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New Model Solves Grandfather Paradox

Zonk posted more than 9 years ago | from the i'm-my-own-grandpa dept.

Science 887

goldfishy writes "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 theory, you could go back in time and meet your infant father but you could not kill him." From the article: "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."

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You insensitive clod! (5, Funny)

Anonymous Coward | more than 9 years ago | (#12847980)

I am my own grandfather!

Re:You insensitive clod! (-1, Redundant)

bob15811 (892769) | more than 9 years ago | (#12848036)

lol

Re:You insensitive clod! (0)

Anonymous Coward | more than 9 years ago | (#12848091)

I am everyone's own grandfather. Who did I do?

1) Luke
2) Mitochondrial Eve
3) Chewbacca

And what will my defense be?

Re:You insensitive clod! (5, Funny)

Fjornir (516960) | more than 9 years ago | (#12848149)

Many, many years ago when I was 23
I was married to a Wider who was purty as can be
This Wider had a grown-up daughter who had hair of red
My father fell in love with her and soon they two were wed

This made my dad my son-in-law and changed my very life
For my daughter was my mother cause she was my father's wife
To complicate the matter even though it brought me joy
I soon became the father of a bouncing baby boy

I'm my own grampa,
I'm my own grampa
It sounds funny I know
But it really is so
I'm my own grampa

My little baby then became a brother-in-law to dad
And so became my uncle though it made me very sad
For if he was my uncle then that also made him brother
Of the Wider's grown up daughter who of course was my step-mother

My father's wife then had a son who kept them on the run
And he became my granchild for he was my daughters son
My wife is now my mother's mother and it makes me blue
Because although she is my wife she's my grandmother too

I'm my own grampa,
I'm my own grampa
It sounds funny I know
But it really is so
I'm my own grampa

Oh if my wife is my grandmother then I'm her grandchild
And every time I think of it, it nearly drives me wild
For now I have become strangest case you ever saw
As husband of my own grandmother I'm my own grampa

I'm my own grampa,
I'm my own grampa
It sounds funny I know
But it really is so
I'm my own grampa

What about... (1)

HyperChicken (794660) | more than 9 years ago | (#12847982)

What does this mean for Fry [gotfuturama.com] and his past-nastification [gotfuturama.com] ?

Re:What about... (2, Insightful)

BurntNickel (841511) | more than 9 years ago | (#12848019)

Destiny, it had to happen. Which now make me realize the importance the several episodes of time travel in Futurama had to the plot. It miss it....

Futurama - Roswell that Ends Well (4, Funny)

havaloc (50551) | more than 9 years ago | (#12847983)

Farnsworth: Oh, a lesson in not change history from Mr. I'm my own Grandpa!

Re:Futurama - Roswell that Ends Well (5, Informative)

SlashThat (859697) | more than 9 years ago | (#12848080)

I think a more appropriate quote would be:
Farnsworth: "Don't do anything that affects anything. Unless it turns out you were supposed to do it, in which case for the love of God. Don't not do it!"

Unless of course... (1, Redundant)

Anti Frozt (655515) | more than 9 years ago | (#12847984)

You become your own grandfather.

Re:Unless of course... (4, Funny)

bravehamster (44836) | more than 9 years ago | (#12848034)

By doing the nasty in the pasty.

First American Pie, now this... (4, Funny)

xstonedogx (814876) | more than 9 years ago | (#12848122)

Well, I, for one, will never enjoy a pasty [ex.ac.uk] ever again.

How? (0)

CypherXero (798440) | more than 9 years ago | (#12847992)

How can that even be remotely possible? Anything and EVERYTHING (no matter how small or big of an event it is) will change SOMETHING in the future. Anyone who thinks any differently needs to go back to school.

Re:How? (1)

cryptoz (878581) | more than 9 years ago | (#12848023)

No. Because, the future that exists was shaped by the event of you being there. For the future to exist as it is, you "already have" gone back in time. That is, there's no change that could occur, as it has already occured.

