14 ms·
It might be possible to detect gravitons after all
- est 2y agoThat's a facinating read. I wonder what are the possible applications of "quantized gravity" ? GPS without satellites?
- MathMonkeyMan 2y agoconstraints on theories of everything
- Vecr 2y agoCheap GPS receivers already have to do a bunch of tricks to get to the "okay" state they're currently at. Military devices either use GPS, star tracking, dead reckoning, or some combination. For submarines, detecting gravity variations could also be used, but it wouldn't rely on the quantization of gravity. In many places on land, you can use terrain landmarks. Since most things are already either covered, or have improvements in development, I don't really see investment for your idea. The improvements might even use "quantum" or "gravity", but I don't think the use of "quantum gravity" is very likely.
- JumpCrisscross 2y agoYou’re mixing up general relativity with quantum gravity.
- Vecr 2y agoI'm not exactly sure what you're saying. I know you can have gravitons without "quantum gravity" (as incomplete theories). I'm responding to a commenter on applications. In a global position finding system, gravitational effects could be used, as could be quantum effects. Maybe even both in the same system. It seems really doubtful to me a practical system would depend on anything graviton related.
- JumpCrisscross 2y agoYou buried your lede. The “tricks” you describe relate to GR. I missed that you’re essentially saying “no.”
- whatshisface 2y agoIf the Romulans were talking to the Klingons over a link secured by the quantum no-cloning theorem, the Enterprise could use quantized gravity to entangle the ship's computer with their adversaries' quantum radios in a way that no matter-based shielding could prevent.
- whatshisface 2y agoI'm with the debaters on this one, the energy levels of a bound quantum system are predetermined to change in quantized intervals irrespective of if they are coupled to a classical or quantum field. What theory of gravity is this experiment intended to falsify? It would be great to have an independent gravitational wave detector though.
- sharikous 2y agothe statistics would be different. Check out Rabi oscillations (classical EM) vs Jaynes-Cummings model (quantized EM) and phenomena like quantum antibunching (only possible for quantized EM)
- whatshisface 2y agoHow would mergers produce antibunched gravity?
- choilive 2y ago> physicists are debating what it would really prove. Well, if we can detect the graviton before we have a working quantum theory of gravity, it would mean that gravity is in fact quantized and that we just need to figure it out. This would be a very big deal.
- toomuchtodo 2y ago> This would be a very big deal. Gravity drive?
- cryptonector 2y agoNope.
- itishappy 2y agoThey can detect an interaction, but they can't prove that it's quantized without (I believe) sub-Poissonian statistics[0], which requires detecting enough events and with enough certainty that it would require planet-scale machinery. > Now graviton chasers find themselves in a peculiar position. On the main facts, everyone is in agreement. One, detecting a quantum event sparked by a gravitational wave is — surprisingly — possible. And two, doing so would not explicitly prove that the gravitational wave is quantized. “Could you make a classical gravitational wave that would produce the same signal? The answer is yes,” said Carney, who along with two co-authors analyzed this type of experiment in Physical Review D(opens a new tab) in February. [0] https://en.wikipedia.org/wiki/Photon_statistics#Sub-Poissonian_light https://en.wikipedia.org/wiki/Photon_statistics#Sub-Poissoni...
- choilive 2y agoIt sounds like the article is saying we could detect many events without using a planetary scaled detector It mentions a single detector being a 15kg Be bar chilled to near absolute zero. Certainly very very difficult, but not in the realm of sci-fi.
- 2y ago
- ars 2y agoI don't understand what a graviton is. The article implies that it's something that communicates changes in gravity? Is that correct? How does it communicate the magnitude of the change? By having lots of gravitons? Or does it have something akin to a frequency?
- whatshisface 2y agoA graviton is the smallest possible unit of a gravitational wave. The amplitude of the wave corresponds to the number of gravitons, like you said, and its frequency to their frequency (quantum particles have frequencies that are related to their momenta). We're aware that light, at least, works like that.
- russdill 2y agoGravitons impacting and imparting momentum seems like it would have a bunch of observational implications. Does a massive object cast a graviton shadow? Is the momentum positive or negative?
- whatshisface 2y agoClassical waves do all of those things too.
- russdill 2y agoSo gravitons are only emitted by accelerating objects?
- whatshisface 2y agoReal gravitons, yes.
