SPACE.com: Your book is largely about how the forces of nature are "fine tuned" for our form of life to exist, and how different strengths to these forces would not have allowed humans to evolve. But since we don't understand all the forces of nature, such as dark matter, dark energy and quantum gravity, can we ever really know what a universe with different traits would be like?
Martin Rees: It is of course hard to conceive how 'alternative' sets of physical laws could manifest themselves -- we can't even envisage more than a tiny fraction of what is allowed by the actual laws of physics. Of course we mustn't be too anthropocentric: there could be complex evolution of a type very different from life as we know it. However, I think we can, with some confidence, say that there are some universes that would not be biophilic: for instance, no complex entities could evolve in universes that lasted only for a short time, that were always in thermal equilibrium, that contained nothing but radiation, or that had only two spatial dimensions.
Can you define what you mean by different universes? What are the possible types that have been conceived?
Several theorists have speculated on different lines. There's the concept of 'eternal inflation' due to Linde and others, in which big bangs recur repeatedly in an ever-expanding substratum. Some theorists have conjectured that new 'big bangs' could sprout inside black holes. And there is the idea that there could be a 4th spatial dimension, so that other universes could exist just a few millimeters away from us in a dimension we can't penetrate (since we are 'imprisoned' in three spatial dimensions). There is also the rather different idea of 'parallel worlds' which some people believe offers the best interpretation of quantum mechanics. Even if other universes existed, we would still need to ask whether they are replicas of ours, or if different laws could govern them.
Do you think we might ever be able to observe other universes in some kind of detail if they exist?
Some variants would allow a gravitational interaction with other 3-dimensional spaces; but other ideas suggest that they could be completely unobservable. Even in the latter case, we might still come to have confidence in the existence of 'other universes' if they were a consequence of a theory that gained credibility by accounting for things that we can observe. By analogy, we already believe in (unobservable) quarks within atoms because they help us to explain aspects of particle physics that would otherwise be mysterious. I'd like to add a semantic point. We should really, of course, use the word 'universe' for 'everything there is', If there's really a multiverse, we'd then need a new word (e.g. metagalaxy) for what astronomers traditionally call 'our universe'. But for the moment, while the whole idea remains conjectural, I think it's best to stick to the usual definition of 'the universe', even though this necessitates a new word 'the multiverse' for the grand ensemble that would make up the entire cosmos.
Might there not be universes that were even better for our kind of life? What might they be like?
There could be universes governed by a 'richer' set of laws that allowed even greater complexity than ours -- but obviously our brains couldn't readily conceive of these. Indeed we can't conceive of all the complexity that could emerge within our own universe during its (perhaps infinite) future evolution.
You write about the possibility that reality is so vast that exact duplicates would have to exist. Isn't this more like science fiction than real science?
No. If our universe was infinite, then all combinatorial options would indeed recur (actually, they'd recur infinitely option). However, as I discuss in 'Our Cosmic Habitat' the nearest duplicate of our Earth would lie far beyond any accessible horizon. To imagine that we could ever visit, or even observe, a 'duplicate world' would indeed be in the realm of science fiction.
What most upsets you about science or scientists?
I find scientists, in general, rather less upsetting and more congenial than many other categories of people (I won't specify which). But of course there are some who are over-dogmatic, and are unduly disparaging of non-scientific modes of thought and knowledge.
What is the most beautiful aspect to space?
Within 10-20 years, when we look up at the stars, we'll view each one not just as a 'point of light' but as a 'Sun' with a retinue of orbiting planets. In many cases we'll know the orbits and properties of these planets -- children will learn these, just as they now learn about the nine planets orbiting our Sun. The cosmos seems more fascinating as our observations probe it in richer detail.
If you controlled a $1 billion foundation, what research effort would you fund?
The responsible answer would be to spend a lot of it on research into tropical diseases (less intensively studied than 'diseases of the rich'). And if it weren't already generously funded I'd certainly be fascinated to support brain research (especially into physical correlates of creativity, aesthetic appreciation, etc) but if I were allowed to spend some on currently underfunded areas of fascinating intellectual enquiry, I would choose the SETI program.
Why should we spend money on space exploration over research into deadly diseases?
We should obviously give high priority to medical research -- as indeed we do. The relevant question is whether we should fund scientific exploration as well -- whether it's more worthwhile than the most marginal other forms of inessential (public or private) expenditure. The resources needed are modest in that perspective. The largest telescope costs less than has been spent on a single advertising campaign for a rebranded soft drink; comparable amounts were wasted on painting and then unpainting the tailfins of British Airways planes. (And one could give dozens of examples). And I'd guess that the people attending a science fiction movie be happy that part of the tax revenues should be spent on science.
What is the most vexing question in modern science?
Hard to give a single answer. The one I suggest in 'Our Cosmic Habitat' is (in Einstein's poetic language) 'Did God have any choice in the creation of the universe?' Others are: 'How did life begin?' and 'is life widespread in the universe?'
