Gravity-Detecting LIGO Also Found To Be Creating Gravity Waves (sciencemag.org)

LIGO is a large-scale physics experiment to detect "ripples in spacetime," as well as gravity waves from outer space. But it turns out that it's also creating gravity waves, according to a team of physicists led by Belinda Pang, a physicist at the California Institute of Technology. sciencehabit quotes Science magazine: Although these waves are far too feeble to detect directly, the researchers say, the radiation in principle could be used to try to detect weird quantum mechanical effects among large objects... Of course, LIGO doesn't generate large gravitational waves -- you could probably make bigger ones yourself by whirling bowling balls around -- but it does so with optimal efficiency [and] the waves could still be used to probe quantum effects among macroscopic objects, Pang says.

Quantum mechanics says that a vanishingly small object such as an electron can literally be in two places in once. Many physicists suspect that it might just be possible to coax a macroscopic object, such as one of LIGO's mirrors, into a similar state of quantum motion. That delicate state wouldn't last long, as interactions with the outside world would make it "decohere" and put it in one place or another. However, one could imagine measuring the rate at which such a state decoheres to see whether it matches the rate expected from the radiation of gravitational waves, Pang says.
"It's unbelievably difficult," Pang says. "But if you want to do it, what we're saying is that LIGO is the best place to do it."

Comments

"...these waves are far too feeble..."

[turkeydance]

"Always with the negative waves, Moriarty, always with the negative waves." https://www.youtube.com/watch?...

Figures

[Ol Olsoc]

This is what happens when you tell scientists to go step on a LIGO

Gravity wave != Gravitational wave

[skoskav]

Hopefully I ruined the fun by being pedantic.

Re:Gravity wave != Gravitational wave

[TeknoHog]

Let me wikipedia that for you:

https://en.wikipedia.org/wiki/... -- waves on the surface of water whose dynamics is dominated by gravity. See https://en.wikipedia.org/wiki/... for smaller ripples dominated by surface tension.

https://en.wikipedia.org/wiki/... -- what the fucking article is about

Re:Gravity wave != Gravitational wave

[x_t0ken_407]

There's a VERY important difference, however. I think it's more about getting this shit fucking correct. Even TFA spells it out properly...not sure how that was missed in TFS. Oh, Slashdot, you keep me young.

Copenhagen Interpretation

[jIyajbe]

No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.

----------------

*Technically, the square modulus of the wave function.

----------------

Sorry for the physics rant; I feel better now.

Re:Copenhagen Interpretation

[JoshuaZ]

Um, it is one thing to assert that FTA and TFS should not have been more clear that what interpretation of quantum mechanics one uses here matters. At the same time you appear to then be making the same mistake by insisting on a specific interpretation as correct and that others are nonsense.

Re:Copenhagen Interpretation

[Anonymous Coward]

The classic double-slit experiment says otherwise; if you pass one electron at a time through the apparatus, and you get an interference pattern, that means the electron passed through both slits (i.e. it was in two places at once), and interfered with itself.

Re:Copenhagen Interpretation

[Anonymous Coward]

The classic double-slit experiment says otherwise; if you pass one electron at a time through the apparatus, and you get an interference pattern, that means the electron passed through both slits (i.e. it was in two places at once), and interfered with itself.

That's bovine fecal matter. You do not detect an interference pattern. An interference pattern would be the envelope of a very large number of detection events. You would only have one detection event. xkcd hails your extrapolation skillz

Next, your understanding of the Young experiment is lacking. It might have helped if you did this in a Physics lab. Or wrote the wave equations, to realize the factors that drive the interference pattern's shape. You might otherwise be surprised to find out that if you pass one electron through the double-slit system you observe one electron behind it. The magical uncertainty thing is the transversal position, that you cannot pre-calculate ahead of observing it. It's a probabilistic thing.

