Michaelson

Howdy, my first post here so go easy on me if I do something wrong. For the record, I'm an undergrad in Australia, very new to these issues.

I have to say that I was pretty much blown away by the standard of arguments I read relating to determinism. Not that the issues are any clearer in my head at all now. Combatabalism is still a strange concept to me indeed, but I'm getting there.

Anyhow, I was just wondering what the consensus is regarding four dimensionalism? Does the theory relate to people's views on determinism? Does a four dimensionalist worldview necessarily lead to fatalism? And anything else you want to say about four dimensionalism.

Incidentally, it may seem as though I'm bleeding you guys for info for an essay or something, and that's not the case. I'm studying certain issues surrounding time travel in a correspondence course at the moment, and there's no student interaction at all and it's driving me crazy.

So I came here.

End of post,
Mik

tronvillain

Well, "four dimensionalism" is probably the position that I hold, though I have never actually used those words. It does not actually require strict determinism, in that the state of the "future" may not be completely explained by the state of the "past", and may be at least partially a brute fact. It does not appear to have anything to do with fatalism, since as far as I can tell fatalism means that something will happen in spite of what you do, and that is not the case here.

Now, exactly what are the issues surrounding time travel which are bothering you? My favourite solution to time travel is that it is only possible to make changes which produce a future that results in those changes being made; otherwise, you just loop over and over until the paradox resolves itself, most likely by the time machine not working.

Keith Russell

Greetings:

I believe in (at least) an eleven-dimensional universe.

Keith.

Michaelson

Allrighty, time travel then, and causal loops. I'll try to summarise a scenario put forth by Robert Heinlein in a short story By His Bootstraps:

...

Well as it turns out that story is far too complicated to summarise briefly.

But I'll try to modify a bit and ask the same question.

Tim goes back in time and meets his past self. To his past self he passes on the plans for a time machine. Tim makes sure not to duplicate the plans, because he is certain that time travel is a risky business. He himself, though, sets about secretly constructing this time machine, and upon construction sends himself forward to meet his grand children or something. Of course he then travels back in time because he realises that he must pass on the information on how to build the time machine to his younger self.

Now, that's all fairly standard time travel stuff, I know. David Lewis defends causal loops by saying that just because they're innexplicable doesn't mean they're impossible. So my question is not where do the plans come from. My question is, because Tim was so careful not to reproduce the plans, and it is the same copy being sent back over and over on what is presumably an infinite loop, won't they become worn and illegible, and eventually even dissintergrate over time? And what happens when they do?

In Heinlein's story, a book of translations which is vital is passed back, but it is actually a new version of the book which is passed back each time, copied out in the time that passes between being sent forward and then sending himself back. In that scenario, since any coherent time travel story, it seems to me, relies on the unchangable nature of the past, will each copy of the book of translations as it is copied out be an exact replica of the previous one?

That question actually just popped into my head. Ignore it if you like.

As I say, this stuff causes me all sorts of strife, so I'm sorry to ask questions without offering any content myself.

Cheers,
Mik

Michaelson

Keith,

Really?

Mik

ex-xian

Greetings and salutations, Mik,

So you side with the string theorists, huh? I've read some of the popular books on string theory, and it seems pretty convincing. I've had one semester of a calculus physics class, and I'm taking the second half as well as a class on relativity and quantum physics this semester. With what I learned about relativity last fall, as well as what we've covered so far this semester, we've only dealt with 4 dimesions.

My current physics professor, who is leaving after this semester, doesn't buy into any of the string theories. We also have a math/comp science professor with a master's in physics. He doesn't hold to any of the string theories either. One of the candidates that we've had to fill the open physics position started as a string theorist, but abandoned it after further study.

Like I said, my own formal training in physics hasn't shown me any more than four dimensions. I'm aware of the mathematical models of higher dimensional space, but you can consistently do math in any number of dimensions.

The PhD's I know seem to think that string theorists are in a sense just "playing" around. I listened to some recordings of lectures by Hawking and got the same idea.

Anyway, if there's any experimental data on string theories, I'd love to read about it if someone has a link or a book recommendation.


I don't know if four dimensions implies determinism. I think that the Hawking/Penrose equations (don't ask me what they are, I've only heard and read Hawking refer to them) allow space time to be either a sphere or an ever expanding three dimensional cone-like object. In either case, future events don't exist and cannot be known. That, to me, forbids determinism. Also, I'm pretty convinced by Kant's argument against strict determinism.

As far as time travel goes. Hawking/Penrose solutions, if correct, also forbid closed timelike curves; no travel into the past. And since the future doesn't exist, you can't go there either.

One more thing, to paraphrase Hawking, time travel is probably impossible because if it were, someone from the past would have gotten here by now. Of course, maybe this era is just too boring to bother with.

crocodile deathroll

I am a strong proponent of four dimensionalism, but isn't four dimensionalism just synomomous to eternalism?

ex-xian

Hmm? Maybe I'm misunderstanding things here. When you say four dimensionalism, does that mean anything other than that space-time is made up of four (x, y, z, t) dimensions? Three spatial, one temporal.

Michaelson

Maybe time travel is possible, but human existence doesn't have long enough to go for it to be developed. The meteor is coming or something, I dunno.

Anyway, four dimensionalism implying eternalism? I don't know, does it? I thought it implied that past and future times are real places, just as with the other three dimensions. Or is time an ever extending dimension, and the present is merely one extremity, so the past would be an actual place whereas the future isn't?

As I say, I don't know. What exactly does four dimensionalism entail? Don't suppose there's a good web resource someone could point me to which would explain in some detail the general theory, so as to give me some grounding when talking about it.

Cheers,
Mik

ex-xian

Mik, have you had any classes in linear algebra or vector calculus? I tend to think of time in terms of just one more vector, as you seem to do also. BTW, what is "combatabalism"?