Above all, I would not expect a wise race, at great expense, to set loose an army of self-replicating robots.

The sun and its retinue of planets drift as a group through the vast gulfs of space that separate the stars.

If interstellar travel is as time- or energy- demanding as the above figures indicate, it is far from obvious what the motive for colonization might be.

Years of science fiction have produced a mindset that it is human destiny to expand from Earth, to the Moon, to Mars, to the stars.

It would be a pity if, frustrated by the price of travel, we elected to become a society that never made contact, that never gave SETI a fair chance.

Present annual world energy consumption is about equal to the annihilation energy of 4 tons of matter.

Antimatter is not a source of energy for us, it’s a method of storing energy, compact but inefficient.

No one can deny the excitement of visiting another world.

Above all, I would not expect a wise race, at great expense, to set loose an army of self-replicating robots.

The factor most ignored in discussing interstellar flight is the kinetic energy that must be invested in the ship to make its tons of matter move at a substantial fraction of the speed of light.

In the past, on Earth, it has largely been to exploit foreign resources and to expand the domestic territory.