• Question: Why Particles???

    Asked by anon-217311 to Savannah, Philippe, Lucy, Joanna, Harrison, Edoardo on 11 Jun 2019.
    • Photo: Edoardo Vescovi

      Edoardo Vescovi answered on 11 Jun 2019: last edited 11 Jun 2019 3:39 pm


      It’s a deep question and a satisfactory answer is still at large. You’re basically asking: why do things that exist exist?
      The idea of small parts arises from the observation of grains of sand or smoke in the air, as well as the human wish to explain complex phenomena in simple ways. Particles do the job: they are small, all equal and combine to produce a variety of forms and shapes.
      This is just an idea, or hypothesis. Ancient philosophers thought of matter as a continuous blob that doesn’t leave any void. You can well say this is true, as water doesn’t look to be made of smaller parts as sand.
      To sort it out, we question nature. We can set up experiments, as Rutherford did in Manchester about 100 years ago, where small bits of matter collide at high speed and decide which model (particles vs. continuum) describes better the outcome of the experiments. “Particle” has won, so far at least. Atoms and other particles cannot be actually seen with the naked eye because visible light passes through without casting a shadow.

      Currently we believe that the real indivisible particles are quarks (which combine to produce atoms’ nuclei), leptons (like electrons orbiting around nuclei) and bosons (like light’s photons or the famous Higgs boson) that carry the forces among them. Google “Standard Model” to know more about their properties. Also keep in mind that a “particle” is not simply a “tiny ball”, as sometimes it behaves like a wave without a definite position in space.

    • Photo: Harrison Prosper

      Harrison Prosper answered on 11 Jun 2019: last edited 11 Jun 2019 4:16 pm


      Even though I’ve had a passion for astronomy and cosmology for a very long time, and still do, I was drawn to particle physics because I wanted to understand the Universe at its most basic level. I thought that the physics of particles would be the place to get that understanding. I think this is true. Moreover, I find it amazing that the proton-proton collisions we study at the Large Hadron Collider (LHC) at CERN are able to reproduce the conditions of the Universe when the latter was a tiny fraction of a second old. So my work in experimental particle physics turns out also to be about cosmology, my other passion! That being said, I have come to realize that the gulf between the particles we study at the LHC and, for example, how DNA works is so immense that it will not be bridged anytime soon. Therefore, it is critical to have different sciences that each work at a different level of Nature. There is no way at present to use particle physics to predict the workings of DNA, but we can use the science of molecules, which is based on the science of atoms, which in turn is based on quantum physics, to build an understanding of how the DNA molecule works. The great physicist Paul Dirac once remarked that given that we know the precise rules that govern atoms, with enough calculation everything in chemistry and biology is “merely” a matter of calculation. At the risk of annoying my biology and chemistry colleagues, this is true, in principle. But, in practice, perhaps impossibly difficult! Even today, we still cannot derive the properties of the atomic nucleus from our exquisitely precise understanding of the properties of particle, let alone the DNA molecule. Therefore, we need sciences at all levels if we are to make progress.

    • Photo: Savannah Clawson

      Savannah Clawson answered on 11 Jun 2019:


      I think studying particle physics comes from the desire to break things down until you know exactly what goes into making them. It’s just like baking a cake – you have to mix up lots of different ingredients like flour and sugar and apply some conditions (like a hot oven) to make the final product. The Universe is no different and it turns out that if we keep breaking things down, from everyday objects, to molecules, to atoms, to protons and neutrons, we finally arrive at the fundamental particles which we (currently) don’t believe can be broken down any further. Therefore, particle physics is basically a recipe to create the Universe! If you know what all of the ingredients/particles are, and you know how they will behave when you mix them all together, you can create whatever you want!
      The only problem is that it is extremely difficult to predict how they will behave when we bring more than a few particles together at once – the only way we can find out is to see what happens when we try it!

    • Photo: Philippe Gambron

      Philippe Gambron answered on 12 Jun 2019:


      It’s because they are the most fundamental building blocks of Nature. The matter surrounding us is made of molecules. These are made of atoms. In turn, atoms are made of electrons, protons and neutron and the latter two are made of quarks. These are fundamental particles and we have no evidence they are made of something else. Studying their behaviour can also help us understand how the world works because it helps us to understand the fundamental forces.

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