Time Travel Paradox Kicked in Balls

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If you went back in time and met your teenage parents, you could not split them up and prevent your birth - even if you wanted to, a new quantum model has stated.

Researchers speculate that time travel can occur within a kind of feedback loop where backwards movement is possible, but only in a way that is "complementary" to the present.


In other words, you can pop back in time and have a look around, but you cannot do anything that will alter the present you left behind.

The new model, which uses the laws of quantum mechanics, gets rid of the famous paradox surrounding time travel.

Paradox explained
Although the laws of physics seem to permit temporal gymnastics, the concept is laden with uncomfortable contradictions.

The main headache stems from the idea that if you went back in time you could, theoretically, do something to change the present; and that possibility messes up the whole theory of time travel.


Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.

So either time travel is not possible, or something is actually acting to prevent any backward movement from changing the present.

For most of us, the former option might seem most likely, but Einstein's general theory of relativity leads some physicists to suspect the latter.

According to Einstein, space-time can curve back on itself, theoretically allowing travellers to double back and meet younger versions of themselves.


And now a team of physicists from the US and Austria says this situation can only be the case if there are physical constraints acting to protect the present from changes in the past.

Weird laws
The researchers say these constraints exist because of the weird laws of quantum mechanics even though, traditionally, they don't account for a backwards movement in time.

Quantum behaviour is governed by probabilities. Before something has actually been observed, there are a number of possibilities regarding its state. But once its state has been measured those possibilities shrink to one - uncertainty is eliminated.

So, if you know the present, you cannot change it. If, for example, you know your father is alive today, the laws of the quantum universe state that there is no possibility of him being killed in the past.

It is as if, in some strange way, the present takes account of all the possible routes back into the past and, because your father is certainly alive, none of the routes back can possibly lead to his death.

"Quantum mechanics distinguishes between something that might happen and something that did happen," Professor Dan Greenberger, of the City University of New York, US, told the BBC News website.

"If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him.

"But if you know he is alive, there is no chance you can kill him."
In other words, even if you take a trip back in time with the specific intention of killing your father, so long as you know he is happily sitting in his chair when you leave him in the present, you can be sure that something will prevent you from murdering him in the past. It is as if it has already happened.

"You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind," said Professor Greenberger.


"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."


Source:
http://news.bbc.co.uk/2/hi/4097258.stm
 
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it makes sense.

thats about all i can say.
 
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Holy **** if that was true, that's just crazy how their is a force that can use all kinds of reasons to prevent you from doing something.

I would personally not mind a "see only" version of time travel. Dozens of historical mysteries could be solved with a no-touch time traveling method.
 
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Wow, so it's like, "look, don't touch"?

Well that's a relief. It'd still be dangerous technology though. Imagine any government being able to go into yesterday and just stroll into a top secret facility to discover everything going on there without worry of discovery. Espionage would be obsolete. Privacy would be a joke.
 
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Wow, so it's like, "look, don't touch"?

Well that's a relief. It'd still be dangerous technology though. Imagine any government being able to go into yesterday and just stroll into a top secret facility to discover everything going on there without worry of discovery. Espionage would be obsolete. Privacy would be a joke.
I can't wrap my mind over something..Lets say someone went back in time and wanted to break into the Pentagon. Now people would try to stop them, but wouldn't that prevent them from doing the task they were going to do before you went back in time? Or will the traveler be unaffected by the past and vice versa? Or, like the article said, to prevent any change, strokes of coincidences will prevent the traveler from breaking in/causing a disruption.
 
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i cant help but think of it in "matrix" terms.

your choice is already decided before you make it, but your personality and beliefs are what decides the choice.

i think it might be a similar concept. when you go back in time, your choices will already be known, and therefore will already be guarded against.

your dads alive when you leave, and you go back with intent to kill him, something happens where he doesnt end up where hes supposed to but preserves the timeline, you miss your chance and he lives. only it keeps happening, no matter how much you try.

kinda cool to think about.
 
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I can't wrap my mind over something..Lets say someone went back in time and wanted to break into the Pentagon. Now people would try to stop them, but wouldn't that prevent them from doing the task they were going to do before you went back in time? Or will the traveler be unaffected by the past and vice versa? Or, like the article said, to prevent any change, strokes of coincidences will prevent the traveler from breaking in/causing a disruption.
The quantum physics theory would most likely capture you, and certain events would unfold

say one week ago, at noon, you were at a hotdog stand.


well, say you went back in time 8 days ago to break into the pentagon. You'd go back into there and they would stop you. Well, from the time travel theory, certain events would unfold to where you yourself would be end up at the hotdog stand. How? Maybe they'd release you and you'd suddenly "change your mind". Maybe they'd keep you captiv, then you'd become starving from being kept, and they'd dump you off at the hotdog stand.
 
