Light speed spaceship time travel conundrum

[Jebus HChrist]

Let’s say we have a spaceship capable of traveling at the speed of light, and a planet we can visit 50 light years away. From earth’s perspective if we can track the ship we would be able to see it was traveling at the speed of light and we would also see it has taken 50 years to complete the journey.

From the travellers perspective time will slow down, so let’s say to them the time only lasts 1Year. Doesn’t this mean that they would experience the journey as if they traveling 50 times the speed of light? If they have instruments on board showing speed what will these instrument show, speed of light or 50 times speed of light?

I’m not a student I’m old and love this stuff hence maybe some young whippersnapper can answer this question for me.

JHC

 

[Doc Al]

Doesn’t this mean that they would experience the journey as if they traveling 50 times the speed of light? If they have instruments on board showing speed what will these instrument show, speed of light or 50 times speed of light?

The speed of the spaceship with respect to the earth/planet frame (0.99c, say) will equal the speed of the earth/planet with respect to the ship (0.99c again). But to the spaceship the distance to the planet is much less than 50 light years.

 

[jtbell]

Let’s say we have a spaceship capable of traveling at the speed of light, and a planet we can visit 50 light years away. From earth’s perspective if we can track the ship we would be able to see it was traveling at the speed of light and we would also see it has taken 50 years to complete the journey.

You need to be careful about saying things like "traveling at the speed of light" because no object with mass can travel at the speed of light with respect to any other object.

From the travellers perspective time will slow down, so let’s say to them the time only lasts 1Year.

Then the ship isn't traveling at the speed of light. It's actually traveling at 0.99980 times the speed of light, and from the Earth's perspective it takes 50.01 years to complete the journey.

Doesn’t this mean that they would experience the journey as if they traveling 50 times the speed of light? If they have instruments on board showing speed what will these instrument show, speed of light or 50 times speed of light?

Using distances and times measured in their own reference frame (in which they themselves are stationary), they would observe the Earth receding behind them at a rate of 0.99980 times the speed of light, and their destination approaching them at the rate or 0.99980 times the speed of light. The distance between the Earth and their destination would be length-contracted to 0.99980 light-year, so the elapsed time comes out right: t = d / v = (0.99980 light-year) / (0.99980 light-year per year) = 1 year.

 

[edpell]

But of course the folks on the ship traveling 0.99980c are not fools. They know before they start that the distance is 50 light years and they know when they arrive that the distance traveled was 50 light years. And yes they only age one year so for them it is exactly as if they had traveled about 50 light years per one year of body aging. So I would say their bodily processes had slowed down. But time remains unaffected as they and we who stayed behind are both able to figure out that when they arrive 50.001 years have gone by.

 

[HallsofIvy]

But of course the folks on the ship traveling 0.99980c are not fools. They know before they start that the distance is 50 light years and they know when they arrive that the distance traveled was 50 light years. And yes they only age one year so for them it is exactly as if they had traveled about 50 light years per one year of body aging. So I would say their bodily processes had slowed down. But time remains unaffected as they and we who stayed behind are both able to figure out that when they arrive 50.001 years have gone by.

"They and we who stayed behind" are both able to figure out that when they arrive 50.001 years have gone by in Earth's frame of reference. It makes no sense to talk about "time gone by" without specifying the frame of reference nor does it make any sense to say "time remains unaffected".

 

[DrGreg]

As has been pointed out above, when you calculate speed as distance / time, the distance and time both must be measured in the same frame.

In fact, there is a name for what you get when you divide the earth-measured distance by the ship-measured time. It is called celerity (or proper velocity, a name I don't like). In this example the celerity of the ship is 50 times the speed of light, but you have to compare like with like. The celerity of light is infinite.

 

[edpell]

I agree both in the same frame. When the travelers arrive 50 light years away they can calculate in the Earth reference frame that they have gone 50 light years of distance and that about 50.001 years have gone by in the Earth frame so a velocity of 0.9998c. They can also look at their bodily aging and say that is great we only aged one year.

 

[edpell]

HallsofIvy by the phrase "time remains unaffected" I mean on arrival (and stopping) both the Travels and the Earthers can measure and agree that the Travels have moved 50.001 years into the future just as the Earthers have moved 50.001 years into the future. No surprise there the surprise is that the bodies of the Travels have only aged one year. So do we want to say time changed for the Travels or do we want to say physical processes went slower for the Travels? We are agreed on the facts this is a question of interpretation, meaning, wording.

