Re: If a photon had a clock ...?

Hi

Special relativity tells us that moving, at any speed, does strange things to our perceptions of time and space. Suppose I look at a clock that is moving relative to me (it doesn't matter if I'm moving and the clock is standing still or if the clock is moving and I am standing still.) According to special relativity, time, as measured by that clock, will pass more slowly than time on a clock that is standing still relative to me (eg. my wristwatch). This is the effect known as time dilation and the size of the effect depends on the relative speed between me and the clock, as a fraction of the speed of light. If the relative speed is very small compared to the speed of light, there is no measurable time dilation, which is why we don't notice time dilation in everyday life.

As the relative speed between me and the clock approaches the speed of light, time dilation will become more and more noticeable and the theory predicts that when the relative speed is equal to the speed of light, the clock should appear to stop completely.

So, I would say that in a photon's frame of reference, which travels at exactly the speed of light, all stationary clocks in the universe would appear to be frozen at the time of the photon's creation. Clocks in moving frames of reference would appear to tick, but very slowly depending on their speed relative to the photon. A clock travelling alongside the photon, in the photon's frame of reference, (if such a clock could exist), would appear to tick normally since it would not be moving from the photon's point of view.

For further information, you might want to have a look at Andrew Hamilton's Special Relativity page (which includes some animations demonstrating relativistic effects) or look at some of the sites listed on the Relativity on the Web page.

Jim O'Donnell