In science it is well known that the lowest temperature possible is 0K. However is it possible to put the same thinking into finding a theoretical highest temperature? Having researched this I found that there is no conclusive answer, merely several different popular theories on whether we can find this temperature. I also found that this is actually a very controversial topic in cosmology and theoretical physics with physicists from other professions steering well clear.
The first theory comes from the standard model of the universe with the theoretical temperature being the Planck temperature. The Planck temperature equals 1032 K or 100 million million million million million degrees. To put that in perspective that is around a billion billion times the largest temperature that physicists have ever dealt with. And these arenâ€™t day to day temperatures found on earth, these are huge energy events in the universe. In laymanâ€™s terms it is really really hot. In the standard model that relies on Einsteinâ€™s theory of general relativity this Planck temperature occurred 10-43 seconds after the big bang began. At this moment the length of the universe was 10-35 meters.
However this theory runs into a rather large problem. At these temperatures the laws of physics are more like guidelines. Space and time are concepts that we like to think of as understood. But physicists predict that the energies found in particles are so gargantuan here, leading to gravitational forces between them that are equivalent to all other forces acting on the particles. This is not what it sounds like, in fact gravity and the other three fundamental forces of the universe become a single unified force. No one knows why. Most physicists refuse to even speculate because not enough is known about the quantum nature of gravity.
The second theory is mainly based around string theory. It hypothesises that due to a theory called string gas cosmology, a theory pertaining to the start of the universe, the highest temperature is the Hagedorn temperature. The exact value of the Hagedorn temperature depends on which physicist you are talking to, the most widely accepted value being around 1030 K. The reasons for this value being too complex to explain in one article.
The third theory leans heavily on data collected from the Large Hadron Collider at CERN. It is one most controversial of the 4 theories here and if proved correct would change the face of physics as we know it. It is also heavily tied in with string theory and the fact that space-time exists in either 10 or 11 dimensions. These extra dimensions are either incredibly tiny, either strings or the Planck scale, or they could be on the TeV scale.
This is the point at which this theory ties into the LHC. Prominent physicist Stephon Alexander speculates that the temperature around the area that the LHC will be observing will be the highest temperature. The LHC will be working at 14 trillion electron volts, this is 1017K and is 15 orders of magnitude below the Planck temperature. That being said this is still 1 billion billion degrees.
The fourth and final theory is probably the most complicated and hardest to get your head around. It is a popular theory that the universe started off at the Planck temperature and then cooled as it expanded to produce this much colder larger universe that we know. However there is evidence to support a theory that the universe started off at absolute zero and then rose as it expanded. However physicists go a step further to say that both could have occurred, according to this theory, the physics at absolute zero is equivalent to that at the hottest theoretical temperature. Some believe that it is logical because below and above these temperatures physics begins to shift and change.
The problem with these theories is that there is so little actual raw data to support any of them. This means that conceivably all of these theories could be completely wrong. Classical relativity supports there being an infinitely high temperature at the beginning of the universe, as well as in the singularity of a black hole. The theories can become even more confusing, with one stating that once you get to infinity (a paradox but an attainable value in this theory nonetheless) you will then go through into negative infinity and back up towards 0K and so on.
To conclude although there are many theories, none can provide the clear proof that shows they are right.