And last, it's getting really tiresome to see people who likely never studied Quantum Mechanics with any degree of rigor repeatedly make this one mistake. Stop trying to assume that macroscopic approximations such as particles apply at the quantum level! It's like trying to apply flat-space Newtonian mechanics to a General Relativity problem and then complaining that the GPS that someone put together using your equations is completely inaccurate. Wrong tool for the job. Here's a hint: all we observe at the quantum level are interactions - those have many 'particle-like' features; what happens in between interactions, a.k.a. propagation, is not particle-like and instead to our macroscopic-trained minds looks like wave propagation. You might have heard of it, some people call this conundrum particle-wave duality. An electron is such a beast, interacts sort of like a macroscopic particle, propagates sort of like a macroscopic wave. Stop trying to force it to be a macroscopic animal, it is not.

Now, if you understand that, you'll stop trying to invoke double-slit experiments, as there's no need. If you want to bring up the wave-like propagation of electrons, a single slit is enough, you get a diffraction pattern out of it. Same thing with light, really, so no need to bring up electrons at all.

Re:Copenhagen Interpretation

[Anonymous Coward]

Then explain the double slit experiment. Why the sinusoids interference pattern?

Re: Copenhagen Interpretation

[hackwrench]

The conclusion, "two places at once" is as good a layman's description as we're going to come up with; does not follow from the premise, since we can't observe it's position before we.... observe it, and it's position can only be defined as a probability of being in a certain set of locations.

I haven't seen any evidence to suggest anyone has actually measured an electrons location and velocity at a given time to absolute accuracy. That's a problem I have with much of the surrounding physics claims.

Re: Copenhagen Interpretation

[hackwrench]

From what I understand, when talking about things as waves, the most accurate layman's term would be that it is spread out over an area.

Re:Copenhagen Interpretation

[Kjella]

No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.

That doesn't really explain the crazy part of QM, it just sounds like a particle bouncing around to form the probabilities, like saying Schrödinger's cat is dead or alive long before you open the box. What's so hard to understand is that it's not just passive observation, the act of observation collapses the wave function. The opening of the box decides if the cat is alive or dead. I think in laymen's terms you can't explain an uncollapsed wave function any more correctly than that a qubit is both 0 and 1 at the same time. Both possibilities exist as a potential, until you try reading it. Except it doesn't really have both values, it's more like a lottery that hasn't been drawn yet. The balls have the potential to make any winning numbers, but the drawing collapses the possibilities down to just one. As long as you don't draw, everything is possible. Actually that is a good analogy, a qubit isn't heads or tails. It's a coin you haven't flipped yet.

Re:Copenhagen Interpretation

[schweini]

So, what would happen if I run a double-slit experiment, but measure which slit each fired electron went through?

Re:Copenhagen Interpretation

[jIyajbe]

(Sorry for the delay in answering; Sunday night movie with the wife. :-) )

The term "superposition" means, in this context, two things--or rather, one thing, but expressed two ways:

(1) Given a particular physical setup--the collections of forces (or, equivalently, sources of potential energy), both internal and external, that act on a quantum particle, along with the initial conditions of the system--quantum theory cannot produce a single answer to any question you might pose, but only a list of possible answers, along with the probabilities that a measurement of the relevant physical quantity will produce each possible result.

For example, if I ask "In my particular experiment, what is the magnitude of the orbital angular momentum of the electron in a hydrogen atom", quantum theory will produce a list of (say) 5 possible values, along with the probabilities of obtaining the 5 values: 2%, 10%, 76% 10%, 2%--when you make the measurement. Thus, after the measurement, the angular momentum has a definite value; but before the measurement, the most we can say is that the electron will be found in one of those states, according to the weighted probabilities.

But, that is a lot of words; so, the phrase "quantum superposition" was invented to mean all of that. The common phraseology is to say that "prior to measurement, the electron is in a superposition of these 5 quantum states".

(2) The math way to say exactly the same thing is the state function (i.e., the solution to Schrodinger's equation for the given potential energy function) is a function that is a superposition (a sum) of so-called "basis functions" (or "basis states"); each basis state is one of the 5 states mentioned above.

This is what people mean when they write things like "the electron can be in two places at the same time", but it is a horribly imprecise and misleading way to phrase it. --But I understand why writers do it; look how many words it took me; what newspaper editors would allow 400 accurate words when 40 semi-accurate words will sort of do, and who the hell besides a few physicists will care, or even know?

