Grandfather paradox solved?

[Andrew Green]

http://news.bbc.co.uk/2/hi/science/nature/4097258.stm

Interesting stuff...

Quantum theory is the reason Advil stocks are where they are today :S

 

[sgtmac_46]

I read that article and I can't help but believe that the "research" had a lot to do with repetative bong hits. Let me surmise the argument as I understood it:

"We don't know that the laws of the universe will allow travel backwards in time, but we do know that you can't do anything to change your present, like kill your father...at least the part of your present you know about....if you are only partially sure, then you might be able to change the present....we think....because, for example, if you know your father is alive, you certainly can't kill him...that wouldn't make sense...but if you're only partially sure he's a live, then you probably can't kill him....probably."

That was enlightening.

 

[Sam]

wait, I want to know about advil stocks.

what?!?!

I am so confused lol.

 

[FearlessFreep]

I think it skirts on the Shroedinger's Cat issue, which I could never quite by. I mean, at a quantum level there is a probability that a particular particle is spinning one way or another and you don't know until you look, but to extrapolate that into saying that the cat is both dead and alive? I think the cat is dead or alive and will be so regardless of whether you observe it. I think the Cat is just an analogy for quantum probabilities and shouldn't be taken too seriously in it's own right.

To extrapolate that into "You can't go back in time to kill your father because you know your father is alive and therefore *something* would keep it from happening" strikes more of mysticism in what that "something" is (or maybe psychology that you wouldn't do something you know is a contridiction).

I think one sci-fi writer to the tact that the past was involitile, but this meant the that it was *really* involitile. Evervy blade of glass was rock hard and razor sharp to the time traveller because for the traveller to walk on grass and bend the blades of grass was changing the past and the past could not be changed

 

[Bob Hubbard]

It is the paradox of time travel.
You can't go back in time and kill your father because then you wouldn't be alive to go back in time to kill him.

By the same token, you can't go back in time and kill Hitler as a boy, because then you wouldn't have wanted to go back in time to kill him since he was never a problem so therefore he wouldn't be killed by you causing you to want to kill him.

Y'all with me on this?

 

[Andrew Green]

yup

Of course I do believe that this impies that once we gain the ability to see the future, the future is no longer uncertain and we won't be able to change it.

 

[bignick]

Unless you see more than one probable future?

 

[arnisador]

All speculation and interpretation, I say. Maybe there's more science buried somewhere in it, but I'm not convinced.

As for me, I liked my grandfathers, so it's all moot anyway!

 

[sgtmac_46]

I think it skirts on the Shroedinger's Cat issue, which I could never quite by. I mean, at a quantum level there is a probability that a particular particle is spinning one way or another and you don't know until you look, but to extrapolate that into saying that the cat is both dead and alive? I think the cat is dead or alive and will be so regardless of whether you observe it. I think the Cat is just an analogy for quantum probabilities and shouldn't be taken too seriously in it's own right.

To extrapolate that into "You can't go back in time to kill your father because you know your father is alive and therefore *something* would keep it from happening" strikes more of mysticism in what that "something" is (or maybe psychology that you wouldn't do something you know is a contridiction).

I think one sci-fi writer to the tact that the past was involitile, but this meant the that it was *really* involitile. Evervy blade of glass was rock hard and razor sharp to the time traveller because for the traveller to walk on grass and bend the blades of grass was changing the past and the past could not be changed

I think you're on the right track there. I actually think they simply based it on Shroedinger's cat. I'm not so sure you can come to a conclusion about what IS or IS NOT possible to do in theoretical time travel (a monumental problem in it's own right) simply be discussing Particle/Wave duality.

 

[arnisador]

Shroedinger's cat is from quantum physics...this is a relativity issue, isn't it?

 

[sgtmac_46]

It is the paradox of time travel.
You can't go back in time and kill your father because then you wouldn't be alive to go back in time to kill him.

By the same token, you can't go back in time and kill Hitler as a boy, because then you wouldn't have wanted to go back in time to kill him since he was never a problem so therefore he wouldn't be killed by you causing you to want to kill him.

Y'all with me on this?

Actually, I heard a far better example of this paradox by a physicist than the killing of an ancestor.

He stated that if you take two ends of a worm hole, and pull one of them at or near the speed of light for a distance, one end will open moments earlier than the other end. Worm holes are a widely accepted theory. Moreover, moving at or near the speed of light is understood to cause temporal differences based on Einstein's theory of relativity. So this presents LESS problems than simply traveling backwards in time, and is more likely possible.

In effect, anything that goes in one end, will come out the other end before it went in.

He proposed this experiment. If we line up the worm holes near each other, what happens if we toss a marble through one end of the wormhole, what happens if the marble comes out the other end and strikes itself, thereby preventing itself from entering the wormhole? Moreover, what happens when an astronaut flies through our imaginary worm hole and comes out before he went in, but this time pre-trip astronaut sees post trip astronaut, something post-trip astronaut didn't see before entering, and decides not to enter the wormhole, thereby making it paradoxically impossible for him to be there?

