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 it’s fun to talk about, that’s all fine with me,” Hossenfelder says in Episode 525 of the Geek’s Guide to the Galaxy podcast. “I have a problem if they argue that it’s 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 it’s possible to create mathematical models that are consistent with multiverse theory, but that doesn’t 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 it’s 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 far—probably deliberately, because it sells—but I think for most of them they’re genuinely confused.”

Hossenfelder is also skeptical of the simulation hypothesis, the idea that we’re living in a computer simulation. It’s an idea that’s 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 there’s a 50 percent chance we’re living in a simulation,’ I’m 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, I’m telling you it’s not easy, and it’s not a problem that you can just sweep under the rug.”

While there’s 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 don’t contradict known science. “This is exactly what I was hoping to achieve with the book,” she says. “I was trying to say, ‘Physics isn’t just something that tells you stuff that you can’t 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 Geek’s 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 it’s typically phrased is that entropy tells you something about the decrease of “order” or the increase of “disorder,” but this is really from our perspective—what 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?” … There’s just too much that we don’t really understand about space and time—and entropy in particular, gravity, and so on—to definitely make the statement. I don’t 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 I’m kind of known to always say, “No, this is bullshit. You can’t do it.” But in this case, it’s 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 isn’t necessary in Einstein’s theory of general relativity. The reason is that if you have an expanding spacetime, it basically creates its own energy. … How much mass you’d need to create a new universe turns out to be something like 10 kilograms. So that’s 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 can’t 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 there’s a lot that we don’t understand about locality. I’m 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 structure—and pretty much all physicists I know believe that it does—it’s 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 you’re 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 weekend—so a time when people could actually come, not during work hours—and 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 we’re interested in, but it’s not the case for everybody else. Some people are interested in, I don’t know, quantum mechanics, and maybe they don’t know anyone else who’s interested in quantum mechanics. To some extent there are online communities that fulfill this task now, but of course it’s still better to actually meet with people in person.

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