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?

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!