• Question: What is the smallest particle you have ever seen?

    Asked by kristjana to Deepak, Francesca on 12 Mar 2014. This question was also asked by blossom1999.
    • Photo: Deepak Kar

      Deepak Kar answered on 12 Mar 2014:

      Very interesting question!

      In our experiments, we no longer “see” a particle directly. All we get to know is the path of the particle inside our detector, and how much energy it has. An example:

      This shows a how a real collision looks like 🙂
      Here the two yellow lines are electrons, and we get them in our detector. From their energy and direction, we calculate that a particle called Z-boson was produced in the collision, and decayed into the electron-pair. This is the closest we go to “seeing” tiny particles in the detector!

      Now in the strictest sense you can say we only see photons, because our eyes only see light reflected from other objects. Going beyond that, there are quite common experiments which you will do in college where you get to see electrons. They are very small indeed.

    • Photo: Francesca Day

      Francesca Day answered on 14 Mar 2014:

      We can’t see sub-atomic particles, even with a microscope, because they are so small. You might know that light is made up of particles called photons. Photons have no mass, and they are “point like” i.e. they don’t take up any space. So that’s about as small as you can get!

      You could say we “see” photons all the time when they enter our eyes as light. So I guess the photon is the smallest particle any of us have ever seen!

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