A question of time travel and paradox.?

Question

If your dog dies and in the future you make a time machine to go back in time to save him, will it work? Of course not, if you in fact made a time machine to save your dog, and were successfull in your attempt then why would your past self need to make a time machine to go back in the first place? Does anyone know of any good books that talk about the theories of paradox? I love the concepts of time travel and paradox together and am looking for a good read.

Answer 1

One theory about this paradox is that by changing the past, you are propelled into a parallel universe with an alternative history. The old universe that you came from will still exist somewhere, but you won't be in it any longer.

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...There is a paradox that occurs if we allow time travel into the past: to put it bluntly, could you go back into the past and prevent your parents from marrying, say by killing them? There is another paradox, called the "free lunch" paradox, that occurs: if you go back to Bach's century and tell him how great he is in our century and show him all the great compositions he is famous for, and Bach then reproduces these compositions note for note, then Bach's music exists without any "artistic" effort being put in to them (a "free lunch", so to speak).

Why should these paradoxes rule out travel into the past? According to the authors of the article, they don't violate any physical or philosophical principles. To explain this further, let's think about the role that time plays. Space-time is a four-dimensional construct. A four-dimensional "worm", whose ends represent the events of your birth and death, is what your life forms in space-time. An object, seen any instant, is a three-dimensional cross section of this worm. The line along which the object lies (ignoring its thickness) is that object's worldline. At any point, the angle your worldline makes with the time axis is a measure of your speed.

Relativity requires that worldlines be timelike. Massive objects distort space-time and bend worldlines. Suppose space-time becomes so distorted so that some worldlines form closed loops. Such worldlines would be timelike all around. Locally, they would have all the properties of space and time, but yet they would be corridors of the past. Such a construct is called a closed timelike curve (CTC). By following a CTC, we could meet ourselves in the past, or if the loop were large enough, visit our ancestors.

CTCs can be created by distorting space time. But unlike a time machine, a CTC gets used up if repeatedly traversed since only a finite number of worldlines can fit into it. Thus if one travels on it to a particular event, one will meet everyone who has ever traveled, or will travel, to that event. We do not know the if the universe contains any CTCs, though there have been several calculations, including one by the German mathematician Kurt Gödel, that predict CTCs.

Let's now go back to the parent paradox and see what principles of physics and philosophy it violates. Classical physics says that if you go back into the past, you must do exactly what history records you doing (i.e., you can't kill your parents or cause their marriage to break up if history didn't record such a thing). The philosophical objection to this, of course, is that it is a restriction of free will. But classical physics says that what you do right now is an inevitable consequence of what happened before you were even born! So this paradox poses no threat to free will than does classical physics itself.

The real problem with this paradox is that it violates the principle of autonomy which says that you can have any configuration of matter that laws of physics permit locally, without worrying about what it is like in the rest of the universe. Without CTCs, both classical and quantum physics follow this principle (though one could argue this isn't really true given the results involving Bell's Interconnectedness Theorem). However, the consistency principle says that the only configurations of matter that can exist are those that are self-consistent globally. In the presence of CTC, classical physics puts the two principles in conflict. But classical physics also says that there is only one history and whatever you do, consistency requires you to act your part out in the way it is dictated. So, if you goto the past, something will happen such that instead of killing your parents and altering the past, you become part of it (perhaps your attempt to kill them allows for them to first meet). Classical physics says something like this must happen, and that consistency requires the autonomy principle to fail. However, this is all moot because classical physics is by no means accurate, even though it is sometimes an excellent approximation to reality. But with CTCs, it is very false.

Stephen Hawking argues that quantum mechanical effects would either prevent CTCs from forming or destroy any would-be time traveler who approached one. This, the authors of the article claim, simply exposes a limitation of current technology and these effects, far from preventing time travel, will facilitate it.

Quantum mechanics deviates from classical physics in that instead of predicting with certainty the outcome of an observation, it predicts all possible outcomes and the probability of each. This, the authors claim, explains CTCs in a consistent way. Everett's many universes interpretation of this "randomness", which is very controversial though it prevails in some areas of study, says that if an event can physically happen with a certain probability, then it does---in some universe. Physical reality consists of a collection of universes, a multiverse, so to speak, that contains its own copy of the observation and its outcome. According to Everett, quantum theory predicts the subject probability of the outcome of the observation by prescribing the proportions of universes in which that outcome occurs....

Answer 2

u sound like a beginner according the silly question put up there about why ur past self.....?

best way is do the research on the internet....an xtemely interesting book is Hyperspace by micho kaku. You can read any of is book b/c there are all on tht topic....and u can also read time travel in einsteins universe, this ones around the same topic with black holes etc.

If you like 2 know from begingin from the time of coupernicus to the einsteins theory then read "on the shoulders of giants"
its a mighty big book....and u can also read any book by stephen hawking.

im only 15 and i started research last year in 10th grade i no a lot about this things in 1 year.....but to understand this things thourghly you also have to be good at math, b/c u need to understand the equation in order to understand wats goin on n wat actually means or sometimes ppl get the wrong meaning.......i no enough tht i propose my own theoies now but only to myself

i had a interest in math at first only b4 and a sudden interest for some reason......so i was taking alg1 in 9th grade and dint knew alg1 either but then sudden interest and by the end of the year i knew up2 calculus easily......then i wondered about einsteins work and now i do quantum physics as well.


i though i was the youngest person to learn calculus at age of 13 but then i found at like year later tht einstein started at 12....lol

Answer 3

Unless it simply creates an alternate time stream, in which case the time stream where you went back in time never happens. However, since it happened in an alternate time stream, it still had an effect in your life.

A good movie is "De JaVue"

Answer 4

If time travel exists then the traveler will be an observer, not a participant.