h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

but... IF a particle wasn't moving then surely it has NO kinetic energy. If you stop a particle moving then it has no kinetic energy so is it not at absolute zero? perhaps this temperature is not -273 degrees, but surely it does exist in theory, even if no one can stop a particle moving.

'Surely it does exist'? You have much faith in our theoreticians. Well, as I said, it depends on how you define temperature. I agree with you (and most experimental physicists would) that if only the zero point energy is left in the ensemble, this means zero temperature.

However, temperature is a thermodynamic quantity and usually very classically defined (I mentioned). At very low temperatures, nature does very strange (quantum-mechanical) things: Bose-Einstein condensates, van-der-Waals crystals, Fermi liquids. Here temperature usually is defined in the context of quantum statistics, and everything is fine.

But some clowns apply the classical definition to the quantum-mechanical cases and find queer oddities (eg the origin of this thread). Nice to talk about, but I doubt that it is actually used somewhere. (I've never heard of it, and I cool my apparatus down to 2,3K every single day, some colleagues in a neighbour lab even to 300mK.)

Unlike so many of you stating that Marwood is wrong I am not going to even go there, he seems to be making sense. What I would like to point out is that the guide entry does not say that the particles have no enery at -273 degrees Celsius, he says that they have minimal energy. So, basically, you are agreeing with him. Sort of.

Surely absolute zero can be defined as either:
1. space in which no matter/energy exists,
2. elemental particle moving away from the center of the universe on the very outer limits of universe (from the point of view of the particle,
3. matter and energy within a space frame without time.

I hope 232175 you are not going to go down the avenue of 1 being infinitely bigger than zero like you normally do.

Well, the difference between 0 and 1 is far greater than between 1 and 100 in some ways. One-hundred is only one hundred times greater than one. But one is infinitely greater than zero.

Oh dear what have I started LOL

Well, tvl, absolute zero can also be defined as the TV programme on Sunday afternoons. But what is this good for?

Well, I just posted that because others asserted that absolute zero could not exist. I think it can and does exist. Trouble is, we're in a fish bowl.

I don't see this trouble actually. The problem is that we all are incompetent. If we asked one of those poeple who work in the field of low temperature records, they would give us a clear definition of T in the milli (or even micro) Kelvin domain.

Of course Nernst's Law forbids to get to T=0, but this doesn't mean that you cannot construct a body of zero temperature theoretically.

"Any entropy changes in an isothermal reversible process approach zero as the temperature approaches
zero" -Nernst just stated the obvious. So, we can't cool a system to absolute zero in steps. That doesnt mean it can't otherwise be done.

Nor that it already exists. We can't 'see' stasis because we experience life as an infinite and progress series of stasis cells. This is perceived as fluid and everchanging with entropy at the end. Not suprisingly, the word 'animation' has to do with life.

Excuse my ignorance, but I don't see the connection between life and zero temperature.

I said that absolute zero could exist thus: "3. matter and energy within a space frame without time.

Any dimensional frame without time would lack all kinetic energy but this could not be observed by someone inside the frame. I was suggesting that perhaps life as experienced by us can be said to be an infinite series of such frames rather like an animation. Metaphysical, I guess. But relativity suggests that we should look at the universe in different ways. One way might be to look at it without time, a snapshot, and look at what properties exist or are absent.

I think that doesn't make much sense. (Sorry, no offence meant.) If you *imagine* a universe in which everything is frozen (ie standing still), well, you have zero temperature, although temperature is a quantity defined for 'our' universe and it may well be of little use in 'other' thinkable universes.

But if you just look at an infinetly small time frame in *our* universe, you still have kinetic energy. If you imagine looking at an infinetly small part of a human being, it's still part of a human being. The coordinate system or the laws of physics are not affected by any arbitrary limits you apply to the coordinate axes.

You're right about it not making too much sense, but this is the "absolute zero/absolute twaddle topic"

Well anyway, you said "if you just look at an infinetly small time frame in *our* universe, you still have kinetic energy". I agree of course that if you have a minute time frame, you still have kinetic energy. But I was suggesting that there may be fundamental frames without time in exactly the same way that a disney cartoon is made up of a series of painted 'cells'.

We know that we can conceive and understand 2 dimensional surfaces without a third dimension or time. We can with 3 dimensions too.

Look, if someone can get away with saying that time doesnt exist outside the boundries of the physical universe or at least before it existed (as there can be no point of reference), I can jolly say this!

Velocity is of course defined as dx/dt. It is unimportant how you chop time or set up any sort of frames. Neither the definition nor the resulting value will change.

Well, you cant use dx/dt to define velocity in a model without time :p

And anyway, you already agreed with me: "If you *imagine* a universe in which everything is frozen (ie standing still), well, you have zero temperature.." -thats all I was saying.

So do you reckon that there are no fundamental slices of time? That there are no 'moments' in which everything is frozen?

> So do you reckon that there are no fundamental
> slices of time? That there are no 'moments' in
> which everything is frozen?

In our universe -- yes. Look at it: Everything is moving.

A disney cartoon moves thought it is made up of still frames.

Life is funny... Something as simple as the wording of a defenition can throw all kinds of people into a fuss.

First of all, a quick reasoning behind why you can't reach zero-energy. The 'jiggling' of the atoms is essentially the rotating imbalance caused by motion within an atom. Think of an unbalanced cieling fan... gets pretty shaky when its moving. Same thing as an atom (only MUCH smaller scale). Its impossible to balance anything perfectly (including an atom) then the jiggling can be thought of as a mass imbalance in the atom. Therefore, if the atom stopped jiggling, nothing would be moving. Since magnetic fields and electric fields (and all of the other interactions within an atom) are created by motion, the atom would simply decompose if it stopped moving. A quick analogy to this is that the magnetic field of a planet is created by a spinning core of material, which is what they used to show that some of Jupiter's moons have spinning cores.

Back onto topic...

Neither the defenition of temperature nor the Kelvin scale are wrong. The initial assumption by Kelvin that energy is zero at 'absolute-zero' is wrong, but it was just an assumption based on old technology. Temperature is a measure of energy (most textbooks say kinetic-energy, but not all, showing that science and its defenitions evolve over time), just like distance is a measure of length, but without units and a scale those defenitions are useless. So the centrigrade scale is based on the melting and freezing points of water at standard temperature and pressure (stp). We used the phase change of water as the scale, and gave them celcius as a unit. Kelvin used this standard to represent a trend he saw (which he based on the relationship between pressure and temperature of a gas I believe). It was nothing more than that.

Energy is actually the key term here, because we can't measure energy directly. So we measured temperature and used that to give energy units and a scale (a Joule is the amount of energy required to raise 1gram of water 1degC at stp). But all of these defenitions are based on measurements made years, decades, or centuries ago. Just like newtonian physics has its exceptions, so does current thermodynamics (don't forget that the ideal gas law works, under every-day conditions).