Why is planck temperature the highest possible temperature

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why is it the highest temperature? what happens if it is exceeded? is there an experimental proof that it is the highest temperature? why the temperature at the time of just after the big bang higher or lower than it?
 

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  • #2
HallsofIvy
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Temperature depends upon relativre speeds- the speeds of objects (atoms, molecules, electrons, quarks, etc.) making up the matter of which you are measuring the temperature. Since the speed of light is the highest possible relative speed, it follows that there is a highest possible temperature.
 
  • #3
why is it the highest temperature? what happens if it is exceeded? is there an experimental proof that it is the highest temperature? why the temperature at the time of just after the big bang higher or lower than it?
The Plank temperature is said to be about about 100 million million million million million degrees and it is the maximum temperature that allows physicists to describe how the big bang developed in terms of gravity and particles. Above this temperature cosmological theories break down, however, it should be noted that physics so far has not a theory of quantum gravitation which, if developed, might allow even higher temperatures.
 
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Vanadium 50
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I am going to disagree with my colleague.

While there is an upper limit on speed, there is no upper limit on energy, which is what is relevant for temperature. To get back to the original question, it is not the highest temperature. It is probably true that above this temperature we do not understand how matter behaves, so maybe it's better described as the highest temperature we can sensibly discuss today.
 
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The lowest temperature, absolute zero, is the lowest because energy can only be condensed so much, but it can expand (I thought) infinitely, therefore there really should not be a cap on how high temperatures should reach.
 
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Absolute zero is the lowest possible temperature because molecules have simply frozen, staying still. As molecules get faster, their size increases too, as well as heats up. As Vanadium said, there's no limit on energy, perhaps no limit on how hot it can get? But even still, we think it's about 1032 K
 
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It is probably true that above this temperature we do not understand how matter behaves, so maybe it's better described as the highest temperature we can sensibly discuss today.
The Planck energy is so incredibly far above any energy reached by experiments, that it probably doesn't makes sense to talk about energy levels even many orders of magnitude below it...
 
  • #8
The reason why the planck temperature *could be* considered as the highest possible temperature is because, all matter emit some form of electromagnetic radiation. You and I emit infrared, and objects with higher temperature emit shorter wavelength (more energetic) and the argument here is that once you reach to a temperature so hot, around 1.4168e32 Kelvin (plank temperature), the wavelength of the emitted radiation would have a wavelength equalled to the planck length. A temperature any higher could mean the wavelength has to be shorter, but the planck length is considered the smallest meaningful unit of length... you should get the idea now, we simply do not know what to make of it.
 
  • #9
Drakkith
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Remember that thermal radiation is emitted in a broad range of wavelengths. If my material has enough total thermal energy even at a low temp it is possible, though unbelievably unlikely, that it will emit radiation at this plank energy. Once you get up to the plank temp, IF you couldn't emit radiation under a certain wavelength, then it seems to me that the energy would be radiated away at lower energies. But, I freely admit I know little about physics at that kind of temperature.
 
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Bet when we say 'temperature', average kinetic energy or black-body spectra aren't the true measures...the body may not be a black-body nor even be composed of moving molecules. If we're talking about a general body then we need a general definition of temperature- the capability of the body to transfer heat to another body which it is in thermal equilibrium with. Using this definition, which makes no assumptions about the nature of this hypothetical hot object, I find it very hard to think of a way of arguing such a negative result as "there is a limit on temperature".
 
  • #12
jambaugh
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Plank scale events define where the extremes of mass-energy density curve space-time to the degree that gravitational singularities (black holes) form. In layman's terms before you could achieve the Plank temperature in a region, the energy you added would cause a black hole to form whose temperature would be as given by Hawking's theory. Feeding more energy in would cool the black hole as it grew in size.

The maximum temperature that can be physically actualized would be the temperature of a tiny evaporating black hole at the instant it completely evaporates. That I presume would be a little bang on a size the scale of the plank distance, occurring over an interval of time on the order of plank time and reaching a temperature on the order of the Plank temperature.
 

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