Ask a physicist anything. (7)

[Wiccan_Child]

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]

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]

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

 

[Wiccan_Child]

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]

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]

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]

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]

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]

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]

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]

Ah those Brits really know their science

Superfluid helium - YouTube

Yeah, superfluids are pretty amazing

 

[Wiccan_Child]

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]

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]

Is their a superferrofluid ?

Don't be silly

Oh, wait, nevermind...

 

[Chalnoth]

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]

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

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?

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]

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]

Why doesn't the chair trick work?

 

[mzungu]

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]

Why doesn't the chair trick work?

What's the maximum velocity you can jump at?