Physicist proposes simple experiment to detect foam-like structure of the universe

Nov 23, 2012 by Bob Yirka report
Set up of suspended blocks showing (dotted) the alternative paths for the photon. E is the single-photon emitter, D and D' are the single-photon detectors. BS denotes the beamsplitter and M the mirror. DL is the fi ber optics delay line, and EB are the electronics that trigger D and D' through cable C. The optical elements to widen the beam before and focus it after each block are left out for clarity. In the real experiment the blocks would hang side by side. Credit: arXiv:1211.3816 [gr-qc]

(Phys.org)—Prominent physicist Jacob D. Bekenstein, of the Hebrew University of Jerusalem, has proposed a simple experiment in a paper he's uploaded to the preprint server arXiv, that he says could be used to measure quantum foam. Instead of looking to ever faster particle accelerators, he proposes using an ordinary block of glass, a laser and a detector.

Quantum foam is a term used to describe the non-smooth nature of the universe. It was coined by John Wheeler who in the 1960's noted that according to , certain properties of spacetime have some degree of uncertainty related to them. Later researchers have expanded on the idea, suggesting that on a , the universe is made up of individual units which are thought to be rife with very small that pop in and out of existence, resulting in foam-like images for those who try to imagine what it might look like.

Until now, trying to measure, or prove that theories about quantum foam are true have failed due to the extraordinarily small scale of the particles involved, 1.6 × 10-35, known as the . In his paper, Bekenstein proposes an entirely new way to approach the problem. He says all that needs to be done is to fire a single photon through a block of glass and then measure how much the block moves.

The idea is to use just the right size block and of a photon such that if the photon did move the block's center of mass, it would be just one Planck length. If the universe is truly grainy, as theorized, the photon would encounter one of the tiny units which would inhibit its progress; if not, the photon would pass all the way through with no problem. Because theory suggests there are a very large number of undetectably small black holes in every part of the universe, it would seem reasonable to assume that the glass block's center of mass could fall into one, which would of course impede the movement of the block. Thus to detect the presence of theoretical foam, all researchers would have to do is fire many individual photons through a block of glass and see how many make it through using a detector on the other side.

Explore further: A quantum logic gate between light and matter

More information: Is a tabletop search for Planck scale signals feasible, arXiv:1211.3816 [gr-qc] arxiv.org/abs/1211.3816

Abstract
Quantum gravity theory is untested experimentally. Could it be tested with tabletop experiments? While the common feeling is pessimistic, a detailed inquiry shows it possible to sidestep the onerous requirement of localization of a probe on Planck length scale. I suggest a tabletop experiment which, given state of the art ultrahigh vacuum and cryogenic technology, could already be sensitive enough to detect Planck scale signals. The experiment combines a single photon's degree of freedom with one of a macroscopic probe to test Wheeler's conception of "spacetime foam", the assertion that on length scales of the order Planck's, spacetime is no longer a smooth manifold. The scheme makes few assumptions beyond energy and momentum conservations, and is not based on a specific quantum gravity scheme.

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User comments : 33

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vlaaing peerd
2.6 / 5 (5) Nov 23, 2012
Hm ... no AWT comment yet?
Steven_Anderson
3.1 / 5 (11) Nov 23, 2012
I can't comment on this cause I know nothing about it. But I am glued to this article waiting for intelligent comments on it. To me it seems like huge news. Instead of using huge costing technologies, a simple table top experiment with cryogenic temperatures could do the same thing. Sounds like we need more scientists like this! Create a network of scientists that each work on solutions to problems all on their own in their own little boxes and then only communicate those ideas once they have all individually looked into the problem. This is supposed to be the ideal method of solving difficult problems instead of working on them as groups from what I read.
Tangent2
3.7 / 5 (6) Nov 23, 2012
Awesome idea.. very simplistic in design and principle. Can't wait to see the results when it is put to work!
brt
3.2 / 5 (5) Nov 23, 2012
It sounds like a good idea, but gives no specifics. Important things are left out which need to be answered in order to conclude whether or not the experiment is viable. Like the "time crystal" that could outlast the universe article that was on here a few months ago; it's a very shallow and nonsensical way to solve a problem which isn't very scientific. In other words, it's a bunch of fluff; something along the line of : I'm starting a unicorn farm or claiming to have built a quantum computer that takes up 8 rooms and maxes out at calculating 5 X 3 = 15...I wouldn't say you've built a quantum computer just yet. There's a reason why it's only on arxiv.com and not in a peer review journal, because it's bullshit.
Pohius
4.2 / 5 (13) Nov 23, 2012
"Because theory suggests there are a very large number of undetectably small black holes in every part of the universe, it would seem reasonable to assume that the glass block's center of mass could fall into one, which would of course impede the movement of the block."

