An Experiment Could Determine Whether Gravity Is Quantized (forbes.com) 134
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.
arXiv links (Score:5, Informative)
More detailed theory: arXiv:1510.01262 [arxiv.org].
See also blog post [blogspot.co.uk].
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While there may be problems with fabrication, I don't think toxic compounds are going to be a problem. They want it to be small enough that they're going to need to shield it from atmospheric contact anyway. No dust, no water condensing, no chemical reactions. They need to avoid all of those in an experiment this sensitive.
I might wonder about the choice of osmium, though, as it *IS* difficult to work, and the techniques for working indium are far more developed (due to it's use in LEDs).
Still, even if i
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He said iridium, not indium! Geez, I hope you aren't a pharmacist!
Besides, indium as used in LEDs isn't fabricated into anything as metallic, elemental indium, but rather as part of compounds with other elements, aka, InGaN, InGaAs, etc.
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Sorry, i did misread. And it didn't matter to the major point. The thing is not going to be exposed where it would have any chance of having chemical reactions.
Re:arXiv links (Score:4, Funny)
I'm curious about the choice to use osmium. Sure, it is the densest element, but iridium is almost the same density and osmium easily forms toxic compounds while iridium doesn't (easily, I mean).
Its very small and no one is going to eat it.
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It's so small you wouldn't even notice if you ate it.
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osmium goes superconducting at 0.66 K, while indium 0.11 K
That's much harder to achieve
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One blank page (Score:1)
Not much gravity ... or anything else on Forbes
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For the newspapers, by not work I mean I get a blank page for a couple seconds, then a normal page for about 1/10 of a second, blank page for a couple seconds, repeat forever.
Re: Cut to the chase (Score:2, Informative)
Yes. The smallest unit of time is called Planck time. Its sort of the frame rate of reality.
Re: Cut to the chase (Score:5, Interesting)
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.
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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 multiply
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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 thin
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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.
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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 a
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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 Natu
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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?
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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.
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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 t
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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 footno
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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.
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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.
Re: Cut to the chase (Score:5, Informative)
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.)
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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.
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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.
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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 me
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> 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.
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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.
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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
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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/... [wikipedia.org] )
It's been a long time, so don't expect me to be able to even mount a defense, but the Planck length
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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 i
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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 parti
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> 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.
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My issue arrives once per week
Re:Cut to the chase (Score:4, Funny)
Does Time come in quanta?
Nope. Cubes.
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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...)
A more detailed explanation (Score:5, Informative)
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THANK YOU! That actually makes sense instead of the gibberish installed as the "article" above.
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You've been here longer than I. However, in this case, I was actually thinking that this was, oddly, one of the summaries that made sense to me. Maybe I've just acclimated to the lack of proper editing?
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The tone of this comment leads me to think that social considerations, including the assumption that nature has to be consistent, are more important here than any real search for truth.
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I don't understand - are you complaining that she points out the truth?
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Yeah, he's complaining that she's pointing out the truth.
Forbes (Score:1)
It's not about gravity, it's investment advice. Long osmium?
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Nope. Corner the market on the tools in general - not just one of them. There are other tools, and gases, that they will need. Get them all. The people who made the money in the gold rush were those who sold the tools - not just a pick or an ax but all of them.
Keep in mind that I actually *do* (sort of) take investment advice from sites like this so you probably shouldn't listen to me. I have no idea what I'm doing but I'm averaging 18% which is pretty good I guess considering that average includes a couple
Well then... (Score:2)
shut up and do the experiment already!
I smell something fishy here... (Score:4, Funny)
Physicists are quantized, so they want everything else to be quantized.
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Not so. Physicists are divisible, albeit only to a limit.
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There's a much easier way (Score:2)
It would have to be. (Score:1)
Mass is quantized, therefore gravity has to be as well.
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It seems that the current set of elementary particles are the highest density
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Achieve that and we've got some great storage at 4.85x10^80 Exabytes per cubic inch.
And then we know ... what exactly? (Score:2)
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?
Re:And then we know ... what exactly? (Score:5, Interesting)
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We'll understand why and how molecules form and why they do it in the way they do? Did I get that right? That's awesome!
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I really like this explanation, as a general motivation for about learning about constraints. I think it can be applied to all of technology -- e.g. 'by realizing things are only allowed to make certain transitions under certain conditions, you can "cheat" and build up high-energy states that are far more stable than they really should be' might well be said for GMO, for example.
