# Zero point energy

1. Aug 25, 2010

### Karoka

Can someone basicly explain what is zero point energy using simple english.

2. Aug 25, 2010

Its the energy of the lowest state. Its kind of the lowest energy you can have. Have you looked at the wikipedia on it?

3. Aug 25, 2010

### Karoka

Yep, the beginnig is easy, but the rest of it... not so much. For example what does it mean "lowest" energy, and does it have practical usage? I'm asking because there's almost no information in "my" language

Last edited: Aug 25, 2010
4. Aug 25, 2010

### alxm

In quantum mechanics, things cannot have a definite position and velocity. Which means they cannot be absolutely stationary (or they'd have a definite position and a definite velocity of zero). This means that things also have a certain amount of (kinetic) energy, even when they're in their lowest-energy state.

For instance, if you consider two balls connected by a spring in classical mechanics, their lowest energy state is simply to be standing still at some distance which minimizes the force from the spring. In that state they have zero kinetic energy (they're not moving) and zero potential energy (the spring is relaxed).

But consider an analogous quantum-mechanical system, for instance, two atoms connected by a chemical bond (which we can approximate as acting like a spring). Here, they will have a certain amount of kinetic energy, even when they're in the lowest possible state. This is then called the 'zero point vibrational energy' or sometimes just 'zero point energy' (which can be confusing, since ZPE is also used for other energies that are related in principle).

5. Aug 26, 2010

### Karoka

Thanks. You helped a lot. But one more question... You said two atoms... It can be any material, could it?

Last edited: Aug 26, 2010
6. Aug 26, 2010

### Curl

I believe you need to compare 2 atoms or else 1 atom cannot be said to have a velocity, since velocity is relative.

Don't listen to me though, I haven't studied this stuff yet.

7. Aug 26, 2010

### presbyope

Anything that can be modeled as a harmonic oscillator. The other common application is a ground state electron bound to a nucleus.

8. Oct 21, 2010

### jdnoslo

We call it zero-point energy because if you were to bring down the temperature of an area to absolute zero, this energy would still be there. It has been hypothesized that there is more than enough zero energy in the cusp of a coffee cup to evaporate all the oceans of the earth. This energy has also been called the energy of the vacuum. Check out the link to this documentary below.

http://www.tudou.com/programs/view/VxQsa3z1x_A/

9. Oct 21, 2010

### Buzzworks

Hmm, do you have something for vacuum?

Did Casimir Effect proved it or Casimir Effect is a different, unrelated phenomenon?

10. Oct 21, 2010

### alxm

The Casimir effect is from vacuum fluctuations (which are predicted by quantum electrodynamics). I would not say that the Casimir effect 'proved' it, but it's one of relatively few readily observable QED effects (another being the Lamb shift), and it's also essentially the same thing as the van der Waals forces (more specifically, London dispersion forces), that everyone learns about in high school. (London forces are a limiting case where the field and special-relativity effects can be ignored, hence London didn't need QED to explain them.)

For whatever reason, the Casimir effect has caught the attention of a lot of crackpots (and at the moment I see two crackpot posts in this thread already), 'speculative physicists', and science fiction writers, although I have no idea why, because I don't see why it's deserving of so much more attention than, for instance, the other related effects I mentioned. Particularly, I don't see where this idea comes from that the Casimir effect (or any other QED effect) could be used to 'extract energy from the vacuum' or some similar. In QED, energy is conserved at every vertex of a Feynman diagram. I see no reason for anyone to believe that the Casimir effect, or any other QED phenomenon allows you to somehow violate the first law of thermodynamics.

Likewise, nobody ever seems to have suggested that London forces would allow you to somehow get 'free energy' either. Probably because they could be explained without (explicitly) invoking the mysterious vacuum.

11. Oct 22, 2010

### Born2bwire

In addition, the Casimir force does not require a zero-point energy. You can always renormalize (which we have to do in some manner to calculate the force) the zero-point energy to zero and still retain the same physics. This is because the Casimir force is a result of the change in the vacuum energy when we displace an object. For further reading about whether or not the Casimir force is proof of the vacuum fluctuations there is an article by Jaffe on arxiv that proves enlightening (though I would expect most here have probably read since I mention it quite often).