I would argue since it's in this loop, it can't really change its temperature. Otherwise the loop wouldn't close. And since also it adjusts to room temperature, it has be room temperature from the beginning all the time to avoid temporal paradoxes. According to the same logic, it doesn't crumble.
In panel 2, the dude has a pizza in his/her hand, and he/she has time to say "Now I have a free snack!" You don't think the temperature of the pizza would drop by even 0.1 degrees in that time?
If this object is permanently warmer than its surroundings, surely it can be used as a means to generate energy.
I would argue that there are infinite timelines of a room temperature "pizza slice" in various stages of decay, and eventually new reactions in the final two panels. If it reach room temperature, which it must, there is bacteria on that 'za.
So from the perspective of the pizza slice, it travels thru time and creates new timelines on the way, allowing even for different reactions from the people, for example once it's mouldy, they won't want it anymore and it stays in one timeline where it will rot eventually.
But: how did it start? I tried to avoid that question but making it timeless with no beginning and end, and no change to it what so ever, which comes with problems on their own. But giving it time, you also have to give it a start. I'm even fine with no end but you need a start. How hot was it in the first iteration?
There's no way to avoid a temporal paradox. Will the dude in panel 3 be able to smell the pizza? If so, there are microscopic particles from the pizza being emitted into the air. That means that by the time the pizza reaches panel 4, it won't be the same pizza that was brought into panel 2.
Yeah, even if it's a pizza enclosed in diamond so nothing can escape, surely they're putting fingerprints on it by handling it, so it will change from cycle to cycle.
Since it's stuck in a loop, maybe its conditions are somehow being reset to fresh and hot as it's pulled over the panel edge. Or else, that thing is ice cold, rock hard, and completely inhospitable to microbial life, since from its perspective, it's probably been looping for a long, long time.
From the naive perspective it's looping infinitely and it ought to be infinitely old because there's no "first loop". Depending on the laws of physics, proton decay could make the pizza slice literally impossible.
Given that it clearly exists and has no rot let alone deep-time decay, I posit that it spontaneously appears/renews in panel three, away from the boundary break, as some kind of near-infinitely improbable entropy break.
He thinks he's discovered panel time travel, but it's far weirder than he thinks.
If the pizza was taken a bite in panel 3, then it's also bitten in panel 4, then it's also bitten already in panel 2 because it's taken from panel 4, then it can't be bitten in panel 3. It contradicts with itself. The pizza cannot be bitten.
And now we know that the pizza can't be altered in any way. It can be large, hot, freezing, or small.
One, and only one scenario of these defies physics the least, and you know which one it is.