Quick disclaimer: I don't know much about physics, so I don't really know what I'm talking about.
The idea is that an object traveling fast enough in space will be receiving more radiation than it is giving off.
This is because time runs slower for the object which is traveling near the speed of light, and therefore it loses energy through thermal radiation slower than it is not moving.
The object, on the other hand is still receiving radiation from "outside" at the "normal" rate. From the object's perspective, the radiation "outside" is getting more and more intense as is speed increases, therefore it should heat up.
According to one hypothesis, the universe is going to end in a heat death where everywhere is the same temperature. But I can stop that by shooting an object into space near the speed of light, assuming it doesn't hit anything, it should continue to go forever gathering energy (from thermal radiation and CMBR) and breaking heat death.
Even if it's slowed down by resistance, by painting its front white and its back black should be able to keep it accelerated, as this will cause it to heat up the gas behind it more to push it forward.
That wouldn't work but there's should be a way to make sure heat is released to the back.
Another thing is it doesn't need to be even close to the speed of light, it just need to have be receiving more energy than it is being slowed down, so there is probably already a bunch of these objects zooming around in space.
If this works then why is it not thought about (that heat death is the most accepted hypothesis), or else can anyone explain what went wrong?