What is the absolute coldest temperature?

[nightelf125]

I'm just wondering something; if there's nothing around for thousands of lightyears in space, and your just in empty space, hold cold is it going to be? How cold can it get in space? Why would it be that cold? How is the temperature defined in space when there's nothing around? What makes it so cold?

 

[MeteorWayne]

The attached image is the "answer".<br /><br />To your other questions, temperature is a measure of the average kinetic energy of the particles in the space.<br />That is probably not technically correct, but it gives the idea.<br /><br />So, if there are few particles (vaccuum) the KE per space is low, even if the particles that are there are highly energetic.<br /><br />If the particles are moving slowly, even if there are a lot, the average will be low.<br /><br />When the density is zero (probably not possible) or the stuff that is there is not moving at all (also probably not possible) then the temperature is "absolute" zero.<br /><br />We've been able to get within millionths of a degree of absolute zero in laboratory circumstances.<br /><br />In space, neither condition above is very likely, so even in the thinnest part of the cosmos the temperature is likely higher. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[vandivx]

most of the answers are found in second year physics course on statistical methods of physics I think<br /><br />on Earth we get cold mostly by convection heat transfer, that is by coming into contact with low energy molecules of air to which the energy of fast moving atoms of our skin transfers their kinetic energy<br /><br />in empty space you loose heat by radiating it off into space mostly in infrared frequency spectrum range, I admit it is not all too clear to me (kinetic energy of particle motion being transfered to radiation) but these are things one doesn't need to know to still be considered clever <img src="/images/icons/wink.gif" /><br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[billslugg]

The cosmic background radiation precludes anything in the universe from passively cooling to below 3 degrees Kelvin. Any cooling below 3 degrees requires a refrigeration system. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[alokmohan]

No confusion.Absolute temp is 0 degree K,minus 273 C

 

[weeman]

Absolute zero is the temperature where all molecular motion stops. Scientists have been able to come very close to absolute zero, but I don't think it has ever been achieved. It is possible that if there is empty space beyond the material universe, the temperature might be absolute zero. This of course has to mean that there is even empty space out there. The inflation theory and expansion of the Universe might mean that there is no space beyond the existing Universe.<br /><br />Are there theories as to what characteristics an element would take if it reached absolute zero? For example, if we could get water to absolute zero, would it still be just ice? Or might it take on a new form? <div class="Discussion_UserSignature"> <p> </p><p><strong><font color="#ff0000">Techies: We do it in the dark. </font></strong></p><p><font color="#0000ff"><strong>"Put your hand on a stove for a minute and it seems like an hour. Sit with that special girl for an hour and it seems like a minute. That's relativity.</strong><strong>" -Albert Einstein </strong></font></p> </div>

 

[doubletruncation]

This is an interesting question, and I think there have been a lot of good answers to it already. I'd just like to clarify one distinction - space itself does not necessarily have a temperature, instead it's the systems of particles that fill space that have temperatures. As many others have mentioned, for particles the temperature is effectively the average kinetic energy per particle. If you have one or two particles and you know their kinetic energies you could say that they have temperatures given by those kinetic energies, but that is a bit misleading. Temperature is a thermodynamic quantity, and as such it only really makes sense when you look at a large ensemble of things (it is used to describe, statistically, a distribution of particles and what happens to them). Space may be nearly a vacuum, but there are particles there. There may only be about an atom per cubic centimeter in the typical interstellar medium, but if you consider the vast numbers of cubic centimeters that fill up the space between stars you can appreciate that there are a vast number of atoms out there. If you were to plot a histogram of the kinetic energies of these atoms you'd find that they have a multi-modal distribution. Effectively you can break it down into different groups of particles with different temperatures (ranging from a very cold tens of Kelvins in "dense" million atom/cubic centimeter molecular clouds to an incredibly hot millions of Kelvins in the hot ionized medium with only 1 atom per ~1000 cubic centimeters). One thing to keep in mind is that in a given volume of space you may have more than one group of particles each with a different temperatures (you can have, for example, a very tenous hot ionized medium filling the same space as a higher density, cooler warm neutral medium) - so assigning a temperature to some place in space is a bit of a misnomer. Another thing to note is that light itself (photons) can sometimes be described as having a temperature, whic <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

I see.

 

[billslugg]

eburacum45<br />Thank you for the link. This is truly amazing. I was unaware of it but agree that there are natural refrigeration processes. <div class="Discussion_UserSignature"> <p> </p><p> </p> </div>

 

[alokmohan]

Why 3 ,not less?Magic number?

 

[SpeedFreek]

It's 3K because that is the temperature the CMB has cooled down to so far, since the beginning of the universe. Give it a few billion years more and I expect that figure will be lower. <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>