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An Experiment Could Determine Whether Gravity Is Quantized (forbes.com)
TheAlexKnapp writes: Physicist Brian Koberlein explains an experimental proposal by Großardt et al, which would attempt to determine whether gravity is quantized. "Their idea," explains Koberlein, "is to take a charged disk of osmium with a mass of about a billionth of a gram and suspend it an electric field. This is small enough that its energy levels in the electric field would take on quantum behavior when cooled to temperatures a fraction of a Kelvin above absolute zero, but its also massive enough that its gravitational pull would affect the quantum behavior."
The two primary approaches to a quantum gravity, the "perturbative approach" and "the semi-classical method," predict different results from this type of interaction. So the results of the experiment, could, in principle, elucidate the right approach for developing future theories of quantum gravity.
The two primary approaches to a quantum gravity, the "perturbative approach" and "the semi-classical method," predict different results from this type of interaction. So the results of the experiment, could, in principle, elucidate the right approach for developing future theories of quantum gravity.
Proposed experiment: arXiv:1510.01696.
More detailed theory: arXiv:1510.01262.
See also blog post.
Not much gravity ... or anything else on Forbes
There's a good explanation by a physicist who thinks about experimental validation of quantum gravity here.
Yes. The smallest unit of time is called Planck time. Its sort of the frame rate of reality.
It's not about gravity, it's investment advice. Long osmium?
shut up and do the experiment already!
Better known as 318230.
Physicists are quantized, so they want everything else to be quantized.
My issue arrives once per week
Just google it.
Just to be clear, Planck units have no physical significance. They're just a convenient way of doing physics calculations because when you use Planck units, you can treat some fundamental constants as equal to 1.
So Planck time isn't the frame rate of reality, it's just a really small unit that makes some calculations easier.
Last post!
Not trying to poop on it, far from it. But could someone explain just what this should prove or show? What insights will this give us?
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
How the charge of a single electron was measured back in the early 1900's - good luck to these scientists.
sigs are for losers (except to point out that sigs are for losers)
gravitons exist? (I remember reading the problem with gravitons is that they were basically impossible to detect because their interactions were so weak.)
Did you know 80 to 90% of the moderators on slashdot wouldn't recognize a troll even if one dragged them under a bridge.
Why is the site covered in cheap clickbait and list articles? Are they that desperate for clicks that they'd list "Grid Girls, Pit Girls photo collection" and "Fame Was The Worst Things That Happened To These 10 Former Child Stars" on the page?
I think those are just advertisments that are deceptively made to look like part of the host site, which is almost worse.
thumby.grvcdn.com, you're going on my blocked DNS lookups list.
Even if mass would be quantized, the Newtonian equation is m1m2/r^2. Even with discrete mass quanta (which is also false, see other replies), you would get a continuous spectrum of resulting forces. Inserting relativity here changes the expressions, but it would really just muddle things. So, no, there is no specific reason to believe gravity to be quantized - outside of an actual theory of quantum gravity.
Does Time come in quanta?
Nope. Cubes.
Faster! Faster! Faster would be better!
That is not what's meant by gravity being quantized. Quantum gravity would mean the gravitation interaction between particles is quantized: i.e. if particle A pulls on particle B (and vice-versa), the energy exchange between them occurs in discrete packets. The alternative would be that the gravitational forces between them are a continuous interaction, so that A pulls on B to change the energy state of both constantly. To use an analogy: the former is like an object rolling down a staircase, where the objects level jumps as it falls down a step, while the latter is like a ramp, where the object's level takes on all continuous values of the ramp.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
So... a fraction of a Kelvin then.
-- Thou hast strayed far from the path of the Avatar.
Kind of an interesting discussion. One of the interesting things that have come out of the whole blackhole information paradox is that tossing an elementary particle into a blackhole increases its spherical surface area by exactly one square planck. They said if you run that backwards, it means you can store at most 1 bit(explicitly state binary bit of "data") of information in a cubic planck. That is the density of a blackhole.
It seems that the current set of elementary particles are the highest density you can get. In that sense, information is quantized. If information in quantized and mass is information.
Either way, I can't wait to see the results of this stuff.
"Oh dear, Watson, I just fell up!"
Table-ized A.I.
from memory the plank length is the distance where the energy to measure it would create a black hole so its the limit of measurement.
plank time is the length of time traveling at c to travel the plank length, so is also immeasurable.
i would say it has the most extreme physical significance, its only in the theoretical it could be less significant.
