There could be whole antiworlds and antipeople made out of antiparticles. However, if you meet your antiself, don’t shake hands! - Stephen Hawking

The eventual goal of science is to provide a single theory that describes the whole universe.

[on the possibility of contact with an alien civilization]: I think it would be a disaster. The extraterrestrials would probably be far in advance of us. The history of advanced races meeting more primitive people on this planet is not very happy, and they were the same species. I think we should keep our heads low.

There's a sick joke that the reason we have not been contacted by an alien civilization is that civilizations tend to destroy themselves when they reach our stage. But I have sufficient faith in the good sense of public to believe that we might prove this wrong.