Is absolute zero possible?

[JennieB]

During a recent conversation about absolute zero with a friend of mine, he claimed that absolute zero had never actually been achieved by scientists. And what's more, if anyone ever did succeed it would spread outward to affect everything (the walls of the space it's contained in, the air outside the container, the scientists etc.) stopping everything on the planet and ultimately the universe. Please reassure me I can tell him he's talking nonsense!

[Mangetout]

During a recent conversation about absolute zero with a friend of mine, he claimed that absolute zero had never actually been achieved by scientists. And what's more, if anyone ever did succeed it would spread outward to affect everything (the walls of the space it's contained in, the air outside the container, the scientists etc.) stopping everything on the planet and ultimately the universe. Please reassure me I can tell him he's talking nonsense!He's talking half-nonsense; It's really difficult to make things cold, because cold isn't a thing, it's the absence of a thing - heat. You make things cold by letting the heat flow into something colder.
Trouble is that by definition, there's nothing colder than absolute zero, so it's hard to find somewhere for that last little bit of heat to escape to.
There are tricks though, involving collapsing magnetic fields and lasers, that can also be used to cool things down, I think.

As regards the second bit about it spreading everywhere; there's simply no reason to suspect that would happen and lots of reasons to suspect it wouldn't. He's talking about a Sci-Fi concept called Ice-9.

[Mangetout]

http://en.wikipedia.org/wiki/Ice-9

[ftg]

In the a little bit of knowledge is a dangerous thing department...

The product of an particle's momentum and uncertainty of position is a (very, very tiny) constant.

If a particle were to stop moving at all (the classical def. of absolute zero) its uncertainty of position would go towards infinity. Very loosely, it would be "everywhere".

However, that wouldn't affect the rest of the Universe in any way.

[CalMeacham]

The problem with ultralow temperatures is that it's kinda like Zeno's paradox, in that you can go in steps that take you halfway. But in this case it takes just as much effort for each step, so that as you get closer to absolute zero you put a huge amount of effort into steps that get you closer by smaller and smaller amounts. To get as close as you can these days requires a repertoire of straightforward methods and nifty tricks.

But you can never get all the way to absolute zero, if you define that as the place where all motion completely stops, because that would violate the Heisenberg Uncertainty Theorem -- you'd have a particle that was absolutely motionless, which would imply that you should have no idea where it was. But you'd know it was in your apparatus. Even if you didn't have its position pinned down any better than that, it would be in violation of the HUT. So you're always going to have some residual uncertainty. (Besides, even the lowest state in a QM harmonic oscillator has a wavefunction that isn't a delta function -- what are you going to do, violate QM?)


The Ice-Nine thing isn't a low temperature thing, anyway. The point was supposed to be that it was solid at room temperature and pressure.

[Sevastopol]

Just how strict is Heisenberg' ?

[randomlyblanks]

A slight nitpick: I agree that absolute zero can not be achieved, but it is not because of the Heisenberg Uncertainty principle. A more accurate definition of absolute zero is not when all molecular motion stops, but when all of the atoms of the system are in the ground state. The ground state is the lowest permitted energy level, but due to quantum effects, there will still be some vibrational motion. If all of the atoms are in the ground state then no energy can be extracted from the system, for it is at its lowest allowed by QM; therefore, that would be absolute zero.

However, thermodynamics does not permit absolute zero to occur. The third law of thermodynamics states that absolute zero cannot be attainted in a finite number of steps.

Thus, at absolute zero some atomic motion would exist due to quantum effects, but no more energy could be taken from the system. However, getting to such a point would require an infinite number of steps, which is impossible.

[CalMeacham]

Just how strict is Heisenberg' ?


The product of thwe uncertainty in position with the uncertainty in momentum must be less than or equal to h/4(pi)


h is the Planck constant, 6.626 x 10-34 Joule-seconds , which is pretty damned small, but the point is, it's not zero.



(h/4(pi) is usually called "h-bar" and designated by the h with a diagonal slash through it. The same uncertainty relation holds for other incomensurate QM quantities like Energy and Time, Angular mementum and angular position, and other pairs that have dimensions of action. If the quantities aren't commutative, they have an uncertainty relationship. Just another weird feature of the world of the quantum.

[Bryan Ekers]

Just how strict is Heisenberg' ?

I'm uncertain.

[Mangetout]

I thought that atoms had been observed to 'smear' into little puddles of Bose-Einstein condensate (or something) at near-absolute zero - if this is the case, wouldn't it neatly deal with the Heisenberg issue?

[Scott Plaid]

No, [dwl]lekatt[/del] Kozmik, that doesn't make any sense at all.

