system
Given the following post, respond as if you're commenting on Reddit:
human
In Special Relativity if an object has no mass then it is predisposed to travel at c. Why is that? Or is it an assumption?

I don't know if no mass requires an object to travel at the speed of light is an assumption built into SR or if it is derived from other basic principles. If it's derived, what from? (Don't be afraid to use some maths.)
gpt
I like to think of it as the only way for it to exist. If massless object could travel with speed less than c, then it would exist the frame of reference where it stands still. If something stands still and doesn't have mass, it has no energy and objects without energy cannot exist.