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Sabine Hossenfelder is a theoretical physicist and creator of the popular YouTube series Science Without the Gobbledygook. In her new book Existential Physics, she argues that some of her colleagues may have gotten a little too excited about wild ideas like multiverse theory or the simulation hypothesis.

If you want to discuss them on the level of philosophy, or maybe over a glass of wine with dinner because its fun to talk about, thats all fine with me, Hossenfelder says in Episode 525 of the Geeks Guide to the Galaxy podcast. I have a problem if they argue that its based on a scientific argument, which is not the case.

Multiverse theory states that an infinite number of alternate universes are constantly branching off from our own. Hossenfelder says its possible to create mathematical models that are consistent with multiverse theory, but that doesnt necessarily tell you anything about reality. I know quite a lot of cosmologists and astrophysicists who actually believe that other universes are real, and I think its a misunderstanding of how much mathematics can actually do for us, she says. There are certainly some people who have been pushing this line a little bit too farprobably deliberately, because it sellsbut I think for most of them theyre genuinely confused.

Hossenfelder is also skeptical of the simulation hypothesis, the idea that were living in a computer simulation. Its an idea thats been taken increasingly seriously by scientists and philosophers, but Hossenfelder says it really amounts to nothing more than a sort of techno-religion. If people go and spit out numbers like, I think theres a 50 percent chance were living in a simulation, Im not having it, she says. As a physicist who has to think about how you actually simulate the reality that we observe on a computer, Im telling you its not easy, and its not a problem that you can just sweep under the rug.

While theres currently no scientific evidence for multiverse theory or the simulation hypothesis, Hossenfelder says there are still plenty of cool ideas, including weather control, faster-than-light communication, and creating new universes, that dont contradict known science. This is exactly what I was hoping to achieve with the book, she says. I was trying to say, Physics isnt just something that tells you stuff that you cant do. It sometimes opens your mind to new things that we might possibly one day be able to do.'

Listen to the complete interview with Sabine Hossenfelder in Episode 525 of Geeks Guide to the Galaxy (above). And check out some highlights from the discussion below.

Sabine Hossenfelder on entropy:

Entropy is a very anthropomorphic quantity. The way its typically phrased is that entropy tells you something about the decrease of order or the increase of disorder, but this is really from our perspectivewhat we think is disorderly. I think that if you were not to use this human-centric notion of order and disorder, you would get a completely different notion of entropy, which brings up the question, Why is any one of them more tenable than any other? Theres just too much that we dont really understand about space and timeand entropy in particular, gravity, and so onto definitely make the statement. I dont think the second law of thermodynamics is as fundamental as a lot of physicists think it is.

Sabine Hossenfelder on creating a universe:

There is nothing in principle that would prevent us from creating a universe. When I talked about this the first time, people thought I was kidding, because Im kind of known to always say, No, this is bullshit. You cant do it. But in this case, its actually correct. I think the reason people get confused about it is, naively, it seems you would need a huge amount of mass or energy to create a universe, because where does all the stuff come from? And this just isnt necessary in Einsteins theory of general relativity. The reason is that if you have an expanding spacetime, it basically creates its own energy. How much mass youd need to create a new universe turns out to be something like 10 kilograms. So thats not all that much, except that you have to bring those 10 kilograms into a state that is very similar to the conditions in the early universe, which means you have to heat it up to dramatically high temperatures, which we just currently cant do.

Sabine Hossenfelder on faster-than-light communication:

I think that physicists are a little bit too fast to throw out faster-than-light communication, because theres a lot that we dont understand about locality. Im not a big fan of big wormholes, where you can go in one end and come out on the other end, but if spacetime has some kind of quantum structureand pretty much all physicists I know believe that it doesits quite conceivable that it would not respect the notion of locality that we enjoy in the macroscopic world. So on this microscopic quantum level, when youre taking into account the quantum properties of space and time, distance may just completely lose meaning. I find it quite conceivably possible that this will allow us to send information faster than light.

Sabine Hossenfelder on community:

When I was at the Perimeter Institute in Canada, they had a weekly public lecture. It was on the weekendso a time when people could actually come, not during work hoursand afterward there was a brunch that everyone would have together, and I know that the people who would attend those lectures would go there regularly, and they would appreciate the opportunity to just sit together and talk with other people who were interested in the same things. This is something that I think scientists take for granted. We have all our friends and colleagues that we talk to about the stuff that were interested in, but its not the case for everybody else. Some people are interested in, I dont know, quantum mechanics, and maybe they dont know anyone else whos interested in quantum mechanics. To some extent there are online communities that fulfill this task now, but of course its still better to actually meet with people in person.

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Have Some Scientists Gotten Too Excited About the Multiverse? - WIRED