"The future ain't what it used to be."




I have a question I've been dealing with. People always talk about paradoxes when traveling to the past. But doesn't traveling to the future also create paradoxes? Because, if you can travel to the future, the future has already happened, otherwise you wouldn't be able to travel to it, you can't travel to something that doesn't exist (yet). So then the future has already happened, just like the past. Take for example that I travel to the year 3000 and change the cause of events, then that would affect all the time that is coming after that. And in fact, then I would have changed the past of the years that come after the year 3000. What do you all think of this? Or is my way of looking at this wrong? If it is right then we must say that nature allows paradoxes, if the relativity theory of Einstein is right. (according to this theory you can travel to the future because when you travel at a very high speed, for example half the speed of light, than your time goes much slower than people who stay on earth, so when you come back on earth, many years would have passed on earth and you would have traveled to the future).
If your doing what your saying your doing in this post, then all you've succeeded in doing, is creating a sideline alternate reality of the future you have visited.
I Agree with you both.
All you have to do is follow the posts past present to see how we all here change the future just by talking about it.
Best Regards
The fact that time can pass at different speeds is prof that the future exists and is therefore unchangable. This only creates a paradox if you know the future, which proves that it is impossible to see into the future.
If the past has already happened and the future has already happened, than the present has already happened. Everything we do affects some one or something else, in that case everything is a paradox if you want to think of it that way. But everything is not a paradox. A paradox only occurs when two undisputable fact contradict each other. Lets say on December 13th 1995 you look at the sky at 12:00 am the blues make you want to time travel, then you get to the past change the sky to red, you see it again at 12:00 am and are not inspired to time travel. That is a paradox. Choosing to eat tuna salad for lunch therefore influencing your brother to have tuna salad for lunch, thereby changing his future, is not a paradox. This can be seen through to a logical conclusion and at no point contradicts itself.

Robert Heinlein's 1941 story "By His Bootstraps" begins with the narrator writing in a philosophy thesis that time travel is impossible because time, in Immanuel Kant's terms, is only empirically real and does not exist independently among things in themselves. The narrator is then suddenly surprised to find two different versions of himself arriving from the future, with conflicting warnings and promises about what he can do. Traveling to the future, he meets an older man who repeats the promises, but whom he ends up distrusting. After some confusion, back in the present, he obtains some supplies and returns to the future to a period significantly earlier than when he would met the older man, intending to contest the future with him. Eventually, however, it turns out that he himself is the older man and his future is in fact, pace Immanuel Kant, secured.

A paradox of time travel arises in relation to this story. The narrator does indeed set himself up "by his bootstraps" -- his present and future selves all interact with each other to produce the events. The paradoxical nature of this comes down to the case of a notebook that was provided to the narrator by the older man in the future. It contained a vocabulary of the language that was spoken by people in the future. The narrator learns the language and, as the book wears out over the years, copies it over into a notebook he had fetched from the present. This notebook, as it happens, is the very one he, as the older man, then provides to his other self. He is therefore the same person who both learns the knowledge from the notebook and put the knowledge into the notebook in the first place. The vocabulary as a certain list of items arranged in a certain way was thus complied by no one whatsoever. The knowledge exists in a closed temporal loop and is in an important sense uncaused or uncreated. The narrator himself notes that there is something peculiar about this.

Peculiar indeed. A very similar paradox, allowed by the possibility of the same kind of temporal loop, can become a reductio ad absurdum for time travel. We see just such a paradox in the 1980 movie Somewhere in Time, staring Christopher Reeve and Jane Seymour. As a young man, Reeve encounters an old woman who gives him a watch. Later he becomes obsessed with the painting of a woman in an old 19th century hotel (actually filmed on the beautiful Mackinac Island, Michigan). He decides that he must meet that woman, and he thinks it is possible because of the theory of a professor he had for physics. The professor thinks that it is possible to will one's self back in time, as long as what one carries along is not anachronistic for that time.

Reeve outfits himself for the 19th century and actually succeeds in willing himself back into it. He meets the woman in the picture, played by Jane Seymour, and he is able to win her heart, so that she returns the love he felt ever since seeing her painting. He gives her the watch that he had acquired many years before from the old woman. Then, as their mutual happiness seems assured, Reeve discovers a penny from the 20th century in his suit, and the anachronism vaults him back into the present. He is unable to endure separation from his beloved, starves himself to death in his hotel room, and, apparently, is reunited with her in the Hereafter.

The old woman who gave him the watch in his youth was, of course, Jane Seymour's character, lived to a ripe old age just to see him again. The watch, therefore, was obtained by Reeve from Seymour and was obtained by Seymour from Reeve. In a closed temporal loop, like the knowledge in the notebook in Heinlein's story, the watch is uncreated. But this is impossible. The watch is an impossible object. It violates the Second Law of Thermodynamics, the Law of Entropy. If time travel makes that watch possible, then time travel itself is impossible.