Re:Copenhagen Interpretation

[jIyajbe]

Sorry, I wasn't clear: I'm not suggesting the other interpretations of QM are nonsense; I am suggesting that the statement that "the electron could be in two places at once" is nonsense. As the poster below me said, there are NO interpretation of QM (of which I am aware) that will make that claim.

(That said, the Copenhagen interpretation, whatever its ontological problems, has the virtue of having stood the test of time and--more importantly--LOTS of experiments.

Re: Copenhagen Interpretation

[jIyajbe]

Mathematically? It's because the function that produces the probability values is time-dependent; the result is that the probabilities of the various values (momentum [not velocity] and position, to take your examples) change over time. Thus, if you wait too long after you made your first measurement, subsequent measurements of the same physical quantities will have "decohered" again.

Physically? Since there are lots of possible quantum states, and since the probabilities associated with those states are determined by the force/energies that surround your electron, then as time passes, the forces and energies interact with the electron, and so the electron's physical state is re-randomized. (Semi-randomized, actually, but never mind.)

Re:Copenhagen Interpretation

[jIyajbe]

You will find that the interference pattern is destroyed! You will instead get two blotches of electrons, one in front of each slit.

Re:Copenhagen Interpretation

[jIyajbe]

Correct; I was attempting to explain what, not why. To the best of my knowledge, the question of why an observation collapses the wave function has only been partly answered. Essentially, you have to ask (for every case) exactly how the observation was done. Most commonly, you bounce one or more photons off of the thing you want to observe (or you arrange for it to emit on or more photons). This appears to be the cause of the collapse. Hopefully someone who knows more than me will chime in with more detail?

Re:Copenhagen Interpretation

[Antique Geekmeister]

One difficulty is that the observation of the interference patterns of double slit experiments with even single photons demonstrates the superposition of quantum states in a macroscopically observable way. It's very difficult to explain or understand the interference patterns of single photons fired through a double-slat experimental array without assuming that the individual photons do, in fact, have multiple locations.

The mathematics is fascinating: I've not explored for decades, but remember well my surprise that such logically confusing quantum effects were so easily measurable.

Re:Copenhagen Interpretation

[jandersen]

No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.

Well, according to the standard interpretation of the theory, that is itself only a model of what we think the world seems to be like. What QM has to say about the subject could also be interpreted as "particles are not actually points in space, and what we see may be an artifact of the way we measure things"; not the orthodox view, I know, but I think it is healthy to try to find a path away from the current orthodoxies, not least because we know that our theories are incomplete. Unless things have moved a lot since I was close to physics, what we are measuring when we do experiments on particles, is not individual interactions, but 'statistically significant' samples of interactions - ie. billions of them - and we extrapolate back to what happened on average, using a model that already makes some strong assumptions about what it is we are looking at. That is OK, as far as it goes, but we have to always keep in mind that we can't speak with any certainty about what is going on in the physical reality; we can at best say that it is consistent with our preferred theory - but there may be other, even better theories. In fact, there must be, all things considered.

Re:Copenhagen Interpretation

[fisted]

Re double-slit, I've always wondered how they can measure a single photon AND have it pass through the slit. Why isn't the photon consumed in the process of measuring it?

Re:Copenhagen Interpretation

[Carcass666]

This is what people mean when they write things like "the electron can be in two places at the same time", but it is a horribly imprecise and misleading way to phrase it.

Yah, I wonder if they said something like "the electron could be in either of two places at the same time" instead if that could be more easily understood (if that phraseology doesn't break the idea of superposition in the first place).

Re:Copenhagen Interpretation

[JoshuaZ]

I think one could reasonably summarize MWI as the object being in more than one place at once in different branches, but I do agree that it isn't a great description. In any event your last sentence in parentheses merits more of a response: other than some very naive collapse interpretations, all interpretations of quantum mechanics agree on predictions for experiments; that's what makes them interpretations rather than models or hypotheses in their own right. So one can't reasonably defend a specific interpretation as meeting experimental data.