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I tend to see this as evidence that you can't travel back in time.

Think about it: the conclusions they come up with are based in mathematics - equations. If they try to force time travel where the past is altered, the equations spit out a zero percent possibility of the past being changed. So, either you change your mind before you kill your dad, or you never went back in time in the first place. Which one is more likely?

Saying "you change your mind" or "you can't find him" is very silly in my opinion. What kind of force of nature has an effect of making you change or mind, or making you somehow miss your chance to change the present? It is illogical.
 
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There's a lot of theories on the subject.

Some people think that any thing that would allow you to go back in time would subsequently destroy itself in order to prevent the paradox of it's own existence.
 
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Suddenly, I feel like I don't have control over my own actions in life anymore :(
I can't change anything in the past.
if we have past, we have a future, which means the future me can't change anything either!

so my life is flowing down a predetermined path :(
 
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Actually i disagree with this. I always believed that if someone goes back in time and did something to alter their future, it would create an alter version of the reality, while the original one continues normally without being changed.
 
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Hmm...I interprated this simply as the idea that you could go back, but you would be like a ghost, unable to interact, or be interacted with. It'd be like a recording.
 
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Oh yes, so that's what ghosts are... :)
 
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Wait, I didn't exactly get this...This quantum model states that one can go back in time, he just can't change anything? That much I get, but...what prevents you from changing anything in the past when you actually get there? The knowledge of you knowing that your father still exists in your current time?

What if you went back to the past, bought a gun, met your father. Put the gun to his head and pull the trigger? What would prevent you from killing him?

Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.


Of course you don't see people fade into ether. Because that would mean you are actively seeing the change of the outcome of an event. While if you kill someone in the past, everything following that event would have never happend. Thus, you won't 'see' anything fade away, because that also never happend. Time would just *poof* everything into a different setting and you wouldn't even notice it, because you don't know any better.

Either that or Einstein's other theory is true. Every action has an infinite amount of reactions. Meaning that if I shoot you, there will a universe that will exist where you die and events play on without you. Or, a second universe is created where you do live and events play with you. Essentialy creating a multiverse with parallel universe. In this case if you go back in time, to the point before I killed you. You'd be in a universe before it split into two parallel universes and anything is still possible.

That and this model somewhat contradicts the Heisenberg's uncertainty principle, basically stating that the future is predetermined and cannot be changed. While the multiverse theory states that everything is possible because every action has an infinite amount of reactions that all happen within their own universe and thus is far more likely as it is 'compatible' with Heisenbergs theory.

But then again, I didn't fully understand the article and those guys are probably a lot smarter than I am and I might have missed something.


 
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It all sounds good, but then I thought "since when do quantum mechanics influence macroscopic events?"
It's exactly like stating the table becomes a table the moment you look at it, being a multitude of possible things when you don't, and there's a chance that your table is a wave function the moment you happen to look at it.

To taht Pentagon example: I guess according to the article, you could disturb the people as much as you'd like, you'd
never stop them from doing something since you didn't know what they were doing in the first place.
 
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Suddenly, I feel like I don't have control over my own actions in life anymore :(
I can't change anything in the past.
if we have past, we have a future, which means the future me can't change anything either!

so my life is flowing down a predetermined path :(
I think it says that once something has happened, a permanent path has been made and can not be changed, but that those paths do not exist in the future until we make them.
 
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inb4splicers

hmm...uncanny resemblance.
 
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The main headache stems from the idea that if you went back in time you could, theoretically, do something to change the present; and that possibility messes up the whole theory of time travel.

Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious.
I personally don't see how that is obviously not a possibility still. Because if something did happen to change the past and it made people dissapear, then all the memories/history along with them would go as well. Changing the way history went about and making it so that you never existed.

Just because we dont see people disappear and dont remember it happening, that doesn't mean it couldn't happen because according to that theory the present would correct itself.

The only problem would be if you went back in time and killed yourself, idk how that works but it really isnt my field of profession so im not gonna stress about it.
 

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