posted
Another topic made me think about a typical scifi/fantasy topic that is both fascinating and full of bologna to me. I've almost never seen it done well, there always seems to be some flawed logic at work when it comes to time travel.
So I just thought I'd see what kind of ideas you guys have on the matter. Have you ever seen it done well? What were the rules and what was the logic? For that matter, do you think you've figured out how it should work to block the kinks?
I might throw some fuel on the fire later, play devil's advocate a little, but first I wanted to see some other people's opinions.
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The only way it comes even close to making sense to me is to see time - all of time - as a spreadsheet with infinite columns and rows. Change one cell, and all related cells necessarily change at the same time.
posted
So far, the most credible theory is that time travel is possible, but that there is always a self consistent solution. Meaning, you can't change your own past, just as you can't multipy yourself spatially and tango with your alternate self.
No credible evidence for 'alternate' realities exists so far, but if time travel were to allow you to change your 'own' past, then it would have to be by travelling to the past of an 'alternate' self, and changing that. You wouldn't be changing your own past, though there would be no way for you do determine this.
Note that I say you can't do something 'anymore than' you could do something else, then say that you could do it as long as you did the other...I'm just weird sometimes.
posted
I think the reason why this topic is so hard to determine is the fact that it isn't possible, at least in the physical sense.
I don't have alot of Science to back up my theory, but I think that if a person was to physically make a leap into another time it would screw everything up. That person can't be in the past as himself, he isn't supposed to be there (twice). I feel that the same would apply to the future as well, although travel to the future seems more plausible, because the future hasn't been determined totally yet. But, it would, at the very least, screw up the possible future due to him seeing that as well.
The "spreadsheet" that CCW mentioned may apply to this as well. The fabric of time just can't be messed with, with any success, in my opinion. Something as simple as this for instance.
You go into the past and steal a lollipop from a normal little kid. This was not supposed to happen. It changes the kid's perception of people in general and he now no longer trusts other people. As he grows he distances himself more and more from society. He becomes a recluse and never reaches his full potential. He was supposed to be a key part of the group that comes up with the cure for AIDS. Since his potential was changed from the theft of his lollipop, the cure is never found.
A more possible form of time travel (in my opinion) would be through mental capacity, or some kind of dream state. You could do this and not physically change the fabric of time. Anything other than this, I think would really mess things up, and cause unrepairable damage.
I am not a Sci-fi person, but this is what makes the most sense to me. Now someone can tell me how wrong I am.
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The best treatment of time travel (a genre of stories I really like) I've every seen is in Kage Baker's novels of The Company. She adds in the further embellishment of immortality, but it all works out.
The rules are:
You can only travel into your past and then back to your own time. There are, it turns out exceptions, but they are very rare and frowned upon.
You cannot change recorded history. Note that little word "recorded". Anything that hasn't made it into the records somewhere is open to manipulation.
You cannot take anything from your past back to your present. Everything and everyone has to travel forward through history from the time of its creation of their birth the hard way, a day at a time. (Say you go back to the time of Michelangelo and commission a sculpture. After he finishes it, you need to find a good hiding place for it; when it gets to your present, then you can go get it and take it home. You can also track it through history and then buy it from whoever has ended up owning it, but why would you want to pay for it twice?)
These novels, beginning with "In the Garden of Iden" are really good. I recommend them highly.
posted
Okay, you hit one of my favorites. I'm a sucker for time travel stories. Neither illogic nor impossibility can deter my reading. Some of my favorites:
Short: "All You Zombies" by Heinlein (This one pretty much ends the need for any further time travel stories. It's in OSC's anthology <Masterpieces>, and lots of other places, too.)
"The Ugly Little Boy" by Asimov
"Mimsy Were the Borogoves" by Henry Kuttner and C.L. Moore writing as Padgett
Jack Finney's collection <About Time>
Novels: "The Door into Summer" by Heinlein "The End of Eternity" by Asimov "F-Cubed" by Daniel da Cruz
posted
The first step in dealing with time travel is determining how time actually works. Is time one line that can be modified and played with by the time traveler? If so what happens if the accidently change something that causes the time traveler to never be born? Does the time traveler disapear, or do the become a paradox and continue to travel through time?
I happen to like the concept of multiple dimensions, even though it is a larger concept to grasp. Every choice we make each day spawns a new alternate dimension. Since they all exist in the same space this would allow for infinite possiblities. Changing something in the past only changes one paticulare moment in time, and only effects the dimensions that decend from that event.
Or you can take OSC's concept, which I also liked, and all time is reset the moment time travel occurs. Wipe it clean and give it another go.
quote:I think the reason why this topic is so hard to determine is the fact that it isn't possible, at least in the physical sense.
