belltower | Talk To Glowfic Characters

So we've started answering comments in "How To Read Effulgence" in character, and that's not really the ideal platform for those conversations. This is! You may address characters here and we may opt to answer in character. You will get a kind of loosely "backstage" out-of-continuity version of the character (in continuity proper, you cannot talk to them, since you aren't there) and if you want them at a specific (past relative to where we're writing) point in time, feel free to specify (e.g. "Addy in 1932", "Shell in her box", "the Joker while committed", "Minus right after he woke up from turning", "the alethiometer on the subject of 1207").

Any glowfic author may use this thread to receive questions.

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Flat | Top-Level Comments Only

From:

linkhyrule5

Aegis's basically answered it above but - in classical special relativity, as understood to this undergrad-but-physics-major, if you accelerate yourself to ten nines of c and then instantaneously travel backwards some distance in your reference frame (pretty sure it needs to be big, like light-years big), instantaneously stop yourself and then teleport back to your original position, you'll have moved backwards in time. This is likely to be done accidentally if, say, you have this arrangement of colonies (roughly)

A------B-----C

and someone departs B going to C, but sends a message by ansible to A that gets rebounded to B.

Which, depending on how fast the ship was moving and how far the colonies are, might never be noticed by the colonists themselves. It should be blindingly obvious to you, though - my naive model of relativity says that every time someone gets up to relativistic speed then some part of your consciousness ends up behind some part it used to be ahead of, so if you haven't noticed anything my naive model of relativity is hilariously wrong.

Which is good! Means I'll still have a job when I finish my PhD. :P

From:

mind_game

Well, nobody has tried sending ships flying around at relativistic velocities outside of Peace - Samaria had something more strongly resembling science-fictional concepts of hyperspace, back when people there roamed the stars, but Jehovah has extremely spotty scientific records so I don't have many details. So it's possible Peace is a physics oddball here and I'll get dizzy if anyone exceeds the speed limit in another world with any of me aboard.

This experiment as described hasn't been tried with a stationary offworld colony proper - that's too recent and ansible bandwidth is too expensive for people who don't know the right people, wink wink - but what I would expect is that B would get their rebounded message a very tiny bit of time after sending it.

But it's possible you're expecting differently because you don't fully understand the architecture around ansibles and not because of some underlying mismatch in physics. They transmit instantaneously, but no mechanism that decides what to transmit - even a very simple automatic algorithm, even me after I ate all those Internets - is instantaneous. And the hardware around the ansible itself isn't instantaneous either.

Once the message is sent, it arrives right away, but the bounce will always take a measureable amount of time at your point A before B gets it back again, because the ansible itself cannot "decide" to turn the signal around, it's just the conduit, it needs formatted input. (Not that the astronauts would notice even if all the ansible operators at point A decided to take the week off.)

From:

linkhyrule5

Oh, the turnaround only needs to be instant instant to be guaranteed. In practice it just needs to be less than, well, however much you've accidentally time traveled, which like I said depends on how fast you're moving and how far back you send your message. If you move back ten milliseconds and the turnaround takes two, then (I'm going to refer to ansible nodes as Janes, do you mind?) B-Jane is still going to get the message 8 ms before ship-Jane sent it - as in, if B-Jane then sent it instantaneously to ship-Jane ship-Jane would get the message before she sent it, though the duration wouldn't be 8 ms it'd be something like 8/gamma.

From:

mind_game

I don't mind calling ansible nodes Janes. Anyhow, this has never happened to me, even when everyone was being relatively prompt and/or automatic about keeping up with their correspondence. Events happen in order, at least on Peace. Just fewer of them happen to people or to bits of me which are moving very fast.

From:

linkhyrule5

... Huh. That is really bizarre and sometime I need to sit down with a Peace physicist about it! :P

(okay, no, it's not bizarre my model is bizarre, point is still made, there is physics geekery to be had.)

From:

theonebutcher

You don't truly understand relativity. Many people don't. Many grad students don't. Time Travel due to superluminous Transmission just looks like time travel if you are watching from any reference point in the universe using light, sound, particles or anything else made of Energy(which is pretty much everything we ever encountered.).

Relativity doesn't tell you what really happens, it only predicts what you see. It outright states that nobody can predict what really happens and it's only possible to observe the universe from a particular reference frame and use that to calculate what another another reference frame sees.

What really happens nobody knows(though there are a few intuitive theories), but what it looks like for Jane A is that you send the information into the future, the other guy reacts and then the response travels backwards in time. Then she can use light to see the guy respond to her message.

Jane B sees that someone send her data from the future, she responds and sends it back into the future. She cannot send it back to before the Data was send, because then it would end up at a different place in space.

Because if you look at it through relativity Space and Time is basically the same.

