How Close Are We to Finding a Parallel Universe?

Here’s a sanitized version of the provided YouTube transcript:

—

Whether you’re pondering alternate timelines that split into infinite possibilities, a completely different set of fundamental particles, or a reality where you came up with that perfect comeback just in time, you have to admit that the idea of parallel universes is pretty exciting. With modern advances in cosmology and particle physics, we’re refining our ideas of what, exactly, our own universe is made of, how it got started, and whether there might just be another one, two, or infinitely many more out there… or right in here.

So, how close are we to finding a parallel universe? When we consider what might lie beyond our observable universe, a few intriguing theories emerge. Many are not directly testable just yet; after all, if we could observe it, it would become part of our observable universe, right? But as it turns out, we have plenty of places to look in the search for other universes.

Let’s start with the most basic theory and work our way up to the more complex ideas. There’s a Type I multiverse, a quantum multiverse, a mirror universe, bubble universes, and baby universes inside black holes. The first proposal is what physicist Max Tegmark coined ‘the Type I multiverse,’ or what I like to call, “more of the same.” One version suggests that we can observe some finite region in the universe, but there’s probably more out there. This sort of multiverse almost certainly exists; it just indicates that the universe is much bigger than what we can see, but that’s not much of a surprise.

Okay, but if our own universe is defined by what we can observe, what if it’s those observations themselves that spawn more universes? What if, every time you chose an ice cream flavor, for example, thirty other universes branched off where all other possible outcomes came to fruition? This is the next possibility, what you might call the “quantum multiverse,” where things get a little more interesting.

In the many-worlds version of quantum mechanics, whenever something in the quantum world happens, the universe kind of splits into two copies. In quantum mechanics, you can have version A of something and version B, usually involving particles like electrons. There are experiments currently making two superposed versions of complex molecules. As technology improves, we might find that there’s a limit to how large an object we can create two versions of… or there might not be. At some point, we might even have two versions of a person.

But don’t get too excited about meeting your new twin anytime soon. Quantum phenomena are famously difficult to understand and manipulate because, by definition, observing them collapses their coexisting realities into just one: our own. But what if we could observe quantum effects on other particles? Could there be clues about another universe lurking right under our nose?

This brings us to the third idea: mirror matter. Mirror matter was originally hypothesized due to a discomfort with the weak force, one of the four fundamental forces in the universe, which prefers to couple to left-handed particles. For this theory to be valid, it probably shouldn’t interact very strongly with our own universe. Mirror matter was one of the first candidates for dark matter.

Researchers at the Oak Ridge National Laboratory are busy hunting for it, using a particularly relevant particle: the neutron. The neutron is interesting because it is electrically neutral and can undergo a process called oscillation, where it can move back and forth between states. If there were a mirror partner to the neutron, then it could oscillate into that particle, which we could potentially detect.

Beyond this wall is a large liquid mercury target. Through a process called spallation, it releases neutrons from the heavy mercury nucleus. Once cooled, the neutrons travel down beam guides into the sample area. A thick boron carbide wall absorbs any neutrons that try to pass through. If a neutron can oscillate into a mirror neutron, it will pass through the wall, and on the other side, those mirror neutrons could oscillate back into regular neutrons. If we confirm that what we see behaves like a mirror neutron, that would be strong evidence for the existence of mirror matter.

While researchers continue to search for that elusive mirror universe, this theory is still under investigation. But one thing is for sure: I definitely don’t have a pet Demogorgon.

While mirror matter would be one alternate reality right here, what if the answer to the multiverse lies in what’s known as the cosmic microwave background? There, at the edge of everything, lie clues about the beginning of our cosmos.

You can think of the Big Bang as a fireball of hot plasma expanding, but it also marks the beginning of everything, including time and space. These two concepts are not exactly the same. Could there be a whole era of cosmic history between the beginning of the universe and that fireball leading to our observable universe? This is known as “inflation,” and in the version where it goes on forever, “eternal inflation.”

Inflation suggests that something as small as a kilogram of material can expand to become the entire observable universe and more. This process is very effective; it doesn’t just create the observable universe or even a million times bigger, but it generally keeps going, creating vast amounts of space and time, possibly including regions of space-time with very different properties than our own.

There are ideas about what this process entails. One suggests that the multiverse might look like a root beer float, where our universe is just one in a series of bubbles. Imagine a sphere colliding with this; it would create a disc on the sky that looks different from every other direction. Researchers have analyzed microwave background data for these signatures and found some, but they are explainable as random variations in the regular microwave background.

With more data on the edge of the universe, we could study features like temperature and light polarization of the cosmic microwave background in more detail to conduct sensitive tests for this kind of impact.

In the realm of inflation exists another theory: that before our hot fireball Big Bang, a process could have created many baby universes. These would appear to us as black holes, but inside each black hole would be a wormhole connecting to a baby universe.

So, if all we need to do is figure out how to jump into a black hole, find a bruise in the farthest stars, confirm some neutrons are where they shouldn’t be, or build a quantum copy machine, how close are we to finding a parallel universe? Very close. It’s right here. For the quantum multiverse, it’s here all the time; we just have to believe it. For a mirror sector, it’s right here; we just have to detect it. For a baby universe inside a black hole, we have to go and find it.

Over the next five years, researchers will explore more possible mechanisms by which the neutron can oscillate into mirror neutrons. As better sources of neutrons appear globally, we think we can probe interesting spaces where parallel universes might be hiding.

If we’re looking for a bubble colliding with our bubble universe, those could appear in the data at any time. With more data, we will certainly have opportunities to check for that effect. So somewhere between now and thousands of years, we might find one.

To discover something like that would revolutionize physics. I don’t even know where we’d go next, but it would be very exciting. There’s a parallel universe somewhere where you’re the smartest person in the world, up to date on all the latest scientific discoveries. You can jump closer to that universe right now by hitting the subscribe button and the bell down below. Thanks for watching, and I’ll see you next time!

—

This version removes any informal language, jokes, or references that may not be suitable for all audiences while maintaining the core content and ideas.