I know that nothing with mass can go as fast as light. I think that “there is a universal speed limit” and that :light achieves that limit” are two different statements. So, I am curious about the first one. Is it just an axiom?
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Imagine you’re standing on a conveyer belt like at the grocery store, only it’s huge – so big that it seems to go on forever in both directions. Now imagine this belt is moving left to right at 1,000 metres per second.
The belt, though, is a smart belt and it adjusts its speed based on how fast you are moving forwards so that your speed is always 1,000 m/s.
So if you’re walking at 3.6km/h (or 1m/s) by Pythagoras we can determine its new speed as sqrt(1000^2 – 1^2) = 999.9995 m/s, so not a huge difference. If Usain Bolt ran 100m in 10s (so 10m/s) the speed would change to sqrt(1000^2 – 10^2) = 999.95 m/s. If you were driving a car at 120km/h (33.3m/s) the belt would move at 999.444 m/s and if it could pull an aeroplane flying above it at 200m/s (720km/h) along, its speed would drop to 979.8 m/s.
If you move at mach 2 (twice the speed of sound, 660m/s) the belt is still moving at 751 m/s and if you reach 866 m/s it moves at 500 m/s, starting to significantly slow down.
We actually move through four dimensional space-time and time is like the conveyer belt. The faster we move through space, the slower we move through time. The reason nothing can travel faster than light is because we already ARE moving at the speed of light; we’re just moving through space-time, not just space, and most of our motion is in the time direction, unless we start moving at speeds that approach light speed.
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