I remember reading that at -90 degrees (celcius or fahrenheit, I dont’ remember) (and if you could even somehow miraculously survice in that temperature), that you can actually watch your breath solidify right in front of you and drop to the ground. Is the freezing point of carbon dioxide -90 degrees?
Well, most of your breath is nitrogen, so if you’re seeing that solidify, you need to close the helmet of your spacesuit damn quick.
-90 isn’t that cold on a cosmic scale. I wonder whether you are thinking of a temperature where the moisture in your breath, that normally shows as vapour clouds in cool air before it dissipates, freezes too quickly to dissipate?
Checking webelements.com, I see that the boiling point of carbon IV oxide (CO[sub]2[/sub]) is around -78C, presumably at standard atmospheric pressure. (The melting point quoted, -56C, is at a higher pressure, I believe.) I don’t think it ever gets cold enough anywhere on Earth for carbon dioxide to solidify at our normal pressures.
And even at the freezing (sublination) point of carbon dioxide, the vapor pressure of dry ice is still well above the partial pressure of CO2 in the atmosphere. Just like water evaporates even though the temperature is below 100C. So I doubt CO2 could condense out of the air at any temperature above the liquification point of air anyway.
While I’m on the topic of freezing, is there really an absolute zero?
-273.15° Celsius
-459.67° Fahrenheit
Do we have any sufficient evidence to support it?
Yes, there really is. I guess the evidence to support it encompasses the entire domain of thermodynamics. Since temperature is the average kinetic energy of molecules in a substance, when the kinetic energy is zero, ie when molecular motion stops, it can’t get any less. Molecules can’t go any slower than not moving at all. And that is what absolute zero is.
I can’t answer your question, but I wish your thread title was more descriptive so I’d have known that before I bothered to open it.
I’m just guessing, but they probably mean that the water vapor in your breath would freeze so fast that it would turn into ice crystals and fall to the ground right in front of you. -90º (either F or C) is probably cold enough that such a thing could happen.
FTR, -90ºF is equivalent to about -68ºC, but -90ºC is equal to -130ºF. Has it ever gotten that cold on Earth?
Slight nitpick. At absolute zero, molecular motion does not stop, but is at a minimum (“the ground state”).
From Wikipedia:
Well…
Damn. One degree off.
The company I work for did a project in Alaska before I started there. Some of the people that were there at the time have told some interesting stories. One of the things I was told by more than one person is that if you take a cup of coffee outside and throw it, it freezes instantly. It doesn’t go plopping to the ground though. Instead it kind of freezes into a dust cloud of ice coffee particles and blows away. You never see it hit the ground, it just sort of disappears.
I imagine your breath (possibly your last breath under those circumstances) would do the same thing. It would be like watching the water vapor freeze in your breath on a cold day, which most people have experienced. I doubt anything would hit the ground.
When 100% of atoms and molecues are in electronic, rotational and translational ground states then motion has stopped.
There’s a previous thread on this, with links to articles saying that thrown water can freeze before hitting the ground. In that thread, ftg posted about seeing ice crystals from his breath sparkling in the sun; I’ve seen that myself.
I’m sure I remember another thread in which somebody here tried throwing water, and posted links to pictures of the experiment. Unfortunately, I can’t find it.
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Careful there — in quantum mechanics the lowest possible energy of a harmonic oscillator is not zero. From here:
So at absolute zero, the particles aren’t necessarily sitting in their equilibrium positions with zero momentum. What they actually are doing is more complicated to explain, and would be a tremendous derail of the OP, but suffice it to say that it all falls under the mantra “Quantum mechanics is weird.”
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Well, technically yes, but not due to natural effects, and not on a large scale. A temperature in the micro-Kelvins (the number i seem to remember is 7uK) has been reached, and probably surpassed by now. This was done to atoms in a magneto-optical trap, or “optical molasses.” In fact, the 1997 Nobel prize in Physics went to Bill Phillips, Claude Cohen-Tannoudji, and Steven Chu for that experiment. I suppose that they and other groups have dropped the bar since then.
Also, i second MikeS on the lowest energy state of a quantum Harmonic Oscillator. I’m not a thermodynamics buff, but i’m pretty sure that absolute zero refers to the point at which classical motion stops. However, as far as i know nobody has ever proposed a theory that suggested quantum fluctuations would cease at any temperature.