Conversation with Brian Greene
January series speaker discusses space, time and the texture of reality
Brian Greene Is a physicist, string theorist and writer.
Brian Greene is a physicist and also the author of the books The Elegant Universe and The Fabric of the Cosmos. He spoke at the January Series a few weeks ago, addressing a packed auditorium. Perspectives Co-Editor Adam Fleming Petty spoke with him before his lecture. With a lot of the work that you do with string theory, fabric of time, etc., it can be hard to grasp the long term implications of it. So, 100 years ago, Einstein was doing his first really experimental work, and a few years later it began having implications in things like atomic bombs and, unfortunately, with real-world applications. On that note, in another 30 or 40 years, what do you think could be some real world implications of string theory?
I have no idea, and the reason is that the scale at which our work really takes place is so tiny, compared to even atomic scales, and therefore compared to everyday scales, we’re talking ultimately microscopic, that it’s a little hard to imagine what the implications of our work might be. But, as you say, the history of science is replete with theoretical ideas, which at first seem to have no bearing on everyday life, ultimately having a big impact. Einstein’s ideas have had an impact on the global positioning system, quantum mechanics has had impact on everything – lasers, computers, CD players, medical equipment, huge number of applications. So, I don’t know if 30 years is the right time scale, or 100 years, but in 500 years, could these ideas make a difference? Could well be.So this work that’s being done is really at that preliminary stage.
Well, I would say it is at a very preliminary stage, but not at the measure of how long it will take for applications to emerge. It’s at a preliminary stage because the ideas are fantastically interesting and starting to be developed, but certainly rudimentary at our current level of understanding. I think that, within the next 10 years, there are going to be a number of leaps in our understanding. I feel like we’re on the verge of a number of different kinds of breakthroughs. The theory will begin to mature. How long that maturation process will be, that’s not what we can predict in science. We just go step by step and see where the ideas lead.These breakthroughs that you mentioned – that could be possible, if you wouldn’t mind giving one specific example of one theory that you find particularly interesting.
Well, in terms of breakthroughs within string theory itself, many of us anticipate that within the next decade or two, we’ll have new formulations of the theory which basically go beyond traditional ideas of space and time, and enter a new formulation in which space and time are viewed as secondary derivative concepts. Not primary concepts in the way that they are in formulations of Einstein’s theory and in current formulations of string theory. So what we look forward to is a day when we have spaceless, timeless theories, and the conventional ideas of space and time simply emerge as secondary ideas, when conditions are right. That, to me, is the biggest revolution that’s on the horizon.The idea that space and time are somehow secondary?
Yes. I mean, a good example that I like to use is an analogy. Think of temperature. Everybody knows what temperature is. You know what it means when things are hot, when things are cold – you can feel it, in everyday experience. But microscopically, we learn that temperature is a reflection of how fast molecules are moving. When molecules of air are moving very fast and they hit our skin, it feels warm. When the molecules are moving more slowly and they hit our skin, it doesn’t feel so warm, it feels cold. So we see that temperature is a secondary idea that relies on the more fundamental notion of how particles move. Similarly, space and time may be like temperature. Space and time may be secondary ideas that we all experience; we know what they are intuitively, but underneath space and time may be a more fundamental explanation in which space and time don’t appear, just as temperature has a more fundamental explanation in the movement of particles, in which the idea of temperature plays no role at the microscopic scale, but emerges on the everyday scale. Similarly, space and time may emerge on the everyday scale, even though the fundamental theory doesn’t involve the concept of space and time at the fundamental level. So space and time, as we observe them, are manifestations of deeper physical laws.
Precisely. And those deeper physical laws may be completely unfamiliar. I mean, if you lived in a world where you didn’t know about temperature and didn’t know about particles and their motion, if someone came to you and said, ‘Temperature is a reflection of the movement of the particles,’ that’d be mind-blowing. You’d learn about particles, you’d learn about how they move, you’d learn about their average motion being responsible for the things that you experience. A similar kind of mind-blowing development is on the horizon in string theory, I believe, as do many others. Because we’ll learn, we think, that space and time are founded on, as you say, fundamental laws of a deeper nature, but those fundamental laws will probably be of a completely different sort. We’ve never encountered a law that didn’t have space and time stitched within the law itself. We’re now seeking laws that don’t have space and time stitched within them. An idea that’s come through in a lot of string theory and the work that you do is the idea that there are several dimensions to the world as we perceive it. I believe the term you use, or that’s being used, is ‘multiverse.’ For a layman such as myself, and for many of the readers, it’s an idea that takes the imagination, but I’m not quite sure what exactly it means.
