Talk:Causality (physics)/Archive 1

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Removed bulk of the text

I've removed the bulk of the text that was here, because it was impartial, unencyclopedic, and seemed rather irrelevant. Much of it was also redundant, when paired with the text that I've moved here from the "physics" section of causality

--Anakolouthon 22:41 3 Jul 2003 (UTC)

It seems to me that causality could be more quantitatively defined in terms of information retained, the degree of correlation across an event boundary. Has anything been developed along those lines? Fairandbalanced 08:38, 23 Aug 2003 (UTC)


Causal contact

The thing about the reader being in causal contact with Edward Witten due to an article on Wikipedia is... odd. I'm not quite sure what point it's trying to convey. It's also a self-reference. Is there an example more motivated by physics that can go there?

RSpeer 19:43, Apr 23, 2005 (UTC)

Well, it's trying to convey that even two things that seem completely independent and remote can still have some kind of causal effect on each other. For example, every particle in space exerts a gravitational force on all other particles. However, the magnitude of this force becomes really small as the distance between two particles becomes really large.

66.143.152.106 04:27, 3 December 2005 (UTC)

Note:Gravity,Electromagnetiscm,etc can be shielded,deflected or weakened (possibly to zero) effect.If we accept that interaction isn't instanteneous,it propogation is affected by the whole universe,it space curvature.magnetic fields,motion of gravity sources,etc.

Causality breakdown

In the quantum mechanical realm does causality not break down, and effect has the potential to preceed cause? I am currently looking for citation on this, I know that I read it somewhere on Wiki... --HantaVirus 13:57, 27 July 2006 (UTC)

The Nature of Causality

There are a wide range of views on causality:

1. To some (e.g. Karl Popper) causality is superfluous. Bertrand Russell said "In advanced science the word cause never occurs. Causality is a relic of a bygone age."

2. Others, like Judea Pearl and Nancy Cartwright are seeking to build a complex fundamental theory of causality (Causality, Cambridge U. Press, 2000)

3. At the other extreme Rafael Sorkin and L. Bombelli suggest that space and time do not exist but are only an approximation to a reality that is simply a discrete ordered set, a "causal set."

4. Or perhaps a theory of causality is simply the theory of functions. This is more or less my take on causality (and possibly that of Herb Simon).

R. Jones, Professor of Physics, Emporia State U. —The preceding unsigned comment was added by 164.113.103.49 (talk) 20:08, 6 December 2006 (UTC).

Those are all very interesting, but since this article is Causality (physics) and not Causality (philosophy) I don't see your point. Physical causality is experimentally verifiable, and a matter of objective measurement. Not philosophical masturbation. --75.49.222.55 01:25, 8 October 2007 (UTC)

Unclear reasoning

The current text says:

For example, the notion that events can be ordered into causes and effects is necessary to prevent causality paradoxes such as the grandfather paradox, which asks what happens if a time-traveler kills his own grandfather before he ever meets the time-traveler's grandmother.

How can a "notion" prevent a paradox? This part of the article is badly argued.

One argument against time travel is that if it were possible for the result of a long sequence of temporally connected interactions to continue from a given year, say 2050, to an earlier year, say 1950, then that train of events could involve itself in the destruction of its own earlier train of events. There would under those circumstances be no grandson to come back in time and kill the grandfather so the grandfather would produce the father and the grandson would come back in time to kill the grandfather. There is an infinite loop. "Cause and effect" does not prevent a paradox. Instead, it ensures that such a paradox (or, rather, such an infinite loop) would occur.

The argument also rests on the assumption that each loop would turn out in the same way. Supposing that the Universe was not planned out from the beginning, the grandson might, on some subsequent loop, not decide to go back in time and kill the grandfather. Then the loop would have a finite number of terms.

Probably it would be better to just cut this part of the article.

A much more important feature of human thinking about causality has been omitted. That is the tendency to look at a "trigger pulling event" as the "cause" of an event, while ignoring all the other factors that need to be present to produce the "result." "The water is boiling in the teapot because I lit the gas."

A third consideration that has been left out are the atomic events that appear to be "backward going" versions of otherwise identical events that are "forward going." These events appear to some to be of a class of interactions that ignore the "arrow of time."

