Brian Greene is a theoretical physicist and best-selling populariser of science who co-founded the World Science Festival in New York. Huw Spanner met him in March 2020 on a visit to London to promote his latest book, Until the End of Time, on ‘mind, matter and our search for meaning in an evolving universe’.
Galileo and others spoke of ‘the Book of Nature’. If you were writing a blurb for the back cover of that ‘book’, what would you say?
The Book of Nature is written in the language of mathematics but needs to be interpreted in the language of human reflection. And it’s only by virtue of these parallel stories that you get the fullest picture of the world.
You describe yourself as a ‘physicalist’. What’s the difference between physicalism and materialism?
I use them pretty much interchangeably. I am a physicalist who is committed to a reductionist perspective, which is itself committed to the notion that the rock-bottom description of reality is in terms of the most fundamental ingredients and the laws that govern them.
Some eminent scientists believe that the rock-bottom description of reality is that the universe was created. What do you make of them?
They may be right – but I see no evidence for it. Of course, a God who wanted to remain behind the scenes could certainly construct the world in such a way that that’s all that we would have direct access to; but that isn’t a perspective that gives me much insight into the day-to-day undertakings that I find fascinating.
So, at the back of my mind I allow for the possibility that all of our research is just revealing God’s handiwork and then I move on with the investigations that I’m able to carry out, which are the ones that access observations of stars and galaxies, that access experiments of particles and fundamental laws.
Is it fair to say that you choose to be a reductionist, or do you feel that actually any scientist who thinks rigorously is bound to be one?
That’s a hard question. Ultimately it is a personal choice, but framing it that way makes it seem as though there’s a shelf-full of possibilities and you just pick the one that appeals to you the most in some aesthetic or intuitive sense – and that diminishes the perspective in a way that I think is misleading. When I look at the power of the reductionist approach to describe so much about the physical world at a level of precision that is utterly overwhelming, I do feel that the perspective is so fundamentally convincing that I’m surprised when people are not drawn to it. But I know clear-thinking people who are not.
All the same, reductionism must be blended with the insights from higher levels of organisation – atoms to cells to brains to conscious reflection – to provide a full account of reality.
When I was a boy, there were electrons, neutrons and protons, four basic forces and the vacuum of space for them to interact in. It all seemed so simple – and the great quest was to simplify it further. But in the book you remark that ‘physicists now are very happy to imagine the universe full of invisible stuff.’ There is the inflaton field, the Higgs field, dark energy, dark matter – and current theories posit as many as 22 extra dimensions and a potentially infinite number of universes.
You seem to be able to countenance any kind of complexity but the simple and elegant idea of a transcendent mind.
I can understand where that reaction comes from; but the important thing to keep in mind is that there are two ways to judge the complexity of a physical theory. One way to judge it is by the qualities of the world that it implies; the other way is by the simplicity and elegance of the underlying mathematical structure. I would argue that it’s very important to focus on the latter and not the former.
You need to be careful not to allow your judgment to be clouded by the richness of reality that a very simple theory can yield. If you don’t speak mathematics and you don’t come from that world, the tendency is simply to look at all the strange implications. The world is incredibly rich and complex – I mean, you are made of trillions of particles that are interacting, with all sorts of particles being exchanged between them in fields that affect their motion – and yet underneath it is a simple mathematical equation, written down by Maxwell in the 1800s.
When it comes to the possibility of extra dimensions of space, that idea naturally emerges from the field I work on, string theory. And look, we don’t know that we have the fundamental mathematical equation for string theory yet, but the equation we use as a starting-point is so simple that you could write it on a T-shirt. Moreover, the basic equations of particle physics do suggest that there are invisible fields filling space, and when we then closely examine the world we find evidence of those fields.
One of the biggest discoveries of the last decade was the finding of the Higgs particle, which is a speck of the Higgs field, at the Large Hadron Collider in 2012. Simple math can yield the possibility of unfamiliar and hence seemingly complex qualities of reality.
You’re evidently a cultured person and I would guess that the things you value most in life are thought, imagination, love. In your reductionist worldview, you begin with the ‘laws’ of nature, the fundamental particles and forces, and then, by an inconceivably long process, you arrive at a life-form that is capable of love, of thought, of appreciating beauty. So, the things that you set the highest value on are actually the most utterly contingent –
Good, good. I understand what you’re saying.
– whereas for the theist it’s the other way round. Presumably, a transcendent mind could have imagined a cosmos that is constituted in a different way, but what it was working towards was one that would develop a life-form that was capable of love, thought and imagination. From that perspective, these things are the least contingent, the most essential, elements in the universe.
Does that idea not appeal to you?
If there was some evidence, I would find it enormously appealing. How beautiful that picture would be! But I come from a place where I look out at the world and I use observation and experiment and mathematics – and introspection – to come to an understanding of reality; and that understanding takes me to fundamental physics and the reductionist story.
