Is there life out there? Are there other planets with intelligent beings? Or is Earth the only one? Science fiction stories are full of aliens, from Mister Spock to Yoda, but is there any real chance that anything even vaguely like these dreams could be real? The scientific facts of the matter are surprisingly optimistic.
Here on Earth, our bodies can function due to the laws of physics and chemistry. Our cells are made of atoms, mostly carbon, hydrogen, nitrogen, oxygen and phosphorus. Astronomers have discovered that when we point our telescopes out across the universe, we find these atoms everywhere. The stars are made of exactly the same types of atoms that we have here on Earth. When we study the most distant galaxies, billions of light years away from us, we find that these galaxies have the same laws of gravity, heat, light and energy that exist everywhere. The laws of physics and chemistry that allow our cells to work are the same throughout the universe.
And our universe is big: Our sun is just one star among several hundred billion other stars in our Milky Way galaxy. Our sun is a completely typical, average, ordinary yellow star. There are billions of other stars in the Milky Way that are absolutely identical to our sun, made of the same mix of atoms, varying only slightly in mass, size and temperature. Recent data from NASA’s Kepler space telescope tells us that most stars in our galaxy have planets, and that about 17 percent of stars have Earth-sized planets.
And our Milky Way galaxy is not alone. With current technology, we can see about several hundred billion other galaxies out there in the universe, and each galaxy contains an average of several hundred billion stars. So how many stars, how many suns, are out there in total? When we multiply several hundred billion stars per galaxy times several hundred billion galaxies visible, we get the following number: 100,000,000,000,000,000,000,000 stars. That number is enormous. It’s insanely big. It is far larger than the number of grains of sand on all the beaches on the face of the Earth. And every single one of those stars is a sun, probably with its own solar system of planets.
When we look at our neighboring planets, Mars, Venus and Mercury, we find that they are very different from the Earth, and very hostile to life. Here on Earth we have vast oceans of water, protected by a thick atmosphere, all held at a nice range of temperatures, which allows life to flourish.
The evidence of our neighbors tells us that most planets are probably not places where life could form. The Earth is probably rare. Perhaps only one Earth-sized planet in a thousand has an atmosphere and oceans like ours. Or could it be only one in a million? Or one in a billion? Our universe is so vast, with so many stars out there, so many places where life could have formed, that it overwhelms reasonable skepticism. Even if only one star in a TRILLION has an Earth-like planet with an atmosphere and oceans, that would still leave us with a hundred billion such worlds out there where life could form.
It is certainly possible that life is so rare in our universe, so distant, that our telescopes will not be able to find it in the foreseeable future. But there must be life out there somewhere. How could there NOT be life out there? How could we have a universe so large, with so many stars, where life formed only once?
Are we alone? Don’t bet on it.
Kelly Cline, Ph.D., is associate professor of astronomy and mathematics at Carroll College.