And a discussion of causality can hardly be divorced from a discussion of that arrow. P0M (talk) 04:12, 3 April 2009 (UTC)

About the sentence you quote. You seem to overlook the very specific (mathematical) meaning of the word "ordered". It implies the property that if a < b and b < c then a < c,and consequently a cannot be the effect of c. This specific property avoids casual loops and their paradoxes. Now I do agree that this can be worded better, since you will not be only person to which this isn't obvious. (TimothyRias (talk) 07:11, 3 April 2009 (UTC))
The argument stated is circular. (It is also in all likelihood just a tautological statement of something that everybody knows, at least as far as macro events are concerned.
Symbolically, one can order things any way one wants to. Math really is not involved here because events are not numbers. Math and some implications drawn in from our general knowledge can be used to make a testable assertion, however. Simply say that a is an event at time t, b is an event at some time t+n, and c is an event at some time t+n+m. The assertion that the article is trying to prove is that there is no way to get an event produced by c that occurs at t or in fact at any time = t+m+n-p. People who entertain ideas about wormholes, etc., etc., also entertain the possibility of just such a sequence of actions.
Another way to look at the symbolical situation that (a) you leave yourself open to, and (b) appears to some to occur in nature on the micro scale, can be explored by changing the symbolic representation a bit. Let says that → means "produces" in the sense that a → b means that a is a trigger event in some physical situation that will result in the appearance of event b. In nature, this kind of thing happens in all kinds of biological clock devices. It is mirrored in computer circuits wherein a number of chips are arranged in a (schematic) circle. When the computer is turned on, a capacitor is charged, the capacitor discharges to send a signal to chip a and following that a→b→c→d→a. The object of arranging the circuit in this way is that all these chips can also send out other signals, either independently of any other input or as the result of an "and" event or an "or" event such that if, say, b is triggered by a and happens to be getting a signal from z then it will send out a signal to some other chip q. The only thing that distinguishes b→c events may be time.
If we look at the "arrow of time," then special attention needs to be paid to micro events that have been described as j↔k. Event j appears to cause event k, and event k appears to cause event j. Observers note these short sequences at other times in their lives, but to them they appear to be the same kind of event just seen moving in a different causal order.
What humans do not often experience are shards of glass on the floor being somehow driven from there and assembling themselves as a sugar bowl on the shelf above. The probability that any one fragment would be thrown up from the floor is incredibly small, and the probability that the whole bowl would come together would be the product of all the individual probabilities, times the product... So one would expect to wait a very long time to see such an event.P0M (talk) 15:00, 3 April 2009 (UTC)
POM following our other conversation below I came to reading this.I know it's kinda late,but could you please explain to me how do you solve the time paradoxes? You have ie written ""Cause and effect" does not prevent a paradox. Instead, it ensures that such a paradox (or, rather, such an infinite loop) would occur."I agree it ensures such a paradox would occur.It's a paradox exactly because of presumed strong causality (cause preceds effect).Yet could you please give a way out of it other than one preserving somehow causality?Could you also please give a reason why this kind of gedanken experiments constitute a paradox other than that a situation like this,like the "gradnson kills grandfather before father is born", messes up causality?If not for running against causality why is time travel to the past a paradox?And why time travel to the future although also very strange, does not seem to produce such paradoxes???In other words answering to this:"The current text says:"

For example, the notion that events can be ordered into causes and effects is necessary to prevent causality paradoxes such as the grandfather paradox, which asks what happens if a time-traveler kills his own grandfather before he ever meets the time-traveler's grandmother.

