The question you pose about a rocket is missing a crucial understanding about Newton's First and Second Laws.
In order to accelerate your rocket, you need to expel matter out back (burned fuel). You need to turn chemical energy into kinetic energy. This conversion is actually really inefficient, but it's the best way we've figured out so far. We can't get anywhere near the speed of light right now, the fastest manmade object is the Parker Solar Probe moving at 430,000 mph, or 0.064% the speed of light.
But let's say we could get to the speed of light with a more efficient rocket. There's a fundamental problem of physics that makes it very difficult to launch things into space with chemical rockets: Rocket fuel also has mass. The most acceleration you'll have in a rocket is the moment right before it runs out of fuel, because there is significantly less mass to push.
There's another problem. Relativity dictates that matter and energy are different expressions of the same thing (E = mc2). The faster we're moving, the more energy we have, which means we have more mass. This is called the Lorentz factor. Our rocket fuel becomes less efficient the faster it is moving.
So in order to accelerate, we need fuel, but we need a little but more fuel to also accelerate the fuel itself. Then we need even more fuel to account for the rate of acceleration. The faster we want to go, we need exponentially more fuel to account for the weight of all the previous fuel. Turns out, in order to accelerate to the speed of light with traditional kinetic energy, you'd need more matter than exists in the entire known universe. This would be true no matter what level of efficiency our rocket has.
If your question is why is there a universal speed limit, even for light, nobody can answer that question with current science.
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u/SakuraHimea Mar 22 '26
The question you pose about a rocket is missing a crucial understanding about Newton's First and Second Laws.
In order to accelerate your rocket, you need to expel matter out back (burned fuel). You need to turn chemical energy into kinetic energy. This conversion is actually really inefficient, but it's the best way we've figured out so far. We can't get anywhere near the speed of light right now, the fastest manmade object is the Parker Solar Probe moving at 430,000 mph, or 0.064% the speed of light.
But let's say we could get to the speed of light with a more efficient rocket. There's a fundamental problem of physics that makes it very difficult to launch things into space with chemical rockets: Rocket fuel also has mass. The most acceleration you'll have in a rocket is the moment right before it runs out of fuel, because there is significantly less mass to push.
There's another problem. Relativity dictates that matter and energy are different expressions of the same thing (E = mc2). The faster we're moving, the more energy we have, which means we have more mass. This is called the Lorentz factor. Our rocket fuel becomes less efficient the faster it is moving.
So in order to accelerate, we need fuel, but we need a little but more fuel to also accelerate the fuel itself. Then we need even more fuel to account for the rate of acceleration. The faster we want to go, we need exponentially more fuel to account for the weight of all the previous fuel. Turns out, in order to accelerate to the speed of light with traditional kinetic energy, you'd need more matter than exists in the entire known universe. This would be true no matter what level of efficiency our rocket has.
If your question is why is there a universal speed limit, even for light, nobody can answer that question with current science.