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Infinite Energy beneath Quantum Vacuum?

by waterfall
Tags: beneath, energy, infinite, quantum, vacuum
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waterfall
#1
Feb21-12, 05:34 PM
P: 381
In the thread http://www.physicsforums.com/showthread.php?t=343049

Science Advisor Born2bwire mentioned: "Since the vacuum state has infinite energy, it has infinite photons. Everytime we add energy into the electromagnetic fields, we just pull a photon out of the vacuum state." How many believe this and is there a refutation to this idea... because it seems that if it is true, then beneath the quantum vacuum lies a source of infinite energy.. literally".

Born2bwire wrote:

A quantum vacuum is simply a fancy name for the ground state. That is, it is the lowest energy state of the system. The interesting thing about the electric and magnetic fields in quantum electrodynamics is that their ground state is represented by zero photons. However, their ground state is not zero energy. In fact, in a completely empty space, the quantum vacuum can have an infinite number of frequencies of fluctuating fields occuring, a continuous spectrum. Each frequency represents a mode, a possible excitation of the fields in the system, and each mode has a certain discrete energy density. So the quantum vacuum has infinite energy if we do not restrict the possible frequencies of electric and magnetic fields. One way to think of this is that in quantum electrodynamics, we think of the photons as being the energy packets (quanta) that occur when we excite the electromagnetic waves. Each energy level of the electric and magnetic fields represents an additional photon being excited. These photons "come" from the vacuum state. Since the vacuum state has infinite energy, it has infinite photons. Everytime we add energy into the electromagnetic fields, we just pull a photon out of the vacuum state. It's an interesting idea, I recall I think it was Dirac who mentioned it.

Where this energy comes from we do not say. All we know is that in quantum mechanics, we often get systems where the energy cannot go to zero. Since we have an energy "bath" that we can draw upon, it forces fluctuations in the system (this is an idea from the fluctuation-dissipation that I mentioned earlier). For example, let's say I have a system that draws energy from a heat bath that surrounds it. It is constantly drawing energy from the bath but it cannot put energy back in. We find out that this stipulates that the system must have fluctuations. In the same way, we must have fluctuations in the vacuum state as well. But since these fluctuations are about a mean of zero, they are not measurable in the macroscopic world. So we never see truly see them. Sure we can get non-zero measurements should we attempt them but statistically we will only get a zero measurement in the long run.

So again, we can't say where the energy comes from, it's a definition of the quantum system. The fluctuations of the field can be explained in a few ways. We an show taht it must occur via mathematical rigor of quantum mechanics. The closest "physical" reason I have found is that the vacuum energy is an energy bath that couples with the electric and magnetic fields. Because of this, the fields must have fluctuations as shown by statistical mechanics. Photons are nothing more than the energy quanta of the electric and magnetic fields. We can think of them as being drawn out of the energy of the vacuum state. When they are created they come from the vacuum and when annihilated they return. Of course this may not be a truly physical picture. Anytime we add energy to the fields we create photons. Since they are nothing more than massless particles of energy/momentum, it is hard to say what they are created of. So if I dump energy into the fields using an antenna, then am I drawing the photons up from the vacuum or just creating them from the energy injection from my antenna.

As for virtual particles, they are not real. It is hard to say what they are but I have not heard of them as being any physically real object. They can be useful calculation tools though in Feynman diagrams. In the quantum vacuum, we can represent the vacuum fluctuations as virtual photons. The idea is that we momentarily create the photon let it interact and then destroy it. In the end, because we created and destroyed the particle we add no energy to the fields, but by allowing the particle to interact it is the same as allowing the field fluctuations to have interacted. For example, in the Casimir force, we can calculate it from the force induced by the fluctuation fields or we could calculate it as the "radiation" pressure force of the equivalent virtual photons. The results are identical.
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questionpost
#2
Feb21-12, 05:38 PM
P: 198
There's experiments that provide evidence for pair-anti-pair annihilation within the vaccum of space, but it's too inefficient of a source to extract energy from. I think if there is "infinite" energy and we can just take whatever we want from it, there's going to need to be some more proof and equations other than just "well its probable isn't it?".
Also, virtual particles aren't real, but they aren't fake. They occupy a sort of "i" realm.
waterfall
#3
Feb21-12, 11:57 PM
P: 381
http://www.amazon.com/gp/product/012...pf_rd_i=507846

How many have read the above book "The Quantum Vacuum: An Introduction to Quantum Electrodynamics" by Peter Milonni. Is it so unique compared to others and worth the $123? (I already own dozens of QED books in ebook form). Note the book cover is entirely black without any title so it's like a collector's item. Or maybe the dusk jacket was simply removed?

Descriptions: "In modern physics, the classical vacuum of tranquil nothingness has been replaced by a quantum vacuum with fluctuations of measurable consequence. In The Quantum Vacuum, Peter Milonni describes the concept of the vacuum in quantum physics with an emphasis on quantum electrodynamics. He elucidates in depth and detail the role of the vacuum electromagnetic field in spontaneous emission, the Lamb shift, van der Waals, and Casimir forces, and a variety of other phenomena, some of which are of technological as well as purely scientific importance."

bhobba
#4
Feb22-12, 12:40 AM
Sci Advisor
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Infinite Energy beneath Quantum Vacuum?

Quote Quote by waterfall View Post
Science Advisor Born2bwire mentioned: "Since the vacuum state has infinite energy, it has infinite photons. Everytime we add energy into the electromagnetic fields, we just pull a photon out of the vacuum state." How many believe this and is there a refutation to this idea... because it seems that if it is true, then beneath the quantum vacuum lies a source of infinite energy.. literally".
That QFT predicts the vacuum has infinite energy is a sickness in the theory like the electron having infinite charge - the theory is wrong. And the answer is the same - we introduce a cutoff until the physics at very high energies is understood better - that's one thing they hope a TOE will solve.

Thanks
Bill
Chronos
#5
Feb22-12, 01:03 AM
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If you assume the empty vacuum of deep space is the ground state of the universe, then whatever energy it may contain is inaccesible because no lower energy state is available. We also know that naive calculations of vacuum energy yield a value that is 120 orders of magnitude too high [compared to observation].
waterfall
#6
Feb22-12, 01:21 AM
P: 381
Quote Quote by Chronos View Post
If you assume the empty vacuum of deep space is the ground state of the universe, then whatever energy it may contain is inaccesible because no lower energy state is available. We also know that naive calculations of vacuum energy yield a value that is 120 orders of magnitude too high [compared to observation].
What is the context of the meaning of "no lower energy state is available", please elaborate. Thanks.
Bill_K
#7
Feb22-12, 03:47 PM
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That QFT predicts the vacuum has infinite energy is a sickness in the theory like the electron having infinite charge - the theory is wrong. And the answer is the same
Yes, the answer is the same: that in fact QFT does not predict the vacuum has infinite energy. Any more than it predicts the electron has infinite charge.
We also know that naive calculations of vacuum energy yield a value that is 120 orders of magnitude too high
Naive is an understatement. I think people like to quote this value just to scare graduate students. The 'naive' value for the energy density comes from assuming an energy density of one Planck mass per cubic Planck length. This is not a serious prediction.


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