Is there anything greater than the multiverse?

"Reality is a much bigger thing"

David Deutsch, 53, is one of the best-known proponents of the multiverse theory, according to which there are an infinite number of worlds that we cannot see. As early as the late 1970s, he proposed an experiment that might one day prove his theory. He designed the concept of a quantum computer and thus laid the foundations for the research area of ​​quantum informatics. He has received numerous awards for his achievements, including the prestigious Paul Dirac Prize from the Institute of Physics. He is currently doing research at the Center for Quantum Computation at Oxford University's Clarendon Laboratory, which he co-founded.

Technology Review: Mr. Deutsch, you say that there is a universe in which the earth, unlike our universe 60 million years ago, was not hit by a comet. Are you sure?

David German: Yes for sure.

TR: Are there also universes in which the dinosaurs survived and evolved into intelligent creatures?

David German: This follows from quantum theory, one of the most fundamental theories in physics. This inference that there are many different universes is not my idea, by the way. It has been known for 50 years and was first published by Hugh Everett.

TR: Where are all the other universes?

David German: We have to take into account that the question of where always relates to a particular universe. For example, I live in Oxford, you don't. We are referring to different places in the same universe. If you ask where the universe is, you are in danger of misleading your imagination by trying to imagine the other universe somewhere in our universe, such as another place.

TR: How can you imagine that better then?

David German: Better to start at the other end. According to quantum theory, physical reality is made up of a much larger thing than the sum total of the things we see, the stars, the galaxies. Reality is a much bigger thing and we call that the multiverse. It has regions that behave almost autonomously from the other regions. And these are the different universes.

TR: You say we all exist in many of these universes. In how many of these universes would we meet you?

David German: We're talking exponentially large numbers here. Among the universes there are those that are clearly different from one another and those that are completely identical. Which ones do you want to count?

TR: Only the different ones in which there is still David Deutsch.

David German: That would still be an extremely large number. If we count all of them, including the identical universes, the answer would even be infinite.

TR: When do universes start to develop differently?

David German: When you toss a coin, you toss it in an infinite number of identical universes, plus a few others. For this example, let's focus on the identical ones: They split into two groups that develop differently, according to the two possible outcomes heads or tails. Each group still contains an infinite number of universes.

TR: For you, all the possibilities that occur according to quantum theory are reality, albeit in different universes. However, according to the Copenhagen interpretation advocated by most physicists, only one possibility can be real. Which, heads or tails, is decided during the measurement. When did you start to doubt it?

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