The Grandfather Paradox

[flobadob]

I read the Grandfather Paradox link that buen posted and correct me if I'm wrong here, but I think I see a flaw. Assuming that there is only one time line, some time in the future someone travels back in time, then kills their grandfather. Ok. Now that person will never be born. However the single time line can surely remain, however now the time traveller never existed. Any takers?

[MarkRae]

You really are serious, aren't you?

Imagine (go on, give it your best shot) that you build a time machine, travel back in time, meet your grandfather AND DON'T ACTUALLY KILL HIM!!!

[flobadob]

What. The time line continues from that point, less me and whoever else. It's a new time line but it's still a single time line, not a parallel one.

[NazNomad]

pmsl@Butch ... Imagine when MarkRae actually does invent the time-machine and all people use it for is going back to killl their Grandfathers ... hahahaaa.

[MarkRae]

> pmsl@Butch

You're easily amused...

[NazNomad]

... but not easily impressed.

[flobadob]

I would find butch's comment a little witty, but this is actually the science section, not shatterbank, so no dogs allowed, sorry butch.

[MarkRae]

I should hope not!

[flobadob]

Dog/Neanderthals then.

[mibn2cweus]

. . . and here’s proof! I just haven’t figured how to travel back to a time before I was born yet.

[mibn2cweus]

I’ve already figured out how to travel back in time . . .

[woofgang]

neat one mibn!

[heathfield]

One of the best time travel short stories is 'By His Bootstraps' by Robert Heinlin. Still one of my favourites, with more twists than you can count! Luckily, it's actually available online. Scroll down here...)

http://www.xs4all.nl/~pot/scifi/

[Loosehead]

There will never be time travel because Ladbrokes exist.

[jake-the-peg]

A lot of the so called paradoxs regarding time travel come from the attachment that people have with the idea of cause and effect.

We see it all around but then we're not in the sort of extreme environments where this sort of thing might break down so I don't think flobadob's argument is bad - In fact I've considered it before.

I do think Loosehead's aregument is fundamentally flawed.

Small changes rapidly multiply and cause large scale changes - small air pressure changes cause large scale differences - the famous butterfly effect.

There are many random events in the form of radiaoctive decays all the time so I think a time traveller with a history of Lottery results would be sorely disappointed!

I'm more troubled by the "new knowledge" paradox whereby a time traveller brings new knowledge to the past - this may be the informational equivilent of breaking the third law of thermodynamics.

Of course it's entirely possible that if you could go back in time a consequence would be that all information of later times would be distroyed in the process - In which case travelling earlier than your date of birth would be suicide and a lot of these paradoxes would not arise

[ludwig]

// are time machines made just so people can go back in time to kill their grandfathers? //

Surely it would be easier just to kill your grandad now, rather than waiting until time machines are invented so you can come back and do it?

[bibblebub]

If your personal spacetime trajectory can take you to the paradoxical situation where you exist before you are born then subsequent actions by you are not going to retrospectively affect that events determining that trajectory.

[jomifl]

whilst on the subject of time and given that the past has gone and the future hasn't yet happened, then exactly how long is the 'present' ?

[ludwig]

// no it wouldn't .............he was dead before i was born. //

Well, there you are then - problem solved.