Unfortunately, this a terrible name, concept, and even article.<p>The vast majority of it is directly from a pop-science NOVA episode and not actually well-backed.<p>There are reasonable bounds you can place on energy density where we expect current physical theories to stop making sense.<p>But energy density is not the same as temperature. It is true that for things like ideal gases, temperature is roughly "energy per degree-of-freedom", which is an energy density of sorts, but that's not fundamentally what temperature is.<p>Temperature is nothing more than a specific measure of how energy will flow due to entropic effects. In the right systems, this can be arbitrarily high without a high energy density. (In fact, elsewhere on this very post, people have pointed out "negative temperatures" where the temperatures become "hotter than infinity", they "wrap around" to negative.)
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?<p>> 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.<p>I see, the gravitation would become a problem even before the speed.
Ooh boy, quantum mechanics is <i>fun</i> :-)<p>Think 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.<p>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])<p>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.<p>That's the limit of current understanding. Any refinement to this story would be a massive breakthrough!<p>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.<p>[1]: <a href="http://scholarpedia.org/article/Bekenstein-Hawking_entropy" rel="nofollow">http://scholarpedia.org/article/Bekenstein-Hawking_entropy</a><p>[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.<p>[3]: <a href="https://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_statistics" rel="nofollow">https://en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_stat...</a>
Good answer from Physics SE on why there's no upper limit to temperature: <a href="https://physics.stackexchange.com/questions/1775/why-is-there-no-absolute-maximum-temperature" rel="nofollow">https://physics.stackexchange.com/questions/1775/why-is-ther...</a>
See also: <a href="https://en.wikipedia.org/wiki/Negative_temperature" rel="nofollow">https://en.wikipedia.org/wiki/Negative_temperature</a>
Hmm, at school we were taught that the maximum temperature is such that wavelength of the emitted black-body radiation would equal Planck length, is this rationale no longer sound?
This is an amazing video by vsauce called How Hot Can It Get and which deals with the same concepts. I very highly recommend it for everyone.<p><a href="https://youtu.be/4fuHzC9aTik" rel="nofollow">https://youtu.be/4fuHzC9aTik</a>
If you like this, you might enjoy:
<a href="https://en.wikipedia.org/wiki/Negative_temperature" rel="nofollow">https://en.wikipedia.org/wiki/Negative_temperature</a>
Planks Constant really changed my understanding of what the universe is made of.<p>Our physics and understanding of matter seems to be relevant under very specific conditions.<p>The moment we can make technology that can impact the smallest of sizes(if this is even possible), we might get an answer for what the universe is. Or maybe it would turn out to be "42" and it still wouldnt make sense.
Wouldn't fusion trigger at much, much lower temperatures?<p>We are talking about the theoretical limit of temperature, but what is the <i>practical</i> limit? There's a point beyond which heating hydrogen just gets you helium and more heat, but heating anything heavier than iron gets you something colder than the inputs.
This video is probably the best explanation
<a href="https://www.youtube.com/watch?v=oHyctwgE6m4" rel="nofollow">https://www.youtube.com/watch?v=oHyctwgE6m4</a>