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I 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??
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.
Let's split the difference and start talking about the "jihad on drugs"
Nice. I think it would probably be more effective propaganda to say the "jihad on Christmas" than the "war on Christmas".
The “war on Christmas” was thought up by a think tank and agreed upon by a group of conservative media that meet weekly to decide agenda to push across talk radio, tv, online. Truly an American phenomenon.
Think tanks that create agendas for groups who meet regularly to decide how to push those agendas through the media and through their politicians are not an American phenomenon, and not specifically conservative.
The people who you work for (and who everyone works for) are probably loosely associated with tons of them.
> [war] is how we communicate in our language.
Is it? Or is it how marketing communicates? (Which apparently is then spilling into how you communicate?)
One influences the other. We have always been at war with Eastasia.
English has a lot of "oh my god", "god-willing", "oh god", "god no", too.
It was pointed out that in American English we overuse "war". I pointed out a language that overuses a different word. I imagine most languages have a bunch of phrases involving an overused word. My point was that this phenomenon isn't unique to American English.
Your response is that English also overuses another word. I don't understand the point you are trying to make.
Your response needlessly called out Arabic for using too much “Allah”.
English overuses it the same amount, given that Allah is their word for God.
> English overuses it the same amount
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".
> "Alhamdulillah" (thank god) is pretty much part of the standard greeting
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"
I had a photoshoot scheduled with a young Somali man. He was late by over an hour, and I had another shoot after so I had to cancel. I rescheduled and told him if he was late for the next shoot I wouldn’t be rescheduling again.
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.
> they’re passing off responsibility
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).
> 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.
Inshallah is just a fun and useful word, I've been hearing it a lot lately from people who aren't even Muslims. I think it's on track to become a common loan word in English.
It already is one from Arabic to Spanish (ojalá for "I hope" or "hopefully")
Sounds similar to "mei ban fa" (it can't be helped) in Chinese. The words suggest something is impossible but in practice it generally just means, nope, don't feel like it.
For one of your next trips I suggest a few months in Ireland, and if you could in particular spend time living in a slightly more rural or at least small-town type family.
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.
Nah. English speakers use God-based exclamations from time to time but they generally do not pepper their sentences with "God willing", "praise God," etc like Arabs do.
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.
It was called out because OP used "Inshallah". The argument is that it's cultural, and complaining about it is silly.
The point I was making is that this phenomenon occurs in other languages. Arabic and its phrases involving "allah" first came to mind. So how was this "needlessly"? I needed to give an example of this occurring in another language.
>English overuses it the same amount,
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.
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.
> I don't like your usage of word "Inshallah" as a mock up of the idea that something will never happen.
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?
Please see my other comment; I used "inshallah" wrongly.
No problem, happens to the best of us. No hard feelings.
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You seem to be frequently flame posting about America. Are you going to be okay?
I think I'm getting an anxiety disorder here seeing as close to 50% of Americans are seemingly OK with Trump, Vance and Elon becoming their new overlords. Seriously.
Normal to be nervous when the stakes are high. One thing that history has taught me is that disaster is always an option lol
It is a cringeworthy hallmark of angsty teens and people who base their entire identity on their political leaning
Replying to myself as I can't edit my post now.
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.
> Please spare me that "war" simile
+1, normalizing "war" as a synonym of effort is pretty much orwellian.
That is part of the original etymology of the word. [1]
> 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.
Yes, but. I have a 1920s edition of the Nibelungen Saga which uses an intentionally old-timey language; there I find "Wortstreit", obviously in contrast to a proper Streit which would have involved physic force and maybe weapons. But in modern German, as in English, to use "Streit" for an armed conflict or "war" for physicists discussing the nature of things is not appropriate except as a rhetoric measure (downplay or exaggerate). Words change.
What you described is not a synonym of "effort".
Plus, in terms of number of civilian casualties modern wars make ancient wars look like skirmishes. Another reason not to dilute the word "war".
Wow, words changing meaning over time. Imagine that. The internet would lead me to believe that’s something horrific that must not be allowed.
The OP doesn't like the meaning of the word "war" changing from a definition they believe to be correct. My example shows that the meaning of words is defined by usage and that usage changes over time. This is especially ironic in this particular case because the meaning that the OP didn't like is one which was actually part of the original etymology of the word.
> This is especially ironic in this particular case because the meaning that the OP didn't like is one which was actually part of the original etymology of the word.
No, it wasn't. Plus I never said that the meaning of a word is written in stone and cannot change "just because".