How do you know if you have never done it. If you told someone 5 years ago that someone would figure out a way of stopping and starting a beam of light no one would believe it. Guess what? They are doing it. The only thing that is impossible is the things we convince ourselves is impossible.
The fact we haven't figured it out does not mean it isn't possible. I do agree it would be a mess, but it does give a writer a wide range of possibilies to use in their stories.
Come to think about it, Andre Norton had a series of books that delt with time travel. But she chose not to deal with all the possibilities and kept most of the time travel to vast ammounts of time (dinosur age).
Ok, now that I think about it, I have like most of the books that used time travel.
posted
Time travel is fun stuff, when handled well and utter dreck when bungled. I've seen both. Many of the ones mentioned above are good. I would also add the Nebula winning novels by Connie Willis (Doomsday Book and To say nothing of the dog?).
I also believe it was Paul Anderson who had the whole Time Patrol series of stories. They were mostly fun.
The key to all time travel stories, and to all good magic, is that there must be rules, they must be followed and they must be internally consistent. Since no one currently knows exactly how time travel would work (though there are actually some pretty good physics based theories out there) an author can posit almost anything, as long as they follow all implications of their rules.
If a crushed butterfly in the mezozoic (sp?) will change current day history, you will need some very powerful safeguards or time travel will muck up everything you know (but you might not know it).
The paradoxes are fun. I just hate it when authors come up with rules that are contrived (just so they can use them to pull out a rabbit at some point in the plot) or silly or inconsistent.
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Time travel to the future is, of course, relatively simple (pun intended.) It's traveling to the past that presents problems.
Current theory allows for time travel into the past through wormholes, although it is impossible to go back to a time before the wormhole was created. (For a good SF treatment of this idea, read Timemaster by Robert L. Forward.) of course, the technical hurdles to creating such a time travel device are tremendous, possibly insoluble.
However, the device of time travel is useful in exploring ideas, so it's one of those things (like FTL travel) that are, by SF convention, allowed without the need for a complete scientific explanation.
I like time travel stories. I like some time travel stories despite their obvious flaws (Back to the Future, for example.) I can evaluate the concept of time travel as used in the story separately from my enjoyment of it.
My main criterion for evaluating time travel is consistency. Therefore, I have no problem with closed loops.
The two movies I have seen that best exemplify closed loops are "The Terminator" and "The Final Countdown."
Strangely enough, I think the movie that made the best use of the possibilities of time travel -- and everything done in the movie was logically consistent, even if some of the things that were said did not make sense -- was Bill & Ted's Excellent Adventure.
posted
Interestingly, apparently 12 Monkeys and Terminator were both based on a French film called La Jetee (synopsis here: http://www.imdb.com/title/tt0056119/ - you can see the traces of both of them, particularly the culmination of 12 monkeys).
I personally prefer the alternative reality theories... they are consistent with some generally accepted physical theories and avoids any kind of unpleasantness with paradoxes.
I have a plot on the back burner involving this kind of time travel...
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I believe there is no reason why time travel cannot exist. For all we know people from the future may already have visited our present or past and had great influence on world events.
I'm not of the opinion that if I develop a time machine tomorrow, use it to travel back 500 years and then step on a butterfly that it will have huge ramifications on our timeline because, for me, it has already happened and been accounted for. The event will already have occurred in our timeline when I invent time travel because I invent time travel so therefore it will change nothing. I won't know I've invented time travel until after I've done it and assuming I told no one else 500 years ago (because who would believe me if I did) no one else would know either.
As for if I kill myself then in my opinon that's it, I die the moment I do it. If I kill myself I'm dead. I know technically if I kill myself, I don't invent time travel, so I can't go back and kill myself so therefore I must be alive but then, if I'm alive then I'll invent a time machine, go back and kill myself. Therefore if I invent time travel in 2014 and travel back to kill myself, no matter what happens next I cannot possibly exist after this point in time so from then on I cease to exist.
Of course these are just my own speculations and I can't back them up with any evidence at the moment, but as soon as I invent time travel I'll conduct a series of carefully thought out scientific experiments and get back to you.
[This message has been edited by Gwalchmai (edited February 18, 2004).]
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Well, like Eric has said, relativity means that time travel in the forward direction is totally possible.
It's the going backwards part that makes a story, but I just can't buy the notion of going backwards. My own non-scientific assumption is that once a second has ticked by, that moment in time is forever gone, used up, and exists only as pictures (of one variety or another) in the synaptic patterns of our brains, or in some other storage media.