You've got to be kidding me!
Ok. Let's assume that a quantum black holes are really exist (which is very unlikely). Then, center of mass is a mathematical point(model), it can not fall into a black hole.
rkolter
5 / 5 (6) Nov 23, 2012
I would like to know how you measure every other potential force acting on the glass block, such that you can isolate a single planck-length movement of the center of mass generated by firing your photon at it?

Still, I like the IDEA.
ValeriaT
1.5 / 5 (8) Nov 23, 2012
At first, we should realize, what the subject of quantum gravity QG REALLY is. The QG is trying to reconcile the predictions of general relativity GR and quantum mechanics QM. So I don't quite understand, why it bothers with Planck scale, when the main scope of interest sits pretty well at the human observer scale. The physicists are seeking for QG phenomena well outside of the scope of interest of QG - the QG phenomena are all around us. The detection of thermal motion of atoms with scattering of light belongs into it - what else do you expect to find with it, after all? Of course, such an experiment doesn't prove the inhomogeneous structure of space-time at the Planck scale, but this inhomogeneity manifests with notoriously known CMBR noise, Casimir force or for example with motion of atoms even at the absolute zero temperature (the liquid helium never freezes at room pressure) - so there is nothing to prove already. We already know, that the vacuum is dynamic inhomogeneous stuff.
ValeriaT
1 / 5 (7) Nov 23, 2012
So that the experiment proving the inhomogeneous character of vacuum with dynamic scattering of light is essentially correct - but after then I don't understand, why myriads of another experiments involving the thermal motion of atoms and Brownian motion shouldn't be considered as the same evidence already. The whole proposal just demonstrates, how deeply the contemporary physicists are confused with their own theories. The quantum gravity theory isn't a theory of some exotic phenomena at the whole boundary of the observable Universe - but the theory which should describe the real life phenomena, including the classical mechanics, biology and chemistry. This is because the dimensional scale of quantum gravity sits BETWEEN the distance scales of relativity and quantum mechanics theory - not outside it. BTW The subject of string theory belongs into it too, because the string theory is essentially just a special version of QG theory.
ValeriaT
1 / 5 (8) Nov 23, 2012
Hm ... no AWT comment yet?
The inhomogeneous dynamic character of vacuum/space-time indeed belongs into basic predictions of AWT, because in AWT the space-time is always formed with density gradient of particle environment. But in this case we can forget the AWT safely, because the common sense is enough for judging of the real meaning of this experiment proposal.

I presume, we could call it an example of professional blindness if not stupidity of contemporary physics. But at the moment, when the physicists will really get the money for such an experiment, then it's rather manifestation of stupidity of layman publics, which is willing to pay such an reinvention of wheel. The layman people are so saturated with information explosion, they're not able to recognize, what is original finding/effect and what not. It seems for me, that the people are willing to check the notoriously known phenomena again and again just at the moment, when some physicists will call it with new name.
Torbjorn_Larsson_OM
4.8 / 5 (10) Nov 23, 2012
"Until now, trying to measure, or prove that theories about quantum foam are true have failed due to the extraordinarily small scale of the particles involved, 1.6 × 10-35, known as the Planck length."

Not at all. Cosmological observations of photons have reached down to the Planck scale. Here the path length blows up tiny fluctuations to be measurable. Eg http://inspirehep...28?ln=sv (supernova photon timing) and http://inspirehep...45?ln=sv (Airy rings in gravitational fields).