Now, to find my time travel machine so that in a few minutes I can go back and write this post.

Re:How? (4, Insightful)

The Good Reverend (84440) | more than 9 years ago | (#12848033)

How can that even be remotely possible? Anything and EVERYTHING (no matter how small or big of an event it is) will change SOMETHING in the future.

Sci-fi writers have had two main theories for a long time. Either you can go back in time and change things, or you can go back in time and "fulfill" the past you expireinced. Just because you have an influence on the past doesn't mean your influence didn't shape time into the way you remembered it.

Anyone who thinks any differently needs to go back to school.

Yes, because I'm sure these quantum physicists haven't spent any time in school...

What about parallel and multi-universes? (3, Interesting)

DoctoRoR (865873) | more than 9 years ago | (#12848151)

It's still hard to grok what this "prevention" means to the time traveller. If you go back, are you physically prevented from firing the gun or will the gun misfire? Or if you make a change, does the timeline establish a new universe with the old one running along merrily as a parallel universe.

When we use our senses, we only see things in the typical 4D realm, so is it possible that all those other postulated dimensions (to 11) give the degrees of freedom to allow bifurcations in the timeline? Geez this is confusing.

Re:How? (1)

plalonde2 (527372) | more than 9 years ago | (#12848039)

I'm wondering if these changes to the future are limited to your observer's point of view. The future may well change, but only in ways that will not be observable to said observer. Then truth goes and gets even more relative.

It's the same question as asking if Schroedinger's cat notices if it is alive or dead. I assume it does, but that doesn't affect the outside observer.

Re:How? (1)

SleepyShamus (599356) | more than 9 years ago | (#12848069)

Exactly! If this is true, most likely you will only be able to go back in time in "Observer Mode". History, once it's happened, is Read-Only.

Novikov? (5, Informative)

WilliamSChips (793741) | more than 9 years ago | (#12847995)

Sounds like the Novikov self-consistency principle [wikipedia.org] to me.

Re:Novikov? (5, Interesting)

Fnkmaster (89084) | more than 9 years ago | (#12848096)

Yes, it sounds similar.

And this frustratingly vague article makes a meaningless argument.

It tries to use the fact that we observe no disappearing people, or other strange temporal modifications as an argument that such things don't happen, and are thus impossible. But if somebody actually changed the way a wave function collapsed at some time in the past, why on earth would we expect to remember things from the way it was "before" it had been changed, since the change by definition happened in our own past, and thus to us it always occurred the way it now occurs? This isn't a logical argument. And it explains part of the aesthetic appeal of the many-worlds interpretation.

In pure quantum mechanics, time is a special property because wave function collapse via quantum operators (i.e. "observation") is a privileged thing that moves in only one direction. In general relativity, time doesn't have a privileged status. I don't see how you are going to reconcile that basic difference without coming up with a more complete theory (i.e. quantum gravity, GUT, etc.), but then again, my undergrad physics major knowledge is a bit rusty five years later.

Already solved (1, Insightful)

Jarwulf (530523) | more than 9 years ago | (#12847996)

Just watch Quantum Leap

Verifying the Theory (4, Funny)

Nova Express (100383) | more than 9 years ago | (#12848001)

I would be most interested in how they'll set up the experiment to verify the theory...

"OK, McFly, here's the gun. If you can kill your own father and thus erase yourself from existence, we'll know the theory was wrong."

Re:Verifying the Theory (1)

PipOC (886408) | more than 9 years ago | (#12848030)

Exactly, theorizing about time travel is about as scientific as "Intelligent Design."

Re:Verifying the Theory (1)

mistersooreams (811324) | more than 9 years ago | (#12848062)

Exactly, theorizing about time travel is about as scientific as "Intelligent Design."

Stephen Hawking has an ongoing bet regarding the so-called Chronology Protection Hypothesis, i.e. that the laws of nature conspire to prevent time travel on a macroscopic scale. Just because it leads to some problems that our brains find difficult to comprehend doesn't mean it's somehow unscientific.