[Scott Plaid]

No, lekatt Kozmik, that doesn't make any sense at all. :smack:

[Chronos]

(h/4(pi) is usually called "h-bar" and designated by the h with a diagonal slash through it.Nitpick: h = h/2pi, not h/4pi. And in fact, one almost never actually uses h (rather than h) in physics, since the latter form shows up a lot more often and more conveniently.

[CalMeacham]

Nitpick: h = h/2pi, not h/4pi


Dammit! That was my recollection, but it's been years since QM, so I checked, and the book I looked in had 4(pi).


So you won't use it, it's the you'd-think-it-was-reliable Penguin Dictionary of Physics.

[The Chao Goes Mu]

Here is a thread I started a while back dealing with ABSOLUTE ZERO (http://boards.straightdope.com/sdmb/showthread.php?t=210463)

This may help.

[HeyHomie]

What's the lowest temperature that's been achieved in a laboratory?

[Rauko]

What's the lowest temperature that's been achieved in a laboratory?

100 pK (2.5 × 10^-10 K) - Lowest temperature ever produced, during an experiment on nuclear magnetic ordering in the Helsinki University of Technology's Low Temperature Lab.

That would be only a few billionths of a degree above Absolute Zero.

http://en.wikipedia.org/wiki/1_E-12_K

[Lumpy]

Can't quantum states briefly have a negative energy value? If so, could you go from very little energy to lowest ground state in one step?

[Stranger On A Train]

Can't quantum states briefly have a negative energy value? If so, could you go from very little energy to lowest ground state in one step?Not quite certain what you mean by "quantum states briefly have a negative energy value"; regions of space can have a so-called negative energy density (see Casimir Effect (http://physicsweb.org/articles/world/15/9/6)), and a particle could have a negative energy relative to a defined reference state, but by definition the ground state for fundamental particles is 0 Kelvin. CalMeacham has it right that there is a fundamental limit for a particle with a given intrinsic mass-energy as to exactly how "cold" (i.e. motionless) it can be, per the Indeterminacy (or Uncertainty) Principle. (Heisengberg, by the way, objected to the christening of that principle after him.) In fact, you can't even reference the particle to the limit described by the IP; your actual measurement will be somewhat greater because of your own interference in measuring it. You can measure the effect it has on a third body to limit your direct interference, but then you have the greater uncertainty of two particles. You can measure a whole system and cancel out various uncertainties to come to a close average, but in the end it's always less accurate than the intrinsic uncertainty.

Although this is a result of quantum mechanics, you have a somewhat similar argument from classical thermodynamics, as elucidated by randomlyblanks. To bring the system to the absolute ground state you'd have to make ΔS=0 (zero change in entropy). But the entropy of a system is always changing while you're moving energy around, and so like a wily fox you can never quite bring it to ground.

This guy (http://www.blacklightpower.com/) lays claim to the idea that QM is all bunk and that you can reduce electrons within an atom to "fractional energy states" (and presumably bring an electron to a ground-reference zero state) but since he's batshit crazy and hasn't been able to produce any of the high temperature superconductors, high density batteries, inert hydrogen gas, or miracle cures for cancer, we can probably safely dismiss his claims.

And Sevastopol, I heard Heisenberg was a pretty easy going guy, as long as you stay within his bounds. Outside of there, he's likely to be pretty flighty.

Stranger

[randomlyblanks]

I thought that atoms had been observed to 'smear' into little puddles of Bose-Einstein condensate (or something) at near-absolute zero - if this is the case, wouldn't it neatly deal with the Heisenberg issue?

Um kind of. If the atom is bosonic (an integer spin overall), then at low temperatures the atoms will collapse into the ground state. Ground state bosons will bunch into the exact same place at the same time. What you end up with is a "jumbo atom" in which many atoms appear to be sitting all in the same place at the same time. Still even in this state, a significant portion of the sample is not in the ground state and, therefore, not at absolute zero. Looking at this image (http://en.wikipedia.org/wiki/Image:Bose_Einstein_condensate.png), one notices that the peak is not a spike, but rather a bit bell shaped. If all the atoms are in the same place at the same time in the condensate, it should appear to be a spike. The spread in the peak is from the Heisenberg Uncertainty Principle; since the momentum is precisely known in the ground state, the position is "smeared" a bit. Nothing gets around uncertainty--its not an error in the equipment or method, it is a fundamental principle that can be mathematically derived fairly easily.

[Phatso]

Is there a symbol for absolute zero the way pi has one?

