# Why is there a universal speed limit?

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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?

In: 13 [removed] As you speed up, you experience time differently. The speed of causality, or the the speed light travels is when that object is no longer experiencing time. If you were moving at the speed of light, you would arrive at your destination instantly. You can’t go any faster because you arrived instantly. The so called limit is how a stationary observer sees it traveling.

There is a concept called spacetime. We all move through spacetime at the “speed of light”. But the faster you move through space, the slower you move through time. So at the limit of speed, your time is 0. You would need to be going backwards through the time period to offset the space portion. This is not likely possible. The universal speed limit is a consequence of Mass and Energy being the same thing (from the famous E=MC2 equation).

So to get something to move faster you have to give it energy, the more mass it has the more energy you need to give it to achieve the same speed. That’s pretty intuative, it takes more energy to speed up a car than a baseball.
But giving something energy means it has more mass equivalence so speeding up something that is already going fast takes more energy then speeding up something that is going slow.
Because of this speeding something up to the speed of light takes infinite energy because of calculus. 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. If there was no universal speed limit, there would be no logical consistency/causality.

That does not mean a universe without a speed limit is impossible, but life as we know it would not be able exist in such a universe.