Re:And then we know ... what exactly? (Score:4, Informative)
It would open up the possibility of observing the effects of quantization of gravitational interaction in the low field limit. Up to now, no one has observed any quantization of gravity. This is a really tiny effect, so you might argue that you don't care, but it would be a small clue in the big mystery of how to reconcile quantum mechanics and general relativity. In the history of physics, this has happened before. We had quantum mechanics in the 1920s through 1940s, but we didn't know how to quantize the electromagnetic field. We simply used classical interactions between charged particles and quantized their motion since we didn't know how to quantize the electromagnetic fields themselves. Then in the late 1940s and early 1950s, Schwinger, Feynman, and Tomonaga figured out how to quantize the electric and magnetic fields. It made only tiny changes in the predictions of quantum mechanics for atoms, but it has turned out to be critical to modern precision measurement and definition of the units we use. Their Quantum Electrodynamics has proved to be one of the great triumphs of theoretical physics.
Now quantization of gravity is a much much smaller effect in conditions that we can study on earth. This proposes that we might be able to observe some effects. Unfortunately, in this low field limit, I think most physicists expect that perturbative methods will give the right answer. In this case, the experiments will not be much help in building a self-consistent quantum gravity theory because perturbative methods are known to fail in the high field regime where the inconsistency between quantum mechanics and general relativity becomes important. But we definitely should make these measurements to see if the effects can be observed. Precision measurements often yield new insights, often unexpected ones.
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I doubt that we will see any effects that are noteworthy because of our frame of reference. We are in the frame of reference of the planet Earth, which is in the frame of reference of the star Sol, which is in the frame of reference of the black hole Sagittarius A*.
Due to galactic rotation curves not being understood (Dark matter? Matter that does not interact with anything but gravity? It is to laugh.)
I do hope that this experiment does shed more light on what we call gravity.
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Deeper understandings of physics usually have unforeseen applications. For example, if we didn't understand quantum mechanics we wouldn't have much by way of semiconductors (cat's whisker diodes and oxide plate regulators are about all we could manage pre QM). And without GR we could kiss GPS goodbye (to get sufficiently accurate timekeeping you need to understand time dilation effects due to spacial curvature). And EM... obscure theory when Maxwell and Faraday wrote the book, indespensible now. And so
Millikan Oil Drop experiment (Score:2)
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Paraphrasing part of https://en.wikipedia.org/wiki/... [wikipedia.org]
Millikan's experiment as an example of psychological effects in scientific methodology
In a commencement address given at the California Institute of Technology (Caltech) in 1974 (and reprinted in Surely You're Joking, Mr. Feynman! in 1985 as well as in The Pleasure of Finding Things Out in 1999), physicist Richard Feynman noted:
We have learned a lot from experience about how to handle some of the ways we fool ourselves. One e
If gravity involves an interaction between masses (Score:1)
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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 obje
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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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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.
So would this be a proof that (Score:2)
I thought Forbes was reputable. (Score:2)
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.
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no, momentum of a bound particle must be quantized but an unbound one can have any momentum
a fraction of a Kelvin above absolute zero (Score:5, Informative)
Results (Score:1)
"Oh dear, Watson, I just fell up!"
Gravity = spacetime curvature (Score:2)
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All forces curve 'space-time'.
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Go ooooon...?
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No, only momentum, pressure, and energy density in the stress-energy tensor, not forces. Forces are associated with a gradient in potential energy and fields, and those have effects on spacetime curvature (except gravitational potential energy which is excluded from the Einstein stress-energy tensor). But having a force at any given point doesn't mean spacetime there is curved, as that depends on the global structure of energy and it is possible to have a force still at a point with zero curvature.
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I can't answer your question directly, but I can quote from my handy textbook on General Relativity which admittedly is 30 years old now ('General Relativity', Robert M. Wald, 1984). From Chapter 14, 'Quantum Effects in Strong Gravitational Fields', "As discussed in chapter 9, spacetime singularities occur in the solutions of classical general relativity relevant to gravitational collapse and cosmology. Thus, in these situations, the classical description of spacetime structure must break down. In particu
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How about an experiment to prove gravity EXISTS? (Score:2)
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... [sacred-texts.com]