No you can't go back and kill your father.

[JohnF]

False requirement. God we have been through this soooo many times on SFN.

 

And how is that supposed to be an explanation then?

[Sayonara]

It's not. It's supposed to be an open invitation for people to use the internal search engine to look for the previous exhaustive threads on the topic, which is what all members ought to do anyway before they create a duplicate thread.

[JohnF]

It's not. It's supposed to be an open invitation for people to use the internal search engine to look for the previous exhaustive threads on the topic, which is what all members ought to do anyway before they create a duplicate thread.

 

That would be a lot of searching and reading to do just to post a response, not a new thread. If you happen to know which thread the particular discussion you are referring to is in then please post a link so that I can read it.

[Sayonara]

When I said "god we have been through this soooo many times on SFN" I did actually mean that this entire thread is a duplication (and not "the second time it has come up", but more like the sixth or seventh time).

 

However, I can see your point about single responses. Ideally the OP would have added his comments to one of the open existing threads instead of starting his own duplicate, and this situation would never have arisen.

 

I don't have the URL for the last thread in which we discussed the energy/matter displacement fallacy to hand. It was done with some time ago.

[bombus]

Hoo-ya unneeded complexity!

 

Well, if time travel (back and forward) is possible this 'complexity' would be needed in order to prevent 'problems'.

 

You could of course be right, and time travel is simply impossible, but if it is possible, it would probably need this 'complexity' to work.

 

Its also similar to certain theories on reality and conciousness that stem from Quantum Theory - I'm sure I don't have to explain why, you guys know all of that stuff don't you...

[JohnF]

Sorry, I misunderstood what you were posting about. It looked like you had singled out my comment that if the time traveller was made from something outside of this Universe he would be able to kill his father.

 

I was rather flummoxed at the thought of trying to find a thread that dealt with that particular element, but I did have a try

 

I assume then that your comment of False Requirement was directed to my comment and the rest was directed at the thread.

[Sayonara]

Yes, sorry. I should have hit return a couple of times between the sentences

 

I'll have a crack at finding the thread but to (very) briefly summarise the counterargument, there is no plausible requirement for the matter/energy contained in the universe to exist in particular quantities at any given time. This is because, if we are already considering time to be a navigable property of the universe, then we have to take "the universe" to mean a container which has time as a dimension - in other words "the universe" as a whole means all places at all times. The total matter/energy therefore does not exceed itself just because it is moving around the universe.

[JohnF]

I'll have a crack at finding the thread but to (very) briefly summarise the counterargument, there is no plausible requirement for the matter/energy contained in the universe to exist in particular quantities at any given time. This is because, if we are already considering time to be a navigable property of the universe, then we have to take "the universe" to mean a container which has time as a dimension - in other words "the universe" as a whole means all places at all times. The total matter/energy therefore does not exceed itself just because it is moving around the universe.

 

Well that's given me something to think about. I assume entropy was considered.

[Sayonara]

I don't recall... certainly mathematical considerations of entropy will become more exotic, but in the case of time travel into the past, entropic principles are conserved.

[ydoaPs]

Well, if time travel (back and forward) is possible this 'complexity' would be needed in order to prevent 'problems'.

 

You could of course be right, and time travel is simply impossible, but if it is possible, it would probably need this 'complexity' to work.

 

Its also similar to certain theories on reality and conciousness that stem from Quantum Theory - I'm sure I don't have to explain why, you guys know all of that stuff don't you...

 

You misunderstand. I said nothing about the possibility of time travel. I've not seen anything which rules out travel backward through time. I did say, however, that it is impossible to go back in time to kill your father before your conception. All one needs to do is analyze the situation chronologically. The "paradox" occurs when one follows the traveler instead of the timeline.

[JohnF]

What if you went further back in time to become your Fathers Grandfather?

 

Your Father is only born because you impregnated his Grandmother.

You now go forward in time and kill your Father.

