A quick question. It's been a long time since I had anything to do with special relativity, so I really can't remember much. But last night I was thinking about the "proof" of special relativity with the case of muons. So basically: Muons are created when particles hit the atmosphere. They can be detected on earth, even though they decay so fast, that even if they were to travel at the speed of light, they would not reach the surface of the earth. But, as stated, we do detect them. The reason for this is, that if I, as an observer on the earth, look at the muon, I see it's internal clock go slower, and therefore it has "more" time to reach the earths surface, before it decays. In the reference frame of the muon, it's clock is not changed, but instead the length of which it needs to travel is contracted, and therefore it doesn't need to travel as far, and can actually reach the surface before it decays. If I'm not mistaken, that's how it works, right ? Now, what happens when particles doesn't have an internal clock ? I mean, a photon will not decay, and I'm guessing some other particles doesn't either ? So how do I, as an observer, see it, and how does the particle itself see it ? Thanks in advance.