drastically. (We can figure out some of this statistically. Given a stream of electrons that are similar in some way, we can measure the spins on the electrons in quantity and get useful results beyond up-down.)

So, could you pick a quantum phenomenon and give us a possible explanation in terms you'd accept as describing what's actually happening?

Re:Limits of Measurement

[hacksoncode]

Which is to say, hidden variables that don't violate causality. It's curious that people desperate to preserve causality in the universe like to raise this particular loophole in Bell's Theorem.

Re:Limits of Measurement

[sillybilly]

OK, you're right. So I correct myself: In absolute void the speed of light is not infinite, but just simply does not exist, because it's undefined, 0/0 division, and there is actually no wave at all, because there is no medium to carry it. The speed of any wave is the square root of a driving force term divided by an inertial term, as in sqrt((1/epsilon) / mu) for electromagnetic waves, or sqrt(E/Rho) for mechanical waves, E being the Young modulus, or stiffness (potential energy), rho the mass density (inertia), epsilon the dielectric permittivity(potential energy), mu the magnetic permeability(inertia). In an almost perfect void inertial terms are zero, or very nearly so, infinitesimal, but we don't know how zero the potential terms are. It is the ratio of these residual infinitesimal quantities that determines the speed of the wave, and for light the potential energy inverse permittivity factor is much greater than the magnetic inertia factor, that's how we have a huge velocity. Obviously, in absolute void there is neither inertia nor potential energy, just as there is sound in air, but in absence of a medium, such as in outer space, you can yell all you want in your space suit, the other astronomers can't hear it, there is no air to propagate it, but through a radio that transmits waves through the non-perfect-void between you two he can, because the "aether", the electromagnetic medium between you two is still present, and were it not, there would be no means of communication such as light or radio, you'd be immersed in a completely blind and deaf world, other than actually shooting dee deet dah dah Morse code bullets at each other and maintaining the sense of touch, or even various chemicals, to maintain the sense of taste (imagine you were a metal robot with HF-like(hydrofluoric acid-reacting like) heavy liquid, that does not boil in outer space vaccuum, acid saliva, tasting rocks.) As a different view, imagine you only had ears like bats, and you were in outer space, and you did not even know light existed, so without air you can't see anything with your ultrasound ears, or talk to each other, but if you use a bunch of ping pong balls to shoot around you instead of ultrasound, and a sensor to detect if any bounce back at you, you got a rough image, and your buddy can ping ping some balls at you in a tee tee tah tah Morse code fashion and communicate. So in absolute void there is no wave of any kind, because there is no transmission medium of any kind. It's like saying what is the speed of sound in outer space? It is zero. It stops at the interface of the sound propagating medium, the hull of your spacesuit, and the high or low impedance outer space, with total reflection. I'm not sure the concept of "aether" that has been abandoned as a scientific concept deemed superfluous because we can't measure our speed against it in the Michelson Morley experiment, so it would require complicated behavior to adapt to these experiments, so I'm not sure this concept is useless, because it does provide a medium to discuss, through which a wave propagates. Enabling it with funky but complicated behavior might be an worthwhile thing to do, and maintain Newtonian absolute time and space, and all electromagnetic things bending in it according to the Lorentz rules, but space itself or time itself would not bend. If you can find any non-electromagnetic objects around you (good luck), you could see if that cares about the constancy of speed of light or not. We still don't know what Newtonian gravity is, is it a force that propagates through a medium, and then what are the potential and inertial terms of that medium that would determine the speed. Obviously gravity propagates either infinitely fast, or very fast, as a simple force measuring experiment along the lines of Eotvos Lorant suspending 50 kg lead Pb balls via a quartz hair, and a mirror to bounce light to measure the torsion and force, you could measure how fast the force signal reacts when you suddenly remove the gravitationally interacting objects, vs. initial distance, i.

