July 18, 2006 1:02 PM   Subscribe

Does absolute zero actually exist in the universe or is it just a theoretical concept?

Settle an argument.
posted by furiousxgeorge to Science & Nature (23 answers total) 3 users marked this as a favorite
For a second I wasn't sure if you meant the mathematical expression of zero or the temperature. I think you mean temperature. The wikipedia article on the subject says about as much on the subject as any. The gist is that it's a theoretical concept, here's the relevant bit:

"Absolute zero has never been reached, and it appears it never will be, although some have come remarkably close. Absolute zero may be asymptotically approached like the speed of light, but never attained."
posted by empyrean at 1:08 PM on July 18, 2006

it's my understanding that if absolute zero was ever reached, no measuring deviices could be used to detect it. it'd be kind of like a black hole of temprature.
posted by lester at 1:11 PM on July 18, 2006

The natural microwave background radiation makes the cold of space actually 2.725 kelvin, so you'd be hard-pressed to find something that's naturally at absolute zero. As for lab work, well, empyrean has that covered.
posted by ewagoner at 1:13 PM on July 18, 2006

Since the question has been answered, I'll give a bit more of a real-world frame of reference:

Absolute zero =0K, ~ -273°C.

- Almost every scientific lab can get to 77K. (liquid nitrogen)
- Many (most in a lot of fields) can get to 4K (liquid helium)
- A handful can get down to the mK range (0.001K)
- I think a few can get into the microKelvin range (0.000001K)

Single molecules can be "frozen" with lasers into similarly low temperature ranges, but you're getting into weird areas of low temperature physics.
posted by JMOZ at 1:14 PM on July 18, 2006

No. It is impossible to achieve absolute zero, either in the lab or in nature. This is a direct consequence of the third law of thermodynamics, but if you want a convincing proof, you'll have to wait until I can get to my bookshelf at home. (Basically, I think you can show that as the temperature of a system approaches absolute zero, the amount of work required to cool the system further approaches infinity.)
posted by mr_roboto at 1:20 PM on July 18, 2006

Actually, the fact that you cannot reach absolute zero is The Third Law of Thermodynamics. So, somebody clearly won that bet.
posted by vacapinta at 1:22 PM on July 18, 2006

According to the above referenced wiki article, you can get very close, but not all the way.

You can also get a system "below absolute zero," but this won't be as cold as or colder than absolute zero.
posted by justkevin at 1:23 PM on July 18, 2006

Short answer: it's an unreachable ideal.

Long answer: there are shades to the answer. It's impossible to cool a reasonable-sized collection of matter down to absolute zero; JMOZ's numbers are slightly off (the record is in the nanokelvins, while microkelvins aren't all that rare) but the sentiment is right.

When you get to the scale of individual atoms, though, the answer begins to blur a bit (as do the other laws of thermodynamics, which are statistical in nature). Temperature isn't terribly well defined for individual atoms, but if you define it as a function of the kinetic energy of an atom, you can imagine that there could be an atom in its ground state at rest with respect to its observer -- if so, it would be at absolute zero in that observer's frame. But there's an additional complication: because of the energy of the vacuum, an atom perfectly at rest will only be at rest for an infinitesimal length of time. So, the long answer is that in some sense, atoms can achieve absolute zero in a given frame, but for no appreciable amount of time.
posted by cgs06 at 1:31 PM on July 18, 2006

Response by poster: Bonus question: If by some act of god, absolute zero was attained, would it cause a chain reaction freezing of everything in the Universe?
posted by furiousxgeorge at 1:47 PM on July 18, 2006

posted by dr. moot at 1:54 PM on July 18, 2006

No. As soon as an object at absolute zero was brought into thermal contact with the rest of the universe, its temperature would increase.
posted by mr_roboto at 1:55 PM on July 18, 2006

No. Assuming the first and second laws of thermodynamics are still true, energy would flow from the rest of the universe to the zero-temperature object until it was no longer colder than its surroundings.
posted by mbrubeck at 1:56 PM on July 18, 2006

Temperatures have gotten into the nanokelvin range, but nobody has successfully created anything at absolute zero.

But really, when you're talking nanokelvins, don't you think that's almost close enough?
posted by chimaera at 2:39 PM on July 18, 2006

Greg Bear's "Heads" is a novel about the unexpected quantum consequences of actually achieving absolute zero.
posted by zanni at 3:12 PM on July 18, 2006

That's a delightfully ironic link. An Absolute Zero URI if you will.
posted by Skorgu at 3:15 PM on July 18, 2006

Even when you're talking about individual atoms, when the temperature gets really, really close to absolute zero then the Heisenberg principle kicks in, and other physical properties begin to change.

