Time paradoxes and theories and stuff

[Flurgenspurg]

I just thought of something about time paradoxes and i haven't heard anyone say this but it seems really obvious... I thought that if you were able to travel through time and then you went back with the intent of killing your dad before you were born it would simply be impossible to kill him. I'm not saying the universe "protects itself" by stopping you creating a time paradox, i'm saying that if you had killed your dad before you were born then you wouldn't have been born, thus not existing to kill him in the first place. So if you went back in time wanting to kill him you would know for definite that you couldn't, SOMETHING would stop you no matter what.

 

Another thing i thought about was, if you said to yourself "if i ever made a time machine i would go back in time and give it to myself" then you would know for definite if you were going to make one or not because if you had you already would of met yourself. Something else about this supports my theory of time, say you did create a time machine in the future (well you didn't, you'll understand in a minute), then made a copy of it and brought them both back to the present to give one to yourself then go off on an adventure or whatever. So the "present" you has already planned for this, and also goes on an adventure or whatever, knowing you have to at some point create the time machine. Of course, you can just go straight there, and then you realise you have a time machine to copy which makes the process much faster. So you make an extra one and then go back and give one to yourself then go on an adventure (the same one as the "first" you had). This lead me to think that that will keep on happening infinite times, and that there are an infinite number of you. Also you may have realised that you didn't at ANY point create the time machine. It's kind of like the chicken and the egg, if this were to happen it could just appear out of nowhere, but that suggests to me that if time travel WERE possible, it might start around this century, because we probably have the tools to copy a time machine around now, though i may be wrong about this.

 

Which leads me to my theory of time, which i've thought for a while now. It's that in our universe time is made up of infinite "frames" of time, the only way i can explain it is an animation which is made up of frames. This would explain the infinite cycle of the person getting the time machine then going back to himself, giving himself the time machine, then that person would go and do the same thing and it would go on forever. My theory of time is like, say in one "frame" of time 9/11 is happening, but it wouldn't go like an animation, each frame would "stay within itself" and would continue, it wouldn't flow between them, but each one frame is a tiny bit more forward in time. I know i said infinite frames, and i know the space between frames couldn't be infinitely small, but i really don't know how many frames per second time runs at (lol).

 

So those are a few of my ideas, just wanted to know what anyone thought although i'm probably completely wrong lol.

[iNow]

Ever heard of the chronology protection conjecture?

 

http://en.wikipedia.org/wiki/Chronology_protection_conjecture

 

http://www.sciam.com/article.cfm?articleID=0004A1CD-BAEA-1D52-90FB809EC5880000

[Flurgenspurg]

Someone always gets there before you

[Edtharan]

Ever heard of the chronology protection conjecture?

If you take a beam of light, split it and send it back along itself, then it can with interfere constructivly or destructivly. Any wave does this.

 

A time traveler could be described by a quantum wave function and when they go back in time, they could interfer with them selves. This might be constructive interference (like in the case where you give your self a time machine, then go back in time and give your self a time machine) or it can be destructive (like going back in tiem and killing your grandfather, or father, or self).

 

Destructive interference will prevent the second scenario from occurring, but constructive interference will cause the first scenario to always occur (if it occurs at all it can't not occur - call it quantum destiny).

[Riogho]

So you believe in free will?

[Slinkey]

A time traveler could be described by a quantum wave function and when they go back in time, they could interfer with them selves.

 

Do you need to go back in time to do that? Sorry. Had to say it!

 

Back on topic now:

This all depends on how you view the universe. Is it one time linear universe or is it a many-worlds universe where every quantum choice leads to a new universe where each possibility is played out.

 

David Deutsch argues for a many-worlds scenario. Others do not. Personally, I don't like the many-worlds scenario as I'd like to know where all the enegry comes from for these new universes to be created every time there is a quantum choice made. Maybe there are an infinite number of universe running concurrently with ours and quantum choices make us leap from universe to universe. ie. we don't have a place in any one universe but our choices determine our position within a "multiverse". Within this kind of universe you might be able to go back and kill your father before you were conceived, but it wouldn't neccesarily play out in any universe you find yourself in at any given moment.

 

In a linear universe where there is only one universe and quantum choices do not lead to more universes the situation is somewhat different. You would not be able to go back in time because in your universe there would already be a history that includes your appearance in that history. ie. you would only be fulfilling what actually happened and you certainly didn't kill your dad.

 

I like the second universe myself as it protects my past!

 

So you believe in free will?

 

No. But then I would say that!

[Mr Skeptic]

If it were for some reason possible for you to travel back in time before you were born and change the past, it would be possible for you to eliminate your own existence. Simply send a letter back in time telling a paranoid government official that your father is an evil terrorist bent on destroying the world, and explain how they need to send the letter back in time to themselves after killing your father because if they don't then they wouldn't receive the letter in the first place. This would be true because otherwise there would be no reason to send the letter.

 

Result: you cause your father to die before you are born, causing you to cease to exist. The cause of your non-existence is then perpetuated by the government instead of you.

[Slinkey]

.....Simply send a letter back in time.....

 

And how do you exist in order to do that?

[Sayonara]

And how do you exist in order to do that?

