"Brute force attacks against 256-bit keys will be infeasible until computers are built from something other than matter and occupy something other than space".
-Bruce Schneier
"I can state flatly that heavier than air flying machines are impossible."
Lord Kelvin, 1895
Brute force, so checking every combination, makes some pretty easily verifiable claims.
If you build a supercomputer that occupies a space of only 1 cubic centimetre, that can brute force 1 trillion keys a second, and cover the entire earths surface with these computers, the Sun will swallow the Earth, before you have time to search the whole 256 bit key space.
I have also seen other calculations that information represented as its absolute minimum energy in the laws of physics, that there is not enough energy in the Sun to search a 256 bit key space either.
These numbers have nothing to do with the technology of the devices; they are the maximums that thermodynamics will allow. So these Laws of Thermodynamics will have to be broken first.