# Relative Speed of Photon!

Yes to some extent, now I understood the dilemma of this relative velocity taking relativity into account. I have some last questions regarding relativity, do we know the reason why a particle moving @c can't be taken as reference frame and why does the behavior/properties and laws change so abruptly when we move from speed c-1m/s to c? [..]
There is no "abrupt" change. Instead, at speed c such a reference frame (even a virtual one) would have (according to us) clocks that do not tick at all (dt'=0) and its rulers would have zero length in the direction of motion; you can't calculate with that.

ghwellsjr
Gold Member
Yes to some extent, now I understood the dilemma of this relative velocity taking relativity into account. I have some last questions regarding relativity, do we know the reason why a particle moving @c can't be taken as reference frame and why does the behavior/properties and laws change so abruptly when we move from speed c-1m/s to c?

Thanks to all for you kind help and precious time.
With regards
Mudasir
No matter how much you have accelerated in the past to achieve some high rate of speed, even c-1m/s, the speed of light to you will still measure to be c. But remember, we're talking about measuring the time it takes for light to make a round trip and then dividing that by 2 and assuming that the one-way speed of light is equal to that answer.

No matter how much you have accelerated in the past to achieve some high rate of speed, even c-1m/s, the speed of light to you will still measure to be c. But remember, we're talking about measuring the time it takes for light to make a round trip and then dividing that by 2 and assuming that the one-way speed of light is equal to that answer.
I think you got my point wrong, when I said moving from c-1m/s to c I didn't mean accelerating from c-1m/s to c rather I meant when we observe/study one object which is moving at c-1m/s and another object moving at c.
Thanks

ghwellsjr
Gold Member
I think you got my point wrong, when I said moving from c-1m/s to c I didn't mean accelerating from c-1m/s to c rather I meant when we observe/study one object which is moving at c-1m/s and another object moving at c.
Thanks
If there's one thing you should have gotten by now in this thread, it's that no object can move at c.

Doc Al
Mentor
and another object moving at c.
This second 'object' must be massless... such as a photon. Not any kind of ordinary 'object'.