 

[Jebus HChrist]

I’m still with you all so far and understand technicalities like the max speed would have to be 0.999 the speed of light etc. Ed I don’t think the travellers experience the 50 years in real time and yet their bodies only age 1 year. If time slows down the closer light speed is reached then the travellers experience must to them appear like a one year journey.
Doc Al you say “But to the spaceship the distance to the planet is much less than 50 light years”. So for arguments sake would you agree that the travellers could experience the journey as though it were 1 year, and that it would therefore appear from their perspective that they were traveling 50 times the speed of light. My original question still stands.

JHC

 

[Nabeshin]

I’m still with you all so far and understand technicalities like the max speed would have to be 0.999 the speed of light etc. Ed I don’t think the travellers experience the 50 years in real time and yet their bodies only age 1 year. If time slows down the closer light speed is reached then the travellers experience must to them appear like a one year journey.
Doc Al you say “But to the spaceship the distance to the planet is much less than 50 light years”. So for arguments sake would you agree that the travellers could experience the journey as though it were 1 year, and that it would therefore appear from their perspective that they were traveling 50 times the speed of light. My original question still stands.

JHC

In the space ship's frame, the distance between them and the planet is lorentz contracted, so 50ly looks like 1ly to these travelers. Then they see the planet approaching them at .9998c ~ 1c, and so the journey takes only one year. That is how things look from the traveler's reference frame. They arrive on the planet and say "Gee, one year has passed for us", the folks on Earth say "Gee, over fifty years for us". The critical part is "for us". Without that, any measurement of time is completely useless. The observers will no doubt agree on what the others experienced, however. I.e, those on Earth will say "Yeah, you really did only experience one year", and those on the ship say "yup, 50 years passed back on Earth."

Make sense?

 

[Doc Al]

Doc Al you say “But to the spaceship the distance to the planet is much less than 50 light years”. So for arguments sake would you agree that the travellers could experience the journey as though it were 1 year,

Yes.

and that it would therefore appear from their perspective that they were traveling 50 times the speed of light.

From their perspective, using their own standards of length and time, they are moving at close to the speed of light, not at 50 times the speed of light--but distances are squashed. But you are correct that they can travel 50 earth-light years in only 1 spaceship year. See DrGreg's comment about celerity.

If you don't use consistent measurements--made in the same frame--you'll get tied up in knots thinking that things are moving faster than light. Only in the mixed-frame sense of celerity.

My original question still stands.

As does my original answer.

 

[edpell]

I am not disagreeing with anyone here. The travelers observe one year of travel over a distance of one light year. The stay behinds observe 50 light years of travel in 50 years (approx. - a little longer). But consistent. Both no faster than light speed. All fine. But after the trip is over A and B both agree to transmit how much bodily aging they have each experienced. A transmits 50 years of aging observed between your departure and your arrival. B reports one year of bodily aging observed between departure and arrival. What do we, A and B who are now both in the same inertial frame, want to say? Time went slower for A or A's physical processes went slower? Or are these both the same statement? To me it does not seem that these are both the same statement. Because if the trip started at the beginning of the year x and ended the beginning of the year x+50 in A's frame which both A and B are now in I think we have to say they both traveled 50 years into the future in frame A. Yet the physical process of body aging progressed only one year for B. In frame A, B has aged one year but "moved" 50 years into the future. For me that would best be described as B's physical process slowed by a factor of gamma. How would you feel it is best to describe the events? After the trip is over and both A and B share the same inertial frame.

 

[ZikZak]

I’m still with you all so far and understand technicalities like the max speed would have to be 0.999 the speed of light etc. Ed I don’t think the travellers experience the 50 years in real time and yet their bodies only age 1 year. If time slows down the closer light speed is reached then the travellers experience must to them appear like a one year journey.

Time is not slowed down for the spaceship in an absolute sense. There is no such thing as "real time," only time as measured in particular frames of reference. There is no universal clock ticking off "real seconds," and if the spaceship travelers experience a 1-year yourney, then it IS a one-year journey to them, no "appearances." Time dilation is not an illusion.

Earth observes clocks on the spacecraft to run slow, this is true, but the spacecraft is at rest relative to the pilot, while the Earth is traveling backwards at nearly c. So the pilot observes the spacecraft s clock running normally and the Earth's clock running slow. Which clock is running slow depends on whose reference frame you are in. Time dilation never happens to you. It always happens to other objects moving relative to you.

