> 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??
Please spare me that "war" simile, it only shows you're an American who can not write too well.
It’s understandable that you don’t like the desensitization of war that comes from our over usage of the word. Perhaps it speaks to a defect in American culture but this is how we communicate in our language. I think Arabic has too much emphasis on allah related phrases. But that’s how they speak. Nothing I can do about it. I don’t think said usage implies anything about their writing abilities.
I will start by agreeing that usage of "war" seems weired. Although scientific drama in fundamental physics is not uncommon but a word like "debate" would be more appropriate.
I don't like your usage of word "Inshallah" as a mock up of the idea that something will never happen. Because it is a complete opposite meaning of when you suppose to use it. It is usually overused by arab moms (I know that people tends to mean that) but I use it frequently. Ironically I was in online meeting at CERN today and used inshallah (sometimes I use it because I am used to) to refer to potential interesting signal I am seeing. I used it to describe the hope that this will not turn out to be a statistical flactuation.
Also I would agree that this is messy at the time when Einstein published his work on quantization. He even got Nobel prize on his work on photon quantization not relativity. Of course he was not alone, Max plank was the first to suggest energy discritization.
First things first, I didn't mean to stir up the discussion in this way. Also, I should have let go of the Caps Lock key. Also, I should've put all that stuff into a single comment or not write some of the things at all instead of creating multiple comments. Sorry.
As for the "inshallah", I probably used that word wrongly; I did not have any meaning of it in mind but used it—somewhat incomprehensibly so—as a moniker for "a standard to start any and all texts with", so "ceterum censeo Carthaginem esse delendam" if you will.
For 1): Yes, the photoelectric effect is frequently told. But that's not what the article is referring to here, it is foreshadowing its discussion on the semiclassical treatment of the photoelectric effect (by Lamb and Scully).
This is the "messy, largely forgotten" part which is rarely discussed. I saw it in a graduate quantum optics course, but even at that level I'm not sure it's part of the standard curriculum.
The "forgotten" part isn't Einstein's proposal, but the semiclassical suggestion of how to avoid it. Have you seen that part commonly retold? I haven't.
It's fine to criticize facets of a culture, but this isn't a very intelligent critique, it's just rude.
On the "war" thing - the culture of many Americans has a martial bent to it, which is why things like "war" made its way into a lot of our idioms and phrases and way of thinking. It's not bad writing just because your cultural mode of thought doesn't consider "war" as an acceptable metaphor or idiom.
Martial cultures don't need to "get a grip" any more than scholarly or pastoral ones need to. Culture is self-preserving and so the martial aspects of ours aren't going away anytime soon, so I suggest you find a way to be more tolerant and understanding of it.
Our ability to solve integrals is much more limited when the dx represents a slight change in a function, rather than a small change in a real number. As a result, a lot of things that are easy to say in English such as "quantized curvature in spacetime," or "strongly coupled gauge theory," turn into a big mess when they're written down more precisely. One of the consequences of this limitation is that we have a model for quantized vibrations in spacetime that only works when they do not interact with each other. General relativity says that no, gravitational fields do interact with each other - so the picture we have at present is incomplete. The model of non-self-interacting gravity is a particle we call a "graviton," and it probably describes reality very well when the gravitation involved is so weak that its self-interaction is undetectable.
String theory and loop quantum gravity fit into this picture by trying to replace the integral over something we can't handle with an integral that matches it at large scales, but turns into something more tractable at small scales. Maybe the fact that we still can't make sense of the integral is Nature's way of telling us that she does not do the integral either...
In theory, if gravitons exist, they should reproduce the same effects as the curvature of spacetime at larger scales. So, while they seem contradictory, they're actually complementary. Gravitons would be the "quantized" particles that, in large numbers, create the effect we observe as curved spacetime.
The problem is that nobody has successfully combined these two views into a single unified theory, known as "quantum gravity". General Relativity and quantum mechanics don't naturally fit together, and that's why we don't yet fully understand gravity in a way that reconciles both the spacetime curvature and graviton perspectives.
> I thought gravity was basically the curvature of spacetime.
Classically, it is. But most physicists believe that there is a quantum theory of gravity that underlies the classical theory, and that that quantum theory will include, at some level of description, a spin-2 gauge boson that mediates the quantum gravitational interaction, called the "graviton". Our classical theory of gravity, General Relativity, would then be the classical limit of that quantum theory, just as classical Maxwell electrodynamics is the classical limit of quantum electrodynamics.
Electromagnetism 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.
That gravity is curvature of spacetime is one view of two equivalent views, but it is the standard view. The other view is that you have flat spacetime with different distortions (of things other than spacetime) than the distortions you get in curved spacetime. The Schwarzschild metric essentially lets you do exactly that projection of curved spacetime to flat, and vice-versa. When you watch an animation like https://www.youtube.com/watch?v=hF7zltx7Ecc or https://www.youtube.com/watch?v=E1mD4C7dBKc you're watching a flat spacetime representation of GR's effects, and the reason for using flat spacetime in these representations is <drum-roll/> that that is what us humans understand.
