Seems like an innocent enough question, right? Absolute zero is 0 on the Kelvin scale, or about minus 460 F. You can’t get colder than that; it would be like trying to go south from the South Pole. Is there a corresponding maximum possible temperature?
Well, the answer, depending on which theoretical physicist you ask, is yes, no, or maybe. Huh? you ask. Yeah, that’s how I felt. And the question doesn’t just mess with the minds of physics dummies like me. Several physicists begged off of trying to answer it, referring me to colleagues. Even ones who did talk about it said things like “It’s a little bit out of my comfort zone” and “I think I’d like to ruminate over it.” After I posed it to one cosmologist, there was dead silence on the other end of the line for long enough that I wondered if we had a dropped call.
I had touched a nerve, because, unbeknownst to me, the highest-temperature question gets to the heart of current inquiries and proposed theories in cosmology and theoretical physics. Indeed, scientists who work in these fields are zealously trying to answer that question. Why? Because, in some sense, nothing less than the future course of physics rests on the answer.
CONTENDER #1—1032 K
Certain cosmological models, including the one that has held sway for decades, the Standard Model, posit a theoretical highest temperature. It’s called the Planck temperature, after the German physicist Max Planck, and it equals about 100 million million million million million degrees, or 1032 Kelvin. “It’s ridiculous is what it is,” said Columbia physicist Arlin Crotts when I asked him if he could please put that number in perspective for me. “It’s a billion billion times the largest temperature that we have to think about” (in gamma-ray bursts and quasars, for instance). Oh, that helped.