How can a "notion" prevent a paradox? This part of the article is badly argued."I would say that the notion,the principle of causality,cause preceding effect with respect to some abstract time variable(a variable with respect to which change takes place),prevents such paradoxes simply by forbidding such paradoxes being possible,taking place(at least in the same verse of a multiverse,if multiverses are allowed :)).Thanatos|talk 01:18, 12 December 2009 (UTC)
Notions do not do things in the real world. If a "notion" adequately reflects a reality, then it is the reality that does the shoving, not the verbal description of it.
I cannot "solve a paradox." I am generally unable to solve anything even mildly intractable. A paradox is just, according to my version of English at least, a state of affairs that ordinary expectations would reject. The orbit of Mercury was paradoxical. Pre-Einstein, it happened but Newton et al. said it shouldn't happen, or at least they had no clue as to what was "causing" it to happen.
In computer programming it is rather easy to program an infinite loop. In the old days, only one process was possible. So if you wrote instructions that created an infinite loop then when you ran the program it would perform as you had hoped until it hit step 13. Step 13 would lead to 14, then to 15, but then the next instruction would take it back to 13 again, and step 16 would never be reached. Killing your grandfather is like creating a double loop. Grandson gets into his time machine but never gets out again. If he had never gotten into his time machine to go kill his grandfather, he would have gone on to live his (ab)normal life and die. If he got into the time machine the first time, then he killed his grandfather. Having killed his grandfather he didn't exist. Therefore he didn't get into the time machine. Therefore his grandfather didn't get killed off early. Therefore he... The process cannot go forward from the point when he got into the time machine (unless he will lose his desire to kill, perhaps).
Another similar situation is called feedback chatter. If you set up an electrical motor with a governor that cut power when the motor reached 100 rpm, but which turned the motor on when the motor reached 0 rpm, you would have heard the motor start up over and over again. It would not have been good for your power bill and it might well have burned the motor out. The "paradox" in this situation might be that you use more power when you "let the motor rest" than you do when you "just let the motor run at its designed speed." I can't solve that paradox either.
What if somebody committed a horrible crime, deeply regretted it, hated himself for it, actually, so he went back in time and killed himself before he could commit the crime? His older self should be, on average, half there at the murder scene. His younger self should be, on average, half dead at the murder scene and buried in due time and half alive and carrying on with his ignoble life, fathering illegitimate half children who are half siblings of each other (or are they quarter siblings? Quiblings?), and so forth. Everything he did in his half life would have half consequences, and only a traditional Indian philosopher in love with infinities could love such a mess. I think I will favor a religious preference for Einstein's view that the whole thing is simply impossible. P0M (talk) 08:57, 12 December 2009 (UTC)
Sorry but these arguments are hardly sufficient.a.You might use loosely 'paradox' for Mercury's orbit.But that's not the proper use or at least the same as with paradox of time travel to the past.Your're just exploiting the ambiguity of words.Mercury's orbit was one of the things that simply disproved Newtonian Physics.The theory predicted A, couldn't be tweaked to predict otherwise.The experiments showed B.Theory disproven(after a more parsimonious one predicted it without the need of postulating unobserved things).It was just plainly wrong.On the other hand, since i)we haven't been able to create a time machine and try to take a trip to the past(that's not a strong argument, absence of evidence is evidence of absence only in a probabilistic way), ii)going to the past is possible via ie wormholes according to theories-models, iii)going to the past would create logical absurdities, we have a fundamental problem,a self contradiction,a paradox, b.if you invoke reality then you are accepting that theories do reflect reality.Please then define reality cause on the one hand there is ie QM, a higly successful theory in great contradiction to what intuitionally we understand as real,therefore we just accept that our intuition on reality is wrong, while on the other hand the time travel paradox is ok by theory, a great contradiction to our intuition but you now are postulating that our theory is wrong and our understanding of reality right, c.programming metaphors are nice,helpful.But they're just metaphors.You cannot get out so easily, d.the paradox in the engineering case you've mentioned is just playing again with words.It doesn't run against physical theories and it can easily be explained by the fact that the motor doesn't really rest,we don't allow it to.On the other hand if it were possible to kill your grandfather before the birth of your father,then that's no game,of words or other...Thanatos|talk 15:21, 12 December 2009 (UTC)
If you want to define "paradox" as self-contradiction, then that is within acceptable English usage. On the other hand, saying "self-contradictory" to begin with would not lead to so many problems of understanding.
Language does not determine reality. Neither does logic. Logic is a set of rules for using language so that the user does not unintentionally affirm two propositions (statements) that are contradictory to each other. The question is always, "What does nature really do?" If it does one thing and humans say it does something else, then humans ought to give up what they have been saying that is wrong. Even so, Einstein claims to have worked things out and to have established a coherent account of reality that explains much that could not earlier be explained. According to him, that same theoretical system denies the possibility of time travel. That should be the end of the discussion. At least I am not going even to waste the time to make a bet with play money, much less real money, that he is wrong.
So somebody comes along and says that there is a way to get around the restrictions Einstein calculated to exist. We don't do it by moving faster than even light can move. O.K., I like science fiction. If we make that premise, then what would the killing of one's grandfather or even the killing of one's self look like? Then you get a situation in which the statements: "It is the case that the grandfather died before he could conceive the father," and "It is not the case that the grandfather died before he could conceive the father," are both true. In your terms, from the time of the killing onward a paradox or self-contradiction exists. It would be merely inconvenient if it were only a matter of words. But the hypothetical situation is one in which both statements would be true. We get a similar thing when one person says, "It is the case that light is a particle phenomenon," and another person says, "It is not the case that light is a particle phenomenon." In that instance all the verbal contradictions do is to tell us to go back and look at reality with eyes cleansed of the two categories, wave and particle. Light will go on doing its own thing regardless of how badly we try to conceptualize matters. But the case of the time traveling killer is somewhat different. If it could actually happen, then for some years after the "killing," the person would be sort of a superposition of an existing person on the streets of Paris and a nothing. I think it might be appropriate to call that a practical contradiction or a practical paradox.
Nobody but a good Buddhist could love such a state of affairs. There are no grounds for saying that it is impossible. It might be possible. It might be impossible. But how would anybody know? I can look at the hypothetical situation and say that it would be interesting to try to work out the consequences, but rather than indulging in fantasy or ungrounded speculation it is better to stick with Einstein -- at least until somebody even smarter than he was comes along. P0M (talk) 19:55, 12 December 2009 (UTC)
a.Yeap,Buddhists are pretty lucky.They need no drugs in order to get high. (no pun intended,it's meant to be a compliment) :) b.Oh come on,please stop playing with words!!!Ok,name it at will.Paradox,contradiction,self-contradiction,endless loop,crazyness,Bob Marley,Sasha Baron Cohen...However you dub it,it's one heck of a problem, it cannot be that easily dismissed! c.As for the argument of sticking to Einstein.Well, wormholes and tachya wouldn't have been "around" if it weren't for Uncle Albert... :D Thanatos|talk 20:58, 12 December 2009 (UTC)
I don't see a problem because Mother Nature (or the Dao) doesn't see a problem. O.K., maybe Mother Nature would die if somebody created a paradox. I'm not the one to diagnose, much less to cure. Go find a reputable physicist who has tried to deal with this stuff and cite his/her research, peer-reviewed articles, etc. The alternative is science fiction. I like it, but I'm not making any travel plans based on anything I've read lately. P0M (talk) 21:17, 12 December 2009 (UTC)
Ok,I'm going through my library;Section:Physics and Technology;Subsection:Time travel machines;Subsubsection.Construction manuals&blueprints.... P.S.There is also the subsubsubsections "Do it yourself books" ,"A beginner's guide to building a time travel machine" and "Time travel machine assembly for dummies" but I don't think they're appropriate as a reference in an article of a respected encyclopedia. :D Thanatos|talk 02:35, 13 December 2009 (UTC)

