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Instantaneous Communications plus Time Dilation Equals ???


Xavier Onassiss

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

It is not so bad to receive comms from 5 years in the future' date=' if you are more than 10 ly from the source, as long an you have no FTL and can only communicate back to that period.[/quote']

 

Reminds me of a story called Beep by James Blish.

 

 

Apologies for not being able to hide the Spoiler below.

 

 

Instantaneous communicator with messages that can be received by every communicator that is ever made. The time differential causes all future messages to be received as a beep.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Reminds me of a story called Beep by James Blish.

 

 

Apologies for not being able to hide the Spoiler below.

 

 

Instantaneous communicator with messages that can be received by every communicator that is ever made. The time differential causes all future messages to be received as a beep.

 

Spoiler tags are just like quote tags.

Example: (spoiler) 'your spoiler here' (/spoiler)

Replace the parentheses with brackets and you get this:

 

 

'your spoiler here'

 

 

 

 

Don't look at me,

Xavier Onassiss

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

In his book "Iron Sunrise", author Charles Stross proposes an interesting solution to the time travel problem: a weakly godlike AI has copied itself up and down the timeline, and doesn't let anyone violate causality in its domain, on penalty of . . . well, I don't remember if it's ever actually detailed, but we can assume that such a being has the resources to make you really, really, wish you hadn't tried it.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

I keep going back and reading the article and the posts about using a wormhole with one end sent on a relativistic journey' date=' for time travel. Either there's something I'm not getting or that's a very wonky concept.[/quote']Let me see if I can clarify it. (I'll give it a shot, anyway.)

 

Start with a wormhole between Unit A and Unit B. Unit A stays stationary. Unit B travels to a distant star system at near-light speed, and returns. Keeping with prior examples, let's say the star system is just under 50 light-years away, so the round trip takes 100 years.

 

But that 100 years is from the perspective of Unit A and others who stayed with it. Unit B traveled at near-light speed, and so experienced time dilation. For purposes of this illustration, let's say that the dilation was 100:1, so that in the 100 years that passed for Unit A only 1 year passed for Unit B.

 

If Unit B leaves Earth in the year 2050, then when it returns to Earth it's the year 2150, even though from its perspective only one year of time has passed. Because the wormhole links the two units in subjective time, anything going through it from Unit B to Unit A will come out in Unit A about one year after Unit B left -- in other words, what enters Unit B in 2150 will exit Unit A in 2051.

 

(This requires either a many-worlds theory or a closed timeline curve to work, but physicists consider either, or even both, to be quite possible if not mandatory.)

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Let me see if I can clarify it. (I'll give it a shot, anyway.)

 

Start with a wormhole between Unit A and Unit B. Unit A stays stationary. Unit B travels to a distant star system at near-light speed, and returns. Keeping with prior examples, let's say the star system is just under 50 light-years away, so the round trip takes 100 years.

 

But that 100 years is from the perspective of Unit A and others who stayed with it. Unit B traveled at near-light speed, and so experienced time dilation. For purposes of this illustration, let's say that the dilation was 100:1, so that in the 100 years that passed for Unit A only 1 year passed for Unit B.

 

If Unit B leaves Earth in the year 2050, then when it returns to Earth it's the year 2150, even though from its perspective only one year of time has passed. Because the wormhole links the two units in subjective time, anything going through it from Unit B to Unit A will come out in Unit A about one year after Unit B left -- in other words, what enters Unit B in 2150 will exit Unit A in 2051.

 

(This requires either a many-worlds theory or a closed timeline curve to work, but physicists consider either, or even both, to be quite possible if not mandatory.)

 

I get all that, I think.

 

What isn't clicking is, why does it matter much time each end of the wormhole "experiences"? Once you have both ends at earth again (in your example), 100 years has passed at earth.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

What isn't clicking is' date=' why does it matter much time each end of the wormhole "experiences"? Once you have both ends at earth again (in your example), 100 years has passed at earth.[/quote']

Less time passes for Unit B than for Unit A (the Earth). At what point would Unit B's passage of time "catch up" to Unit A? The act of returning to Earth doesn't speed up Unit B's passage of time to normalize things.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Less time passes for Unit B than for Unit A (the Earth). At what point would Unit B's passage of time "catch up" to Unit A? The act of returning to Earth doesn't speed up Unit B's passage of time to normalize things.

