Question: is the analogy of thermal energy as particles flying around and bouncing into each other just analogy? At what temperature would the particles fly at the speed of light? > Above about 10^32K, particle energies become so large that gravitational forces between them would become as strong as other fundamental forces according to current theories. I see, the gravitation would become a problem even before the s…
Absolute Hot
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Re: Absolute Hot
#22Question: is the analogy of thermal energy as particles flying around and bouncing into each other just analogy? At what temperature would the particles fly at the speed of light? > Above about 10^32K, particle energies become so large that gravitational forces between them would become as strong as other fundamental forces according to current theories. I see, the gravitation would become a problem even before the s…
Right, this was how I was taught about temperature, and I'm just realizing now it probably isn't the best analogy... Like, do particles shot through a particle accelerator have a super high temperature? They're moving awfully fast! Or does it have to be "vibration," in which case, "vibrating" relative to what?
Re: Absolute Hot
#23Looks like they found a way to measure my mix tape
If this were reddit I would've upvoted you, but this kind of cleverness should, if it constitutes the whole post, should be left to reddit. Now, should this thread ultimately hehehe a discussion on the virtues and approaches to creating mixtapes it would be another thing, but at this point in time I'm not seeing this as a positive contribution to discussion. That is why I downvoted your genuinely amusing comment.
Re: Absolute Hot
#24See also: https://en.wikipedia.org/wiki/Negative_temperature
Re: Absolute Hot
#25See also: https://en.wikipedia.org/wiki/Negative_temperature
So +0K is the lowest low, and -0K is the highest high.
Re: Absolute Hot
#26Question: is the analogy of thermal energy as particles flying around and bouncing into each other just analogy? At what temperature would the particles fly at the speed of light? > Above about 10^32K, particle energies become so large that gravitational forces between them would become as strong as other fundamental forces according to current theories. I see, the gravitation would become a problem even before the s…
You can't accelerate anything to the speed of light without an infinite amount of energy. It just takes more and more energy to get closer to that speed. https://en.wikipedia.org/wiki/Speed_of_light#/media/File:Lor...
Re: Absolute Hot
#27Re: Absolute Hot
#28Question: is the analogy of thermal energy as particles flying around and bouncing into each other just analogy? At what temperature would the particles fly at the speed of light? > Above about 10^32K, particle energies become so large that gravitational forces between them would become as strong as other fundamental forces according to current theories. I see, the gravitation would become a problem even before the s…
In physics we talk about the "degrees of freedom" of a system -- this is just the count of all of the independent ways that it can move. For each degree of freedom of a system you can calculate the average energy in that degree of freedom. By the equipartition theorem, at thermal equilibrium, all the degrees of freedom will have the same average energy, which will be T (if you measure temperature in units of energy).
So if you think about dropping a bouncy ball in a tube and it bounces until it slowly comes to rest, it has these degrees of freedom -- the internal degrees of freedom of the atoms of the ball, the internal degrees of freedom of the atoms of the floor/tube -- and then two really obvious degrees of freedom, the center-of-mass position of the ball, which gains an energy scale due to the gravitational force, and the center-of-mass momentum of the ball, which trades energy with this position degree-of-freedom.
Statistical mechanics says that as this system progresses, the location of the energy will slowly become more uncertain until it is on-average-evenly distributed across all of the degrees of freedom. That's why it bounces lower and lower: there is so much energy in the two "main" degrees of freedom -- maybe half a joule? -- whereas in the vibrations there is something closer to 10^-21 J of energy at room temperature.
But the flip side of dissipation is always fluctuation -- this is in fact the subject of a major theorem! So the fact that this can randomly lose energy to these other degrees of freedom means that those degrees of freedom are also randomly kicking the ball. As you can imagine with ~20 orders of magnitude difference between the two, they don't kick this ball by all that much. But you have a lot of experience with a lot more tiny balls that are bouncing off the ground all the time. Take a deep breath. There they are.
If everything were to come to its minimum energy configuration, why are these air molecules so stubbornly not falling to the floor? Well, they are trying to! But they are so light that they are being kicked back upwards by these random thermal kicks, so high that they can in principle go the many kilometers to the uppermost atmosphere.
(Of course if they could go all that way in a single kick then air would have to be so non-interactive that we could not use it to talk to each other... the mean free path in air is actually about 68 nm, so in practice every air atom is getting its random thermal kicks from other nearby air atoms. But the ultimate origin of these random thermal kicks is the random kicks of the floor on the few hundred nanometers of air sitting above it, and that energy comes from the Sun and is mostly conserved as these atoms collide with each other -- but a tiny bit is often converted to little photons of infrared light that sometimes escape the atmosphere.)
With that said as others have noticed, the free-particle energy relation in special relativity is E = γ m c². Famously, at rest, this factor γ = 1/√(1 − (v/c)²) is 1 and the energy of a particle at rest is E = m c². But as v gets closer and closer to c, v → c, this energy grows without boundary, E → ∞. So there is no finite temperature where a kinetic degree of freedom would exceed the speed of light. Indeed you can solve for v, as 1/γ² = 1 − (v/c)². So the velocity corresponding to any given total energy is v = c √(1 − (mc²/E)²). For a rest particle with E = mc² this is v = 0 as you would expect; or when the kinetic energy first gets to mc² we would have E = 2mc² and thus v = c √(3/4) = 0.866 c.
Re: Absolute Hot
#29Think of the quantum vacuum as having a large number of degrees of freedom waiting to get excited by energy -- like a fleet of unused AWS instances in a system with very effective load balancing. The moment the load (roughly, energy) on the running instances (particle present in the system aka "quanta") increases beyond the threshold for creating a new one (aka rest mass of a new particle), a new instance is spontaneously created. Heating the system is akin to increasing the load on your system, and new instances will keep getting spun up.
Is there a limit on how many such particle instances can be created? If we neglect gravity, no -- you can just keep adding instances/quanta and never run out. (and how much ever energy you dump in, the system's temperature will not increase beyond the Hagedorn limit [2])
But if you stop ignoring gravity, the gravitational attraction between the spun up instances will keep increasing as you spin up more of them, eventually forming a black hole at some point (because you cannot squeeze in more than a certain amount of information in a given volume [1]). This is roughly where you wave your hands and and come up with heuristic explanations using Planck length, Planck mass, etc.
That's the limit of current understanding. Any refinement to this story would be a massive breakthrough!
PS: A relatively sobering (nonetheless exciting) possibility is that much before gravitational effects become important, your "effective field theory" proves insufficient to model the system, and you are led to a "more fundamental" model.
[1]: http://scholarpedia.org/article/Bekenstein-Hawking_entropy
[2]: A technical explanation of the Hagedorn limit: At finite temperature, the occupation probability of states is exponentially decaying with energy (i.e. energy divided by temperature gives the log-probability) [3]. But, if the degeneracy of high-energy states grows exponentially, then that could entropically compensate for the exponential decay of the occupation probability, to have more occupation at higher energies than lower energies! The transition point in this tradeoff is the Hagedorn limit. That is why, additional energy is more likely to create new particles/states than simply increase the per-particle energy of the existing ones.
[3]: https://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_stat...
Re: Absolute Hot
#30Earlier quoted context omitted.
There's no finite level of kinetic energy at which the speed of an object exceeds c.
I believe you mean, "There's no finite level of kinetic energy at which the speed of an object equals c." Exceeding c is, of course, not known to be possible at all, even with infinite energy.