I just finished reading the Lost Fleet series and was having a discussion with some friends and thought I’d ask the question here. In the books, one of the themes (without giving away major spoilers here) is that the ships can travel at relativistic speeds (.1 to .2c), but that communications are still light speed, which brings about some interesting plot points about communications lags. What I’m wondering, however, is what if there was an instantaneous communications method, but the ships were traveling at different fractions of the speed of light. What effect would the conversations have between a ship traveling at, say, .1c and one traveling at .2c?
Would there be no noticeable effect in the conversation (i.e would it be just like talking face to face with someone normally), or would one ships conversation be lagged due to relativistic effects, due to time dilation differences between the two ships?
(For the purposes of this discussion, assume there IS some magic black box that allows for instantaneous communications over any distance)
Well simple logic would lead me to assume that it would seem like a face to face conversation since the communications are instantaneous. But relativity often requires more than simple logic, so I’m also curious to hear the resident physicists address this. Maybe one person seems to be talking fast, and the other slowly.
If the ships aren’t accelerating (i.e., you just need Special Relativity for the calculations, not G.R.) then what matters are the two ships’ velocity relative to each other; you can’t say that one or the other “is” moving at a certain speed- that’s the point of Relativity. I’d also point out that even if we’re talking a relative speed of 0.3 C that’s not enough for a huge dialation effect; enough that chronometers will get out of synch but not enough to notice in a face-to-face chat. Finally, even if we invoke a magic “black box” and say instantaneous communication is happening, never mind how, the problem with that is that leads to a direct contradiction with how the universe is observed to behave, unless you handwave Relativity away somehow. There’s no way to meet the criteria of the OP: time dialation AND instant communication.
If it’s instantaneous in some preferred reference frame, there wouldn’t be a true Doppler shift between the two ships. However, if the ships were traveling a different speeds relative to that preferred reference frame, they would have different amounts of time dilation as you mentioned. The effect would be similar in that there’d be some change in pitch. At 0.1 to 0.2 c, this wouldn’t be a large effect, though, roughly a difference of 1.5 percent.
Instantaneous communication breaks causality. i.e you can arrange some set of relativistic spacesheep speeds and reference frames that allows you to send a message back in time. See: Sharp Blue: Relativity, FTL and causality - Richard Baker
It’s just a way of taking the means out of the discussion to focus on the actual question I’m asking. If you want to answer that instantaneous communications are impossible (full stop), then do so. I’m cool with that, if that’s the answer to the question I’m asking.
I think you can certainly get to the science by glossing over specific details, as I’ve seen done with speculation about time travel machines. You can basically black box (or call it ‘magic’) certain aspects and then focus on the physics of the question being asked.
If communication is instantaneous in one preferred reference frame, then there is no causality violation. In the link, the author is assuming instantaneous communication in multiple reference frames.
Though I want to keep the specifics about the means of instantaneous communications as general as possible (which is why I mentioned it was a black box), unless it has a direct impact on the answer, this is sort of what I was thinking of for that black box (I read about it years ago).
It it DOES have a direct impact on the question I’m asking (like, say it makes it impossible) then that’s fine too. I was just curious and I know a lot of physics types hang out here in GQ so thought I’d ask.
Here’s a though experiment. Suppose one person is in a motionless space station. His twin is in a space ship that can travel at really high speeds - enough so that it slows down his perception of time passing. The twin in the space ship floors his accelarator for one minute. When he stops the other brother on the space station says that he was actually moving for ninety seconds - the difference between their two perceptions being due to time dilation.
Now suppose they hook up an instaneous radio between the space station and the space ship and each brother will count off the seconds on his watch while the twin in the space ship once again accelerates for what he perceives as a minute.
What will each twin hear? Will the brother in the space station hear his brother count off sixty seconds while he’s counting off ninety seconds and vice versa?
It would seem to me that each brother would think his twin’s pace is off. The brother in the space ship would think his brother was counting off too fast and the brother in the space station would think his brother is counting off too slow.
There are questions about time travel that can be answered by relativity, but virtually all the answers about time travel given here are fictional. You can say anything you want about how time travel would behave and interact and experience or avoid paradoxes. None of them mean a damn thing.
There are questions about instantaneous communication that can be answered by current relativity theory as well. They have been answered here. Instantaneous communication doesn’t lead to effects, it leads to paradoxes.
