It is impossible to imagine a four-dimensional space. I personally find it hard enough to visualize a three-dimensional space!

Time and space are finite in extent, but they don't have any boundary or edge. They would be like the surface of the earth, but with two more dimensions.

The human race is just a chemical scum on a moderate-sized planet, orbiting around a very average star in the outer suburb of one among a hundred billion galaxies. We are so insignificant that I can't believe the whole universe exists for our benefit. That would be like saying that you would disappear if I closed my eyes.

I don't think the human race will survive the next thousand years, unless we spread into space.

I would like nuclear fusion to become a practical power source. It would provide an inexhaustible supply of energy, without pollution or global warming.

It matters that you don't just give up.

There is a very real danger that we will kill everything on this planet now that we have the technological power to do so.