For me, time travel backwards could only be possible if, [1] Time - real time and not just a memory of time - were somehow saved on some infinite back-up hard drive (thinking metaphorically here) that could be accessed somehow, or, [2] If every moment of time, no matter how small a moment can be broken up, exists simultaneously (my spreadsheet motif). [3] I dislike the "alternate earth" theories - usually it's just a sloppy subterfuge.
Building on my options above, I see that time travel backwards is possible only if I am willing to assume that there is an infinite number of me. In option [1] an infinite number of me exists on a celestial back-up drive, so all the me's are frozen. If one gets accessed,what happens to the current me (it's pretty amusing to talk about myself like this)? Can more than one of me be active at the same time? That's the assumption behind option [2], which I also reject. It could only work if [a] I am built to be blind to all my other selves in the seconds and minutes and hours that exist both behind and ahead of me, or [b] what I call the passage of time is just my present consciousness passing from the current infinite me to the infinite me of the next micro-second, or, alternately, the passage of time consists of each moment of me turning quickly on then off in a straight line succession. Or, [3] says that there's a different me for every moment of my life, but they exist in a different dimension or alternate earth. I don't see that this solves the problems of [1] or [2].
My head hurts. I wonder if I could start my own Hollywood religion?
Anyway, the way I see it, either I am unique and time, if it moves at all, only moves forward, or there's a whole lot of me, and a whole lot of everybody else, but if that's the case, there's really no such thing as time at all, just an infinite collection of moments that we are aware of, which brings us to the problems of fate vs. freewill, and, oh, the philosophical list of issues could go on forever (clumsy pun intended).
Bah.
Say - can I interest you in a pamphlet about my Church of the Infinite Cuckoo Clock?
[This message has been edited by ccwbass (edited February 18, 2004).]
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The real problem is not where the watch came from. The real problem is that any object capable of decay cannot be passed all the way through a fixed closed loop. Eventually it will change enough to alter the flow of events. (A variable closed loop could be maintained, alternating between patterns in which the object is so decayed that it is repaired and patterns in which the object does not need repair.)
There is no problem of decay for an idea. So, if my future self appears and tells me how to construct a time machine, and I follow the instructions, then go back in time and tell myself how to build a time machine, there is a fixed closed loop. Where did the idea of how to build a time machine originally come from? It does not have to have originally come from anywhere; it is merely a part of the loop.
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The only thing I remember about Somewhere In Time is that my date absolutely loved the story whereas I couldn't get past what a babe Jane Seymour was.
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Stories about travelling through time . . . what a wonderful idea! Why didn't I think of that?
Seriously, the limiting factor with time travel stories isn't logic and it isn't physics. The problem is good, old fashioned story-telling.
A reader must experience the plot of a story in a straight line. The events need not be written in chronological order, but they must happen in [u]some[/u] order, and that order must make the story as exciting as possible. For a plot to be exciting:
1) Characters must make choices that effect the story's outcome. 2) The realationships between choices and consequences (cause and effect) must be clear.
Time travel stories stumble on these two points. They often violate a reader's instincts for cause-and-effect and the illusion that fictional characters have free will.
Think of the Terminator or Planet of the Apes stories. They all break down to predestiny, no matter what the characters do the future is already written.
Or look at the Back to the Future stories, where time can branch off into infinite variations depending on the choices made by the characters. But if the world where Biff is a tycoon is just as real as the world where he isn't, then what's the point of trying to change anything?
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Doc, I don't think that choice and causality are as problemmatic to time-travel storytelling as you indicate.
For example, in The Terminator, we have a causality loop: If John Connor didn't exist, the machines would not have sent back a terminator to kill his mother. But if they hadn't sent back a terminator, the man who became his father wouldn't have been sent back to save her, and John Connor would never have been born.
The way that the movie concludes, it appears that things are going to proceed as they had before, and so it seems that the future is already written. (The sequels show that it is not, but let's just consider the first movie.)
Does that mean during the events of the movie the characters had no choice about their actions? That's the level at which we care about free choice in the story, not at the level of whether their actions make a difference in the eternal scheme of things.
What would have happened if Sarah Connor had said, "The future is ordained because my son is a leader in the future, and since I haven't had him yet, obviously I cannot be killed. Therefore, I'm just going to stand here and let that terminator try to kill me, because it's impossible for it to do so without causing a paradox."
The terminator would have killed her, then holed up somewhere until the machines took over. Then it would have communicated its knowledge to the other machines, they would have built a time machine, and sent a terminator back to kill Sarah Connor. They would have succeeded in eliminating John Connor from the timeline.
The future is determined by the character's actions. They cannot count on destiny to take care of everything; they must act as best they know how.
And even knowing what the future holds, they still have the choice of how to face it.
* * *
I hate to question someone going by the name of Doc Brown about time travel in Back to the Future, but my take on it was that time was fluid and history could be changed, not that there were infinite branches that were all real. Thus, the world where Biff was a tycoon was only real until history was changed again to prevent it.
