[j. d. worthington]

Originally Posted by Interference

I take your point, JD, but I don't think the Universe is a stranger to dealing with cataclysmic events. What do black holes do if they don't locally mess with spacetime?

There's a rather large difference... black holes are something that are (so far as we know, anyway) are created naturally... they are the end result of certain aspects of the physical universe without any conscious control or development. Time travel would require a conscious manipulation of the basic fabric of spacetime (at least, as said, for anything larger than the tiniest particles), as it does not naturally allow flow both ways, only one for anything of larger size.

Of course, I have a conveniently non-scientific view of spacetime. In it, I can envisage all time and space taking a form where if you mess around with one bit of it, the rest doesn't get too upset about it, certainly not to the extent of going into self-destruct mode.

Here's where I start running into serious problems with the concepts behind the terminology... it may simply be a different idiom, but the universe doesn't "get upset" about anything. It isn't conscious. It is a machine. Period. Living beings within the universe may be a different matter, but the universe itself shows no signs whatsoever of consciousness, and therefore does not have any emotional state of any kind.

Therefore, it doesn't "go into self-destruct mode"... it's more of an analogy to an unravelling of a garment, once a tiny piece of it gets snagged on something; though it may be something completely negligible in itself, the physical effect of the disruption of the fabric, beginning on an almost unnoticeable level, can eventually cause the entire garment to unravel... yet the garment doesn't "self-destruct"... it it "chaoticized" by a random element. So with humans time-traveling. We can't consciously will to affect the universe in such a way and bring it about because we willed it; instead, the very fact of such time travel may (note, may... there is a heated debate on this one ongoing, though the evidence seems once again to be piling up in favor of the older model ruling time-travel out for just this sort of reason) be just such a physical disruption of a sort not naturally part of the fabric of spacetime, to cause such an outcome. Which leads us to --

I think even some of the more enlightened humans are really two-faced. We say "Oh, the insignificance of our existence" when we see a picture of our planet from the moon, but then we go right ahead and place ourselves at the top of the importance chart when it comes to a hypothetical list of things that could bring the universe to an end. Is it so hard for us to believe that nothing we can ever do will ever have a lasting impact on a Universe that, let's face it, only endures our existence for a fraction of a fragment of a microsecond in cosmic terms?

Again, it isn't us as human beings that are important here... the same is true for anything that would create an artificial disruption of this sort in the fabric. It has nothing to do with our ego... it could be a slug, should such exist with such a power. It could be a conscious planet... it could be a conscious galaxy (given any such unlikely phenomena). The point is that is it a disruption of naturally-occurring physical laws, and therefore a disruption of the very nature of entity itself. Which, frankly, is why I still think that time-travel is always going to be an impossibility in actuality... however much of a theoretical possibility it may be.

On a couple of other points:

Agreed, but the difference would be minor, like an abrasion. Important to humanity and possibly our planet, but of no real import to the rotation of the galaxy or the galaxies around us.

Again, you're making the mistake of comparing the universe to a biological organism, and an abrasion (again, something which occurs naturally all the time) to a genuine disruption of the naturally-occurring order of the universe. There's a huge difference there. And, again, anything that affects time (which is predicated on the very movement of the universe itself) will necessarily have an effect upon the whole, as it is all involved in creating that state which we call "time". (Actually, Clark Ashton Smith did a rather neat little bit with this in his "The Chain of Aforgomon", where a sorcerer's demon threatened him that, when he conjured him again, the pentacle wouldn't hold him. Of course, the sorcerer didn't ever call him again... but a friend of his, many incarnations later, cast a spell to recover memories of past lives, and thus relived a spell where he had turned time back on itself... and so everything in the universe repeated at that point, and the demon's prophecy was fulfilled. Note: None of the actions were repeated in any sense we would understand... yet, paradoxically, they were, in effect... and that was quite enough.)

If I create a localised paradox, why should it have any more repurcussions than my amplifier feeding back would have on a West Life gig in Sydney (sadly, can't get them much further away from me than that). Would the Universe - and that means every part of every part of everything from what we see to what we can't possibly imagine - really reel in pain if I went back in time and gave myself a better career or a better lunch? Yes, there'd be knock-on effects, but only locally, only on this biosphere.

Again, the biological analogy. No, the universe would not "reel in pain"... the universe would not be aware. Beings within it might be aware of something happening (or might not, depending on the effect and the rate of speed of its result). And yes, this would be the case even in such a minor thing... because a macrocosmic body violated the normative physical laws under which the universe works. You are seeing the relationship as too limited. What is time? How is it "created"? What makes it? How does it relate to the working of the universe? I think you'll find that you simply can't have a paradox in time without involving everything in the universe. It is impossible for it to be localized. Earth, our solar system, our galaxy, have some peculiarities in the way time flows here, but the basic nature of time is related to the basic nature of the structure of physical entity, and cannot be separated from it, or isolated from the whole in any way.

As for your other query:

Would Hawking have been stupider if Einstein had died in a Nazi concentration camp?

No, not stupider. But he wouldn't have had the information he has found necessary to build his own models. Again, interrelationships such as this are actually specious... they don't apply; but taking the question qua question... Einstein himself would not have developed relativity had it not been for Galileo, Copernicus, Tycho Brahe... or Michelson and Morley. They would each have been as brilliant in essence... but without the foundation to work on, they would not have achieved what they have. (They may have achieved other things equally valuable, but they would not be the same things.)

Incidentally... it may not "destroy" the universe, but it would cause a major disruption, because time cannot be turned back on itself, nor created before it exists, without involving the whole. One might as well expect to drop a 10-ton boulder and expect it to fall up under normal conditions... it's physics, not teleology, involved here.