Q: How big is the universe … and is it the only one?
Our cosmic horizons have grown enormously over the last century, but there is a definite limit to the size of the observable universe. It contains all the things from which light has been able to reach us since the Big Bang, about 14 billion years ago. But the new realisation is that the observable universe may not be all of reality. There may be more beyond the horizon, just as there’s more beyond the horizon when you’re observing the ocean from a boat.
What’s more, the galaxies are likely to go on and on beyond this horizon, but more interestingly, there is a possibility that our Big Bang was not the only one. There may have been others, spawning other universes, disconnected from ours and therefore not observable, and possibly even governed by different physical laws. Physical reality on this vast scale could therefore be much more varied and interesting than what we can observe.
The universe we can observe is governed by the same laws everywhere. We can observe a distant galaxy and see that the atoms emitting the light are just the same as the ones in the lab. But there may be physical domains that are governed by completely different laws. Some may have no gravity, or not allow for nuclear physics. Ours may not even be a typical domain.
Even in our own universe, there are only so many ways you can assemble the same atoms, so if it is large enough it is possible that there is another Earth, even another avatar you. If this were the case, however, the universe would have to be bigger than the observable one by a number which to write down would require all the atoms in the universe. Rest assured, if there’s another you, they are a very, very long way away. They might even be making the same mistakes.
Q: So how likely is alien life in this vast expanse?
We know now that planets exist around many, even most, stars. We know that in our Milky Way galaxy there are likely millions of planets that are in many ways like the Earth, with liquid water. The question then is whether life has developed on them – and we can’t yet answer that.
Although we know how via Darwinian selection a complex biosphere evolved on Earth around 4 billion years ago, we don’t yet understand the actual origin of life – the transition from complex chemistry to the first metabolising, replicating structures. The good news is that we will have a better idea of how that happened within the next ten or 20 years and crucially, how likely it was to happen. This will give us a better understanding of how likely it is to happen elsewhere. In that time, we will also have technologies that will allow us to better search for alien life.
But just because there’s life elsewhere doesn’t mean that there is intelligent life. My guess is that if we do detect an alien intelligence, it will be nothing like us. It will be some sort of electronic entity.
If we look at our history on Earth, it has taken about 4 billion years to get from the first protozoa to our current, technological civilisation. But if we look into the future, then it’s quite likely that within a few centuries, machines will have taken over – and they will then have billions of years ahead of them.
In other words, the period of time occupied by organic intelligence is just a thin sliver between early life and the long era of the machines. Because such civilisations would develop at different rates, it’s extremely unlikely that we will find intelligent life at the same stage of development as us. More likely, that life will still be either far simpler, or an already fully electronic intelligence.
On intelligence
Q: Do you believe that machines will develop intelligence?
There are many people who would bet on it. The second question, however, is whether that necessarily implies consciousness – or whether that is limited to the wet intelligence we have within our skulls. Most people, however, would argue that it is an emergent property and could develop in a machine mind.
Q: So if the universe is populated by electronic super minds, what questions will they be pondering?
We can’t conceive that any more than a chimp can guess the things that we spend our time thinking about. I would guess, however, that these minds aren’t on planets. While we depend on a planet and an atmosphere, these entities would be happy in zero G, floating freely in space. This might make them even harder to detect.
Q: How would humanity respond to the discovery of alien life?
It would certainly make the universe more interesting, but it would also make us less unique. The question is whether it would provoke in us any sense of cosmic modesty. Conversely, if all our searches for life fail, we’d know more certainly that this small planet really is the one special place, the single pale, blue dot where life has emerged. That would make what happens to it not just of global significance, but an issue of galactic importance, too.
And we are likely to be fixed to this world. We will be able to look deeper and deeper into space, but travelling to worlds beyond our solar system will be a post-human enterprise. The journey times are just too great for mortal minds and bodies. If you’re immortal, however, these distances become far less daunting. That journey will be made by robots, not us.
Q: What scientific advances would you like to see over the coming century?
Cheap, clean energy, for one. Artificial meat is another. But the idea is often easier than the application. I like to tell my students the story of two beavers standing in front of a huge hydroelectric dam. “Did you build that?” asks one. “No,” says the other. “But it is based on my idea”. That’s the essential balance between scientific insight and engineering development.