Quantum physicist David Deutsch describes why alternative universes may not just be the stuff of science fiction – and that’s why he loves Fringe
And it’s all nonsense, right? More sci-fantasy than something based on the latest revelations in New Scientist ?
Maybe, maybe not.
Meet David Deutsch, a “controversial” quantum physicist, scientific philosopher and writer, author of such books as The Fabric Of Reality and his latest (published earlier this year in hardback, and in January 2012 in paperback), The Beginning Of Infinity . A staunch believer in the esistence of alternate universes, he’s also found the way Fringe deals with the idea refreshing… even if it doesn’t quite fit in with the theories.
SFX: Do you genuinely believe alternative universes exist?
Deutsch: Yes. The alternate worlds are definitely there, in my opinion. We’ve done a lot of work on them, and although this a minority view among people who work on the foundations of physics, in my view it is the only known explanation for certain quantum phenomena. Other universes are definitely there, and the universe that we see around us is just one of countless numbers of such things that exist in reality. The whole of reality is therefore a multiverse, rather than just a mere universe.
But do they exist in the way we see them in Fringe ?
No. Not exactly. Some of the processes that are depicted in science fiction in general, and Fringe in particular, are ruled out by the very theory that tells us that these parallel universes are there. In particular, the ways in which these universes can affect each other are dramatically limited in real physics, whereas they are rather free with allowing for such things as travel and communication between universes in Fringe .
That’s perfectly alright in science fiction. What one does is look for a variant of an existing bit of science, and use that variance to probe what the real world might be like. So, for example, one of the things that philosophers have spent a great deal of paper and ink analysing is the issue of identity among different copies of the same person in different universes. You can discuss that in theory, but in a piece of fiction you can do better than that. You can say, “Supposing they really could cross over, as they do in Fringe, then to what extent do the slight differences in a person make them a different person?” And they explore that quite regularly in Fringe. They don’t come up with an answer; it’s too much to ask, perhaps. But they explore the question and show why it’s interesting.
There are ethical questions as well, presumably. In Fringe one universe wants to destroy the other. Can you actually be said to be killing people if they’re copies?
Quite so. Although this is done with fictional science, because in reality the universes can’t be created or destroyed. But in fictional science you can ask questions about what it means to be responsible for something. Let me give you an example. Whenever you make a decision to do something, what that really means is that vast numbers of you are facing the same decision all in different universes, and when you say that you definitely decided to do a certain thing, what you really mean is the overwhelming majority of copies of you chose that thing, and only a tiny proportion of copies that happened to get hit by cosmic rays or something made a different decision.
Now, when you do that, what you’re doing is making a whole set of events that could have happened not happen. Or to be more precise, you’re making a set of events that could have happened in a lot of universes not happen in very few universes. And this issue comes up in many different discussions about all sorts of things. Let’s say, abortion. People say, well how can it possibly be wrong to have an abortion at a time before the person has a brain? And other people say, well it is wrong, because you’re destroying a potential person. In other words you’re preventing some universes that would have that person from having that person. The potential idea gets translated into a "how many universes" idea.
And then the first person can reply, "Well yeah, but by that argument you’re also destroying potential people whenever you refuse to have sex with somebody." So it’s interesting how close everyday debates are to the edge of what is philosophically known. And it’s also interesting to me, because I’m interested in the boundary between physics, mathematics and philosophy, it’s interesting to me how often apparently esoteric questions about that boundary enter into perfectly ordinary debates one might have in a pub.
Is there any connection with time travel?
Yes, there is a connection. It’s like this. We don’t know if time travel is possible or not in the sense that we don’t whether gravity can be bent or twisted in just the right ways. It’s certainly not forbidden by any known laws of physics, but it might be as far as we know. But if it is possible , one thing we do know is that it wouldn’t be a paradox. When you go into the past, you don’t go into the past of your own universe. That’s not just a hand-waving way out of the paradox, that’s something you can actually deduce from the equations of quantum theory. So you go into another universe and it happens in such a way that everything is consistent. The typical thing is that you end up with two copies of you in the universe that you went to, and the universe that you came from, you disappeared into the time machine and you never returned.
MIchael Moorcock was writing about his multiverse in the ’60s, so presumably the idea isn’t a new one?
The Quantum Multiverse theory was first published in 1957, by Hugh Everett III who was at that time was a graduate student at Princeton University. It had already been thought of already a few years before by Erwin Shrödinger, who you have probably heard of, but he never published it. He just gave one talk on it in Dublin University where he said, “Right, now I’m going to tell you about something that’ll make you think that I’ve gone insane.” But actually, it’s the other way around. The many universes theory is the sane version. And it’s the prevailing view that 90% of physicists believe in that’s wholly irrational. But that, of course, is just my view.
