• Question: What is the empty space made up of? Consider hydrogen gas.It is made up of H2 molecules. Each molecule is made up of two hydrogen atoms. Each atom made up of a nucleus and an electron. But what is the space other than an electron and the nucleus inside a hydrogen atom made up of?

    Asked by rajathjackson to Chris, Dave, David, Fiona, Jack on 21 Jun 2013.
    • Photo: Fiona Coomer

      Fiona Coomer answered on 21 Jun 2013:

      I am sure that the physicists can probably give a better answer to this question, but essentially most of the universe is indeed empty space, though it isn’t quite as simple as that.

      As electrons are so small and light, we can also think of them as being a wave rather than a particle. This means that rather than thinking of the electron in a hydrogen atom as being at one particular point in space at any particular point in time, we can work out the probability of where the electron might be. We do this by solving an equation called Schroedinger’s equation, which we can do exactly for a hydrogen atom, but it becomes unsolvable for other atoms. It turns out that there is a finite probability that the electron in a hydrogen atom may be located at any distance away from the nucleus. If we think of electrons in this way, there is no such thing as empty space, but always the chance that there may be some electron density there.

    • Photo: David Freeborn

      David Freeborn answered on 21 Jun 2013:

      Hi rajathjackson,

      That was a good answer from Fiona. The other thing I would add is that the “Quantum Vacuum” is everywhere across all of empty space.

      In Quantum field theory, the “vacuum” is never totally empty. Heisenberg’s Uncertainty Principle can be used to show that nature can “borrow” very small amounts of energy for very brief amounts of time, to make particles appear and disappear. This means that the vacuum is really a seething mass of very short-lived particles.

      Some physicists have mathematically treated this mass of particles as a liquid, when trying to understand it’s behaviour, but it’s more complex because particles will keep appearing and disappearing all the time.

      We call these “virtual” particles, but it’s a bad name, because they are real, and can have real implications if they interact with real particles. In fact, we need these “virtual” particles to hold matter together. Protons are mostly held together by “virtual” gluons from the quantum vacuum, and atomic nuclei are held together by much larger virtual particles called “pions”.

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