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In BTTF, the funny thing with history being changed is that it's the future for Marty and Doc as they are existing at a point in the past previous to Biff's becoming a tycoon, so in essence, history is never changed, only the future from the point at which the change is made.. Are you with me?
Posts: 20 | Registered: Jan 2004
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quote:The fact we haven't figured it out does not mean it isn't possible. I do agree it would be a mess, but it does give a writer a wide range of possibilies to use in their stories.
I don't think time travel is possible. It can't be. Why? Because it hasn't been invented yet. People are greedy, and if time travel were ever invented, it would be worth beaucoup bucks. And somebody would steal the idea and invent it before the original inventor. This cycle would most likely repeat and would wind up in our current time eventually. Just my two cents on the thought.
I'm currently experimenting with time travel of a sort in one of my stories, though I'm still working out how exactly it will work. The character first discovers he can bend time, i.e. speed it up and slow it down. But I want him to be able to go back and forth through it, even if only like watching a movie in fast forward and rewind. I've also thought about letting him see his ancestor's lives in this way.
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If you want time 'travel' that works more like the Tempoview things in Pastwatch, I can see absolutely no physical or theoretical barrier at all (though the physics would be different from the machines in Pastwatch, which after all permitted travel-back-and-change-the-past-so that-the-present-never-existed time travel). A time machine that could extract all the historic information embedded in, say...a pebble, by detecting the various quantum level events that had affected that pebble over the course of its existence, could provide you with all the history that pebble had ever 'seen' or 'heard'.
As I said, current theory suggests (but does not prove) that any time travel back in time would result in a closed loop...which is to say, mathmatically, the solution would be self consistent. If you tried to kill yourself in the past (or some other person that did not, in your past, die), then 'events' would conspire to prevent the alteration from succeeding. Given that one of the most plausible events to prevent your success (and one you couldn't really do much about) is the sudden collapse of the wormhole you use to travel back in time due to a quantum fluctuation...I think that there would be no way to actually change the past if the universe wanted to stop you.
I have to agree with TheoPhileo's clever argument about time travel being impossible...though logically this argument can only apply to time travel in which the past is changed. And of course there is also the caveat that time travel may only be physically possible once someone 'invents' it for the first time. I put that in quotes because a working theory for time travel has already been invented, the limitation is that we haven't figured out how to capture both ends of a wormhole, accelerate one to a relativistic velocity for long enough to make it 'younger' than the other end, and then send something through the younger end so it comes out the other end when it was young...in the past.
As someone has already mentioned (or should have mentioned...I'm too lazy to check ), it wouldn't be possible to travel back in time to before this was first accomplished...thus TheoPhileo's argument would be null. But then again, it is for just this type of time travel that the theory indicates a mathmatically consistent solution will always exist...meaning that it wouldn't necessarily make actually changing the past possible.
If there were alternate universes, then you could travel to what would roughly correspond to your past in an alternate universe, change that past, and live in the future created in that alternate universe. But doing this would in no way affect the present of the universe you left.
posted
Of course, time-travel is a concept that is almost laughably ridiculous. No matter how it's disguised, whether a magical machine, a necklace, or a delorean, the concept in its purest form is absolutely implausible.
However when disguised well-enough to dismiss the reality conflicts that initially run through a reader's mind, then it is a device that can make for an exciting adventure.
I'll read a time-travel sci-fi, if its good, just as soon as I'd read a more typical sci-fi about man travelling hundreds of light-years in mere months and battling aliens in space...which in its purest form is just as ridiculous, but curiously less criticized.
[This message has been edited by Alias (edited February 19, 2004).]
posted
Of course time travel is possible. In fact, it is inevitable. See, that is why the dinosaurs died out. They were hunted to extinction by time traveling adventurers from our future who will have no opportunities for real excitement and danger in their own time. Unfortunately, time travel, as it will be developed, also causes pollution: everytime someone travels into the past, a large load of irridium is deposited at the arrival point, as a fine aerosol that gets defused through the atmosphere, and eventually deposited on the ground. The time travelers will, of course, be unconcerned about this pollution, since the phenomenon of the KT boundary will already seem to be part of the natural environment by the time they start making their trips. Posts: 550 | Registered: Sep 2003
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posted
I would say that time travel is improbable. To successfully travel in time would require motion that is faster than the speed of light. Seeing as this has never been observed, I am inclined to say that it is improbable. If it is indeed possible, then people would be able to exert an incredible force: the force required to accelerate a mass to over 299792459 m/s, or 186282 miles per second approaches infinity. Even supposing that it could be done, there would be the issue of paradoxes. glogpro's theory easily illustrates this. If adventurers killed the dinosaurs, and we know this, what if we killed those adventurers before they have a chance to do this? Or supposing that iridium is indeed deposited each time time travellers time travel (oof da...) then there is already that iridium in the world. What if this person does not move back in time? Where does this excess iridium come from? It brings up the issue of predestination as well, which I am inclined to disbelieve. How can predestination be truly enforced so as to prevent ripping of the time-space continuum? Perhaps my views are way off the mark, but... there you go.
