h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

ASSUMING TIME FLOWS FORWARD IN ONE DIRECTION WITH NO "BRANCHES"

Many people believe that you would have to do something big to cause a paradox. However, even the act of going back in time and changing something deliberatley would cause a paradox. For instance, if you write yourself a note to send to the past, your former self receives it, follows the instructions to do or not do something, then when your past self becomes present, you will not know you should go back in time and write the same note.

However, I believe that "forwards" time travel may be possible, but not "backwards". Therefore, you can go to the future and steal a technology, but can never return from "when you came from" to take credit for it.

All this is rooted on the fact of weither you believe in time as a constant, or if you believe in the multiverse.

---Fadkie The Frdy

'Course, then again you have to take in the other side...
Say you are going back in time to... stop the Titanic from leaving port. You go back, yell and scream and blow up the main deck. You go back in handcuffs. If you had checked the past newspapers of that day before you had left, you would find that what you did ALREADY HAPPENED. So technically, by this view, you could go back in time with every intent in the world, and you could do nothing to change the past, because it was all taken in account.
-Mystrunner

I believe that the reason we THINK paradoxes can occur is because of our one-sided view that time is a constant, flowing forward gently. However, multi-universe theories makes some sense to me (they all basically state that there is an infinite amount of universes where every single possibillity (argh-spelling) is existing parallel to the others, and we are the ones flowing through them- or that's what I can make of them)...
You will notice my disclaimer at the top of the last post...

---FTF

yeah. but who will know...?

The problem in going to the past would be the temptation to change history. I've been sitting here thinking where would I go? Back to see Cullodin Moor? See my Granny as a girl? Witness the discovery of America? It would be so tempting to change things. From the vantage point of the future to these events, we know how its all turned out, and it would be too tempting to try and change it.

Nature abhors a paradox

of course, it is also believed that paradox is sort of the scar tissue of space-time. A little bit of paradox never hurt anybody.

Post 6 ias the whole point of the movie 'The Time Machine'.
Annie

Post 6 is the whole point of the movie 'The Time Machine'. I saw it last night.
Annie

One theory is that if you were to travel back in time and make a change, you will move into an alternative timeline in which that change actually happened. You would not actually change the timeline in which you originally existed. This would mean that if I went back in time and killed one of my ancestors, which would prevent my own birth, it would not affect me. However, on returning to the present nobody would know who I was. That would take a bit of explaining...

The fact that the paradox exists dismisses the idea that Time Travels in a "straight line". There must be branches or the universe wouldn't work. The universe is a logical machine.

The problem with believing that you can change something in a multiverse and just follow another path is that the path could be disastrous. I recently read Stephen Hawking's "The Universe in a nutshell" and from how I understand it, every possible univere was created at the beginning of time, but based on their shapes and other things some existed and some fizzled out. So, if you were to go back far enough, you could change something in the very fabric of our universe, causing it to cease to exist. Not exactly pleasant, I'd think.

I have done some fairly ... no... down right stupid things in my days on this earth. To go back and fix these moments would save me the embarrassment or the consequence of the actions which time has taken away from my ability to change. But I have become a better person from the effect of my deeds. A person is the some total of their experiences and to change any would mean I would be a different person and I am pleased with the person I have become. However, if time would allow me the chance to change actions of the past and yet retain the lessons learned I would surely take it. But I believe to negate an action means to negate the experience learned and possibly send me down the path of selfdestruction I was not intended to take. My going back and choosing to not stay at that party with my friends and end up being grounded for one week might mean I would have had the freedom to ride my bike to a different party and find myself in front of a speeding truck. All our actions and those acted upon us bring us to this present point in life. Changing a moment in time allows perhaps my obliteration or the finding of a winning lottery ticket lying discarded by the roadside. I'll trust in my destiny and learned wisdom than to tempt fate by circumnavigating the already walked path. Paradox may have been created to protect us mortals from ourselves.

Okay... here's my view on this whole 'altering time' thing:
1) It is impossible to alter the past because it has already happened.
Take the titanic, say you went back in time to warn them about the iceberg. With all the fuss you kick up, the lookouts get distracted, and so don't give the warning until it's too late. Therefor the Titanic still sinks and IN EXACTLY THE SAME WAY.
2) It is impossible to alter the future because there is no future yet.
This means you can go backwards, but not forwards.
3) You can't alter the future by changing the present.
Since the present will instantly become the past the moment it is no longer THE present. Since we have already determined that the past is immutable, inflexible and totally unalterable, whatever you do now makes absolutely no difference whatsoever.
4) We are all just wasting our time here...
Since everything is either unalterable or unaccessable, we might as well all commit mass suicide right now...
...That's the theory anyway.

Nah... still got to go bungee jumping yet!

What if time travel existed as a way to switch between alternative universes, rather than move through different points within our own?

"the universe is a logical machine"
No it's not, humans are. And vulcans.

Humans? Logical?
Correct me if I'm wrong, but for 2000 odd years, people believed (and still believe) that the world was created by an all powerful entity. He created one man (Adam) and one woman (Eve). Now, surely if they were the only humans, we'd all have died of interbreeding by now...

OK, I rephrase it; we *like* logic. We try and explain things we cannot understand and once the idea of God was logical enough to provoke widespread belief that still survives today. But that's a different argument...

No... Humans /are/ illogical. The Vulcans say so.