Ok, I apologize in advance if this has been asked before. I tried googling for it, but didnt find anything related. Im a comp sci guy, not a physics guy, so its possible Im not googling the right terms.

So my understanding is that:

A) Photons of light do not experience time in their reference frame. I.e., the time taken for a photon to travel from point A to point B is 0 (in the photons reference frame).

B) Light can and is bent by gravity.

So now lets say you shine a really bright flash light across the universe. Assume at the time you shine it, the light wont pass near any objects on its way across the universe.

In the lights reference frame, its just going to immediately end up on the other side of the universe (assuming that photon didn't hit anything).

However, since this example universe is so big, tons of objects had time to get near the path of the light without hitting it. Their gravitational pull altered the photons' path ever so slightly.

So, to my actual question:

In the example above, the moment the light photon is send flying across the universe, nothing is near its path of travel. However, in its reference frame, it immediately arrives at an altered location due to objects that got in its path.

How can this be possible? If light truly experiences no time, the time at point A and the time at point B should be equal. In either reference frame, the universe objects have not yet moved near its path when the light is at point A.

  • $\begingroup$ I feel that it would be better you ask a similar question only after you have studied a little of Special Relativity. There is nothing like a photon reference frame. $\endgroup$ – GiorgioP Feb 24 '20 at 9:07
  • $\begingroup$ Not only time does not exist for a photon, bud distance does not exist either. The point of origin is the point of the destination. This is why the path of a photon is called “null”. Your question will not be well received, because you mention the reference frame of a photon that does not exist. Instead of photons, you could use neutrinos. They move with practically the same speed and practically along the same path as photons, but they do have a reference frame. In this frame, time is not exactly zero, it is very very short, but at least it exists and can be mentioned without objections. $\endgroup$ – safesphere Feb 24 '20 at 14:54

In the frame of an observer, a photon follows a geodesic. . In the observer's framemork the moving masses create moving geodesics for the incoming photon which is traveling with the speed of light in vacuum. In the photon's framework there is no time to be defined as "before" and "after" the motion of masses in the observer's framework .

  • $\begingroup$ @safesphere I am answering the question, which states "apj=hoton does not experience time", it is that "experience" I call framework. . The question wonders how in some framework gravitational lensing is seen, when the photon does not "experience" time. If you have a different and better answer please write it. $\endgroup$ – anna v Feb 24 '20 at 17:01
  • $\begingroup$ This is very unclear. What do you mean by frame? A reference frame? Then something being geodesic is independent of the frame, and there is no such thing as the photon's frame. $\endgroup$ – MBN Feb 25 '20 at 9:55
  • $\begingroup$ @MBN please feel free to write a clearer answer, I explain in my last comment how I use the words. $\endgroup$ – anna v Feb 25 '20 at 11:31
  • $\begingroup$ feel free to take my feedback any way you want to. I said what's wrong with your answer, it is up to you to make it better or leave it as is. $\endgroup$ – MBN Feb 25 '20 at 14:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.