light has inertia?

[D H]

Note: A photon does have non-zero relativistic mass given by [math]m=h\nu/c^2[/math], which results directly from the Planck relation and the relativistic mass–energy equivalence formula.[/quote']Not sure I would quite say that. Really you mean it has momentum.

No. Really I meant to say it has energy. Momentum is a separate issue.

 

Let me be real clear: A photon has zero invariant¹ mass, non-zero momentum, and non-zero energy.

 

¹I much prefer the terms "invariant mass" and "intrinsic mass" to "rest mass". A photon always moves at c, so the term "rest mass" is a bit of an oxymoron to me. The qualifiers invariant and intrinsic when applied to mass don't ring any jumbo shrimp / death benefit alarm bells in my head.

[Severian]

And once you have established that you are interested in invariant mass rather than relativistic mass, you have to decide whether or not you want pole mass or running mass...