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Consider a Photon from Sun and travels with a velocity $c$. Now think we are that photon. For us, it looks like Sun is moving away from us with a velocity $c$. So, why don't we get attracted back towards Sun, because the mass of Sun would be infinite for us since it moves away from us with a velocity $c$.

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Related to your second q: physics.stackexchange.com/questions/27794/… . I can't seem to find a post explaining why photons do not experience passage of time, though. –  Manishearth Dec 29 '12 at 8:49
Hi Inquisitive. Could you please revise your second question. I don't force you. But, Manish has already given you a link. If you think its helpful, you could erase your second question. Or, you could clarify it to ask something specifically. But - to me, it looks the same. It is a good question though. But, There are many questions related to yours. I'll try to provide some useful links. Another piece of advice: A revision may sometimes enable the undownvoting for other users :-) –  Waffle's Crazy Peanut Dec 29 '12 at 9:11
@CrazyBuddy Done –  Inquisitive Dec 29 '12 at 9:14
@Inquisitive probably the biggest issue with this question is that it shows a significant lack of understanding of even the basic concepts of special relativity. You're asking what we'd see if we pretend to be that photon, but we can't do that; a photon does not have a reference frame. So it's a meaningless question. –  David Z Dec 29 '12 at 9:59
@DavidZaslavsky: Now, it reminds me of this question: physics.stackexchange.com/q/16018 –  Waffle's Crazy Peanut Dec 29 '12 at 10:00
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1 Answer

up vote 1 down vote accepted

You have completely mixed the modern and classical concepts of relativity. If you're talking about mass increment, you shouldn't calculate speed of Sun based on absolute time & space notion.

For you as a photon, space will be contracted to zero and time will be dilated to infinity. So, you can't calculate a speed (which is a time-like spacetime event) of Sun.

While its a nice satisfactory explanation, its not the real one.
Real Answer:
Relativistic physics doesn't allow you to take position of a photon. In other words, relativistic physics doesn't allow photons to be an observer. Its because a photon can see itself stationary which breaks the framework of relativistic physics. Relativistic physics doesn't allow photons to be at rest in any reference frame.

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How it is possible for a photon to be in motion w.r.t to itself? –  Inquisitive Dec 29 '12 at 9:57
There is no such thing as "with respect to a photon." –  David Z Dec 29 '12 at 9:59
@Inquisitive Its not possible. That's why Relativistic Physics doesn't allow photons to be an observer. –  Sachin Shekhar Dec 29 '12 at 10:00
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