Instantaneous Communications plus Time Dilation Equals ???

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Sure, but I thought we were trying to reconcile things to be playable, thus without time machines.

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Question: if wormholes would really work this way, and it's theoretically possible to do this, does that mean that we are already living in a universe where causality is only a convenient general guideline? If so, what implications would this have on the "FTL, relativity, causality: pick any two" argument against FTL travel? As far as that goes, couldn't you just make a trip at high relativistic sublight speeds and then jump back into the past? If FTL gives you effective time travel, it seems like time travel would give you effective FTL.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

There's a paradox here that 's far bigger than time travel.

 

If one end of the wormhole is on the ship, and the ship gets back to earth at 3100 AD earth time, how does that end of the wormhole get back to earth any earlier than 3100 AD earth time? How can the end of the wormhole that's on the ship be back at earth at both 3100 AD, and at some year between 2100 and 3100 AD?

 

Between 2100 and 3100 AD earth time, there's only one end of a wormhole at earth. You can't enter the earth end and then emerge at earth at any time between 2100 and 3100.

 

You could enter the earth end, appear at the ship end, spend time on the spaceship, and then come back, to find that less time had passed for you than had passed on earth.

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Question: if wormholes would really work this way' date=' and it's theoretically possible to do this, does that mean that we are already living in a universe where causality is only a convenient general guideline? If so, what implications would this have on the "FTL, relativity, causality: pick any two" argument against FTL travel? As far as that goes, couldn't you just make a trip at high relativistic sublight speeds and then jump back into the past? If FTL gives you effective time travel, it seems like time travel would give you effective FTL.[/quote']

It's a pretty good argument that wormholes aren't that simple. If they're even possible to use for transportation, odds are they won't be portable holes you can load into a cargo hold and toodle around with. Michio Kaku was on the Science Channel the other day saying that the amount of negative energy needed to stabilize a wormhole would be "the size of Jupiter." I didn't follow that wording, but the gist is pretty clear. We're not talking about portal guns.

 

There's a paradox here that 's far bigger than time travel.

 

If one end of the wormhole is on the ship, and the ship gets back to earth at 3100 AD earth time, how does that end of the wormhole get back to earth any earlier than 3100 AD earth time? How can the end of the wormhole that's on the ship be back at earth at both 3100 AD, and at some year between 2100 and 3100 AD?

 

Between 2100 and 3100 AD earth time, there's only one end of a wormhole at earth. You can't enter the earth end and then emerge at earth at any time between 2100 and 3100.

I'm unclear what scenario you're describing. Gate B starts on Earth in 2100. It spends 1000 years of Earth time in space. It returns in 3100. It doesn't exist on Earth in the interim.

[ajackson]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Question: if wormholes would really work this way' date=' and it's theoretically possible to do this, does that mean that we are already living in a universe where causality is only a convenient general guideline?[/quote']

Well, if we knew of a way to create traversible wormholes (all solutions I'm aware of involve negative energy densities, and as far as we know negative energy densities are not actually possible), maybe. There are arguments that a wormhole network with a closed timelike curve would collapse in on itself due to virtual particle formation.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Question: if wormholes would really work this way' date=' and it's theoretically possible to do this, does that mean that we are already living in a universe where causality is only a convenient general guideline? If so, what implications would this have on the "FTL, relativity, causality: pick any two" argument against FTL travel? As far as that goes, couldn't you just make a trip at high relativistic sublight speeds and then jump back into the past? If FTL gives you effective time travel, it seems like time travel would give you effective FTL.[/quote']

 

Got it in one.

Under relativity, time travel and FTL travel are two different terms for the same thing. So yes, if you have one, you have the other.

 

The dirty little secret of physics is that there is nothing that specifically forbids time travel. This makes physicists quite upset, since time travel generally does terrible things to causality. Most physicists console themselves by wishfully assuming that there is some as-yet-undiscovered principle of physics that will outlaw time travel and make the problem go away. Because otherwise it would be Just Awful. (e.g., "There are arguments that a wormhole network with a closed timelike curve would collapse in on itself due to virtual particle formation.")

 

Other physicists postulate some some as-yet-undiscovered principle of physics that will prevent time travel from causing paradoxes and thus destroying causality (e.g, Novikov self-consistency principle)

 

In the meantime, there are quite a few theoretically possible mechanisms for time travel, all of which can be used for FTL travel.

http://en.wikipedia.org/wiki/Time_travel#Time_travel_to_the_past_in_physics

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

It's a pretty good argument that wormholes aren't that simple. If they're even possible to use for transportation' date=' odds are they won't be portable holes you can load into a cargo hold and toodle around with. Michio Kaku was on the Science Channel the other day saying that the amount of negative energy needed to stabilize a wormhole would be "the size of Jupiter." I didn't follow that wording, but the gist is pretty clear. We're not talking about portal guns.[/quote']

Yes, they will be massive.

