# Will it reach the speed of Light? [duplicate]

So, I was just wondering if in an isolated environment where there is no external force acting on the body and the body (with any mass) is pushed with a force such that it has a constant acceleration, so that would mean that the body's velocity will gradually increase with time and would never decrease (since body in motion stays in motion until an external force acts on it).

So, wouldn't this mean eventually it will reach velocity as same as light and even more and thus violating various laws of physics? Because lets say somewhere very very far into the universe there us bound to be an relatively isolated area and if we perform such an experiment wouldn't that cause some violations?

• @JohnRennie i don't have much knowledge into the relativity side of the things but what I understood is that the velocity will gradually increase and it will eventually come very close to c but never will be equal to it, as time to reach such an velocity would be so great that eventually it will never will be able to reach c. Is this correct?
– bm27
Feb 5, 2023 at 8:18
• Correct. For us watching the accelerating spaceship from Earth we'll see the rocket approaching the speed of light but never quite reaching it no matter how long we wait. Feb 5, 2023 at 8:21
• Great! But does this argument apply for as great the initial velocity or acceleration (obviously not when equal to c) is?
– bm27
Feb 5, 2023 at 8:25
• It makes no difference what the initial velocity is or what the acceleration is. Even if the rocket starts from $0.999999c$ it will still never reach $c$. Feb 5, 2023 at 8:26
• OK got it, thanks :D
– bm27
Feb 5, 2023 at 8:29