what's your favorite physics fact that seems fake but is actually real?

@FinitePhysicist Due to the expansion of space, everything moving through space will eventually slow down and stop without any outside forces acting. Newtons laws don’t apply when space/time is changing.

@CodysLab @FinitePhysicist I feel that I could probably argue for about half an hour about what stop means in this context, and whether it's the right verb.

@Naitso @FinitePhysicist Stop as in loose all kinetic energy and be not moving through the space that it is in.

@Naitso @FinitePhysicist The particles in gasses like hydrogen and helium actually speed up as they expand. the energy content of the gas is the same no matter the volume. So how did the gas particles slow down enough to form stars? Answer: it wasn’t just adiabatic expansion.

@CodysLab @Naitso @FinitePhysicist KE = 0.5*m*v^2. What is velocity relative to here?