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Nicholas_Bostaph
2005-Sep-30, 04:56 PM
I just had a (hopefully simple) physics question I was hoping someone could answer. I'm a layman, so go easy on me. ;)

As I understand it, the Casimir effect refers to the repulsion or attraction of two objects that are a very small distance away from one another. This occurs because not as many virtual particle pairs can pop into existence, which creates an energy differential between the space between the objects, and the space on the other side of the objects. Much like the way a pressure differential can lift an airplane or apply pressure to a container with low pressure, this energy differential pulls the objects together (or pushes them apart). Is this correct so far?

Assuming it is, doesn't that mean that work is being done on these objects by particle/anti-particle annihilation? If so, then what stops us from using or storing that energy? If nothing, doesn't that violate the conservation of energy principle? It would technically be (crudely) harvesting zero point energy. I'm assuming there is something that prevents this, or something that balances the equation. Can someone set me straight?

Thanks. :)

eburacum45
2005-Sep-30, 06:45 PM
One problem with the Casimir force is that it is very small, and another is that it is effectively negative; you have to expend energy to keep the plates apart.
Actually that does not mean you can't get work out of the system; long ago, atmospheric steam engines were designed to obtain work from the negative pressure of a relative vacuum.

But as I said before it is an incredibly small force, and it takes a lot of energy to make the equipment to detect it. So I would expect that if you totalled up the amount of energy it would take to make a hypothetical Casimir energy generator and the tiny amount of energy you obtained, the input would be larger than the tiny output.

Nicholas_Bostaph
2005-Sep-30, 07:59 PM
Thank you, I had a feeling it was almost negligible. The simple fact that the force exists still seems like a violation of the conservation of energy to me though; if the energy could be harnessed then it is basically 'free' energy. Could you possibly enlighten me on why this is not the case (since I'm assuming no such violation actually occurs)?

grant hutchison
2005-Sep-30, 10:07 PM
New Scientist magazine ran an article (http://www.newscientist.com/channel/fundamentals/mg18825191.800) this week, pointing out that there are theoretical approaches to the Casimir effect that do not invoke vacuum energy at all, deriving the experimentally measured force entirely from a consideration of van der Waals' forces.

Robert Forward certainly thought real work could be extracted from the Casimir effect: he described the concept of a "Casimir battery", consisting of many interleaved sheets of conductor at minute separations, from which energy would be extracted as it collapsed to form a single lump.

Grant Hutchison

electromagneticpulse
2005-Sep-30, 11:16 PM
Well if the Casimir effect is just van der Waal's force then doesn't that take away all our evidence for zero point energy?

One better way to extract Casimir energy might be instead of making flat sheets that tend to bend easily but make cylinders each one a few nanometers larger than the other and mount them one inside the other. To be honest I don't have a clue how you could collect the energy but maybe a strong enough Casimir force would cause the cylinders to heat up enough to run them through thermoelectric generators, or it could do the exact opposite and cause the cylinders to loose energy and then we could make cool heat syncs.

These are just guesses but then again what do we know, I mean we can’t even agree if we landed on the moon or not and for the past 40 years we’ve been sat around worrying about oil running out when we could have used the Apollo technology to start setting up solar farms in the Earth-Luna Lagrange 4/5 points. Oh how smart are we? :rolleyes:

grant hutchison
2005-Sep-30, 11:36 PM
Well if the Casimir effect is just van der Waal's force then doesn't that take away all our evidence for zero point energy?Sure does. It appears that this is the object of the exercise, for at least some of the alternative theories. It's something of an embarrassment that the theoretical predictions of zero-point energy are so many orders of magnitude greater than the observational constraints - some people would apparently like to get rid of it entirely.

Grant Hutchison

jkmccrann
2005-Dec-14, 12:26 PM
Well if the Casimir effect is just van der Waal's force then doesn't that take away all our evidence for zero point energy?

One better way to extract Casimir energy might be instead of making flat sheets that tend to bend easily but make cylinders each one a few nanometers larger than the other and mount them one inside the other. To be honest I don't have a clue how you could collect the energy but maybe a strong enough Casimir force would cause the cylinders to heat up enough to run them through thermoelectric generators, or it could do the exact opposite and cause the cylinders to loose energy and then we could make cool heat syncs.

These are just guesses but then again what do we know, I mean we can’t even agree if we landed on the moon or not and for the past 40 years we’ve been sat around worrying about oil running out when we could have used the Apollo technology to start setting up solar farms in the Earth-Luna Lagrange 4/5 points. Oh how smart are we? :rolleyes:


And we're still worrying about oil running out!, somewhat incongruosly at the same time as we're worried about the burning of oil causing catastrophic global warming. As for the putative Lagrange Solar Farms you mention electro, I think to be honest we'll sadly be waiting at least another 40 years on that front.

Anyway, here's what Wiki has to say about the Casimir Effect.

Casimir Effect (http://en.wikipedia.org/wiki/Casimir_effect)

Weird Dave
2005-Dec-15, 09:53 PM
We can't get energy from Casimir for the same reason that you can't get energy out of two magnets. You have to put exactly the same energy into separating them as you get out when they come together. Perhaps a Casimir battery would work, but only as a way to store energy, not produce it from scratch.

