It might be possible to detect gravitons after all
quantamagazine.org
quantamagazine.org
> 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??
If this was a war, the UN headquarters has been a war-zone continuously since it started, as has every parliament, congress, and senate.
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.
Your response is that English also overuses another word. I don't understand the point you are trying to make.
English overuses it the same amount, given that Allah is their word for God.
Not even close! I only have experience in the Gulf but they use "allah" words all the time!
"Alhamdulillah" (thank god) is pretty much part of the standard greeting (Pretty much just two people rapid firing a list of phrases at each other simultaneously "peace be with you / and also peace with you / how are you / thank god / how's the family / thank god") and a frequent response to almost any question.
Anything dealing with the future or uncertainty will bring in "Inshallah" (God willing). I remember the first time I asked my cab driver to take me to my destination and he said "Inshallah" that did not give me confidence!
Then there's "bismallah" and "mashallah" which I heard a bunch. And I'm not sure if we can count "yallah, yallah" which is like "hurry, hurry, let's go" which you hear all the time and is derived from "Ya Allah".
I would be willing to bet that Gulf Arabic speakers say "Allah" literally at least 10x if not 100x more than Americans say "God".
Jaysus lads, that chap... Christ, sure how would ya... Holy lord! I've never heard... My God, did you hear... Lord help us and save us, she'd only...
And I'm leaving out the more vulgar variants here.
I'm not saying we'd beat some of the Arabic countries, but I definitely am saying we very well might give them a good run for their money. I'll consciously try tone it down if I'm conversing with a non-Irish person, and then with my family I'll let loose.
Maybe Americans use God-related idioms a lot less than us, of course. The U.S. is a relatively big place though, so I'd be curious to know if there aren't some corners closer to (rural?) Ireland's usage.
He said he wouldn’t be…inshallah.
I know it’s part of their language but just as with your cab example it can be a bit annoying as an outsider, as it feels like they’re passing off responsibility. I feel the same way about some of the things Christians say too, for what it’s worth.
Anyways, that’s my infuriating inshallah story. He was late again - and he needed to find another photographer after that.
On the other hand. For example in Kiswahili "Shauri ya Mungo" (God's business). Perhaps not exactly the same, but sufficiently similar to be interesting: that some things are in fact beyond human capability and comprehension has largely disappeared from the English language (or any language from predominately secular countries).
It's still common in insurances agreements or other contracts that have to consider force majeure - natural disasters and other phenomena fall under the blanket term "Acts of God".
Also, plenty of "secular" curses/exclamations have religious connotations (because it was taboo, and cursing and the taboo are inextricably linked). "Geez", "Gazooks" (God's hooks), etc.
Same goes with English! When parting ways, people commonly say "bye" or "goodbye" which is an evolution of "Godbye" - a contraction of "God be with ye"
That said, I do not care at all that Arabs used "God" a lot or that Americans (supposedly) use "war" a lot. If anything, I like these sorts of differences.
Nah, even a short interaction with a muslim would key you into the fact that they use allah based phrases way more often than the typical american or christian.
The people who you work for (and who everyone works for) are probably loosely associated with tons of them.
Is it? Or is it how marketing communicates? (Which apparently is then spilling into how you communicate?)
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.
+1, normalizing "war" as a synonym of effort is pretty much orwellian.
> late Old English wyrre, werre "large-scale military conflict," from Old North French werre "war" (Old French guerre "difficulty, dispute; hostility; fight, combat, war;" Modern French guerre),
Note the old French part including difficulty dispute, hostility and fight.
No, it wasn't. Plus I never said that the meaning of a word is written in stone and cannot change "just because".
Plus, in terms of number of civilian casualties modern wars make ancient wars look like skirmishes. Another reason not to dilute the word "war".
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.
Oh, I read it differently (perhaps misunderstood). I interpreted the usage as "a required rote phrase/story rubber-stamped onto every piece". I understand how that, too, could be offensive, but I didn't see how inserting the literal meaning of the phrase made sense?
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.
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.
Can someone who understands this please explain it to me, thanks!
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.
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.
We have anomalies (deviations from standard model) in many measurements done by several experiments. This is a good summary [1] from them up until now (sorry for the pay-walled)
https://home.cern/news/news/physics/incredible-lightness-hig...
More relevantly to the previous question, I'm not aware of any of those which affect interactions with the strong or weak nuclear forces.
At first I thought this was a great pun. But then this is perhaps also the reason the word is actually "matters"? Where "matters" is what means something? What matters is what has an observable effect?
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...
