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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Because the speed of light IS the resolving rate of causality, not an actual cosmic speed limit.
So being in a universe with time that goes forward, cause must come before effect. Send a text, then someone will get the text, and that takes a certain amount of time. Light is interesting in that it doesn’t actually experience time, because it’s a massless particle. From a photons perspective it is created and then immediately absorbed by whatever it hits. When you do have mass it takes quite a bit of energy to get up to light speed, more and more as you get closer to it. But the speed of light (in a vacuum) is a constant, it never changes, if you imagine a hypothetical guy on a spaceship going the speed of light, what would happen if he shined a flashlight forward? Well it turns out that as a consequence of maintaining causality, time slows down to compensate for this and it will for you as well. So as speed goes up, times ticks slower, your energy goes up. Eventually if you run the calculations your speed will reach that of light, time will reach zero, and the energy will become infinite, and it’s here you find your problems. Because you can’t have more than infinite energy, and time can’t become negative as cause must come before effect (I will say no one knows why this is). So it’s not that you could use a mass effect thing to reduce mass and reach speeds beyond that of light, it’s that nothing with mass can ever do so. Even something as small as an electron, you can only get incredibly close. 99.99999999999% is totally fine, 100% is impossible. 101%? Straight to time jail
This video explains it perfectly with visuals to help.
Light is the fastest way information can travel. Faster than information travel can violate causality because the result of an action can reach an observer before the action itself.
It’s often explained like a graph where on one axis you have space and the other is time. Any vector you take is a product of traveling through space and time. If you accelerated to the universal speed limit, then you would be on a line parallel to the space axis which means time isn’t changing. You can’t point any more in that direction so you can’t speed up.
Because the speed something is traveling at changes the passage of time for that object. The faster you go, the slower time gets. The speed of light (in a vacuum) is the speed at which the flow of time stops for the object traveling. Any further acceleration would have to make the passage of time slower than time just not passing at all and that is functionally impossible. Even if time was reversed, it would still be passing faster than if it was halted.
I hope that was ELI5 enough
Because the faster you go the more energy it takes and it increases exponentially. Once you get very close to the speed of light the amount of energy required becomes several galaxies worth and if you somehow reached the speed of light you’d have infinite energy which isn’t possible. Another issue is that the faster you go through space the slower you go through time. At the speed of light you aren’t moving through time(photons don’t age or decay) so time for you would stop, going faster than that would technically make you go back in time which we beleive isn’t possible.(would need more than infinite energy)
We have never found anything that goes faster than c.
So we do not know what should happen.
The math behind this was not intended to explain what should happen at speeds greater than c so it can not tell us anything.
C as a maximum is an axiom therefore has no explanation
ELI5: What would happen if you saw the light before you turned flipped on the light switch? You could decide not to turn on the light. Then where did the light come from. This is how causality is broken.
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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