You may have seen it happen in the movies, or on TV: an astronaut swims their way through space to get from point A to point B. It may look a little fun, but unfortunately, humans can’t swim through space because there’s not enough stuff to swim through.
We can easily swim through water because water is dense enough to allow us to push back on it with our hands and get something for our effort. By conservation of momentum, when we push on the water, the water pushes back on us, propelling us forward.
However, the same swimming motions don’t work out so well for us in the air because our atmosphere is 830 times less dense than water. When we wave our hands and push on the air, the air is technically pushing back on us, but not enough to count.
Airplanes and flying animals can still manage ...
