karthik · created · flag · 4

If you are in space and shine a torch in an arbitrary direction, the photons (although being massless) will impart a thrust on you that will propel you in the opposite direction. This is due to the conservation of momentum as well.

In other words, when photons are ejected out of the torch, they travel outward with a momentum*. And due to this, your momentum changes to conserve the total momentum of your initial state, pushing you in the opposite direction.

* Photons have a relativistic mass and they do have momentum, given by $p = \dfrac{h}{\lambda}$.