 

Right. So why does that matter? It's not as if it's 99 years earlier outside "Unit B" -- after the ship gets back, A and B are right there at Earth, at +100 years.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Right. So why does that matter? It's not as if it's 99 years earlier outside "Unit B" -- after the ship gets back' date=' A and B are right there at Earth, at +100 years.[/quote']

But A and B don't exist only on Earth in the year 2150. From a spacetime perspective they also exist in the past, along their own world-lines.

 

We're not just talking about Unit B as an object outside of which time follows Earth's rules. We're talking about Unit B's reference frame, which is no more or less privileged than Earth's. Via a freaky extreme edge-case of relativity (the wormhole) it stays connected to the Earth in that same Unit B reference frame. So at the end of the trip, while Unit B itself realigns with the Unit A reference frame, the other end of the wormhole remains on Earth in the Unit B reference frame, because that end of the wormhole doesn't undergo any process of realignment.

 

Consider this:

                  elapsed            elapsed         Unit B
                  time for           time for        connects to
Earth date         Unit A             Unit B          Earth date
----------         ------             ------          -----------  
2050                  -                 -             2050
(spaceship leaves)
2075                25 yrs             3 mos          2050 + 3 mos
2100                50 yrs             6 mos          2050 + 6 mos
2125                75 yrs             9 mos          2050 + 9 mos
(spaceship returns)
2150                100 yrs            12 mos         2051

For the last entry in the fourth column to read 2150, some event must take place to elapse the missing 99 years. For ease of play in a campaign, you can posit such an event as occurring automatically. But the real-world math (as I understand it) does not require such an event.

 

Relativity is freaky.

 

 

 

 

Edit: Rereading your posts, it seems like the fact that A and B both exist in 2150 is a point of confusion. The A that exists in 2150 is irrelevant to the scenario. You can destroy A in 2052 and the scenario is exactly the same. The extra 98 years don't affect B.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

But A and B don't exist only on Earth in the year 2150. From a spacetime perspective they also exist in the past, along their own world-lines.

 

We're not just talking about Unit B as an object outside of which time follows Earth's rules. We're talking about Unit B's reference frame, which is no more or less privileged than Earth's. Via a freaky extreme edge-case of relativity (the wormhole) it stays connected to the Earth in that same Unit B reference frame. So at the end of the trip, while Unit B itself realigns with the Unit A reference frame, the other end of the wormhole remains on Earth in the Unit B reference frame, because that end of the wormhole doesn't undergo any process of realignment.

 

Consider this:

                  elapsed            elapsed         Unit B
                  time for           time for        connects to
Earth date         Unit A             Unit B          Earth date
----------         ------             ------          -----------  
2050                  -                 -             2050
(spaceship leaves)
2075                25 yrs             3 mos          2050 + 3 mos
2100                50 yrs             6 mos          2050 + 6 mos
2125                75 yrs             9 mos          2050 + 9 mos
(spaceship returns)
2150                100 yrs            12 mos         2051

For the last entry in the fourth column to read 2150, some event must take place to elapse the missing 99 years. For ease of play in a campaign, you can posit such an event as occurring automatically. But the real-world math (as I understand it) does not require such an event.

 

That's a different version of the same explanation that has been posted repeatedly. I get the whole "time passes more slowly for Unit B". I really do.

 

What I don't get is how that makes Unit B in 2150 connect to Unit A's past, not Unit A in 2150.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

So let's say Gate A gets destroyed in 2052. When Gate B arrives in 2150, Gate A hasn't existed on Earth for 98 years. What does Gate B connect to? Or is there a point at which the people on the spaceship looked through the wormhole and saw Gate A disappear?

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

So let's say Gate A gets destroyed in 2052. When Gate B arrives in 2150' date=' Gate A hasn't existed on Earth for 98 years. What does Gate B connect to? Or is there a point at which the people on the spaceship looked through the wormhole and saw Gate A disappear?[/quote']

 

To make the math easier, Gate A at Earth is destroyed in 2075. Using your table post above, my guess would be that the wormhole would collapse 3 months into the journey as experienced by the people on the ship.

 

Destroy Gate A at 2125, and from the point of view of the ship crew, the wormhole collapses 9 months into the journey.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

To make the math easier, Gate A at Earth is destroyed in 2075. Using your table post above, my guess would be that the wormhole would collapse 3 months into the journey as experienced by the people on the ship.

