Quote:
Originally Posted by Pastor
Will you explain the wave/particle duality of light to me, I never could get a grip on that
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That's relatively easy. Light has in the same time properties of a wave (like for example an electromagnetic wave), and in the same time properties of a particle (like for example an electron). Einstein's Special Theory of Relativity explains why. Even if you are not a physicist, you probably know that objects moving with the speed close to the speed of light are changing their weight and length. Better told, they just appear to be lighter and longer to the static observer, but should you be moving with the same speed as the object, it will have the same length and weight as you are used to (from your standpoint). So in fact, very simplified told, it is somehow just a kind of a "visual effect" - similar to fast moving objects in cartoons - they are being designed prolonged too
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Now, the photons move with the maximal possible (measurable) speed (the speed of light) - hence due to the above mentioned principle, they are (better told, appear to be) extremely long (imagine them as very long strings), and endlessly light (weightless). So from this point of view they have most features of a wave that transfers no particles, no matter. But then, when you manage to slow down the light by passing through material or by reflexions, the photons show their real face, and you observe their particle properties - for example light is able to mechanically move a light mill, similarly as a beam of material particles - you certainly saw it in the school too.
The light/photon hence behave in the same time as a wave and as a particle - in contrary to (for example) the electromagnetic wave and electron - unlike at light where photons move from one point to another, electrons are not being transported at electromagnetic radiation (though they interact with it).
These principles are perfectly demonstrated in Photonic Laser Propulsion: imagine a spacecraft turning on a massive laser. Normally, nothing would happen - the spacecraft would not gain any speed, just because the photons shooting out have no weight. But using a simple trick - slowing down the photons slightly through millions of reflexions in the reactive chamber, they gain some weight and when they then finally shoot out of the space craft, they push it in the opposite way, and hence can accelerate it to a great speed. The
BAE Institute demonstrated a
small laser propulsion in their laboratory - with a stock laser they managed to generate thrust of 35 µN - that seems tiny, but if scaled up, it could thrust a space craft to Mars in about a week (instead of many months we currently need for it).
Erratum: as pointed out by other further below in this thread - what I wrote above about the weight is complete nonsense and in fact it is exactly the opposite case. Sorry for the confusion, next time I should first dust off my school knowledge before posting. I should better remove or correct the text above, but since it was already quoted below, I am keeping it here for reference as a wisdom of my stupidity.
PS: the laser thruster is for real though