Time and distance at constant C: A sieries of questions for Umbran or other physicists.

[Scott DeWar]

Ok, As the title says, Questions that has my brain in a twist: A thought experiment on travel at the velocity of C.

in the picture I post here,

given: The clock on a ship moving at Velocity of C for 100 years

would the star we travel around here on earth move 100 years worth while the shp moves to the end point at the far right, off the page?

and on the return, would it arrive where Sol wold have traveled another 100 years?

According to what I am to be told thus far, the answer should be no. Is that correct?

 

[tomBitonti]

Do you mean 'C' to be the speed of light? A ship couldn't actually travel at the speed of light, but, in theory, it could travel close to the speed of light.

A ship traveling close to the speed of light will experience time dilation: Clocks on the ship will appear to advance more slowly to an observer which is not in motion (say, someone still on the earth). A clock on a ship moving close to the speed of light will advance quite slowly, and the closer the ships speed gets to C the more slowly the clock will advance.

An observer on the ship won't notice any slowdown of the clock; they are moving more slowly, too. However, an observer on the ship will notice other effects: Distances outside of the ship will shrink in the direction of motion of the ship.

If the ship travels 100 light years away from the earth, then travels back to the earth, both at close to C the speed of light, then, to an observer on the earth, the trip will appear to take 200 years, and the earth will circle the sun 200 times during the journey.

On the other hand, the observer on the ship will notice a much reduced passage of time. How much depends on how long the ship takes to accelerate from a standstill up to C, but in principle the journey can be made arbitrarily short. For the observer on the ship.

Thx!

TomB

 

[Umbran]

Ok, As the title says, Questions that has my brain in a twist: A thought experiment on travel at the velocity of C.

Travel *at* c is impossible. How about I answer as if you said "0.9c"?

given: The clock on a ship moving at Velocity of C for 100 years

100 years as measured by who? Remember, the clocks are relative.

A ship leaves Earth, and travels at 0.9c for what people on Earth call a century. The Earth and Sun and all will all do their normal things, moving pretty slowly, just as they have since WWI until now.

Folks on the ship will experience about three and a half years of time passing. Earth would think the ship had moved 90 light years away. Let's say they went to check out https://en.wikipedia.org/wiki/HD_70642

and on the return, would it arrive where Sol wold have traveled another 100 years?

Pretty much, yes. I mean, Earth is a moving target, so they have to aim where the target *will* be, but yeah, in general.

Overall, about 7 years of time will pass on the ship (not counting times to accelerate or decelerate here), while 200 pass on Earth. The Earth will have moved much as it has since the War of 1812. People will have died, new ones born, wars fought, technology developed, and all that jazz.

 

[Scott DeWar]

Do you mean 'C' to be the speed of light? A ship couldn't actually travel at the speed of light, but, in theory, it could travel close to the speed of light.

Thx!

TomB

Travel *at* c is impossible. How about I answer as if you said "0.9c"?

100 years as measured by who? Remember, the clocks are relative.

A ship leaves Earth, and travels at 0.9c for what people on Earth call a century. The Earth and Sun and all will all do their normal things, moving pretty slowly, just as they have since WWI until now.

Folks on the ship will experience about three and a half years of time passing. Earth would think the ship had moved 90 light years away. Let's say they went to check out https://en.wikipedia.org/wiki/HD_70642

Pretty much, yes. I mean, Earth is a moving target, so they have to aim where the target *will* be, but yeah, in general.

Overall, about 7 years of time will pass on the ship (not counting times to accelerate or decelerate here), while 200 pass on Earth. The Earth will have moved much as it has since the War of 1812. People will have died, new ones born, wars fought, technology developed, and all that jazz.

Ok, I should have been more detailed of what I was thinking. Sorry.

I meant to say at .99C, but we will go with the theoretical .9 C

Also, I meant to mention two clocks synced on earth - both atomic clocks for accuracy

Also, let us say, for the sake of argument they can "instantly accelerate to C" for passing of time.