Re:Verifying the Theory (1)

PipOC (886408) | more than 9 years ago | (#12848113)

Stephen Hawking has an ongoing bet regarding the so-called Chronology Protection Hypothesis, i.e. that the laws of nature conspire to prevent time travel on a macroscopic scale. Just because it leads to some problems that our brains find difficult to comprehend doesn't mean it's somehow unscientific. I meant that there's no way to prove possibility or impossibility, while it's certainly possible that any theory is correct about either subject, it's not a product of the scientific method, but rather hypothesis by "scientists" with no scientific evidence.

Re:Verifying the Theory (3, Insightful)

Malicious (567158) | more than 9 years ago | (#12848060)

Um Doc... how about we test on a monkey first?

Re:Verifying the Theory (1, Redundant)

Fortyseven (240736) | more than 9 years ago | (#12848116)

Yeah, but then we'd never know Marty existed, and we'd have to test it on someone else over and over into infinity.

Okay, [hated group] form a line to the left!

Re:Verifying the Theory (1)

climbon321 (874929) | more than 9 years ago | (#12848135)

Does this mean that Back To The Future was based on fiction and didn't really happen? I don't believe it!

The movie seemed so lifelike....

I posted this back in time (0)

Anonymous Coward | more than 9 years ago | (#12848002)

Behold! This was posted in the past!

Pseudo Science (0)

Anonymous Coward | more than 9 years ago | (#12848003)

I can't help but think this article is flawed pseudo-science with little actual evidence to support this theory. The 'universe sorts itself out' theory is all well and good in something like the hitchhiker's guide to the galaxy, but to present it as science seems a little dubious.

sounds exactly like the move "the time machine" (1)

Pr0xY (526811) | more than 9 years ago | (#12848006)

this was a principle plot point in the move the time machine.

Re:sounds exactly like the move "the time machine" (2, Funny)

Flunitrazepam (664690) | more than 9 years ago | (#12848074)

not to mention the best-selling novilization of the movie that followed shortly there after!

Re:sounds exactly like the move "the time machine" (1)

RevengeOfPoopJuggler (872968) | more than 9 years ago | (#12848131)

This was a principle plot point in every single time machine movie ever made...

Solved? (0)

Anonymous Coward | more than 9 years ago | (#12848008)

How does this "solve" the grandfather paradox? This seems to just be re-stating the problem. We already KNOW that if I can go back in time, I can't kill my grandfather. So what is new in this article?

Summary (4, Insightful)

823723423 (826403) | more than 9 years ago | (#12848010)

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

Re:Summary (1)

Mahou (873114) | more than 9 years ago | (#12848130)

yeh but the past doesn't have your future self. so how, in the future(our present), could you go back in time to even try to kill your father? by going back you have inherently changed the past and made our present non-existent. people might say the future you was there the whole time, but how does future you exist without first waiting for the past to change from present to past?

if you have a circle of dominoes and knock down the first one, you can't send the last one back in time to be the cause of the first one to fall. of course it doesn't really matter if it's such a clear case of impossible cause/effect such as killing your own bloodline.
if the dominoes are a straight line you still can't send the last one back in time while it's falling and have it fall in the past
rumble rumble and so forth

anyway, are they saying as long as no one saw something happen or not happen, then someone can go back to that time and change something? does that mean human eyes control space-time? wtf?

That's great! (5, Insightful)

cytoman (792326) | more than 9 years ago | (#12848012)

This means that you cannot be killed when you go back in time, nor can you kill or destroy anything! That's just perfect!!

Go back in time and be able to observe, only... no ability to interact with anyone either... it should be kinda like ghosts... we go back in time and observe and be like ghosts in the sense that we cannot interact and change anything that has already happened but only observe!

Imagine the possibilities of history classes of the future... maybe there are already a lot of ghosts watching us right now... the future students studying history!!