So if you take the gravity curves spacetime view, then gravity is not a force and all that. But if you take the alternative view then gravity is a force. Now, I'll leave what the distortions are that gravity produces in flat spacetime for another time, or for the reader. But I'll say this: this view is both controversial (perhaps replies will show this) and not (see above -and many other- animations).
Not an expert, but: the curvature of spacetime is modeled as a tensor field (the metric tensor). That field can have (classical) waves in it, which is what LIGO detects (I believe). Then you can certain hypothetically quantize that field, in which case it definitely has to be a spin-2 particle and it seems likely that there will be a way to do it since all the rest were.
The "geometry" comes from the fact that the way we measure distances (or, well, experience time) uses the metric tensor field to do it. But it is still ultimately just a value attached to every point like any other field.
There are some ideas that spacetime is an emergent phenomenon. One such proposal is that it is produced by the large-scale presence of entanglement between particles: that entanglement creates spacetime. Where entanglement between regions of spacetime is stronger, the space is closer together, and where that entanglement is cut things get farther apart. This idea is known as "ER=EPR" [0].
That's the link bridging gravity as a particle (small-scale) and gravity as a feature of a manifold (large-scale). Physicists are trying to find a way to make spacetime emerge from quantum field theory, or make both emerge from some common framework.
Gravity is similar to an electric field here. A wave function for a field consists of an amplitude for each field configuration, where a “field configuration” refers to a value for the electric field for each point in space. In GR each field configuration would correspond to a space time geometry for the universe. We have quantized excitations as distinct “valid” solutions to the wave function, which we call a particle, though it is nothing like an electron. The notion of space time geometry holds throughout. (Edit: in practice, people never calculate wave functions for fields like electric fields. That would be too hard. Different methods are used in calculations. Second edit: the wave function wouldn’t be composed of complete space-time configurations, histories of the universe, but time slices from it, like space geometries. Maybe this can be expanded in responses/comments.)
To my understanding (not the best) there's a huge disconnect between the physics of the very small (quantum mechanics and the standard model) and that of the very large (general relativity).
The disconnect seems to be unresolvable (I don't understand this part at all) and so efforts are being made to quantise gravity and incorporate it into the standard model.
it's important to realise that particles are an artefact of living in a monkey sized body. at the basic level, the equations are useful if they match observations, not if they make sense intuitively.
> So I thought gravity was basically the curvature of spacetime. But if there's a "gravity" particle, those two things seem mutually exclusive?
It does not have to be either or. It can be both. Both models can be useful to understand the nature of gravity and make predictions about natural phenomenon.
Yes. I've seen lots of twitter/X posts lately about how Gravity is not actually a force. But how can that be true if there is a force carrying "gravity" particle? Or is the word 'force' being used loosely here?
> 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.
They 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.
I'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.
A 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.
Can 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.
So 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?
I 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.
Since 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.
> 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.
the 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.
[+] [-] DemocracyFTW2|1 year ago|reply
> 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??
[+] [-] skhunted|1 year ago|reply
It’s understandable that you don’t like the desensitization of war that comes from our over usage of the word. Perhaps it speaks to a defect in American culture but this is how we communicate in our language. I think Arabic has too much emphasis on allah related phrases. But that’s how they speak. Nothing I can do about it. I don’t think said usage implies anything about their writing abilities.
[+] [-] elashri|1 year ago|reply
I don't like your usage of word "Inshallah" as a mock up of the idea that something will never happen. Because it is a complete opposite meaning of when you suppose to use it. It is usually overused by arab moms (I know that people tends to mean that) but I use it frequently. Ironically I was in online meeting at CERN today and used inshallah (sometimes I use it because I am used to) to refer to potential interesting signal I am seeing. I used it to describe the hope that this will not turn out to be a statistical flactuation.
Also I would agree that this is messy at the time when Einstein published his work on quantization. He even got Nobel prize on his work on photon quantization not relativity. Of course he was not alone, Max plank was the first to suggest energy discritization.
[+] [-] evantbyrne|1 year ago|reply
[+] [-] DemocracyFTW2|1 year ago|reply
First things first, I didn't mean to stir up the discussion in this way. Also, I should have let go of the Caps Lock key. Also, I should've put all that stuff into a single comment or not write some of the things at all instead of creating multiple comments. Sorry.
As for the "inshallah", I probably used that word wrongly; I did not have any meaning of it in mind but used it—somewhat incomprehensibly so—as a moniker for "a standard to start any and all texts with", so "ceterum censeo Carthaginem esse delendam" if you will.
[+] [-] goodpoint|1 year ago|reply
+1, normalizing "war" as a synonym of effort is pretty much orwellian.
[+] [-] sva_|1 year ago|reply
[+] [-] criddell|1 year ago|reply
It's not a simile, is it? They aren't saying it's like a war.
My dictionary lists a bunch of definitions for war that fit this usage.
