🚀 go-pugleaf

I would like to point out that that if you interpret the question originally
asked to mean "what would be different in the world if no particle ever
went at relativistic speeds", then there would be VERY noticeable differences
in the chemistry of all elements heavier than, very roughly, argon. This
is because the inner electrons in very heavy atoms are (in our real world)
quite relativistic. Any changes in the motion of inner electrons would produce
changes in outer electrons, where chemistry (and ordinary visible spectroscopy)
take place. For example, the spectrum of mercury would change dramatically,
since it is so heavy that the outer elecrons are a bit relativistic. Thus the
familiar ugly bluish glow of mercury street lights would change to some other 
color. The familiar smell of iodine would change. And, of course, since heavy
elements such as iodine, bromine, molybdenum and a few others are involved
in common life processes, many common things, such as nitrogen fixation by
plants, would not work, or would work in a modified way. It is far (and I 
mean really far) beyond the state of the art of computational chemistry to
predict exactly how things would change.

Doug McDonald
Professor of Chemistry
University of Illinois