# 2022-10-27 - David Deutsch - Why Is Everettian Quantum Theory Not in the Consensus [YouTube](https://www.youtube.com/watch?v=x29h12iOWFY) Duration: 00:09:39 ## Transcript ### David Deutsch 00:00:00 - 00:02:17 Lev Vaidman has asked us this question. Why is the Many Worlds interpretation not in the consensus? And he adds, I firmly believe that the Many Worlds interpretation should be in the consensus and want to know why it is not. I agree and I too don't know why. It may be that only future historians of ideas will succeed in explaining it after the reality of multiple universes has become as uncontroversial as that of dinosaurs and their evolution is today. But perhaps I can say a few things that might make this seem a little less mysterious and less reprehensible. One thing that future historians might notice is that today there are strong divergences of opinion among proponents of the theory. We all agree that it describes reality, not just predictions, not just our confidence in predictions, not just our states of knowledge and so on. But we disagree about what reality it does describe. Is the world that we perceive as n particles in a three dimensional space actually a complex function on a three n dimensional one? Does that function describe reality? Or is it itself the reality? Is the reality described by Q number observables, as I think? And what about time? What about space time and quantum fields and quantum gravity? And are the effects of one quantum object on another purely local or non-local? What is the origin of probability in this theory? On all these issues, we disagree. 00:02:17 - 00:04:36 Indeed Lev's question asks about the many worlds interpretation. I disagree with that very term. Who would call the theory of evolution the many dinosaurs theory? Nor is Everettian theory an interpretation of quantum theory or anything else. It is quantum theory. It should just be quantum theory or call it Everettian if you want to give due credit to the corrector of earlier untenable misconceptions. In my view, splitting an explanatory theory into its formalism and its interpretation is itself a reinterpretation which, if insisted upon, is never more than institutionalised casuistry. It follows from the existence of these disagreements that most or all of today's advocates of Everettian quantum theory must be mistaken about what the world according to quantum theory is actually like. Hence, those future historians might ask what exactly were the unpersuaded unpersuaded of? But this internal dissension theory won't do as an explanation of Lev's mystery. In the early days of relativity, people disagreed about what the so-called Schwarzschild singularity was, whether space was finite or infinite, static or expanding. Einstein even wrote to the Times in 1919, categorically denying that his theory supersedes Newton's. Nevertheless, the vast majority of physicists were soon incorporating Einsteinian relativity into their worldviews. Lev's problem, our problem, is that the same has not happened in regard to quantum theory. 00:04:36 - 00:06:54 We won't find the answer in Kuhn's theory of scientists being stuck in so-called paradigms. Such theories would apply to all fundamental progress, including relativity. The people most prominently stuck in their paradigm are actually the believers in paradigms. So what is special about quantum theory that makes physicists reluctant to do what physicists do, namely apply the theory, test it, see what it says about the world, and let that inform your worldview? Why do they spin off into magic and double-talk or denial or wishful thinking? Many other insights about reality with which science confronts us are much more jarring. For example, although no one is jarred by the idea that when we see the Andromeda galaxy in the sky we are seeing it not as it is now but as it was a long time ago, everyone is jarred by the Einsteinian idea that there is no such thing as how it is now. If you make an arbitrary choice of an event in Andromeda to be now, all you have to do is walk up and down the street on earth to change what is now at Andromeda by weeks backwards or forwards. The relativity of simultaneity. Surely that's harder to accept than other universes. Except for one thing, there aren't other instances of ourselves at Andromeda. No other me's, some identical, some different, and some very different, in which case who am I? Nothing in relativity raises any such issue of personal identity. In fact, the only other fundamental theory that does so is the theory of computation with its implication that artificial minds are possible. 00:06:54 - 00:09:26 There too, people are wont to talk nonsense in order to avoid plainly applying the theory in the way they would apply any other. I don't claim that any of this could fully answer Lev's question even if it's true. Still less would it provide a way to restore reason to this issue. But in regard to reason, let me close with a wild guess. In the 18th century, when they thought of themselves as living in the age of reason, they were much more gullible about the scope of science than today. People were ready to accept that chess-playing automata already existed, that horses had been trained to count, and in the 19th century that Mary Shelley's Frankenstein and Jules Verne's submarines were just around the corner. But in parallel with this unreasonable gullibility, or perhaps it was reasonable, the 19th century also saw rising scepticism with Ada Lovelace of all people denying that machines can think, and later the introduction of positivism and other poison into the thinking of scientists. So here's my speculation. What else was growing during the 19th century? Science teaching, science lessons and courses in universities in which generations learned that you don't have to change your worldview, you don't have to understand, you only have to learn to say what one is supposed to say, be able to calculate what one is supposed to be able to calculate, sneer at what one is supposed to sneer at. I don't mean just astrology and creationism, but eventually at reality itself. That may be how we got into this mess. 00:09:26 - 00:09:33 How to get out of it again, I must leave as an exercise for the audience.