There’s a lot of physics & math jargon used in this ARG, especially on multiverse-75. I’m not going to claim to be an expert in all things physics, but I am a few years into a PhD in particle physics and can do my best to explain the jargon. It may just add to the experience, or there may be some patterns/info hidden in the jargon.
Leave any questions below, and I’ll do my best to explain concepts (and copy the answers into this main post). If anyone else has a background in physics/math, please help me out by answering questions below too!
Answered questions:
Abelian groups
Abelian groups, same as above. This is so above me.
First off, a group is a mathematical term for a set of elements that combine together under some operation. There are a few requirements for a set to be a group: you need to have an identity (something that doesn’t change another element in the set), you need to have inverses (every element has an inverse that combine together to form the identity), and the group must be closed (when you combine any two elements in the group, the result is also an element in the group). It also needs something called associativity but that isn’t as important for you to know - basically, it has to do with the order of operations and parantheses, saying that (1+2)+3 = 1+(2+3).
An example of this would be the integers {…, -2, -1, 0, 1, 2, …} with the operation of “addition”. For some integer a, a+0 = a. The inverse is -a, since a + (-a) = 0. And if you add any two integers together, you get another integer, so a + b = c, where a and b are any integers, and then c must also be an integer.
Now, an abelian group is one with a particular extra property: commutativity. Meaning, in our example, a + b = b + a. This is true of most groups that most people would be familiar with. One of the simplest examples of a non-abelian group is the group of 2x2 matrices (under matrix multiplication). For a matrix A and a matrix B, AB is not the same as BA in general.
Computationalism
Question: What even is ‘computationalism’?
Answer by @Orioncrush here.
Followup by @Dolnor here.
Wiki: Computational theory of mind
Manifolds
Official answer from @bcatrek here
Partial answer by @TooSoonForNow here.
More from @solarparty here
Particle accelerator
What does a particle accelerator do? And why is that useful?
A particle accelerator is used to, well, accelerate particles! It is used to probe interactions between charged particles (electrons & protons, mainly). Linear particle accelerators speed up particles in a straight line and typically direct them to strike some target, while circular particle accelerators (e.g. the LHC at CERN) speed up particles in a circular path before colliding them with another beam sped up in the opposite direction. In general, to probe the properties of fundamental particles, you need very energetic collisions to see the desired signatures, which is why we need these special particle accelerators in the first place to speed these particles up to very near the speed of light.
Because we speed up the particles to such high energies, the resulting collisions produce an incredible amount of reactions and particles, so lots of different types of detectors are set up around the collision sites to collect data on the types and properties of the products of the collision. Using some extremely fancy physics/math and computation, these results are analyzed to try to measure the properties of, for example, intermediate particles that we cannot detect directly. These intermediate particles usually decay in very particular ways that lead to certain “signatures” in the resulting particles that we can look for. This is exactly how we found the Higgs boson at the LHC a few years ago!
Quantum Electrodynamics
See another answer from @bcatrek here
Electrodynamics is the classical theory that describes how charged particles interact. It goes through all the fun stuff like charged particles interacting with electric and magnetic fields, and how electric and magnetic fields interact with each other. It also explains how electromagnetic waves propagate through the vacuum of space! It’s a very robust theory, and you can even work special relativity into it very easily.
Quantum field theory is basically the theory behind the Standard Model, saying that there are certain particles in nature that cannot be split into constituent parts. It models these fundamental particles as being excitations of some underlying field - something that permeates the entire universe. So an electron is a particular excitation of the electron field. A common visualization is the field is some flat surface, and an electron is a little spike jutting up from that surface.
Quantum Electrodynamics (QED) takes the ideas of electrodynamics and unifies them with quantum field theory and special relativity. It is the underpinning of all interactions involving electrically charged particles and photons. It is one of the most successful physical theories ever, leading to the most precise agreement between theory and experiment in physics history.
There is a similar but, in many aspects, more complicated theory regarding the interactions of quarks called Quantum Chromodynamics (QCD).
Solar wind / cosmic rays
Follow-up to the radiation belts section.
Solar wind refers to a stream of charged particles - primarily protons, electrons, and alpha particles (a.k.a. helium nuclei, 2 protons + 2 neutrons) - that is steadily discharged from the Sun. It is a form of heat given off by the intense temperatures in the Sun’s corona. The heat gives these particles, which exist freely (i.e. outside of atoms) in the plasma of the Sun, enough energy to overcome the Sun’s escape velocity and fly off into space. However, they are still continually slowed by the Sun’s gravity as they travel outward, so the solar wind is faster on average the closer you are to the Sun. At Earth, the average speed of the solar wind particles is 468 km/s (a little over 1 million mph).
Cosmic rays are a form of high energy radiation, mainly in the form of protons and alpha particles, that originate outside the Solar System. The sources of these particles are, unsurprisingly, some of the most energetically intense phenomena in the universe, including supernovae and active galactic nuclei. It wouldn’t really be right to talk about an “average” speed since they cover a much wider range than solar wind, but suffice to say these particles can get extremely, absurdly fast.
We have all of these particles constantly bombarding us, so you might wonder how we’re all alive in the first place. And the answer is, primarily, Earth’s trusty magnetic field. It does wonders to protect us from these dangerous particles by simply deflecting them (or trapping them in the Van Allen belts). However, many particles still get through, and they generally hit our atmosphere and then react with the air molecules before ever reaching us. Even that doesn’t fully protect us though, so we are constantly exposed to the remaining radiation that makes it through all of Earth’s defenses. Luckily, the amount that ends up reaching us is small enough to not really matter.
Van Allen radiation belt
Question: What’s the ‘Van Allen radiation belt’? and why are the conditions of it something you’d want to recreate? and I guess I’m curious as to how they could possibly recreate one of the van allen radiation belts in their laboratory.
See a followup comment to my explanation from @jojo here
The Van Allen radiation belts are two regions around Earth caused by the planet’s magnetic field. The magnetic field traps energetic charged particles particles (electrons, protons) from the cosmos, solar wind, and reactions in the atmosphere in these two regions - the inner and outer belts (separate Q&A entry forthcoming for these sources of particles).
The trapping occurs because magnetic fields cause a force on charged particles as they move, so even though the details are somewhat more complicated, it’s similar to how we use gravity to “trap” satellites in orbit around Earth.
The reason there are two belts is because electrons and protons have the exact same charge, but the proton is roughly 1800 times more massive than the electron, so their typical orbital radius will be different. The inner belt is primarily protons, while the outer is primarily electrons.
Getting into speculative territory for me here, but I don’t think you can really recreate the exact circumstances of the Van Allen belt in a laboratory. However, we do use magnetic fields to manipulate charged particles all the time. In fact, this is one of the main ideas in CERN’s Large Hadron Collider. We use magnetic fields to “trap” the protons in a particular circular path while speeding them up to near the speed of light. More on this in the particle accelerator section.
Unanswered questions:
Supersymmetry
No question about this yet, but I’d like to write up about it when I have time later.
Edit 6/18 13:16 EST: Everything answered so far save for Supersymmetry, since that one will take some time/effort for me to write up. Stay tuned (and keep asking questions if you have any!).