Re:That's great! (2, Funny)

cryptoz (878581) | more than 9 years ago | (#12848042)

No sane history teacher would force his/her students to watch people post to /.

Re:That's great! (1)

h0ts4uc3 (886948) | more than 9 years ago | (#12848053)

Very witty.

Re:That's great! (1)

cei (107343) | more than 9 years ago | (#12848068)

rent Grand Tour: Disaster in Time [imdb.com] some time... Not ghosts, but world disaster time-travel tourists.

Re:That's great! (1)

cytoman (792326) | more than 9 years ago | (#12848146)

From the summary of the film, I gather that this is the film adaptation of Vintage Season by Lawrence O'Donnell... an excellent story. I read it in Science Fiction Hall of Fame Volume 2A ed. Ben Bova. The point is that even though these time travellers could possibly change the events that they are witnessing, they are forbidden by the rules in the future where they come from because changing anything could potentially wipe out the future. Seeing how one of the characters (a woman who is not fond of following rules) interacts with the main character (a man), any such dependence on the lawfulness of the time travellers would hardly work and end up destroying the future. I like time-travelling people becoming ghost-like when they go to the past much better.

Re:That's great! (2, Funny)

njcoder (657816) | more than 9 years ago | (#12848070)

"Imagine the possibilities of history classes of the future... maybe there are already a lot of ghosts watching us right now... the future students studying history!!"

Great. It's not like I wasn't uncomfortable enough having sex in front of the just the dog. I have to worry about porn technology from the future.

Re:That's great! (2, Interesting)

bfioca (695852) | more than 9 years ago | (#12848084)

Actually, there's nothing that would prevent you from being killed on your journey to the past. You just couldn't kill your past self. Your present future is unknown, so you may not survive your trip to the past.

Re:That's great! (0)

Anonymous Coward | more than 9 years ago | (#12848126)

Damn, where is my tinfoil hat

Considering both of my grandfathers died before me (1)

WillAffleckUW (858324) | more than 9 years ago | (#12848014)

How do you know they're not me?

For all I know, it's totally possible.

But highly unlikely.

The question is - if you exist in the same timeline as yourself at a different age - wouldn't the cells in your body have been replaced atom by atom over time anyway?

So what if I exist here in Seattle and in China at the same time.

Ugh... (1)

helioquake (841463) | more than 9 years ago | (#12848015)

....Huh?

Re:Ugh... (2, Insightful)

MrP- (45616) | more than 9 years ago | (#12848026)

i think it means you're your own grandpa

or something

No no no! (5, Insightful)

jerald_hams (725369) | more than 9 years ago | (#12848020)

"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."

That's not clear at all. If I went back in time and killed the baby George W Bush, it's like he would disappear in the middle of a speech. Rather the entire course of history branching from that moment would be changed, so that in the "present" no one would ever know GW had existed.

-Alex

Re:No no no! (1)

coop0030 (263345) | more than 9 years ago | (#12848090)

How could that possibly work though?

Would the people in the present suddenly vacuum to a moment where George Dubya is gone?

Your explanation does not make any more sense than what you quoted.

If you were to travel back in time two years, and were to murder my dog that I was walking at the time, what would happen? Would the leash just go empty, and or would I teleport back to a time before I knew the dog?

Re:No no no! (1, Funny)

Anonymous Coward | more than 9 years ago | (#12848098)

That's not clear at all. If I went back in time and killed the baby George W Bush, it's like he would disappear in the middle of a speech. Rather the entire course of history branching from that moment would be changed, so that in the "present" no one would ever know GW had existed.

Who?

Re:No no no! (5, Funny)

crow (16139) | more than 9 years ago | (#12848138)

You mean like when my friend went back in time and killed President Barnes when he was in first grade?

Re:No no no! (2, Insightful)

nitehorse (58425) | more than 9 years ago | (#12848140)

It's actually slight more complicated than that.