If there are multiple atoms then the result is a Bose-Einstein condensate.

The Heisenberg Principle says that the product of the error in knowledge of the position of an object and the error in knowledge of its momentum will always exceed Planck's Constant.

At absolute zero, the momentum is exactly zero, and we know that it is zero with no error in our measurement. That means the error in measurement of the position must infinite, and the object -- in one interpretation -- fills the entire universe (though not to the exclusion of other mass).
posted by Steven C. Den Beste at 3:52 PM on July 18, 2006

Well, SCDB, we can't say that the object fills the universe unless we're using an incredibly dishonest interpretation. The error with which we know its position becomes infinite, so we don't know its position at all; it can be anywhere in the universe. In other words, the wave function is nonzero (but infinitesmal) everywhere throughout the universe.
posted by JMOZ at 4:09 PM on July 18, 2006

That's a different way of interpreting it. But it's not correct to say that the way I mentioned is "dishonest".

It's the wave-particle duality. When we talk about electrons, we can think of them as being particles, and ever experiment that's ever been done suggests that they are mathematical points with no radius. But because of the Heisenberg principle, they're always moving around the atom, and the wave function of an electron at any given time describes the area where it can be found, though of course not telling us exactly where within that it is at any given instant.

So in the "particle" way of looking at things, the electron is bouncing around inside that region somewhere. But if we look at it as a wave, then it makes some sense to think of the region as being the electron, and to think of the electron as being the region described by the wave function -- and that's how chemists tend to conceptualize it.

My "dishonest" (only it isn't!) interpretation is to think of the atom as a wave, not as a particle, and to point out that the wave for an atom at absolute zero would fill the entire universe.
posted by Steven C. Den Beste at 4:27 PM on July 18, 2006

What JMOZ said (what interpretation?)

Also, another Heisenberg Uncertainty Relation is applicable here as well (there are a whole class of them relating conjugate variables) that of Energy-Time which all but guarantees that approaching Zero in our Universe runs you up against all this energy of the vacuum itself.
posted by vacapinta at 4:28 PM on July 18, 2006

By the way, the universe might not be big enough to hold it, because current theory is that the universe is not infinitely large.
posted by Steven C. Den Beste at 4:29 PM on July 18, 2006

My "dishonest" (only it isn't!) interpretation is to think of the atom as a wave, not as a particle, and to point out that the wave for an atom at absolute zero would fill the entire universe

Welll, but...this is true for any electron in free space. Although the wavefunction must be normalizable that doesnt mean it cant extend out to infinity. In fact, the spread of the wavefunction is the basis for quantum tunneling. But nobody says the particle is everywhere just because the wavefunction is non-zero everywhere. I think thats what JMOZ meant.
posted by vacapinta at 4:35 PM on July 18, 2006

This is a sweet post.
posted by rleamon at 7:16 PM on July 19, 2006

I see that this is still open, and though we're drifting a bit, I wanted to comment on quantum tunneling.

The old explanation for that was that the wave function of the electron was discontinuous, and that there was a chance that when it collapsed it would be on the other side of the barrier, having gone from one to the other without passing through.

There's an alternate explanation which I believe is now in favor. It turns out that conservation of energy at the quantum level is not absolute. It's possible for the energy of a particle to vary somewhat, within certain limits. In particular, it can borrow energy from nowhere, as long as the product of the energy and the time that it exists is less than Planck's constant. This turns out to be another manifestation of the Heisenberg Principle.

So to "tunnel" from one place to the other, it turns out that an electron borrows enough extra energy, from nowhere, to be able to surmount the barrier and fall down the other side. And the extent to which tunneling takes place statistically is a function of how high the barrier is (thus how much energy is needed to go over the top and how wide it is. If it's high enough or wide enough, no tunneling takes place at all.

[Note: "high" refers to electrical potential, not to altitude.] In this interpretation, the electron does travel the entire distance from point A to point B.

This idea of temporarily borrowing energy is also the explanation for how electric fields form. A charged particle is constantly borrowing energy from no where to create "virtual photons" which travel away in all directions at the speed of light. The photons carry different amounts of energy -- and the ones with more energy vanish sooner. The ones with less energy last longer. And that is why an electric field decreases with range!

...or so it was explained to me. Myself, I think I'll go with what Feinman said: "If you think you understand quantum mechanics, you don't understand quantum mechanics."
posted by Steven C. Den Beste at 8:25 PM on July 20, 2006

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