IF quantum field theory is real, and IF gravity is indeed a fundamental force... Can spacetime be considered the quantum field of gravitons?Could gravitons gain mass through an Higgs interaction? Can such process be behind the expansion of the universe (more massive gravitons repel each other)? Or would it be the other way around?
>>17089475bump?
>>17089475quantized gravity is merely an intuition. doesn't have to be. it could be, but doesn't have to be. honestly it would be boring if it was
>>17089524why "boring"?
>>17089530because it would be expected.
>>17089475Spacetime isn't a field. Its described by the robertson walker metric. Quantum fields describe spacetime in a fock metric.
>>17089475>IF quantum field theory is real, and IF gravity is indeed a fundamental force... Can spacetime be considered the quantum field of gravitons?yes, basically. Quantum gravity is a problem in normal QFT but in approaches like string theory (which reduces to QFT in appropriate limits), spacetime is basically a coherent system of gravitons. Like for example the claim in string theory is that a flat spacetime with a bunch of gravitons in it could represent a curved spacetime, but if you change your background metric around then it looks like there’s zero gravitons there gravitons but just a curved background. This is how string theory escapes from complaints about “background independence” even though naiively string theory sort of starts out as a theory in flat space>Could gravitons gain mass through an Higgs interaction?there are theories about massive gravity, but they are not very realistic. In general gravitons are massless. From a basic QFT perspective having a massive graviton would screw up the long distance 1/r^2 dependence of the force of gravity, and in cosmology gravitational waves propagate as if gravitons are massless. So most people don’t think highly of “massive gravity” theories>Can such process be behind the expansion of the universe (more massive gravitons repel each other)? Or would it be the other way around?I wouldn’t be surprised if this were an idea somebody has explored before in the context of massive gravity theories , but again those theories are really riddled with issues in multiple ways and massless gravitons are a much more reasonable baseline
>>17089475there are no gravitons, that's nonsense
>>17089475>IF gravity is indeed a fundamental forceIt's not. It's not "transmitted" by particles. There are no gravitons. How the fuck would a "gain mass"? First they don't exist. Second that's like saying a photon can gain electric charge. Gravity is an effect, not a force. It can't be quantized because spacetime isn't quantum.
Completion of f(R) gravity to a full exponential leads to string theory
>>17089674Ok, so here's a thought maybe a quantum string theory guy would know (although I think string theory at face value has already been depreciated).You know how like, a guitar sting oscillates up and down? Well the also rotate around a central point while they do it. Kind of like a spiral decay as the vibration dies down Does that concept/pattern relate to "string theory" somehow? Seems like it should. If not the probably got it wrong
>>17089715I'm not a physicist I just have an undergrad math degree
>>17089715This is a good question but answering it in a proper string theory way is kind of complicated, unfortunately . At a basic level, string theory definitely does incorporate how strings can vibrate along multiple axes (even more than 3D) as well as rotating (or spinning). But in the way string states are represented, if for example an open string is just rotating end-over-end like a propellor, there may be ways to represent that in terms of just vibrational “guitar string” modes in a certain superposition.Often when you learn string theory the first step they teach is the “light cone gauge” way of looking at quantizing strings, which really helps to simplify the theory down from having vibrations in full 3D down to a much simpler way of looking at it where you only need to think about motion in two dimensions. So answering your questions about how things look in 3D gets a little obscure by rhetorical standard way of how string theorists simplify the analysis. If you are curious about whether and how this makes sense, you can watch Leonard Susskind’s lectures on youtube in his Intro Sting Theory videos. He explains it pretty much as well as anyone
>>17089883Alright cool thank you, I'll probably check out that video series.Is string theory as a whole still considered a relevant area of study? I mean, quantum physicists are known for their mental masturbation...would string theory be an example of that or does it actually apply to something? Please be aware I have no idea so not trying to say I know one way or the other.
>>17090000>Is string theory as a whole still considered a relevant area of study?This is kind of a controversial question, if you ask me. There is a high-profile conference every year called “Strings” and it attracts a lot of big names, not only oldsters but a lot of postdocs and grad students involved in active research. But a common criticism you hear (mostly from outside hep-th, though it seems true to me) is that what they are doing is mostly not proper string theory. Very few people do actual perturbative string theory — the main areas of research have been things related to AdS/CFT so you have a lot of conformal field theory and scattering theory in supersymmetric QFTs and some meme stuff like Celestial Holography, all of which connects with string theory but at this point the connection is primarily historical. the old-school hopes of finding that one Calabi-Yau or braneworld setup that gives you the nice explanation for the standard model plus gravity are mostly inactive aside from some non-prominent groups mostly in Europe> I mean, quantum physicists are known for their mental masturbation...would string theory be an example of that or does it actually apply to something?Mental masturbation, yes. There are a few things where they try to connect to other fields like quantum chromodynamics or actual black hole physics (like using string-inspired scattering theory to explain LIGO gravitational waves from black hole inspirals) but it usually comes across as the figleaf they use to cover up how incredibly abstract what the bulk of what they do is. In terms of actually predicting how particle scattering works, which is really what the point of string theory always was, they have really no hope of connecting with experiment since all the energies are way higher than any foreseeable collider or any cosmic ray stuff. Especially since their main prediction of supersymmetry and the WIMP explanation for dark matter basically has failed in the LHC era
>>17090153Ok thanks.Would string theory be more broadly described as a probabilistic or deterministic interpretation of quantum physics?From what I understand, David Bohm's Pilot Wave theory is considered to be deterministic where most modern "expert" interpretations are thought of as probabilistic.Remember, David Bohm hypothesized the the expirement that was later used to prove the existence of the Magnetic Vector Potential using an electron holography with a tunneling microscope (I think, feel free to correct me).