 

For details, this method is used in Stephen Baxter's novel Timelike Infinity.

http://en.wikipedia.org/wiki/Timelike_Infinity

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

It's a pretty good argument that wormholes aren't that simple. If they're even possible to use for transportation, odds are they won't be portable holes you can load into a cargo hold and toodle around with. Michio Kaku was on the Science Channel the other day saying that the amount of negative energy needed to stabilize a wormhole would be "the size of Jupiter." I didn't follow that wording, but the gist is pretty clear. We're not talking about portal guns.

 

 

I'm unclear what scenario you're describing. Gate B starts on Earth in 2100. It spends 1000 years of Earth time in space. It returns in 3100. It doesn't exist on Earth in the interim.

 

Right, that was kinda my point.

 

If one end of the wormhole is gone from earth for 1000 years, you can't go back in time at earth by entering one end and exiting the other.

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

If one end of the wormhole is gone from earth for 1000 years' date=' you can't go back in time at earth by entering one end and exiting the other.[/quote']

Gate A is the opening in the past. When you enter Gate A and exit Gate B, you've gone into the future. You'll either be in the spaceship or on Earth after 3100, depending on when you enter Gate A.

 

Gate B is the opening in the future. When you enter Gate B and exit Gate A, you've gone into the past. You'll emerge on Earth at some point after 2100, because Gate A has been on the planet since 2100.

 

What's really interesting is if Gate A persists until Gate B's arrival, and they both persist long into the future. At that point you have a gateway arbitrarily far into the future. If the wormhole exists for a million years, you now have access to a million years of time, with stopping points at 1000 year intervals.

 

Of course this could all be totally naive analysis. I have no idea what the math actually allows to happen.

[Kristopher]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

You can't actually get one end to a different time than the other, though. If one end is gone for 1000 years, then comes back to earth at 3100 AD earth-time, then both ends are at 3100 AD earth time.

 

Just because time passes more slowly on the ship, doesn't mean that the ship arrives any sooner than 1000 years later earth time -- it's still gone for ~1000 years as experience by the people and objects in the neighborhood of Sol.

 

While the ship is gone, the end of the wormhole that stays at earth is there for 1000 years. When the ship gets back, both ends are there, at earth, in the year 3100 AD. How does a ship entering either end of the wormhole at 3100 AD go to any other time than 3100 AD?

 

And how does the anyone entering the earth-end of the wormhole between 2100 and 3100 end up anywhere other than on the ship that's carrying the other end?

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

As I understand it, the wormhole we're discussing isn't a tunnel from one point in spacetime to another point in spacetime. We're talking about a persistent wormhole, which means each end exists along a world-line through time (if I'm using that term correctly). So instead of a conduit from point A to point B, it's more like a ribbon cable connecting slot A and slot B (where the "slots" are the world-lines of each end). Any given point along slot A is connected to some point along slot B. The scenario is that, due to time dilation, there are fewer points along slot B. So if slot A and slot B converge (i.e., the ship returns to Earth) the futuremost point of slot B is not connected to the futuremost point of slot A, but to some point farther back along slot A. That point corresponds to Gate A in an earlier time.

[Egyptoid]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

>>> Instantaneous Communications plus Time Dilation

 

I thought that's how they did the Chipmunks songs.

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Out of curiosity, does anyone here actually know the math? I'm curious about the degree to which these discussions are oversimplified to the point of being largely meaningless, a la the "instant creation" period of nanotech speculation. When we talk about actual wormholes, what does the math say about what a "traversible" one looks like?

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Out of curiosity' date=' does anyone here actually know the math? I'm curious about the degree to which these discussions are oversimplified to the point of being largely meaningless, [i']a la[/i] the "instant creation" period of nanotech speculation. When we talk about actual wormholes, what does the math say about what a "traversible" one looks like?

 

Well, it is math from relativity theory, which is way above my pay grade. Example:

http://en.wikipedia.org/wiki/Wormhole#Metrics

 

There is a FAQ here

http://www.webfilesuci.org/WormholeFAQ.html

[sobran]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Assuming that quantum entanglement was capable of carrying information, it is important to note that quantum entanglement ignores causality anyway. It isn't just instantaneous. It's been proven (insofar as we know) to violate causality. So the short version? Feel free to ignore time dilation in relation to QEC. It's basically irrelevant.

 

If a group of people travel to a star system at sub-light speeds and are five years younger than their friends and relatives back home on Planet X... it simply doesn't matter. There might be delays between communications during the trip, from the perspective of Planet X, but the actual communications needn't be slowed down, nor does causality matter in the slightest.

