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In 1912, chemist Walther Nernst proposed that cooling an object to absolute zero is impossible with a finite amount of time and resources. Today this idea, called the unattainability principle, is the most widely accepted version of the third law of thermodynamics—yet so far it has not been proved from first principles.
Now for the first time, physicists Lluís Masanes and Jonathan Oppenheim at the University College of London have derived the third law of thermodynamics from first principles. After more than 100 years, the result finally puts the third law on the same footing as the first and second laws of thermodynamics, both of which have already been proved.
To prove the third law, the physicists used ideas from computer science and quantum information theory. There, a common problem is to determine the amount of resources required to perform a certain task. When applied to cooling, the question becomes how much work must be done and how large must the cooling reservoir be in order to cool an object to absolute zero (0 Kelvin, -273.15°C, or -459.67°F)?
The physicists showed that cooling a system to absolute zero requires either an infinite amount of work or an infinite reservoir. This finding is in agreement with the widely accepted physical explanation of the unattainability of absolute zero: As the temperature approaches zero, the system's entropy (disorder) approaches zero, and it is not possible to prepare a system in a state of zero entropy in a finite number of steps.
https://phys.org/news/2017-03-physicists-impossible-cool-absolute.html
[Abstract]: A general derivation and quantification of the third law of thermodynamics
(Score: 2, Interesting) by anubi on Friday March 24 2017, @05:53AM (12 children)
I get the idea if things are in discrete quanta, it oughta be able to quieten every one of 'em. Like getting every last marble out of a jar.
For this thought to be valid though, the quanta have to be indivisible.
Otherwise, its like trying to get every last speck of marble dust out of a jar. The division just keeps going on and on and on.
Attaining the speed of light seems to be the same problem, yet my flashlight supposedly emits photons traveling at that speed. Its quite puzzling to me why my flashlight does not create thrust.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]
(Score: 4, Interesting) by maxwell demon on Friday March 24 2017, @06:06AM (6 children)
Photons are basically like the marble dust: While each photon is an elementary particle, there are always photons with lower energy (that is, dust particles with lower dust), and while stable on its own, when interacting with matter, photons can be replaced by others with smaller energy (sort of like breaking dust particles to make smaller dust). As far as we know, a photon can have an energy arbitrary close to zero.
Your flashlight does create thrust. However that thrust is extremely small, therefore you don't notice it.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 3, Interesting) by aristarchus on Friday March 24 2017, @07:23AM (4 children)
I get the idea if things are in discrete quanta, it oughta be able to quieten every one of 'em. Like getting every last marble out of a jar.
For this thought to be valid though, the quanta have to be indivisible.
Otherwise, its like trying to get every last speck of marble dust out of a jar. The division just keeps going on and on and on.
Photons are basically like the marble dust: While each photon is an elementary particle, there are always photons with lower energy (that is, dust particles with lower dust), and while stable on its own, when interacting with matter, photons can be replaced by others with smaller energy (sort of like breaking dust particles to make smaller dust). As far as we know, a photon can have an energy arbitrary close to zero.
Interesting. Arbitrarily close, you say? Like no matter how much energy this photon has, it can always be halved? Have you met my friend from Elia? Zeno is his name, and he proposed, following his teacher Parmenides, that motion was impossible, since before anything could get where it was going, it would have to go half-way! And before it could go half-way, it would have to go half of half-way. And not to belabor the point, the moving thing could never get started, since it faced an infinite divisibility at the very inception. But our conclusion here, mutandis mutandum, is that everything is already at absolute zero, since it never could have left.
And my other friend, Aristotle, tried to take the opposite tack. I was never sure what was up with him, although I never met him in the flesh, he having died before I was born, but he seemed to think that infinite regresses of any sort were just, well, absurd. And thus any approach to an infinite was for him absurd. These scientists seem to be up against a similar presumption. So I have to ask, why not start with an infinite regress? Of course absolute zero has to be possible, for if it were not, non-absolute zero would equally be impossible.
I just love physics using only first principles. Maybe we should just use the term that Aristotle himself used for stuff like this: "Metaphysics".
And let me assert, for all you unreflective and unthinking materialists out there, this is not a bad word.
(Score: 3, Insightful) by maxwell demon on Friday March 24 2017, @07:59AM (3 children)
Well, a zero-energy photon is known as "no photon". OK, strictly speaking, the no-photon state would still have the zero point energy, but that isn't accounted for in the temperature so we can neglect that here.
And yes, if the universe would be globally at temperature zero, it would remain at temperature zero, thanks to conservation of energy (well, I'm not sure how General Relativity and the cosmological constant/dark energy would play into this, so let's ignore everything related to gravitation as well). But as far as we can tell, the universe never was at temperature zero.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 3, Funny) by aristarchus on Friday March 24 2017, @08:13AM (2 children)
When Zeno of Elea learned to do stand-up comedy, he would prove that motion is impossible. The paradoxes are well known, the Arrow, Achilles and the Tortoise, the Moving Ranks; but when it came right down to it, and people said, "Yeah, but things still move!", Zeno's reply was, "Who you gonna believe, logic, or your lying eyes?" As far as we can tell, eh? Do you think that is heat energy you are breathing?
(Score: 0) by Anonymous Coward on Friday March 24 2017, @01:04PM (1 child)
Friendly reminder that whoever states movement is an illusion deserves an imaginary kick in the balls.
(Score: 2) by aristarchus on Saturday March 25 2017, @06:12AM
Obvious rekickall, Of course you realize that "Ow, My Balls!" is a TV show, in the movie "Idiocracy", which is at least as many removes from reality as, well, as reality itself is from reality if it is at absolute zero balls.
(Score: 1, Funny) by Anonymous Coward on Friday March 24 2017, @09:37AM
I get the idea if things are in discrete quanta, it oughta be able to quieten every one of 'em. Like getting every last marble out of a jar.
That actually got an answer by maxwell demon?
I love this place :)
(Score: 0) by Anonymous Coward on Friday March 24 2017, @06:17AM
think of the flaslight as a radio.
the universe works faster then light. however we are made of the universe .., we are embed in it.
i believe the receiving elektron "knows ahead of time that a photon will hit.
just "seconds" before you turn on a flashlight all elektrons in the universe jump to an undetectabke state signaling to the elektrons in the flashlight bulb that they are ready to receive the photon that it will emit once you move (or pass electricity) thru the bulb.
anyways, if flashlights (and radios) dont generate thrust, why then is there a radio in every car?
;-)
(Score: 4, Informative) by stormwyrm on Friday March 24 2017, @06:38AM (3 children)
Numquam ponenda est pluralitas sine necessitate.
(Score: 2) by stormwyrm on Friday March 24 2017, @06:42AM
Numquam ponenda est pluralitas sine necessitate.
(Score: 4, Informative) by maxwell demon on Friday March 24 2017, @07:46AM (1 child)
No need to take such detailed assumptions. From E=pc you get dE/dt = c·dp/dt. Now dE/dt is the power of the light (which is upper bounded by the electric power you put into generating it), and dp/dt is the force generated.
So if you've got a one watt light source, neglect any losses, and assume perfectly directed light, you'd get about 3.3·10-9 N. The real force is of course lower since even LEDs lose about 75% of their energy as heat, [candlepowerforums.com] so a more realistic figure would be 8.2·10-10 N. A bit less, as the light is not perfectly directed.
Comparing with your calculation, this is about the power you get with 200 lumen. 200 lumen per watt is well in the range of LEDs, so everything seems consistent.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by maxwell demon on Friday March 24 2017, @07:46AM
Errr … s/the power you get/the force you get/
The Tao of math: The numbers you can count are not the real numbers.