Posts: 101 | Registered: Dec 2002
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posted
Well, there seems to be a common misperception that time travel would necessarily allow changing the past. Mathmatically, this makes no sense.
Faster than light travel does seem to be possible, though not by accelerating things conventionally up past light speed. That also makes no sense mathmatically.
Fighting aliens once you get there doesn't seem impluasible at all. There is lots of extra-terrestrial life, humans like to fight, one and one make two. That seems to make a lot of sense, mathmatically speaking
Of course, most SF shows humans as being the good guys, which I'm not sure I buy....
posted
Of course humans are the good guys, we're humans. You always root for your team to win. That doesn't mean that humans are necesarrily doing what's right when they go to war with the aliens, but we're still going to root for the humans. A lot of Americans thought it was wrong for us to go to war with Iraq, but how many Americans were actually rooting for Iraq to win? I don't know any. Even an American who believed that we were doing the wrong thing in conquering Hussein's regime still rooted for us to win the war, simply because it's us. People would rather see their own country (race, planet, galactic federation, whatever) win an unjust war than lose one.
Posts: 1528 | Registered: Dec 2003
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posted
wetwilly, I agree that "good gouy" depends upon POV. To us humans may be the good-guy, however I believe Survivor was referring to "good-guy" in a moral sense. And if it is indeed our belligerent tendencies and greed that spawn the war, we would not be the "good guys," if you follow.
Survivor,
quote:Fighting aliens once you get there doesn't seem impluasible at all. There is lots of extra-terrestrial life, humans like to fight, one and one make two. That seems to make a lot of sense, mathmatically speaking
I agree that there is extra terrestrial life, but you can't say there are lots of it. I believe that in a universe as great as our own it is likely, but there is no hard physical evidence to really say anything like that.
Also my implausible I meant the actual distance/time in that vast distances "hundreds of light years" could never be travelled by a person in mere months. Not even light can do it, humans certainly can't. First there's the argument that says faster than light is impossible, second there the body sustaining "g" forces argunment, but the trump card is that anything going the speed of light become energy.
Don't believe that theory, that's too bad, because I do.
posted
Well, what you describe does make about as much sense as running backwards to travel back in time...so if that were the suggested method of FTL travel, I would vote nay.
But of course, just as very few of us have read many time travel stories that involved running backwards as the travel mechanism, so too I have read very few stories where it is suggested that the mechanism for traveling faster than light would involve anything like conventional acceleration.
After all, airplanes don't fly by negating the Earth's gravitational field, a steam engine doesn't work by burning water, and fleas don't jump by farting.
posted
A few questions for people, and interesting thoughts.
First, why should time travel require accelerating beyond the speed of light? I don't understand this concept. I _know_ that it can be proven with General Relativity that faster than light travel allows _communication_ back in time (the EPR paradox, I believe it's called, although I'm not entirely certain). But I don't think it says anything at all about time _travel_.
Secondly, what do people make of Alcubierre's ideas about FTL travel, which are generally speaking consistent with relativity, but just require us to do other things that we have no idea how to do (or even whether they are possible or not). Is this a possibility for the future, or is it as unlikely as it seems?
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Time slows down as you approach the speed of light. This is true. We have actually observed this phenomenon with some of our faster jets that have broken the time barrier. I admit that I know little about physics, but the idea that we can *definitely* go back in time if we break the speed of light is bogus. The truth is, the equations used to determine the first principle I mentioned, that you slow down as you approach the speed of light, are *undefined* once you reach the speed of light. It is a possibility that you could go backward in time, it could also be that you go forward, or something else entirely, but the equation itself (don't ask me what the equation is, I don't know) is undefined.
Posts: 3567 | Registered: May 2003
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posted
The idea that time travel to the past requires going faster than the speed of light is the result of a logical fallacy.
At least under some circumstances within the framework of relativity, traveling faster that the speed of light would cause something to move backward in time.
That does not mean traveling faster than the speed of light is the only method of time travel.
Perhaps now is the time to invoke the other Clarke's Law: "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."
My (limited) understanding of Alcubierre's FTL drive is that it requires forms of matter/energy that are currently entirely theoretical, and that may not even exist in our universe.
