All matter we know has a positive mass and is attracted to other matter due to gravity – like an apple falling to Earth. Matter with a negative mass would push other matter away from it.

A politician, historian and academic answer kids' questions on Black Lives Matter.

Dark matter is not black holes: Black holes are gravity lenses that bend light. Astronomers do not see enough lensing events to account for the amount of dark matter that must exist.

What is exotic matter, and could we use it to make wormholes? – Julia, aged 14, London Matter is “stuff”. It is anything that is made up of particles that take up space. Everything we can ...