[Andrew Askew]

Andrew Askew  asked the Naked Scientists:
   Hi Chris & Team,
 
Please can you explain zero point energy and its potential uses?
 
Regards,
 
Andrew Askew
What do you think?

[Dr.IC]

In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may have and is the energy of the ground state.

A related term is zero-point field, which is the lowest energy state of a field.

Zero-point energy is sometimes used as a synonym for the vacuum energy, an amount of energy associated with the vacuum of empty space.

[graham.d]

It is postulated (and widely accepted) that even a total vacuum can have a finite energy density: there is the spontaneous creation and destruction of particle - antiparticle pairs. This zero-point energy concept is not without its problems because it turns out that the total energy in the universe would be huge as a result, and this is even after the equations have been "adjusted" to remove the infinity value. The theory is thought to have been possibly verified by the existence of the Casimir effect but actually there are also other explanations for this effect. (Simply put, this is were two precisely machined plates experience an attractive force when brought very close together - there being insufficient space to permit the creation of particle - antiparticle pairs and thereby resulting in there being more pressure pushing them together than holding them apart).

Although featured in science fiction as a potential source of energy, it is not known how that such energy could ever be made use of. To make use of an energy source there needs to be a lower energy state than the source. By definition, there is not thought to be one in this case.

[Mr. Scientist]

It also means that the ZPF is itself a type of quantum aether - made from vitrual particle pairs in every square box of spacetime.

[DoctorBeaver]

Although featured in science fiction as a potential source of energy, it is not known how that such energy could ever be made use of. To make use of an energy source there needs to be a lower energy state than the source. By definition, there is not thought to be one in this case.

I assume that is because no matter how much of a vacuum you have there will always be the same amount of particle pair creation thereby evening out the energy states.

[graham.d]

Actually DB, if the Casimir effect is truly down to ZP energy, then, in theory, you could get some energy out; bringing two plates close together will result in an increased attractive force which then pulls them together and you could get some tiny amount of energy out from this. It's a bit useless practically though as the plates have to be very close as the force falls off as the 4th power of the separation distance. And, of course, to re-use the apparatus you have to get the plates apart again.

It's all rather speculative at the moment with quite a lot of competing theories. I have just found an excellent and concise review of the state of knowledge about ZP energy:

http://www.calphysics.org/zpe.html

Definitely worth a read!!

[Mr. Scientist]

Although featured in science fiction as a potential source of energy, it is not known how that such energy could ever be made use of. To make use of an energy source there needs to be a lower energy state than the source. By definition, there is not thought to be one in this case.

I assume that is because no matter how much of a vacuum you have there will always be the same amount of particle pair creation thereby evening out the energy states.

By the way -  Particle creation goes by CP-Invariance which can be broken, meaning that particles in the vacuum do not always have an antiparticle, which is also an attempt to answer why there are more ordinary particles to antimatter.

[graham.d]

Hmm, to be fair the whole subject is a matter of some debate. In any case most of the theories concerning zero point fields only attempt electromagnetic fields and it is generally accepted that the universe is charge balanced even if there is a distinct shortage of positrons :-) It is certainly a "field" for speculation.

[Mr. Scientist]

As far as i am concerned, there no is debate to its existence whatsoever. There is no concurrent and plausible theory other than to say the vacuum has an energy in the presence of the confirmed pheomenon of the casimir effect, a repulsive and attractive force of virtual particles within the vacuum. Every experiment we have conducted has varified the ZPF's existence. There is really no credible scientists about who refute its existence.

[graham.d]

I did not say I was debating its existence but merely that the subject is of much debate. There is a small matter of the theoretical energy of vacuum field being 120 orders of magnitude greater than could be sustained without the total collapse of the universe for example. Also the Casimir effect has not been shown conclusively to be an effect of ZPF at all and could have one of a number of other plausible explanations. In fact most credible scientist interested in the subject are debating it quite a lot. It is also true that this is a subject that attracts a large number of cranks and people who have formed companies on the basis of pseudo-science and the prospect of free energy making fortunes for investors.

[Mr. Scientist]

Again, i can't say it could be anything else.

Quantum electrodynamics prooved its existence even before it was found. That is a good sign everything about its predictions are understood.

[graham.d]

Are you speaking of the Casimir effect or Zero Point Energy?

I am trying to point out that zero point energy is far from being understood (not that it doesn't exist) because, although predicted and consistant with the measured Casimir effect, its magnitude is not at all consistant with the existence of the universe as we see it - at least not without some highly dubious arm waving arguments. And a quote from one of the more devout, though respectable workers in this field (B Haisch) says of the Casimir Effect "It is not necessarily true, however. It is perfectly possible to explain the Casimir effect by taking into account the quantum-induced motions of atoms in each plate and examining the retarded potential interactions of atoms in one plate with those in the other".

[Mr. Scientist]

I disagree Haisch. It's a controlled experiment with expected vacuum outcomes, not quantum interaction of potential states of the plates. If that where true, would it not suffice to say this interaction would have not been accounted for by the greater physicists of our time?

[DoctorBeaver]

It's a bit useless practically though as the plates have to be very close as the force falls off as the 4th power of the separation distance.

Is it known why it falls off so sharply?

[LeeE]

It's a bit useless practically though as the plates have to be very close as the force falls off as the 4th power of the separation distance.

Is it known why it falls off so sharply?

Yes, that's a good question.  Inverse square rates, and even cube rates make a lot of sense in 4-dimensional space-time but that 4th root has some interesting implications.

[Mr. Scientist]

pg47

http://home.fazekas.hu/fizika/fazekasban/Regos2.pdf