The universe has several dimensions

Physics and philosophy : Multiple Universes: Science or Modern Fairy Tales for Intellectuals?

Physics has conquered worlds far beyond the everyday, at least in thought. String theory, for example, explores the cosmos of the very smallest. According to her, the universe is made up of vibrating “strings”. The cosmic dance of its vibrations creates the universe with all its forces and elementary particles.

What at first sounds as simple as it is elegant, however, requires breathtaking assumptions in order to be mathematically consistent. The superstring theory is based on ten dimensions of space-time, the boson string theory even from 26. The theory of the multiverse sounds even more fantastic. Its representatives claim that there are many more besides our universe. The number of parallel worlds, finite or infinite, depending on the model, is a rendezvous in the multiverse.

No question about it, strings and multiple worlds inspire the imagination. Nevertheless, with solid evidence for the actual existence of these head births in theoretical physics, things are looking bad so far. So it is not surprising that string theory has been subject to criticism, scorn and ridicule since its inception. The possibly fictitious strings exist in a world that is trillion times below the "resolution" of the Large Hadron Collider, the world's most powerful "particle searcher" at the Geneva nuclear research center Cern. Are these theories science or rather speculation, modern fairy tales for intellectuals? The dispute has broken out.

Now the opponents have met at Munich's Ludwig Maximilians University to fight for the “soul of science”, as one reviewer wrote. The main reason for the conference was an attack by physicists George Ellis (University of Cape Town) and Joe Silk (Paris Institute of Astrophysics / Johns Hopkins University) in the journal "Nature". Ellis and Silk saw the integrity of physics threatened by strings and multiverses. These delicate structures of thought are seductive, but not verifiable. What is beautiful does not have to be true for a long time.

The predictions of the theory of relativity came true

The critics argue with Karl Popper (1902–1994). The philosopher had demanded that a scientific theory should be refutable (falsifiable). You have to make clear predictions that can be clearly assessed as right or wrong. Unlike quantum or relativity, which made concrete (and later confirmed) prophecies, tempting ideas led astray without any anchoring in reality, or more precisely: into a no-man's-land between physics, mathematics and philosophy.

The opposite is true, counters multiverse researcher Sean Carroll, a physicist at the California Institute of Technology. Popper applied the standard of falsifiability to psychoanalysis and Marxism. Because they build whatever happens into their argumentation. Everything seems to confirm them, so they are irrefutable - and therefore not scientific.

The multiverse helps to explain natural constants

But Karl Popper has left the building, says Carroll. The philosopher's once keen instrument against erroneous doctrines of salvation of his epoch has become blunt. Carroll suggests that a good scientific theory these days must be "definitive" and "empirical". You should make clear ("definitive") assumptions about how reality works. And it should be judged according to how well its models do justice to the available data, how “empirical” it is. The multiverse could be a good way to explain the size of certain natural constants. Even if we cannot (or never) observe other parts of the multiverse - that is, other universes.

This will not convince skeptics, nor will the appeal to Thomas Bayes (1701– 1761). Its statistics can help to legitimize assumptions like the multiverse by giving it a degree of probability. Whether the multiverse really exists to 94 percent, as the string theorist Joe Polchinski of the University of California claims, remains to be seen. After all, the controversial theorists obtained permission in Munich to continue speculating. A few more or less universes don't matter anymore.

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