How is it possible that photons can move without mass, wouldn’t they have to carry some sort of inertia in order to travel?
In: Physics
No, mass is literally *resistance* to changes in velocity (speed or direction of movement).
Something that doesn’t resist changes in velocity would logically be really good at moving wouldn’t it? It requires literally zero “push” to get started and to go really really fast. Which is exactly what we see with light
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I should point out that travel does not require mass. A stadium wave, for example, can travel and it does not by definition require any mass.
OTOH, photons do actually have momentum, even without mass
Photons are quantum particles and, as such, are described by quantum physics. The first thing to know about quantum physics is that none of it makes any sense, and all intuition you have about how things work no longer applies.
[this comment](https://www.reddit.com/r/AskPhysics/comments/p9nz1m/comment/ha00nby/?utm_source=share&utm_medium=mweb3x&utm_name=mweb3xcss&utm_term=1&utm_content=share_button) goes into more detail about what it means to be massless but photons do (kinda) have inertia but not quite in the same way as we are used to thinking about it.
But simply put, since photons have no mass, it doesn’t require any energy to make it go “infinitely” fast it is sort of like trying to divide by zero, and it approaches infinity. Accept nothing can actually go infinitely fast as the universe has a speed limit of the speed of causality (more often referred to as the speed of light) that is just under 300,000,000 m/s that is how fast light moves.
One thing to remember is that particles aren’t really objects in the way we normally think of them, and to accurately describe their behaviour, you need lots of maths that people study for years to try and understand.
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