“A definite yes - but the real question is "Do aliens exist close enough for us to ever discover them?”
You see, the thing is, space is unbelievably big. We've learned in the last couple of decades that planets are ubiquitous - pretty much every star in the cosmos has planets. What does that mean? Well our galaxy, alone, has around 400 BILLION stars - that's 400,000,000,000.
If each of those stars has five planets, that means we have two trillion planets in our galaxy alone (2,000,000,000,000). And there are more galaxies in the cosmos than there are planets in our galaxy - more galaxies than grains of sand on the Earth.
Each of those galaxies has billions of stars, and trillions of planets. In other words - there's an awful lot of real estate out there. With such an incredible variety of planets, and such a vast number of them to choose from, I find it impossible to believe that the Earth is the only one that has life - and the only place where intelligence and technology have evolved. But will we ever find it? That's actually the tougher question.
Imagine, for a minute, that life is so rare that only one star in a million has a planet that develops life. Well, that still means that life will be everywhere - in that scenario we'd have 400,000 stars in our galaxy that host life.
But what are the odds that any of those stars is close enough to us for us to detect that life? What if one in a billion stars gets technologically advanced life, like us, that can scream its existence out to the cosmos?
Well, that would give us 400 stars in our galaxy with technologically advanced life. But our galaxy is vast - 100,000 light-years from side to side. That's so big that, with 400 stars with communicative life out there, those stars would, on average, be something like 10,000 light years apart. That's way too far for us to hear alien signals - at least at the moment - unless they're way more powerful than anything we can send!
So - do aliens exist? I'm sure they do! But I think that finding them will be astonishingly hard. They'll be so distant that it's like looking for a needle in a haystack. But you don't know what a needle is, and you've never seen a haystack. I certainly don't think they keep visiting Earth to find out what humans had for dinner last night.”
Professor Jonti Horner is an astrobiologist and planetary scientist at the University of Southern Queensland’s Centre for Astrophysics.