You are not born so you don't go back in time to become your Fathers Grandfather.

Your Father is not born; you haven't actually killed him but he is not alive.

You are still not born; no Father

[ydoaPs]

JohnF, you are still analyzing the situation anachronistically.

[JohnF]

JohnF, you are still analyzing the situation anachronistically.

 

 

You exist in the present.

You go back in time to become your Fathers Grandfather.

You still exist.

 

Your Father is born because you impregnated his Grandmother.

You still exist.

 

You go forward in time to just before your Father impregnates your mother; with you.

You still exist. You have done nothing to threaten your existence.

 

Now the tricky part

 

Assuming that so far everything is OK, you have free will; and perhaps a loaded gun.

You kill your Father.

Now what happens? Where in the chain of events does the break now occur?

 

EDIT: Perhaps all that is required to create the paradox is having the means and the intent. It's ironic that the Mens Rea will be required to prosecute you for murder but it will also stop you committing the act.

[Robonewt]

How about this for a paradox.

 

You go back in time, but rather than kill your grandfather, you go visit the young Einstein and explain to him the theories of Relativity, which you have learnt from his teachings.

 

The question is, where did the theories come from? He would not have known them had you not gone back to explain them, but you would not have been able to teach them to him if you had not learnt them from his teachings……..

[Sayonara]

How about this for a paradox.

 

You go back in time, but rather than kill your grandfather, you go visit the young Einstein and explain to him the theories of Relativity, which you have learnt from his teachings.

 

The question is, where did the theories come from? He would not have known them had you not gone back to explain them, but you would not have been able to teach them to him if you had not learnt them from his teachings……..

 

This is not a paradox but another instance where the reasoning is tracking the wrong commodity.

 

You might as well ask "Einstein proposed relativity but where did the information come from?" and leave time travel out of it all together.

[JohnF]

Perhaps there is no past or future to visit; just the present. If you could move to the past or future you would find that you are the only thing that exists there. You can't kill your father in the past because he doesn't exist there; unless he went with you from the present to the past.

 

An analogy might be two dimensional beings living on the floor of a lift.

The lift is constantly moving up through a dimension they only see in passing.

One of them uses energy to lift himself off the lift floor, to the the future, and in doing so finds he's alone.

Using energy to move down, to the the past, he would find himself alone again.

He has to keep using energy to maintain his position above or below the floor but once the energy is exhausted he just returns to the lift floor; the present.

[Kailassa]

The Australian New Scientist once published an article proposing a mechanism for time-travel. First you catch a worm-hole, then you anchor it. From then on you can travel back along the worm-hole to the time in which it was anchored.

 

They said you could only travel back, not forward, but I have a hunch that travel must be possible both ways once it is set up, and that you will be able to travel to any time in the future in which the worm-hole will be anchored.

 

Much as I like the explanation for why you can't kill your father before you were born, I'm sceptical. I believe the time-line in which your father lived will remain unaltered, and a new time-line will branch from it in which you don't exist. So we have two time-lines from the moment that you changed the past, and you no longer belong in either of them, as, by your actions, you have taken yourself out of the time-line in which you can be born, and landed yourself in a time-line in which you cannot. Therefore, at the moment you change your past, you will simply cease to exist.

 

From the point of view of your peers in the future you came from, your father was not killed, and you got into a time machine and were never heard from again.

[Edtharan]

Think of the time line like a Laser beam.

 

You fire the beam towards a beam splitter (this is the event that would create two separate time lines).

 

After the beam hits the splitter, two separate beams are created. One beam travels towards a light meter that detect the arrival of the laser beam (to represent a time line where no time travel occurs) - Path 1. The other is shone towards a mirror that bounces the light beam directly back towards the beam splitter (this is is to represent a time traveller travelling back through time towards the critical event) - Path 2.

 

We adjust the position of the mirror so that the reflected light does not deconstructively interfere with the light coming from the splitter on the second path.