If the hypothesis was that there is no such foam, it can't be rejected at 3 sigma. If the hypothesis was that there is such foam, it can be rejected at 3 sigma.
RealScience
4.5 / 5 (8) Nov 23, 2012
An elegant proposal - fire known numbers of photons of various wavelengths through a glass block, and see if there is a transmission decrease at a wavelength corresponding to the block's mass, then calculate whether it occurs where the block would move one Plank length.
Either there is an increase in absorption at a wavelength that depends on the block's mass, or there isn't, with almost no interference from other factors, and if there is either it corresponds to the plank wavelength or it doesn't.
The great thing is that in all cases we learn something fundamental.
Torbjorn_Larsson_OM
4.3 / 5 (6) Nov 23, 2012
@ vlaaing_perd: Of course there were sooner or later, despite that aether has been firmly rejected by observation since a century. Anti-scientific beliefs die hard...

@ Pohius: Nice catch.

Bekenstein derives that the center of mass (c.m.) position components are canonically conjugates of the block momentum vector. As the latter is an observable, the former should be "a faithful proxy". (And he adds something else in the appendix - I'm not _that_ interested.)

So: "In any case, our arguments presume that what happens to the c.m. matters physically."

And of course a physical observable position can be momentarily trapped in a not-yet-evaporated fluctuated-into-being black hole. Could be interesting to see if there was a c.m. physicality.

Of course, to see that one needs the quantum foam as well. Unlikely.
ValeriaT
1.6 / 5 (7) Nov 23, 2012
Here the path length blows up tiny fluctuations to be measurable
I do appreciate, you're remembering and rising that observation in this context - but unfortunately, the behavior of quantum foam is less straightforward in this matter, than you may think. Above certain distance/mass-energy density scales the lack of photon scattering not only cannot serve as a conclusive proof of the lack of foamy structure of space-time - but it even may serve as an evidence for it instead! It's because at such wast cosmological distances the photons of extreme energy not only violate the general relativity, but they even tend to violate the quantum mechanics and quantum gravity theory. The scattering of photons is observable at smaller distances, but at large distances the gravity interaction of photon may cause, that the whole bursts will arrive at Earth at the single moment, despite the photons are scattered differently.
ValeriaT
1 / 5 (5) Nov 23, 2012
If the hypothesis was that there is such foam, it can be rejected at 3 sigma.
What IMO really happens during distant gamma ray bursts is, that the long wavelength photons are really moving faster, but they tend to revolve the heavier short wavelength ones around spirals, so that the whole cluster of photons still arrives at the Earth at the single moment, despite all photons in it are moving along quite different paths. The heavy energetic photons in the gamma burst cluster are behaving like stars in stellar cluster in this extent, thus proving their particle nature for johannprins sufficiently and fooling both quantum gravity proponents, both opponents in this way. Best of all, the gravity field and mutual interaction of energetic photons in the gamma ray burst can be interpreted as a direct consequence of the inhomogeneous structure of space-time (after all, like the gravity field of all massive bodies).
Pressure2
3 / 5 (6) Nov 23, 2012
Quote from article: "Until now, trying to measure, or prove that theories about quantum foam are true have failed due to the extraordinarily small scale of the particles involved, 1.6 × 10-35, known as the Planck length. In his paper, Bekenstein proposes an entirely new way to approach the problem. He says all that needs to be done is to fire a single photon through a block of glass and then measure how much the block moves."

How could one measure how much the block moves? Even if you rested the block on one single atom it would be nearly impossible to measure any movement. The diameter of an atom is trillions of billions of times the one Planch length.

Second problem, true a photon quantity of light would move the block of glass forward upon entering it but wouldn't it also move it backward by an exactly equal amount when exiting the other side in order to conserve energy and momentum?

ValeriaT
1 / 5 (6) Nov 23, 2012
Because theory suggests there are a very large number of undetectably small black holes in every part of the universe, it would seem reasonable to assume that the glass block's center of mass could fall into one, which would of course impede the movement of the block.
In dense aether model the only micro-black holes existing permanently in the vacuum are the atoms and their nuclei. So if the photon will get absorbed with atom nuclei, then it will indeed transfer its momentum into block permanently. Such an experiment has been done already with gamma ray photons, which excited the atom nuclei flying through mass spectrometer. The atom nuclei gained their mass after then in measurable way. IMO the experiment proposed is naive in many ways thinkable, because the quantum foam structure of vacuum/space-time manifests itself in many ways, which were observed already many times before. And there are many possible ways, which could interfere its results in an way consistent with QG.
ValeriaT
1 / 5 (7) Nov 23, 2012
The main source of confusion here is the poorly defined subject of quantum gravity as such. Which effect does still belong into quantum gravity effects - and which isn't? If we consider, that the quantum mechanics and general relativity - and their combinations - drive all observable effects in our Universe, then all these effects are evidence for quantum gravity at the same moment: you, me and all objects around us.