There is a huge difference between something being smaller than any single event and it being quantized by that amount. Even if you can't find an event quicker than that, it is possible time is continuous in such a way that the spacing between events is not an integer number of Planck time. In fact, there isn't really anything in quantum mechanics that says that time behaves that way at all, unless you want to tack on additional hypotheses (and it makes a mess of things).
The Planck units are just multiplying fundamental constants together so that you get some value with the right units, and the significance of that is not necessarily quantization, but limits where extreme gravity and quantum mechanics would be present in the same setup. This either means we can speculate that such situations would require an understanding of quantum gravity, or would do something based on GR instead of quantum mechanics. The Planck mass is nothing extremely large or small for example, at a couple nanograms, although could be the largest mass a point particle can have before being a black hole (with some speculation).
If Gravity is nothing more than a curvature of spacetime and objects moving through it fowls "straight" lines, then why do people still also say that gravity is a force? Or try to unify it with the other forces? Or tat it can be quantized?
If you reply, do so only to what I explicitly wrote. If I didn't write it, don't assume or infer it.
Maybe.
I sort of tend to agree with you that everything is quantized at the Planck scale, but it's so small that I doubt we'll ever be able to check on it.
OTOH, I'm a finitist. I don't believe in infinities or infinitesimals. I think that they are calculation aids that have been hypothecated. I, therefore, don't think ANY continuous function accurately maps onto reality. Many of them, however, come close enough that you can't tell the difference.
To put it in other words, I believe the universe is digital, not analog. But we are parts of the universe, and so are the tools we use to observe it. And we are at a large enough scale above the level of granularity that we can't see the difference. (Just try to understand how small 10^-33 cm is.)
I think we've pushed this "anyone can grow up to be president" thing too far.
Good paper. Anyone really interested should read it. But I feel he assumes continuity in places that I don't accept. (OTOH, I couldn't do a decent refutation, I just don't accept everything he says. Perhaps if I read it a few more times...)
I think we've pushed this "anyone can grow up to be president" thing too far.
Were that to be the case, you'd need to worry about the gravity of neutrinos, as they are currently the least massive particle known. But good luck trying to measure the mass accurately, or trying to get one to change it's speed, or even bend its path.
I think we've pushed this "anyone can grow up to be president" thing too far.
So, no example is forthcoming?
No, I would want to see something faster than it. Something slower than it, but non-integral, could be explained as a summation of multiple processes that average out that way (or whatever).
But do you have an example of something that is 23 quadrillion + 1/3 Planck units, or whatever?
Just to be clear, Planck units have no physical significance
False. The Plank length is the smallest length that it could be possible to measure by any method. Classical ideas of size and distance likely fail many orders of magnitude above the Plank length, but it's certain that a distance or length shorter or more precise than Plank length is non-physical.
It's the smallest scale at which a metric (from which concepts like "distance" and "length" come) makes physical sense. And from relativity we know that the Plank time is the same - no concept of "duration" makes physical sense at finer granularity than Plank time.
The Plank mass is likely unimportant, however, unless those String theorists are actually right about something for once. Color me skeptical.
However, none of this should be taken as justifying a view that the universe has a "frame rate" or could be described in terms of voxels. We know from relativity that those ideas also make no physical sense. (Also, anything like that would have a grain that would be totally obvious. There's no "special" directions at right angles to one another, no preferred physical axes.)
Socialism: a lie told by totalitarians and believed by fools.
Your memory faults you.
How something so small in your imagination meight cause a black hole by measuring it, is byond me.
A 'plank length' is the distance light travels during one 'plank time'.
How long 'one plank time' is, is left as an excercise to the reader.
Cost free eBook I read (by iBook/Kobo/Amazon/ObookO/Gutenberg etc.): "The Green Odyssey" by Philip Jose Farmer.
Achieve that and we've got some great storage at 4.85x10^80 Exabytes per cubic inch.
The lack of an example doesn't give your theory any physical significance. A few hundred years ago, people could provide no examples of events that were quicker than a few hundred milliseconds and them suggesting that their observed value was the "frame-rate of the universe" would have been just as silly.
Can you give some justification for why you think that a unit that was defined arbitrarily, to allow us to simplify calculations, is in fact the smallest unit of time possible? Additionally, why do you think that time is quantized at all?
If you want a vision of the future, imagine a youtube comments section scrolling - forever.
Do you have an example of something that takes an exact integer number of Planck units to occur? Do you know of something that takes ten or one hundred Planck units to occur? Why are you so fixated on this unit having such special properties?