Basically, if time travel is actually possible, the instant that you travel back in time, you would create a fork in the past; you go back to 1978, and every single event prior to the time that you land in may be the same, but as soon as you land in 1978 you create a version of 1978 where you existed. Getting back to your own future would be really difficult, if not impossible.

The cool thing is, if you kill someone, in that timeline that person completely ceases existing. The problem with this, of course, is that it only affects *that* timeline and any future forks created from that point onwards; it doesn't change the fact that back here, in our timeline, W became the president and launched another Gulf War.

What about... (2, Interesting)

paul248 (536459) | more than 9 years ago | (#12848021)

Couldn't you go back in time to kill your grandfather, only to have him rematerialize out of quantum randomness 5 minutes later? It's not impossible, just really improbable... maybe that's the protection mechanism.

This is just a cop-out (1)

myowntrueself (607117) | more than 9 years ago | (#12848025)

One great big unscientific cop-out;

"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.

Sounds more like 'faith' to me.

Re:This is just a cop-out (1)

ninejaguar (517729) | more than 9 years ago | (#12848127)

Or, something will kill you before you can kill him. Deus ex machina. Definitely smells like faith-based fate.

= 9J =

Ridiculous (1)

The Clockwork Troll (655321) | more than 9 years ago | (#12848028)

Consider the event "I have never gone back in time."

H'uh? (1)

still_sick (585332) | more than 9 years ago | (#12848031)

"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.

Anyone else having difficulty imagining a scenario where it would be "impossible" to kill somebody?

I mean sure, there could be the above difficulties - but short of a divine miracle, what could possibly stop (for example) a determined psychopath from doing everything possible to kill his own father?

Re:H'uh? (1)

The Clockwork Troll (655321) | more than 9 years ago | (#12848048)

Anyone else having difficulty imagining a scenario where it would be "impossible" to kill somebody?
No because there's always the degenerate case - for example, such a scenario could manifest itself as your having an inability to go back in time ;-)

Re:H'uh? (1)

queondatavo (875346) | more than 9 years ago | (#12848101)

If the father lives in the present, it means that his assasination failed in the past. When psyco-boy goes back in time, it's not like he's re-writing the past, he's just living what was written in the past. Kinda sucks, but a time traveler that goes to the past really has no free will as whatever he does in the past has already happened.

Re:H'uh? (1)

still_sick (585332) | more than 9 years ago | (#12848136)

OK - Sure. But what would actually happen?

He goes back in time, goes to stab his Father with a knife - and then what? The knife just disappears? The boring scenarios listed in the article could only save the father's life for so long if the guy was a true Psycho, and really determined.

Re:H'uh? (5, Funny)

daft_one (532587) | more than 9 years ago | (#12848107)

"Anyone else having difficulty imagining a scenario where it would be "impossible" to kill somebody?"

*cough* Bin Laden *cough*

Re:H'uh? (1)

SleepyShamus (599356) | more than 9 years ago | (#12848143)

I find this a bit overly dramatic also. Most likely, you would be able to OBSERVE but not INTERACT on any level.

Like a previous poster said, ANYTHING you interact with will have an effect on the timeline.

Think of the Butterfly Effect postulated by Chaos Theory.

*HALT. message from your simulation overlords (0)

Anonymous Coward | more than 9 years ago | (#12848032)

stop picking at our simulation, or we turn it off.
final warning.

love,

the operators

time travel? (0)

Anonymous Coward | more than 9 years ago | (#12848038)

Another example of logic gone awry. If the number of possible states has been reduced to one, then time travel is again impossible. Not only can you not kill your father, you can't meet him either. You can't be anywhere at all in the past because you weren't there.

Re:time travel? (1)

John.P.Jones (601028) | more than 9 years ago | (#12848086)

But maybe you were always there, you could have been there but you most certainly didn't kill your father.

