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Originally Posted by Tensor
I think your confusion comes from thinking that EM radiation is a mechanical wave (like water or sound waves) requiring something physical to move. But, EM waves are not mechanical, nothing is really waving. It's simply the changing electric and magnetic fields producing properties similar to that of a mechanical wave.
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I'm aware that the general view is that EM waves do not require a medium, they simply propagate through space. However, Tim was suggesting that they are waves in the spacetime medium. If the latter were true it could explain why photons could be stretched out in the Big Bang model. If it weren't true, it's hard to see why such stretching would occur. I am just curious about how the theorists look at this.
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I also believe (and I may be wrong, if so I apologize), from reading your posts, that you still aren't really fully reconciled with the idea of photons having wave and particle aspects at the same time.
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It seems the wave-particle duality just tells us that we don't know much about light. I'm OK with it, in the sense that it highlights our ignorance about it. But I wonder whether you are using wave-particle duality to dodge the tricky question of why photons redden during the BB. My understanding is that we can't say the reddening is straight Doppler (recessional) or straight gravitational. The spacetime expansion seems to be needed. In that case what is it that tacks down the photons to spacetime? If the reddening occurs through spacetime stretching, they have to be tacked don't they? If you say "No, photons are particles too, so they don't need a medium", then what causes them to redden? Somehow I don't think wave-particle duality could be at the core of the Big Bang model. For one thing, Einstein would have complained!