My Warped And Twisted Theory of Space Travel

[Tumbleweed]

Actually, it's Auther C. Clarke's idea: Lets say you have two space ships , one hurtling towards Earth at a mere 10,000 MPH, the other at 99% the speed of light. They both pass checkpoint Charlie some trillion fixed earth miles from Earth. Would both agree that there is still a trillion miles to go OR would the one going 99% the speed of light say that's obviously wrong, we are practically there, and then prove it via how much time elapses on THEIR clock, that shows mere seconds have passed to travel that trillion miles. As far as they are concerned it took practically no time at all to get to Earth, not 4 long years.
Well that's great you say but we can't hurtle space ships at 99% the speed of light. Fixed speaking no, but relatively yes. Are there not plenty of objects, including galaxies, in the Universe already hurtling around at near the speed of light, relative to Earth? So why the need to propel something if the velocity is already built into the system? You are already going near the speed of light relative to that speeding galaxy. Well then wouldn't somebody going in that galaxy's direction also say it took practically no time at all to get there even though here on Earth we would say it took many billions of years? Another point: do photons age at all? Sure we can say it takes one 4 years to reach the nearest star. But what does an itsy bitsy tiny clock strapped to the photon say? It says no time AT ALL has elapsed on that journey to the nearest star. Or any place for that matter. The photons clock shows that no time has elapsed at all since its creation. And its odometer is always going to show 0 miles travelled. Am I on course, Einstein?
So just do the 2001 -A Space Odyssey star gate thingie: Find a moving point in space where the gravitational forces from various and sundry objects cancel each other out, aim your space ship in the direction of an object/ galaxy moving near the speed of light, relatively speaking , and simply GO there! Nearly instantly, no matter HOW far the folks on Earth say it is. And no black hole necessary --- maybe. This has bugged me ever since I saw the movie in 1969

[drkitten]

[SIZE=2]Actually, it's Auther C. Clarke's idea: Lets say you have two space ships , one hurtling towards Earth at a mere 10,000 MPH, the other at 99% the speed of light. They both pass checkpoint Charlie some trillion fixed earth miles from Earth. Would both agree that there is still a trillion miles to go OR would the one going 99% the speed of light say that's obviously wrong, we are practically there, and then prove it via how much time elapses on THEIR clock, that shows mere seconds have passed to travel that trillion miles. As far as they are concerned it took practically no time at all to get to Earth, not 4 long years.


Well that's great you say but we can't hurtle space ships at 99% the speed of light.

Yup, that's exactly what I say.

Are there not plenty of objects, including galaxies, in the Universe already hurtling around at near the speed of light, relative to Earth? So why the need to propel something if the velocity is already built into the system?

Because the objects are the things that have the velocity, not us. The velocity may be in the system already, but it's not in the right place.

You are already going near the speed of light relative to that speeding galaxy. Well then wouldn't somebody going in that galaxy's direction also say it took practically no time at all to get there even though here on Earth we would say it took many billions of years?

Not if that someone were at rest relative to the Earth, no.



Another point: do photons age at all? Sure we can say it takes one 4 years to reach the nearest star. But what does an itsy bitsy tiny clock strapped to the photon say? It says no time AT ALL has elapsed on that journey to the nearest star. Or any place for that matter. The photons clock shows that no time has elapsed at all since its creation. And its odometer is always going to show 0 miles travelled. Am I on course, Einstein?

Not in the slightest, no.


So just do the 2001 -A Space Odyssey star gate thingie: Find a moving point in space where the gravitational forces from various and sundry objects cancel each other out, aim your space ship in the direction of an object/ galaxy moving near the speed of light, relatively speaking , and simply GO there!

Except you can't simply "GO" there. If it's a moving point in space --- and moving relative to what, I ask? --- in order to "GO" there you will need to accelerate yourself until the point is no longer moving.

And that takes time and energy.

You're almost right. If we had a way to instantaneously accelerate ourselves to some very large speed (and equally, to decelerate at the end), then we would be able to travel to arbitrary points in the universe in very little apparent elapsed time (as far as the traveller was concerned). But since we don't have that ability, this doesn't mean much in practice.

And as far as an observer on Earth were concerned, the trip would still take a long time; you might be able to travel from here to Proxima Centauri and back in a lazy afternoon, but everyone would be ten years older when you got back (your daughter, the cute little toddler, would be in middle school and have discovered boys). You could even go to Andromeda and back in what you thought was a week --- but millions of years would have elapsed for us and your descendants would have evolved into god-knows-what. If you were lucky.

[Soapy Sam]

Are there not plenty of objects, including galaxies, in the Universe already hurtling around at near the speed of light, relative to Earth?

Stacks of 'em. It's really just a matter of arranging for one to impact the other end of the seesaw you are standing on.

Wear a seat belt , hard hat and acceleration pants.
And please stand the hell away from me!

[Fredrik]

Lets say you have two space ships , one hurtling towards Earth at a mere 10,000 MPH, the other at 99% the speed of light. They both pass checkpoint Charlie some trillion fixed earth miles from Earth. Would both agree that there is still a trillion miles to go OR would the one going 99% the speed of light say that's obviously wrong, we are practically there, and then prove it via how much time elapses on THEIR clock, that shows mere seconds have passed to travel that trillion miles. As far as they are concerned it took practically no time at all to get to Earth, not 4 long years.

The faster ship would say that Earth is a mere 141 billion miles away. You have the right idea (so far), but the wrong numbers.


Well that's great you say but we can't hurtle space ships at 99% the speed of light.

It's difficult, but possible in principle.


Are there not plenty of objects, including galaxies, in the Universe already hurtling around at near the speed of light, relative to Earth?

Not really. The distance to a galaxy far, far away can change (increase) with time at a rate that exceeds c, but this is due to the expansion of the universe. The galaxies themselves are moving at small speeds (a few hundred km/s I think) relative to objects in their vicinity.


So why the need to propel something if the velocity is already built into the system?

Because a spaceship isn't going to change its velocity unless something gives it a push.


You are already going near the speed of light relative to that speeding galaxy. Well then wouldn't somebody going in that galaxy's direction also say it took practically no time at all to get there even though here on Earth we would say it took many billions of years?

First of all, we're "going" in the opposite direction, possibly faster than light. Second, what you asked in the second sentence has nothing to do with what you said in the first, but yes, if you manage to accelerate to a high enough speed relative to Earth, you can get to a location a million light-years away before you die of old age. (The star you're going to might however have "burned out" in the mean time).


Another point: do photons age at all? Sure we can say it takes one 4 years to reach the nearest star. But what does an itsy bitsy tiny clock strapped to the photon say?

The question doesn't make sense. Clocks are massive so they must travel at speeds <c. Photons are massless, so they must travel at c. There's also no way to associate an inertial frame with a photon's motion, so you can't even define the "photon's point of view" mathematically.

However, if you imagine a clock going from here to there at speed v, then the time measured by the clock is smaller when v is higher. The time goes to zero in the limit where v goes to c, but the clock can't actually move at c.


Find a moving point in space where the gravitational forces from various and sundry objects cancel each other out, aim your space ship in the direction of an object/ galaxy moving near the speed of light, relatively speaking , and simply GO there! Nearly instantly, no matter HOW far the folks on Earth say it is.

What's a "moving point in space"? And how do you "simply go there".

[Roboramma]

Velocity includes direction as well as magnitude.