Timeline for Did NIST fudge this news story about absolute zero?
Current License: CC BY-SA 3.0
18 events
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| Jan 20, 2017 at 6:08 | history | edited | DanielSank | CC BY-SA 3.0 |
added 222 characters in body
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| Jan 19, 2017 at 21:29 | comment | added | Emilio Pisanty | Of course, this is all just in-theory, but then so is the third law of thermodynamics ('can never reach absolute zero in a finite number of steps', but it doesn't say anything about procedures that take $10↑↑↑↑↑↑↑↑10$ steps, which I think you'll be equally uncomfortable with). The question is at heart a theoretical question about the third law, so I don't see how those arguments are irrelevant. | |
| Jan 19, 2017 at 21:19 | comment | added | DanielSank | @EmilioPisanty I think everything you're saying would be correct if the map between theory and real life were arbitrarily accurate. See my comments on your answer. | |
| Jan 19, 2017 at 21:17 | comment | added | Emilio Pisanty | @DanielSank The way I see it, saying $T=0$ means that the phase-space volume occupied by the state has collapsed to a single, mathematical point: no matter how precise my measurement instrument, I will never observe the system away from that point. Saying $T=\delta T>0$ means that there exists (in principle) an instrument that will be able to resolve that phase-space cloud (/not-quite-pure quantum state). If $\delta T$ is tiny then I will need to work correspondingly hard to detect it, but if it's zero then I will never resolve it. | |
| Jan 19, 2017 at 21:16 | comment | added | DanielSank | @EmilioPisanty I guess I don't understand why $T=10^{-10^{10000}} $K is different from $T=0$. Are there real, not just in-theory phase transitions that only happen at $T=0$? My experience has been that this sort of thing never actually happens because e.g. phase transitions are always rounded off by finite size effects and coupling to the environment, etc. | |
| Jan 19, 2017 at 20:53 | comment | added | Emilio Pisanty | @DanielSank uh... one of them is consistent with the third law of thermodynamics and the other one isn't? $T=0$ and $T>0$ look very different to me, no matter how small a positive temperature you've got. | |
| Jan 19, 2017 at 20:07 | comment | added | DanielSank | @EricTressler Yes I understand that distinction, and for mathematics it's an important one. For a physical system, I think this distinction is unimportant. | |
| Jan 19, 2017 at 20:03 | comment | added | Eric Tressler | @DanielSank They're logically different. Saying "I can get arbitrarily close to 0" means "for any epsilon > 0, I can reach a temperature below epsilon". That does not imply that I can reach 0. | |
| Jan 19, 2017 at 18:41 | comment | added | DanielSank | @EmilioPisanty please explain how those are very different. | |
| Jan 19, 2017 at 9:37 | comment | added | Emilio Pisanty | Also, it's important to note that "arbitrarily close to absolute zero" is very different to actually reaching absolute zero. | |
| Jan 19, 2017 at 9:35 | comment | added | Emilio Pisanty | Just to mesh with other standard terminology, I imagine this 'quantum backaction limit' is not the Doppler limit (i.e. $\hbar \Gamma$ in energy) but rather the Sisyphus cooling limit (i.e. $\hbar k$ in momentum)? | |
| S Jan 19, 2017 at 9:15 | history | edited | DanielSank | CC BY-SA 3.0 |
homophone correction
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| S Jan 19, 2017 at 9:15 | history | suggested | Neil_UK | CC BY-SA 3.0 |
homophone correction, and gratuitous zero-effect formatting to get to the character count
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| Jan 19, 2017 at 9:04 | review | Suggested edits | |||
| S Jan 19, 2017 at 9:15 | |||||
| Jan 19, 2017 at 8:00 | comment | added | zeldredge | And note that conventional laser cooling (Doppler, Sisyphus, etc) does have such a hard limit set by the atomic transition in question, so having a cooling technique which is not fundamentally limited is a significant advance. | |
| Jan 18, 2017 at 23:26 | comment | added | user140606 | +1 I learnt an (embarrassing large) amount from your answer, ta for posting it. | |
| Jan 18, 2017 at 23:20 | vote | accept | Sasha | ||
| Jan 18, 2017 at 23:16 | history | answered | DanielSank | CC BY-SA 3.0 |