“How could gravity affect something that has no mass ?” Easy. Gravity warps space, and the path of the photons is curved along with it. ______________________________________________________ Cool. Thanks To be clear. Do photons have mass ? No ?
"When the photon exits the medium, its identity is preserved," Lukin said. "It's the same effect we see with refraction of light in a water glass. The light enters the water, it hands off part of its energy to the medium, and inside it exists as light and matter coupled together, but when it exits, it's still light. The process that takes place is the same it's just a bit more extreme – the light is slowed considerably, and a lot more energy is given away than during refraction." Mass, energy ?
something doesn't add up.
I don’t believe photons have mass. They couldn’t travel at the speed of light in a vacuum otherwise. However, they do carry energy, expressed as a frequency. The higher the frequency, the more energetic. Mass and energy are equivalent. Each can be converted to the other. But they are not the same thing, only equivalent in a mathematical sense and in the ability to convert from one form to another. And if there is something wrong with that, it is only because I know just enough physics to be dangerous, and an embarrassment. :-)