If they end on different branes though, then they can’t. If two strings end on the same brane, those ends can meet up and interact. Branes (short for membranes) are surfaces that strings can end on. Each new way the string can move or vibrate can give rise to a new particle.Īnother option to introduce diversity in particles is to use branes. These new options make the strings look different in our four-dimensional world: a string curled around a donut hole looks very different from one that moves freely. There are lots and lots ( and lots) of ways to do this compactification, and different ways of curling up the extra dimensions give different places for strings to move. They have to be curled up, in a process called compactification. Since our world looks four-dimensional, something has to happen to the other six dimensions. The strings of string theory live in ten dimensions, it’s the only place they’re mathematically consistent. You need something else, like compactifications or branes. In a sense, string theory sticks a quantum field theory inside another quantum field theory, in a way that would make Xzibit proud.Įven with supersymmetry, string theory doesn’t give rise to all of the right sorts of particles. In string theory, it means that along with vibrations that go higher and higher, there are also low-energy vibrations that behave like different sorts of particles. Supersymmetry relates different types of particles to each other. The first and most important trick here is supersymmetry.

So how does string theory go from one fundamental type of string to all of the particles in the universe, if not through these vibrations? As it turns out, there are several different ways it can happen, tricks that allow the lightest and simplest vibrations to give us all the particles we’ve observed.* I’ll describe a few. They’re not how string theory explains the fundamental particles of nature. They’re particles we haven’t observed, and may never observe. They’re not electrons, they’re not dark matter.

Those aren’t the particles you’re used to. From our perspective, that energy looks like mass, so the more complicated harmonics on a string correspond to extremely massive particles, close to the Planck mass! String theory’s strings are under a lot of tension, so it takes a lot of energy to make them vibrate. It’s a lot harder to wiggle a thick rubber band than a thin one, if you’re holding both tightly. Making a string vibrate takes energy, and that energy is determined by the tension of the string. But it gives a completely wrong idea of where the particles we’re used to come from.

Vibrating strings theory