In the fourth installment of Pop Mech Explains the Universe with Neil deGrasse Tyson, the astrophysicist and science communicator discusses how the idea of the multiverse could be explained with things we already know about. Could future scientists eventually prove the most far-out ideas scientists have today?
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New episodes in our multi-part video series will debut every week, so be sure to check back for more of Tyson’s thoughts on simulation theory, aliens, and the greatest scientific achievement of 2022 (so far). And if you missed the first three videos, check out our episodes on Tyson’s start as an astrophysicist, why he says we’re not living in special times, and how the James Webb Space Telescope lets us see “ghosts” of the past.
The Limitations of Our Senses
In his chat with Deputy Editor Courtney Linder, Tyson explains that our senses evolved because they helped us in the most immediate ways within our environments. Basically, we need them not to be eaten by lions, he says—a set of skills that doesn’t always translate to the abstract or the cosmological, to say the least.
But that means we run into a fundamental cognitive dissonance as human beings. We want to look into the sky and into the past and make sense of what we observe, but our brains, in the most literal way, don’t have the common sense (or senses!) to grapple with questions like quantum mechanics or the multiverse.
With that in mind, it’s no surprise that people find multiverse theory—highlighted in the video above with clips from Doctor Strange—equal parts scary, fascinating, and unfathomable. In Ted Chiang’s 2019 short story collection Exhalation, he posits a multiverse where startups have invented ways for people to use their parallel doppelgängers to make money.
It’s not really too much for our brains, though, Tyson says, because we’re used to a lot of things that otherwise might seem outlandish. We’re surrounded by ice and ice machines, something that changes water from liquid to solid beginning in just a few minutes. “How can water ever be solid?” Tyson says. “You’ll just freak out if you’ve never seen that before.”
The Centennial of Quantum Physics
Tyson says we’re now in the centennial decade of the discovery of quantum physics, something that completely changed the nature of how we study the universe. Phase changes, like liquid water into ice, happen on the most macro scale as well. “Our hunches tell us phenomena in the universe can go through phase transitions,” Tyson says. “One of these is a period of rapid expansion of the spacetime continuum.”
General relativity, as posited by Albert Einstein, is an explanation for how many macro-scale phenomena are working: how the planets orbit, for example, and how we can wrangle physics to help us travel from Earth to other planets. “So general relativity gives us our tools, but it doesn’t work for the very smallest of scales,” Tyson says. “It doesn’t play nice in the sandbox with quantum physics.”
That leaves some large gaps that we must fill with something if our goal is to understand how the universe works in a complete way. Quantum physics enters the picture as a way to explain how very tiny things behave, filling one of the empty spots left by classical mechanics like general relativity.
But it doesn’t have to stop there. Remember that the rapid expansion of the universe is one of the “phase changes” we may be able to help our minds understand. That means everything around us today was once on the so-called “quantum scale.” “What happened in the very early universe when the large was small?” Tyson says. “Would the quantum phenomena affect the entire universe if the entire universe were the size of quantum phenomena?”
Doing the (Quantum) Math
Cosmologists roll back time as completely as they can, to within seconds or even fractions of a second after the Big Bang. If, indeed, the rules of quantum mechanics apply, then this is where the fun work of imagining the multiverse can begin. “That’s where all these weird wacky expectations emerge from, when you manipulate the equations of the early universe,” Tyson says.
“The equations allow this naturally without having to invoke it by fiat, and that’s why it’s received such attention,” Tyson says. “Even though we haven’t discovered one yet, the theories and the math give it to us. So maybe in the future there’s some clever way we’ll get access to this parallel universe that previously we had no idea was there.”
Tyson also points out that, when it comes to far-out scientific theories, what’s calculable today should never prevent scientists from trying to think about and build new models—especially when it comes to more abstract ideas, like phenomena that might exist in some parallel dimension. “Just because you can’t experimentally verify something now doesn’t mean you shouldn’t keep thinking about it,” he says, “because later solutions might arise that will make that possible.”
Caroline Delbert is a writer, avid reader, and contributing editor at Pop Mech. She's also an enthusiast of just about everything. Her favorite topics include nuclear energy, cosmology, math of everyday things, and the philosophy of it all.
