I understand that it’s impossible to bring a photon to a state of rest, therefore impossible to collect them into a cup to weigh them and calculate their mass. A guy in a pub explained to me, quite smugly, that photons are just expressions of energy and that’s that. From my understanding solar sails would be just large surface areas being hit by photons, pushing the spacecraft in a desired direction, just like normal ship sails are being pushed by wind. But air particles do have mass. How could photons push the spacecraft if they don’t weigh anything?
In: Physics
Solar sails do function (as described by other comments). In 2018 was some theorizing around ‘Oumuamua being an alien solar sail, which led to [this interesting preprint](https://arxiv.org/abs/2105.09435) against interstellar travel with solar sails. From the abstract:
>even if we neglect slowing (and damage) by interplanetary material, there exists an effective terminal velocity beyond which the sail barely accelerates. This velocity is much lower than the relativistic speeds proposed […]
‘Oumuamua would take two million years to cover the distance to the nearest extrasolar star (at just 4.22 light years distance).
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