eli5: If space is a vacuum, how can rockets work? What are the thrusters pushing *against* if there is nothing out there?

Question

I’ve never really understood the physics of this. Obviously it works somehow — I’m not a moonlanding denier or anything — but my (admittedly primitive) brain continues to insist that a rocket thruster needs something to push *against* in order to work.

So what is it pushing against if space is essentially a void?

In: 7157

Answer 1

In very simple terms, the thrust is pushing against the rocket body.

It doesn’t need to push against the air or lack there of, unlike a fixed or rotary engined vehicle that generates lift via that interaction.