That doesn't mean it might not be possible to create them. After all, the Bose-Einstein Condensate is a form of matter which cannot occur naturally, and so it was entirely theoretical and did not exist in our universe until we humans made it (unless some alien race did it first, of course.)
posted
The problem with going faster than light to go back in time is that you wouldn't go back in time as we understand it...rather, in your frame of reference, time would be going backwards compared to the rest of the universe.
So, you put a guy on a spaceship, take him up to the speed of light. At the speed of light, he is frozen in time. If you somehow managed to get him going faster than light (which is impossible but oh well) then he would start getting younger, walking around backwards, light would be emitted from his eyes and illuminate surfaces in the ship and then go into the light fixtures...all that crazy stuff. Of course, that's what it looks like to us outside (assuming we can see into his spaceship, which would be difficult but not impossible).
The net result is not for him to go back in time...he still thinks he's been transported forwards in time, with the added effect that the time he spent on board the spaceship has been 'undone' because the physics was all working backwards, so maybe he doesn't even remember getting on a spaceship and accelerating up to the speed of light. What happens is that we've all gone back in time relative to him, so we could probably change any of his 'future' we saw played out on the spaceship (like if we saw him sucking a bunch of barf out of the head and then getting sick and then feeling okay and then spitting out a piece of raw meat--when he got off the ship we would know that he was likely to eat some raw meat in the future and warn him that this would be a bad idea).
But of course, we can do this because the physical reversal of all physical processes in the FOR of the spaceship means that those events have literally unhappened...it wasn't time itself that was in reverse on board the spaceship, but only the rest of physics
By the way, you don't need a really fast jet to observe the time dilation effect, any passenger jet or even tramp steamer will do as long as you use accurate enough clocks. What matters is how far you travel, not how fast.
Time travel to the past doesn't require going faster than the speed of light, rather, if you can go back in time, you have the ability to perform faster than light travel. You simply travel back in time to give yourself plenty of time for the journey, then you make the journey in conventional space. Hey presto, you arrive at your destination exactly when (or a little before) you left your point of origin.
I'm going to guess that it is possible that somewhere in the universe a Bose-Einstein condensate could have formed naturally, we just have no idea where or when and it doesn't matter anyway. Just like sometimes a coin will land heads up a hundred times in a row just by chance.
posted
To add to who handles time travel well, I think Michael Crichton did a good job with it in "Timeline". The movie sucked to no end, but the book was fast-paced and fun, with nice little quips about time travel and answers to most of the questions that arise with time travel (paradox, changing the future, etc.) I liked his idea that the future is what it is, as is the present, and no amount of tinkering in the past will have any meaningful impact on the "present" or "future".
I also absolutely loved the time paradox episodes of star trek TNG, just as pretty fun examples of "what if" writing.
To me, that is what makes a story that involves obvious guesses as to possibility fun...the "what if" factor. Does the author present a great reason to be exploring time or FTL travel? If not, then it tends to break down and have a negative impact overall, for me at least.
quote:First, why should time travel require accelerating beyond the speed of light? I don't understand this concept. I _know_ that it can be proven with General Relativity that faster than light travel allows _communication_ back in time (the EPR paradox, I believe it's called, although I'm not entirely certain). But I don't think it says anything at all about time _travel_.
What do you mean "proven," (?) Nothing can be proven by theory.
quote:Time slows down as you approach the speed of light. This is true. We have actually observed this phenomenon with some of our faster jets that have broken the time barrier.
Lol, I don't believe we have any jets that can breach the time barrier.
quote:To add to who handles time travel well, I think Michael Crichton did a good job with it in "Timeline". The movie sucked to no end, but the book was fast-paced and fun, with nice little quips about time travel and answers to most of the questions that arise with time travel (paradox, changing the future, etc.) I liked his idea that the future is what it is, as is the present, and no amount of tinkering in the past will have any meaningful impact on the "present" or "future".
Timeline was astonishingly awful..... But just my opinion
Posts: 295 | Registered: May 2003
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posted
And I'm telling you it doesn't matter. You could walk and as long as you were willing to walk thousands of miles carrying a high precision atomic clock, you could measure the time dilation effect.
Posts: 8322 | Registered: Aug 1999
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posted
Really? If that's true, the rotation of the earth would cause a time dilation effect. Has anyone placed an atomic clock at the equator and one near the poles to test that?
Everything in the universe is in motion all the time. With all the whizzing, whirring, expanding, contracting, spinning, and rotating going on, time must be very hard to measure. In fact, time must become meaningless once we reach a large enough scale.