- hhdhdbdb 2y agoA gravitational wave requires an event like a black hole merger, or basicially somerhing to move and change the field, right? In this case, how does the fact that a big object is still influencing space/time around it communicate that fact when it is not moving. Is that still gravitrons?
- ta93754829 2y agoSo I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive? Can someone who understands this please explain it to me, thanks!
- deleted 2y ago[deleted]
- gary_0 2y agoElectromagnetism is both a continuous wave and a discrete particle, so it makes sense to me that a continuous spacetime curvature could also be a discrete particle at the same time. (Keeping in mind we're not talking about tangible shapes but mathematical models that describe aspects of reality that are hard for humans to intuitively conceptualize.) Of course, our idea of how to reconcile quantum gravity with general relativity is much less developed than our understanding of electromagnetism and the nuclear forces.
- Willingham 2y agoWhen you mention nuclear forces, are you referencing weak force and strong force? Do we understand these forces at the same level that we understand electromagnetism?
- deleted 2y ago[deleted]
- btilly 2y agoYes. The Standard Model has completely explained all experiments involving them for around 50 years now. In fact the outstanding success of the Standard Model has posed its own problems - the lack of deviations from it makes it hard for experiments to point in a useful direction for better theories to be developed along.
- elashri 2y ago
- cyberax 2y agoTIL that Freeman Dyson looks like a house elf!
- DemocracyFTW2 2y agoI choked on this part: > The discussion recalls a messy, largely forgotten episode from the dawn of the quantum era. In 1905, Einstein interpreted experimental data to mean that light is “quantized,” coming in discrete particles now called photons. Others, including Niels Bohr and Max Planck, thought that the classical, wave nature of light might still be saved. [...] Most physicists presume that everything in the world is quantized, including gravity. But proving that assumption will entail a new war, one that has only just begun. 1) No, that is not a "messy, largely forgotten episode", rather, it is frequently re-told and almost a required Inshallah of every piece on quantum physics. 2) Please spare me that "war" simile, it only shows you're an American who can not write too well. War on drugs. War on poverty. War on whatever. The Browser Wars. Dude get a grip. Don't always "killer feature", "shot him dead", "waged war on the germs in her refrigerator". We have to fight a "war" to find out whether spacetime is quantum? Rilly??
- canadianfella 2y ago[dead]
- iknowstuff 2y agowhoa this comment took a turn
- 7373737373 2y agoRe. 2), what word should be used instead? "Massive concerted/collaborative effort"?
- skhunted 2y ago
- DemocracyFTW2 2y agoAnother goodie: > You need huge masses — think planets — to significantly warp space-time and generate obvious gravitational attraction. By way of comparison, a credit card-size magnet will stick to your fridge. By way of comparison, even an Olympic pool-size balloon of hot air will float.
- tsimionescu 2y agoIt's not clear what problem you have with that comparison. It's a classical example of just how weak gravity is compared to the electromagnetic interaction. A whole planet's worth of mass is weaker than the EM field generated by a tiny magnet. And the strong and weak nuclear interactions are even stronger still.
- DemocracyFTW2 2y agoI just found it funny that the author uses such a specific measure for an object that typically looks nothing like a credit card. I think the only credit-card sized magnet I've ever seen might have been an elastic magnetized floppy piece of plastic that was rather weak (I think it was used to fix paper on sheet metal). How about "even a small magnet can pull up things and overcome the gravity caused by a whole planet's worth of mass"? BTW the comparison to the strong and weak nuclear forces is sort of strange too because not only do they only matter on nuclear scales, they also behave strangely not to an inverse-square law; Don Lincol of Fermilab explained that in a Feb 2024 video[1], from the description: "Popular science explanations [...] claim that some of the forces are stronger than others. What they don’t tell you is that all of those claims are only valid for distances comparable to the radius of a proton. For different size scales, the order of the strength of the forces can be wildly different."
- tsimionescu 2y agoCredit-card shaped and sized magnets are actually pretty popular as tourist mementos. It's true that they are typically slightly smaller than a credit card, but they're a common occurrence. And while it's true that the strong force has very complex interactions which make it both stronger and weaker than EM in certain situations, I don't think there is any situation in which EM is weaker than gravity. Of course, the comparison is ultimately apples-to-oranges, as it basically amounts to comparing the amount of electrical charge to the amount of "mass charge". Still, if we compare by, say, the total number of particles with mass/charge respectively of any kind you need two bodies to have to have an equivalent effect on motion through gravitational VS EM interactions, in every situation that we know how to model, you would end with the same conclusion.
