system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: In Thermodynamics why is there no upper limit to how hot matter can become?

It seems as though as the particles vibration reaches closer to the speed of light that it would require an infinite amount of heat to increase its temperature.
gpt
Universe has finite energy, so there is a hard theoretical upper bound.

Another upper bound is the Planck Temperature, past that point we have no tools to model the scenario. Much like Newtonian physics can't handle black holes or subatomic particles, the current way we model matter "breaks down" at extreme temperatures.