Hank Solo asked if absolute zero exists in the Universe.....
The PBS show I just saw stated that we have taken Hydrogen to as cold as something like a billionth of a degree above 0 degrees Kelvin (Absolute Zero)- but to reach Absolute Zero would take the age of the Universe to achieve and also take a device the size of the Universe. The closer you get the longer it takes to cool down. Similar to as you approach the speed of light -mass increases to the point at which the energy needed would equal the energy of the Universe- so to travel at the speed of light would take as much energy as the Universe has entirely. I'm pretty sure that's how that was explained. But it's also 6 am and I'm still wrapping that one brain cell around the concept.

They also said that atoms at these cold temps become a wierd type of matter that transitions into a single wavy structured substance (??). Said the matter at this point suffers an "identity crisis" so I'm going to have to get the 2 part series DVD from PBS to see it again.
The new substance called - "Einstein Condensate" (I think) -they were able to slow light down to a Human scale of about 20 miles an hour.

They were talking about gases in the program. They worked with Hydrogen, Helium, and a few others, but then one scientist worked with Sodium, which I didn't think was in a gas form - so I'm confused if they meant all matter or not.

They used lasers and evaporation to get the coldest temps which was REALLY cool!!!

OOOPS. Sooner or later I'll figure this out!!

Absolute zero is the temperature of a particle that has no kinetic energy.
because you cant have less than nothing, that's as cold as anything can be.
in any case, its value was first determined by Lord Kelvin, who worked out that when you cool a gas in a vessel of fixed volume, its pressure decreases linearly with temperature.
At some point most gasses will turn into liquids, and cease contracting, but if you extend the line of temperature vs pressure all the way to zero pressure, you find a theoretical value for absolute zero.
Any gas will give you the same value whether it is a cloud of superheated metal, or supercooled helium.

Side note - the laser 'trick' is quite nifty, if you shine an infra-red laser through a cloud of super-cold gas, the colder fraction of the gas will travel down the laser beam, and the hotter fraction up it. you have to get the frequency of infra-red exactly right though.

This posting may contain many ommisions or innacuracies. corrections are welcome, the wikipedia article on absolute zero looks pretty good.

also, Bose-Einstien condensates are cool too. (very) basically, you have a cloud of gas (probably rhobidum atoms) at such a low temperature, that in some sense, the entire cloud can be treated as a single very large atom.
You can even try to take a photo of it, although the heat from the flash will blow it apart.

Heisenberg's uncertainty principle, a foundation block of quantum mechanics, assumes that one can never know the position and velocity of a particle.

As you cool down a sample, the speed of the atoms/molecules decreases. As a result, they're not moving very fast at all, and therefore aren't changing position quickly either. This would make us think that at absolute zero, the position will be known and the velocity of all particles nil. This violates the founding principles of quantum mechanics. Sure enough, when you get close to absolute zero, particles can form a Bose-Einstein condensate.

About the laser thing. Imagine a particle coming straight towards the laser pointer. If the color of the laser is correct for the speed of the particle, it will slow it down. As the particle slows down, it no longer reacts to that color of light and keeps going at the slower speed. Now you can increase the wavelength of the laser to go catch even slower particles. Lather rinse repeat until you're happy. The fact that the effect is very dependant on the speed and direction of the sample particles makes it extremely useful.

What is the absolute high temperature? There is obviously a ceiling on how hot something can get as well. Has anyone figured it out? Would the interior of a huge star be the hottest substance the universe can create?

See topic entitled, not so surprisingly, Absolute Zero.

Like watching history repeat...

(Or, peruse topic Absolute... Highest tempreture. Or, topic Absolute Kelvin?.)

__________________
0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 1 0....

The highest absolute temperature is, amazingly, absolute zero too, but approaching from the other side. Negative absolute temperatures relate to higher energy states than positive ones.

There is a change of variable involved, just taking the inverse and reversing signs. This makes another temperature scale in which absolute zero (positive side) relates to minus infinitum in the new scale, both absolute infinita relate to zero in the new scale and absolute zero (negative side) relates to plus infinitum in the new scale.

In this new scale neither infinitum (positive or negative, arising from the negative and positive sides of our absolute zero) can be reached (of course).

I found this surprising concept some time ago in the final chapter of my old thermodinamics text book and it involves something called "inversion of population" that the book did not explain so I don´t really understand it yet. Maybe there is some expert here who can explain it better.

Googling "absolute negative temperatures" will also give you some places to start with.

I've read that the Sun's temp is hotter on the surface than the interior. So the hottest temp in the Universe can't involve most stars, could it? The hottest temp I've ever heard of was the gazillionth of a sec after the Big Bang, but the number associated with that temp was never discussed in that article.

I've always assumed if there is an absolute temp for cold, there should be one for heat. Any ideas out there??

Articles discussing Gamma Ray Bursts talk about many millions of degrees Fahrenheit....... but again, never stuck to a number.

Still doesn't explain what determined the minus 273 Celcius number that will never be achieved either.

The surface of the Sun is hotter (~1 million K) than the interior near the surface (as low as 4000 K), but the temperature again rises as you get deeper into the Sun. The center is actually the hottest, at 170 million K.

One measure of temperature is the average kinetic energy of the atoms or molecules in some object. Absolute zero would occur when there is no kinetic energy. Since you can't have negative kinetic energy, you cannot go below absolute zero. Classically, there is no upper limit to how much kinetic energy a particle has, so there is no upper limit to the temperature. You can always increase the temperature of a system by adding more energy. Quantum mechanically, however, there may be an upper limit to how much energy you can fit into a system and the Planck temperature, about 10^32 K, is probably an effective upper limit.

