Absolute Zero - Why?

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Absolute Zero - Why?

Postby ok0510@126.com » Sun Sep 12, 2010 9:36 pm

Why is there an absolute zero and how do we know it's accurate? Is there a maximum temperature limit and if not why not?

Please keep solutions as simple as possible, thanks!
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RE: Absolute Zero - Why?

Postby ronin » Sun Sep 12, 2010 9:53 pm

In a simple way temperature is a measure of "movement".
As an atom or molecule moves faster then its temperature rises.
So by slowing it down, the temperature decreases.

In what we term a solid, say a crystal, then the atoms are "fixed" but are able to vibrate. If they vibrate enough then the crystal is broken, it melts.

Slow the vibration down and the temperature drops more.
Eventually the vibration stops, but still not absolute zero.

We are now dealing with entrophy, just general choas.
The atoms have spin. (Don't ask).
So apply a magnetic/electric field and all the spins line up, less chaos = less temperature = colder.

Eventually there is no movement and nothing else to reduce. The material is as low down the entropy scale as you can get.

As you can get no "colder" then that is absolute zero. Nothing "colder".

As to the maximum, never heard of one, but suspect that there may be ideas.
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RE: Absolute Zero - Why?

Postby brianb » Mon Sep 13, 2010 12:56 am

[quote]As to the maximum, never heard of one, but suspect that there may be ideas. [/quote]
Depends on how you define temperature. If by vibration of molecules / atoms / ions there's clearly a limit because the energy of vibration will eventually cause the "particles" to break down ... somewhere above 5x10^9K (depending on pressure) you will get an instability causing a loss of pressure and a runaway collapse (the mechanism behind a pair production supernova). If you define temperature by energy per unit volume there's no theoretical upper limit except for the compression of all the matter/energy in the universe into a space smaller than the Planck dimension.

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RE: Absolute Zero - Why?

Postby ok0510@126.com » Mon Sep 13, 2010 8:10 am

Thanks for the responses.

Where does dark matter sit in this equation? Is it possible that it could be below our known absolute zero and hence be difficult to detect?
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RE: Absolute Zero - Why?

Postby brianb » Mon Sep 13, 2010 10:06 am

[quote]Where does dark matter sit in this equation? Is it possible that it could be below our known absolute zero[/quote]
Pass ... but absolute zero is exactly that, it's a physical impossibility to cool anything to absolute zero, let alone "below" it ... there isn't even a quantum route to tunnel through the barrier ... we can be quite sure of this, as if there was a loophole in the law of entropy, we'd see examples of violations of the Second Law of Thermodynamics all over the place.

Whether dark matter consists of heavy particles predicted by supersymmetry theory or Something Else, it's governed by the same laws that apply to the rest of the universe ... and it has a positive "temperature".

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RE: Absolute Zero - Why?

Postby ok0510@126.com » Mon Sep 13, 2010 1:26 pm

[quote]
Whether dark matter consists of heavy particles predicted by supersymmetry theory or Something Else, [b]it's governed by the same laws that apply to the rest of the universe ... and it has a positive "temperature"[/b].


[/quote]But why and how do we know if we can't detect it? What if it's beyond our universe, say in a different dimension, which could occupy the same space/time as we know it, but not be detectable to us. How do we know that the laws of our universe would apply to something of this nature if it's possible for it to occur?
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RE: Absolute Zero - Why?

Postby arthur dent » Mon Sep 13, 2010 3:23 pm

[quote]ORIGINAL: Star Watcher

Whether dark matter consists of heavy particles predicted by supersymmetry theory or Something Else, [b]it's governed by the same laws that apply to the rest of the universe ... and it has a positive "temperature"[/b].[/quote]
Hi there,

Do you accept the idea of absolute zero? If you do, then by extension, [b]every other temperature would have to be positive[/b]

If you don't then here's an analogy. You have a mean bank, mean family and mean friends. No-ne will lend you any money. When your bank balance hits zero, there's nowhere else to go (as the bank won't give you an overdraft and friends & family won't lend you anything). So, the zero of your bank balance is like absolute zero - you can have nothing less than this. Anything else is a positive in your bank account (ie there is no "negative" money).

In the same way, although we can have minus temperatures in degrees Celsius (centigrade) that's only because 0ºC isn't the coldest possible temperature - it is some 273.15ºC above the coldest possible temperature which is absolute zero. So, we can only have positive temperatures too.

To make the distinction clearer, scientists use the Kelvin scale of temperature. Absolute zero is at 0K (note there is no degree sign) and 0ºC is at +273K (pronounced 273 Kelvin not 273 degrees Kelvin).

[quote]But why and how do we know if we can't detect it? What if it's beyond our universe, say in a different dimension, which could occupy the same space/time as we know it, but not be detectable to us. How do we know that the laws of our universe would apply to something of this nature if it's possible for it to occur?[/quote]
We can only state that [b]in our universe[/b] the laws are such and such. These have been well tried, tested and developed in the 400 years or so since Newton's time. We can speculate about other universes or other dimensions but we have no way of detecting them or establishing their properties - except theoretically.

If you [b]really[/b] want to scramble your brain, study Quantum Physics!

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