Ask a physicist anything. (7)

Wiccan_Child · Oct 20, 2011

Zippy the Wonderslug said:
What is the coldest temperature a fire could withstand?

It's a complex question, because 'fire' is quite a nebulous concept, especially when you take it to extremes. Wikipedia calls it 'rapid oxidation', and the flame is a mixture of glowing solids and gases. I suppose there's no lower limit to how cold it could be, depending on how loosely you interpret 'rapid' oxidation.

Interestingly, NASA recently found a star that was a balmy 27-70°C. Not exactly chilly, but pretty darn cold for a star.

Chalnoth · Oct 20, 2011

Wiccan_Child said:
Interestingly, NASA recently found a star that was a balmy 27-70°C. Not exactly chilly, but pretty darn cold for a star.

Presumably that would be a brown dwarf, not a star undergoing nuclear fusion in its core

Tuddrussell · Oct 20, 2011

Browndwarf, the next time I play DnD that's what I'll call my character.

Wiccan_Child · Oct 20, 2011

Chalnoth said:
Presumably that would be a brown dwarf, not a star undergoing nuclear fusion in its core

Apparently it's one of the newly discovered Y Dwarfs, the coldest of the brown dwarfs. NASA's article is here.

Wiccan_Child · Oct 20, 2011

Tuddrussell said:
Browndwarf, the next time I play DnD that's what I'll call my character.

It sounds like a dwarf that's been pooped out. Though the way we treat our dwarf, it's quite an apt nickname

Chalnoth · Oct 20, 2011

Wiccan_Child said:
Apparently it's one of the newly discovered Y Dwarfs, the coldest of the brown dwarfs. NASA's article is here.

Interesting.

Of course, I should mention that this isn't so much a discovery of a new class of object, but rather the extremely low temperatures of these objects makes them very, very hard to detect. We generally expect compact objects to be more numerous the smaller they are. So there are likely more of these sorts of objects than there are the heavier stars that we can more readily see.

Wiccan_Child · Oct 20, 2011

Chalnoth said:
Interesting.

Of course, I should mention that this isn't so much a discovery of a new class of object, but rather the extremely low temperatures of these objects makes them very, very hard to detect. We generally expect compact objects to be more numerous the smaller they are. So there are likely more of these sorts of objects than there are the heavier stars that we can more readily see.

Probably, but they're still newly discovered inasmuch as, not long ago, we hadn't seen one before. As good as theory is, there's nothing quite like seeing the hypothetical star. Which is the great thing about science: we can go out and see that it works!

mzungu · Oct 20, 2011

At absolute zero (naught Kelvin) all molecular movement ceases and thus all chemical reactions such as oxidation cannot take place! Of course reaching naught Kelvin is almost an impossibility but we have come extremely close to it!

Chalnoth · Oct 20, 2011

mzungu said:
At absolute zero (naught Kelvin) all molecular movement ceases and thus all chemical reactions such as oxidation cannot take place! Of course reaching naught Kelvin is almost an impossibility but we have come extremely close to it!

Actually, one of the cool things there is that quantum mechanics starts to become extremely important even for very large systems as their temperatures get closer to 0K. And instead of all motion ceasing, a system at 0K in quantum mechanics has its wavefunction in the ground state. And the ground state, as it turns out, doesn't have zero motion.

mzungu · Oct 20, 2011

Chalnoth said:
Actually, one of the cool things there is that quantum mechanics starts to become extremely important even for very large systems as their temperatures get closer to 0K. And instead of all motion ceasing, a system at 0K in quantum mechanics has its wavefunction in the ground state. And the ground state, as it turns out, doesn't have zero motion.

Ah those Brits really know their science

Superfluid helium - YouTube

Chalnoth · Oct 20, 2011

mzungu said:
Ah those Brits really know their science

Superfluid helium - YouTube

Yeah, superfluids are pretty amazing

Wiccan_Child · Oct 20, 2011

Whenever I see magnets and ferrofluids and superfluids, I'm sure there's a way to break some thermodynamic law. It reminds me of these sorts of troll physics:

pgp_protector · Oct 20, 2011

Wiccan_Child said:
Whenever I see magnets and ferrofluids and superfluids, I'm sure there's a way to break some thermodynamic law. It reminds me of these sorts of troll physics:

...snip...

Is their a superferrofluid ?

Wiccan_Child · Oct 20, 2011

pgp_protector said:
Is their a superferrofluid ?

Don't be silly

Oh, wait, nevermind...

Chalnoth · Oct 20, 2011

Wiccan_Child said:
Don't be silly

Oh, wait, nevermind...

I somewhat doubt that's actually a superfluid. Looks more like the "super" was just appended to make the product sound cool.

Naraoia · Oct 20, 2011

Wiccan_Child said:
It's easy to see how the naive might think it would work, though. I read once that people in a neighbourhood in Africa were shown how to use condoms with a cucumber - and they ended up buying cucumbers en masse, putting condoms on them, and then having unprotected sex, thinking they were baby-proof.

That sounds almost crazy enough to be true

Wiccan_Child said:
It's a complex question, because 'fire' is quite a nebulous concept, especially when you take it to extremes. Wikipedia calls it 'rapid oxidation', and the flame is a mixture of glowing solids and gases. I suppose there's no lower limit to how cold it could be, depending on how loosely you interpret 'rapid' oxidation.

Interestingly, NASA recently found a star that was a balmy 27-70°C. Not exactly chilly, but pretty darn cold for a star.

Doesn't the definition of a star include sustained fusion?

Chalnoth said:
Interesting.

Of course, I should mention that this isn't so much a discovery of a new class of object, but rather the extremely low temperatures of these objects makes them very, very hard to detect. We generally expect compact objects to be more numerous the smaller they are. So there are likely more of these sorts of objects than there are the heavier stars that we can more readily see.

I thought the whole herd of starless Jupiters that they discovered a while ago was way cool.

cupid dave · Oct 21, 2011

Wiccan_Child said:
Whenever I see magnets and ferrofluids and superfluids, I'm sure there's a way to break some thermodynamic law. It reminds me of these sorts of troll physics:

Hahaaaaa.
911?

The real trick is to do it with the karate slap at exactly the right moment and with exactly the right amount of time expended doing it.

Tuddrussell · Oct 21, 2011

Why doesn't the chair trick work?

mzungu · Oct 21, 2011

Wiccan_Child said:
Don't be silly

Oh, wait, nevermind...

So supercooled helium does not act the way they showed it on the video If the video I posted is a scam then please let me know (but explain it not just dismiss it)! I have no problem if superfluids do not exist because this will mean I have learnt something new and that is what science is all about!

Menander: Κάλλιστόν ἐστι κτῆμα παιδεία βροτοῖς.
'Education is the most valuable treasure for mortals.'

chris4243 · Oct 21, 2011

Tuddrussell said:
Why doesn't the chair trick work?

What's the maximum velocity you can jump at?

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