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At atmospheric pressure, all known materials would become solid at absolute zero with the exception of one; helium. Pressures around 25 atmospheres or above must be added to helium in order to freeze it or else you'll just end up with a superfluid at cryogenic temperatures. Air becomes solid quite a bit above absolute zero.A vacuum has no physical substance, and thus cannot freeze.If it were possible to bring an object to that temperature, it would definitely be possible to heat it up again by adding thermal energy (actually, it would be nearly impossible to keep it from heating up, given all of the random radiation and subatomic particles that flit through all of space at all times). As far as it freezing the Universe goes, that would be impossible. The only way that could happen would be if the object became a kind of infinite heat sink that could continuously absorb heat from any and all sources. Since all materials have a finite heat capacity, this cannot occur (no matter how cold you make it).I'm sure there are some kind of complex calculations involved that allowed us to arrive at that figure of -459.69 degrees Fahrenheit for absolute zero, but I don't have any idea what those would have been.
I just had this notion that if absolute zero was indeed obtained then it would have a chain reaction and freeze everything else around it too .The helium issue is really interesting cos I thought at absolute zero all movement must cease...it's hard to imagine that it will be a fluid...albeit super !!...would it still move ?
Quote from: neilep on 03/10/2012 17:20:00I just had this notion that if absolute zero was indeed obtained then it would have a chain reaction and freeze everything else around it too .The helium issue is really interesting cos I thought at absolute zero all movement must cease...it's hard to imagine that it will be a fluid...albeit super !!...would it still move ?Because of quantum effects, it is not the case that at absolute zero "all motion must cease". http://en.wikipedia.org/wiki/Uncertainty_principleThe Heisenberg Uncertainty principle ensures that we cannot know both position and momentum of a particle at any time beyond a certain accuracy. If motion were to cease, we would know that the momentum was exactly zero, and we would have the opportunity to measure the position of an atom as exactly as we wanted to.All atoms are still moving at absolute zero. In most substances the interatomic attractions are strong enough that atoms are locked into a solid, and the residual motion is just a vibration around the average position in a lattice; with helium, the atoms are still able to move past one another.Superfluid helium displays many strange properties, which arise from other aspects of quantum theory (Bose-Einstein statistics).
This fact may now be outdated:Scientists have actually come within a few hundreths of a degree of absolute zero. This fact, however, I know is true:It will be very difficult to achieve absolute zero because whatever chamber you are trying to achieve absolute zero in will have something touching it. Consequently, this means that heat can be transferred from the object to the chamber. The only real way to achieve absolute zero in a chamber would be for that chamber to be contained in a complete vacuum. This is a problem in and of itself. A complete vacuum calls for a space with absolutely no matter contained in it. If there is no matter surrounding the chamber, that eliminates the possibility of heat transfer. So, until a complete vacuum is created, it will more than likely be impossible to achieve the temperature of absolute zero.
The 25 atmospheres pressure needed to solidify superfluid Helium is shown in the graph here: http://en.wikipedia.org/wiki/Superfluid_helium-4#PropertiesBelow a temperature of 2.2K, Helium progressively turns into a Bose-Einstein condensate, where all the atoms fall into the same quantum state. This quantum effect keeps it liquid, even at absolute zero.Some contentious research has been conducted into the extremely orderly crystals of solid Helium near absolute zero. When subjected to pressure, the crystal structure is deformed, and the "grain boundaries" can apparently move more easily than expected. So perhaps the solid is still somewhat fluid? http://en.wikipedia.org/wiki/Supersolid#ExperimentsAn estimate of -240C for absolute zero was produced by Guillaume Amontons in 1702, based on experiments on air thermometers (http://en.wikipedia.org/wiki/Absolute_zero#Limit_to_the_.22degree_of_cold.22). If you cool air, it takes up less volume; he extrapolated this volume to zero. We now know that the molecules of air take up a finite volume, so the volume doesn't really drop down to zero. Once the air molecules get close together, Van Der Waals forces cause them to clump together forming a liquid, which is almost incompressible (until you get near the pressures at the center of a star...). The current low-temperature record is 100 pico-Kelvins http://en.wikipedia.org/wiki/Absolute_zero#Very_low_temperatures