Do aliens exist? If they did, would we know? | NASA astronomer Michelle Thaller | Big Think

One of the biggest questions is, could there be other life besides us out there in the universe? And I think pretty much every scientist I know feels that there must be. I mean, just simply the numbers— in our galaxy alone, there are half a trillion stars. And we're now beginning to realize that nearly every star has its own solar system. So at the very least, our single galaxy has hundreds of billions of planets. And some of the stars out there are even older than our sun. There may have been a chance for a civilization to start billions of years before life began on earth.

And if that's true, could there be alien civilizations out there that are far more advanced, technologically, than we are? The unfortunate thing, of course, is we have no evidence of this. They're not making it very obvious. So is there a way that we might be able to see some of, at least, the artifacts of one of these super-civilizations around a distant star?

And one of the people who thought about this in a really wonderfully scientific way was a man named Freeman Dyson. And his name got lent to something called a Dyson sphere. And what a Dyson sphere is— the idea is that a very advanced civilization would probably need a lot of energy. And one of the best sources of energy is solar energy, the energy of their star that they orbit around. But instead of waiting for that starlight to come all the way to a planet, and to get put into little detectors and solar cells, what if civilization was a little bit more assertive about that, and actually went to the star and built giant collectors around that star?

The idea of a Dyson sphere is probably a bit extreme, because some people wondered if a civilization could build an entire shell around a star. And that shell would collect all of the radiation available from that star that they could use for whatever alien purposes in their super-advanced civilization. A lot of people have suggested that maybe a shell wouldn't be stable. It would be very hard to keep that actually working and orbiting around a star. So maybe you could make a giant grid of huge collectors that would orbit around the star and pick up as much radiation as possible.

So a Dyson sphere, or sort of the equivalent of that, there being many, many orbiting detectors around a star, is a wonderful idea in science fiction. The question is, is there a way you could detect one of these? And for some time, actually, people have wondered, what if you saw a lot of infrared radiation, heat radiation, coming from a star-like object, but you didn't see any visible light?

Is it possible that there was a shell of material around that star used to collect all of its energy, and that shell was getting warm because it's around the star, but it wasn't letting any light through? There are very serious scientists who proposed looking for star-like objects that just have heat, but no light associated with them. Unfortunately, we never found any of those either.

A couple years ago, however, something very dramatic happened. And it happened as part of the Kepler mission. This was a mission that was looking for planets around other stars. And the way Kepler looked for planets is it basically looked at a part of the sky where you could see a couple hundred thousand stars all at once, and it just stared at that for years. The telescope never moved. It looked at the same part of the sky for a very, very long time.

And then over time, scientists looked to see if the starlight varied. Over all of these stars, could each star be varying as a planet went around and made a little eclipse so that the planet has to be lined up perfectly along our line of view—but that can happen, there's a lot of planets in many different orientations around the stars in the sky. So if what's lined up perfectly, you would see a little eclipse. The planet would go in front of a star. You wouldn't see the planet itself, but you would notice the starlight drop. The star would get a little dimmer.

So what happens if you notice that a single star in that field gets a little dimmer every three...