Talk:Novikov self-consistency principle

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This is the talk page for discussing improvements to the Novikov self-consistency principle article.

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[edit] Clarify

this article need more clarification i think. does it simply means that it time is unchangeabe and you cannot go back in time and marry you mother because you haven't done it already? No paradoxis are possible beacause everything has already happened?

then it should say so. --Alexandre Van de Sande 17:19, 5 Aug 2004 (UTC)

Novikov didn't use an example ("Rather than consider the usual models for such a paradox, such as the grandfather paradox..."), he used a mathematical/quantam model. Salasks 21:29, Aug 5, 2004 (UTC)

This quote from the article makes no sense: "if an event exists that could give rise to a paradox, then the probability of that event happening is zero"

Let's say that a time traveller has gone back in time to when his grandfather, a paratrooper in WWII, is going to parachute down into occupied France during the Normandy invasion. He knows that his grandfather is going to survive the war and go on to father his father, but the time traveller is perverse and so he arranges a minefield in the area his grandfather's going to land. There are many different scenarios for how this could play out, with a certain probability of his grandfather landing on any given square foot of land and then subsequently stepping on any given square foot of land. However, according to the Novikov principle, the probability of him stepping on one of the patches where there's a landmine is exactly zero - there's no chance of it ever happening, because it didn't happen, and if it did then it would "change history" (actually, there's a small chance he could step on a mine, but if that happens the mine will turn out to be a dud with 100% probability). Novikov proved this mathematically, using certain assumptions of how physics worked and a simpler model involving billiard-ball-like particles. Bryan 16:05, 18 Jun 2005 (UTC)
My problem with this proposition is that even if the landmines don't blow up his grandfather, the time traveller will have changed infinite things in the past by his mere presence. The same deal with the "historic fire" example in the article: the traveller could bump into people on the street, distract people, leave his footprints, etc. which would alter the outcome of the future, perhaps dramatically. The only way the self-consistency principle can be true, as I see it, is that the universe maintains self-consistency by not allowing time travel at all. 65.11.216.245 08:55, 15 March 2006 (UTC)
But the point of the principle is that none of those things is different from what "originally happened." There always were footprints there, the time traveller just never knew about them until he made them himself. The distractions are what caused people to do the things that ultimately led to the time traveller's version of the present. Etc. Novikov applies to everything that happens, both big and small. Bryan 17:12, 15 March 2006 (UTC)

[edit] Philosophy

Some philosophers like Richard Hanley claim that the self-consistency principle is just non-contradiction which philosophers have used for thousands of years. gren 05:02, 18 Jun 2005 (UTC)

[edit] Flaw

This principle has a major flaw: one travelling into the future to pick up some object and take it back shall get the object, whatever it may be (including non-adherence to physical laws), because relatively to them, the people giving one the object have already recieved it from him when one returned.

I don't get your post but, if the NSCP is correct then whatever it is you're talking about won't happen (it might happen but then cancel itself out to achive an equilibrum), even if you have to be crushed by cement prior to doing whatever you said, if (and only if) what you said was a paradox. If it wasn't then the law does not apply. I might be terribly wrong, but this is how I understand it. -- Hexagon1 15:42, 15 January 2006 (UTC)

[edit] My interpretation

This principle is very straightforward if you look at the universe with certain assumptions:

  • there are a set of equations that are the laws of physics (some of which we may know, some which we may not), which describe how things work through spacetime in the universe
  • you assume counterfactual definiteness
  • the universe (or a universe) is just a solution of the above equations over all of space and time (like solutions of differential equations in math), from an external point of view

Consequences:

  • for some initial conditions, the solution may not be unique (there may be many equally plausible universes that satisfy the same initial conditions)
  • in any particular universe, there is only one thing which happens at any given place and time, which is predetermined; but they may not necessarily need to have a cause
  • by the nature of being a "solution", a universe must by definition be consistent; so that hypothetical universes containing "inconsistent" actions must somehow violate the laws of physics

—The preceding unsigned comment was added by Spoon! (talk • contribs) .

Please sign your posts. +Hexagon1 (talk) 07:27, 4 March 2006 (UTC)

[edit] A presentist view which makes the principle redundant

The principle is based upon an assumption that if time travel were possible the time traveller could return to an earlier state of the universe. The following explanation shows that asumption to be wrong, and as a consequence makes the principle redundant. Every particle in the universe, including those that make up me, travels on a trajectory through spacetime. Suppose I was to travel back through time to a point in spacetime that used to be occupied by the atoms that comprised my grandfather (say the year 1906): I would find that the atoms which comprised my grandfather were not there, as they were 'still' in 2006 where I had left them at the start of my travels. The only atoms that travel back in time are the ones that constitute the body of the traveller- all of the other atoms in the universe continue on their spacetime trajectories as before, and so are not found by the traveller when he/she arrives in the past. Given this, none of the supposed paradoxes arise, and so the self-consistency principle (in this context at least) is redundant. This seems pretty self-evident to me- am I missing something?

DoctorDen 1 April 2006 17.44 GMT (not logged in).

Yes. You're missing the fact that particles travel through space, not spacetime. In spacetime, the particles occupy positions. The whole of spacetime is a single construct. "The atoms that comprised my grandfather in 1906" (where we implicitly understand "1906" as some exact point in time) have a definite constant position, that we assume our time traveller can reach. Those atoms have a trajectory that will show them in a different spatial position in 2006, but they do not "travel" from the point of someone who can oversee all time.
Your point of view would imply that the past doesn't exist (physically), and hence time travel as a whole is impossible. This is a fine way of looking at things, in principle, but if time travel is impossible (as it likely is) then obviously none of this discussion is relevant. In any case, this is more relevant to the time travel article. 81.58.51.131 08:24, 7 April 2006 (UTC)

Doctor Den says: Thank you- that is very helpful. Can you recommend any references that explain how atoms have a definite constant position in spacetime, as I would like to read more.

DoctorDen 7 April 2006 20.35 GMT (not logged in).

A good article to try might be block time, it's all about this sort of conceptual model. Bryan 22:18, 7 April 2006 (UTC)

[edit] No mention of quantum mechanics?

Arn't the strongest arguments for the self-consistency principle all based upon quantum mechanics? For example, if your billiard ball was a quantum particle, then its interfearing with itself merely makes those trajectories rediculously improbable? I don't know enough about it to add this intelligently, but please get some input from someone who knows about quantum mechanics. JeffBurdges 19:35, 20 June 2006 (UTC)

Seems that way to me as well, in classical (non-quantum) physics if you know the position + velocity of the billiard-ball precisely the system is entirely deterministic and there is no probalility involved at all; so talking about the probability of when happens when the billiard ball hits itslef makes no sense unless you invoke quantum mechanical ideas (i.e. the unceratintly principle). Tomgreeny 18:24, 5 September 2006 (UTC)

Part of what makes this approach so intriguing is that it clearly shows that macroscopic objects, moving according to simple Newtonian Dynamics, cease to behave deterministically if self-interaction via time-travel into the past is introduced. The collision itself is still entirely "classical", but since the position and time at which the collision occurs is dependent on the trajectory of the future ball, which in turn is dependent on the position and time of the collision, things become non-deterministic without resorting to any specific kind of non-classical physics.
TeraBlight 00:04, 20 September 2006 (UTC)
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