- #1

- 60

- 17

My understanding of space (not near any gravity and therefore no spacetime curvature) is that a body in motion will continue to move at said speed unless acted on by another force. So let's use an example. Let's say I am moving at 10mph through space but I want to reach the speed of light. (Now I'm going to use fictious numbers and equations to keep the math simple). Let's say in my spaceship I fire off my rockets to increase the speed, which requires 5 amount of newtons (or whatever else the metric is for force – it doesn't really matter for the point I'll make). And that 5 amount of newtons increases my speed by 10mph, so I'm now I'm going at 20mph. At this point I stop the rockets and i continue indefinitely at 20mph. So I now apply another 5 newtons to reach 30mph, and so on until I reach the speed of light. This does not require an infinite amount of energy.

Now I know the above is wrong (for many reasons) but bear with me for a minute. So from E=mc2 (I think) it states that the reason we can’t reach the speed of light is because as you get closer to the

*speed*of light your mass increases, and therefore requires infinitely more energy – I get that. But the first issue I have here is that I thought

*speed*was all relative. So in my example above I

*know*that I am wrong when I keep saying my

*speed*in increasing. But if my 30mph is the equivalent of being still in space, then how can my ship gain mass when increasing in

*speed?*and therefore need infinitely more energy if speed is relative? To demonstrate more, imagine nothing is close by to judge our

*relative*speed to it. To put it another it seems that speed is relative to everything but not light. I have come to the conclusion that when we say we can’t reach the

*speed*of light that maybe it actually means the

*acceleration to*the speed of light - because to reach the speed of light (relative to another body) we’d have to accelerate at an insane amount (which would require a lot of energy). So my question is, is it more accurate when we say “it requires an infinite amount of energy to reach the speed of light” to change that to “it requires an infinite amount of energy to reach the speed of light”

Or have I completely missed the point? Where I am coming from is that there is no speed in space unless it’s relative to another object. The other thing that is weird, is that, if light speed is always constant how can light still travel at said speed if I were to speed up just half the speed of light in the same direction as the light beam? I should perceive the light traveling at half the speed of light but I know (from reading up on GR) that light is always the speed no matter the reference frame. The explanation to this is that apparently that time is slowed down the faster you move – but again, I thought speed was relative.