Throughout history, many ideas have been discovered independently at the same time. Newton/Leibniz is the most famous example.

There are so many people looking over so much of the idea landscape that this seems like the norm rather than the exception. And if it's the norm, that means for any given groundbreaking idea there are likely a few people within a few years of discovering it.

It's impossible to know for sure, but it has interesting implications if it's true. For example, publishing first is more important than being correct in every detail.

I meant specifically for Einstein and Shannon. I’m not so sure anyone was right on the heels of Einstein, and at least physics seems to be full of discoveries that nobody even anticipated.

Lorentz and Minkowski were developing special relativity at the same time as Einstein (albeit in a mathematical context). And Hilbert arguably produced general relativity prior to Einstein as well.