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Haroon1
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I was reading about this effect called the 'Casimir Effect' which provides evidence for the existence of Quantum Vacuum. What is Quantum Vacuum, and how is it different from the ordinary Vacuum?
Born2bwire said:In the quantum vacuum, despite the fact that no photons are present, there are still fluctuating electromagnetic fields. However, the fields fluctuate about an expectation value of zero. In addition, the energy of the quantum vacuum state is divergent, infinite if you assume no bound to the frequencies of the vacuum (but this is usually truncated for various reasons). There are a lot of insights into the necessity of the vacuum fields, Peter Milonni has a good book that covers this in detail. For example, fluctuation-dissipation theorem can be used to help explain it though it is of course derivable from QED for fields in free-space. As for Casimir force providing evidence for its existence, Jaffe has an article that he wrote where he feels that this is not something that can be claimed. He feels that since we can characterize the Casimir force in a number of ways, one of which does not use the quantum vacuum at all, then it cannot be used as proof. Jaffe has been coauthor on some good Casimir force papers so I do not dismiss his assertions though I would have liked to have seen him get the paper published to read some responses to it.
http://arxiv.org/abs/hep-th/0503158
Fredrik said:I'd like to recommend this really cool article about vacuum to those who know a lot of math already. (DarMM recommended it to me in another thread).
italiano vero said:I have some questions:
these processes broke the conservation of energy?
Some physicists claims that Casmir effec is not a valid proof of the existence of vacuum fluctuations (http://arxiv.org/abs/hep-th/0503158). Are they right? But the quanta of foundamental interactions are VIRTUAL bosons, so how can virtual particles don't exist?
How is considered quantum vacuum in loop quantum gravity? What LQG says about vacuum fluctuations and virtual particles?
Freeman Dyson said:Thank you for taking the time with that answer, Born2bwire.
So it is incorrect to say that these quantum flucuations come from "nothing"? Physicists just calculate and don't worry about where fluctuations come from. They just deal with them.
And what is the difference between vacuum energy and dark energy?
Freeman Dyson said:But for those who don't know a lot of math...this article touches on another thing I was wondering. Where is spacetime in all this? The gravitational field? Is the gravitational field the background in all of this?
Freeman Dyson said:Where is spacetime in all this?
Born2bwire said:As for Casimir force providing evidence for its existence, Jaffe has an article that he wrote where he feels that this is not something that can be claimed. He feels that since we can characterize the Casimir force in a number of ways, one of which does not use the quantum vacuum at all, then it cannot be used as proof.
http://arxiv.org/abs/hep-th/0503158
Halcyon-on said:If there are no proofs, they are not explanations but conjectures. Would this means that the vacuum energy is a conjecture?
italiano vero said:Thanks Born2bwire for the answers.
This is a question I'd like to ask. Vacuum without space is possible? Vacuum is the space itself? The infinite energy of vacuum is the energy of spacetime? Vacuum energy is the spacetime itself?
Born2bwire said:There are several phenomenon that require the vacuum fluctuations to exist, the Lamb shift is one example. However, it seems that this is a bit independent of the question of the vacuum energy. As stated previously, the vacuum energy can be renormalized to be zero, but this does not remove the vacuum fluctuations. Rereading Jaffe's abstract it seems I should have mentioned that he is more specifically focusing on the proof of the vacuum energy, not the existence of both fluctuations and energy. I do not know if there is anything that conclusively supports the vacuum energy.
Born2bwire said:I did not say that the Lamb shift is related to the vacuum energies, but the fluctuations. There is coupling with the vacuum fluctuations that is required for the correct Lamb shift to be calculated.
See the QM model described above.And I have yet to find any classical interpretation for the vacuum fluctuations.
It is not the fields who are directly quantized but the oscillator energies. Fields flictuate and they are just usual "fluctuations" in a compound system like an electron position in an atom (it's uncertain there).Born2bwire said:They can only arise by the quantization of the electric and magnetic fields.
Born2bwire said:There are several phenomenon that require the vacuum fluctuations to exist, the Lamb shift is one example. However, it seems that this is a bit independent of the question of the vacuum energy. As stated previously, the vacuum energy can be renormalized to be zero, but this does not remove the vacuum fluctuations. Rereading Jaffe's abstract it seems I should have mentioned that he is more specifically focusing on the proof of the vacuum energy, not the existence of both fluctuations and energy. I do not know if there is anything that conclusively supports the vacuum energy.
What do you mean by space though? The vacuum fields require four-space. A common method of describing the vacuum is to assume that we have a cavity with periodic boundary conditions. The true vacuum state is assumed to be the modes of this cavity when we take the limit of the cavity's size to infininty. In this way, we have assumed an infinite Minkowski space. Well, Minkowski space may be a bit of a stretch as I believe that most derivations do not strictly assume Minkowski space but obviously the vacuum can be expressed relativistically.
I am not sure what you mean by energy of spacetime or energy being spacetime. These are concepts I have never heard of.
There is no such a relation. Vacuum energy cannot be used so its value may be taken to be zero.italiano vero said:Is there anyone that has the patience to explain me the relation between vacuum energy and vacuum fluctuations?
Vacuum energy is certain, it does not fluctuate. It is zero. But it can be considered as a sum of "potential" and "kinetic" energies that vary in time. Their sum is constant and is minimum possible. This is the definition of quantum vacuum for a specific system. Think of atom as a model.Aren't fluctuations the fluctuation of vacuum energy? So how can be proved fluctuations without proving energy?
The Quantum Vacuum, also known as the Zero-Point Energy Field, is the lowest possible energy state that exists in empty space. It is a fundamental concept in quantum mechanics and is thought to be the source of all matter and energy in the universe.
The Quantum Vacuum is different from regular vacuum in that it is not truly empty. It is filled with fluctuating quantum fields that constantly produce and destroy particles and energy. This activity gives the Quantum Vacuum its unique properties and makes it an essential part of our understanding of the universe.
The Quantum Vacuum plays a central role in modern physics as it is the foundation of quantum field theory, which is used to describe the behavior of subatomic particles. It also helps explain phenomena such as the Casimir effect and the Lamb shift, and is a key concept in attempts to reconcile quantum mechanics and general relativity.
While the Quantum Vacuum is a fascinating concept, it is currently not possible to harness its energy for practical use. The energy contained in the Quantum Vacuum is extremely small and difficult to access, making it challenging to utilize in any meaningful way.
Scientists are continually conducting research to better understand the properties and behavior of the Quantum Vacuum. This includes experiments to measure its energy density, investigations into its role in the expansion of the universe, and attempts to develop a unified theory that incorporates the Quantum Vacuum into our understanding of the laws of physics.