• Question: How can something (e.g. some particles) have no volume? Surely it's just that we can't measure it because it's so small...

    Asked by fish238 to Clara, Daniel, Simon, Thomas on 19 Mar 2014.
    • Photo: Clara Nellist

      Clara Nellist answered on 19 Mar 2014:

      Hi @fish238. We often talk about particles that are ‘point-like’, and say that they have no volume. When we do this, we’re talking about particles like the electron or quarks (which are the particles that make up protons and neutrons) which don’t have any internal structure (as far as we know, there are not smaller particle inside of them).

      This doesn’t mean that they don’t take up volume, because there is a volume of space that an electron will take up, but you’re right, that often it’s because we don’t know how small they actually go as we’re not able to measure it.

      Quantum mechanics also comes into play here and something called the ‘Heisenberg uncertainty principle’. We cannot measure exactly where the particles are, only predict where they’re most likely to be.

    • Photo: Thomas Elias Cocolios

      Thomas Elias Cocolios answered on 19 Mar 2014:

      The concept of volume is also one that we understand in classical terms, as in what we can experience at our size. When you get into the extremely small scale, things tend to behave differently, as nicely explained by Clara.

      As such, if you consider an electron, although its size is probably too small to grasp, its behaviour is such that we actually have to consider the volume it occupies, rather than the volume of the particle itself. This volume is called an ‘orbital’ and represents the area of space where you have a 95% chance of finding the electron. The most simple orbital is a sphere around the nucleus, but then you have some more fancy ones that look like funky crystals with spikes in all directions. Those orbitals are much bigger (of the order of 10^-10m) than the particle is thought to be.

      It is also naturally a question of scale. When you study an atom, you start from the principle that the nucleus is point-like, because its size is so small with respect to the atom that it could not possibly have any impact. We are talking of 100,000 times smaller! However, the point of my research is that it does have an effect, which I can study with lasers.

      Maybe we will eventually be able to probe the substructure of the particles we currently believe to be fundamental in the future. Something for the next generation to look forward to!

    • Photo: Simon Albright

      Simon Albright answered on 19 Mar 2014:

      This is something I’ve often pondered as well @Fish238. A recent measurement showed that electrons are the most spherical object in the universe and put an upper limit on their size but we don’t have a lower limit.

      It could be that we lack the ability to measure them or it could be that they truly are dimensionless, we’ll probably be able to provide a definitive answer one day but I don’t think we can yet.

Comments

  • Photo: Clara

    Clara commented on :

    Thomas is right that we only think electrons and quarks are point-like because we’ve not been able to measure anything smaller inside them. Interestingly, the word “atom” comes from the greek word ‘atomos’ – it means indivisible, or cannot be divided. This is because people used to think that atoms were the smallest things possible. Then, we found out that atoms have protons and neutrons in the nucleus (the middle) with electrons around the outside. After that we found out that protons and neutrons are actually made up of three quarks (and some gluey particles, called gluons which stick them together)!

    So although we think that quarks and electrons are the smallest things possible and cannot be divided into smaller pieces, who knows, we’ve been wrong before! Maybe there’s something *even* smaller that we haven’t found yet.