Time paradox

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Time-travel is physically impossible due to the fact that you would require energy equal to about, say, over half the total mass of our Universe.
And if you travelled in time but not space you'd find yourself in the empty patch of vacuum where Earth was a couple of months ago.
Then, as the esteemed DarkStrider pointed out, Time is only a concept developed by the human need to quantify everything and give us a feeling of linearity in our lives.

 

That's (the first) assuming that time is a Newtonian Dimension, which it wouldn't really work if it were, not unless all of existance were travelling in one infinitely flate plane of time. Most likely, time is not a Newtonian dimension and if we could go back in time, we would find things as they were back then.
As for the energy requitements, since we have no idea how to do something like that, we really have no idea how much energy it would take. Who knows, maybe human-powered time machines aren't so impossible.

 

what theory is this based on? while time travel is currently called impossible you should know that no true scientist would ever use the word impossible, its used far to often to describe something someone doesnt understand... go back 50 years ago and ask people if you could split the atom and they'd tell you to sod off, but today its something far different.

i remember reading a theory where for every time effect in the universe there is a seperate universe for the other effects, so if someone had indeed travelled in time and changed the past you would never know about it.

time feels very real to me, its felt very real to the universe for billions of years where stars have existed and died. yes the unit of time may be man made- seconds, minutes, hours but the effect has existed for far longer then the human brain can comprehend

 

I agree with the multiple-universe theory that you mentioned, Shoshino. The mechanics of time travel aside (and this thread is not really about the mechanics of time travel, but about how a specific paradox involving time travel could be resolved), I think the only feasible way for the particular paradox mentioned above to be resolved is the theory that when you go back in time, you are actually travelling into another universe that exists in that particular time. So if you are vistited by a furute you that gives you plans for a time machine, that future you actually hails from a parrallel universe. And when you, after completing the time machine you are given plans for, then travel back in time to give yourself directions for the time machine, you are traveling to yet another universe. This cycle would repeat indefinitley, however it means that some verision of you, in some universe, must have thought up the plans origionally. Unless the cycle of giving the plans to parrallel yous throughout the dimensions loops over across the infinite number of universes, which would create the same paradox we had to begin with. But thinking about that makes my head spin, so I'm going to say thats probably not possible...

 

Im sorry to reference something that really isnt scientific, but when ever you see some sort of movie or TV program about time travel (except Back to the Future) they always talk about avoiding meeting yourself in the past and making sure they do not see you, and making sure you do not directly influence anything in your past life, this is so that they avoid Paradoxes (or destroy the world, eg one of the Dr. Who episodes when Rose goes back to see her father, sorry for the spoiler, people who have seen the episode will understand).

 

"Probably" not possible? I'll stick my neck out and say "definitely" not possible - mostly because it's just too nutty.

Unless you have a modified Delorean, of course.

 

i dont agree on that, the idea of where the plans came from could make your eyes bleed, its not possible for the human mind to understand a quasality loop because we are not capable of that kind of thinking, we need a beginning, a middle and an end.

what youve got to realise is the instant those plans came 'back from the future' they existed in that time where they came from in a time relation is irrelevent, they existed there and then for you to create your time machine..... the plans always existed because time doesnt have a beginning for them.

 

First off, its causality loop, not quasality loop, sorry but that bugged me. Second of all, that makes no sense and is impossible if you believe that effect must have a cause, thus in a causal universe. If you don't believe that EVERY effect must have a cause, something quantum physics is really starting to question, then the causal loop is entirely possible.

 

Um, everything in this thread is impossible and makes no sense so that's OK. Except becoming a zillionaire by betting on sports games you already know the outcome of. That'll still work.

 

@Shoshino:
"My" theory is based off of a documentary I watched a while ago that concluded that it WAS possible to technically travel forwards in time (using spin or something, details are fuzzy) but that the amount of energy required would far exceed anything we could be capable of producing, equal to roughly half the mass of the Universe.
And did time exist before sentient life? how can time pass if there is nothing to percieve it's passing? It's the whole "if a tree falls in the forest, and no-one is there to hear it, what colour is it?" argument.
And there's the valid point that, if we DID at some point learn to travel in time, why aren't we seeing tourists or historians from the future?

 

Ok, you screwed yourself over when you said the details were fuzzy. A lot of people like to pretend they know what their talking about with this stuff, but the details are always fuzzy. The truth is we have very little idea about how time works and any theory about traveling through it at this point is about like theories of the movement of the planets when you think the Earth is flat and the center of the universe.
And where did everyone get the idea that things only exist if there is a sentient being there to percieve it? Are you saying that nothing existed before the first sentient human (or whatever) arose? If that's true, where did the first human come from? If a tree falls in a forest, and there is no one there to hear it, it still crushed the little bunnies, the birds aren't chirping in it anymore, and it will die and rot, just like if there were a person watching the whole thing.

 

Hehe, and how can my plants be dead when I return from vacation, if I wasn't there to watch them die ?

 

I would like to think that barring all the scientific mumbo jumbo associated with time travel even being possible, if anyone was smart enough to find a way to do it, they would not because of causality. Change anything and his own present could be altered in ways he cannot imagine. Just because something can be done, doesn't mean it should.

 

This type of situation is called a predestination paradox.
I will attempt to list as many solutions to this scenario given current scientific thought, the reference material I have available (primarily Wikipedia), and my understanding of the material. The Wikipedia article on time travel goes in to these in more depth, as do many of the links I am including in my post.