Try to disprove, what I'm saying right now - and you'll see..;-)
brt
1 / 5 (5) Nov 23, 2012
Quote from article: "Until now, trying to measure, or prove that theories about quantum foam are true have failed due to the extraordinarily small scale of the particles involved, 1.6 × 10-35, known as the Planck length. In his paper, Bekenstein proposes an entirely new way to approach the problem. He says all that needs to be done is to fire a single photon through a block of glass and then measure how much the block moves."

How could one measure how much the block moves? Even if you rested the block on one single atom it would be nearly impossible to measure any movement. The diameter of an atom is trillions of billions of times the one Planch length.

Second problem, true a photon quantity of light would move the block of glass forward upon entering it but wouldn't it also move it backward by an exactly equal amount when exiting the other side in order to conserve energy and momentum?


I was thinking the exact same thing. There are so many holes in this experiment.
brt
1 / 5 (5) Nov 23, 2012
"Because theory suggests there are a very large number of undetectably small black holes in every part of the universe, it would seem reasonable to assume that the glass block's center of mass could fall into one, which would of course impede the movement of the block."

You've got to be kidding me!
Ok. Let's assume that a quantum black holes are really exist (which is very unlikely). Then, center of mass is a mathematical point(model), it can not fall into a black hole.

Even further illustration that this experiment is pathetic. Look; this isn't an absolute rule, but it's about 95% true: good experiments usually cost a lot of money because engineering precision is expensive. Simple analogy, a Ferrari costs a lot more than a corvette. And even though the amount of money relative to the increase in performance isn't worth it, the performance is dramatically increased.
lengould100
2 / 5 (4) Nov 23, 2012
Quote from article: "Until now, trying to measure, or prove that theories about quantum foam are true have failed due to the extraordinarily small scale of the particles involved, 1.6 × 10-35, known as the Planck length. In his paper, Bekenstein proposes an entirely new way to approach the problem. He says all that needs to be done is to fire a single photon through a block of glass and then measure how much the block moves."

How could one measure how much the block moves? Even if you rested the block on one single atom it would be nearly impossible to measure any movement. The diameter of an atom is trillions of billions of times the one Planch length.

I don't agree. See
"to detect the presence of theoretical foam, all researchers would have to do is fire many individual photons through a block of glass and see how many make it through using a detector on the other side."

boater805
1 / 5 (7) Nov 24, 2012
This is a perfect example of why I generally oppose "big" science instruments like the LHC. Not only can human ingenuity find ways to do without generational instruments (in size and cost and number of careers dedicated to their operation) but in fact such large projects inhibit ingenuity and make experimentalists lazy. There will ALWAYS be another way to do things for those that are clever enough.
House1234
1 / 5 (3) Nov 24, 2012
An experiment done with 3 photons from a gamma ray burst already proved space-time is smooth and continuous and has no foam like structure. The research was published in one of the physics review letters.
Shinobiwan Kenobi
3.3 / 5 (7) Nov 25, 2012
This is a perfect example of why I generally oppose "big" science instruments like the LHC. Not only can human ingenuity find ways to do without generational instruments (in size and cost and number of careers dedicated to their operation) but in fact such large projects inhibit ingenuity and make experimentalists lazy. There will ALWAYS be another way to do things for those that are clever enough.


When you figure out how to accelerate particles to 99% the speed of light without big (not sure why you'd put quotes around it, the damn thing is really big) science instruments like the LHC then your dismissal would hold some water.
ValeriaT
1 / 5 (6) Nov 25, 2012
This is a perfect example of why I generally oppose "big" science instruments like the LHC.
Sometimes the "brute force" approach is useful, but it shouldn't drain the money from "smart research" like the cold fusion or antigravity research. If nothing else, than just because the results of smart cheap science are applicable in common life more easily, than the "big-science", because for implementation of LHC results you just need an expensive collider for this application too.