Acting as if the failure of others to attempt to disprove your wacky theory gives it some weight, while providing no rationale for it yourself, only makes you come off as a crackpot.
If you want a vision of the future, imagine a youtube comments section scrolling - forever.
> Just to be clear, Planck units have no physical significance.
Technically, we have no way to measure anything smaller then Planck Length and Plank Time, so whether they have any physical significance is undetermined.
No one can measure time at intervals anywhere near Planck time, and no one can measure distances anywhere near as small as Planck lengths. Planck time is defined as the length of time it takes a photon to travel a Planck length.
It's a handy unit, but it may not have any special significance -- any more than a meter, a yard, or a rod.
From the wiki:
"Because the Planck time comes from dimensional analysis, which ignores constant factors, there is no reason to believe that exactly one unit of Planck time has any special physical significance. Rather, the Planck time represents a rough time scale at which quantum gravitational effects are likely to become important. "
no, momentum of a bound particle must be quantized but an unbound one can have any momentum
This post is a good example of what happens when someone thinks the current model is absolutely true. The map is the territory!
The current model will be wrong in ways that are consistent with existing observations. That doesn't leave room for a "graph-paper universe", nor for energy densities above which a black hole forms.
Socialism: a lie told by totalitarians and believed by fools.
No, because the Planck time is 10^-44 seconds. We have trouble measuring events that occur within 10^-20 seconds (we can do it, but only indirectly). 10^-44 is so vastly below any of our detection thresholds that events that occur in that timespan may be literally immeasurable, simply due to practical experimental problems.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
It's not a matter of not having a small enough ruler. The problem is that there can be no measurement smaller. There can be no way to infer anything smaller. It's the absolute smallest.
IIRC, the plank scale, or actually slightly above it, is where space-time is supposed to turn into a foam. (I'm not sure what is meant by "foam", but that was the term I read.) At any rate, the structure of space-time collapses. So it's not arbitrary, if the theories were properly based. (The theory was called Geometrodynamics. And I was reading about Wheeler's version. https://en.wikipedia.org/wiki/... )
It's been a long time, so don't expect me to be able to even mount a defense, but the Planck length wasn't an arbitrary choice.
I think we've pushed this "anyone can grow up to be president" thing too far.
Love the nutjob people who say they hate religion and Love science ... and then tell you in the same breath that they believe in Darwin AND global warming. Cant get more unprovable missing linky than that.
Except for every religious bit of mysticism ever.
Darwin/evolution and global warming are both empirically observable and confirmed. Darwin's finches demonstrated the so called "micro" evolution anti-science people like to quibble over, but DNA provides lengthy "macroscopic" examples in incredible detail.
There was no mass "global cooling" consensus in the 60s, 70s - that was a cover story because one contrarian made wild claims and mass media journalism goes with the crazy stories on the cover and the footnote correction on page 68.
Newsweek had a story about planet killing asteroids to hit Earth in the 1990's too:
http://www.newsweek.com/attention-incoming-object-170672?piano_d=1
That doesn't mean that 97% of astronomers thought it was likely either.
Throw your other nutjob red herring shifting goals posts out as you like, you are a fraud and a bad person. You are bad and you should feel bad. Or are a sociopath. Your call.
Well, for making this "frame rate" theory relevant, the question is not only if anything happens at or close the frame rate, but what is the frame stepping function? And, throwing relativity into the mix, in what reference frame?
A discretized spacetime would mean that the continuous solutions to the Schrödinger/Dirac equations are actually approximations that are better expressed by some discrete time stepping scheme. That could have macroscopic consequences. Especially so if for some weird reason Nature has a rather simple first-order scheme at its frame rate core. But, it does also mean that we would get slightly different results from different objects in free fall, depending on their overall speed relative to the reference frame. This would control the factor between the "local passage of time", and the actual number of "Planck time frames" used by the process. In addition, the discretization of time almost necessitates a discretization of space. This not only means that space has some small grid (not likely either, based on current theory). It also means that there are some absolute directions in space and that some physical processes would behave slightly differently (even if aggregated along macroscopic distances) if they are algined to these directions, or not.
No, he's saying the map says there's a road here, therefore any map that doesn't indicate a road here is in some way inaccurate.
Like, monitor a speck of dust near a mountain. I'm convinced we don't have "gravity" here, it's just "density". But then I'm also convinced the world is flat.
Read "Zetetic Astronomy" for convincing arguments, experiments, and proof: http://www.sacred-texts.com/ea...
I feel fantastic, and I'm still alive.
