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What is the Highest Possible Temperature?

Michael Anissimov
Updated May 21, 2024
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There is no agreed-upon value, among physicists, for a maximum possible temperature. Under the current best-guess of a complete theory of physics, it is the Planck temperature, or 1.41679 x 1032 Kelvins. This translates to about 2.538 x 1032° Fahrenheit. Since the current theories of physics are incomplete, however, it is possible that it could be hotter.

The answer that a typical physicist gives to this question will depend on her implicit opinion of the completeness of the current set of physical theories. Temperature is a function of the motion of particles, so if nothing can move faster than the speed of light, then the maximum may be defined as a gas whose atomic constituents are each moving at the speed of light. The problem is that attaining the speed of light in this universe is impossible; light speed is a quantity that may only be approached asymptotically. The more energy that is put into a particle, the closer it gets to moving at light speed, though it never fully reaches it.

At least one scientist has proposed defining the maximum possible temperature as what someone would get if she took all the energy in the universe and put it into accelerating the lightest possible particle she could find as closely as possible to the speed of light. If this is true, then discoveries about elementary particles and the size/density of the universe could be relevant to discovering the correct answer to the question. If the universe is infinite, there may be no formally defined limit.

Even though infinite temperature may be possible, it might be impossible to observe, making it irrelevant. Under Einstein's theory of relativity, an object accelerated close to the speed of light gains a tremendous amount of mass. That is why no amount of energy can suffice to accelerate any object, even an elementary particle, to the speed of light — it becomes infinitely massive at the limit. If a particle is accelerated to a certain velocity near that of light, it gains enough mass to collapse into a black hole, making it impossible for observers to make statements about its velocity.

The Planck temperature is reached in this universe under at least two separate conditions, according to some theories. The first occurred only once, 1 Planck time (10-43 seconds) after the Big Bang. At this time, the universe existed in an almost perfectly ordered state, with near-zero entropy. It may have even been a singularity, a physical object that can be described by only three quantities: mass, angular momentum, and electric charge. The Second Law of Thermodynamics, however, insists that the entropy (disorderliness) of a closed system must always increase. This means that the early universe had only one direction to go — that of higher entropy — and underwent a near-instantaneous breakdown.

The second set of conditions capable of producing the Planck temperature are those occurring at the final moments of a black hole's life. Black holes evaporate slowly due to quantum tunneling by matter adjacent to the black hole's surface. This effect is so slight that a typical black hole would take 1060 years to radiate away all its mass, but smaller black holes, like those with the mass of a small mountain, may take only 1010 years to evaporate. As a black hole loses mass and surface area, it begins to radiate energy more rapidly, thereby heating up, and at the final instant of its existence, radiates away energy so quickly that it momentarily achieves the Planck temperature.

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Michael Anissimov
By Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology, astronomy, chemistry, and futurism to his articles. An avid blogger, Michael is deeply passionate about stem cell research, regenerative medicine, and life extension therapies. His professional experience includes work with the Methuselah Foundation, Singularity Institute for Artificial Intelligence, and Lifeboat Foundation, further showcasing his commitment to scientific advancement.
Discussion Comments
By anon338515 — On Jun 14, 2013

The highest temperature ever achieved on earth is 7.2 trillion degrees! That is over 250,000 times hotter than the sun!

By anon329940 — On Apr 12, 2013

@anon262076-- Energy never "condenses" into matter.

By anon291007 — On Sep 12, 2012

Transmission of kinetic energy is a passive affair, so you can siphon-off energy to other molecules in a quest to reduce temperature, but I'm not aware of any way to make a substance 'steal' energy from another if its own energy already exceeds that of the target. If there was a way to suddenly reduce the kinetic energy of a molecule, you could then force that energy into another substance - that is the only way I can see this working.

non-scientist, just an interested thinker.

By anon262076 — On Apr 18, 2012

Surely the maximum possible temperature would be defined by color confinement, i.e., the point at which the excess energy in the matter essentially 'condenses' into new matter.

By anon241476 — On Jan 18, 2012

mc/3k=T where k is boltzmann's constant 1.381x10^-27

Learn it.

Basically, because heat is defined by the movement of molecules in a substance, and because nothing can exceed the speed of light, the average velocity of molecules in a substance at its highest temperature would be c.

In other words, the highest temperature possible depends entirely on the mass of the object in question and therefore, the only way to know it would be if everything in the universe were to smash together into a big ball and someone (while being part of that ball of stuff) were to know his/her exact mass.

Therefore, it's impossible for mankind to ever know the highest possible temperature in the universe.

By anon180028 — On May 25, 2011

Highest temp measure is depends on what substance in the whole universal can be converted into Energy. I guess!

By anon156493 — On Feb 27, 2011

@anon111478: anon120909 is referring to the equation:

E = 1/2 m v^2

Though at relativistic speeds, the energy would become mass. He's saying that temperature is dependent on kinetic energy.

This is true. Temperature can be thought of as a measurement of the "average kinetic energy of a randomly moving particle." If you assume that a particle other than a photon "packet" can reach a photon's scalar speed, then kinetic energy is dependent on the particle's mass. Using this equation is an oversimplification, but it shows the paradox of an "infinitely" small mass particle which approaches a photon's speed thereby approaching infinite "temperatures."

By anon142498 — On Jan 13, 2011

Space is the absence of matter. Matter cannot move faster than the speed of light; we are *assuming* that space is expanding but the point is moot, as it is the matter in space that we are looking at. Since there's matter out there, there has to be space to keep it in.

For all we know, the size of space (room in it, really) of the universe what established at the very moment the big bang created the dimensions it is in. Space, very probably, is infinite. If you want to adhere to space expanding from a null-point, you might be better off asking yourself 'What is the maximum speed of nothing?'.