John Titter (1)

lebedev (620945) | more than 9 years ago | (#12848043)

This sounds a lot like that John Titor character. http://www.johntitor.com/ [johntitor.com]

Re:John Titter (1)

bob15811 (892769) | more than 9 years ago | (#12848095)

I am John Titor.

Then You could NOT change ANYTHING (1)

John.P.Jones (601028) | more than 9 years ago | (#12848044)

Not only could you not kill your father, you could not change any event to which you or anyone else had observed and recorded. Essentially this is the 12 Monkeys interpretation of time travel, you are only to observe.

Huh? (0)

Anonymous Coward | more than 9 years ago | (#12848045)

"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."

Why is this obvious? For all I know this might be happening. How do I know the immediate past is truly as I recall it and hasn't 'changed'?

Perhaps not... (1)

posternutbaguk (637765) | more than 9 years ago | (#12848047)

So they are saying the past is deterministic (since the quantum state has already been resolved). But surely that means that since there was no state in the past determined in which your forefather met you, you can't go back to meet him, since that state does not exist.

Well thanks, Slashdot. (1)

ChePibe (882378) | more than 9 years ago | (#12848051)

You just ruined my weekend...

So basically... (1)

Gaima (174551) | more than 9 years ago | (#12848057)

If I went back in time, and killed my mum, I wouldn't have been born to go back in time to kill my mum?
So she wouldn't have died, leaving her to eventually give birth to me, for me to go back in time and kill her, preventing her from getting pregnant with me, meaning I would never have existed to go back and kill her?

Where's the paracetamol, mum?

Re:So basically... (0)

Anonymous Coward | more than 9 years ago | (#12848121)

Yeah, that's the whole paradox that TFA claims to solve.

what is _wrong_ with this reporter?! (3, Insightful)

Blymie (231220) | more than 9 years ago | (#12848058)

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.


So let me get this straight, BBC reporter. Your proof that time can't be changed, is simply that you don't remember it happening?

There are just so many flaws in that reasoning. ;)

First, time changes could be happening everywhere, but perhaps you have not witnessed one. Wait! How about this? How about time changing, and altering your memory at the same time?

What's the matter with you? Do you believe that it is impossible for something to occur, without you being aware of it?

Is this a God complex?

What unmitigated self-importance, BBC reporter!

Now sure, I know this reporter was likely trying to parse some marlaky that they were told, but this has to be the worst use of logic I have seen.

Terminator (1)

Deathlizard (115856) | more than 9 years ago | (#12848059)

So, I guess this makes the Terminator Series pretty much infinite then, since basically they've been trying the grandfather paradox against SkyNet all these years.

That and John Conner will apparently never die, at least from a time traveling robot.

titor says f you all (0)

Anonymous Coward | more than 9 years ago | (#12848061)

parallel world lines.. its you -2%

Where is schrodinger's cat when you need it? (1)

technoextreme (885694) | more than 9 years ago | (#12848063)

It's dead or is it alive. We don't know and we will never know. Perhaps it's lying in an semid dead/alive state. Perhaps there are multiple realities each one witha cat with a differnt possiblity. Damn if I know but the only way this article makes sense if you use the second model. In that case you probably would create a new realitiy with the slim probability that you went back and time and killed someone. Now I feel like bashing my head up against the wall because quantom mechanics makes no sense whatsoever.

Re:Where is schrodinger's cat when you need it? (1)

Kahless2k (799262) | more than 9 years ago | (#12848155)

Wasnt it Janeway who said "The best way to consider a temporal paradox, is not to consider it at all."

Hah! I threw in the Trek quote, can I have my geek licence back?

Stupid machines! (1)

wiresquire (457486) | more than 9 years ago | (#12848071)

I knew those Terminator's would never kill John Connor or his mother.

Humans rule!

The Divergent Timeline Theory (0)

Anonymous Coward | more than 9 years ago | (#12848072)

I much prefer the divergent timeline theory that states that if you go back in time and kill your father, all you do is split yourself off into a parallel time stream. You don't die, because you ARE alive. Your father in the original stream stays alive. If you return to the future though, no one in that timeline will know who you are because you were never born in that timeline.