Re:Copenhagen Interpretation

[Antique Geekmeister]

I mis-spoke. The experiment typically involves electrons, not photons.

Re:Copenhagen Interpretation

[fisted]

AFAIK the experiment typically involves photons.

Not that this is relevant to my question...

Re:Copenhagen Interpretation

[MindStalker]

Many interpretations are that it is actually a wave, and not a particle at all during travel. So it isn't "two places at the same time" so much as it is a wave. From the perspective of this wave though travel is instantaneous (time does not pass), so its not breaking a law being a particle at one place, a wave during the travel, then a particle at the end point.

Re:Copenhagen Interpretation

[rgbatduke]

Hey, somebody had to do it. Using English with embedded classical logic to describe quantum phenomena is a waste of time. And even most physicists have never read Schwinger or studied the Nakajima-Zwanzig equation and hence have little idea of how to formally obtain the classical measurement projection in an open system interacting with a classically described statistical bath when the combined closed system is in a stationary state and has no probabilities at all. And then there is relativity and time reversal invariance.

I'm just sitting here, wondering if the back of the envelope computation is dead. When did we get to the point where we could resolve 30+ orders of magnitude effects in the lab? We haven't even -- as far as I know -- experimentally verified whether normal matter gravitation attracts or repels antimatter, which seems like it would be a pretty important first step in building a QFT with gravity or GR, but even that seems beyond us so far.

rgb

Re:Copenhagen Interpretation

[rgbatduke]

It is. The point is that if you measure which slit it passes through, the interference pattern that implies that it passed through both AS A WAVE, not a particle, disappears. The rule for this sort of thing is that if you measure wavelike properties, you don't get a definite particle position/state. If you measure a definite particle position/state, you don't get wavelike behavior any more. This is called complementarity and is the basis of the uncertainty principle. Electrons and photons alike behave the same way. Even at very low intensities where you can effectively observe single photons or electrons AT THE DETECTOR, if you don't look to see which slit they go through you get interference, implying that the electron passed through both as a wave (function). If you do look and measure the slit the photon or electron passes through, no more interference pattern, no more waves.

The electron in some sense isn't in two places at once -- it is "everywhere" at once, but with a low probability, if it has a very well defined momentum and hence wavelength. If you measure it or confine it to some specific location, you do so at the irreducible expense of having a well-defined momentum (and hence wavelength).

I'm actually teaching this stuff right now at the most elementary level. There aren't a lot of good intro level books on it, but I'm using Harris's "Modern Physics", which is at least pretty readable and has some of the real math in it. Beyond intro modern physics books, you can try Wikipedia (often has surprisingly good articles on this sort of thing) or a real quantum textbook. Or two. Or three or four. It takes years to not quite understand quantum mechanics, and an important step along the way is to UNlearn all of the nonsense you "learned" about it in English statements and to concentrate on the consistent mathematical and conceptual formulation of the theory.

rgb

Re:Copenhagen Interpretation

[fisted]

Thanks, but the one thing your comment does not do is answer my question :-).

It is [consumed].

So then why do we see *anything* at the detector screen when measuring at the slits? How do you measure a single photon passing by without consuming it?

Re:Copenhagen Interpretation

[rgbatduke]

OK, I'll try again. YOU DON'T. All you see is electrons being "consumed" as they hit the screen, forming the interference pattern.

If you DO look for them as they pass through the slits -- where one can do this without "consuming" them by e.g. putting a conducting loop around the slit that will experience a voltage pulse as the electron passes THROUGH it or by illuminating the volume right behind one of the slits with intense light that can scatter off of the moving electron and hence detect the slit the electron passed though -- then the interference pattern goes away.

This is a fundamental sort of "goes away". It isn't just that we gave a small extra push to the electron, as in principle you can CLASSICALLY make the detection so weak that it wouldn't affect the classical trajectory. It is that the detection itself shifts the PHASE of the electron and hence destroys its coherence with the electron(s) passing through the other slit, so there is no longer any interference.

Also, you can read:

https://en.wikipedia.org/wiki/...

which both walks through all of this and provides you with references to at least some of the actual experiments that verify it.