QM acausal but deterministic??? :O

All things following a mathematical-logical law are causal by definition. If they weren't they would be totally-truly random (whatever that may be). In plain words if there is a formula , a pattern describing a phaenomenon at some basic level, then it's causal. If no formula or pattern exists then it's truly and totally random. If this were to be valid for a phaenomenon then all science would break down.

Unclear what the referent for "this" is supposed to be.P0M (talk) 04:25, 10 December 2009 (UTC)
This refers to"If no formula or pattern exists then it's truly and totally random." Think about it,no pattern at all,no mathematical-logical formula,no science.Thanatos|talk 16:26, 10 December 2009 (UTC)

In order wordes for (at least) Physics-Science to exist (sic), causality must be true at least at the basic level. Determinism is in other words let's say isomorphic (1-1) causality.

QM like all other fundamental physics and science theories IS causal. But unlike all other fundamental physical-scientific theories, it is inherently random, not totally-truly random, just inherently random enough 1 level above causality, hence non deterministic but STILL causal. On the other hand Chaos Theory IS causal, IS also deterministic since its randomness isn't inherent, it's de facto and not de jure.

What does law, civil or criminal, have to do with anything?
Forget law and try to translate these latin expressions more abstractly and you might get it :) .Let me put it in other words:"Practical" vs "theoretical".In(or due to) principle vs in practice.Inherently probabilistic(->QM equations) vs inherently non probabilistic(->Classical Physics equations).Thanatos|talk 16:26, 10 December 2009 (UTC)
It was a mistake to call the thing "chaos" theory since the math that describes apparently random and "chaotic" changes is perfectly ordinary math. Given a determined set of initial values, after a certain number of iterations have been run there will be a determined set of values for that stage of development. No matter how many times you do the math, starting at the same point you will "end" at the same point. What is "chaotic" about it is that starting with some value such as "0.000000098..." will get you to one answer in the nth iteration, whereas starting with something like "0.000000088..." will get you somewhere much different in the nth iteration.
Irrelevant to what I've written but somewhat ok from one perspective.I guess the (shocking) discovery of the de facto indeterminism of deterministic systems was the cause of this "field" or "phaenomenon" to get the status of a theoryThanatos|talk 16:26, 10 December 2009 (UTC)

The article imo needs a major retouch. People (no pun intented) get your terminology straight!!!! :) Thanatos|talk 03:07, 10 December 2009 (UTC)

It would be helpful if you would state what you would like to have changed and then give a reason for those proposed changes.

P0M (talk) 04:25, 10 December 2009 (UTC)

