• Question: How do you conceptualise/comprehend empty space such as the empty space between atoms. What kind of properties does empty space have? And if it does have properties how do they interact with matter and different forces?

    Asked by Toni V on 12 Sep 2023.
    • Photo: Joel Goldstein

      Joel Goldstein answered on 12 Sep 2023:

      That is an excellent question, which is really difficult to answer. So let me answer a slightly different question: is there really such a thing as “empty space”.

      We can imagine a region of space with nothing in it and that is so far from anything else (and that has been so far away for so long) that nothing else in the universe has had any influence on it. Such a region is a “true vacuum”: it is still permeated by fields (e.g. the electromagnetic or photon fields, but these fields are in their ground state. In classical physics, this would mean they have zero value and zero energy, but amazingly enough in quantum mechanics they must have some minimum energy. One picture of fields is there are tiny little springs throughout the space – in the classical vacuum they would all be stationary, but in the quantum vacuum they are humming quietly away even at their lowest energy state.

      In any real “vacuum”, it is even more complicated as there will be atoms or other particles in the surrounding space that put energy into the fields that influence the vacuum, making particles or transmitting forces.

    • Photo: Kay Dewhurst

      Kay Dewhurst answered on 14 Sep 2023:

      I think “empty space” is a pretty difficult concept. Usually, when we say “empty space” we mean a place with a lack of… other “stuff”.
      For example, outer space is the universe beyond our atmosphere but most people think of it as the gaps between planets/ stars/ galaxies. That space actually contains quite a lot more “stuff” than you first think, such as small amounts of gases, photons of light from the stars, particles like neutrinos, microwaves (as in the Cosmic Microwave Background) etc.

      Things can pass through empty space such as:
      – Forces (gravity keeps planets and moons in orbit)
      – Particles (like electrons / charged particles from our Sun – they cause the aurora borealis)
      – Energy (like photons of light; this is a bit of a cheat because we can consider photons to be particles)

      An interesting thing to think about is, if a particle enters your region of empty space (just passing through) is the space still empty? 🤯

      Forces and particles don’t interact with empty space, but they can pass through it and influence particles on the other side. For example, all the particles (mass) that make up the Earth produce a gravitational force. That force can extend through empty space and affect other distant particles, such as all the particles making up the mass of the Moon, causing it to stay in orbit around the Earth.

      In the 19th century, physicists thought that forces needed something to help them propagate, like how ripples on a pond need water to exist; at the time they called this ‘something’ the ether (or aether). We’ve since found no evidence of an ether. Forces CAN just propagate through nothingness – empty space, which is pretty cool!