Information cannot travel back in time? (1)

tigre (178245) | more than 9 years ago | (#12848075)

I'm quite sure someone like Hawking will soon step in and say that though time travel of something is theoretically possible, that no intelligent being would be able to make the trip successfully because no information would be able to travel back in time.

Clearly, the present never is changed... (1, Informative)

Anonymous Coward | more than 9 years ago | (#12848077)

"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."

Oh yes quite obvious!

Or not.

If you went back in time and changed the past, those in the future would instantly be changed and would have no reccolection of past events being different!

One sperm in a million (5, Interesting)

Saeger (456549) | more than 9 years ago | (#12848081)

The one thing that always bothered me about those time travel movies (besides the ridiculous timetravel part) like "Back To the Future", is that you wouldn't have to go to extremes to prevent your birth. All you would have to do is bump into your Mom or Dad to delay them for 1 second; that slight change in the timeline would guarantee that it would be a different sperm that won the race to impregnate your mom.

Sounds like double-talk to me. (1)

wealthychef (584778) | more than 9 years ago | (#12848082)

"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."

There must be more here than it sounds, as this sounds like "once something has occurred, it has occurred, not something else." Well, duh. I didn't know that.
But it really proves nothing. I mean, if you go back in time and kill your grandparents, then you would never have observed their existence, so the basis of the paradox is removed, no? It's all just a rehash of whether time travel suspends logic.

So wait, that means... (1)

RyanFenton (230700) | more than 9 years ago | (#12848083)

That means, the Roadrunner is the Cayote's daddy, Tweety bird is Sylvester's pappa, and GI Joe and Cobra are the world's most incestous family?

Egad!

Ryan Fenton

Lame! (5, Insightful)

khasim (1285) | more than 9 years ago | (#12848085)

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.
Ummm, if you prevented their births, they wouldn't exist to "fade into the ether".

It could be happening all the time and you wouldn't be aware of it (by definition).
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.
Sounds like bad fiction to me.
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.
Sounds like the techno-babble "justification" in the bad fiction.
So, if you know the present, you cannot change it.
And the easiest way to not change it is for time travel to be impossible.
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.
If, for example, you knew a picture would be taken, you could reflect light from your body and appear in that picture, thereby altering the future.

So, travelling back in time, you cannot reflect light, and, by the same token, you cannot absorbe light.

And it just moves up from there for all other physical effects. Nothing touched, no air breathed, no light disturbed, nothing.

So, how would you even know you were in the past?

idiot savant (1)

terloon (893015) | more than 9 years ago | (#12848088)

It says if you are 90% sure that you're father is alive you have a 10% chance of killing them in the past. What if we send someone who knows nothing about past events and tell them to say, kill Hitler?

it's pretty simple really (0)

Anonymous Coward | more than 9 years ago | (#12848094)

Consider your whole existance as a time traveller as a probability function. Each possible path you could take has a probability of happening. Anything paridoxical has 0 probability, just can't happen. It's like seeing shrodinger's (sp?) cat dead and then going back to try and save it. The probability of anything that's happened and been observed is already 1, if you go back in time it'll still have been observed already even before it's technically happened, so the outcome is already determined and can't be changed.

If that made no sense it's probably because i'm stoned.

Time travel? Impossible (0)

Anonymous Coward | more than 9 years ago | (#12848104)

We all seem to assume that there is some sort of record of what has happened in the past that we can actually travel to.

What is keeping this record? Do you think that the past is happening again in another dimension, or something of that nature?

It's not as if it's a place you can travel to. By this theory, there wouldhave to be infinite seperate dimensions for each and every 'whatever the smallest measure of time is', because I doubt the universe uses anything so mundane as milliseconds or anything of that nature.

Where are we traveling to. How do we know that there is a past to go back to? We assume that since things have been done and we have recorded them as having happened, that the universe has as well.