Doc Al you say “But to the spaceship the distance to the planet is much less than 50 light years”. So for arguments sake would you agree that the travellers could experience the journey as though it were 1 year, and that it would therefore appear from their perspective that they were traveling 50 times the speed of light. My original question still stands.

No, in their reference frame they are at rest and the Earth and destination are traveling at nearly c. the reason the destination reaches them in 1 year rather than 50 is that the distance between Earth and the destination is 1 light-year, not 50 light years. The distance between Earth and Destination is not "really" 50 light-years. There is no absolute answer to how separated the two planets are. The distance between them depends on reference frame.

 

[DaveC426913]

What the OP is struggling with is that the spaceship occupants know that "the distance between their lift-off planet and Earth is 50 light years", yet they made the trip in 1 year.

Yes, they know this when measuring from their planet. But once they accelereate to .999c they will see the distance between their planet and Earth shrink to one light year. The universe along the axis of their travel will flatten by fifty times.

 

[Al68]

Time went slower for A or A's physical processes went slower? Or are these both the same statement? To me it does not seem that these are both the same statement. Because if the trip started at the beginning of the year x and ended the beginning of the year x+50 in A's frame which both A and B are now in I think we have to say they both traveled 50 years into the future in frame A. Yet the physical process of body aging progressed only one year for B. In frame A, B has aged one year but "moved" 50 years into the future. For me that would best be described as B's physical process slowed by a factor of gamma. How would you feel it is best to describe the events? After the trip is over and both A and B share the same inertial frame.

The only reason SR predicts less aging is as a result of less elapsed time. If there were not less elapsed time for the traveler, why would he age less?

 

[Ich]

How would you feel it is best to describe the events?

As the difference between proper time and coordinate time.
Don't start with physical processes slowing. Since every conceivable process has to "slow down" consistently, there cannot be an operationally defined intrinsic time relative to which physical processes are slower than normal.
It is common (and mandatory in SR) therefore to call any suitable operationally defined intrinsic time "time" or, specifically, "proper time". Under constraint, one may speak of time slowing down, but not processes.
Ideally, one would avoid these phrases and give instead a precie definition between which events which time has elapsed.

 

[edpell]

What sets the time scale for all physical processes is inertia. The inertia of the travelers increased which set a different time scale for the travelers. This is how I read Einstein's 1905 paper "Does the Inertia of a Body Depend Upon its Energy-Content?".

 

[otas]

Earth observes clocks on the spacecraft to run slow, this is true, but the spacecraft is at rest relative to the pilot, while the Earth is traveling backwards at nearly c. So the pilot observes the spacecraft s clock running normally and the Earth's clock running slow. Which clock is running slow depends on whose reference frame you are in. Time dilation never happens to you. It always happens to other objects moving relative to you.

If I am on such space ship. After accelaration I see that Earth's clock is running slow. After a (my) year I get on that planet and ask my friends in Earth how much time have passed.
Would they say 50 years or less then a year?

 

[Al68]

If I am on such space ship. After accelaration I see that Earth's clock is running slow. After a (my) year I get on that planet and ask my friends in Earth how much time have passed.
Would they say 50 years or less then a year?

50 years, after the ship decelerates. When the ship reaches the planet, Earth's clock reads less than a year before the ship decelerates, and 50 years after the ship decelerates.

Relative to the ship clock, Earth's clock "jumps ahead" or runs fast during the deceleration.

 

[otas]

if my deceleration takes 1 day. Does that mean if I observe Earth's clock during deceleration it goes 49 years in one day (approx. 49x365 faster)?

 

[edpell]

Relative to the ship clock, Earth's clock "jumps ahead" or runs fast during the deceleration.

I disagree completely. As the ship travels it's occupants can always calculate their "time position" in the initial inertia frame (A). If gamma is 50 than a the end of day one they can calculate that their position in A is 50 days after the start of the trip. They can do this in a smooth and continuous manner. There are no jumps. On day 364 they know that in frame A they are at "time position" start+64182 days. The folks in both frames know SR theory and can both calculate the position of the other at any moment they want to. If you were in frame A you might think the inertia of all the particles in the accelerated ship has increased by a factor of gamma so they should slow down by a factor of gamma. It is the velocity not the acceleration that messes with time. Yes the acceleration caused the velocity (and the work done by the force doing the accelerating that increases all the masses from there rest mass to rest mass times gamma) but it is the velocity (and/or increased inertia) that causes the effect. The longer you stay at velocity (at high inertia) the more the mis-match between time in one frame versus time in the other frame.