[+] [-] wasabi991011|1 year ago|reply
[+] [-] Sniffnoy|1 year ago|reply
[+] [-] iknowstuff|1 year ago|reply
[+] [-] VoodooJuJu|1 year ago|reply
On the "war" thing - the culture of many Americans has a martial bent to it, which is why things like "war" made its way into a lot of our idioms and phrases and way of thinking. It's not bad writing just because your cultural mode of thought doesn't consider "war" as an acceptable metaphor or idiom.
Martial cultures don't need to "get a grip" any more than scholarly or pastoral ones need to. Culture is self-preserving and so the martial aspects of ours aren't going away anytime soon, so I suggest you find a way to be more tolerant and understanding of it.
[+] [-] 7373737373|1 year ago|reply
[+] [-] GranularRecipe|1 year ago|reply
[+] [-] canadianfella|1 year ago|reply
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[+] [-] ta93754829|1 year ago|reply
Can someone who understands this please explain it to me, thanks!
[+] [-] whatshisface|1 year ago|reply
String theory and loop quantum gravity fit into this picture by trying to replace the integral over something we can't handle with an integral that matches it at large scales, but turns into something more tractable at small scales. Maybe the fact that we still can't make sense of the integral is Nature's way of telling us that she does not do the integral either...
[+] [-] LeoPanthera|1 year ago|reply
The problem is that nobody has successfully combined these two views into a single unified theory, known as "quantum gravity". General Relativity and quantum mechanics don't naturally fit together, and that's why we don't yet fully understand gravity in a way that reconciles both the spacetime curvature and graviton perspectives.
[+] [-] pdonis|1 year ago|reply
Classically, it is. But most physicists believe that there is a quantum theory of gravity that underlies the classical theory, and that that quantum theory will include, at some level of description, a spin-2 gauge boson that mediates the quantum gravitational interaction, called the "graviton". Our classical theory of gravity, General Relativity, would then be the classical limit of that quantum theory, just as classical Maxwell electrodynamics is the classical limit of quantum electrodynamics.
[+] [-] gary_0|1 year ago|reply
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.
[+] [-] cryptonector|1 year ago|reply
So if you take the gravity curves spacetime view, then gravity is not a force and all that. But if you take the alternative view then gravity is a force. Now, I'll leave what the distortions are that gravity produces in flat spacetime for another time, or for the reader. But I'll say this: this view is both controversial (perhaps replies will show this) and not (see above -and many other- animations).
[+] [-] ajkjk|1 year ago|reply
The "geometry" comes from the fact that the way we measure distances (or, well, experience time) uses the metric tensor field to do it. But it is still ultimately just a value attached to every point like any other field.
[+] [-] renegade-otter|1 year ago|reply
Not just some dumbed down Discovery show - it pushes the limits of what a layperson can understand.
[+] [-] philipov|1 year ago|reply
That's the link bridging gravity as a particle (small-scale) and gravity as a feature of a manifold (large-scale). Physicists are trying to find a way to make spacetime emerge from quantum field theory, or make both emerge from some common framework.
0: https://en.wikipedia.org/wiki/ER_=_EPR
[+] [-] gpsx|1 year ago|reply
[+] [-] unknown|1 year ago|reply
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[+] [-] yarg|1 year ago|reply
The disconnect seems to be unresolvable (I don't understand this part at all) and so efforts are being made to quantise gravity and incorporate it into the standard model.
[+] [-] exe34|1 year ago|reply
https://arxiv.org/abs/1204.4616
[+] [-] blenderob|1 year ago|reply
It does not have to be either or. It can be both. Both models can be useful to understand the nature of gravity and make predictions about natural phenomenon.
[+] [-] dcl|1 year ago|reply
[+] [-] 1024core|1 year ago|reply
[+] [-] swayvil|1 year ago|reply
[+] [-] ruthmarx|1 year ago|reply
That's just part of the picture.
I always thought that Veritasium video did more harm than good.
[+] [-] choilive|1 year ago|reply
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.
[+] [-] itishappy|1 year ago|reply
> 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-Poissoni...
[+] [-] DebtDeflation|1 year ago|reply
Relevant paper:
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.
[+] [-] whatshisface|1 year ago|reply
It would be great to have an independent gravitational wave detector though.
[+] [-] ars|1 year ago|reply
How does it communicate the magnitude of the change? By having lots of gravitons? Or does it have something akin to a frequency?
[+] [-] whatshisface|1 year ago|reply
[+] [-] ricksunny|1 year ago|reply
[+] [-] eterevsky|1 year ago|reply
My question is: what's the difference between the proposed Beryllium slab and Dyson's theoretical detector?
[+] [-] omnicognate|1 year ago|reply
[+] [-] Seb-C|1 year ago|reply
[+] [-] est|1 year ago|reply
[+] [-] DemocracyFTW2|1 year ago|reply
> 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.
[+] [-] revskill|1 year ago|reply
[+] [-] knodi123|1 year ago|reply
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-o... , search for "may as well"
[+] [-] DemocracyFTW2|1 year ago|reply
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[+] [-] DemocracyFTW2|1 year ago|reply
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[+] [-] cyberax|1 year ago|reply