I'm not so sure of that.

Dupe!!! (1)

isny (681711) | more than 9 years ago | (#12848108)

Just kidding. I was just traveling back in time to say hi to gramps when I decided to see how the "old" internet was working. let me tell you about the future:
- still lots of spam
- geeks still not getting laid
- cmdrtaco promoted to admiral taco.

This is incredibly stupid. (1)

michaeltoe (651785) | more than 9 years ago | (#12848109)

But nobody is going to question it because it involves quantum mechanics... idiots.

"Complimentary to the present"? (0)

Anonymous Coward | more than 9 years ago | (#12848114)

Has anyone ever told you what a fine present you are? No, really, I've visited many moments in my life, and I have to say that 'now' is by far the finest. Two thumbs up, *way* up, for the current time.

This can't be right... (0)

Anonymous Coward | more than 9 years ago | (#12848117)

FTA:
So, if you know the present, you cannot change it.

But as far as history knows you weren't ever there, and since you being there at all would change history, this would either disprove Einstein's general theory of relativity or the researchers that came up with this theory.

Two simple rules... (2, Interesting)

JuliusRV (742529) | more than 9 years ago | (#12848118)

To avoid contradictions in time travel, two simple rules must apply:

1) You can observe, but not alter the past.
2) You can alter, but not observe the future.

false analogy (1)

Muchacho_Gasolino (868337) | more than 9 years ago | (#12848119)

That principle of quantum mechanics has nothing to do with whether time travel can alter the future. The key phrase in it is "has been measured". Yes, the person named Joe who is here right now's past is known and unalterable, but the Joe of five minutes ago, lacking five minutes of memories and air chemicals, has a clean future in front of him which has not been observed. They are two totally different Joe's, and may take two totally different paths.

other possible theories to prevent the paradox (1)

raist21 (68156) | more than 9 years ago | (#12848128)

What about the parallel universes theory in regards to time travel? Does this mean it's no longer a viable possibility as well? I don't see how this article stated/proved anything new in regards to time travel and quantum theory that we hadn't already hypothesised.

The Proteus Operation (1)

aztec1430 (242755) | more than 9 years ago | (#12848129)

You need to read "The Proteus Operation" by James P Hogan...

And excellent SciFi story on how time travellers change history (but actually are creating new time stream branches)

Stupid (0)

Anonymous Coward | more than 9 years ago | (#12848132)

This "theory" is stupid, as it's impossible not to affect things in a different point in time. That is, everything we do affects everything else. The scale starts small, but becomes astronomical as it ripples outward. Therefore, the only sensible possibilty is that time travel creates a new, independent timeline.

My nose-picking friends came up with this one in.. (0)

Anonymous Coward | more than 9 years ago | (#12848145)

1989...
Is this actually a new theory? Any forth grader who watched star trek could have figured this one out...

This is new? (1)

UglyRedHonda (893014) | more than 9 years ago | (#12848153)

I'm surprised they're calling this a new theory. I mean, it's not like somebody couldn't have figured this out decades ago. (I've had a short story idea along these lines in my head for a couple of years.)

For those having trouble grasping it, it works kind of like this:

Say you decide you're going to the store to buy milk. You get in the car and start driving there, with the one thought in your mind being going to the store and getting milk.

On the way there, you get in a car accident. You never reach the store.

Stuff like that happens every day. Things happen that are out of our control and are impossible to predict. It's the same concept, just taking place in the past rather than the present.

In my story idea, I summed it as "Nature will right itself". It's not like people don't die random and unexpected deaths every day.

Time travel violates causality (1)

Marvin_OScribbley (50553) | more than 9 years ago | (#12848156)

By necessity, since traveling backwards in time causes effects to occur before their cause. The universe stops making sense when causality is violated because causality is what makes the universe make sense in the first place.

Anyway, I think the authors may have seen this movie [imdb.com] . The idea is certainly not new.
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