Martin Rees is Emeritus Professor of Cosmology and Astrophysics, at the University of Cambridge, the Astronomer Royal, a member of Britain's House of Lords, and a former President of the Royal Society. The following interview was conducted at Trinity College, Cambridge, by The Conversation's Matt Warren.
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 four 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.
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.
Q: Michael Gove [the British politician who was a leader of the campaign for the UK to leave the EU] said people have had enough of experts. Have they?
I wouldn't expect anything more from Mr Gove, but there is clearly a role for experts. If we're sick, we go to a doctor, we don't look randomly on the internet. But we must also realise that most experts only have expertise within their own area, and if we are scientists we should accept that. When science impacts on public policy, there will be elements of economics, ethics and politics where we as scientists speak only as laymen. We need to know where the demarcation line is between where we are experts and where we are just citizens.
If you want to influence public policy as a scientist, there are two ways to do it. You can aspire to be an adviser within government, which can be very frustrating. Or you can try and influence policy indirectly. Politicians are very much driven by what's in their inbox and what's in the press, so the scientists with the greatest influence are those who go public, and speak to everyday people. If an idea is picked up by voters, the politicians won't ignore it.
Q: Brexit – good or bad?
I am surprised to find myself agreeing with Lord Heseltine [former UK Conservative government minister] and Tony Blair [former Labour prime minister], but it is a real disaster, which we have stumbled into. There is a lot of blame to be shared around, by Boris Johnson et al, but also by Jeremy Corbyn [leader of the UK Labour party] for not fighting his corner properly. I have been a member of the Labour Party for a very long time, but I feel badly let down by Corbyn – especially as Labour voters supported Remain two to one. He has been an ineffective leader, and also ambivalent on this issue. A different leader, making a vocal case for Remain, could have tilted the vote.
On the other side, Boris Johnson [now UK foreign secretary – who campaigned for Britain to leave the EU] has been most reprehensible. At least Gove has opinions, which he has long expressed. Boris Johnson had no strong opinions, and the honourable thing to do if that is the case is to remain quiet. But he changed his stance opportunistically (as in the Eton debating society) and swung the vote.
Q: But why is it such a disaster?
My concerns are broad geopolitical ones. In the world as it is now, with America becoming isolationist and an increasingly dominant Russia, for Europe to establish itself as a united and powerful counterweight is more important than ever. We are jeopardising something that has held Europe together, in peace, for 60 years, and could also break up the United Kingdom in the process. We will be remembered for that and it is something to deplore.
One thing astronomers bring to the table is an awareness that we have a long potential future, as well as the universe's long past – and that this future could be jeopardised by what happens in the coming decades.
Q: More broadly, how much danger is the human race in?
I have spent a lot of time considering how we as a species can make it into the next century – and there are two main classes of problems. First, the collective impact of humanity as its footprint on the planet increases due to a growing population more demanding of resources. Second, the possible misuse by error or design of ever more powerful technology – and most worryingly, bio-tech.
There is certainly a high chance of a major global setback this century, most likely from the second threat, which increasingly allows individual groups to have a global impact. Added to this is the fact that the world is increasingly connected, so anything that happens has a global resonance. This is something new and actually makes us more vulnerable as a species than at any time in our past.
Q: So terrorism will pose an even greater threat in the coming century?
Yes, because of these technologies, terrorists or fanatics will be able to have a greater impact. But there's also the simple danger of these technologies being misused. Engineering or changing viruses, for example, can be used in benign ways – to eradicate Zika, for example – but there's obviously a risk that such things can get out of control.
Nuclear requires large, conspicuous and heavily-protected facilities. But the facilities needed for bio-tech, for example, are small-scale, widely understood, widely available and dual use. It is going to be very hard indeed properly to regulate it.
In the short and intermediate term, this is even more worrying than the risks posed by climate change – although in the long term, that will be a very major problem, especially as both people and politicians find it very difficult to focus on things further down the line.
I have been very involved in campaigns to get all countries involved in research and development into alternative, clean energy sources. Making them available and cheap is the only way we are going to move towards a low carbon future. The level of money invested in this form of research should be equivalent to the amount spent on health or defence, and nuclear fusion and fourth generation nuclear fission should be part of that.
Q: In the medieval world, people would start building cathedrals that only later generations would finish. Have we lost that long-term perspective?
That's right. In fact, one very important input behind the political discussion prior to the Paris climate agreement was the 2015 Papal Encyclical. I'm a council member of the Pontifical Academy of Sciences, which helped to initiate the scientific meetings which were important in ensuring that the encyclical was a highly respected document.
Whatever one thinks of the Catholic church, one cannot deny its long-term vision, its global range and its concern for the world's poor. I believe that the encyclical, six months before the Paris conference, had a big impact on the leaders and people in South America, Africa and Asia. Religion clearly still has a very important role to play in the world.
Q: Have you ever encountered anything in the cosmos that has made you wonder whether a creator was behind it?
No. Personally, I don't have any religious beliefs. But I describe myself as a cultural Christian, in that I was brought up in England and the English church was an important part of that. Then again, if I had been born in Iran, I'd probably go to the mosque.