 

[Janus]

I disagree completely. As the ship travels it's occupants can always calculate their "time position" in the initial inertia frame (A). If gamma is 50 than a the end of day one they can calculate that their position in A is 50 days after the start of the trip. They can do this in a smooth and continuous manner. There are no jumps. On day 364 they know that in frame A they are at "time position" start+64182 days. The folks in both frames know SR theory and can both calculate the position of the other at any moment they want to. If you were in frame A you might think the inertia of all the particles in the accelerated ship has increased by a factor of gamma so they should slow down by a factor of gamma. It is the velocity not the acceleration that messes with time. Yes the acceleration caused the velocity (and the work done by the force doing the accelerating that increases all the masses from there rest mass to rest mass times gamma) but it is the velocity (and/or increased inertia) that causes the effect. The longer you stay at velocity (at high inertia) the more the mis-match between time in one frame versus time in the other frame.

Al68 is correct. During the period during which the ship decelerates at the end of the trip, compared to the ship clock, the Earth clock will run fast.

Two ways to look at this is by either invoking GR or applying the Relativity of Simultaneity.

With the GR approach you apply the equivalence principle between gravity and acceleration. The ship can claim that the acceleration it feels is really due to it being at rest in a gravity field. In this gravity field, the Earth is overhead and is thus higher in the field than the ship. Clocks higher in a gravity field run faster than clocks lower in the field, so the Earth clock runs faster than the ship clock during this period.

The Relativity of Simultaneity approach works like this: The clocks on Earth and on the planet are not synchronized according to the ship while the ship is moving relative to both. the clock on the planet will be 50 years - 7.3 days ahead of the Earth clock.

According to the Ship, both clocks advance by 7.3 days during the trip so that upon arrival at the planet the Earth clock reads 7.3 days and the planet clock reads 50 yrs. The ship stops at the planet. But this puts in the same frame as the Earth and Planet, and in this frame, the clocks on these two bodies read the same. Thus from the Ship's perspective, the Earth clock has to jump forward to read 50 yrs when the ship changes frames.

Note that his means that if you had someone at the planet and you asked him what time it was on Earth the instant the ship arrived, he would say 50 yrs(0 yrs being when the ship left Earth). If you asked a passenger on the ship the same question at the same instant (assuming the ship has not yet decelerated), he would say that 7.3 days has passed on Earth since he left. Two people at essentially the same spot will disagree as to what time it is on Earth by virtue of their relative velocity to each other.

 

[Al68]

Relative to the ship clock, Earth's clock "jumps ahead" or runs fast during the deceleration.

I disagree completely. As the ship travels it's occupants can always calculate their "time position" in the initial inertia frame (A). If gamma is 50 than a the end of day one they can calculate that their position in A is 50 days after the start of the trip. They can do this in a smooth and continuous manner. There are no jumps. On day 364 they know that in frame A they are at "time position" start+64182 days. The folks in both frames know SR theory and can both calculate the position of the other at any moment they want to. If you were in frame A you might think the inertia of all the particles in the accelerated ship has increased by a factor of gamma so they should slow down by a factor of gamma. It is the velocity not the acceleration that messes with time. Yes the acceleration caused the velocity (and the work done by the force doing the accelerating that increases all the masses from there rest mass to rest mass times gamma) but it is the velocity (and/or increased inertia) that causes the effect. The longer you stay at velocity (at high inertia) the more the mis-match between time in one frame versus time in the other frame.

Why would you say you disagree completely, then not make any claims that contradict my post in any way? I never claimed there were any jumps in time in frame A, regardless of who uses frame A to keep track. The jump is in the ship's accelerating frame, so the jump is only observed when using that reference frame, not frame A.

 

[edpell]

There is a one to one mapping (continuous and smooth) between the one year time line in frame B and the 50 year time line in frame A. The only snapping is if you are thinking in terms of frame B time at one moment and then you switch and think in terms of frame A time (1->50). But this has no physical significance it is just a thought in your mind. The two paths join smoothly at the start of the journey and are just as smoothly joined at the end of the journey. You need a more elastic mapping not a rigid one year maps onto the first one year in the other frame. More like every 1/50 of a year maps onto a one year piece of time line in the other frame.