>The model of non-self-interacting gravity is a particle we call a "graviton,"
This needs to be emphasized even more, because it has
>when the dx represents a slight change in a function
*see the discussion around sharikous’ comment below
Physicists love to be wrong! If there is an experiment that disagree with the current theory, then is like the will west and everyone can publish their own pet theory that "fix" it. It's like raining free paper for them, their graduate students and everyone. Also, it's fun!
When experiments and theory agree, they have to use imagination to get a new "interesting" tweak that can be published. In some case the the tweak may be interesting, but most of the times it's not.
I remember a talk about a 2-sigma "particle". There was a small disagreement in some experiment, so someone did a thesis about a possible fix adding a new particle. A lot of hard work and hard calculations. It was a nice talk, and someone asked what what happened then. The sad new was that later the 2-sigma disappeared, it was only a fluke :( . This kind of work is important, but it's more boring that looking for new particles.
Theorists would also love for experimentalists to be wrong, but the most efficient way to do it would be by inventing new maths… [sad but still fun]
Can you please elaborate, the first part of the sentence says graviton is for non-self-interacting gravity, the second part of the sentence says graviton is for self-interacting (if 'its' in 'its self-interaction' refers to the graviton).
I don't intend to nitpick the sentence, just trying to understand the theory and I don't even know if particle means self interaction or the opposite and can't parse it here either...
If the answer is graviton is for non-self-interacting: what is the model for the other case (where gravity does self interact) and what would cause that self interaction if not the graviton?
The point is, we know gravitation does self-interact. But our best model, the graviton, doesn't model self-interaction. So the model is probably accurate in regimes where you'd expect little self-interaction anyways.
just like the massless photon, the massless graviton would be bent by the gravity of black holes... hence self interaction?
In QED, photon and photon do interacts too and you can calculate its effect to be small. In GR, you can expect self interaction is small if the space time curvature is small.
(Photon is the particle that mediates QED, and graviton is the hypothetical particle that mediates gravity.)
That said, an easier question to ponder (and many have tried) might be:
Do photons self-interact? With each other? In free space?
I disagree with that part. For the strong force we have the "gluons" and they are considered particles and they have a strong self-interaction. The strong self interaction makes it a huge mess and a lot of things that involve gluons are impossible to calculate.
It's more like:
fake quote> Let's pretend for 30 minutes that the strong field don't self-interact, so we have this nice particles call gluons. Now we add this interaction to the Lagrangian to make gluons interact with other gluons, and now we have a problem.
I agree that that when gravity is small enough, then gravitons give an easy to calculate aproximation. IIRC at high enough energies calculations with gluons get not impossible to calculate too.
We see interacting particles in detectors, but since nobody can write down what field configuration they mean by "a photon," I can defend my phrasing - but you can defend yours too because I know what a bird is even if I don't know how they work.
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.
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.
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.
That is true. Classically, gravity is a fictitious force, merely a result of inertia from moving in a curved space-time.
> But how can that be true if there is a force carrying "gravity" particle? Or is the word 'force' being used loosely here?
Because we _suspect_ that the classical view is not correct. And there's a quantum description that may or may not involve curved space-time.
It's not impossible that the spacetime curvature is a mathematical artifact of a deeper theory. Merely a kinematic explanation, just like epicycles.
It's also possible that the space-time _is_ really curved, and gravitons simply cause the curvature by somehow coupling with it. And then other matter experiences this, in the manner described above.
So you have a thing, that gets interpolated updated with various functions, that overlap, and those functions only get updated at lightspeed, cause caching.
Cachesize limit should show as farway gravity sources getting bundled into lower density information functions.
There is not. Or maybe there is not. At least so far there is not. We have never observed one. "Graviton" particle is just a hypothesis. Outside of some people theorizing that graviton could exist, there is no observations that it exists.
"In theories of quantum gravity, the graviton is the hypothetical quantum of gravity"
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.
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).
I follow a few educators/communicators in this field and I have a feeling they're using this "gravity isn't really a force" to bridge the gap between their deep understanding and us mortals that don't poses the language / understanding to get the entire meaning behind it. Is that feeling correct or am I missing something?
To that extent you can build 3 fundamental forces, electro magnetic, weak (that are called together electroweak) and the strong force. You have an extra force carrier through the Higgs that allows you to give mass to everyone.
Now you need to consider gravity because you know that gravity exist and since everything under the sub is quantised, well so should gravity.
