There may be aliens in our Milky Way galaxy, and there are billions of other galaxies. The probability is almost certain that there is life somewhere in space.
The stars look the same from night to night. Nebulae and galaxies are dully immutable, maintaining the same overall appearance for thousands or millions of years. Indeed, only the sun, moon and planets - together with the occasional comet, asteroid or meteor - seem dynamic.
Who are we? We find that we live on an insignificant planet of a humdrum star lost in a galaxy tucked away in some forgotten corner of a universe in which there are far more galaxies than people.
String theory has the potential to show that all of the wondrous happenings in the universe - from the frantic dance of subatomic quarks to the stately waltz of orbiting binary stars; from the primordial fireball of the big bang to the majestic swirl of heavenly galaxies - are reflections of one, grand physical principle, one master equation.
It's everywhere, really. It's between the galaxies. It is in this room. We believe that everywhere that you have space, empty space, that you cannot avoid having some of this dark energy.
For example, if the big bang had been one-part-in-a billion more powerful, it would have rushed out too fast for the galaxies to form and for life to begin.
Traditional science assumes, for the most part, that an objective observer independent reality exists; the universe, stars, galaxies, sun, moon and earth would still be there if no one was looking.
There are at least as many galaxies in our observable universe as there are stars in our galaxy.
The ultimate aim of all science to penetrate the unknown. Do you realize we know less about the earth we live on than about the stars and the galaxies of outer space? The greatest mystery is right here, right under our feet.
The principal reason for the universe's poker face is that its constituents are far away. Stars careen through space, and galaxies spin at speeds thousands of times faster than a jet plane. But given their distance, you'd need the patience of Job to notice much change in their appearance or position.