Whether space or not is infinite is another moot point. If you managed to get 'past' all the other matter that's had a few billion years' head start on us, there'd be nothing to see. It'd be empty!

By Eric Hoskam — On Dec 05, 2010

I have a stupid question. If a particle reaches the speed of light, it gains more and more mass. Does it borrow or suck out this mass from its environment? And if so, then is it theoretically possible to borrow all the mass from the universe? In that case it should be the highest speed and temperature that is possible in this universe?

By webgrunt — On Oct 24, 2010

anon120909: I think the universe can expand faster than the speed of light because space expands with it--so it's able to expand faster than light as a whole, though nothing inside it is moving faster than light. I wish I could explain it better, but I don't understand it all that well myself--my point is that physicists have stated that the big bang theory is not incompatible with speed-of-light as a maximum possible velocity.

I, of course, don't know enough about it to judge that statement as correct or incorrect. If you can shed further light on this, please do so because I am curious about it.

By anon120909 — On Oct 22, 2010

The maximum temperature is easy to calculate. you simply take the kinetic temperature equation, and shove in c instead of v. Due to there being three variables, this would indicate that the maximum temperature achievable is dependent on mass. you could reach the maximum temperature of a substance more easily if it is lighter, because you will require a larger temperature to achieve the maximum with heavier molecules.

Surely though, this is going to be a flaw in the big bang theory, as you can relate the maximum temperature to the maximum energy achievable within our universe. if you take all the energy in the universe, this will be packed into a tiny space early on in the universe. once this becomes critical, there will be too much energy in the universe, and our understanding of what is occurring breaks down.

Surely, the universe cannot come from a point-like space, as it would totally violate the maximum velocity of anything within the universe. I think this is the proof that something is wrong - either you can go faster than the c, or the universe did not come from a point.

By anon111478 — On Sep 16, 2010

To anon90369: the formula for finding energy is e=mc^2, where e is energy, m is mass, and c is the speed of light. Since the speed of light is constant, if energy increases, mass needs to increase.

By anon90369 — On Jun 15, 2010

I'm intrigued. How exactly does adding energy adds to the mass of the particles at near-light speed?

By anon49438 — On Oct 20, 2009

what is the highest possible temperature in the whole universe? maybe in the brightest star? black hole or quasar?

By anon36155 — On Jul 10, 2009

What is the highest temperature actually measured on earth?

By anon19696 — On Oct 17, 2008

Petertlin, just to add to what Webgrunt just said. You must also realize that reaching absolute zero is a lot closer to our known temperatures than any absolute maximum. The highest measured man-made temperature was a approximately 2 billion kelvin by the Z-machine, not even remotely close to what's theoretically possible. However, your home freezer is only about 200 degrees celsius off of absolute zero. Not only that but to reach absolute zero you need to retract energy, to cool it down, and not add vast amounts of energy which is necessary to reach such high temperature as measured by the Z machine.

By webgrunt — On Aug 11, 2008

petertlin, About your comment that we don't hear about efforts to achieve a maximum temperature. We do, but it's not commonly described as such. Reaching the highest possible temperatures is what the superconducting supercolliders do. Rather than referring to these extreme temperatures as heat, articles tend to use words such as "energy" or "conditions in the universe a few (tiny fractions of a second) after the big bang."

This makes sense, because the energy state achieved is so intense, it's hard to even relate it to what we think of as heat.

Those extreme temperatures can't be created on a scale much larger than the atomic, or the radiant heat would vaporize everything around them. Achieving a really high heat is essentially what a nuclear bomb does, but with ounces of matter rather than single particles.

By anon9936 — On Mar 16, 2008

Metaphysically speaking, it would make sense that one cannot comprehend the greatest possible temperature. You see, from a Christian, yet somewhat scientific position, "our God is a consuming fire." And I chuckled to myself when I saw that the maximum possible temperature requires infinite velocity and zero mass because "God is Spirit" and "He is through all things and above all things". It would make sense, spiritually speaking that God Himself in a Judeo-Christian only sense is the absolute highest, and absolute zero is not far off from us, showing us via science that our existence is far lower and negligible than that of the spiritual (mass-less) realm, but God made us in His image, so we are promoted well beyond our current existence thanks to Christ Jesus. I am not unaware of how much disagreement these blanket statements will cause, but intuitively an infinite limit to highest possible temperature and the supreme nature of the eternal God is highly congruent. - Mark

By petertlin — On Jan 17, 2008

It is interesting that we hear so much about the quest to achieve absolute zero, but so little about any efforts to achieve a maximum temperature. I would guess that a lot of mysterious (and perhaps useful) phenomena would occur at extremely high temperatures, just as superconductivity and superfluidity occur near absolute zero.

Is there a reason why? I suppose this is more of an experimental question than a theoretical one. In other words, if we can create experimental conditions to approximate absolute zero, why shouldn't we be able to create conditions to approximate the "Planck temperature"? Intuitively, I can understand that absolute zero and the "Planck temperature" (or whatever the maximum temperature actually is), is purely theoretical and would imply a universe either at complete standstill (infinite mass, no velocity), or complete chaos (no mass, infinite velocity), so neither is achievable, but if one end of the spectrum can be approximated, I don't see why the other can't. Am I missing something?



By EdwardST — On Dec 11, 2007

Though a moving particle increases in mass, this relativistic mass does not increase gravitational strength thereby not contributing towards the production of a black hole. In a frame of reference stationary with respect to the object, it has only rest mass energy and will not form a black hole unless its rest mass is sufficient. If it is not a black hole in one reference frame, then it cannot be a black hole in any other reference frame.

Michael Anissimov
Michael Anissimov
Michael Anissimov is a dedicated All The Science contributor and brings his expertise in paleontology, physics, biology...
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