How does making protons collide with each other (in the LHC) (re)creates the conditions that were present after the Big Bang?
In: Physics
When any object is moving with some velocity, it has kinetic energy. The goal of a particle accelerator is to bring particles up to absurdly high kinetic energies so that when they collide, that energy can be converted into a different form of energy, mass! Particle can pop into existence by putting a ton of energy into small amounts of space and usually decay into a shower of smaller particles in what are known as jets.
When they talk about recreating quark gluon plasma or early universe conditions, they mean that the resulting after products have a temperature similar to that of the early universe. The QGP is a material so hot that the quarks cannot bind together to make any of the composite particles that feel the strong nuclear force. Which is saying something since that force is so.. strong.
“the conditions that were present after the Big Bang” means extremely high energy/temperature. All our data on the universe (especially the cosmic microwave background) points to an extremely rapid expansion of space itself, expanding a hot dense soup of matter and energy into many light-years across in a fraction of a second. We **don’t know** that this process started with a singularity, or what might have existed before this expansion began. So we “rewind” this process on paper, and ask “what does our existing physics say happens when stuff is hotter and denser?”
We can run back this clock on paper for a while, but the problem is that when we get close to 0 volume and infinite energy, our math starts to break down. We get nonsense answers, and the answers we do get aren’t consistent with other things we’ve directly measured. We clearly don’t know everything about how physics works. Even the “singularity” itself is actually *probably* just our math not working, rather than a real thing that can exist in the universe.
So, how do we learn more? By getting direct data about how particles and energy behave in these conditions. That’s extremely hard to do, as you might guess. Our best way of doing that is to accelerate particles to outrageous speeds and then crash them directly into each other. This makes a brief explosion of enormous energy and heat, and weird things happen – particles are created and shot out that simply don’t exist at lower energies. By doing this a million times, and looking at what happens every time, we can figure out how things behave in those extreme conditions. This helps us figure out what might have been going on, closer and closer to that “0 time” singularity that may or may not exist.
Example: one of the better theories for making gravity work with particle physics is called Loop Quantum Gravity, and it predicts a Big Bounce. This theory happens to predict that when matter is super dense (but not infinitely), gravity becomes strongly *repellent* and pushes things apart. This is cool because it could give us a theory of a universe a) without a singularity that feels like a calculator error, and b) get rid of the question of “what was before the big bang?” A lot of buddhists would love to hear that there’s evidence for an eternal, cyclical universe.
But we don’t know if Loop Quantum Gravity is correct. We know it differs from existing physics in what it *says* happens in certain conditions, but we don’t know what *actually* happens to actually prove or disprove it. So data from particle colliders is one way to get that data that might tell us which theories are right.
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