The watch, indeed, must be absolutely identical to itself in the 19th and 20th centuries, since Reeve carries it with him from the future instantaneously into the past and bestows it on Seymour. The watch, however, cannot be identical to itself, since all the years in which it is in the possession of Seymour and then Reeve it will wear in the normal manner. It's entropy will increase. The watch carried back by Reeve will be more worn that the watch that would have been acquired by Seymour.

The reductio ad absurdum created by the watch can be fixed up in a couple of ways. First, we might think that entropy could be reversed by time travel, so that forms of matter would be restored to that state they would have been at the earlier period. But this will not do, since Reeve himself would then be restored to the state his matter was in in the 19th century, which, whatever it was, would not be in the form of Christopher Reeve.

Second, we might think that time travel puts one in an alternative universe. In some universe, the watch is manufactured and bought in the ordinary way, and then the older Jane Seymour, for whatever reason, gives it to the young Christopher Reeve. He goes back in time, to an alternative universe where Seymour did not acquire a manufactured watch, and gives her his. Then she gives it to him later; and he returns to a different universe, where Seymour does not buy a watch but acquires a somewhat more worn watch from him. The temporal loop thus generates a spiral of alternative universes. Unfortunately, it would require a spiral of an infinite number of alternative universes, as each watch in a particular universe is returned to a new universe where it can exist in its increasingly worn state. In some universe, the watch would disintegrate while in Seymour's or Reeve's keeping and need to be discarded; but Reeve would keep returning to the past, unless the watch turned out to be some causal factor in his falling in love with the picture..

Every instance of time travel generating an infinite number of alternative universes might be thought to violate Ockham's Razor, especially since the idea that an alternative universe could be generated in the first place has disturbing consequences for the metaphysics of identity. What does it mean if there are an infinite number of each of the characters, all facing a universe slightly different? Simplicity and common sense rebel against such principles -- although serious versions of such metaphysics have been produced to deal with quantum mechanics, and multiple real universes were proposed by the philosopher David Lewis to explain possibility and necessity (after Saul Kripke used Leibniz's idea of "possible universes" to produce a quantified version of modal logic) [note]. But without them, time travel, that would allow for the sort of temporal loop in which the paradoxical and impossible watch of Somewhere in Time becomes possible, is itself impossible.

Kant's theory of time may go unrefuted after all.
John, the past has already happened but the future has not. The future is already decided however. We only have the illusion of free will. Choices we make do not create universes.

Secondly, time travel to the past is always paradoxel. For example if I trip over a pebble, it wouldn’t stop me from traveling back in time but it would effect the way I travel. I might make a different decision, I might be in a different mood, or walk with a limp. The point is that little things can create paradoxes, in fact they must. Any change to the past, changes the future thus changing the way we change the past and so on.

I take it your not a big believer in the chaos theory? The fact is that everything effects everything else. The placement of a single grain of sand in China(due to it's gravity) effects everything we do even if the effect in immeasurable.

So how do we know that paradoxes are not possible? They create a never ending loop. If the universe were a computer program, a paradox would crash it. The loop prevents time from going forward much like it would trap a computer into running the same lines of code over and over.

Feel safe in the knowledge that time travel to the past is not possible because it would destroy the universe or stop the passage of time!

PS. Makes for great stories though...
Amazing how someone can state with such fact and conviction that "time travel to the past is not possible". This from the same person that quotes the chaos theory?

Definition: "What exactly is chaos? Put simply, it is the idea that it is possible to get completely random results from normal equations."

So how does someone talking about a time travel theory get to "know" exactly what would happen? And to make statements like "The future is already decided however. We only have the illusion of free will."

How about this, known as the butterfly effect. The amount of difference in the starting points of the two curves is so small that it is comparable to a butterfly flapping its wings.

"The flapping of a single butterfly's wing today produces a tiny change in the state of the atmosphere. Over a period of time, what the atmosphere actually does diverges from what it would have done. So, in a month's time, a tornado that would have devastated the Indonesian coast doesn't happen. Or maybe one that wasn't going to happen, does. (Ian Stewart, Does God Play Dice? The Mathematics of Chaos, pg. 141)"

Just a small change in the initial conditions can drastically change the long-term behavior of a system. Such a small amount of difference in a measurement might be considered experimental noise, background noise, or an inaccuracy of the equipment.
Global_1, it is strange that you can demonstrate an understanding of chaos without seeing how it removes any possibility of time travel to the past? Here's how chaos applies to time, and thus time travel:

The impact of any change is multiplied by the time since the change occured.

For example, I build a time machine and go back in time about a million years, during my one second stay, I accidentally move a single grain of sand out of place. To tiny insects walking along the sand, each grain is a boulder they must climb over. The path these insects decide to take is altered slightly because of the change I made.