The main issue with gravity is that it is interpreted so far as a curvature of space time, it's mainly fine for big items, but the implications for quantum field theory is that you should modify the small integral element that you use (space shouldn't have the same size) except that you look locally at space that is mainly flat... And changing the integral does not lead to well behaved behaviours.
You can start to introduce new fields but doing so also causes an issue...
Funnily enough even in the standard model something is missing, everything mostly fits, but that's the trick, mostly, neutrinos have mass and this in itself is a problem because the Higgs mechanism doesn't provide mass to them ...
Long story short, people take shortcut when explaining the messy gritty part of it, which is "fine" but not really, and from a simple standpoint one would like to have a simple field from which gravity is born, which might be but so far, to my simpleton understanding, this hasn't been too successful, unless some form of string theory is realised. But the pre requisite for this is a form of supersymmetric theory existing which is currently disfavored, but could exist in the unproved energy scales from here to the plank energy scale.
Sorry this ended being a tad long and I'm not sure this is clarifying things.
The Higgs mechanism doesn't provide all mass, even of the things that it provides mass for. They each have a "bare" mass, that is, a mass without any Higgs interactions. They just have a much greater mass because of the Higgs interaction. (And maybe that's why neutrinos have so little mass...)
The W Z have only mass from the Higgs and nothing else for example.
But to answer your point completely here is an answer which is in the two following links making the point for the Dirac fields
https://physics.stackexchange.com/questions/607435/what-part...
https://cds.cern.ch/record/292286/files/B00008237.pdf at page 46
Or have I misunderstood your point?
Yes, that is the main issue. It doesn't have to be that way though. If you look at the Einstein field equations, and solutions like the Schwarzschild and Kerr metrics, the key component is a metric tensor that is nothing more than a mapping from flat spacetime to curved spacetime. We have the ability to choose which interpretation to use. The metrics are nothing more than Mercator-like projections.
If you take the curved spacetime view then you get distortions of spacetime. If you take the flat spacetime view then you get other distortions like that the speed of light -though always seen as the same locally- varies according to the gravitational potential (there are other distortions as well).
We seem to have a bit of a fetish for the curved spacetime view. But oddly when you look for animations depicting interactions with black holes and photons or particles / small bodies what you almost invariably find are of two types: a) flat spacetime representations, or b) the funnel representation, and (b) often comes with a flat spacetime representation above the funnel. How do you think the authors produce the flat spacetime representations? A: By applying the metrics to go from curved spacetime to flat! And why do they use flat spacetime for their animations? A: Because it's easier for humans to understand!
The reality is that flat and curved spacetime are two sides of the same coin. If curved spacetime is the sticking point for quantizing gravity, then switch to flat spacetime.
The core idea is that when you move a mass, its contribution to the spacetime geometry changes, but the effects of the change of the geometry doesn't apply instantaneously to all the universe but instead the change propagates at the speed of light.
So that explains why any sudden movement of a mass creates a "crest" that moves through space at the speed of light.
Furthermore, the sources of fast movement of extremely heavy mass just happen to involve an object that wiggles back and forth in a periodic way because those events involve heavy objects orbiting other heavy objects.
That's the reason we can measure a wave with multiple crests and we can talk about a wave length of the gravitational waves: the wave length of the gravitational waves matches the period of the orbit of the heavy mass.
You wouldn't expect to find quantums of centrifugal force in a rotating frame of reference, and no quantums of centrifugal force in a non-rotating frame of reference. They're both describing the same situation; either quantums exist in both frames, or they exist in neither.
So either gravity really exists as a force, or it doesn't. If it does, then I would expect gravitons, and expect them in all frames of reference. If it doesn't, then I would expect no gravitons in any frame of reference.
Except... If I understand correctly, static electric and magnetic fields are not carried by photons - they just sit there. It's only changing E/M fields that are carried by photons. So maybe only changing gravitational fields are carried by gravitons, and the static fields are just curved space-time?
That's just part of the picture.
I always thought that Veritasium video did more harm than good.
Not just some dumbed down Discovery show - it pushes the limits of what a layperson can understand.
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.
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.
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.
Gravity drive?
> 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...
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.
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.
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.
It would be great to have an independent gravitational wave detector though.
How does it communicate the magnitude of the change? By having lots of gravitons? Or does it have something akin to a frequency?
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?
Assuming our guess about quantum gravity are correct, the normal gravitation force use gravitons too, they are virtual gravitons but the distinction between "real" and "virtual" particles is another whole can of worms.
My question is: what's the difference between the proposed Beryllium slab and Dyson's theoretical detector?
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.
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.
> 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.
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."
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.
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"