Re:Limits of Measurement

[sillybilly]

If by GR you mean general relativity, it does not conclude or arrive at as a result, but postulates, presupposes, just like special relativity does, as an axiom, that the speed of light is constant. Also I just read the speed of gravity wikipedia page, and it smells like absolute bullshit, other than Laplace saying something that the speed of gravity must be 7x10^6 times the speed of light, which is an interesting number, but I don't know how he arrived at it. Then the page goes on discussing how Earth would be attracted to where the Sun was a while ago, as I assume, just like we see light get to us from the Sun in 8 minutes, so we see where the Sun was 8 minutes ago, and would have no idea if it disappeared or some extraterrestrial invaders suddenly stole it from us and towed it away, 2 minutes ago, for another 6 minutes, and see where it is now. Duh. But the arguments that finite speed of gravity would make the Earth spiral out of orbit is ludicrous. It is the direction and intensity of force vector that matters as it is encountered by Earth, and just because you see where the Sun was 8 minutes ago, and with gravity you feel where the Sun was distance/speed ago, it does not mean you get a forward or backward pull, because, where ever you are on the orbit, you meet up with the force or wave the Sun sent there 8 minutes ago, pulling you in a direction and intensity just right to maintain the same orbit as if it was sent 1 minute ago or 2 minutes ago, or even two millenia ago if that's how slow gravity propagated, or even instantaneously, you see the same force vector, pointing in the same direction at that point, with the same intensity. So why do you care it was sent right now or a while ago if it does the same thing? There is a lot of fallacy around this. Also observing a quasar as Jupiter passes in front of it, to measure the speed of gravity? What a fucking quack! A quasar and Jupiter are not gravitationally interacting, nor are you with the Quasar or Jupiter, practically speaking. The quasar does interact with its nearby objects. You can't measure speed of gravity between distant galactic objects, they don't interact, unless the mass you're dealing with is huge, and their corresponding distance is very small, so you're dealing with huge gravity forces, and almost the same dots in the picture image from the Hubble telescope. Then theoretically you could get some time measurements, as Kepler kept record, and once you calculate the GM (gravitational constant x mass) for the interacting objects, and can predict their orbits in the Kepler-like relativistic way, and then measure distance accurately too of a 3rd object flying by so close that it's a 3-body system instead of two, and affecting the quasars time periods by turning them into this 3-body system, and plotting the quasar frequency vs. distance of the 3rd object as it collides with them, and knowing the accurate distance, could let you calculate the speed of gravity. There are no accurate ways to measure distances in far galaxies. And good luck waiting out such a collision as they take millions of years to happen, and you need one that slams into a quasar with a timing on the order of the quasars pulses, so that's very fast, and the chances of catching one of these happenings in the sky, i.e. a 2 second event, colliding object position accurately plotted vs. time for those 2 seconds, while it blasted away the quasar, the chances of seeing one of these are pretty much zero in a lifetime, probably zero in a millenium too.

So quit trying to measure the speed of gravity waiting for and hoping to catch high speed gravitational events far away in the sky, and accurately plotting positions too, or computing them from a system of equations, for which you still need measurements of some kind, even if less accurate, for all the 7 actors involved in the system of 7 equations). So the best chances to measure speed of gravity are in the lab, repeating Cavendish's experiments (see the wikipedia page). Just like in the formula for attraction between electric charges, F=

Re:Limits of Measurement

[sillybilly]

For such an experiment to work, you have to get the ratios to do the magic, and, an exaggerated case would be having a lead ball the size of Jupiter inside the lab pulling on the spore of a plant suspended on a hair of quartz torsion spring, exerting a huge force on the spore by virtue of Jupiter's gravity. Then you suddenly pull Jupiter through the door out of the lab with a blast at the other end of the shaft outside the lab, and, because the spore does not have much inertia due to its own weight, the torsion sensor almost has to fight its own inertia as opposed to the spores, but the system is light and reacts fast to a gravitational change, you get a reaction, a sort of high speed gravitational sensor by virtue of its light weight that has just been influenced by huge gravity. If anything a super light sensor like spider web suspended stuff might be better than a quartz hair, and again you're looking for ratios, strength vs. mass, to minimize the mass of suspension equipment vs. the suspended small weight weight, and even going under a microscope to watch position vs. time of a 10 angstrom carbon nanotube suspended 1 microgram weight as a 50 kiloton "Jupiter" suddenly gets jerked out of the lab with a blast on the other end, might come up with some results. Even one significant digit, or just a hint, like a half a significant digit, might be useful, in the measurement of the speed of gravity, or at least provide a lower limit, as in is it the same or more than the speed of light. So one could budget for at least 2 light speeds, and if the experiment does not give a measurement, but comes up with no result in the sense that the speed is still infinite within the confines of the experiment and we can't measure it accurately, but definitely higher than 2 speed of lights, that would be a step forward.