I guess I have to repeat myself:"Determinism is in other words let's say isomorphic (1-1) causality".Also the de facto vs de jure thing.If you understand what these mean (a.a cause -> an effect (causality) vs one cause -> one effect (determinism),b. existence of a formula-pattern <=> causality and !<=> determinism) then the theme of the whole article (and even the main,more general causality article) breaks down and needs major rewriting.In other words when you write determinism I mostly have to read causality, when you write causality I mostly have to read determinism, and vice versa.Quite a mess! :)P.S. You've messed my initial comment up.:) Yes it's easier to reply this way,it's also easier for me to reply to you.But now my point is a bit difficult and obscure for people to read and get as a whole.Thanatos|talk 16:26, 10 December 2009 (UTC)
I do understand what "these things mean," and my understanding jibes with Webster's New World Dictionary of the American Language:
de facto: in fact; actual (regardless of legal or moral considerations); as, de facto government; distinguished from de jure.
de jure: by right; in accodance with law: as, de jure government; distinguished from de facto.
So while we are at it:
determinism: the doctrine that everything is entirely determined by a sequence of causes.
causality: principle that nothing can exist or happen without a cause.
The single-photon at a time version of the double-slit experiment made people realize that language appears not to be adequate to deal with the complexities of Mother Nature. Is is generally accepted that no photon suddenly appears on the detection screen unless the laser (or other light source) had fired an appropriate fraction of a second earlier. In fact, that preconception is so firmly fixed in everybody's minds (and even declared in the philosophy of St. Thomas Aquinas) that (to borrow a fairly recent paraphrase), "Nothing comes from nothing. Nothing ever could," if an unexpected photon happened to be detected in the apparatus the investigators would look for a light leak or some way other than ex nihilo creation to account for it. So the general belief governing these expectations and corrective activities is:
If and only if something happens at t = 1 will a photon be detected at the screen at t = t+n.
Supposing that a laser fires at time t and a photon is detected at t+n, the above statement is considered true.
Supposing that a laser is not fired at time t and a photon is not detected at the screen at t+n, the above statement is still considered "true" because it has not been disproven by experiment.
Supposing that a laser fires at time t and a photon is not detected at t+n, the above statement is considered disproven. (Of course people will do everything possible to try to establish that the laser didn't really fire, a fly intercepted the photon on its way out of the laser, etc., etc.)
Supposing that the laser does not fire at time t and yet a photon is detected at t+m. the above statement is considered disproven. (And, as I said, people will try to find a secret laser, a hole in the experimental device, a chewed piece of wintergreen candy -- anything to preserve the precious preconception. And it is well that they should.)
People could have been happy with this picture of events forever if they had not introduced the double-slit apparatus into the path of the photons being generated for the experiment. It was "determined" that a photon being emitted at one end of the experimental device would result in the certain arrival of a photon at the other end of the experimental device. And the appearance of a photon at the detection screen was surely caused by the emission of a photon by the laser. Any slight departures from the expected results could be chalked up to experimental error. The key point is that the appearance of a photon on the detection screen is determined by the firing of the laser.
It is also possible to write a logically weaker claim and make it easier to ignore the occasional unexpected photon on the detection screen:
If something happens at t = 1 then a photon will be detected at the screen at t = t +n
Supposing that a laser is fired at t = 1 and a photon is detected at the screen at t + n, then we count the statement immediately above as true.
Supposing that a laser is fired at t = 1 and a photon is not detected at the screen at t +n, then the statement is considered disproven.
Supposing that a laser is not fired a t = 1 and a photon is detected at the screen at t + n, then the statement is still considered true since it may no prediction about what would happen if the laser were not fired. Maybe the speaker knew his apparatus was leaky.
Supposing that a the laser is not fired at t = 1 and a photon is not detected at the screen at t + n, then the statement is still considered true. It simply has not been subjected to any experimental test.
If we were doing an analogous experiment with bullets we would be unhappy if somebody fired a high powered weapon from outside our laboratory and it scored a bulls-eye on our target, but that would not offend our sense of normal causality. On the other hand, if we put a bullet in a single-shot rifle, fired the rifle, and then could find no sign of the slug anywhere in the enclosing lab, we would be most puzzled. We would gladly say that anything that hit our target was a caused event, and that where and when the hit was made was determined by the firing apparatus and all the other factors involved. (Even coin flips are said to be determined in this sense.) When we say that the bullet hole in a target was due to a determinate process, we mean that something(s) caused the bullet to follow its trajectory. It did not get there "for no good reason." With enough control over all the factors involved, we could cause another bullet to follow exactly that trajectory.
As stated in the next section below, the ideas of "cause" and "effect" tend to focus on certain factors that are relevant to civil damage trials, murder trials, vendettas, etc., etc. But let's take an idea from George Gamow and reexamine what we really are describing in cases such as the experiment outlined above. We can depict an event by transposing the time dimension into one of the space dimensions, e.g., we can depict a man's life as a sort of rubber bar cross section of a human body that starts from a microscopic dot, grows larger while it is moving arms, legs, etc., etc., and finally the outlines of the cross-section start to decay and we are left with a pile of bones and eventually maybe a fossil or maybe nothing. An equivalent picture of the flight of a bullet from gun to target would (arbitrarily) start with a cross-section element that is roughly circular, and then that circle would be extended forward, would pick up some indentations from the rifling of the gun barrel, and would follow a trajectory to the target where we would lose interest in it after noting that its original circular shape had been disturbed by impact with the backing to the target.
The idea of determinism/causation can be explained in terms of this "rubber-bar bullet flight" by saying that given another one of the same type, and guarding against differences in experimental conditions such as a strong wind perpendicular to the direction of flight, any bullet that starts out the same way and endures the same conditions in flight will end up at the same point on the target. We can strengthen this idea of "true causation" by observing that the more exactly we can control all of the conditions, the more perfectly the end results match. What one calls "cause" and what one calls "effect" is a matter of choice as long at the cause parts of the stretchy bar (and their attendant circumstances in time, e.g. the net wind force at any point) come before the effect parts of the stretchy bar in time.
When one considers the double-slit experiment, severe cracks develop in this picture. Photons going through a single slit get a little boisterous, but they generally manage to behave fairly much like a well-mannered .22 bullet. If photons acted like bullets, then we could study bullets and see their behavior. So suppose that bullets were to behave like photons. The double-slit apparatus now is of an appropriate width that a bullet can either go through one slit or the other. If there are two slits, the bullets behave differently than if there were only one slit. With one slit, the stretchy rubber rod that traces its position in time goes almost straight and each rod then goes to almost the same spot. But with two slits, the bullets pass through a slit and then take one of many possible paths. The conclusion that one might take from this experiment with imaginary bullets would be that the bullets each has some "preference" for where it will hit. That impression would be strengthened if investigators could see no signs of bullets physically interacting with the slits that they passed through. Expending a whole box of ammunition will create a fringe pattern of bullet holes.
The result of the double-slit experiment (however you may try to imagine what the photon is "really" doing on its way to the target) is that photons "preferentially" strike the detection screen at some points and "preferentially" avoid hitting the screen at other points. The big argument is, "Why?"
People who accept the idea of hidden variables will explain the arrival of a photon at one of the fringe zones by saying that it was caused to show up there by the known and measurable features of the experimental apparatus, viz;, the wavelength of the photon. the dimensions of the slits, the distance between the slits, etc. It was determined, they will say, to show up where it did because of all of the causal factors involved. Was its arrival at the detection screen caused? Certainly. No photon would have shown up there if one had not entered the apparatus from the other end. Was its arrival at that point on the screen determined? Certainly. There is nothing in nature that behaves by laws like ones that would declare what percentage of photons must show up at each fringe position, yet somehow allow the photons to decide, or to allow chance to decide. In other words, even though humans do not know all of them, there are causal factors that surely guide each photon from laser to its point of detection on the screen. That is one view.
People who doubt the wisdom of declaring the existence of things for which there is as yet no evidence (for fear of prejudicing some other judgment if nothing else) will say that when a photon shows up on some point on the detection screen, it was not an ex nihilo event. So in that sense it was not an uncaused event. But it was not a "caused" event in the sense that a factor or factors determines which apparent "trajectory" the photon follows. Likewise, it was a determinate event in the sense that once a photon was emitted it was sure to show up somewhere, but not a determinate event in the sense that it could have just as easily shown up at some other fringe location.
I hope we can arrive at a common language. My preference is to start with standard English dictionaries and then carefully wing it when our existing stock of words fails us.P0M (talk) 03:45, 11 December 2009 (UTC)