So, the time dilation would be:

a. they wold have traveled a total of 180 light years, round trip

b. it took 7 years to those on the ship

c. Earth has moved through the cosmos the distance it would have after 200 years at the present movement that we are at right now, baring any form of "eternal force"

d. To the earth, It would look like 200 Years had passed

e. (and of course I HAVE to have the humor) it is caused that way because it is a wibbly wobbly timey wimy thing.

Do I have that correct?

 

[Morrus]

Talking of time dilation and relativistic speeds, I was wondering if there were games other than my WOIN system which addressed that? GURPS, perhaps? Does Traveller?

 

[Scott DeWar]

I don't remember anything on GURPS, but it has been a while since I played. It was never addressed In any star trek, Firefly or other interstellar travel show/movie except one and that was way inflated in the single season show called Outcasts. And to be honest, Outcasts is a major reason for this question.

 

[tomBitonti]

There is a discussion here:

https://en.m.wikipedia.org/wiki/Time_dilation

The ratio of elapsed times is represented by the lower case gamma, and is (sorry about the representation):

1/sqrt(1-v^2/c^2)

There is a table here:

https://en.m.wikipedia.org/wiki/Lorentz_factor

For 0.9c, the value is 2.3, for 0.99c -- 7.1, for 0.999c -- 22.

A trip which starts with synchronized clocks, one of which goes on a trip while another stays at home is a version of what is called The Twins Paradox, with clocks and twins exchanged.

Basically, if you put one twin on a rocket and send one on a trip of 11 light years and back (so 22 ly total), at 0.999c, the twin on the rocket will age 1 year while the twin that stays at home will age 22 years.

What happens on the rocket won't affect what happens at home (unless it crashes on return without slowing down!). And other than accelerations, the twin on the rocket won't perceive anything different inside the rocket.

Thx!

TomB

 

[Umbran]

Talking of time dilation and relativistic speeds, I was wondering if there were games other than my WOIN system which addressed that? GURPS, perhaps? Does Traveller?

The games I know of don't go into it, largely because they either use distance scales in which you'd not travel at such speeds (like Firefly, where all the worlds are within fairly short distances), or they have FTL travel.

 

[Mustrum_Ridcully]

I don't remember anything on GURPS, but it has been a while since I played. It was never addressed In any star trek, Firefly or other interstellar travel show/movie except one and that was way inflated in the single season show called Outcasts. And to be honest, Outcasts is a major reason for this question.

The problem migh be that it's not really a rules thing, but a world-building problem.

If you travel across half the Galaxy with a very close-to-lightspeed speed so it is for you only a 3-day trip, 50,000 years would pass in the mean-time on Earth and any other planet that isn't flying that fast.
How could you possibly build a world - as DM or setting book author - thta could deal with such long timespans?

And even if you stay at closer distances of, say, Alpha Centauri, every trip would take over 4 years. Imagine you had to pace an RPG adventure over several years every time the players decide to travel a bit...

 

[Morrus]

The problem migh be that it's not really a rules thing, but a world-building problem.

If you travel across half the Galaxy with a very close-to-lightspeed speed so it is for you only a 3-day trip, 50,000 years would pass in the mean-time on Earth and any other planet that isn't flying that fast.
How could you possibly build a world - as DM or setting book author - thta could deal with such long timespans?

And even if you stay at closer distances of, say, Alpha Centauri, every trip would take over 4 years. Imagine you had to pace an RPG adventure over several years every time the players decide to travel a bit...

I've tackled this in various ways.

1) You create settings of a size appropriate to your speeds. No FTL, then you stay in the solar system! You can have some amazing space adventures in one solar system.

2) If nobody else can move faster than light either, it really doesn't matter, as you'll never know what's happening back at home, and it can't affect you. Freeze the PCs for the time required, wake them up. Have some fund with time dilation.

3) Make time and age part of your advancement system. You can "spend" XP in real-time, or "years" in downtime to purchase character advancements, at the cost of growing older.

4) Say screw it, and allow FTL travel, wormholes, spacegates, what-have-you.