Light year sun, won't you come, and wash away the raiiiin?
Have you never noticed that if you get two identical lamps and put them close to each other, it gets dark in between them? Common phenomenon that anyone can replicate in their homes.
I know that when I'm sitting watching telly with one lamp on, thinking "it's too bright in here", the obvious answer is to put ANOTHER lamp on in the opposite corner so that the light cancels out and the room gets darker.
Light can cancel out light, and one demonstration is the double-slit experiment:
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On this, patches of light and dark can be created where two light waves interact to make destructive interference. But, to work the two light sources need to be the exact opposite.
Light is a wave so if you picture two waves colliding, if the two peaks collide you get a higher intensity light. But if a peak or a trough collide then they cancel each other out to zero. But if one of the light sources was only half the intensity of the other, it would not work. You might dim one light source by a half but that is it. There is also the issue of polarisation. It is easy to draw a light wave on paper as a 2d object. But if you imagine light from a lamp moving away from a bulb, some waves will be up and down, some will be left to right and the rest anywhere in between.
So to cancel each other out, light needs to be the same intensity, the same polarisation and sufficiently out of phase so peaks meet troughs. Because this is so complex to create, nobody has ever demonstrated the effect you describe where a lamp, screen or projector turns black by shining another equal and opposite image at it. Even two lasers pointed directly at each other are unlikely to do this. To work in the scenario of the moon being a reflection of the sun and for god only knows what reason, turning back on itself to cancel itself out, the moon would have to be exactly the same intensity as the sun. We know the intensity of both differ across the surface. The sun has sun spots, the moon has all the features we can see and the obvious one, it is not as bright. Then the final inconvenience to this fuckwittardry, you only get a solar eclipse during a new moon, where from the point of view on earth, the moon has zero intensity because the light side is that facing the sun. We fall into the shadow of the moon, we are on the dark side.
Then there is the other inconvenience. I'm saying this effect can be carefully manufactured in a lab to some degree (not a complete wipeout) because light is a wave. Except that is reality physics. We need to remember to apply fantasy physics to this cancel itself out daftness and remember that light doesn't travel at all and is not a wave. So it cancels itself out without actually moving.
Don't worry, this can be easily explained by stringing loads of sciency sounding words together that don't really go or having any meaning and having the smug satisfaction of a job well done. And I've just had the pleasing realisation that this effect we see is exactly the same as Del Boy's attempts at French. Mange Tout fly2u, mange tout.
Meanwhile back in reality, this is a handy conversation as we have a partial solar eclipse visible here on October 25th. Details available here:
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What is notable is that London will see a different amount of the sun covered than Sunderland, exactly like you would expect if it were caused by one relatively close object passing in front of something much further away. The complete opposite of what would happen if it were an effect on a fixed screen, where everyone would see the same eclipse.
If you are interested in this, never look with the naked eye and sun glasses are not sufficient. You will seriously damage your eyes. If you search for eclipse glasses now, they will arrive in plenty of time to view this. If the weather holds, I'll try to get a few images of it and join it together into an animation.