 

"We sent ten years worth of data, so you should have received the last of it before you reached Planet Y."

 

"Uh, you did send ten years worth of data, but we were still receiving it long after we reached Planet Y."

 

They're both right. And it doesn't matter. From a RP perspective, I suppose it matters that two parties might have different ideas of exactly when a communication occurred. But if one party receives a message and then immediately travels to the source, via FTL travel, they don't find themselves arriving at a point back in time from when they left or anything crazy.

 

Sometimes people overthink the whole reference frame thing. It doesn't really work like that.

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

The "whole reference frame thing" is not really intuitive. For starters, when you talk about "instantaneous communication", you are now stuck with the question "instantaneous in what reference frame?" Relativity theory tells us that simultaneous events separated in space are, and can only be, simultaneous in ONE reference frame. In any other reference frame, one of the events will occur before the other. If you have, for instance, a ship with an instantaneous (instantaneous according to who? For this discussion, I'll assume it's always instantaneous according to the people on the ship) jump drive, it's possible to go on a trip and arrive before you left. First, make a long jump. No problems here, since you and your starting planet are in the same reference frame. Next, accelerate to high relativistic speeds away from your starting point. Finally, jump back home. To you, your departure and arrival on the second jump will be simultaneous. To anyone in a "stationary" reference frame (i.e. one in which your starting planet is stationary and you were stationary before you accelerated) your arrival on the second jump will occur before your departure.

[sobran]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Not exactly. More time passes for the stationary reference frame (i.e. your home planet) than for you on your relativistic ship. You jump away and accelerate for (say) a day, and (say) it is two days for your home planet. When you then jump home, instantaneously, you still arrive after you left. The point of disagreement would be that to them, you jumped home after two days and to you it was only a single day.

 

EDIT: Er, I had that backwards. I see what you did there.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Assuming that quantum entanglement was capable of carrying information' date=' it is important to note that quantum entanglement ignores causality anyway.[/quote']

As it turns out, that is a crippling assumption.

There are theoretical reasons that show it is impossible to use quantum entanglement to carry information faster than light. If you assume that it is possible, then you are into science fiction anyway.

 

The reasons are complicated, and I'm sure that eventually I'll be forced to dig up my reference books and give a full explanation. But the practical outcome is that after you've transmitted a message by quantum entanglement, the outcome is one string of totally random numbers at the source and another string of totally random numbers at the destination. Only by comparing the two strings can the message be discovered. And the only way to compare the strings is by transmitting the source string to the destination by using radio or other as-fast-as-light method.

 

So you can prove that FTL communication occured, but only after the fact. Which is worthless.

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

There is a FAQ here

http://www.webfilesuci.org/WormholeFAQ.html

That is an astoundingly interesting faq. Many thanks for the link.

[Xavier Onassiss]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

As it turns out, that is a crippling assumption.

There are theoretical reasons that show it is impossible to use quantum entanglement to carry information faster than light. If you assume that it is possible, then you are into science fiction anyway.

 

The reasons are complicated, and I'm sure that eventually I'll be forced to dig up my reference books and give a full explanation. But the practical outcome is that after you've transmitted a message by quantum entanglement, the outcome is one string of totally random numbers at the source and another string of totally random numbers at the destination. Only by comparing the two strings can the message be discovered. And the only way to compare the strings is by transmitting the source string to the destination by using radio or other as-fast-as-light method.

 

So you can prove that FTL communication occured, but only after the fact. Which is worthless.

 

It's understood that communications using quantum entanglement defies current theory. But this is one of those cases in which I made a conscious decision to insert a bit of 'handwavium' into the campaign, because it has so much potential as a plot device. Quantum entangled communicators are extremely rare in this campaign -- some star systems can't afford any, most systems have one, and a very few have multiple units. They aren't gadgets for the PC's to buy at the Rigel Kent branch of Sharper Image; they're strategic assets, only used for government, military, intelligence, and sometimes high-level academic data transfers.

 

The result is a distinctly two-tiered interstellar communications network. The 'Powers That Be' have access to instantaneous communications, while everyone else has to use courier vessels which take up to a month to reach the next system. These so-called fast courier ships are often derisively referred to as the "phony express."

 

Sure, I could insist on scientific rigor and chuck the whole idea, but this set-up makes things...interesting. (The bad pun is also a nice bonus.)

 

 

Don't look at me,

Xavier Onassiss

[Zeropoint]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Not exactly. More time passes for the stationary reference frame (i.e. your home planet) than for you on your relativistic ship. You jump away and accelerate for (say) a day, and (say) it is two days for your home planet. When you then jump home, instantaneously, you still arrive after you left. The point of disagreement would be that to them, you jumped home after two days and to you it was only a single day.

