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But another question: If a photon which has mass and is travelling at light speed "can" be pulled by gravity, would that "pull" not add a net velocity to the photon?

It's generally easier to talk about beams or pulses of light than photons, as quantum mechanical photons are odd beasts that don't really behave like little bullets flying along through the universe. So if we have a pulse of light, it's velocity can change, since velocity includes direction and gravity can deflect it. It's speed doesn't change, since we measure speed locally, meaning as the pulse flies by us. We could sit anywhere along its bent path and measure it to travel at the speed of light. The total time it takes to go between two points will change if you put a large mass in the way, since light travels on a curve and even though it moves at a constant speed along that curve, the total distance it has to travel increases.

Just a muse, but are photons and other parts of the electromagnetic spectrum pushed or pulled after propagation?

By the way, someone could complain that speed + direction = V is sloppy notation since you can't add a speed to a direction.

I am confused? What is the difference between velocity and speed?

The total time it takes to go between two points will change if you put a large mass in the way, since light travels on a curve and even though it moves at a constant speed along that curve, the total distance it has to travel increases.

Quote from: JPBy the way, someone could complain that speed + direction = V is sloppy notation since you can't add a speed to a direction. Yeah but you can tell from the context that the plus sign is being used as a logical and rather than a summation off terms, right?

Yeah, I can, but someone who hasn't taken enough math to see vectors might not know the distinction. Or maybe I'm being too pedantic. :p