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Pikkugnome
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What is the difference between the GTR vacuum and the vacuum of quantum theory? What is the speed of light in the vacuums, specifically what can be predicted and what must be measured?
Um, that they are two different theories?Pikkugnome said:What is the difference between the GTR vacuum and the vacuum of quantum theory?
Our physical theories based on Lorentz invariance predict that there should be a finite invariant speed. Our measurements bear this out.Pikkugnome said:What is the speed of light in the vacuums, specifically what can be predicted and what must be measured?
You seem to be confusing theoretical models with reality. GR and quantum theory are theoretical models. As I have already said, both of them agree that there should be a finite invariant speed. And as far as the numerical value of that speed, as I have already said, that depends on your choice of units; in natural units it is ##1##. It doesn't even make sense to ask whether GR or quantum theory predicts a particular value for the speed, since humans' choice of units is not something theories of physics can predict.Pikkugnome said:I am wondering about the speed of light in GTR vacuum, since it predates quantum theory. It is surprising that the speeds should be the same, as the vacuums could be different.
You've labelled this thread as B-level, but it's really an A-level question. Here's my attempt at an answer that's somewhere in between...Pikkugnome said:What is the difference between the GTR vacuum and the vacuum of quantum theory?
Note, though, that in the algebraic approach to QFT, all of these unitarily inequivalent constructions can be handled in a unified manner. So I think the jury is still out on exactly what the physical meaning is of the mathematical fact that unitarily inequivalent constructions exist.strangerep said:the short (probably still puzzling) answer to your question is that, in curved spacetime, there is an infinity of inequivalent versions of the simplistic vacuum of ordinary (non-interacting) QFT.
The "physical meaning" is that the choice of mathematical framework (Fock space) is not quite right. Find the right structure and collect your Clay Institute prize.PeterDonis said:Note, though, that in the algebraic approach to QFT, all of these unitarily inequivalent constructions can be handled in a unified manner. So I think the jury is still out on exactly what the physical meaning is of the mathematical fact that unitarily inequivalent constructions exist.
Pikkugnome said:What is the difference between the GTR vacuum and the vacuum of quantum theory? What is the speed of light in the vacuums, specifically what can be predicted and what must be measured?
Ahem.pervect said:Informally, though, the quantum vacuum is full of virtual particles, while GR, being a classical theory, is not.
Which can be reached here:strangerep said:Arnold Neumaier's insight articles on virtual particles.
Those theories complement each other to predict the very accurate experimental evidence.Pikkugnome said:I am wondering about the speed of light in GTR vacuum, since it predates quantum theory. It is surprising that the speeds should be the same, as the vacuums could be different. Are the speeds different, should they be, I have no idea.
The General Theory of Relativity (GTR) and Quantum Theory are two different frameworks used to explain the behavior of the universe at different scales. The GTR Vacuum refers to the vacuum of space-time as described by Einstein's theory of gravity, while the Quantum Theory Vacuum refers to the vacuum of space as described by quantum mechanics. The main difference between the two is that GTR describes the large-scale behavior of gravity, while quantum theory describes the behavior of subatomic particles.
In GTR Vacuum, the speed of light is considered to be a constant and the maximum speed at which anything can travel. This is a fundamental principle of Einstein's theory of relativity. In Quantum Theory Vacuum, the speed of light is also considered to be a constant, but it can be affected by certain factors such as the medium it is traveling through or the energy of the particles it is interacting with.
Both GTR and Quantum Theory have been extensively tested and have been found to accurately describe the behavior of the universe at their respective scales. However, when it comes to the speed of light, GTR is considered to be more accurate as it has been validated by numerous experiments and observations. Quantum Theory, on the other hand, is still being researched and developed, and our understanding of it is constantly evolving.
According to GTR, the speed of light is the maximum speed at which anything can travel. It is considered to be a fundamental constant of the universe and cannot be exceeded. In Quantum Theory, there are some theories that suggest the possibility of particles traveling faster than light, but these are still speculative and have not been proven.
GTR and Quantum Theory are both important frameworks that have greatly expanded our understanding of the universe. GTR has helped us understand the behavior of gravity and the large-scale structure of the universe, while Quantum Theory has helped us understand the behavior of subatomic particles and the fundamental forces that govern the universe. Both theories are necessary to fully understand the complexities of our universe.