There are other ways of describing temperatures that allow for negative temperatures (which can apply to lasers), but those descriptions are statistical in nature and are cannot really be thought of in terms of the "hot" and "cold" we use in referring to, for example, the weather.

01101001 and Tempus,
M'thinks you jest, esp 01101001. Very clever! I've never seen an iterative link before. Sad to say, it doesn't add anything.

And Tempus - you just made that up! As materials are heated, they undergo phase shifts ( I think that's the right phrase) - solid into liquid into gas into plasma. Each phase shift incurs an added cost in heat, above merely increasing the kinetic energy of the particles of the material, to change the relationship of the material particles to each other (EG Specific Heat of Vapourisation). Heating a plasma even more just raises the speed of the particles, their energy, with no sign so far of another phase shift.
To see if there IS another phase shift above a plasma is one object of the Large Hadron Collider. But there is no absolute high temperature.

John

No energy or mass can have zero energy. It is unattainable.

Heat is defined by energy, and energy defines mass. Therefore nothing can have zero energy (zero temperature).

(Laymans version)

no really! nothing CAN... but there is no Nothing. There is something evrywhere. Space is completely full.

You are right, population inversion is the working mechanism behind old MASER and the like named LASER.

But on statistical descriptions, "average kinetic energy" is itself a description statistical in nature. Do you know of a working definition for temperature which does not involve statistics?

On Planck units, I would not bet on any of them being a limit per se. You have to consider that they are a product of dimensional analysis, and dimensional analysis fails to produce values for constants; these have to be fit afterwards based on experimental. The Planck mass, for sure, is not a limit neither upper neither lower for any other conceivable mass. Why should the Planck temperature be? Not to mention you can have two sets of units, one using Planck´s constant and another one using Dirac´s. But they are good for taking away the constants from some equations or at least reducing them to integers, pi factors and the like.

No, I did not make it up. Why do you say so? And what have phase changes (phase shifts are quite a different thing) to do with it?

And did I understand you right that you hold there is no limit to high temperature (absolute or other scale) because there is no known phase beyond plasma?

Please explain what a negative absolute temperature is to me.

Absolute zero is just not possible. From there on up, there is no known limit.

Why do I say that? This bit:
"There is a change of variable involved, just taking the inverse and reversing signs. This makes another temperature scale in which absolute zero (positive side) relates to minus infinitum in the new scale, both absolute infinita relate to zero in the new scale and absolute zero (negative side) relates to plus infinitum in the new scale."
You have to explain that to persuade me that you didn't just make it up. Dowes the range of temperature in the cosmic scale go around in a circle, or do you mean that there are very small differences either side of zero? Not, when it comes to temperature, I thought.

And phase changes? I was thinking of the whole range from solid to plasma. The phase changes demand a greater input of heat energy to raise the temperature any further; they are limits, albeit partial; but there seemed to be no limit to the heating of a plasma, unless there is another phase change at higher temperatures.

Plank temperature? Thank you! There is a limit! But that is in the 10^34 C range, and even the core of a star is only at 10^6 C, so there is a long way to go. Is there a phase change on the way there?

John

I will answer your acusation just by naming my source.

"Curso de Termodinámica", Prof. J. Aguilar Peris, Primera edición 1981, Editorial Alhambra S.A.
ISBN 84-205-0842-X
Capítulo 28, Termodinámica estadística. Apartado 28.8, Temperatura absoluta negativa. Páginas 674-679.

It is a 101 book on Thermodynamics (sorry foy my english typo in my first post) so I guess it has been peer reviewed according to mainstream Physics. If you are interested I hope you will not have problems in finding an equivalent one in English which addresses the subject.

What it indeed says and I relayed here is that there are VERY BIG diferences either side of zero, being the lowest (+0K) and highest (-0K) posible energy states for a system. Both sides are not conected at all. To go from +0K to -0K you would have to go all the way up from +0K to higher positives, eventually go beyond + infinitum / -infinitum (both are the same energy state) and keep ascending (modulus decreasing) the negative temperatures by ADDING energy all the way up to -0K, where you would have to stop.

Not that I´m saying it is possible with our means, but that is how the continuum of temperatures seem to work and that is the reason the -1/T scale was developed (and not by me). In fact a 1/T scale would have sufficed to make it continuous but that would have been a "coolness" scale so I guess the minus sign was introduced to turn it back to our "normal" everyday perception of temperature as a measure of "warmth". Side effect is that we live in the negative region of the -1/T scale.

alainprice, I hope this last part serves as an answer for you too.

So we need to add infinite energy and then some. This is not practical.

You are right; "average" itself is a statistical concept . What I meant by "statistics" was more along the lines of statistical mechanics and quantities like entropy.

The "average kinetic energy" description of temperature is basically equivalent to the statistical mechanics definition in the case of gases or free particles. They are not so much different definitions as one is a subset of the other. The "average kinetic energy" description is far more understandable to the layman, though, than one that involves entropy.

The Planck mass is an upper limit of sorts for a fundamental particle. At that mass, the Compton wavelength is about the same as that of the Schwarzschild radius, so quantum effects are comparable in scale to gravitational effects. At this point, quantum field theory and GR must break down, to be replaced with some other theory (for example, String Theory). It is not clear that mass or energy above that scale are possible (or even well defined), but things would look very different.

The Planck units are not meant to be exact limits, more order of magnitude. Factors of 2 or pi are usually ignored, so Planck vs. Dirac units is not really a concern.