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# Pressure differences near 0 deg K

Fri 8 Mar, 2013 06:56 am
Hi,

Is it possible to express, say, the difference between 2.7 deg K and 0.25 deg K as a pressure difference i.e. in bars, millibars, femtobars etc?

I'm thinking of a void between one galactic cluster and the next and wondering if, although very sparsely populated, whether a region like this can be considered a gas (and use the gas laws - Boyle and Charles... )?

Thanks!
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Fri 8 Mar, 2013 09:04 am
@JeremyF,
JeremyF wrote:
I'm thinking of a void between one galactic cluster and the next and wondering if, although very sparsely populated, whether a region like this can be considered a gas (and use the gas laws - Boyle and Charles... )?

Gas laws are useful when there is enough matter to matter. The molecules have to be close enough to interact with each other.

My understanding is that the conditions you describe are too sparse for gas laws to be used.
dalehileman

1
Fri 8 Mar, 2013 11:32 am
@JeremyF,
I'd think so Jer but it's a good q and looking fwd to response from those who know

Somewhat OT but I had always wondered what happens to gas at close to that temp and falling. For instance in approach do all the molecules all at once flop to the floor

2
Fri 8 Mar, 2013 11:45 am
@JeremyF,
Deviations from Idal Gas Law Behavior

Quote:
The behavior of real gases usually agrees with the predictions of the ideal gas equation to within 5% at normal temperatures and pressures. At low temperatures or high pressures, real gases deviate significantly from ideal gas behavior. In 1873, while searching for a way to link the behavior of liquids and gases, the Dutch physicist Johannes van der Waals developed an explanation for these deviations and an equation that was able to fit the behavior of real gases over a much wider range of pressures.

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rosborne979

1
Fri 8 Mar, 2013 01:48 pm
Gas laws are useful when there is enough matter to matter. The molecules have to be close enough to interact with each other.

My understanding is that the conditions you describe are too sparse for gas laws to be used.
I agree with DD on this.
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JeremyF

1
Sat 9 Mar, 2013 07:42 am
@JeremyF,
Thanks for that everyone.

So if I can't treat intergalactic space as a gas, what should I treat it as?

??
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dalehileman

2
Sat 9 Mar, 2013 11:26 am
@dalehileman,
Still wondering what a few gas molecules might do in a vacuum bottle approaching zero K. Would they continue bouncing around or would they eventually settle to the bottom
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