August 25, 2022 7:00 AM EDT
Hossenfelder is a research fellow at the Frankfurt Institute for Advanced Studies, Germany, and has published more than eighty research articles about the foundations of physics, including quantum gravity, physics beyond the standard model, dark matter, and quantum foundations. She has written about physics for a broad audience for fifteen years. Her first book, Lost in Math: How Beauty Leads Physics Astray, appeared in 2018.

Our universe contains about 200 billion galaxies. These galaxies are not uniformly distributed – under the pull of gravity, they lump into clusters, and the clusters form superclusters. Between these clusters, galaxies align along thin threads, the “galactic filaments”, which can be several hundred million light-years long. Galactic clusters and filaments are surrounded by voids that contain very little matter. Altogether, the cosmic web looks somewhat like a human brain.

To be more precise, the distribution of matter in the universe looks a little like the “connectome,” the network of nerve connections in the human brain. Neurons in the human brain, too, form clusters, and they connect by axons, that are long nerve fibers which send electrical impulses from one neuron to another.

The resemblance between the human brain and the universe is not entirely superficial; it has been rigorously analyzed in a 2020 study by the Italian astrophysicist Franco Vazza and neuroscientist Alberto Feletti. They calculated how many structures of different sizes are in the human brain’s connectome and in the cosmic web, and reported “a remarkable similarity”.

Brain samples on scales below about 1 millimeter and the distribution of matter in the universe up to about 300 million light years, they found, are structurally similar. Could it be, then, that the universe is a giant brain in which our galaxy is merely one neuron? Maybe we are witnessing its self-reflection while we pursue our own thoughts?

Sure, we don’t know what consciousness is. But we do know that the only things we’re reasonably confident can think – brains – have a lot of connections, and send a lot of information back and forth through those connections. Even leaving aside that we don’t understand consciousness, high connectivity and rapid signaling seem conductive to thinking. That the universe is structurally similar to the brain raises the question whether it has similar thinking capacities.

Too big to think

The universe, however, is different from the human brain in a number of ways, notably because it expands, and its expansion is speeding up. If galaxy clusters were the universe’s neurons, then they’d be flying apart from each other with ever increasing speed – and they have been doing so for some billion years already.

Another important difference is that it takes a long time for signals to cross the universe. Neurons in the human brain send about 5-50 signals per second. Most of these signals (80%) are short-distance, going only about 1 millimeter, but about 20% are long-distance, connecting different parts of the brain. We need both to think. The signals in our brain travel at about 100 meters per second, a million times slower than the speed of light. But the brain is small and it takes only fractions of seconds for signals to zip around in it.

The universe, in contrast, is presently some 90 billion light years in diameter, and – as Albert Einstein taught us – nothing travels faster than the speed of light. This means if one side of the hypothetical universe-brain wanted to at least take note of its other side, that would take 90 billion years even at the speed of light. And sending a single signal to our nearest neuron, the galaxy cluster M81, would take about 11 million years at least.

This means that, optimistically, the universe might have managed about 1000 exchanges between its nearest neurons since the Big Bang. If we leave the long-range connections entirely aside, that’s about as much as our brain does in 3 minutes. And the capacity of the universe to connect with itself decreases with its expansion, so it’ll go downhill from hereon.

This means if the universe is thinking, it isn’t thinking very much. For most physicists, this is the end of the story. But what if the universe isn’t as big as it seems?

Everything is connected

Researchers at the Google-owned company DeepMind recently taught physics to an artificial intelligence. They fed the computer program hours of videos and it learned, among other things, that objects don’t spontaneously disappear, they always continuously move from one place to nearby places. In physics, we call this “locality.” It’s one of the most basic properties of nature. And it’s among those we understand the least.

It’s not only that we don’t understand why the universe respects locality. We’re not sure that locality remains valid in the subatomic realm. If it doesn’t, then that could have profound consequences. It could be that space itself has many more connections than we observe, non-local ones, not unlike portals: You go in one end and are instantaneously teleported to a different place.

These non-local connections would have to be very small tough, too small for us, or even elementary particles to go through – otherwise we’d have noticed already. But they would still connect space with itself. This way, two places we think are at opposite ends of the universe might be very close to each other. The universe would only seemingly be large, an illusion born out of our limited perception.

My colleagues in physics are speculating about this for several reasons. First, we know that quantum effects can create strong non-local connections between particles. This “entanglement,” as it’s called, is what gives quantum computers their edge. Entanglement doesn’t allow non-local transfer of information, but it tells us that the familiar locality of balls rolling down inclined planes isn’t all there is to say.

We also know that Einstein’s theory of gravity contains wormholes that are shortcuts between places which appear far away. While large wormholes can’t exist in our universe because they would close immediately, what wormholes would do in the quantum realm, no one really knows. To find out, we would need a theory for the quantum properties of space, which – despite 80+ years of search – we still don’t have. Quite possibly, however, quantum wormholes give rise to non-local connections.

Finally, there’s the issue that black holes can destroy information. Once you have crossed the event horizon, it seems you’d need to move faster than light to get back out. But a non-local connection across the horizon would also get information out. Some physicists have even suggested that dark matter, a hypothetical type of matter that supposedly makes up 85% of matter in the universe, is really a misattribution. There may be only normal matter, it’s just that its gravitational attraction is multiplied and spread out because places are non-locally connected to each other.

A non-locally connected universe, hence, would make sense for many reasons. If these speculations are correct, the universe might be full with tiny portals that connect seemingly distant places. The physicists Fotini Markopoulou and Lee Smolin estimated that our universe could contain as much as 10 (to the 360 power) of such non-local connections. And since the connections are non-local anyway, it doesn’t matter that they expand with the universe. The human brain, for comparison, has a measly 10 (to the 15th power) connections.

Let me be clear that there is absolutely zero evidence that non-local connections exist, or that, if they existed, they’d indeed allow the universe to think. But we cannot rule this possibility out either. Crazy as it sounds, the idea that the universe is intelligent is compatible with all we know so far.

A source of wonder

I’ve made a name, for better or worse, by debunking nonsense physics headlines. That’s anything from the alleged observation of negative mass (no such thing) to messaging faster-than-light with the quantum internet (you can’t) to contact with parallel universes (I assure you we haven’t had any).

But as more of my colleagues are out there with me on social media debunking fake science news, I have found that we paint a one-sided picture. Science has more to say than “nope, you can’t”. It also opens our mind to new possibilities, new sources of wonder, and new ways to make sense of our own existence.

The universe might think, the Big Bang might repeat, and copies of you might live in parallel worlds. Those are possibilities which we found in our theories in physics. They are not supported by evidence and they might never be. But they are not contradicted by evidence either. And those are stories that deserve to be told, too.

Adapted from EXISTENTIAL PHYSICS by Sabine Hossenfelder, published by Viking, an imprint of Penguin Publishing Group, a division of Penguin Random House, LLC. Copyright © 2022 by Sabine Hossenfelder.

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