At least that's what I'm going to say the next time I get to work a few minutes late.
posted
As it just so happens, the Earth's rotation does cause a detectable (though not particularly noticable) dilation effect. In fact, since the speed of sound is only about 760 mph and the surface of the Earth is going about a thousand mph near the equator, breaking the sound barrier is hardly even significant in terms of the absolute velocity we're all experiencing as a matter of routine. Of course, the whole Earth is going around the Sun at something over 30,000 mph, and I don't even want to know how fast the Sun is going around the center of the Milky Way.
For cosmological reasons having something to do with relativity and the way the universe expands, we consider the Milky Way to be stationary...just the same way that observers in other galaxies think that they are stationary and we are the ones moving away at a crazy speed.
So yes, human time is essentially pretty arbitrary...much like your state of 'employment', which is why your boss can fire you for something that has no cosmic meaning.
posted
All I was pointing out, Survivor, was that we actually have clocks sensitive enough to measure the time dilation at the speed of sound and have done so. While it is true that there woul be some time dilation simply by walking, we have not been ableo to measure this effect because it is so small.
Posts: 3567 | Registered: May 2003
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It is not how fast you go that matters. It is how far.
I know that a lot of people will tell you differently, but the majority of people still believe that cavemen and dinosaurs coexisted. Majority opinion has no bearing on matters of scientific fact.
As I said, if I'm willing to walk thousands of miles (or wait for someone else to do so) carrying a high precision atomic clock--of a type that is available today--then that clock can be used to measure the dilation effect of that walk.
The effect isn't any smaller or less measurable just because we're not moving as fast. In fact, because of the distances involved, it is impractical to use supersonic jets to demonstrate the effect. Passenger jets work just fine (you may have to buy an extra ticket for the clock, though).
posted
OK, oh physics expert, enlighten us. Give me an equation (or series of equations) that demonstrates this effect. Show it to me in a mathematical proof.
Posts: 3567 | Registered: May 2003
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posted
Survivor is right that someone walking carrying an atomic clock would eventually produce a measurable time dilation. He's incorrect in saying that "[t]he effect isn't any smaller or less measurable just because we're not moving as fast."
Here is the formula for determining time dilation:
t' = t/(1-(v^2/c^2))^0.5
t' = time in the moving system t = time for the stationary observer v = velocity of the moving system c = the velocity of light
As you can see, the smaller the velocity of the moving system, the smaller the time dilation effect.
However, the more time that elapses, the greater the difference between t' and t, and if enough time passes, the dilation effect will be great enough to be measured by comparing the moving and stationary atomic clocks.
posted
I've also seen studies that show gravity affects time as well. This is why scifi stories (i.e. Sphere) often connect black holes with time travel.
Posts: 292 | Registered: Feb 2004
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posted
Yes, I've read, in fact, that in black holes time doesn't work at all. That in the singularity time freezes. Any word on that?
Posts: 697 | Registered: Mar 2003
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posted
Thank you, Eric. I suspected what you said, but I did not have the numbers to back me up. That helps a lot. Posts: 3567 | Registered: May 2003
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Okay, a couple of points (why do things always have to get complicated?).
First off, as I pointed out above, we are all in moving FORs already. Any motion we add to the FOR is a small percentage of the total velocity of the FOR.
Now look at the equation provided. Notice that the placement of the term v doesn't produce a geometric effect except at extreme values...in the range where the difference between walking about on the face of the Earth and flying about in a jet plane on the face of the Earth can be measured, the resulting curve is essentially linear, and that linear curve intersects the point where we would find 'standing at rest on the surface of the Earth'.
Now consider the fact that if you go at a slower velocity, you will have to move for a longer time...wait for it...and that means that you can get the overall time displacement (the intensity of the time dilation multiplied by it's duration) by simply finding out how far you went.
Eric, don't tell Christine that the math means what she's saying, because it doesn't mean that. It means what I'm saying (which is, of course, why I say it).
The black hole freezing time thing is because when you approach the event horizon of a black hole space/time around the black hole is...is there a good layman's term for explaining this?
Look, as far as you can tell, you just get ripped to shreds in the blink of an eye. But to an outside observer, you would seem to spend a lot of time getting ripped to shreds and then an infinite amount of time crossing the event horizon (in little pieces). That's because the space/time is being stretched out near the black hole...what normal geometry would tell you is only a few light seconds becomes a light-year, then two, then when you get to the event horizon it essentially takes an infinite amount of time for light to travel out of the black hole (which is why they call them 'black' 'holes', because the higher dimensional geometry resembles a bottomless pit so deep that light can't ever get out--I'm sure you've all seen the cheesy 2D representation of what a black hole looks like, right?).
To put it another way, you don't ever actually hit the bottom, you just get accelerated to the speed of light shooting down a bottomless pit, so yeah, you kinda are frozen in time...but really....