It now appears like there is a war on the inflationary use of the term 'war' in common linguistic use.
We don't want it to escalate to a word war.
> spare me that "war" simile
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.
Yeah you're probably right, I'm not great on rhetoric vocab.
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.
OK that makes sense.
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.
I agree, I misread that.
whoa this comment took a turn
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.
Re. 2), what word should be used instead? "Massive concerted/collaborative effort"?
"Polite debate".
If this was a war, the UN headquarters has been a war-zone continuously since it started, as has every parliament, congress, and senate.
Quest, undertaking, chapter.
It's not an inshallah, it's a masha'Allah.
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So 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!
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...
> 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.
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?
> 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).
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.
Would self-interaction mean something like:
just like the massless photon, the massless graviton would be bent by the gravity of black holes... hence self interaction?
Photon-photon interaction is photon self interaction. Gravity/graviton self interaction then means graviton-graviton interaction. In general relativity, all form of energy would have an effect of gravity, and also react to gravity. Since all matter, including photon and graviton, has energy, then they should self interact.
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.)
This needs to be emphasized more, by the TFA too — most (theoretical) physicists think that detecting gravitons is an engineering exercise that has no implications* for quantum gravity (as understood by the public)
>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
Because they don’t want to run the risk of being wrong, eh?
Probably because the number of detection will be too few to test old theories or make new theories with the experimental results.
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.
Haha i remember! friends got caught up in that! (Wasnt it 3-sigma tho?)
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]
> 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.
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.
The thing is, no particle is defined when it interacts. At our present level of understanding the only defined particles are the individual green's functions that appear in perturbation expansions, the lines in Feynman diagrams.
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.
I don't know if it was just sheer luck that your comment fit my particular flavor of ignorance perfectly, but it struck me as great writing! I think I learned a little thing today. When I read the article I thought, too bad I can't ever understand anything of this, but now my personal model of the universe is just a little bit richer.
Even with gravity being "self interactive" can't we have stable particles ("gravitons"?) that behave like solitons do?
If you’re young (or if you’re old but your mind remains flexible) i urge you to think hard about this problem.. i do and i will! my mind is already quite inflexible so i’m not going say anything definite about this question out of fear of saying something dumb/misleading. Your q hides monsters ready to snipe any serious mind of the planet!
That said, an easier question to ponder (and many have tried) might be:
Do photons self-interact? With each other? In free space?
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.
My understanding is the particle model of electromagnetism, the photon, really only shows up where the em field interacts with matter(electrons really), the em field itself is not quantized, or at least not quantized at the level of the photon. Not that this really matters(intentional), we can only interact with the em field as matter so that is what matters.
> matter so that is what matters
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?
The most elegant description of electromagnetism is also in terms of curvature, but the curvature of a certain mathematical structure called "connection on fiber bundles" and the math field is called differential geometry.
When 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?
Yes. 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.
That's not quite accurate. There are a few things that the Standard Model doesn't exactly account for--neutrino oscillation being the most famous. The trouble is that these issues aren't really big enough to suggest new physics, and the experiments aren't good enough to really suggest how much patching actually needs to be done.
Also the unexpectedly large mass of the Higgs, which suggested (to string theorists), super symmetry. Which unfortunately turned out to not exist unless it’s at some configuration that’s quite different from what was suggested
I thought the Higgs had an unexpectedly small mass.
https://home.cern/news/news/physics/incredible-lightness-hig...
Yes, there are some deviations. But minor adjustments to the Standard Model handles those. And don't really point in the direction of a better theory.
More relevantly to the previous question, I'm not aware of any of those which affect interactions with the strong or weak nuclear forces.
Neutrinos predominantly work via the weak interaction, don't they?
> 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)
Comment was deleted :(
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).
I last took a physics course when Pluto was a planet, so excuse my possibly outdated question, but isn't the detection of gravitational waves proof of gravity being a force?
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?
Fwiw gravitational waves were predicted by Einstein himself (Einstein, Albert, Ueber Gravitationswellen, 1918) as a consequence of general relativity.
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.
s/movement/acceleration/g
So the main issue here is how people were presenting it, in Quantum field theory, as stated by other people, each force is associated with a field and has at least one force carrier, the exact number is linked to the specifics of the mathematical framework underlying it
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 main issue with gravity is that it is interpreted so far as a curvature of space time,
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.
> neutrinos have mass and this in itself is a problem because the Higgs mechanism doesn't provide mass to them ...
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...)
Uuuuh... No...
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?
I stand corrected.