 

Nope. What I described is not in any way dependent on time spent moving at sublight speeds; it happens even if the ship can accelerate instantly. The fact is, if the ship is moving relative to the planet, the departure and arrival of the ship cannot be simultaneous in both frames.

[sobran]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

EDIT: Forget it. I need to do more reading as I'm just confusing myself at this point.

[austenandrews]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

Suppose you have a pair of communicators linked by a wormhole; is it even possible to transport one of them via an FTL wormhole drive without destroying the link in the process? I'm thinking No.

Incidentally, the FAQ that Nyrath linked to addresses bringing a wormhole into another wormhole:

 

What would happen if two wormhole mouths were to collide?

 

If one mouth were much larger than the other, the smaller mouth would simply pass through the wormhole with the larger mouth, as any other object would. If the colliding mouths and their associated wormholes were identical, there would be two possible outcomes: 1) If the effective mass of both mouths is negative, they will approach, possibly coalesce briefly (if their relative momentum is high enough), emit gravitational waves, and separate. 2) If the effective mass of both mouths is positive, they will approach, coalesce, emit gravitational waves, and remain joined. In neither case would the topology of space have changed. When the mouths of the two wormholes coalesce, they do not become a single wormhole. Rather, they become a three-mouthed system roughly resembling a stethoscope: A mouth in one universe branches internally to connect to two separate mouths in separate universes (or distant regions within the same universe). Unfortunately, no one has yet taken the trouble to perform calculations that would confirm or refute this speculation.

 

Short answer: a tiny communicator-wormhole should pass through a big spaceship-wormhole without incident. Though the convolutions regarding time dilation boggle the mind.

[IndianaJoe3]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

The "whole reference frame thing" is not really intuitive. For starters' date=' when you talk about "instantaneous communication", you are now stuck with the question "instantaneous in what reference frame?" Relativity theory tells us that simultaneous events separated in space are, and can only be, simultaneous in ONE reference frame. In any other reference frame, one of the events will occur before the other. If you have, for instance, a ship with an instantaneous (instantaneous according to who? For this discussion, I'll assume it's always instantaneous according to the people on the ship) jump drive, it's possible to go on a trip and arrive before you left. First, make a long jump. No problems here, since you and your starting planet are in the same reference frame. Next, accelerate to high relativistic speeds away from your starting point. Finally, jump back home. To you, your departure and arrival on the second jump will be simultaneous. To anyone in a "stationary" reference frame (i.e. one in which your starting planet is stationary and you were stationary before you accelerated) your arrival on the second jump will occur before your departure.[/quote']

 

OK, I think I understand the problem now, so let me try to handwave around it.

 

It's a common conception that FTL travel can't be used near a large mass because the mass distorts spacetime. We can have velocity do the same thing - the faster you are traveling (relative to, say, the cosmic microwave background), the more energy it takes to jump into hyperspace (or whatever). FTL isn't used as time travel because it would take too much energy.

[Nyrath]

Re: Instantaneous Communications plus Time Dilation Equals ???

 

It's understood that communications using quantum entanglement defies current theory. But this is one of those cases in which I made a conscious decision to insert a bit of 'handwavium' into the campaign' date=' because it has so much potential as a plot device.[/quote']

 

That's OK. I'm just trying to set the record straight before more impressionable people jump to the incorrect conclusion that is how things operate in the real world.

 

Quantum entangled communicators are extremely rare in this campaign -- some star systems can't afford any' date=' most systems have one, and a very few have multiple units. They aren't gadgets for the PC's to buy at the Rigel Kent branch of Sharper Image; they're [i']strategic assets[/i], only used for government, military, intelligence, and sometimes high-level academic data transfers.

 

The result is a distinctly two-tiered interstellar communications network. The 'Powers That Be' have access to instantaneous communications, while everyone else has to use courier vessels which take up to a month to reach the next system. These so-called fast courier ships are often derisively referred to as the "phony express."

 

There is a similar situation in Glen Cook's STARFISHERS trilogy. The starfishers have plentiful FTL communicators, while the Confederacy only has a precious few. The starfishers has a smaller space navy, but the FTL coms multiply their effectiveness.

 

The local color is colorful. There are creatures called star whales whose bodies are composed of magnetic fields, ionized hydrogen, and nuclear fusion. They are also quite intelligent. Unfortunately they are vulnerable to star sharks.

 

The starfishers use their combat starships to defend star whales from star sharks. In exchange, the star whales give the starfishers "ambergris nodes", which are the sine qua non of FTL coms. So the starfishers have a virtual monopoly on FTL com.