You wrote: 1."determinism: the doctrine that everything is entirely determined by a sequence of causes." 2."causality: principle that nothing can exist or happen without a cause." Ok let's have a go on these definitions. I urgue you to focus and reflect on the meaning of the word "entirely". Because 1 follows logically 2.If everything has a cause,then it's an effect which then becoming a cause causes another effect, so here comes naturally a sequence of causes and effects for everything.So if 2 is true why do we need 1???? Isn't it superfluous????

Here enters randomness and probability.

So let's forget QM for a minute,let's pretend we live about Laplace's age. We know we cannot practically predict the outcome of a throw of a dice (or anything else seeming to be what we call random). But since Classical Physics reigns, here enters Laplace's Daemon. In principle if we somehow we have a full measurement for all particles of the universe (which theoretically is a process we can do,we can disregard herein thermodynamics,etc as second level randomness,as practicalities while on the other hand randomness in QM is first level being inherent in its equations) then because of our classical physics equations we can exactly predict the outcome of the throw of the dice. So although a throw of a dice appears random,it really isn't,at least truly. Young's double slit experiment doesn't alter that because we have to remember that Maxwell demonstrates light is a wave (with a really nice causal and deterministic wavefunction). Yet we shorty discover after Einstein and so on that light besides being a wave, is also a particle. So now we have the conundrum of a really nice wavefunction that from time to time strangely collapses to a really nice particle. We have QM and Young's double slit experiment has proven to be although extremely fundamental to our comprehension(or not :) of QM (Feynman),also really,really crazy.

Your go on the Young's experiment doesn't satisfy me regarding the herein writing about causality and determism. Cause QM doesn't determine where the photon will appear.The collapse of the wavefunction is not deterministic.The wavefunction is.Where a photon will be measured is random.So how random? Here comes the very tricky and obscure part. Cause if we add up photons we have a pattern and a distribution based on the probabilities coming from the wavefunction. At this point you say determined,I say caused.And whether it's based on hidden variables or not,something I'm certainly not referring to (and which anyway according to Bell's inequalities isn't valid) is something irrelevant.

