[baytrailcat]

This is an intuitive way of thinking about this without diving into the math. Here are the postulates: speed of light (c) is same for everyone. And there is no special reference frame; your physics is as good as the physics of your friend moving away from you in a space-ship in a constant velocity v. Now consider that your friend is actually moving in a spaceship away from you. He has an experimental setup with him using which he measures speed of light. You are sitting at home postulating about his experiment. Consider he is moving at velocity v, so is his experiment equipment. How can he arrive the same result (3*10^8 m/s) for speed of light? You conclude that only way is that whatever clock he is measuring the experiment with is running slower than yours (velocity=distance/time, he is measuring less distance, so time must be less too). Now imagine he is going at the speed of light. (The actual equations breakdown at this point, but you can imagine he is infinitesimally close to speed of light). How is he arriving at c? Only way is time is not passing for him (according to you). Now imagine he is going faster than speed of light. At this point, the equipment he is sending photons with is traveling faster than photons itself! How does he arrive at c? His clock must be running backwards! And keep in mind, your friend in all these cases is happily measuring speed of light as c without any of these conundrums you have. And now you can publish a paper claiming that your friend travelled back in time! Did he really do that in a "Back to the future" kind of way? Perhaps not.

[nercht12]

I did used to ponder over this sort of mystery, but I realized the actual answer to this lied at the particle level as explained in QED by Feynman: A positron can be treated as an electron traveling backwards in time. When it collides with an electron, the two create a photon. Should you ever come close to the speed of light, one way to "exceed" it would require a collision with your anti-matter self, resulting in (self-obliteration and...) photons from everyone's else's point of view. Of course, assuming my understanding is correct, it's also possible that you transform into your anti-matter self... bizarre. Going forward again would require some similar interaction, but I seem to recall formulating a thought experiment where this violates causality, making either the whole idea impossible even from a Relativistic standpoint or forcing some denial of causality, which would make other dependencies on causality (such as science itself) unreliable.