I think the argument for Everett’s theory is incontrovertible now. It seems to me that there is as much evidence for the existence of parallel universes as there is for the existence of dinosaurs. The logic for the evidence in both cases is very similar. No-one has ever seen a dinosaur, we’ve only seen fossils, and similarly, no-one has ever seen a parallel universe, but we have seen interference phenomena. And just as there is no other explanation of dinosaurs, so there is no other explanation for interference phenomena. And what most physicists do nowadays is they adopt what is called the “shut up and calculate” interpretation. Which says just use the equations to predict the outcome of experiments but do not ask what brings about those outcomes. Which is just the same logic as saying, “Do not ask what brings about fossils.” It’s similar to creationists and pealeontologists disagreeing about things we can’t see. They don’t disagree that we can see fossils. They just disagree what the fossils are due to. The same thing has happened in physics, regrettably. Except that in physics it’s the majority of physicists that hold that irrational view.
What is interference phenomena and how does it “prove” the existence of multiple universes?
Basically, it’s an experiment you can do in the laboratory, with individual particles like photons. It has been done with molecules and somebody’s even managed to do it with entire viruses. Little objects anyway.
And they go through an apparatus; they can go on one of a variety of different paths. And then these paths are brought together. And then the object is measured to see what has happened to it on the way. And what’s happened to it turns out to depend on stuff that is there on all the paths. Now that means that something must have gone round all those paths . But the object… there’s only one object going through at a time, only one virus, or one atom, or one molecule, or one photon, and it could have at most gone along one of those paths. But the outcome that you measure at the end depends on what you put on all of the paths.
There are things that you have to rule out before you come to the obvious conclusion. That the thing splits into two, for example. But you can rule those out, by doing various measurements along the path and seeing that in fact, whenever you measure it inside the apparatus there’s only one of it. You never see it in more than one place at a time. So you can only ever see it in one place at a time, but it is, in fact, in all places, which you can tell directly afterwards from its effects, just like the fossils of dinosaurs.
It is the strangest thing I know. Far more freaky than exceeding the speed of light or anything pedestrian like that. And yet this has been verified. This is not a controversial effect. To predict that this will be the outcome is perfectly standard quantum theory. It is part of quantum devices that are used routinely used in labs to measure other stuff and so on.
What is controversial is why the outcome is as it is. And the majority of physicists wish to avoid the implication that it is because particles in other universes are affecting their counterparts in our universe. You may ask why they want to believe this. I don’t really know.
So what alternative theory do they have?
You have to understand that the alternative theory is not an explanation in the same sense that I have been advocating my own explanation. It is more of the form, “There is no such thing as what happens in between two experiments. Unless you actually measure something it is meaningless to ask whether it is there or not.” It is that kind of equivocation and semi-mysticism that has become the prevailing view about quantum mechanics, quite different from what the prevailing view is in the rest of physics about everything else.
I just wrote this book, The Beginning Of Infinity (opens in new tab) , in which I make some speculations about why people want to believe stuff like that. What it leads to when you believe that. And on the contrary, how fruitful the idea of the world really existing and making sense is.
So do you watch Fringe in a state of “suspension of disbelief?”
No. not really. There are two approaches to fictional science, one of which I like and the other of which I hate. The one I hate is where you just make up stuff and anything goes. That’s no good, because there is no integrity to such a story.
The good way of doing science fiction is to invent a premise, perhaps totally unjustified or totally fictional in terms of science, but you invent that premise and then investigate what the world would be like if that premise were true. And investigate that premise ideally in the way scientists use to investigate the implications of real scientific theories. The best science fiction is of that kind. But unfortunately it’s only science fiction books that reach the really high standard of that sort of thing. Books like Greg Egan, for example.
I think you can divide Fringe episodes into two kinds. There’s what you might call “joke” episodes which are just about a one-off idea and the interest in the story is not really in the fictional science. But Fringe also does the other thing. There are some episodes – and also the main thread of the plot as it runs through all the episodes – where what they’ve done is they’ve taken parallel universes theory and they explore it. They’ve changed it a bit, so that for instance, there are only two universes instead of countless numbers of them, and so that you can move between them instead of not being able to and so on. But they stated up front what these differences are, and then they used that fictional science to investigate not only issues that would arise in that fictional world, but some of the philosphical issues, like I said earlier, about personal identity and so on. In that respect, I think the authors of Fringe have done a fairly good job. I watch it for entertainment, but I’m more entertained when it’s exploring those issues.
I don’t get angry about bad science like some scientists do. What I get angry about is bad fiction.