My naïve understanding is that you can model gravity as a force in a flat, static spacetime. Equivalently you can model gravity as a forceless distortion of curved spacetime. Both models can be translated faithfully into one another, so you can solve problems related to gravity in either domain.
My naive understanding is that forceless spacetime distortion predicts somewhat different things than the old model. That's how general relativity finally explained the procession of Mercury's orbit for example.
GP means that you can take the Einstein field equations (and their solutions) and use the metric tensors to map between flat and curved spacetime, with either way being equivalent. GP did not mean that those tools map from Newtonian flat spacetime to curved.
Consider centrifugal force. In a non-rotating reference frame, it doesn't exist. In a rotating reference frame, it does, that is, it shows up as a term in the equation of motion.
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?
It's a bit of an internet meme, gravity can take momentum away from one object and transfer it to another, and that's what Newton said a force was. The meme is that the way it happens makes "changing momentum" (3-momentum, the one Newton was talking about) and "going straight" (geodesically, in curved space-time) hard to separate in English.
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.
I just watched this a few days ago on the Space Matters channel about gravitational waves: https://www.youtube.com/watch?v=9bg2NINW8a0
Not just some dumbed down Discovery show - it pushes the limits of what a layperson can understand.
The YT algorithm is so damn bizarre sometimes. I'm subscribed to probably a dozen different astronomy and physics channels, some for 8 years, and never once saw this channel you recommended. It recommends plenty of AI-TTS bunk too. But somehow didn't decide to show me that channel. Thanks for recommending it.
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.)
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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?
> Yes. I've seen lots of twitter/X posts lately about how Gravity is not actually a force.
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.
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You can make a lot of pseudo particles in semiconductors which definitely exist, but also aren't "real" - i.e. semiconductor electron holes are capably modelled as positive particles which can move freely with momentum/position within a semiconductor.
> if there is a force carrying "gravity" particle?
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"
In a sim, it would fall into the "configurable parameter" category and dynamically altered parameter whos laws depended on locations are function lookups. And to execute performant, it would be a constant factor field only updated onAlteration with fun(x)
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.
Sort of like how light is both a wave and a particle...?
Maybe all particles are twists in spacetime.
> So I thought gravity was basically the curvature of spacetime.
That's just part of the picture.
I always thought that Veritasium video did more harm than good.
> 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.
[0] https://en.wikipedia.org/wiki/Photon_statistics#Sub-Poissoni...
It 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.
Right, but this event just confirms gravitational radiation exists (which we already know). It can't tell us how it behaves (is it quantum? it it classical?) without detecting many events in sequence to be able to run statistics on (and if you miss one, your stats are wrong). One bar has a very low probability of detection, we'd need many, hence the expectation of planet-scale machinery.
> This would be a very big deal.
Gravity drive?
Nope.
The 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
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.
So... 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.
Rather, 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.
Does 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.)
There are tons of effective QFTs that can be used very accurately to predict experiments below a certain (high) energy threshold, but which are not renormalizable. This is well understood. It means that the theory needs to be augmented to understand the higher energies, but does not at all mean the more fundamental (augmented) theory has to be radically different, such as classical. Everyone already agrees that the non-renormalizability of naive low-energy quantum gravity means something must be added.
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.
the 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)
How would mergers produce antibunched gravity?
I 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?
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.
A 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?
Everything creates gravitational waves. They are very difficult to detect, so we can only detect the ones created by black hole merger or something similar.
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.
Gravitons 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?
Classical waves do all of those things too.
So gravitons are only emitted by accelerating objects?
Real gravitons, yes.
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.
Or, something like the simulation hypothesis is real and different models of reality are used at different length scales and the overlap is fuzzy.
The issue is that the overlap becomes large and very important near black holes (and near the big bang, but that's probably not important in a simulation).
Yeah, I do have a suspicion that they are optimisation strategies to reduce computational complexity.
That's a facinating read. I wonder what are the possible applications of "quantized gravity" ? GPS without satellites?
If 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.
constraints on theories of everything
Cheap 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.
You’re mixing up general relativity with quantum gravity.
I'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.
You buried your lede. The “tricks” you describe relate to GR. I missed that you’re essentially saying “no.”
Another 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.
It'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.
I 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."
Credit-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.
But the whole atmosphere is pushing it up, isn't it? (Well, not the "whole" atmosphere, but...)
That means there's no Gravity before The BigBang, right ?
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.
cite: https://www.hawking.org.uk/in-words/lectures/the-beginning-o... , search for "may as well"
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The 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.
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TIL that Freeman Dyson looks like a house elf!
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