How heavy?
The heaviest.
How fast?
How heavy?
Let's say an electron, a particle we are all at least vaguely familiar with. Prasumably, all electrons must have arisen from a primordial vacuum at some point, no? And they last a hell of a long time, no?
If the assumptions on the ultimate origins of electrons are bogus, just humor me and assume I wanted to create one out of the vacuum of space. How long (rough order of magnitude and units) could it stick around and not violate various conservation laws? Would the answer also depend on how fast the particle was moving?