Alcubierre drive research

[Rakaydos]

I heard one argument that any particle attempting to go backward in time would destructively interfere with itself, and therefor time travel would only result i the liberation of the time traveler's mass energy, not a potential time paradox. Causality is preserved despite the theoretical possibility of time travel, because nothing can actually REACH the past without being canceled out completely..

[PB666]

I heard one argument that any particle attempting to go backward in time would destructively interfere with itself, and therefor time travel would only result i the liberation of the time traveler's mass energy, not a potential time paradox. Causality is preserved despite the theoretical possibility of time travel, because nothing can actually REACH the past without being canceled out completely..

That is the favored argument thiugh now-days-days i think it will come with exception 'except at quantum scales' so subatomic quanta maybe able to go back in time.

[K^2]

I heard one argument that any particle attempting to go backward in time would destructively interfere with itself, and therefor time travel would only result i the liberation of the time traveler's mass energy, not a potential time paradox. Causality is preserved despite the theoretical possibility of time travel, because nothing can actually REACH the past without being canceled out completely..

Doesn't have to. There is going to be self-interference, but this can result in a number of outcomes. Effect of time loops can actually be demonstrated with lasers quite elegantly, because a photon can be delocalized enough to interfere with itself along an earlier part of the beam. You can easily set up a grandfather paradox situation, for example and show that in QM it's trivially resolved without contradictions.

[GeneralVeers]

Does anyone else here get the feeling people are arguing in this thread just to be arguing.

No, with me it's the sense that most people in this thread have forgotten that the concepts being argued are almost entirely theoretical. And also (currently!) impossible to test.....

[problemecium]

My brother and I had a discussion recently about time loops in which he gave me a pretty interesting idea.

If a time loop, i.e. a closed timelike curve, occurred, we'd have a situation akin to Groundhog Day where a person or other object returns to the same point in time repeatedly. There are three hypothetical ways in which this can go down (that I can think up anyway):

- The time traveller "rewinds" along with everything else (Groundhog Day style), and Physics is deterministic, meaning that any given event has a single, calculable outcome (but perhaps difficult or impossible to measure)

- The time traveller "rewinds" along with everything else (Groundhog Day style), and Physics is nondeterministic, meaning that a given event has an element of randomness affecting its outcome (and thus information can be lost forever, a horrifying concept for modern physicists)

- The time traveller does not rewind along with everything else: time travel in the style of "The Time Machine" or "Harry Potter". I'll leave a discussion on this for another time, partly because while it entails a closed timelike curve in a technical sense, it's not really a "time loop" as generally understood.

In the first situation, every single time the loop "loops", the exact sequence of events occurs the exact same way, including any and all information that may or may not exist. Thus people within the loop will experience the same sequence of events in exactly the same fashion - not like in "The Time Machine" where the first time his wife is shot and the second she is run over; spacetime does not care whether an event is "important" or not. Rather everything will happen the exact same way in every reference frame within the curve, and the people will even have the same memories and sequences of thought. In such a situation, the curve itself is undetectable by anyone. It could be happening to all of us, right now, and we would have no way to tell or reason to care. So for all practical purposes, the loop never really counts as happening to begin with.

In the second situation, every time the loop "loops", there is a nonzero chance (big or small as you like) that any event might be slightly or significantly different. So you might stub your toe the first time, but just barely avoid stubbing it the second. Whether or not you remember previous iterations, if the loop is allowed to repeat infinitely, there is a 100% (or at least infinitely close to 100%) chance that an event will occur within the loop that breaks the loop, i.e. prevents further iterations from occurring. Thus the loop will inevitably cease to exist sooner or later. Since the nature of a time loop is such that its "start" and "end" points are not separated by any distance in time in the outside universe (a closed loop), this means that as soon as any CTC forms, in that same exact instant it will collapse and cease to exist.

This is currently only a logically-based hypothesis, but if true (I have a good feeling), it means we needn't worry about whether or not we generate CTCs - we'll either not care or they'll take care of themselves.

Edited November 1, 2015 by parameciumkid

[Silver_Swift]

I think I get it now, if I understand Silver_Swift's story about the drones correctly.

That said, I guess all of us on the doubting team were right in our hunch that it wouldn't be easy.

Yes, I think part of the confusion is that (like K^2 mentioned) even though you can use every kind of FTL communication to travel through time, you don't get time travel from every individual instance of FTL communication.

Also worth mentioning, for purposes of science fiction stories I think you could get around the problem by throwing relativity out of the window and outright stating that FTL communication can only happen in one specific reference frame (that might make it hard to use FTL if your star system is moving at high speeds in that reference frame, but that could be a plot point).

Also, if I understand everything correctly, C will not self-destruct, because it is programmed to do so only after receiving the order from D, which cannot occur until C has itself informed D, regardless of whether A1 occurred. And since C is moving forward in time, in its own reference frame it cannot send a message and receive a reply to that same message before sending it.

Ah, but the self-destruct message is sent at the exact same time as A1 in both reference frames. So when B1 happens, if C is not destroyed, it will/has sent the "I have seen B1" message and it will receive/has received the self destruct message so it will have/will self destruct.

Verb tenses are weird when talking about time travel

[GeneralVeers]

I suggest Dr. Streetmentioner's book of grammatical expertise: "Time Traveler's Handbook of 1001 Tense Formations".

[PB666]

 

Well at least its good for its comedic value [or not]. I am really not impressed with this D-news science stuff. But to give them credit they do make 60% of the critiques.

 

[fredinno]

6 hours ago, PB666 said:

 

Well at least its good for its comedic value [or not]. I am really not impressed with this D-news science stuff. But to give them credit they do make 60% of the critiques.

 

Sensational science is sub-par science, and that's what D-news is.

[PB666]

1 minute ago, fredinno said:

Sensational science is sub-par science, and that's what D-news is.

I like their ship, its totally impractical for light speed travel, you would need a blast shield facing forward.

[WinkAllKerb'']

sound tricky for now imho