Why don't photons experience time?

[Naty1]

PeterDonis

Because c dt = dl. Look at the two events I wrote down:

(0, 0, 0, 0) and (1000, 1000, 0, 0)

I used units where c = 1, so we have dt = 1000 and dl = 1000; the interval is null because the two are equal.

very helpful insight...I had forgotten the distinction between a null interval in space versus a null interval in space-time...

a nice brief discussion here for others who may be learning:

http://en.wikipedia.org/wiki/Spacetime_interval#Spacetime_intervals


and also 'null events of a photon' trace out a lightcone...illustration here,
in flat space-time

http://en.wikipedia.org/wiki/Light-cone

This kind of light-cone has some characteristics of null surfaces in cosmological,
also accelerated, horizons, right??

 

[PeterDonis]

This kind of light-cone has some characteristics of null surfaces in cosmological, also accelerated, horizons, right??

Light cones are null surfaces, and all null surfaces have properties in common, yes.