Could Everything We Know About String Theory Be Wrong?

The elusive theory of everything. A theory that could resolve the most fundamental roadblock in our understanding of how the universe behaves. And tie everything neatly up with string. It's been 50 years since string theory was first proposed, and new work calls into question not only essential parts of the theory itself, but also our working understanding of the universe. Let's start at the beginning. We have two primary ways to describe how all the stuff in our universe behaves. One big, and one small. The first is Einstein's theory of general relativity, which tells us how gravity interacts with space and time to form the world around us. That's the big. Then there's the small, the standard model, which works on the quantum level. This says that all matter is made up of building blocks called elementary particles. You can break us down into molecules, then into atoms, then into subatomic particles like electrons, neutrons, and protons. And smaller still are those elementary particles, divided into two broad categories, quarks and leptons, of which there are different kinds. Okay, groovy. The standard model works mathematically in most cases, but it only incorporates three of the four fundamental forces of our universe. There's the strong, the weak, and the electromagnetic forces, and then there's gravity. Gravity is the odd one out, the ugly duckling of the standard model, because it doesn't fit. Each of the other three forces has a carrier particle. Photons carry the electromagnetic force, gluons carry the strong force, and W and Z bosons carry the weak force. But we haven't discovered a carrier particle for gravity, which we would call the graviton if we could find it. This means the mathematical calculations of the standard model, and those that underpin Einstein's theory of general relativity, don't match up with each other. If we could find some way that they could work together, we'd have a theory of everything. It's this misalignment, and a desire for unity, that gave birth to string theory. So how does string theory tie our ideas of the universe together? Instead of picturing elementary particles as distinct points, string theory posits that all elementary particles can be pictured more like a vibrating string. Each particle is technically the same string, it's just vibrating in a different way. The way that a string on a musical instrument can play different notes, including that elusive note gravity. Okay, that sounds pretty tempting, but of course, there are issues. The level on which we would be able to observe strings vibrating is way outside our current capabilities. Famous string theorist Brian Greene says we'd need to build a particle collider the size of the galaxy to be able to directly observe strings in action. So since observation is off the table, how about math? The math tells us something pretty freaky. The equations that make string theory work require that the universe has at least ten dimensions. We're only able to observe four of these, the three dimensions of space, with time as a commonly proposed fourth dimension. The extra dimensions required by string theory is where parallel universes start to come into play. Since strings are so small, the math tells us that they would not just be vibrating in the large dimensions we know of, but in other tiny dimensions too. If we know the shape of those tiny dimensions, we might be able to predict and then observe properties of elementary particles, like their charge or their spin, that would be attributed to those extra dimensions, which would mean that we're seeing evidence of the other dimensions. But the problem with that is that once scientists tried plugging in different potential shapes for these extra dimensions, they found that most of them worked. The more they tried, the more of them fit, which meant that they had way too many possibilities to consider, and they lost hope that finding out the shape of the dimensions could help us observe their existence. Until someone proposed that perhaps there wasn't just one right shape for each of the extra dimensions, but they're all right in each of their own universes, meaning there are other universes, potentially over ten to the five hundred others, each ever so slightly different from our own. And yeah, I'm still talking about theoretical physics, not science fiction, although it's a pretty thin line if you ask me. That's where we all were up until a few weeks ago, when controversial new mathematical papers may have blown all of this apart. And this big upset involves dark energy. We think we've observed that our universe is slowly expanding. Our explanation for this is dark energy, and there's lots of theories about what it is and how it behaves to make the universe expand, but we don't have anything nailed down on that front just yet. These recent papers provide new evidence that the math of string theory may actually prohibit the existence of alternate universes in which dark energy is stable. Which means one of a couple of things. Either string theory is wrong, or we're wrong about our universe. Maybe it didn't explode in a big bang, it's not expanding, and it'll eventually contract in what some physicists call a big crunch. Or maybe there's an entirely new way of fitting the existence of dark energy into our string theory calculations that no one has tried yet. Now string theorists are still divided about these new claims. Many are not at all convinced of the paper's claims and think that the existing theories work just fine. So while there are no hard answers, this latest work has sparked a renewed urgency to understand dark energy, how it behaves, and how it might inform our theories about the behavior of our universe and the potential existence of others. Still with us? We know string theory often presents more questions than answers, but we want you to keep untangling the universe with us. So subscribe to Seeker for more videos on topics like this and let us know what you want to talk about. And check out this video here on quantum retrocausality. Thanks for watching, I'm Maren.