 

[matheinste]

There is a one to one mapping (continuous and smooth) between the one year time line in frame B and the 50 year time line in frame A. The only snapping is if you are thinking in terms of frame B time at one moment and then you switch and think in terms of frame A time (1->50). But this has no physical significance it is just a thought in your mind. The two paths join smoothly at the start of the journey and are just as smoothly joined at the end of the journey. You need a more elastic mapping not a rigid one year maps onto the first one year in the other frame. More like every 1/50 of a year maps onto a one year piece of time line in the other frame.

As the ship decelerates its relative speed with respect to the Earth decreases and so the Earth's clock appears to run less slowly, that is it speeds up and finally, when the ship reaches its destination, it is at rest in the same reference frame as the Earth's clock and so runs at the same rate.

The jump occurs in the unrealistic scenario of infinite acceleration/deceleration, often used in the twin paradox to minimize the time of the acceleration periods so as to counter any proposed effects on the traveling clock due to the time spent accelerating.

This is the same as the ship instantly coming to a halt when reaching its destination. Of course this cannot happen but it is a useful device for the same reason as used in the twin paradox. So perhaps you should ignore the "jumps ahead" and just take notice of the "speeds up".

And of course nothing whatsoever happens to the Earth's clock when viewed from the Earth's frame.

Matheinste.

 

[otas]

As the ship decelerates its relative speed with respect to the Earth decreases and so the Earth's clock appears to run less slowly, that is it speeds up and finally, when the ship reaches its destination, it is at rest in the same reference frame as the Earth's clock and so runs at the same rate.

Does that mean that from ship's perspective:

• before deceleration Earth's clock ticks at 1/50 rate compared to ship's clock ticking
• during deceleration Earth's clock goes amazingly fast, it must pass almost 50 years during deceleration time
• after deceleration Earth's clock slows down and ticks at the same rate as ship's clock

 

[matheinste]

Does that mean that from ship's perspective:

• before deceleration Earth's clock ticks at 1/50 rate compared to ship's clock ticking
• during deceleration Earth's clock goes amazingly fast, it must pass almost 50 years during deceleration time
• after deceleration Earth's clock slows down and ticks at the same rate as ship's clock

Without going back and looking at the originally proposed scenario, anyway it is the concept and not the numbers that is important, and I am lazy, so forgetting the actual figures:-

From the ships perspective, during the inertial part of the outward journey the Earth's clock runs slow compared to the ship's clock. (and vice versa)

From the ship's perspective, during the ship's deceleration phase, the Earth's clock speeds up relative to the ship's clock, towards the same rate as the ship's clock. It does not go any faster than the ship's clock as it is still moving relative to it.

Until, at the end of the ship's deceleration phase, from the ship's pespective, this speeding up of the Earth's clock with respect to the ship's clock results in the two clocks running at the same rate when the Earth's clock and the ship's clock are at rest relative to each other.

Of course the rates of this speeding up at deceleration depends on the deceration profile.

Matheinste.

 

[Al68]

Does that mean that from ship's perspective:

• before deceleration Earth's clock ticks at 1/50 rate compared to ship's clock ticking
• during deceleration Earth's clock goes amazingly fast, it must pass almost 50 years during deceleration time
• after deceleration Earth's clock slows down and ticks at the same rate as ship's clock

That's right. Earth's clock runs at the rate of T * sqrt(1 - v^2/c^2) for the inertial legs, and T * (1 + a*d/c^2) during the acceleration, all in the ship's frame.

 

[Al68]

From the ship's perspective, during the ship's deceleration phase, the Earth's clock speeds up relative to the ship's clock, towards the same rate as the ship's clock. It does not go any faster than the ship's clock as it is still moving relative to it.

Not in an absolute sense, but in the accelerated frame of the ship, Earth's clock does run faster than the ship's.

This is assuming that the accelerated frame is defined as a large series of co-moving inertial frames, so that as we switch between each one, Earth's clock jumps a little ahead due to the SR simultaneity shift. If we take this to the limit as we consider a greater and greater number of co-moving inertial frames, it will approach a smooth, constant acceleration, and the incremental simultaneity jumps of Earth's clock becomes equivalent to running faster than the ship's clock in this series of co-moving inertial frames we call the ship's accelerated frame.