 

If we turn down the laser so that only 1 photon is emitted at a time, then we should get half the photons reaching the detector (taking path 1) and that means that the other half of the photons are travelling along path 2.

 

In terms of time travel, this second path is a time traveller travelling back in time and not interfering with events to the point that they could not go back in time and change events.

 

Now we adjust the mirror so that it's reflected light would exactly cancel out the incoming light (deconstructive interference). This makes any light travelling along path 2 impossible. What we will find is that the photon detector in path 1 will detect 100% of the photons.

 

This is what the situation would be like if a time traveller changed the past to the extent that they could not have been able to travel back in time (like killing their grandfather, father, mother, or any other ancestor).

 

This negative interference essentially acts as protection against drastic changes to the past.

 

Remember, if you don't exist to go back into the past, you can't go back into the past. Therefore, if you are back in the past, you must be able to go back into the past, and a scenario where you can't go back into the past can not exist. So it doesn't.

 

The question is, where did the theories come from? He would not have known them had you not gone back to explain them, but you would not have been able to teach them to him if you had not learnt them from his teachings……..

Or try this one:

 

You travel into the future and find a statue of you as the first time traveller. As proof of this you take the statue and return to the past. As the reward, the people erect the statue that you brought from the future as proof of your accomplishments (however at some time in the future it mysteriously vanishes, assumed to be stolen by some vandal).

 

Question: Who carved the statue? (and extra points if you can say why the statue doesn't weather away?).

[Kailassa]

(and extra points if you can say why the statue doesn't weather away?).

 

I travel to 3007 AD, and find a newly erected marble statue of myself and bring it back with me to 2007, and it's erected at the same latitude/longitude/altitude as I took it from. The people looking at that statue in 3007 see it suddenly age, looking strangely eroded. In 1000 years time, (3007 again,) I'm looking at that same statue, having travelled forward in time, but it's rather old, and barely recognisable. I take this decaying statue back, and erect it in the same location. In 1000 years time I am at the location of the statue again, but now the lump of broken rock there is not recognisable as a statue at all, and I don't touch it. So this time, returning, I bring nothing, and nothing is erected.

 

In 1000 years time, I again find a nice new statue and bring it back, and so the loop continues.

[Edtharan]

I travel to 3007 AD, and find a newly erected marble statue of myself and bring it back with me to 2007, and it's erected at the same latitude/longitude/altitude as I took it from. The people looking at that statue in 3007 see it suddenly age, looking strangely eroded. In 1000 years time, (3007 again,) I'm looking at that same statue, having travelled forward in time, but it's rather old, and barely recognisable. I take this decaying statue back, and erect it in the same location. In 1000 years time I am at the location of the statue again, but now the lump of broken rock there is not recognisable as a statue at all, and I don't touch it. So this time, returning, I bring nothing, and nothing is erected.

 

In 1000 years time, I again find a nice new statue and bring it back, and so the loop continues.

It comes close. However, in the last part, you state that a nice new statue is there for you to pick up, but you don't give a reason for that statue to be erected. In the initial example the statue is erected because you brought it back. You broke the loop with the statue eroding away so that eventually there was no statue to bring back to be erected.

 

Once a new statue is created at some point in the timeline, an entirely new timeline is entered into. One where you didn't bring a statue back from the future, but one that was carved in the intervening period of time.

 

This new proposed time line can lead into the paradoxical time line and can therefore be the source of the statue (that is the solution to the paradox is that the statue was constructed in a different time line altogether).

 

The main problem with this solution is it side steps the entire loop situation. It states the "loop" starts with a statue being carved after a time traveller returns from the future, the cycle then continues with time traveller finding the statue in the future and returning with it. It eventually weathers away and the loop is exited.

 

It is more like the loop on a roller-coaster than a true closed loop. It is an open loop rather than a closed loop.

 

Nice try though