Wrong. You cannot say “ignore everything we know about science but give the scientific effect of this”. It leads nowhere. (As apparently did the QM hypothesis in your link, since more than 11 years later it is still accepted that quantum entanglement cannot be used for instantaneous communication.) People do like to speculate, and do speculate about time travel and FTL travel and what aliens are like and what’s inside a black hole and what would happen if you saw a miracle or encountered god and a hundred more threads than I’ve seen. Our current science has very little to say on the effects in the real world of any of these.
The Science Fiction Writers of America were founded in 1965 by a bunch of veterans of the genre who were already grousing at the time that most of the sf being written was actually fantasy, and they wanted to keep that icky fantasy stuff out. They lost. They lost big, they lost completely, they mostly lost their whole field to a tsunami of fantasy and its ugly brother horror. Almost nothing is left of true science in the sf ghetto. Space military empires have no science in them at all. It’s all fantasy because its all magic at the bottom. Adding more magic won’t return them to science.
Exapno, I sense a great precision in your postings on this board, so perhaps there are better formed questions in this area you could address. Maybe you could tell us more about the paradoxes that would result, or possible similar circumstances that would be possible. I can’t speak for xtisme, but it didn’t sound like he was proposing the existence of nonsense, just looking for information about the hypothetical situation. At least in my case have mercy on the ignorant desiring knowledge.
Only if it is instantaneous in more than one reference frame. If there is one preferred reference frame, and communication is instantaneous in that frame only, it does not lead to causality violation.
Sounds like a bunch of guys who are still bitter that their story got rejected for Dangerous Visions.
“Why, back in my day, John W. Campbell would have put a stop to all this nonsense. None of this ciderfunk shenanigans. Our heroes didn’t have emotional problems. The only problems they had was Martians trying to steal their women and they solved that with a zap gun.”
I think the question really has more to do with… given this scientific principle, and applying a certain magic principle, what does the resulting magic outcome look like? Or if fantasy isn’t your cup of tea, explain why the paradoxical results of the magic rule demonstrate that the magic principle isn’t real. It’s just a thought experiment; mathematicians do it all the time.
Right, this is how it works while there is acceleration, but if they did the same thing after the the brother has taken his foot off the accelerator, then the interesting thing happens. Brother 1 sees brother 2 as a moving frame of reference and so he hears brother 1 counting extra slowly due to time dialation, so he will reach 90 before his brother reaches 60. Meanwhile brother 2 sees brother 1 as counting too slowly for the same reason and will reach 90 before his brother reaches 60. Clearly both can’t be true so that is why you can’t have instant communication. If messages were passed at light speed then this is not a contradiction because the delay is can be accounted for by transmission time.
The problem with instantaneous communication is that it is equivalent to time travel. Science fiction writers not only know this, they practice this by starting an organization in 1965 being bitter for an anthology that won’t happen until 1967. Everybody wins! (That includes us. Look at the first Nebula Award winners. Classics all!)
Buck Godot is correct about the problem with your scenario. You’re taking an event which occurs solely because there is a limitation of light speed and applying it in an environment in which there is no limitation to light speed and assuming that it remains true. But that can’t happen. (And there is no privileged reference frame. That creates its own set of problems.) And you don’t need instantaneous communications to understand the result, since you’re applying an answer we got without it. So you’re saying that the effect of instantaneous communications is… nil. That can’t be right either.
20% of the speed of light is fast, but it isn’t really “relativistic”, as some people have pointed out.
Here’s a proposal for a means of near-instantaneous radio - a small wormhole, with one end inside the comm unit of each ship, so it functions like a telephone line. Sort of.
So from outside, the ships are far apart, and moving at very different speeds. But from the point-of-view of the comm units, they are sitting next to each other.
Time-dilation would show up, I suppose, by a doppler-like effect on the signal coming though.
(We could imagine the communication officers literally holding tin cans on the end of some string going through the wormhole, but I think it more realistic to have it microscopic in size, with the signals sent through as high-frequency transmissions.)
The fallacy I see here is that certain things are just not possible. Hypothesizing a “black box” to obviate the mechanism does not change that. Here’s a mathematical thought experiment:
Suppose division by zero is a permissible operation in the set of real numbers.
Therefore: 1 = 2.
Actually, you could easily “prove” any number is equal to any other number. The “hypothesis” that division by zero is possible leads to no useful conclusions, but creates a tidal wave of paradoxes.
The same with instantaneous communications. All the talk of time dilation and relativistic effects is predicated on the unvarying speed of light in a vacuum being the limit to the speed of “communication”, however you choose to define it.
Allowing instantaneous communication dismantles all of relativity, and allows any conclusion to be drawn from any premise.