Re:Copenhagen Interpretation

[fisted]

e.g. putting a conducting loop around the slit that will experience a voltage pulse as the electron passes THROUGH it

Thanks.

WARNING: Geekiest joke ever dropping here

[SuperKendall]

LIGO my EGO!!

Re:WARNING: Geekiest joke ever dropping here

[Tablizer]

An ego big enough to generate gravity waves? Hmmm, who could that be?

Well of course.

[hackwrench]

I would expect all matter possessing a Higgs boson would generate gravity waves. Which is pretty much all matter.

Nobody explains this in a way that makes sense

[hackwrench]

Alright, you have one electron. How do you detect the interference pattern?

Re:Nobody explains this in a way that makes sense

[PPH]

You have lots of electrons, but only one at a time.

Re:Nobody explains this in a way that makes sense

[hackwrench]

Well, of course I've
heard of it. How would I be saying that nobody explains the experiment in a way that makes sense if I hadn't heard of it. You have some serious reading comprehension issues.

Re:And again people sound off...

[hackwrench]

All the comments so far are just people who like to type and do nothing at all to clear matters up and for that matter don't seem to understand the experiment themselves. The Wikipedia article, for that matter speaks of an experiment involving light, not electrons. https://en.wikipedia.org/wiki/...

Re:Physics breaking things

[hackwrench]

Oh, physics breaking things. I'm so scared. Wait, no I'm not. What have you got against "physics breaking things"? From what I've been able to figure out however is that nothing, electrons included, are all that well defined.

Re:Lack of detail

[hackwrench]

And what was that smashing of keys supposed to clear up? It's not like the article offers any details of the experiment, merely noting that it exists.

Looks like it's time for "the talk"

[burtosis]

No, the electron is NOT "in two places at once". That is nonsense. Prior to measurement the electron (and indeed, any quantum particle) simply does not have a well-defined position; rather, there is a set of points in space where it could be found (weighted by the probabilities returned by the* wave function of the electron in the given physical setup ("the potential well")). It is only when a measurement is made that the probabilities resolve to a certainty--and the electron is then found in literally one position in space.

----------------

*Technically, the square modulus of the wave function.

----------------

Sorry for the physics rant; I feel better now.

The good ole story of what happens when two particles feel really entangled.

At least what you say makes sense.

[hackwrench]

Above I said an experiment has never been explained very well. Then a bunch of people made a bunch of extremely unhelpful replies.
Your statement makes sense, and is pretty much topical and if people feel they don't understand it, could stand to read it several times until they get a better understanding. Better yet they should take a moment and think through what a good question might be and ask it.

Re:Physics breaking things

[ClickOnThis]

Oh, physics breaking things. I'm so scared. Wait, no I'm not. What have you got against "physics breaking things"? From what I've been able to figure out however is that nothing, electrons included, are all that well defined.

And that is where you fail. Science will never claim to know everything. But it is indisputably the best way to shrink-wrap the tightest boundary about what things we do know.

That is all. [mic drop]

Re:What might be happening

[hackwrench]

Not sure what is happening, but one explanation I've come up with that is consistent with science from other sources is that when matter encounters space, space curves. Now people seem to think that space springs back after the matter passes, but what if there is a deformation left on space that future particles interact with?

Re:Where I fail

[hackwrench]

Nothing you have said indicates that I have failed. Perhaps you didn't understand what I wrote. This would not be entirely your fault, not because I am somehow so brilliant, but that I seem to have a completely different take on reality than other people. But both I and everyone else is still here, so neither of us is entirely wrong.

Re:Superposition

[hackwrench]

I found that https://en.wikipedia.org/wiki/... answered questions I had better than the one on quantum superposition, possibly because the latter requires the reader to understand concepts in this one in order to understand it.

Not worth arguing over [Re:Lack of detail]

[Tablizer]

There are different models to "explain" quantum physics. Some versions imply things can indeed be in two places at once. For that matter (no pun intended), what is a "place" and "at once" exactly? English wasn't meant to be precise enough for sub-atomic behavior.

