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If gravity bends light, how do we know we're not looking at the same old light going round and round in circles?

I've been musing over this for years but never thought of putting it on here. Happily, I came across Jah Kable's post suggesting the same thing. His conversation was closed though, but I don't think the question was answered. The question is; if light can be refracted by a strong gravitational field, black hole, sun, etc. then given enough objects in its path, could it not be slingshot all over the universe? If this is true, all the stars we can see at night might be (have once been) in a radically different position to where we see them now. We might even be seeing light from the same star in two places, or more. Imagine light is a ribbon strewn around the universe, twisted round gravitational objects. If that ribbon happened to pass by Earth more than once, we'd count it more than once in our sky, and each time it would look a different age and as if it were coming from a completely different direction.
There must be someone who can calculate whether this is possible or not! Trouble is, how would we know which objects are (were) real and therefore capable of bending the light and which are the resultant image of light that's already done umpteen laps of the cosmos?! It's bending my head, I know that much!


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  • Jun 27 2013: Hi Pabitra! Yes, you understand what I mean! Light does bend all over the place, deflected by gravitational bodies! Okay, so the photon that hits us in the face will stop, but a light source emits a lot of photons (as pointed out by Edward), so some of these photons that we don't see will continue past Earth (possibly being bent a bit again by Earth) and onward through space. Given the size (infinite?) of the universe and the number of gravitational bodies available, it stands to reason that the photons will pass by and be slingshot by more gravitational bodies. To paraphrase Einstein, given an infinite universe and and infinite number of gravitational bodies (Ok I know the mass is finite but there's alot of it!), one photon could eventually do a full 360 degree loop and smack me in the face from another angle. Of course, the additional time that photon takes to travel to my retina means that the image perceived will be that of a much younger star (light source). It's occurring to me though, that these photons will be scattered more every time they are slingshot as photons nearer to the gravitational object will be more effected than those further away, therfore the "image" will be spead out (unfocused), so multiple slingshots will reduce the image to nothing and individual photons will be strewn out all over the universe (?).
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      Jul 1 2013: Since you made a fresh post, I didn't get an alert and missed your question entirely. That explains the late in my reply.
      I think in all probability a single photon's journey from a distant stellar object may be exactly what you are saying. However a photon is a quantum particle and its path between point A (the source) and B(retina of your eye) has infinite number of histories and it's observable trajectory is the sum over histories of all those paths. So with or without gravitational lensing a single photon's journey is almost infinitely indeterminate - which means it will take an infinitely long time before another photon from the same source smacks on your face, You will not be there to observe it by then.
      So, it will be rather practical to talk about a stream of photons separated by very small time interval, such that we can say it is a ray of light. Such a ray or its path is described under classical theories and your question regarding gravitational lensing becomes relevant.
      Unfortunately chances are nil that you will receive two rays of light from a same stellar object at different time on account of gravitational lensing simply because the gravitational lensing effect is possible only when light from same stellar object seem to come to you from two different locations SIMULTANEOUSLY.
      Gravity can bend a light ray to go past you and make a 360 degrees sweep and reach you - but you will see the object for the first time and make a wrong estimate about its distance and location in all likeness.
      However please remember that the physical universe is expanding and the objects at the edge of it are receding almost at the speed of light. Your solitary ray of light may get lost in an insurmountable distance.
      I think you will like to know about Olbers' paradox.
      I hope that you know however you wish you cannot see the sun right at this moment? That you will always see it 8 minutes younger than it is now?
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      A wal

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      Jul 7 2013: "(infinite?)"

      NO! You know there isn’t an infinite amount of matter and space-time is what’s in between, so it can’t be infinite. It’s a closed system, it has to be.

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