An easy example is this: You have two different guns and are on really far away hills. You fire Gun A vintage model named CauseTM and immediately afterwards the other one sees the muzzle flash and fires his Gun B a modern Effect brand. A blind man stands next to Gun B and says:"Whoa! Fist Effect, then Cause! Awesome, we have invented Time Travel!" Because without Ansibles we are all Blind. If we rely on slow light. Relativity is the Art of maneuvering our Huge Lightless world with only the slow echoes of Sound. Especially if you wanna communicate over large distances using these waves or want to calculate your position from them.

From:

linkhyrule5

... Um.

No.

... I could be very sardonic and snarky and take apart that argument, but instead I'm just going to ask if you've actually taken a course? Because if not I'm just going to suggest that either you do, or you read a textbook.

From:

theonebutcher

Yes. Theoretical Physics one to five, in five I had a One Point Zero. You don't really get paradoxes out of FTL-comms. I left most things out. Time dilation and space contraction for example. But the core that there wouldn't be any paradoxes if we could teleport FTL stands. The Light-Sound Analogon is not something I would present to any professional... because it leaves a LOT of things out.

Anyway there are a lot of things which move more than c relatively. But they might as well be in different universes.
http://en.wikipedia.org/wiki/Hubble_volume

From:

linkhyrule5

I am going to be unapologetically very suspicious of that, because most of what you just said is pretty much irrelevant, but in the interest of taking you seriously: What is the problem with this diagram? Blue path is the path of a teleporter.

(http://tinypic.com/r/2rgdrba/5)

Edited Date: 2013-10-21 12:08 am (UTC)

From:

theonebutcher

I'm sorry but this will sound snarky: What's wrong is that the axes are not labeled and arrowed and I have no Idea what it should represent. First I thought the yellow lines are supposed to be some kind of light cone of the object in the red line, as viewed from a moving observer, but that doesn't make it make sense.

As far as I can tell a teleporter was moving with a large speed in front of the yellow lines and then teleported onto the line whose speed he matched. I did not see any instance of cause preceding effect or someone being able to percieve his own future.(My definition of time travel here.)

From:

linkhyrule5

I whipped it up in five seconds to call your bluff, sorry. Your average pretender to relativity won't know what a Minkowski diagram is.

Taking you significantly more seriously: Yellow lines are the reference frame of the teleporter. The teleporter starts at the origin, instantaneously accelerates to the velocity indicated by the yellow lines, teleports against his direction of travel, instantaneously decelerates, and teleports back to his original position; blue lines therefore trace spacelike paths, since teleportation takes place along a line of simultaneity. When the teleporter reaches the end of the blue line, he is separated by a negative timelike interval from the beginning of the blue line; Novikov aside, he is capable of "changing the past."

From:

theonebutcher

Yeah here lies the crux of the matter. Ever heard of the Twin Paradoxon? Each twin could say HE is the one resting and the other one is the one traveling by using their own spaceship as a frame of reference. From an observer in the middle they remain the same age until the moment one of them changes speed. But one of them feels the acceleration of turning around. Same thing here. You change frames of reference. Which means acceleration. Einstein said one couldn't tell the difference between accelerating and standing still in a gravity well. Which is why you have to use General relativity to model the speed change as a spacetime curvature. An instant velocity change might as well be an event horizon. Even a gradual but really speedy change would bend spacetime in a way he would STILL arrive after he departed. Only to see the light of himself zipping into the past(If I understood your diagram correctly It would have been better to continue the blue line a bit in both directions).

The problem with simultaneity in a Minkowski diagram is that it's still just a way of looking at the data we get. What things are truly "simultan"(excuse my German, I can't find the correct English spelling...) nobody knows because we don't have ftl signaling yet.

I will now move out of my area of expertise:
Maybe we are moving at outrageous speeds relative to some aether and simply don't notice because we can't see the effects of the True Laws because we are smack dab the middle of a linear looking section of a more complex term. The Universe only turned opaque when Atoms formed.

Or, more importantly: Big Bangs are entirely possible to be an event that happens fairly often, bending spacetime into pocket Universes by virtue of their extreme densities.

On to personal matters:
Now that was rude. If you are who I thought you are you should already know me for my accurate and trustworthy comments to your fics. Oh but wait, you are the guy from Innocence, not the one from Dark Lords of Nerima. Still I thought you knew me from Dungeon Keeper Ami, where I do a ton of physics and metaphysics therefore you are forgiven and next time:

If it costs you little:Trust but verify, not only verify. A proper diagram would have saved me a quarter of an hour of trying to make sense of this one.

From:

linkhyrule5

Hm. That is a very interesting point. I'll get back to you after I take my GR course in a year or so :P. I don't think it should affect the trajectory but GR has proved me wrong before, so.

And apologies - illusion of transparency and all that, I knew it wasn't spectacular but I didn't know it was incomprehensible. I wasn't going to spend a quarter-hour making a really good drawing, either, before I had decent confirmation I was talking with someone who knew what they were talking about.

(And huh, you're on DKA? I should pay more attention to usernames.)