• Question: what is the most complicated thing u have come across in particle science

    Asked by anon-217190 to Savannah, Philippe, Lucy, Joanna, Harrison, Edoardo on 12 Jun 2019.
    • Photo: Joanna Huang

      Joanna Huang answered on 12 Jun 2019:

      Probably deriving the mathematics of the theory that accompanies particle physics – called the Standard Model. This is a very elaborate theory that (to-date) is the best description of the fundamental forces and particles of the universe. Needless to say it’s very very complicated, and actually working out the maths for it takes ages! The main equation for the Standard Model takes up a WHOLE PAGE :O

    • Photo: Edoardo Vescovi

      Edoardo Vescovi answered on 13 Jun 2019: last edited 12 Jun 2019 11:37 pm

      “Particle-wave duality” is the most difficult to grasp and easy to forget.

      Particles — whether giant molecules or indivisible ones like electrons — are not “tennis balls”. We seem leaving linear traces through matter and scatter like billiard balls in detectors in CERN. You are led to think they’re spherical balls with a surface. Measuring the radius seems a problem of better technology.

      Wrong! They pass through two nearby slits at the same time, like water waves pass through two cracks.

      Punchline: “particle” and “wave” are two sides of the same coin. The best description is a “quantum object” that we are not used to in our world at human scale.

      Start with https://en.wikipedia.org/wiki/Wave–particle_duality. If too dense, I’m sure you’ll find “Mr Tompkins in paperback” more enjoyable. It’s a collection of short adventures that happen to the said gentleman when physical constants get changed. In our case, the wavy behaviour is stronger for larger value of the so-called Planck constant.

    • Photo: Savannah Clawson

      Savannah Clawson answered on 13 Jun 2019:

      I agree with everything that the others have said here – there are loads of crazy and complicated things in particle physics and that is part of the reason why it is so interesting!
      .
      To add to what Eduardo said about wave-particle duality – this is one of the first things you learn about in quantum mechanics, the fact that particles are not just particles but also behave as waves! Even though I learnt this years ago, it still baffles me. I did an experiment in university where we sent one particle of light from a laser through a slit one at a time and we could see it interacting with itself as it was a wave all along – however, if you tried to measure where it was, it acted like a particle again! This experiment is known as Young’s double slit experiment and is definitely worth a google.

    • Photo: Philippe Gambron

      Philippe Gambron answered on 14 Jun 2019:

      Calculating processes in quantum field theory. In a simple way, you can say that 2 electrons repell each other because they exchange a photon (a grain of light). But, because they accelerate, they can emit other photons as well which can later interact. And these photons can fluctuate into particle-antiparticle pairs. In the end, things can become quite messy and complicated.

    • Photo: Harrison Prosper

      Harrison Prosper answered on 14 Jun 2019: last edited 14 Jun 2019 1:44 pm

      There are lots of complicated things in physics, such as the calculations needed to make predictions using the theory of particles called the Standard Model. But, there are also many things that are conceptually extremely difficult to wrap one’s head around. It has taken me a long, long, time to disentangle the confusing language which even experts use to describe quantum mechanics. Even today, you still see books and papers in which physicists write that things can sometimes behave like particles and sometimes like waves. This is absolutely wrong!!! The truth is that things like electrons are neither particles nor waves. All that quantum mechanics tells us is that if we interact with things like photons, electrons, etc., we shall record definite values of the quantity our device is designed to measure. That’s it! There is a classic experiment called the double-slit experiment in which you fire one photon or electron at a time at the double slit. What is found experimentally is signals randomly distributed in individual pixels of a camera facing the double slit. But, and here’s the kicker, after sending through millions of electrons and photons, it is found that the distribution of dots on the camera retina follows what you would expect if you had sent in a wave! But, it does not follow that electrons and photons are sometimes waves and sometimes particles. We simply do not know what these things are. What we know in extremely precise detail is their behaviour and their properties. And, even that last sentence is misleading because we cannot prove that an electron had a charge before we measure it, nor for that matter any other property! It simply makes it easier to think about electrons if we assume they carry their properties with them at all times. Here’s a question to you: is the electric charge and the mass of an electron in the same place? If the mass is all concentrated at a point, then why is the electron not a black hole? If the mass is spread out, well how spread out is it? And how does that square with the idea that electrons like every quantum object cannot have a definite position and a definite momentum at the same time? Is the electron truly a point or is it not a point? Ok, my head is beginning to hurt, so got to stop! The world is a very, very, strange place.

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