From my perspective, it is a wondrous and beautiful fact that this hugely contingent (in the language that you’re using) development does yield conscious beings that can experience beauty and wonder and love and illuminate mystery. And that takes me to a place of gratification and reverence for this moment in the cosmological unfolding when these kinds of behaviours can and do take place.
So, it doesn’t in any way diminish for me the value and the wonder of what we humans are capable of. Quite the contrary! It aggrandises it by virtue of seeing it as the tail-end of this long, purposeless, meaningless cosmological unfolding that yields these beings that can then turn back and ascribe purpose and meaning to their lives.
That purpose and meaning being –
Of their own manufacture.
But the very concepts of purpose and meaning are their own invention –
Absolutely.
– and may therefore be worthless?
Well, my definition of ‘worth’ is tied to that idea ‘emerging from us’. To have purpose and meaning imposed on me by a God, however loving and well-meaning, to me feels quite limited when compared to it emerging from ourselves. That feels organic. To me, that feels more noble – that it comes from us, it’s of our own making, and it’s wondrous and beautiful nevertheless.
But you accept that wonder and beauty are –
Manufactured, artificial. Completely.
My dog seems to find fox shit beautiful.
Yeah. And you can’t argue with that. In his world, it absolutely is.
How does your understanding of the cosmos impinge on your daily life?
Well, at one level it doesn’t, because I go about the world in daily life just like anybody else does. I’ve got to take out the garbage, I’ve got to do the dishes, I’ve got to pick up the kids, right? But at the same time I often find myself being aware of a parallel story, and that can take many forms.
I sometimes really do think of myself as just a collection of particles inside a bag called ‘my skin’ that is meandering around the world encountering other bags of particles, both animate and inanimate. And that perspective – that physical law is moving my particles around and moving other particles around and we’re all just carrying out our quantum-mechanical marching orders – gives me a different insight into the world.
Sometimes I pull back and think about planet Earth in the ‘Pale Blue Dot’ picture, where we’re just this little collection of beings scrambling around on this rock that’s in orbit around this ordinary star in the suburbs of an everyday galaxy. And that gives me a different perspective, a kind of humbling perspective.
Sometimes, I take that a little further and I say: That’s all true – but look at what we’ve been able to understand and accomplish and think about – things that go well beyond the limits of planet Earth, that reach out to the stars and beyond. And that gives me a yet different perspective on things.
My view is that you need a collection of these ‘parallel nested stories’. And I do live my life within the collection of those stories in order to have the deepest experience of reality.
Where have you found you struggled most to get these ‘nested stories’ to fit together?
One of the deepest intuitions that we human beings have is that we have free will, and I think that the sharpest notion of free will – that we are the ultimate authors of our actions, our decisions originate within us – is incompatible with our understanding of the physical development of the world. And so I have come to the conclusion that to get the stories to blend in a consistent and coherent manner requires that we don’t trust that intuition of free will. We have to recognise that the sensation of freedom that we experience is a real sensation but does not accurately describe reality.
When we interviewed Richard Dawkins in 1995, we said: ‘Suppose some lads kill someone on the grounds that he was old and sick and didn’t contribute anything to society. How would you show them that what they had done was wrong?’
His answer was: ‘I think I would be fairly hard put to it to argue on purely intellectual grounds. I think it would be more: “This is not a society in which I wish to live and I’m going to do whatever I can to stop you.”’
When we suggested that they would reply, ‘This is the society we want to live in,’ he said: ‘I think I could finally only say, “Well, in this society you can’t get away with it” and call the police.’
I consider that a fine answer. The only thing I would add is that the laws that we have in a society are a product of the human brain experiencing reality and finding that certain behaviours are acceptable to group living and certain behaviours are not. And we come to that as a group.
There can be other groups in which those individuals’ perspective is the dominant point of view, but in this group (as in most groups around the world) the behaviour of killing the elderly is unacceptable for a number of reasons. We love the elderly. The elderly do contribute. The value of human life is something that we deeply respect and we simply don’t snuff it out because we have a whim to do so.
Most people in this group buy into that perspective, and that’s why it is the controlling perspective. And if you don’t like that perspective, go find another group that agrees with yours – and good riddance to you!
This interview is extracted from High Profiles, interviews which engage with people who help shape our world or the way we perceive it. Read the complete interview on High Profiles.
Brian Greene, professor of mathematics and physics at Columbia University, is co-director of the Institute for Strings, Cosmology and Astroparticle Physics. In 2008, with his wife, the US television producer Tracy Day, he founded the annual World Science Festival in New York. His latest book is Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe.
Photos: Luiz Munhoz/Fronteiras do Pensamento under CC BY-SA 2.0
