If photons have no mass, why does gravity effect it?

It is the curvature of space. According to general relativity, *all* gravitational actions are due to the curvature of space time, and that this space-time curvature is dependent on the mass-energy of any matter or radiation present. Even though photons have no "rest mass", they do still have "relativistic mass", which you get by dividing their energy by c^2.

So yeah, physicists actually consider gravity to be caused by the curvature of space-time, not as an actual "force". Newton's model describes it as a force between objects with mass, and this is a very good approximation for everyday scenarios, however it is not the "correct" picture. We are not entirely sure yet if relativity actually provides the correct picture either (it and quantum theory have a few seemingly irreconcilable differences), however it provides very accurate descriptions of gravity in almost all circumstances- it's only at subatomic scales that it fails.

Incidentally, satellite orbits are calculated using Einstein's model (assuming space-time is curved), as using Newton's model actually gives inaccurate results.

confident. If Earth's gravity did reason an enhance in the cost of sunshine, then it would coach that gentle has mass. in spite of the undeniable fact that, this has been examined in many techniques. One classical attempt is composed of an elevator shaft, the place an extremely precise gentle source became located on the desirable, and the receiver became located on the backside. What became talked approximately is that gentle stored occurring the comparable speed, however the frequencies have been extra beneficial (the sunshine became blue shifted). The photons gained "power" from falling with gravity yet their relax-mass remained at 0. The test became reversed (source at backside, receiver at desirable) and the effect became any incorrect way around; the sunshine nonetheless got here up on the comparable speed, in spite of the undeniable fact that it became pink-shifted (photons had much less power; frequency became decreased). end, Earth's gravity did not enhance the cost of sunshine. --- The test I defined became performed in 1960 in Jefferson Tower (physics development at Harvard college), over a top of seventy 4 feet (22.5 m).