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Asked by TaraKinney to Alice, Bose, Christian, Emma, Steve on 13 Mar 2016.
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Steve Marsden answered on 13 Mar 2016:
That’s a really good question! There’s a whole zoo of sub-atomic particles that we want to study. Many of these particles don’t exist normally, and haven’t existed since a split second after the big bang. The best way of studying these is thus to recreate the conditions, and so make these particles pop into existence for a brief instance. This process is performed in the LHC to allow us to study them.
But it isn’t the only way. We know that there are particles that we haven’t yet discovered in colliders like the LHC. The most prominent of these are dark matter. Dark matter is a particle (or set of particles) that are stable, and pass through regular matter. We know that they must exist because of how they interact gravitationally with the visible matter in galaxies. By looking at how galaxies behave, we can study certain properties of the particles. This form of study is very limited however, and we probably won’t truly understand what dark matter is until we manage to create it in a collision experiment.
There are also particles that we do know of, that collision experiments cannot study. The prime example of this is neutrinos. These are almost massless particles which can travel through normal matter, only interacting very occasionally. Because of how little they interact our knowledge of them is very limited. In order to learn more about them we have giant detects detectors buried underground that attempt to measure the neutrinos after they’ve passed through the Earth. These are far less spectacular experiments in terms of explosions, but their results are just as vital to our understanding of the universe. In fact there are far more of these experiments than there are collision experiments, and currently there are over 20 in operation.
Ultimately, for some particles we know of no better way of studying them that running high energy colliders. For other particles, colliders are useless, and running less explosive experiments is necessary.
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Alice Harpole answered on 14 Mar 2016:
We can study a lot about particle physics by using the universe itself as our laboratory. There are lots of objects and events in space where there is matter at much more extreme temperatures and pressures than we could ever hope to recreate on Earth (at least not in my lifetime!). By understanding how these objects and events work, we can therefore discover a lot more about particle physics.
A good example of this is neutron stars. These are incredibly dense objects formed when massive stars explode at the ends of their lives. They are so dense that if you took all the people of the Earth and squished us down so we were the same density as neutron star material, we’d all fit inside a cubic centimetre! We think it’s very likely that the material in the centre of these stars is very unusual indeed (and indeed at higher energies that can be created at the LHC). Some people think it’s made up of superfluid, superconducting neutron-degenerate matter (i.e. neutrons at very high pressure with some cool properties). It’s also believed it might be made of something called a quark-gluon plasma, which is when neutrons get so squashed they break down into quarks (the fundamental particles neutrons are made of). We can work out what the most likely case is by producing models of the entire structure of the neutron star, then comparing these to properties that we can measure (e.g. radius, how fast they rotate and how this changes with time, the strength of their magnetic field).
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