So what I'm saying is that if causality is defined (as I usually think is) as a cause,an effect <=> a pattern,a formula then everything is ok,everything is well noetically ordered. The fact that we don't know why a single photon appears here and not there is a problem but perhaps only if we regard this as a single phaenomenon by itself (which then seems to be neither causal nor deterministic).But if we regard causality as if A then B or C or D or E or ... and determinism if A then (strictly) B (so for determinism there is an exactly predetermined chain of events), there is no (major) problem. B,C,D,... are the effects of A.Causality stands.Determinism falls cause for single effects (whether B,C,D,...) the only way we can determine what will happen because of A is measuring.But we still have a cause and an effect.We still have a sequence of events.It's just that we cannot entirely predict,determine the exact chain from before.But we still have a chain of events,there is an order but we simply cannot exactly predetermine it.

So what seems to be our disagreement? First of all I don't see a constant usage of the same definition for all regarded concepts. At some points what causality and/or determinism mean are really obscure in this and other articles. At other times articles seem to follow a more historical tradition. But most importantly at points trying to be more precise and scientifically relevant,especially in this article, I get the picture that the naming and underlying definitions are equivalent to if A then B or C or D or E or ... for determinism and if A then (strictly) B for causality.As you see causality then becomes a special case of determinism and not the other way around which is the way I think causality has been thought of for ages,being the most basic principle of all. Then there is the chain of events thing.My understanding of determinism is (pre-)determined chain of events,of cause and effects. Yours seems to be just the very fact,the very notion of a chain,a sequence... Note that as I have named this section ,it is written that at the same time QM both non causal and (mathematically) deterministic. Do you get that this makes no sense at all based on the definitions you have mentioned and the interpretation of them that you seem to be implying????

So ending my present reply (and waiting for yours) here, I have return to Laplace's Daemon.Suppose QM hasn't been discovered yet. Could you please answer to me what's the difference from a physicist's (or more generally a scientist's) position of the following two sentences? 1."determinism: the doctrine that everything is entirely determined by a sequence of causes." 2."causality: principle that nothing can exist or happen without a cause." What do they really mean for the change,for the evolution of a system from a physicist's perspective?Are they equivalent?If not,what's the salient point of their inequivalence? What kind of distinct predictions can we make based on each of them? What's their importance on specific systems and on the system of the whole universe?

P.S. a.We certanly would have the same trouble and arguments if we tried to reflect on what randomness really is.Try to think of a randomness of no pattern...That's what I would name really,really non causal!How,what would you name that???? b.I also have to remind you that English dictionaries are imo somewhat irrelevant here.The concepts of causality and determinism are too basic,too fundamental,too universal to restrict ourselves just to english and especially to english general dictionaries.Heck I'm Greek but I also have to be able to communicate with Anglophones ( in Greek causality is "aitiotes",determinism is "aitiokratia"(aetiocracy) or "determinismos").What am I then to do,define causality and determinism just based on a English Lexicon????Or a Greek one? For a general(initial,superficial,a layman's) use ,dictionaries-lexica are ok.But we're very deep now and they're hardly sufficient!!!! :) Thanatos|talk 18:05, 11 December 2009 (UTC)