 

Destroy Gate A at 2125, and from the point of view of the ship crew, the wormhole collapses 9 months into the journey.

Which works out to time running faster at A than at B. So people on the ship look through the wormhole and see people on Earth moving 100x faster. People on Earth see the ship's time moving 100x slower. That way 25 years can pass on Earth, 3 months can pass on the ship, and the collapse happens simultaneously for both sides. That's the scenario I proposed upthread. I think it'd be playable, though it doesn't match the real-world physics.

 

(If you don't have time running at two different speeds, you get a non-simultaneous collapse, which again gives you time travel/causality issues.)

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Right. So why does that matter? It's not as if it's 99 years earlier outside "Unit B" -- after the ship gets back' date=' A and B are right there at Earth, at +100 years.[/quote']

 

No, it does not work like that.

Consider that the crew on the starship carrying unit B are only one year older from their age when the ship departed Earth, while their twin brothers who stayed on Earth are 100 years older.

 

When the crew set foot on Earth at the end of their journey, they do NOT suddenly catch up the missing time and age 99 years in an instant.

 

Neither does the wormhole mouth.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

No, it does not work like that.

Consider that the crew on the starship carrying unit B are only one year older from their age when the ship departed Earth, while their twin brothers who stayed on Earth are 100 years older.

 

When the crew set foot on Earth at the end of their journey, they do NOT suddenly catch up the missing time and age 99 years in an instant.

 

Neither does the wormhole mouth.

 

How does the "age" of the mouth change when someone entering the wormhole at one end comes out at the other, though?

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

How does the "age" of the mouth change when someone entering the wormhole at one end comes out at the other' date=' though?[/quote']

It's in a different frame of reference. Correct me if I'm wrong, Nyrath, but it's essentially an extreme case of how relativity redefines simultaneity.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

according to relativity if you have a wormhole with one end on a spaceship, and the other end on earth, and both ends have clocks near their mouths so you could see the clock on the other side of the wormhole, they would appear to be BOTH going at a normal rate. This us a contrast to how relativity affects clocks. so one year seems to pass "through" the wormhole, even though 100 years pass otherwise.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Reading the Wiki article, this is where I said "Wait, no."

 

A popular picture for understanding this idea is provided by a thought experiment consisting of one observer midway inside a speeding traincar and another observer standing on a platform as the train moves past. It is similar to thought experiments suggested by Daniel Frost Comstock in 1910 and Einstein in 1917.[1]

 

A flash of light is given off at the center of the traincar just as the two observers pass each other. The observer onboard the train sees the front and back of the traincar at fixed distances from the source of light and as such, according to this observer, the light will reach the front and back of the traincar at the same time.

 

The observer standing on the platform, on the other hand, sees the rear of the traincar moving (catching up) toward the point at which the flash was given off and the front of the traincar moving away from it. As the speed of light is finite and the same in all directions for all observers, the light headed for the back of the train will have less distance to cover than the light headed for the front. Thus, the flashes of light will strike the ends of the traincar at different times.

 

Sorry, but this is subjectivist nonsense. Maybe it's a bad example, but either the back of the train is "catching up" to the light, or not.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

The light itself cannot hit both ends of the train at the same time' date=' AND hit the ends at different times, though.[/quote']

 

I think the key words here are "same time" and "different times." When time dilation becomes a measurable effect, these phrases don't really mean anything. (which is why the situation I presented in my original post was giving me difficulty)

 

 

Don't look at me,

Xavier Onassiss

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

Right, "simultaneous" only has meaning in one inertial frame of reference. The concept of "simultaneous" seems universal to us because on Earth, we all effectively occupy the same inertial frame of reference. (We don't really, but the delta-v between reference frames on Earth is so small compared to relativistic speeds that the differences are negligible. At least until you talk about syncing digital signals from satellites.)

 

Common sense didn't evolve to handle this weird crap. You have to rely on the math.

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Re: Instantaneous Communications plus Time Dilation Equals ???

 

You can't have it both ways. Either the train is moving relative to the photons from the flash' date=' or it's not.[/quote']

 

Well, you see, there's this guy named Einstein who had a few thoughts on that very subject....

 

 

 

Don't look at me,

Xavier Onassiss

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