Renato Renner: Quantum Mechanics Contains Its Own Contradictions
episodePreviously titled “Renato Renner: Quantum Mechanics Contradicts Itself (and He Proved It)” — renamed by the publisher on Aug 3, 2026
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What is the fundamental contradiction in quantum mechanics that Renato Renner proved?
It really troubles me that there is this problem, this contradiction. I had some students who said for psychological reasons not be able to work on such projects, this would disturb them too much.
Most physicists apply quantum theory and never turn it on themselves. It turns out there are scenarios where quantum mechanics leads you to contradictions when applied to quantum observers.
You're absolutely certain its heads. I see its tails.
That's Professor Renato Renner of ETH Zurich telling me that it turns out one of these things must break. Number one, quantum theory applies to everything, including observers, that seems natural. Number two, that measurements give single outcomes. And number three, that reasoning stays consistent. All of these are already assumed to be true. We think that the large world is made up of the small, and thus quantum theory applies to everything else. Yet we don't know which one of these is wrong, and getting rid of any is just as unsettling. On this channel, I, Kurt Jaimungel, interview researchers regarding their theories of reality with rigor and technical depth. Today, we discuss why this drove the professor from many worlds through to what he calls no man's land.
We connected back to the black hole information paradox, to the limits of probability, and to why some of his students refuse to continue because these projects are about the fundamental question of what you are. Professor, you've proved that quantum theory can't consistently describe itself. What does that actually mean?
So maybe I should first explain what type of question we are really trying to answer here. So what we have learned from quantum theory, or what at least I think I've learned from quantum theory, is that there is a constraint on what we can know about the world. So this kind of starts already with the Heisenberg uncertainty principle, which tells us we cannot really know the position and momentum at the same time. Time, but this is really a constraint on the knowledge. It's n I don't see it as a constraint on what we can technically measure because we can individually measure position very precisely and momentum very precisely, but somehow we cannot have the knowledge of both at the same time. So quantum theory somehow very substantially restricts what we can know about the world in a sense.
And now this raises The question that when we cannot know everything about the world, can we actually do still do physics in the way we thought we do physics? Or in other words, we can say that usually when we did classical mechanics or electrodynamics and so on, we kind of assumed that in principle we can know everything about the physical system. Of course, we knew we will not know all the positions of the planets and every atom in the world. To to an arbitrary precision, but we always thought in principle it can be known. So there would, in principle, be a very powerful physicist who would know all the positions and momenta of all the particles in the world, and then we can make predictions and so on.
How does the idea of applying quantum theory to the observers themselves lead to a consistency test?
And now when quantum theory tells us that apparently there is a constraint on knowledge, we can turn this into the question: is there a constraint on doing? Physics in a sense. And so, what does this now mean for me? It means for me that if I want to, or how can I answer the question whether we can do physics in our world? I could now say a physicist is itself a physical system. So I could, for example, try to describe you doing physics. So you could, for example, let's say interact with an experimentalist. I'm not sure you are not doing experimental. I guess. No. No. Except this right now. So let's suppose you're interacting with an experimentalist, your experimentalist friend. And so this experimentalist friend tells you about an experiment, and maybe you go to the lab and and do some checks there.
And then um you do calculations, let's say, and make a prediction for what he's going to measure. Now, what I could do is to kind of analyze how you are doing that. So I kind of take you as a physical system that interacts with the experimentalist, who is also a physical system.
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Chapters
8 chapters
1
What is the fundamental contradiction in quantum mechanics that Renato Renner proved?
0:00–3:05
2
How does the idea of applying quantum theory to the observers themselves lead to a consistency test?
3:05–7:20
3
Why do classical analogies (coin toss, chess pieces) help illustrate the quantum‑observer paradox?
7:20–16:52
4
What are the three core assumptions (universality, consistency, single‑outcome) behind the no‑go theorem and how might they be escaped?
16:52–1:40:42
5
Why does choosing a quantum interpretation feel like an emotional decision?
1:40:42–2:02:19
6
What problems arise when probabilities are used to represent knowledge in multi‑agent scenarios?
2:02:19–2:30:31
7
How do emotions and hidden assumptions shape disagreements over collapse versus many‑worlds theories?
2:30:31–3:01:37
8
Why does the speaker argue that physics is fundamentally about communication of information?
3:01:37–3:19:12
Speakers
1 identifiedMore from Theories of Everything with Curt Jaimungal
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