Ken G
2005-Dec-18, 05:22 AM
And the same may be said about "hydrogen energy" as well, a point that a lot of people still don't seem to get. You can release energy by dropping an anvil too-- why doesn't "gravity energy" produce as much of a buzz as "zero point energy"? To harness zero point energy, you'd actually have to come up with a way to end up with less space. Then again, a simple look at my garage would show that perhaps loss of space is possible after all...

grant hutchison
2005-Dec-18, 02:14 PM
Hang on, though. My entire house runs off dropping anvils. :)

Scotland has a lot of hydroelectric power, which is simply the extraction of potential energy from water. The Universe (in the form of sunlight and evaporation) does the work, and we extract the energy.
So I guess I've imagined that a "Casimir battery" would release "Universe energy" on first usage, when its plates fell towards each other for the first time, but thereafter would be just a lump of stuff that would require more energy to recharge than it would subsequently release.

Grant Hutchison

Ken G
2005-Dec-18, 02:32 PM
Good point, what I really mean is that any energy that can be used to actually run your society has to result in (1) a change in your environment, and (2) the initial "excited" state has to be provided by the environment too. Those are the two key elements. Generally the second is provided by radioactive decay or nuclear fusion, be it geothermal, nuclear, or solar energy. In the case of hydroelectric power, it is energy from the Sun that you are using to power the water cycle. But if you want to use hydrogen as a power source, you have to find hydrogen energy appearing naturally. Zero-point energy is fine in that regard, plenty of it occurs naturally, but its problem is that other key element-- you have to be able to change the environment to extract it. You either have to end up with less space, which would take advantage of a resource there is plenty of (except in my garage), or you would have to utilize some specially prepared space that is already handed to us, such as the space inside two Casimir plates. Since our environment doesn't hand us much of that space to work with (so very little of Grant's "Universe energy"), it would be a fools errand to try to use that principle as an energy source (a battery is another thing altogether), as it is with hydrogen energy also.

grant hutchison
2005-Dec-18, 03:04 PM
Unless it is possible for the same amount of space to have less zero point energy. Some phase change we might manipulate, for instance, with the reward for a small amount of energy input being a large amount of energy released.
Messing with the fundamental structure of the Universe! All in favour?
Hmmm.

Another problem for my single-use Casimir battery might be the energy overheads of building one. As an analogy: you could extract energy from naturally occurring magnets by bringing them together for the first time: but the energy required to find and transport them outweighs any possible payoff.

Grant Hutchison

Ken G
2005-Dec-18, 04:10 PM
I agree on both counts. And like I said, nobody knows how to end up with less space by transforming it into something else, perhaps via a phase transition. It would certainly seem that realistically, the only energy sources that we can use to power our society are going to be radioactive decay of existing isotopes, or extracting, directly or indirectly, energy brought to us by the Sun. This suggests there are no energy sources that we have not already investigated and used, with nuclear fusion being the one that is still under development. There's not going to be a "magic bullet" coming from future technology, the information for the near future is already on the table.

eburacum45
2005-Dec-18, 10:09 PM
Don't give up in ultimate energy sources yet; I think the ultimate one would be Hawking Radiation (assuming it is real; what experimental evidence do we have for it?)

The theory is this; a small black hole about a hundred million tonnes gives off a lot of Hawking radiation, and is very small; if we could manufacture one* it would convert its own mass into energy over time. If it ever shows signs of running out of mass we could chuck some more in (this might be difficult, as the pressure of the hawking radiation would be very strong).

*this turns out to be the difficult bit; but probably easier than shrinking space.
Perhaps a small black hole could be manufactured by accelerating multiple masses together in the same way that fissile masses are accelerated together in an a-bomb; but much faster.

Ken G
2005-Dec-18, 10:22 PM
I'll admit your idea is the best science-fiction energy I've heard of, but I'm not clear on how one makes such a black hole. Is a beanstalk involved? And remember, we already know how to get about 1% of mc^2 using fusion, but it's not stable enough to control and maintain. Would making black holes be more so? It would sure be nice to get the 100%, I'll grant you, and just use any old junk. I can see it, "honey, the garbage is full again, would you please empty it into the black hole?"

Halcyon Dayz
2005-Dec-19, 01:37 AM
I really hope you would put your power/waste disposal plant
in a stable orbit, not to close to Earth.

Enki
2006-Sep-05, 10:19 PM
Hi!

Listen my theory! I don't quite understand the thing, but what came to my mind is using many of these plates and extract the energy that forces them together (so using pairs of them?). :razz: I mean can somehow the forcing energy be extracted from the atomic structure, that is the Casimir effect bends the plate, and then this bend creates energy within the plate (that why it bends) I mean you have to put energy into the plates to bend them, or no? If this bending energy can be extracted from the plates, then you have the Casimir battery. The plates have to resist the bend (to not touch together) but this seems reasonably that the energy that you extract bends the plates back to their oroginial position. Just curious...

Enki