I always felt this was a more straight forward version of the problem that side steps a lot of irrelavent conjecture and gets to the core of the problem. No killing, no long term historical questions, just one HUGE PARADOX.

For example, are we now stuck with TWO marbles? If we are stuck with two marbles, where did it come from? There would appear now to be more mass in the universe that existed before, one marbles worth.

If there is only one marble, where did the other marble go? If you are post-trip marble, do you simply disappear, die? Irregardless, there were two marbles present at the same place and time where only one previously existed.

 

[MA-Caver]

yeah... I've read versions a plenty of this concept. One of them was very complex involving a story where a guy was (all at once mind you) his father, grandfather, brother, cousin, uncle, aunt, grand mother and sister. Seems that when he traveled through time he was also changed alternately from a woman to a man... thus through the course of time became either or the other grandparent/sibling. How's that for a mind bender? Wish I can rememeber who wrote that.. I keep thinking Heinlien or Foster.

Another one of my favorite time travel (short-stories) involves a big game hunter that goes back 65 million years to hunt a T-rex... he accidently stepped on a catapillar and didn't say anything about it... when he came forward through time the world was destroyed and he couldn't go back because the device relied on modern technology to run it.

Lots of the Grandfather paradoxes can be found... but is it really solved? I dunno. The theory still has some discrepencies to it.
But it is fun to bend one's thought waves all twisty and such once in a while.

 

[Deuce]

I've always thought the infinite time lines idea of solving the paradox problem to be interesting.

Within the universe there are infinite dimensions or time lines in which every possible "time" or situation exists. By travelling back through time, you are actually entering a different dimension that is very similar to your own, but at an earlier perceived time. In this time line, if you kill your grand father, you will not have been born, and the future will be changed in this particular time line only. So you can alter the paths of other dimensions, which would have been very similar to your present if interferance was non-existant.

With this theory, you can't travel back in time in the traditional sense (in one particular dimension or time line), but can visit other dimensions that are very similar to our past. So, if you return to the exact dimension that you originally came from, the amount of time that you were gone will have passed in that dimension. Or, you could go to another dimension very similar to your own where you had just left. To the people of this dimension, it would appear that you returned the instant you left, even though, the two "yous" (the one that left, and then one that returned) are actually from different dimensions, but nobody would notice the difference because the two dimensions would be nearly exactly the same.

Does anyone know if current physics supports or discouarages this theory? I have very limited knowledge on the principles of black holes, space-time, etc.

 

[Andrew Green]

Does anyone know if current physics supports or discouarages this theory? I have very limited knowledge on the principles of black holes, space-time, etc.

Yes, it's usually refered to as the many worlds theory in Quantum Theory. http://en.wikipedia.org/wiki/Many_worlds

 

[still learning]

Hello, Why change things? Do you think if we change some bad guys in the past that life might be easier? Maybe we may have a more worst person than Hitler or Stalin. Who knows? Maybe the bad guys erase the good guys? Who knows? Arn't you glad we can't change the past but the future? .....Aloha

 

[Tgace]

I once put instant coffee in my microwave oven...I almost went back in time.

If they invented powdered water, what would you add?

 

[Sam]

If they invented powdered water, what would you add?

oxygen, obviously.

( I don't know why that is obvious but what the hey it was the first thing that popped to mind)

 

[Andrew Green]

Hello, Why change things? Do you think if we change some bad guys in the past that life might be easier? Maybe we may have a more worst person than Hitler or Stalin. Who knows? Maybe the bad guys erase the good guys? Who knows? Arn't you glad we can't change the past but the future? .....Aloha

Well its not always a wanting to change things...

If time travel does become a reality, and historians go back a couple thousand years to watch the Crucifiction of Jesus... The fall of Rome...The building of the pyramids... Dinosaurs... or any other historical event, what danger to the present (if any) does that pose.

I don't think any scientist would go back and try to change a bad event in our past, the bad things help define who we are, and getting out of them made us stronger. Any changes could be either very bad, very good, or do nothing at all.

50 years ago there was a question of "If we walk on the moon, what will happen?" Fortunately scientists figured out enough to keep the people doing it alive before they stepped out of the ship

Let's hope they figure out enough about time before sending someone back...

 

[Flatlander]

Travelling backwards in time is categorically impossible. I say this because, were we to develop this capability in the future, would we not have already travelled back in time and screwed things up already?

 

[Andrew Green]

Can you prove that we haven't?

Not to say that anyone can prove that someone has come back. But hopefully by the time that sort of technology is around those using it will know enough not to go back and start messing with things. Or, if that multiple worlds theory is true, it doesn't matter. As all you will do is spawn off new dimensions anyways. And they would have been spawned no matter what you did, as long as there was the possibility of you doing them.