Sure. Let me distinguish between two ways in which those terms are used. Within string theory itself, there is this idea that there are more dimensions than the one that we can see. In everyday life we move through back and forth, up and down, left and right. We know about those dimensions. We can see them, we can experience them. The theory, however, claims that there are more dimensions than those, more directions, if you will, that you could move. An interesting question is, ‘Where are they?’ And we have some answers to that. The term ‘multiverse’ is often applied in a somewhat different setting. The multiverse idea imagines that we consider to be the universe would be just one smaller piece of a grander cosmos.
Think about a bubble bath. Imagine that our universe is one bubble in the huge bubble bath, and the other bubbles would be other universes. Put all those universes together and we use the term multiverse. So the multiverse suggests that there are many, multi, universes, and our universe is merely one among the plethora. If that is the case, then is there – and this is pretty speculative, from what I gather – is there any way to communicate with or observe these other universes?
In many situations, the answer is no. So you might ask, ‘Is that science?’ If you’re talking about things that are unobservable or beyond our ability to interact with. But there are some potential consequences in which we do, every now and then, interact with these other worlds. And in fact, one of these new notions gives a new version of how the universe began – that is, the Big Bang. We often imagine the Big Bang as some kind of cosmic explosion, out of which our universe was created. But if the multiverse idea is correct and implemented in a very specific way (may be right, may be wrong), but let me just throw out the specific ideas. For example, it could be that our universe collides with another one of these universes, every trillion years or so, and the force of that collision is what creates a Big Bang-like deposit of energy, that gives rise to a new beginning, every time the universes collide. So the idea, speculatively speaking, would be that our universe regenerates every trillion years or so when it collides, slams, into one of these other universes. So that would be a big impact on what we see in the world around us. But I need to stress that these are, at the moment, interesting ideas that people are developing the mathematical description for, but they’re completely speculative. I get the sense that a lot of the ideas that come from this work have to do with looking at mathematics on very close levels, and in very close detail, and that many theories are a consequence of that.
Absolutely. String theory is basically a mathematical undertaking where you follow where the mathematical analysis leads and try to draw conclusions about what it might mean to the world. Something that you’ve mentioned before is that, while this is certainly scientific, a lot of it is speculative and imaginative in nature. How do you imagine, as this becomes more concrete and accepted, what effect would that have on a more general level. Maybe in the teaching of physics, for example.
Well certainly, we already see that these ideas are starting to be taught, not just at the graduate level but at the undergraduate level. The most concrete example of that is there’s now an undergraduate textbook on string theory that people are starting to teach courses from. So it may be that, in the next few years, part of the standard undergraduate curriculum for those physics students who are going to focus on theoretical approaches may involve string theory, and I think we’ll see more and more of that. At a more general level, what I suspect that these ideas help us do is to understand our own place on the universe just a little bit better. And, while that doesn’t affect many people at a detailed, everyday level, I think the broad way in which we live our lives is ultimately impacted by this kind of understanding. So I think the impact may be subtle, but I think it will be there. Our place in the universe sounds like it could be ... well, certainly not central, and maybe even on the fringe, as it were. Getting away from the science of it and onto the effect that it has on people’s imaginations, in your experience, what is the effect of this idea that we’re one of many universes and there are many, many things that we can’t see? What effect does that have on the way humans view themselves?
I guess I would say that it emphasizes a lesson that has been in evidence previously, in the history of science, but never quite as vibrantly illustrated as with the current ideas, which is that there’s a level to reality which lies beneath the surface of everyday existence. Our eyes and our senses can tell us some things about the world, but it requires mathematical analysis to pull away, to lift the veils of obscuring materials that cover the true nature of reality and that’s what we’re heading toward. The lesson, therefore, is that the true nature of reality is not what we think it is. And that’s pretty startlingCertainly. As a closing question ... what has compelled you to go out and give lectures at places like Calvin College in Grand Rapids, Michigan? What about these ideas and this material makes you want to publish it for a wider audience?
I would actually slightly flip the question around. My view is that we have a fundamental urge, as a species, to understand the world that we live in. You look through the history of our species, and that’s in evidence. The sad thing is that, as we’ve gone deeper, the language that we’ve used to explore the universe has become ever more remote from everyday language. We use mathematics, and most people aren’t trained in mathematics, and therefore they’ve lost track of where we’ve gone in this search for the true nature of the world. So what I try to do, in a small way, is to allow people to rejoin the train of discovery, to rejoin our attempt to understand the world, because these ideas are compelling when explained at the conceptual level, stripping away the mathematics that many people find intimidating. So that’s basically the point, to allow the ideas to be taken in without requiring the person to go to graduate school. And, as evidenced by the packed auditorium, there are quite a few people who are interested.
Yeah, there are quite a few people interested and want to know about this stuff, and I don’t think that’s surprising. I think it would be surprising if we didn’t care, collectively. But we do, and I think that’s great.