Does Life Need a Multiverse to Exist?

SPEAKER_1 (0:00)

This episode is brought to you by Accenture. When you're advertising operations fall out of sync, everything else follows. Spotify and Accenture are working together to reinvent the rhythm of ad sales. Using automation, analytics, and smarter workflows to simplify campaign delivery and access better data across the business. The result? Less time spent on operations, more time connecting brands with the moments and fandoms that matter most. Learn more at accenture.com/spotify.

SPEAKER_2 (0:31)

This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome, that's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses set up required compatibility and availability varies 18 plus.

Matt O'Dowd (0:56)

Here's one totally uncontroversial statement. Life exists in our universe. Okay, let's try another one. Therefore our universe is capable of producing and supporting life.

Okay, let's try one final uncontroversial statement. Therefore there are countless universes.

Our universe seems to operate according to a set of fundamental rules that we try to understand and model with the equations of our laws of physics. Those equations always include one or more fundamental constants. Simple numbers that set the scale for the equation. We can't determine the values of these constants from pure theory. We have to measure them in the real universe. These are things like the speed of light, the Planck constant, the masses of the elementary particles, and the constants defining the relative strengths of the fundamental forces, the so-called coupling constants.

Between the general theory of relativity and the standard model of particle physics, there are something like 20 independent fundamental constants of nature. 20 free parameters, like movable dials that seem to be tuned to very specific numbers in this universe. Perhaps in other universes they could be set to other values entirely, or perhaps they're connected and controlled by some master dial or dials whose nature awaits discovery in the long-sort theory of everything. But whether there are few or many free parameters defining the physics of this universe, one thing is becoming increasingly clear. It's good that they have the values that they do. If the constants defining our universe were different — a tiny bit different in some cases — then our universe would be vastly different, and probably unable to produce galaxies or stars or life. We seem to live in a fine-tuned universe, a Goldilocks universe. And this seems to imply one of the following must be true.

One, we got lucky. The 20-odd dials just happened to land in the very narrow range of numbers that allow life to form.

Or two, someone fiddled with the dials, be it God or whoever built the simulation. Or three, we didn't get lucky and there was no fiddling, it's just that there are enough universes that somewhere the dials had to end up with the right settings for life. And naturally that's where we find ourselves. This last possibility draws on something called the anthropic principle. In the last episode we talked about the anthropic principle as related to where we find ourselves in this universe, necessarily within what may be an extremely rare habitable biosphere. We must find ourselves at a place and time in the universe capable of producing observers. This is the so-called weak anthropic principle.

SPEAKER_1 (3:56)

This episode is brought to you by Accenture. When you're advertising operations fall out of sync, everything else follows. Spotify and Accenture are working together to reinvent the rhythm of ad sales. Using automation, analytics and smarter workflows to simplify campaign delivery and access better data across the business. The result? Less time spent on operations, more time connecting brands with the moments and fandoms that matter most. Learn more at accenture.com/spotify.

SPEAKER_2 (4:27)

This episode is brought to you by Google Chrome. You think you know a browser, but Gemini and Chrome? That's new. It can help you with practically anything on the web, like restoring a vintage motorcycle from a 50-page restoration block, or finally break down that long article you've had open for weeks. Gemini and Chrome is here for it. Ready to make anything online make sense? There's no place like Chrome. Check responses set up require compatibility and availability varies 18 plus.

Matt O'Dowd (4:52)

As defined by astrophysicist Brandon Carter in 1973, Carter also has a strong version. The universe must be such as to admit the creation of observers within it at some stage.

By themselves, neither version of the anthropic principle explain why life-friendly planets or universes exist. They just say that if such places do exist at all, that's where we must find ourselves. The strong anthropic principle tells us that there's an observer selection bias that may help us understand why we live in such a finely tuned universe. But in order for that explanation to work, we need to propose that many non-finely tuned universes exist as well, in the same way that many uninhabitable planets exist. We're going to delve much more deeply into the implications and validity of that argument in an upcoming episode. Today, I want to set the stage by showing you just how finely tuned this universe seems to be. Let's start with chemistry. In our universe, quarks tend to stick together to form protons and neutrons, which stick together and attract electrons to form atoms. The periodic table is filled with different elements, different atom types, which interact with each other according to their complex electron shell structures. These chemical interactions give us different states of matter and a vast family of molecules which in turn are capable of forming structures of incredible complexity including life. There's no other mechanism in the universe capable of similar natural complexity, at least as far as we can tell, which is frankly pretty far. But it wasn't at all inevitable that our universe had to be capable of life-enabling chemistry or of complex chemistry at all.