Over time slight changes can become Earth changing. The larger bugs that feed on the smaller ones have altered their paths by following the sent trails of the smaller bugs. Birds that feed on the large bugs have found them in a different places. The birds spread seeds that cling to their feathers and fall off during flight. The location of small plants and even trees will be altered, and all this within the first year. 999,999 years later(the present) the world is a very different place. The time traveler(Me) no longer exists because the oak tree my great grand parents met under wasn't there.

It is not possible to visit the past without changing it, all changes to the past create a paradox. Even if the change is too small to stop the time traveler from making his trip, the traveler himself has been changed by the changes he made and will therefore make different changes.
Chaos: Original onfusion in which earth, sea, and air were mixed up together. It was personified by the Greeks as the most ancient of the gods. The egg of Nyx, the daughter of Chaos, was floating on Chaos and from it arose the world.
-Bulfinch's Mythology

Your theories on the paradoxes of time travel are well founded. However, just as any theory seems to make sense, there is a theory to counter it. I encourage you to look at this link and scroll down to the: Does time exist / Is time an illusion section. It explains something called forward and backward causality. Basically it says that the past, present, and future are all aware of each other, and so change accordingly. A balancing act if you will.

Good post - but shouldn't you be giving Kelley L. Ross, Ph.D., Department of Philosophy, Los Angeles Valley College credit for his copyrighted article which you posted verbatim?
We are not allowed to travel to the future! There are laws that prohibit future exploration. However, you can travel to designated areas of history. These are areas that are chosen as safe and you cannot effect the future by traveling here because the federation has actually managed to lock the other times and use computers to secure the areas of the past that would be harmed with human contact.
can we change the outcome if we already know it??

Many years ago i owned a boat on the river , one day my friend came to see me and said lets go out on the boat for the day! good idea thought i and went to change into more warmer gear , as i was coming down the stairs i saw in my mind my car with me and my friend being crushed under the weight of a car transpoerter as we approached the road near the river , this unsettled me and i did not want to go , but i found my body going thru all the preparation for the trip, i was not only worried , but damded scared by now as i believed this event was going to happen but try as i might i could not stop it , then i had an idea ! isaid to my friend lets go in your car, he was mystified as my wife had put all our gear in my little car (my friends car was larger and brand new that week)
my wife was furios with me changing my mind , but we went in my friends car, as we got to the very spot i had forseen , a car transporter hit us up the rear , all was chaos i saw john struggling to keep us on the left side of the road (were in england) and another lorry came close on the opposite side then glass and everything was flying around , THEN ABSOLUTE SILENCE i looked around us we were still alive my door fell open i got out as did my friend , was hysterical at this time , my friend said whats up with you my cars a write off, and so it was it was two thirds the size it started out . i turned to my friend and said dont you get it were alive without even a scratch!!!

now if i had not been warned about what was to happen in the future i and my friend would be dead as my car was smaller and would have been obliterated by the transporter , unfortunately for my friend it was a stolen vehicle so no recompense , but we are still alive because WE CHANGED SOMETHING .if i hadnt you would not be reading this now .

(the incident happened on the hull road in yorkshire 12 years ago near bransburton)

yours sincerely


Good post - but shouldn't you be giving Kelley L. Ross, Ph.D., Department of Philosophy, Los Angeles Valley College credit for his copyrighted article which you posted verbatim?

Not only that, but he should realise one mistake and one missed opportunity in the article. First, the missed opportunity is of a better example from Heinlin's literature for a very similar paradox.

In "All You Zombies" a young man goes into a bar where he meets an old barman. The old barman tells the young man that when he was born he was born a little girl. He grew up as an ugly girl with no-one really loving him until a young man with loads of money showed up and wooed her. He got her pregnant and then dissappeared. She eventually gave birth by Ceasarean and the surgeons found that she had both sets of working organs, but the childbirth had damaged the female organs beyond repair. So, they gave her a sex-change and she is now a he. At the same time, his daughter is stolen from the hospital...

The old man then gives the young man lots of money and tricks him into going back in time, where he meets and falls for a girl...you can see where this is going, right? Yes, the man was that baby. And that girl. And the boy...in fact the man was his own mother, father and every other relative. He was also the barman who recruits him into the time corps and enables the entire thing to happen.

Now that's a time paradox.

Secondly, Occham's Razor is not a law, and thus cannot be "violated". What it states is "all things being equal, the simplest explaination tends to be the correct one". "Tends to be", not "is". For a quick example of the difference; if you were to toss a coin 20 times, you would tend to get a result of about 50% heads, and 50% tails. That doesn't mean that it's a violation of probability if you get 20 heads or 20 tails.

Good thoughts on the paradox.

The bigger paradox in "All You Zombies" is that there is no perspective from which you can determine who among all of the Old Barman "progeny" came first. (Scare quote on progent because The Old Barman is his own progeny.)

In many time travel paradoxes you have effect preceeding cause. In Heinlen's story you have effect absent any cause.