He would probably have made it more difficult to weaponize nuclear fission. The prospect of atomic war horrified him.

He'd have sought out a way to mitigate time dilation and the power of radiation to cause mutations in living tissue so that it would be easier to build ships that could conceivably carry humans to the stars and back again within their lifetimes and allow them to report their findings to their peers and families.

And having seen and correctly modeled what happened millennia ago on Venus, I bet he would have laid the groundwork for a way to capture high-atmospheric carbon, and perhaps create useful and beautiful diamonds out of it.

Who knows -- maybe ways to achieve such things are out there and someone just has to think of them.

HUGE fan of Sagan, Hawking and their views of the universe! So much out there and Im certain we're not alone in the universe...

With no poverty, mental illness, cancer, diseases, and stupid people.