Transcription
If I was to guess, and this is a guess, right? If I was to guess why we see no evidence of other civilizations out there, the so-called great silence is what astronomers call it, is because there aren't any and there never have been any. That's my guess.
The reason I guess that, and I emphasize it's a guess, is biology. So, if you look at the history of life on Earth, then we see that life began 3.8 billion years ago, let's say. But then we see for the best part of three billion years on this planet that there's nothing more complex than a single cell. Three billion years. It's only in the last billion years or so, perhaps a little bit less, that multisellular life has existed on this planet.
And there could be good biological reasons for that. Um, one that springs to mind is the evolution of what's called the ukarotic cell, which is the cell with the cell nucleus and all little organels and chloroplasts and plants and all those things, which form all multisellular living things on the planet. Those cells which seem to be prerequisite for complex multisellular life evolved once on this planet as far as we can tell. It's pretty widely accepted. It's called the fateful encounter hypothesis. And so it seems that there was a very unusual evolutionary event at some point maybe a billion, a billion and a half, even two billion years ago that laid the foundations for us.
If that's typical, if it typically is the case that it takes 4 billion years from cell to civilization, then I think there may be very few planets in a typical galaxy which are stable enough for long enough for that process to to to proceed. And we could be, for all we know, on the fortunate end [laughter] of evolutionary time scales. We don't know.
Let's imagine that actually we were on the lucky side and really on a typical planet, there is such a thing, then it takes three or four times as long. That would exceed the current age of the universe. My guess is that whilst I think there might be microbes all over the place, I wouldn't be surprised. I'd be delighted, but I wouldn't be surprised if we found evidence of microbes on Mars, uh, Europa.