There is “absolute zero”, the point at which all molecular movement ceases. I believe that scientists have gotten to within 1/10,000 of the actual “absolute zero” figure, but it is impossible to ever reach it.
Is there an "absolute boiling" temperature? I guess it would be the temperature at which all matter is broken down into quarks or something. If I’m wrong, don’t hesitate to correct me.
Maybe Heat Death?
Or this page: Is infinite temperature possible?
At the pressure and temperature of the Big Bang, estimated to be on the order of six billion Kelvin, none of the “normal” particles which go to make up matter can exist other than virtually, causing the overwhelming composition of the Universe to be photons.
While it’s possible to conceive of higher temperatures than that, I fail to see how they would be physically possible.
With tongue only partly in cheek I’d ask, “What’s twelve billion kelvin like?”
I’m sure The Great One wrote about this… <searches> here it is: What is the opposite of absolute zero?
And to complicate matters further, you can also have negative temperature, which is hotter than any positive temperature…
(Although this can only happen in certain exotic configurations, that only have any application in theoretical thermodynamics. And in order to get a grip of that, you really need to understand what temperature is. - It’s not the same as heat! ) (interresting read from the Physics FAQ)