> The smallest unit of time is called Planck time.
Except in New York City, where's the time between the light turning green and the guy behind you honking his horn.
The metric therefore *must* be a continuously differential, smooth, or real analytic function.
We don't have a good theory of quantum gravity. This is one of the problems with reconciling QM and GR that any such theory must explain. But current ideas include requiring entanglement between locations in space in order to have distance, or any positional relationship, and that makes some sense.
There is no *proven* physical significance to the Planck length. It is important in some models of quantum gravity
It's physical significance is that it's the minimum wavelength you can have without creating a black hole. Proven? Proof is for math, not science, but general relativity certainly seem solid.
Finally, 'Also, anything like that would have a grain that would be totally obvious' -- no. We know from observation that if spacetime is discretized the minimum length must be very small.
I'm not talking merely about "discretized", I'm talking about a "graph paper universe" with the discrete allowed loci lining up in neat rows and columns. Simple ideas about physics as cellular automata, or us being a simple VR simulation, require this. It's a bit of nonsense. and there are quite clever cellular automata models, and other "what is spacetime" models that don't require neat rows and columns, but rather irregular, spontaneously-formed, and somewhat random granularity.
There is nothing really *blocking* observations that would clearly distinguish between discreteness at the Planck scale and either discreteness at a smaller scale or even continuousness; we just don't have the observational tools to do that yet
Again, the whole "you can't make a wavelength that small without getting a black hole" thing is a solid blocker (the bigger issue is the energy density required in general for such fine-grained observations runs afoul of that limit). The Plank length is really quite small, after all - I'd be amazed if the universe isn't granular on some much larger scale. Plenty of room at the bottom.
Socialism: a lie told by totalitarians and believed by fools.
OK. Something interesting could happen earlier. But where? The Planck scale is the only significant point in current knowledge (well, about 4-5 decades ago isn't really current, but...). It's like looking for the next sub-atomic particle. Our current theories don't justify building something smaller than Neptune's orbit to act as an accelerator ring when looking for the next level of particle. (Some of them say it should be even larger.) It's quite likely that somewhere in there we'd find something interesting, but what? And how many EV does it need to generate?
FWIW I'd be all in favor of building a couple of telescopes 5 miles in diameter, putting them 180 degrees apart in Neptune's orbit, and carefully synching them so that their resolution could be combined. If it must be radiotelescopes rather than optical that would be too bad, but still worthwhile. The 5 miles diameter is for light gathering power. The separation is so that when they were synched together you have a long baseline for high resolution. This would allow us to directly check some of the "standard candles" that the astronomers have been using to figure distance. It would also allow us to directly see planets in other solar systems.
Do I expect that to happen? No. It would be incredibly valuable, and would let us verify many theories, and explore new ones, but it's too expensive, and we can't know that we'd find anything worthwhile before we do it.
If it hadn't been for the Higgs the current big accelerator wouldn't have been built. Now that it has been built it can be used to find lots of different things, and to test theories in lots of places where they couldn't previously be tested. But there's currently no big target for the next accelerator...not one that's reasonable to build. Perhaps one will turn up.
So. The Planck scale is out of experimental reach, but there's no reason to expect anything interesting before we get there. I'll agree that it's quite likely that if we looked we'd find something, but unless the tools we already have are powerful enough to yield strong hints of something within reasonable reach, it's not going to be built.
Perhaps someone will find another approach.
I think we've pushed this "anyone can grow up to be president" thing too far.
Without doing the actual math myself, I think I can present an example.
Imagine you have a ship going at a certain relativistic speeds. The observers inside the ship could observe themselves arriving at a destination in x Planck units of time (where x is an integer), but depending on the exact speed of the ship, a stationary observer would likely observe them arriving at the destination in y Planck units of time (where y is a real number that is not also an integer).
Let me know if you want me to take this beyond a mere thought experiment and come up with an actual velocity for the ship.
Or, to put it another way, and probably horribly inaccurately to boot, 'quantized' gravity is like constantly throwing a ball at something, only when that ball hits the object, it casues the object to move towards, instead of away from, the direction of impact.
Non-quantized gravity is like everything being attached to everything with ropes, constantly pulling on everything.
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Let me rephrase that:
The Planck scale is out of experimental reach, but there's no reason to expect anything interesting at any particular point before we get there.
I'd like to be wrong, and there be some experimentally reachable point that should be interesting (for an important theoretical reason), but if that's so I haven't heard of it.
I think we've pushed this "anyone can grow up to be president" thing too far.