Re:Limits of Measurement

[sillybilly]

We simply cannot measure the speed of gravity because we cannot get the long distance out of it with exact position and accurate force measurements on a small time scale, like we can get out of measuring light, which can be bounced around with a mirror and stays high intensity for miles. Gravity always decays by r squared, an as far as I know there are no mirrors for gravitational phenomena, or high impedance zones for reflection or refraction of gravitational waves if it does indeed propagate by waves, and finite speed. Even the Sun's gravity, which is a huge mass, is barely pulling on my hair to make it stand up when the Sun is overhead, at noon, high up in the sky. It's too far, and its effects decay by r^2. So the best way to measure the speed of gravity is not through large distances, but short distances (and the need for mass and matter density puts a limit on how close you can get in r^2, as Iridium and Osmium are the densest things that we know of, at 22 g/cm3, only twice as dense as lead, and to build up weight you need to put some distance between the objects. There are some unstable artificial nuclei in the Periodic Table right under Iridium and Osmium, which may be the heaviest, densest things in existence under the physical conditions on this planet, but you can't really measure that if all you get in a reactor is like 5 atoms total that decay in 1.7 seconds half life. But if you could get a 50 kton dot 2 micron away from another one, that would be the way to go, as even a humongous weight Sun gives you almost nothing to measure. The shorter length drops linearly the speed measurement quantity, but it increases by the square the gravity effect. And under such short distances ultrashort time measurements are needed. Whatever the limits of short time measurements are, they can be pitted against this need of measuring speed of gravity in the lab, under the shortest possible distances.

Re:Limits of Measurement

[sillybilly]

That's pretty neat that if you have a few planets orbiting a star, they pull on each other to end up in the same plane long term. I didn't know that was the case. So flat galaxies come about from the stars themselves pulling each other into a flat orbit and organizing the galaxy like that. So that would mean an elliptical galaxy is a young one, and a flat one is an old one, where enough pull on each other interactions have happened. I think officially they claim it the other way, that elliptical ones are the old ones. Hmm.

Re:Limits of Measurement

[Anonymous Coward]

it smells like absolute bullshit,

Because physics results are trumped by smell and intuition...

A quasar and Jupiter are not gravitationally interacting, nor are you with the Quasar or Jupiter, practically speaking.

Of course not, which is why such experiments look at the interaction of Jupiter with the light from the quasar...

And of course your statement that such measurements are impossible because of some loose reasoning is all that is needed to make a firm conclusion, unlike detailed, quantitative calculations of actual detection thresholds in various papers.

Re:Limits of Measurement

[DahGhostfacedFiddlah]

I think my biggest problem was the phrase "ISTM your question is meaningless". It reinforced my general impression that a lot of physicists treat the math as the be-all-and-end-all of physics, without trying to develop an overarching (for lack of a better word) "narrative".

You end up with statements like "going faster than c makes you travel backwards in time" or "an electron doesn't have a position until it's measured". Both fit the math, but are probably simplifying things greatly. I suspect the physics of the future will provide intuitive explanations, with new underlying rules that will seem inscrutable. Dismissing the importance of the ACTUAL reality shuts down avenues of investigation and harms discourse.

That said, your last paragraph makes me think I was just overreacting. You've made it clear that intuition is an important aspect of theoretical physics, and people aren't blindly following the math.

Re:Limits of Measurement

[yndrd1984]

Which is to say, the statement was entirely correct. It's curious how people who are enamored with one interpretation see neutrally stated clarification as desperation.

Re:Limits of Measurement

[Anonymous Coward]

Your "improved theory" explaining the double slit experiment is so full of holes that 'double slit' becomes a misnoma.

Re:Limits of Measurement

[sconeu]

Hasn't Bohm come up with a working HVT? ISTR that his works, provided reality is non-local, and the EPR/Aspect/entanglement experiments have proven that such is actually the case.

then/than

[Anonymous Coward]

Syntax error in line 8.
I see this mistake far too often.

THEN denotes a sequence. this THEN that, in that order.
THAN denotes a comparison. this OR that.