Depends on how time travel actually works (if at all), but there are several possible answers. Bridged timelines and pre-intercession influence are two of them.

 

This topic has done the rounds on SFN again and again and again and oh my god again, and it is very rare to see an original or thought-provoking discussion.

[Slinkey]

I guess it is one of those discussions that when anyone comes across it they immediately have a flood of thoughts on the myriad possibilties. Kip Thorne did an interesting discussion on it in his "Black Holes and Time Warps" and I am just finishing "The Fabric of the Cosmos" where Greene talks about time machines also highlighting Deutshe and Thorne.

 

In both cases there is universal agreement that although time travel may be possible you would not be able to travel to before a time before the time machine was invented which satisfies the chronology protection conjecture up until the machine is invented (in this case by moving one end of a wormhole at high speed relative to the other end). After this causality could likely suffer.

 

There is also a problem with radiation feedback in the above scenario not to mention the technical difficulties with creating a wormhole in the first place let alone putting one end on a spaceship and flying it at near light speed! As such they have pretty much ruled out it ever happening in reality.

 

It will forever be the domain of science fiction I reckon.

[Mr Skeptic]

And how do you exist in order to do that?

 

You don't. You never existed. The government sent the letter to themselves.

[Slinkey]

Who told them to do that?

[Mr Skeptic]

Who told them to do that?

 

They did, of course.

[Slinkey]

They did, of course.

 

I think you'll find that you did.

 

Simply send a letter back in time telling a paranoid government official that your father is an evil terrorist bent on destroying the world, and explain how they need to send the letter back in time to themselves after killing your father because if they don't then they wouldn't receive the letter in the first place.

 

You explain how they need to send the letter back in time after killing your father. Who told them to do that? You did.

 

Wihtout you initiating the letter sending no one sends a letter in any direction through time. You have to exist in order to do this and you can't if your father is dead.

 

A linear time does not allow for these kind of paradoxes.

 

A many-worlds universe could however allow for such chicanery.

 

Something just occurred to me.

 

You go back in time and give the letter to a military official. The letter details how your father should be killed for whatever treasonous activities. The officials act immediately kill your father. You stay in order to see that they have done exactly as you ask.

 

Now what happens? Can you get back in your time machine and return to a future that no longer exists?

[Mr Skeptic]

Slinkey, you didn't read the second part in which the letter says that not only should they kill your father, but that they need to send the letter back in time or they wouldn't receive it. This would be obvious to them because otherwise there would be no one to send the letter in the first place since the events in the letter would have never happened.

[Sayonara]

If you are imagining a single timeline, this scenario still attracts the Origin of Information problem.

[Mr Skeptic]

If you are imagining a single timeline, this scenario still attracts the Origin of Information problem.

 

You mean like how a time machine might be used to generate infinite knowledge by repeatedly sending information back in time?

[Slinkey]

You mean like how a time machine might be used to generate infinite knowledge by repeatedly sending information back in time?

 

It's like this:

One day you are sitting in your room and there is a knock at the door. You answer it to find a much older version of yourself with a noticably wild look in your eye. Your older self explains to you that he has come from the future and has something for you, and hands you a package. He then leaves without further ado and you never see your older self again.

 

You open the package and find the blue prints for a time machine. The same time machine your older self just used to come back and give you the blue prints. It takes you 30 years to build the machine (hence your wild eyes) and you use it to go back in time and give yourself the blue prints because if you don't, then you won't have the blue prints to build your time machine!

 

However, where did the blue prints come from in the first place because you simply gave them to yourself?

 

Here's another scenario which shows no matter how you cut it, a single time line universe, just doesn't allow you to play games with the past:

 

A serial killer decides you are his next victim. He has picked you at random by some strange serial killeresque reasoning but his method of killing is unusual. He likes to go back in time and eradicate members of your family and thus expunge you from existence entirely.

 

He goes back in time and finds your grandfather. Your grandfather has just narrowly avoided death in the war but his time is nigh as the serial killer kills has his evil way as soon as granddaddy arrives home from leave.

 

Can this happen?

 

No. Not in our above described universe.You have to exist in order for the serial killer to pick your grandfather as his victim. If you don't exist he can't choose your granpappy!

[Edtharan]

Result: you cause your father to die before you are born, causing you to cease to exist. The cause of your non-existence is then perpetuated by the government instead of you.

This chain of events can occur if (and only if) you exist to start the chain of events in the first place. So if you don't exist, then you can't have started the chain of events. If the chain of events dosn't exist, then you could exist.

 

This all depends on how you view the universe. Is it one time linear universe or is it a many-worlds universe where every quantum choice leads to a new universe where each possibility is played out.

I think that it is a bit like the Particle/Wave duality. Just as the Universe can be though of as linear (particle) it can also exist as a multiverse (wave).

[J.C.MacSwell]

Someone always gets there before you

 

Don't feel bad. I'm heading back now to give your idea away to the person who will get the credit for it. Neither he nor I are original thinkers but we manage to pilfer lot's of ideas with our time machine (we stole the design for it also)

[iNow]

Someone always gets there before you

 

If you look and see who is actually credited with coining the term/idea, you'll notice that you're in pretty good company.