Some sort of memedrive

So why doesn't it work, Veeky Forums?
I'm serious.

wtf am i looking at? a torch and a piece of paper?

anyway i think the answer to this is heat loss

>photons have mass

Yes, a torch and some reflective surface, like a light sail. Can you explain?

They have a mass when they're moving at c.

Surely the photons would only propel the grey stuff by absorption? If the grey stuff absorbs the photons the flashlight feels the same amount of recoil.

A reflective surface would propell it twice as much because of the distribution of impulse.
The grey stuff is something like tin foil or a mirror.
What I'm trying to say is picture 1 works, which has been demonstrated with light sails.
But picture 2 doesn't work, because it would essentially be a memedrive.
So if accelerating (creating) photons creates no thrust, but reflecting them does, then picture 3 should produce some amount of thrust.

Not proved.

...

why do you assume, that the toch doesn't experience force in the second pic?
It's not much, but it would move just like a rocket (but reeeeally slowly) without any outside forces interfering

*torch

photons have energy (hf)
and e=mc^2 so hf=mc^2
m=hf/c^2

If you assume the surface receives a net force in that direction from the photons, which is debatable, you must also assume that the flashlight is experiencing an equal and opposite force.

Look up photon rockets, op.

that would only work if the flashlight was travelling at relativistic speeds.

Yes, but if picture 2 works, it means that the memedrive is completely legit and you can move without expelling mass (an object with resting mass)
We know that pic 1 works.
So, ether pic 2 or pic 3 must work aswell.

Your premise is false. The torch will feel a force opposite the direction of the light regardless of what's behind it. If you attach a mirror to it like that the forces will balance.

So you can convert electricity directly to force?

In order for it to work, you need to make sure that you can abuse the forward energy much more efficient than the backwards energy. It should be possible to achieve this.

user, 2 produces thrust, it's a photon rocket.

And the point of the memedrive is that
1. the hull is closed so photons can't get out, it's not a photon rocket
2. it produces a thrust much higher than a photon rocket, otherwise nobody would care

And if you wonder, photon rockets are useless because their efficiency both in terms of thrust/energy and thrust/weight is pure garbo.

>thinks that is proof

lol kid

Ok, thanks for explaining, so the point of light sails is that you don't have to carry around a photon generator. I think I get it now.

the point of light sails is, that we could use the sun to power the spacecraft, or that we could use lasers mounted on planets, moons, asteroids... to power the spacecraft, saving in expensive fuel (why is fuel more expensive, then lasers? --> the more fuel you need, the heavier the rocket gets, the more fuel you need). We can reach higher speeds in the end aswell. While fuel rockets (with our current rocket fuel atleast) are capping out at one point, because of the limitations i mentioned, you can send a laser out for a very long time, accelerating your spacecraft for far longer

Yes. But it's very weak.

>OH MY GOD IT'S INCREDIBLE!! IT MOVES 1 NANOMETER PER YEAR

That's for an object at rest.

Photons have momentum, not mass.