[tlj009]

But the quwstion still applies. Once I come to rest at AC, my point of origin (Earth) will be 4.7ly away. Travelling near the speed of light, my travel time will have been (from my frame) less than 4.7 years. I don't see how I can manage both without something moving faster than light from my frame, once I come back to relative stop.

It is a perception problem. If you were going the speed of light and arrived 4.7ly away then you will perceive that you got there instantaneously and you and the light are at the same spot. Then the light still runs off and leaves you at the speed of light when you stop. So you didn't percieve that you went faster than light because time stopped for you while you were traveling. If you then went back to your original starting poing in the same way, then you will find that 9.4 years have passed and the light that originally started with you is 9.4ly away even though basically 0 time has passed for you.

Which now that I read it, the return trip doesn't seem right. But the rest I think is right.

[JerryLove]

Originally Posted by tlj009

It is a perception problem. If you were going the speed of light and arrived 4.7ly away then you will perceive that you got there instantaneously and you and the light are at the same spot. Then the light still runs off and leaves you at the speed of light when you stop. So you didn't percieve that you went faster than light because time stopped for you while you were traveling. If you then went back to your original starting poing in the same way, then you will find that 9.4 years have passed and the light that originally started with you is 9.4ly away even though basically 0 time has passed for you.

If I percieved that I crossed 4.7ly instantly, then I did indeed percive movement faster than light. And since the time dilation is real, I did move faster than light from my reference.

[tlj009]

If I percieved that I crossed 4.7ly instantly, then I did indeed percive movement faster than light. And since the time dilation is real, I did move faster than light from my reference.

Actually in that instant you are standing 4.7ly away and the same light that was with you on earth is there with you 4.7ly away from your original position. So until time starts moving again (you slow below the speed of light) you and the light are at the same spot. When you stop and time begins again light leaves you and the speed of light is percieved to be constant. Kind of like you and the light were one place and then the other without actually traveling there.

[JerryLove]

Originally Posted by tlj009

Actually in that instant you are standing 4.7ly away and the same light that was with you on earth is there with you 4.7ly away from your original position. So until time starts moving again (you slow below the speed of light) you and the light are at the same spot. When you stop and time begins again light leaves you and the speed of light is percieved to be constant. Kind of like you and the light were one place and then the other without actually traveling there.

Your problem is simpler to illustrate if you drop my speed so that it takes some time to cross the distance. let's say it takes me 4 hours.

In 4 hours I cross 4.7ly. I'm moving faster than the speed of light. Of course, that doesn't mean I'm outrunning th elight I see. I'm not. It's still moving at the speed of light relative to me. But it does mean that I'm my distance/time is faster than c.

Time dilatoin means I can't outrun light as I percieve it, but it does allow me to travel faster than light I percieved when I was still by travelling through time more slowly.

What I'm having a lot of trouble with is the simlutaniousness thing. It's hard to wrap my brain around.

[tlj009]

Your problem is simpler to illustrate if you drop my speed so that it takes some time to cross the distance. let's say it takes me 4 hours.

In 4 hours I cross 4.7ly. I'm moving faster than the speed of light. Of course, that doesn't mean I'm outrunning th elight I see. I'm not. It's still moving at the speed of light relative to me. But it does mean that I'm my distance/time is faster than c.

Time dilatoin means I can't outrun light as I percieve it, but it does allow me to travel faster than light I percieved when I was still by travelling through time more slowly.

What I'm having a lot of trouble with is the simlutaniousness thing. It's hard to wrap my brain around.

Well you are looking at it from two different perspectives. You have said that you can't outrun light as you perceive it and you can't. Neither did you travel faster than light because your distance traveled is less than 4.7ly in 4 hours. Now from an outside point of view of someone at rest. You travel 4.7ly in something over that length of time say 4.8 years. So not only is time dilated but so is space.

[Niflmir]

Originally Posted by Lightknight

Perhaps we'll find that the energy requirements to increase speed at those extremes doesn't just increase Arithmetically. I mean, it may become geometric. It isn't so crazy to think that physics may require a bit of tweaking past light speed.

You are correct in fact. The energy requirements are basically inversely proportional to the difference between your velocity and the velocity of light. It requires stupid amounts of energy to increase the speed from 0.9c to 0.99c.

As to the journey and turning back... we probably shouldn't discuss that. When you accelerate (or decelerate if you prefer) so that you can turn around, you aren't really an inertial observer anymore. This causes a lot of weirder things to happen then just time dilation and length contraction. The important point to remember is that all distances and times from the same reference frame must be used in calculating velocities for that frame. So if you want to calculate how fast the rocket is moving from inside the rocket, you measure the distance that the rocket observes and measure the time for the travel that the rocket observes. The incredible thing is that the velocity that the rocket bound observer calculates for himself will agree with the Earth bound observer who observes a larger distance of 4.7ly and a time on the same scale. I think I really would need some diagrams to discuss some of the finer points.

[JerryLove]

Originally Posted by Niflmir

You are correct in fact. The energy requirements are basically inversely proportional to the difference between your velocity and the velocity of light. It requires stupid amounts of energy to increase the speed from 0.9c to 0.99c.

That fits fully with my hypothesis regarding time dilation and speed. Since dilation increases in a curve approaching infinity, so would the power requirements. You are paying to move through the universe faster in accordance with *your* perception of speed (relative to the universe, not relative to light)

[Lightknight]

Hmm, very interesting. Thanks for bringing this up, Jerry.

[Moon Boots]

I agree with Lightknight, a fascinating read.