[Crafter_Man]

Is there a symbol for absolute zero?Yes. It is

|0|

[Malacandra]

Absolute zero rules 0K. :D

[Fromage A Trois]

Absolute zero rules 0K. :D
Ouch.






:D

[CC]

This from a layperson: Couldn't absolute zero be a condition in which the HUP does not apply? From the tiny bit I can understand from the conversation here, much of the reasoning sounds like this: It can't happen because the law of XYZ says it can't. But that sounds a little like the pre-Einstein thinking that assumed that time is a constant. The most reasonable (to an ignoramus such as I) answer stated so far is that the heat from something has to go somewhere that it's colder in order for something to cool off. Don't laws (e.g. the HUP) DESCRIBE our observations? They don't determine them, do they? I see this is pretty jumbled, but I guess I am put off by answers that invoke law rather than reason. Is quantum physics so counterintuitive that reason, as we know it, doesn't apply? Heeeeelllllllppppp!!!!

[CalMeacham]

This from a layperson: Couldn't absolute zero be a condition in which the HUP does not apply? From the tiny bit I can understand from the conversation here, much of the reasoning sounds like this: It can't happen because the law of XYZ says it can't. But that sounds a little like the pre-Einstein thinking that assumed that time is a constant. The most reasonable (to an ignoramus such as I) answer stated so far is that the heat from something has to go somewhere that it's colder in order for something to cool off. Don't laws (e.g. the HUP) DESCRIBE our observations? They don't determine them, do they? I see this is pretty jumbled, but I guess I am put off by answers that invoke law rather than reason. Is quantum physics so counterintuitive that reason, as we know it, doesn't apply? Heeeeelllllllppppp!!!!



Not reason, but "common sense". Our sense of what's "right" is derived from our experience with the macroscopic world (and with velocities much slower than light, and distance scales much smaller than galactic, etc.) When something seems "wrong" we fall back on our experience with the way things behave in our realm of experience. Outside of our realm of experience -- the really small, really big, really fast, etc. is outside our experience, and "common sense" isn't a very good guide. Down on the quantum level things get weird. This is one of the weird things.

The Uncertainty Principle isn't the result of describing our observations -- it follows from logical and mathematical rules based upon a plethora of other observations. As long as you buy that matter is describable by de Broglie waves, you're going to get an uncertainty principle limiting the state of knowledge of pairs of properties like position and momentum. And there's too much evidence from other observations (and consistency of theories) that indicates that matter is composed of such waves.

[Myglaren]

Just how strict is Heisenberg' ?

Just don't get on his nerves or you'll find out.

[randomlyblanks]

This from a layperson: Couldn't absolute zero be a condition in which the HUP does not apply? From the tiny bit I can understand from the conversation here, much of the reasoning sounds like this: It can't happen because the law of XYZ says it can't. But that sounds a little like the pre-Einstein thinking that assumed that time is a constant. The most reasonable (to an ignoramus such as I) answer stated so far is that the heat from something has to go somewhere that it's colder in order for something to cool off. Don't laws (e.g. the HUP) DESCRIBE our observations? They don't determine them, do they? I see this is pretty jumbled, but I guess I am put off by answers that invoke law rather than reason. Is quantum physics so counterintuitive that reason, as we know it, doesn't apply? Heeeeelllllllppppp!!!!

The Heisenberg Uncertainty Principle is not actually something we have as a law to describe our observations but rather something that is mathematically derived from the quantum conditions. In fact there is not just one uncertainty product, but many. For instance, energy and time also have an uncertainty; how to derive these is something that is a little to in-depth for a posting here.

But try to picture it this way. Imagine you have a camera and are trying to take a picture of a person riding a bike. If you have an instantaneous shutter speed, the resulting picture will be from an exact instant in time. Except at that instant, you can get no information as to how fast the rider is moving. You know her precise position, but her speed could be anything from 0 to infinity (at least theoretically). But say your camera shutter now moves a little bit slower. The picture will appear fuzzy and smeared out. Now you have some information about her speed, but unfortunately, the fuzziness of your picture prevents you from knowing where precisely she is. Now imagine this continuing with progressively slower cameras. The riders looks fuzzier and fuzzier, but you can start to get a better and better picture of how fast she is moving. That is uncertainty.

Yet, you might ask why not use two cameras, one fast and one slow. Well at this point the thought excercise breaks down. A quantum unmeasured particle will simultaneously be moving to the right and to the left; what we call a superposition of states. Similarly, it will also be smeared out within the boundaries in no fixed location. A fixed position or momentum will not occur until it is measured. Thus, when momentum is measured, the particle will have no fixed position, it will be smeared out. When position is measured, it will have no measureable momentum. You can't have two cameras operating at the same time.