• The "Presentist" view: This scenario would not happen because everything only exists in the present. Even if you were to travel back in time, only the material that travels back would exhist because you have left behind the rest of the material of the universe.¹ This theory, in part, reminds me of the Stephen King short story "The Langoliers".
• Novikov self-consistency principle (AKA Novikov self-consistency conjecture): You gave yourself the plans, because you were meant to give yourself the plans. This theory proposes that contradictory causal loops (for example, the grandfather paradox) cannot form, but that consistent ones can.
• Many-worlds interpretation: Traveling back in time to give yourself the plans creates a new universe² where you give yourself the plans. Another interpretation is that you didn't really travel back in time, you just traveled to another universe². This view is an extension of an interpretation of quantum mechanics most often used by science fiction writers. The problem is that the interpretation this is based on says that no information can pass from one universe to another.
• Another quantum mechanical time theory³: While you would be able to see the past you, the future you would not be able to change anything. That is not to say that things are predetermined. While looking forward in time, things are probabilistic. Once an outcome occurs, however, it is set in stone. Thus, looking backward in time, things are deterministic. This is kind of hard to explain to those who don't know about or understand wavefunction. I'd link to the article on Wikipedia about wavefunction, but seeing as how it is almost entirely equations, I'll refrain from doing so.
• Chronology protection conjecture: This scenario would not happen. Quoting Wikipedia directly, "Many attempts to generate plausible scenarios for closed timelike curves have been suggested, and all seem either implausible, contradict other principles of physical law, or appear to be contradicted by experiment. The question then arises: is this apparent prohibition a global constraint of physics, in the same way as a conservation law, or is it a series of accidental coincidences?"
• Self-eliminating time travel⁴: This scenario might happen but we would never know. Time travel will never exhist that we know of, even if theoretically possible, because as long as the circumstances that created time travel exhist, time travel will occur, constantly changing history. Once a change in history occurs that changes the circumstances that caused time travel to arise, time travel will no longer exhist in the timeline, with us none the wiser to what occured.
• Time travel without moving through space⁴: When the future you travels through time, you don't travel through space as well. Thus, you don't end up where you were expecting. The location you end up in depends on how far forward or backward you go. Seeing as this scenario says two months, chances are good you'd end up in the vacuum of outer space. This theory assumes that the time machine doesn't move great distances to keep up with the space as it moves through time. It also assumes that there isn't some combination of spatial temporal inertia that keeps you moving with space as you move through time. Like how if you stood in the back of a flat bed truck while it was moving and jumped up and down. You weren't connected to the truck while you were in the air, yet you stayed with it because of inertia. On the flip side, using the same analogy, say the truck (symbolizing time) suddenly goes in to reverse while you are in the air. The cab of the truck will most likely bang in to your legs because they are trying to occupy the same space.

These theories deal with traveling in to the past. Traveling to the future is already possible, albeit in very small amounts. (See time dilation.)

Notes:
¹Of course, this would instantly kill you. This also brings up interesting questions. Since there is nothing else that exhists in this "place", would your dead body be concidered a universe unto itself since it is the only matter and energy that exhists?

²Use of the word dimension to refer to another universe, though common in movies, television, and comic books, is incorrect. While the definition of dimension differs between mathematics, physics, and non-technical use, no definition of the word comes close to implying it's use as a synonym for another universe.

³This has no specific name. I suppose, in part, it is a variation on the Copenhagen interpretation. While I don't understand the equations, the authors of this paper explained well enough with normal terms and diagrams what they were trying to explain.

⁴These don't have specific names, so I made up ones I thought fit.

 

50 years ago? 1956. How many years was that after WWII ended in an atom bomb been dropped? Make it 70 years ago

If anyone has ever read Hitch-Hikers Guide to the Galaxy (which I'm sure you all have) you will know that Time Travel was invented at the same time throughout all times. One moment it did not exist, the next it did. Simple as that.

 

There's actually a very good point in all this: we always think we're right. We've come up with a lot of theories and ideas, limited them on our understanding of the universe, and utterly failed to take into account that 80 years ago the best scientific minds in the world said that the human body would liquify if it passed the speed of sound, that Einstein was totally wrong on many counts, that we used to think the world was flat.
Everything we know is only a drop in the bucket. We may, just may, be right, but odds are we're missing something, and odds are, it's big.

 

Never heard that one -- in fact, the best scientific minds were trying to determine HOW to pass the sound barrier (so it was already determined that it could be done). The only problem was keeping the plane together. There will always be fanatics and lunatics that spout their opinions as fact (no matter how well educated they are).

Not the scientists. Christopher Columbus was ridiculed because he though the world was about the size of Mars -- the scientists of the day thought he would die of starvation before he could reach china. They were right, Columbus was lucky there was a land mass between. I'm amazed that we, in America, have a holiday for such an ignorant slaver.

I would also like to hear an example of something significant Einstein was completely wrong about.

 

Even the Greeks knew the world was round. It was obvious to them every time a ship went 'over' the horizon that the world couldn't possibly be flat.

 

1.) In the 1920's and 30's it was common scientific theory that if one passed the speed of sound, the resulting shockwave would rip the plane apart, liquify the bones of the pilot, boil the blood, combust the atmosphere in the cockpit, and a few other wacky things that really remind me of what they now say should happen if you aproach the speed of light. By the time we even got close to the speed of sound (1950's), the planes were more than capable of holding up under it all.
2.) So I'm talking about longer back than you. The Egyptians thought the world was flat, so did the Babylonians, I think the early Chinesse did. Certainly people in the early dark ages (1000-1300).
3.) MY point was that the best estimates of humanity have repeatedly been proven wrong. Surely we all 'know' that nuclear fusion powers the stars, but all we really have is corillary studies to back that up. Its the best theory at the moment and certainly seems to work, but I wouldn't be TOO surprised to see it disproven at some point.