The gravitation time dilation formula [T*(1+gh/c^2)] for a linearly accelerating reference frame was derived from the lorentz equations exactly this way. Maybe I can find that derivation online and post a link.

 

[matheinste]

Not in an absolute sense, but in the accelerated frame of the ship, Earth's clock does run faster than the ship's.

This is assuming that the accelerated frame is defined as a large series of co-moving inertial frames, so that as we switch between each one, Earth's clock jumps a little ahead due to the SR simultaneity shift. If we take this to the limit as we consider a greater and greater number of co-moving inertial frames, it will approach a smooth, constant acceleration, and the incremental simultaneity jumps of Earth's clock becomes equivalent to running faster than the ship's clock in this series of co-moving inertial frames we call the ship's accelerated frame.

The gravitation time dilation formula [T*(1+gh/c^2)] for a linearly accelerating reference frame was derived from the lorentz equations exactly this way. Maybe I can find that derivation online and post a link.

Yes. I understand what you are saying. It is the same mechanism as at the turnaround in the twin paradox.

I was thinking along the lines that in each instantaneous comoving reference frame of the ship, because the ship and the Earth are in relative motion, each observes the other's clock to be running slow. I obviously, mistakenly, did not take into account the simultaneity changes with chage of reference frames. Its a mistake I hope not to make again.

My apologies to otas for my incorrect response.

Matheinste.

 

[Jebus HChrist]

Greatly appreciate the contributions to this question of mine, I guess the issue for a designer of the spacecraft is what should the instruments display regarding speed and distance travelled, since the travellers are experiencing time at a different rate to their fellow earthlings. Maybe the first display would be the true speed of the craft say 0.9999 of a light year 2nd instrument apparent speed from the travellers perspective which would be say 50 times speed of light 3rd how far time had slowed down compared to Earth (true speed divided by apparent speed) in this case 50 times slower than earth. This is assuming the instruments could work, after all clocks will slow down the faster they travel. I would also add the older you get the faster time goes, but I'm that bloody old dave "OP" thanks very much.

 

[ZapperZ]

I must have experienced a time-dilation here, or it took you 2 years to respond to your post.

Zz.

 

[Jebus HChrist]

I must have experienced a time-dilation here, or it took you 2 years to respond to your post.

Zz.

Seems like only 2 weeks to me, something about time flys when you're enjoying yourself!

 

[harrylin]

Let’s say we have a spaceship capable of traveling at the speed of light, and a planet we can visit 50 light years away. From earth’s perspective if we can track the ship we would be able to see it was traveling at the speed of light and we would also see it has taken 50 years to complete the journey.

From the travellers perspective time will slow down, so let’s say to them the time only lasts 1Year. Doesn’t this mean that they would experience the journey as if they traveling 50 times the speed of light? If they have instruments on board showing speed what will these instrument show, speed of light or 50 times speed of light?

I’m not a student I’m old and love this stuff hence maybe some young whippersnapper can answer this question for me.

JHC

Hi JHC,

You gave a nice example of what Einstein meant with "the velocity of light in our theory plays the part, physically, of an infinitely great velocity".

Indeed, it is possible to travel that great distance with an experienced time that is arbitrarily short; calculated in Earth's distance measures, and reckoned with the travelers' clocks, their "speed" exceeds by far the speed of light.

I suppose that you understand that this is a special way of reckoning, thanks to using such a mixed bag of units.

However, what their instruments will show depends very much on how they are tuned. If they use a kind of radar-Doppler then the instruments are auto-tuning to the inertial system in which they are in rest. Then the distances* will simply look shorter and the speed will look the same as measured from earth.

Cheers,
Harald

*PS: in fact they have no time to do an active radar measurement of that planet after take-off. Thus they would need to utilise passive clues to estimate the distance.

 

[yuiop]

Doc Al you say “But to the spaceship the distance to the planet is much less than 50 light years”. So for arguments sake would you agree that the travellers could experience the journey as though it were 1 year, and that it would therefore appear from their perspective that they were traveling 50 times the speed of light. My original question still stands.

JHC

Lets say at the time the ship launched, a "spaceship launched" signal is sent from Earth to the distant planet. When the ship arrives at the distant planet, the proud astronaut announces he has traveled from Earth at 50x the speed of light. The greeter at the planet says "That is odd, because the launched signal arrived just before you and it was traveling at 1X the speed of light. Did you take the scenic route?".