- DemocracyFTW2 2y ago[flagged]
- DemocracyFTW2 2y ago[flagged]
- omnicognate 2y agoThe only thing making me feel like that is your obnoxious spamming of this post. Four top-level comments now and not a single interesting thing said. Stop it, please.
- DebtDeflation 2y agoThe fact that QED and QCD are renormalizable while gravity is not is probably trying to tell us something deeper than we think. Relevant paper: https://arxiv.org/pdf/0709.3555 https://arxiv.org/pdf/0709.3555 You can read the first two paragraphs of the Introduction and then skip to the last sentence of the Conclusion if you want to bypass all the math.
- marcosdumay 2y agoSo... If gravity is quantized, then black holes must be only a low-energy approximation of whatever phenomenon is really happening there? If there's some proof that they aren't black (AFAIK, the only thing we know empirically), I've missed it. All I see is a point that the current theory would be wrong.
- DebtDeflation 2y agoRather, the existence of black holes demonstrates that gravity is not renormalizable. The last sentence in the paper: "It seems that gravity is a low energy effective field theory description of something else that is not a quantum field theory." QFTs like QED and QCD are renormalizable. This is a technique used to eliminate the infinities that arise in calculations from self-interaction. For a very long time, renormalization was viewed as hocus pocus (including by the person who discovered it). Later, mathematicians were able to provide a solid theoretical foundation for it.......but only as an effective field theory valid at particular size and energy scales. Net net, the standard model is an approximation of something more fundamental. Gravity being nonrenormalizable shows that "something" is not a QFT.
- marcosdumay 2y agoDoes it contest anything that we have observed? Because I couldn't find anything there that won't allow objects that behave the same way as the black holes we've seen, and differ only on details we can't see. (But IANAP, and could easily have missed something.)
- jessriedel 2y ago
- Seb-C 2y agoSince I read the story "The Road Not Taken" from Harry Turtledove, I cannot stop thinking that we might eventually discover that the question of the conflict between the general relativity and quantum theories is something so simple and elegant that we never even considered it before.
- mensetmanusman 2y agoOr, something like the simulation hypothesis is real and different models of reality are used at different length scales and the overlap is fuzzy.
- revskill 2y agoThat means there's no Gravity before The BigBang, right ?
- knodi123 2y agothe big bang is a singularity; we can't ever experimentally learn anything about what came before it. that doesn't mean there was no time before the big bang, or no gravity, or that there wasn't another universe just like ours. But due to the singularity, for the sake of convenience, we simply _say_ that those things came into existence at the big bang. cite: https://www.hawking.org.uk/in-words/lectures/the-beginning-of-time https://www.hawking.org.uk/in-words/lectures/the-beginning-o... , search for "may as well"
- wetpaws 2y ago[dead]
- eterevsky 2y agoSo the article says that Freeman Dyson calculated that only one graviton capture event would happen per billion years in a detector the size of the Earth. The new experiment however proposes to use 15 kg of super-cooled Beryllium. My question is: what's the difference between the proposed Beryllium slab and Dyson's theoretical detector?
- omnicognate 2y agoI don't fully understand it, but I think the difference is in the source of the gravitons rather than the detector. Dyson's earth-sized detector was imagined to be detecting gravitons produced by mass moving around within the sun, but this detector would be detecting gravitons associated with gravitational waves produced by ridiculously powerful events like black hole mergers, where two massive objects circle each other at mind-boggling speeds before colliding. It sounds like these are expected to produce vastly more gravitons, making a detection much more likely.
- ricksunny 2y agoCan we take a metascience / meta-scicomms perspective? Quanta magazine, like all scicomm journos, relies on the receptive access to researchers for source content, especially exclusive results. So scicomms is essentially the same kind of access-journalism evryone comolains about in DC beltway rwporting, but amplified & couched in the 'but science" brand. In Quanta's case, its sources are quantum physicists / particle physicists. So couching everything in terms of quantized particles (bonus points if somehow 'spooky') avails of the continued access. Articles from the likes of Quanta get cited in particle physicists' onward grant proposals. Pwrticle physicists get grant, get results which get reported just so, and the scicomm journo gets invited to show up once again to scribe away. The circle repeats, meanwhile everyone just hopes it's a virtuous one.