This might be a stupid question, but I am trying to understand the fundamentals.
The closest I've come to is
Newton's Third law of Motion which states
for every action (force) in nature there is an equal and opposite reaction. So if we are expending energy by firing rockets in one direction there must be a reaction that push us forward. This seems easy to understand on earth (ie. pushing back the ground or atmosphere) but in vacuum of space what are we pushing backwards.
I don't want to accept, with all due respect, Just because Newton said so.
While this seems so obvious that this is the expected behaviour but is there some underlying physics that can help me understand this better?
One surprising theory might be dark matter but that rises many more questions like does it still qualify as vacuum if there is dark matter and also an obvious one, have we ever calculated that?
Edit: ground pushing us forward might seem a bit abstract so here is what I remember from my high school physics, If Object A pushes Object B, then Object B pushes Object A at exactly the same time, with exactly the same amount of force, but in the opposite direction.
The reason the Earth pushes up on you with the same force has to do with the nature of solids. When you stand on the ground, you are actually compressing the dirt beneath you. This compression also applies to the billions of interparticle and intermolecular electrochemical bonds in the solid matter of the Earth, which act a bit like little springs holding things together down at the atomic level.
Cars, boats, airplanes, and humans move forwards by pushing back on the ground, the water, or the air. Above text is copied from here -> Blog post on Third law of Motion
ps. Not related, but will the airplanes stop working is we take away the atmosphere from Earth.