Re:Where I fail

[ClickOnThis]

Looking at this thread again, I am inclined to concede graciously. You and I may very well share the same take on reality.

My point was that science is not infallible, but that it is the best tool we have for understanding the universe. And whatever counter-intuitive theories we come up with must be accepted if they fit the data. And that means that electrons are very well defined by our current theories, even if it means they can be in two places at once.

Peace out.

Re:Not worth arguing over

[hackwrench]

Well when you are talking about waves, it's generallly better to talk about areas. But we're talking at this point about the double-slit experiment and how from my experience it isn't explained very well. Subsequent science seems to support a wavicle model, but the experiment remains poorly explained. The limitations in most languages can be highly alleviated by how one couches one's terms.

Part of the problems with describing quantum...

[hackwrench]

When they describe quantum computers they mostly ignore trying to describe operations and throw the word superposition in front of 0 and 1. Only, superposition, it turns out, has a mathematical meaning, one that has to do with wave functions. https://en.wikipedia.org/wiki/...
So qubits apparently involve encoding of functions, not just states.

Re:Well, what would be different?

[hackwrench]

From the article:
1. It would take more than eight minutes for changes (caused by its motion around the Milky Way galaxy) in the sun's gravity to reach the earth and even longer for the more distant planets.
2. So the earth's orbit around the sun would depend on where the sun was eight minutes ago, the time it takes changes in the gravitational field to reach the earth, and not on where it is now.
3. This is not observed.

So how is what would be observed given 1 and 2 be different from what is observed?

Re:Clocks

[hackwrench]

Well that bit about clocks was helpful... in the sense that it jogged something in my mind that allowed me to find an article that explains the clock situation and how it doesn't have anything to do with gravity. So your article's assessment of the countertheory is wrong. https://www.quora.com/Does-acc...

Re:Time not a dimension

[hackwrench]

Now this is the one that was wrong based on facts on hand. An argument for why time is not a dimension is applicable to making space not dimensional as well.

Now you border on something that begins to make sense with the only one speed bit, but here is an observation for you: An object at motion is also an object at rest.

Re:Your AI nonsense

[hackwrench]

As for your more recent stuff, AI neural nets do not model reality, either.

Re:Where I fail

[cb88]

You don't *have to* accept anything... you can and should sometimes try to come up with alternative theories...that explain things better.

Sometimes 2 ore more theories may explain the data equally well ... but one is more elegant, or less complex etc...

Theory on faster than the speed of light

[hackwrench]

They talk about warping space as a method of going faster than the speed of light, but it seems that space warps whenever there is motion, so maybe the math is just a little off or just not reflected in speech, or the connection isn't made in physicists heads.

Re:Magical thinking

[hackwrench]

How does any of that require magical thinking? For that matter, define "magical thinking".

Gordon doesn't need to hear all of this.

[malditaenvidia]

We've assured the administrator that nothing will go wrong.

Finally, quantum theory and gravity unified!

[K. S. Kyosuke]

The measurement changes the experiment! Right?

Comment

[WallyL]

This topic sounds like a Star Trek episode. Think Star Trek: Voyager where the crew has to rescue a planet from itself because they were experimenting with gravity waves!

Experimental setup

[DrYak]

In an over simplified-way that might make physicist angry... ("I am a doctor, Jim ! Not a quantum physicist !")

Design a machine that fires approximately 1 photon per second.
Measure and confirm rate of photo firing.
Then put double slit in front.
Expose picture.
As during any given second, there's (an avarage) maximum of only photon,
then (in average situation) this single photon should not have any other to interact with.
Classic physics should predict only a (predominant) picture of the slit with (nearly no) pattern at all (except for the few outlier situation where 2 photons ended up in flight due to imprecision, but then their pattern should be much fainter).
Quantum physics should predict that even if (most of the time) only one photo is in flight, you still see a diffraction pattern predominantly. (and not only faintly for the couple of mis-firing)

In short : do the measurement AND the experiment at 2 different times, otherwise the measurement will destroy the photo.

Now again, this is NOT my area of expertise, so I probably made have of the physicists on /. cringe (and the other half laugh uncontrollably).