Well, normal black holes tear you to shreds before you hit the event horizon and get frozen in time. But apparently large and internally complex black holes can have surfaces where a physical object could theoretically penetrate the event horizon before being destroyed. So in the former case, you just get killed and then your constituent particles get sucked into the black hole, but in the latter case, you just get sucked in and frozen forever in time...unless you happen to have an FTL drive, in which case you can get back out.
I actually use this as the basis of my interstellar travel...you use a relatively slow form of FTL (which requires being shrunk down inside a tiny particle) to jump in and out of normal sized singularities that are connected by wormholes (the ends of wormholes are subject to stuff like gravity). Because you are tiny, the black hole is huge and you can exploit irregularities in its geometry.
What was the original question? I'm pretty sure I answered it by now, at any rate.
posted
Survivor, I said you were right that walking with it would eventually produce measurable time dilation. And nowhere did I tell Christine that the math meant what she was saying.
However, since the difference in velocity between a supersonic jet and a walking person is far greater than the difference in velocity between a walking person and a stationary one, the difference in time dilation between the jet the stationary person would be measurably larger than the time dilation between the walker and the stationary person. Which means you were incorrect in saying that the effect isn't any smaller.
Just admit you were wrong to say that, rather than try to justify it with a correct but completely irrelevant explanation regarding geometric and linear curves.
[This message has been edited by EricJamesStone (edited February 27, 2004).]
posted
OK, both of you! What did you think I was saying? First of all, I do not need anyone to interpret the equation for me. I resent the implication that you think I do. Alos, I NEVER said that there would be no time dilation if you were moving really really slowly. Show me where I said that, because I looked and I never did.
All I said, essentially, is that it is that the time dilation effect has only been measured at top speeds (That I know of....if you know of such an experiment with such an accurate clock please let me know, I'd love to read about it.) So YES, you COULD walk and see a time dilation effect, but as far as I know it's never been done!!
Now that I've gotten that out of my system, let me plug some numbers into that equation for our dear Survivor to show him where he is wrong that the effect is not smaller. And by time dilation effect what I mean, just so we're not arguing about definitions later, is a measurable difference between elapsed time for the stationary observer versus the traveller.
First of all....let's repritnt the equation:
t' = t/(1-(v^2/c^2))^0.5
t' = time in the moving system t = time for the stationary observer v = velocity of the moving system c = the velocity of light
Second, let's pick two different speeds...the speed of a jet breaking the sound barrier (let's assume the temperature is 0 degrees celcius to make the math a little easier)
v of sound in air = 331.4 + 0.6T m/s or 331.4 m/s
and the speed of me walking. I can walk liesurely at about 4 miles per hour, in meters per second that is 6437.376 meter/hour or 1.788 m/s
Now, let's assume we travel, in both cases, 1,000,000 meters. To an observer, walking this will take 559234.07 seconds (155+ hours). Flying this will take 3017.5 seconds (little less than an hour)
At this point I have to confess that my calculator cannot work these equations. The denominator of the equations keeps being reduced to 1. (I'm really frustrated, I wanted to work out the numbers.) However, if you run the numbers yourself, you will see that for the speed of walking we end up with a denominator that is much, much closer to 1 than with the speed of sound. This means that the the time elapsed for the observer, t, will be modified more significantly at the speed of sound.
And here is where I think dear Survivor has gone wrong. The time dilation effect is essentially a ratio. time in the system/time observed. The fact that you get a greater number because you have spent more time moving is meaningless without comparing it in this manner.
So to make sure there are no confusions, let me sum up. There is a time dilation effect at any velocity, however; the effect is much greater at higher velocities. Furthermore, I said this all along. It actually was never my main point, whichi is perhaps why you were all so confused. I skirted around the issue because I didn't care. I trust that now the confusion has all been cleared up.
quote:It is not how fast you go that matters. It is how far.
I trust that I have proven this point to be incorrect.
Actually, I feel the need to restate what I said that first got survivor on my back. I said...
quote:Time slows down as you approach the speed of light.
This is true. The time ilation effect increases with increased velocity toward the speed of light. I also said...
quote: The truth is, the equations used to determine the first principle I mentioned, that you slow down as you approach the speed of light, are *undefined* once you reach the speed of light.
This is also true. If you are going exactly the speed of light the denmoinator will be 0.
[This message has been edited by Christine (edited February 27, 2004).]
[This message has been edited by Christine (edited February 27, 2004).]
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), it wouldn't be possible to travel back in time to before this was first accomplished...thus TheoPhileo's argument would be null. But then again, it is for just this type of time travel that the theory indicates a mathmatically consistent solution will always exist...meaning that it wouldn't necessarily make actually changing the past possible.
