Ok just kidding, we don’t know that. BUT scientists are looking into it! Spinning along in our Milky Way galaxy are billions of planets that are similar to Earth that astronomers have dubbed “Goldilocks planets” – not too hot, not too cold, but just right for life to evolve.
There are about 42,000 sun-like stars in the Milky Way alone, with 603 planets, 10 of which are earth-sized and orbit close enough to these stars to have liquid water. But these are just the ones they saw with the Kepler telescope:
“With an estimated 200 billion stars in our galaxy, the scientists have extrapolated that 40 billion of them are similar to our sun. With roughly one-fifth of those with Earth-size planets in the habitable temperature zone, it means ‘just in our Milky Way galaxy alone, that’s 8.8 billion throws of the biological dice,’ study co-author Geoff Marcy, from the University of California at Berkeley, told AP.”
And the Milky Way is just a drop in the galactic bucket: the Andromeda Galaxy has an estimated 30 trillion stars, and there are even more galaxies than the 30 that comprise our cluster. In fact, a recent German supercomputer simulation using information collected from the Hubble Space Telescope estimates there might be as many as 500 billion galaxies in the Universe, many older than our own.
With all of these Goldilocks zones in the universe, chances are astronomically high that we aren’t alone.