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Is Faster-Than-Light Travel or Communication Possible? (1997)

math.ucr.edu

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Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#41

Post by Udo »

gizmo686 wrote: post #39
Udo wrote: post #33

The consensus interpretation is that FTL is not possible in normal space, since the speed of something is just another way of looking at how "fast" it travels through time - FTL becomes impossible by definition. However, there is reason to assume a lot of things may be going on that are not strictly speaking taking place in normal flat space. The article mentions the expansion of the universe as an example, and that'…

>Another observation worth considering: cosmic travel times seem utterly problematic right now because we individually live for extremely short periods of time. Doesn't relativity "solve" this this problem if we can reach near lightspeed, and don't mind it being a one way trip?

Sort of. While being on the move at extreme speeds you would take advantage of the local slow-down you're experiencing. Of course, a lot of time will still pass in the meantime both at the origin and the destination locations. I'd argue for the traveler it's subjectively not much different from being in a state of stasis while going at sub-relativistic speeds for thousands of years.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#42

Post by gnufied »

Ono-Sendai wrote: post #36
Udo wrote: post #33

The consensus interpretation is that FTL is not possible in normal space, since the speed of something is just another way of looking at how "fast" it travels through time - FTL becomes impossible by definition. However, there is reason to assume a lot of things may be going on that are not strictly speaking taking place in normal flat space. The article mentions the expansion of the universe as an example, and that'…

"since the speed of something is just another way of looking at how "fast" it travels through time" In what sense do you mean that? Can you elaborate?

It is mentioned in the linked article. Since speed is always relative (to a frame of reference), Special relativity by definition proposes that, nothing can go faster than C. The article gives an example, if a spaceship is traveling at 0.6c, and another spaceship is traveling at 0.6c - away from first first ship. Their relative velocities are not 1.2c, but 0.8c (http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity...)

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#43

Post by TrainedMonkey »

gizmo686 wrote: post #39
Udo wrote: post #33

The consensus interpretation is that FTL is not possible in normal space, since the speed of something is just another way of looking at how "fast" it travels through time - FTL becomes impossible by definition. However, there is reason to assume a lot of things may be going on that are not strictly speaking taking place in normal flat space. The article mentions the expansion of the universe as an example, and that'…

>Another observation worth considering: cosmic travel times seem utterly problematic right now because we individually live for extremely short periods of time. Doesn't relativity "solve" this this problem if we can reach near lightspeed, and don't mind it being a one way trip?

I was wrong, see edit below.

No, there is still an lower limit of 4.37 years to get to alpha-centauri within any frame of reference no matter how much you accelerate within conventional space.

What relativity does, is that if you travel close to speed of light time taken for the trip as measured on ship versus on earth could be different by many orders of magnitude.

edit: Was wrong, as per [0] "This is something many readers don't understand well, so it bears repeating: The journey times as experienced by those on the ship are not limited by the speed of light. Instead what they experience is the planetary reference frame getting relativistic."

[0] http://en.wikipedia.org/wiki/Space_travel_using_constant_acc...

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#44

Post by Ono-Sendai »

Udo wrote: post #40
Ono-Sendai wrote: post #36

Earlier quoted context omitted.

"since the speed of something is just another way of looking at how "fast" it travels through time" In what sense do you mean that? Can you elaborate?

Whenever two objects are in relative motion to one another, they each perceive a time dilation taking place at the other object. The flow of time is directly linked to the relative speed of an object. On an object that moves at the speed of light, time stands still. For more information on the mathematics, I refer you to the Lorentz transformation ( http://en.wikipedia.org/wiki/Lorentz_transformation ), but it's actu…

Ok. When you say 'how fast an object moves through time', you mean 'how fast time passes for a moving object, as seen from the inertial reference frame of another object'.

I regard objects as moving at the same speed through time - 1 second per second.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#45

Post by Udo »

Ono-Sendai wrote: post #44
Udo wrote: post #40

Earlier quoted context omitted.

Whenever two objects are in relative motion to one another, they each perceive a time dilation taking place at the other object. The flow of time is directly linked to the relative speed of an object. On an object that moves at the speed of light, time stands still. For more information on the mathematics, I refer you to the Lorentz transformation ( http://en.wikipedia.org/wiki/Lorentz_transformation ), but it's actu…

Ok. When you say 'how fast an object moves through time', you mean 'how fast time passes for a moving object, as seen from the inertial reference frame of another object'. I regard objects as moving at the same speed through time - 1 second per second.

It's of course a matter of taste what expression sounds more fitting to you, precisely because time is such a fluid concept.

Personally, when I think about a neutrino for example, I'd say that neutrinos go crazy fast, and they experience time unimaginably slowly, so it feels more natural for me to think that velocity and time are tradeoff values of each other.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#47

Post by aaron695 »

> Is Faster-Than-Light Travel or Communication Possible?

No.

Pretty simple stuff. No, it is not.

No matter how many sci fi movies tell you other wise. It is not.

Every experiment that comes out saying different is either lying/incompetent or the news reporting on it is lying/incompetent.

Just because you want it to be true does not make it either true or possible.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#48

Post by lfuller »

TrainedMonkey wrote: post #43
gizmo686 wrote: post #39

Earlier quoted context omitted.

>Another observation worth considering: cosmic travel times seem utterly problematic right now because we individually live for extremely short periods of time. Doesn't relativity "solve" this this problem if we can reach near lightspeed, and don't mind it being a one way trip?

I was wrong, see edit below. No, there is still an lower limit of 4.37 years to get to alpha-centauri within any frame of reference no matter how much you accelerate within conventional space. What relativity does, is that if you travel close to speed of light time taken for the trip as measured on ship versus on earth could be different by many orders of magnitude. edit: Was wrong, as per [0] "This is something many…

That's not true. From the perspective of the travelers space will appear to contract dramatically - though the speed of light remains constant, the distance traveled is reduced.

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#49

Post by Retra »

jljljl wrote: post #28
Retra wrote: post #18

Earlier quoted context omitted.

That's still ~500x faster than any man-made object has ever moved.

While true, Isn't this more an "engineering problem" barrier (like the sound barrier) instead of a "theoretically impossible" barrier?

There may be an engineering barrier below c when you account for fuel efficiency. Once you start requiring large volumes of nearly impossibly efficient (thrust-weight) fuels, then you will be stuck, even if you aren't anywhere near the speed of light.

It depends how much material you are transporting. If you are sending a few photons, the speed of light it no barrier at all. But if you are sending a crew of humans...

Re: Is Faster-Than-Light Travel or Communication Possible? (1997)

#50

Post by readerrrr »

TrainedMonkey wrote: post #43
gizmo686 wrote: post #39

Earlier quoted context omitted.

>Another observation worth considering: cosmic travel times seem utterly problematic right now because we individually live for extremely short periods of time. Doesn't relativity "solve" this this problem if we can reach near lightspeed, and don't mind it being a one way trip?

I was wrong, see edit below. No, there is still an lower limit of 4.37 years to get to alpha-centauri within any frame of reference no matter how much you accelerate within conventional space. What relativity does, is that if you travel close to speed of light time taken for the trip as measured on ship versus on earth could be different by many orders of magnitude. edit: Was wrong, as per [0] "This is something many…

lfuller is right.

For example, if you have a ship capable of continuous acceleration at 1g, you can reach any point in the universe on the order of ~50 years.

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