Unfortunately, the so-called "big science" tends to behave like "selfish-meme" due to various synergies and it tends to consume resources for smarter research. For example, the maintenance of large colliders is a long term job for many generations of scientists, so that the people who are seeking the stable long term perspective tend to support large projects into account of these smaller ones. The mainstream physics becomes separated from the needs of human society in this way gradually.
ValeriaT
1 / 5 (5) Nov 25, 2012
Unfortunately, the layman people tend to ignore these psychosocial synergies and physicists have no reason to point for it, so that the support of large projects becomes gradually political and ideological: the colliders and cosmic flights were claimed as important for national security. This research represents an overgrown remnants of previous era, when the human society was still relatively rich. Now the resources are depleted, the results of "big-science" have still no practical usage and we are ignoring the "smart-research" for years (cold fusion as an example). The change in general strategy is urgently needed: the people shouldn't serve to interests of limited group of scientists and politicians, but vice-versa. We shouldn't evolve like the silly culture of bacteria, which just consumes all its resources and it simply dies out, when they're depleted. Or we will get doomed in global nuclear conflicts without even recognizing their actual deeper reasons.
RealScience
5 / 5 (5) Nov 25, 2012
@Shinobiwan - desktop wakefield accelerators have been able to accelerate electrons to well beyond 99% of C for several years (a good example of the sort of ingenuity that boater805 is referring to).

However big science has its place: the LHC does it with protons (~2000x harder), in huge numbers, collides the beams head on, and has amazing detectors to record the results.

@boater805: The clever low-cost solutions are great because they open up a field to huge numbers of independent research efforts. But in general it is the big science 'searchlights' that lead ingenious people to invent the desk-top science 'flashlights' that over the years grow to exceed the power of earlier-generation searchlights.
Look at the sequencing of the human genome, for example, which inspired the creation of devices that can already do the job for 1/1000000th the cost.
gwrede
4.3 / 5 (6) Nov 25, 2012
Because theory suggests there are a very large number of undetectably small black holes in every part of the universe, it would seem reasonable to assume that the glass block's center of mass could fall into one, which would of course impede the movement of the block.
This is utter crap, as many have already commented. I think the writer didn't grasp the idea, and was too busy to really try to read what he wrote.

I wish all such articles were sent to the original scientist for proofreading. As things currently stand, some young person might remember the above quote for a long time, not knowing it's erroneous. Prior misconceptions like this make it harder to learn physics, because you eventually have to unlearn stuff that may be the foundation of other things, so you potentially have to unlearn and relearn lots of stuff, which is a waste of time and effort.
hudres
5 / 5 (1) Nov 25, 2012
In order for this to be a valid test, it would have to differentiate between the quantum foam effect and the well documented radiation pressure that such a photon would exert on the test masses. It is not clear how Bekensteini differentiates these closely related effects.
RealScience
4.6 / 5 (5) Nov 25, 2012
@hudres: The effect of radiation pressure would depend smoothly on the wavelength of the photons. This test could see if anything anomalous happened as the photon wavelengths crosses when the block's movement would be one Plank length. One would pick a block mass where the key wavelength would be in a region of consistently high transparency, and then vary the wavelength of the photons across that key wavelength.

If nothing unusual is observed, then Bekenstein can figure out why not, and science advances incrementally. But if something unusual is observed, then science advances by a bigger amount.

In either case the cost of trying the experiment is so many orders of magnitude lower than other potential Plank-length experiments that have been discussed that it will inspire others to find clever attacks on seemingly intractable problems .
nuge
3 / 5 (2) Nov 26, 2012
When you figure out how to accelerate particles to 99% the speed of light without big (not sure why you'd put quotes around it, the damn thing is really big) science instruments like the LHC then your dismissal would hold some water.


You might find this interesting: http://en.wikiped...leration
Shinobiwan Kenobi
3 / 5 (4) Nov 26, 2012
Perhaps I should have qualified the necessity of the detectors at CERN. Regardless, thank you all for the feedback.
OdinsAcolyte
1 / 5 (3) Nov 27, 2012
On the Plank level. If we can squeeze through the holes in the foam we can teleport and thus have star travel and time travel (at least to the past) and also slip to other dimensions if one has the balls. I wouldn't advise it...
NoelPeak
not rated yet Nov 29, 2012
Additionally, the experiment, if successful in moving the center of gravity of the glass would tend to settle the question as to whether photons have mass, or not.

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