The Energy of Empty Space != Zero

Raindeer writes "Lawrence Krauss (well-known physicist and author of The Science of Star Trek) invited a group of 21 cosmologists, experimentalists, theorists, and particle physicists and cosmologists. Stephen Hawking came; three Nobel laureates, Gerard 'tHooft, David Gross, Frank Wilczek etc. He wrote about the conclusions of this session in Edge; in short: 'there appears to be energy of empty space that isn't zero! This flies in the face of all conventional wisdom in theoretical particle physics. It is the most profound shift in thinking, perhaps the most profound puzzle, in the latter half of the 20th century. And it may be the first half of the 21st century, or maybe go all the way to the 22nd century. Because, unfortunately, I happen to think we won't be able to rely on experiment to resolve this problem.'"

Re:Zero-point energy?

[pHatidic]

Zero-point energy is predicted by both the leading quantum physics and relativity models. This is like 70 years old.

Wrong Book Title

[Skidge]

Dr. Krauss's book is actually called The Physics of Star Trek [amazon.com] and has a forward written by Stephen Hawking.

Re:Zero-point energy?

[tb()ne]

It sounds like they are talking about zero-point energy, the energy in the quantum vacuum. This has been known about by theoretical physicists for some time, and has even made it into popular science fiction. There is some debate, I believe, as to whether it is possible to extract this energy in a usable form, but its existence is hardly new.

Debate? What debate? Syndrome clearly demonstrated the practical application of zero-point energy while thrashing Mr. Incredible.

Vacuum energy

[Anonymous Coward]

As others have noted, the idea of the energy of empty space being nonzero isn't an new idea. The quantum zero-point vacuum energy is nonzero. However, our predictions of its value are ridiculously large, which led some to speculate that either we should redefine the zero point of energy to equal the zero-point energy so that the energy of space exactly equals zero. It's also possible that our ways of doing the accounting are naive (e.g., ignoring quantum gravity), or that some kind of cancellation is going on (e.g. bosons cancelling out fermions in supersymmetry).

This is related to what may be the biggest open question in cosmology, the cosmological constant problem. The energy of space is intimately related to the "cosmological constant". We now know from the accelerating expansion of the universe that there appears to be a nonzero cosmological constant, implying a nonzero vacuum energy. Its experimentally measured value is many orders of magnitude smaller than a naive calculation of zero-point energy based on the Planck scale, however. Another possibility is that the cosmological constant is actually zero, and the accelerating expansion is actually due to the energy/pressure content of some kind of dynamical "dark energy" field (as opposed to the static cosmological-constant form of dark energy).

More on vacuum energy [ucr.edu] and the cosmological constant [ucr.edu], plus a tutorial [ucla.edu].

P.S. Contrary to some science fiction applications (cough-StargateAtlantis-cough) and crank physics (cough-Puthoff-cough), you can't extract free energy as work from the zero-point energy. The zero-point energy is by definition the lowest energy state that a system can have; to extract usable energy, you'd have to decrease the energy of the rest of the system below that minimum value, which is by definition impossible.

Re:New news?

[nowaycomputer]

Is this really news? I took an undergraduate quantum optics class last year that had a large part about the infinite zero point energy which exists in 'empty' space. Casimir force anyone?

Re:New news?

[Danny Rathjens]

The Casimir Effect [wikipedia.org] has been observed/measured.

Re:Zero-point energy?

[internic]

Here is a this very nice discussion of the zero-point energy [ucr.edu] by mathematical physicist John Baez. You're right, the idea is hardly new, but some of the experimental evidence about the cosmological constant is relatively new.

I think it's fair to say that almost no physicists believe you can extract useful work from the vacuum energy. Most of the people claiming you can are con men trying to swindle people into buying "free energy devices" that supposedly tap the zero-point energy (it's the modern day incarnation of perpetual motion machines). While you may be able to setup a situation where the vacuum does work (i.e. with the Casamir force), I think it is simply less than or equal to the energy it took to put the apparatus together. Essentially, it's equivalent to sitting in a room with uniform atmospheric pressure and trying to use that atmospheric pressure to do work. You can certainly use a vessle with low or high pressure to do work, but you're never going to get out more energy than it took to create that high (or low) pressure. While one can think about this in terms of thermodynamics, that's really litte more than making concrete the common-sense proposition that you can't get something for nothing. Thus far, nature has not given us any good reason to abandon that idea.

Sometimes people do talk about things like pair creation from the vacuum and the energy-time uncertainty relation, but they are speaking about virtual particles rather than actual particles. The bottom line here is that when you make a measurement, what you will find is actual particles and energy will be conserved, even according to quantum field theory.

Re:Zero-point energy?

[aquabat]

You would have to use more energy to get the stored energy out of your theoretical zed-p-m. In fact, more than is stored in it. You need a differential across the boundary of your trap to cause energy to migrate into it. As energy migrates, the differential decreases, and the migration slows, until the net migration stops.

Consider an energy trap which did not follow this rule, but rather continued to collect energy forever, such that the total energy does not converge to any finite limit (i.e. you can get any amount of energy you want if you leave the thing out long enough). If you left it out forever, then it would suck all the energy out of the universe, which is equivalent to saying that the universe would be in your box.

Re:New news?

[Anonymous Coward]

I Googled "argument from conditional probability" and found nothing that has anything to do with picking a Universe so that we can observe it.
You are thinking of the anthropic prinicple http://en.wikipedia.org/wiki/Anthropic_principle [wikipedia.org]

Re:Zero-point energy?

[Manchot]

What you've just described is commonly known as Maxwell's demon, [wikipedia.org] and is thought by most physicists to violate the Second Law of Thermodynamics.

Re:New news?

[naasking]

I actually thought of this exact idea myself! :-)

Casimir forces are extremely sensitive to geometries however, and the solutions are very hard to derive. A sphere was recently found to have a repulsive Casimir force IIRC[2] (ie. the force is expansive rather than contracting as with parallel plates). So while this idea would be cool, I suspect that any non-parallel plates would yield a null result, or perhaps so small as to be useless, even if you had nano or pico-scale manufacturing.

[1] http://en.wikipedia.org/wiki/Casimir_effect [wikipedia.org]
[2] http://arxiv.org/abs/quant-ph/0106045 [arxiv.org]

Re:Confused...

[Anonymous Coward]

If you include observations using a magical device based on principles of "physics that we don't understand", then you may be correct.

However, using the physics that we do understand, even with an infinitely precise measuring device you would still not be able to determine position and velocity exactly because, in the quantum mechanical world, things do not exist in a single place with a single velocity but are spread out into a probability wave. This does not appear to be a limitation in our technology but. It is feature of the natural world.

Re:Zero-point energy?

[colmore]

entropy can be viewed as the inverse of the usefulness of energy.

a differential (your bug trap) requires energy to work, in that case the bugs provide a lot of energy flying into the trap under their own power and operating nervous systems that intelligently differentiate inside-the-trap and outside-the-trap. a bug trap can be passive because the bugs are active.

it might be the case that zero-point energy, like ambient heat, is incapable of being translated into other forms of energy in nature, but then somehow (unlike ambient heat) we would be able to engineer a useful means of extracting work, but it doesn't seem likely.

entropy is the law that over time, energy gets less useful.

Re:Zero-point energy?

[domanova]

Nearest I've seen to Maxwell's demon is stochastic cooling, as used for antiproton sources at CERN at FERMILAB. It takes a lot of input energy to enthuse the demons, so it ain't a break of the rules