How can we talk about a photon's frame of reference in special relativity?

[Nora.W]

I’ve been trying to wrap my head around the concept of a photon’s frame of reference. If a photon is massless and travels at c, then in its own “rest frame” time would be frozen and distances contracted to zero, but special relativity says such a frame doesn’t actually exist. I’m struggling to reconcile this—how can we talk about properties from a perspective that’s mathematically invalid?

[KevinWS]

I've tried explaining to a friend that we never ride along with a photon. In lab frames a photon has energy and momentum that depend on the observer, but there is no clock on its own. So the idea of its rest frame is a math fiction we use to talk about limits, not a real perspective you can inhabit.

[Chloe40]

I drew a light clock once—two mirrors and a pulse bouncing between them. In a fast frame the tick distance changes, but for the photon itself the ticking isn’t a thing. It helped me stop trying to assign a personal time to it and focus on how different observers measure energy or arrival times.

[Chloe.R]

From the math side you can push v toward c in the Lorentz transform. Gamma grows without bound and length contraction goes to zero; the proper time along the photon's path is zero. So there is no valid rest frame to talk about. We study photons by using null intervals and by taking the limit from subluminal frames or by looking at field behavior in a fixed frame.

[Emma92]

Is the problem maybe asked in the wrong way, asking for a perspective that doesn't exist? Maybe we should frame it around how signals relate between frames and what stays invariant instead. If you want, we can try to stick to lab frames and talk about redshift, phase, or polarization instead—does that help?