The way I think I understand it, even if we had some “element 0” like in mass effect to keep a starship from reaching unmanageable mass while accelerating, faster than light travel still wouldn’t be possible because you’d be violating causality somehow, but every explanation I’ve read on why leaves me bamboozled.
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Everything moves at the same speed of causality in 4D spacetime. That’s the speed of somethings ability to affect its neighbors.
In 3D space, that ‘speed’ is split between moving through space and moving through time. Massless partials like light, can put all that speed into moving through space (in a vacuum). Particles with mass have some of that ‘speed’ used to move through time as well.
It’s not so much that we can’t go faster than the speed of light, as it’s not really possible to change the speed of the universe in 4D spacetime. Or, how fast something can impact a neighbor.
A massless particle has all that speed moving through space and doesn’t experience time. A particle with mass, if stationary, would not be moving through space and all its speed would be in time.
Side note: there is no good ELI5 for spacetime topics in general. It’s not an intuitive subject.
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