This is Slashdot ffs, programmers should not have this problem.

REM: pet peeve

Quantum strangeness is when...

[Mister Liberty]

my BIOS has enigmatic quirks.

Bankers will study this hard ...

[Alain Williams]

in the hope that this might provide them with yet another way of separating the public from their properties (especially money).

Dupe?

[Brucelet]

This was on here 6 months ago when the preprint hit arxiv.

Re:Dupe?

[Anonymous Coward]

This was on here 6 months ago when the preprint hit arxiv.

Perhaps a quantum dupe, caused by the effects of Beta? >:)

Re:Dupe?

[ray-auch]

Yeah but that one had a different spin on it (different route)

Re:Dupe?

[drouse]

From the perspective of certain points on a light cone, the article showed up both today and 6 months ago. :-)

Re:Dupe?

[t_ban]

Nope, that's the article interfering with itself.

Limits of Measurement

[Anonymous Coward]

This rather sounds like Hidden Variable Theory, and that's been pretty much discredits. Bell's Theorem, I believe it is.

Mod parent up...

[enharmonix]

Now that I understood. I am actually a little interested to see what kinds of experiments they do along these lines. It seems like string theorists might actually have the opportunity to predict behaviors that the standard model cannot. Unless it just ends up being some previously unknown new elementary bosons... but we already got Higgs. Do we really need more elementary bosons?

Re:Mod parent up...

[sillybilly]

I too am an elemtary bozo. And so are you.

Good example

[nospam007]

It's a good example for life.
Take the high road and nothing can affect you.

Proof?

[Integrator]

Sounds like a bug in the Matrix to me. It will probably be fixed in the next release.

Re:Proof?

[Tablizer]

Sounds like a bug in the Matrix to me. It will probably be fixed in the next release.

No, the Matrix learned from Microsoft: you don't have to fix anything if you have no competition.

Re:Proof?

[CaptnZilog]

It's easy to fix, all you have to do is reverse the polarity of the neutron flow and you'll save the day.

Limits of Measurement

[Anonymous Coward]

You're wrong, you see the interference pattern even with single particles. That's the weird part.

Bullshit

[Anonymous Coward]

Quantum mechanics is total bullshit. We're too stupid to figure out how it all really works.

MORE strangness?

[briester]

First: when we have established a universal law, and something obeys that law, it is not strange. Two: when you assert that something flies against intuition, you'd better ask some gradeschool kids first. Mine called the author an idiot. (They're 8 and 10.) Three: if someone's experiment results in the observation of a well known, well documented, scientifically named phenomenon, (superposition,) it is rude to call it "more." Or "new." Just rude.

Re:MORE strangness?

[wonkey_monkey]

First: when we have established a universal law, and something obeys that law, it is not strange.

Strangeness is a subjective quality.

The laws themselves are strange to the majority of people because they run counter to everyday experience, therefore things that obey those laws also appear strange.

Two: when you assert that something flies against intuition, you'd better ask some gradeschool kids first. Mine called the author an idiot. (They're 8 and 10.)

Then they probably didn't understand the experiment, or you explained it just poorly enough to get the response you wanted for your Slashdot post to make it look all clever and stuff.

Three: if someone's experiment results in the observation of a well known, well documented, scientifically named phenomenon, (superposition,) it is rude to call it "more." Or "new." Just rude.

This goes beyond "simple" superposition, and is indeed a new phenomenon.

Sooo....

[penguinoid]

So they split a beam based on the spin, then applied a magnetic field that would shift the spin from down to up, either on the particles that already had spin up or on particles that had spin down... and AMAZINGLY only the latter had any effect on the spin. And they also put a blocking filter either on the particles that had spin up, or on the particles that had spin down... and AMAZINGLY only the former reduced the number of particles with spin up. Truly mind-boggling, this quantum stuff.

Re:Ugh... another editor fail

[Anonymous Coward]

No, this is not just quantum superposition.

Did you even consider the possibility that you might not have as deep a grasp of quantum physics as these scientists?

Re:Ugh... another editor fail

[Anonymous Coward]

I would mod parent up and root down if I wasn't an Anonymous Coward

Don't quite understand

[Anonymous Coward]

How do you split neutron beams and then bring them back together? A neutron has no charge or magnetism and therefore electrical fields don't work on them.