Usually I only think somebody speaks a different first language from mine. :-)
The word "determinismos" is a borrowing from Latin, no? The other words all indicate what I was trying to get at above, that "determine" and "cause" are just different words for the same general kind of thing. If there are nuances or slight variations of meaning among these words, I'd be surprised to find that everybody splits the differences the same way.
To answer your question, I don't see any salient difference between (1) and (2) -- except that "ism" has some additional ideas that are associated with ideologies, normative behavior, etc. that don't belong here. Usually that would not be a problem because we mash meanings around to fit contexts.
I learned a hard lesson in another time and place: It is better to get clear on the nature/characteristics of the phenomenon or entity that you are interested in first, and decide what to call it after the debris from the first fight has cooled. I don't know of a good word in any language for situations that get described in quantum mechanics.
As for randomness, in computer science and other such fields there is the idea of quasi-random numbers. They look like they come in no predictable order, but that is because of a trapdoor phenomenon. It is very difficult to look at the output and guess what the inputs and rules are that generate the "random" numbers. If I give you a string of numbers that starts with 1, 5, 9 and you guess the next one will be 12, you will be wrong. It might take a long time unless I tell you that just before those three digits there were first the numbers 1 and 4. Then, if you know the value of pi to a few digits and know how to compute pi, you will have the "random" series. The idea that there is some formula that will generate the time intervals between successive clicks of a geiger counter is, I believe, generally denied. The numbers that are generated in that way do not have a "program" behind them.
There is, according to those who do not believe in hidden variables, a similar randomness in the sequence of "hits" on a detection screen in the double-slit experiment. But there is also a very puzzling kind of orderliness in the process since the percentages of hits that occur at each fringe always come out the same. So there is a "rule" somewhere. But where does that controlling factor tip its hand? When an electron or a photon emerges from the double-slit apparatus, is it already a sure thing that it will hit one fringe location or another? It is a sure thing only after wave fronts emerging from both slits become superimposed? Is it a sure thing only after the superimposed wave fronts hit the detection screen? Or does Mother Nature care not a hoot for any of these things that loom so prominently in our experience of this phenomenon? Maybe it works to say that if there is a 25% chance for a quantum mechanical pachinko ball to fall in any of four pockets at the bottom of the pachinko machine, then whatever happens happens and there is no causation involved. To wax Aristotelian, in a way, maybe wavicles are moody. They feel like going to quadrant one, two, three, or four for no particular reason. But like a thoroughly demented person there is no reason why they feel one way one day and another way another day. All we can ever know, because that is all there ever is, is that a quarter of the time they favor one of the four alternatives. But why, one may ask, are there four alternatives? Doesn't somebody have to make the rules?
Back to the language problem, what would we call it if we were dealing with a benevolently fixed roulette wheel? "Round and round she goes, and where she stops nobody knows," except numbers 4,7,8, and 15 pay low and get stopped on frequently. It's "random" in that nobody can say for sure what the next winning number will be. It's "determinate" because the wheel is designed never to stop between detents on its rim. But it is also "determinate" in that somehow inside the wheel where nobody can see the mechanism there is a fudge factor that makes sure that one rarely hits the high payoff numbers. If we were doing this thing with a computer we might make rules such as, "if '4' has been hit more than 25% of the time on this iteration, recalculate a new hit." What would we call the behavior of such a gambling device? Jiggered randomness? P0M (talk) 01:55, 12 December 2009 (UTC)
I'll take your answer as an instrumentalist argument.Although I don't usually think of myself as belonging to that school of thought,I have to say that it's fine by me.But that's hardly how I would put it in an article of an encyclopaedia.Especially when the article is about CAUSALITY. P.S.a.You anglophones!!!! Well,I guess you at least think sometimes of the fact that other people's native language may not be english. :) b.Also consider my comment on the previous section of this page.Either independently or in relation to what we have been discussing here. —Preceding unsigned comment added by Thanatos666 (talk • contribs) 03:49, 12 December 2009 (UTC)
You have it backwards. When I was in Taiwan one of my dorm mates gave me the funniest pieces of literature to read that I have ever seen. I asked him how it was possible for a Chinese person to write such a funny story in English. "He's a native speaker of English." "But the grammar is all wrong." "No, really, he's from England!" Confident that I could quickly come up with a grammatical error that no native speaker would make (even those who "lay" down to sleep -- breaking their own eggs, no doubt), I carefully re-read the long, funny story. I could not find a single error. All the "mistakes" were just differences in idiom.
I'm a Daoist, not an instrumentalist. I do play the harmonica and recorder, but I don't think that qualifies me. ;-)
Now the question is how to name the kind of causation/determinism that we are accustomed to seeing in everyday life, e.g. expensive rifles that shoot a tight pattern at 100 meters and shoddy rifles that put anybody in front of a barn in danger at the same distance, vs. the kind of causation where the "rifle" delivers precise fire to a large number of fringe patterns but in unknowable sequence. Whether one would choose causality and determinism, or determinism and causality, I think either would be unhelpful.P0M (talk) 06:55, 12 December 2009 (UTC)
Divide by a not common language.Or is it non,hmmmm... :) Thanatos|talk 15:25, 12 December 2009 (UTC)

distributed causality

Does anybody understand what the writer of this little section was trying to say? Claiming that "chaos theory" is something that "opens up the possibility" of some unusual kind of idea of causation needs more than a perfunctory assertion. P0M (talk) 04:53, 10 December 2009 (UTC)

Probably the writer wants to convey the popular idea that according to a certain interpretation of chaos theory a butterfly may cause a hurricane to develop somewhere far away. Whether you find this idea acceptable depends on your definition of `cause'. The question is whether you make a distinction between `causing' and `triggering'. In general this would make a difference in the sense that with a `cause' there is a certain proportionality between cause and effect that is lacking with a triggering activity. For this reason, within physics I would prefer to uphold a difference between the concepts. I can imagine, however, that someone sitting on a branch of a tree, and slightly pushing a heavy stone in order to hit someone passing beneath him, would be charged for causing the death of that person, rather than that gravity would be seen as causing that event. So, outside physics things may be quite different.WMdeMuynck (talk) 16:40, 10 December 2009 (UTC)

quantum physics or article murkiness

I think that Thanatos (why, at age 70, does that name bother me?) is seeing problems with the paragraph that begins:

The possibility of such a time-independent view...

The paragraph and the attendant links to things that need to be sorted out through reference to further links reminds me all to much of making a pile, starting with a grand piano and followed by two chests of drawers with slightly unequal heights, then larger tables followed by smaller tables followed by a chair or two, and then trying to stand at the highest point to cut something using a chain saw.

Ideally, there would be a Loglan version of Wikipedia, and these rickety language compromises could be avoided. That not being a current possibility, we need to work out a way to name the "causality with a gambling problem" in some way that communicates clearly what is really going on.

If we lived in a world in which two-handed pitchers were faced off against several batters (each with his/her respective catcher), and one ball could end up getting hit by any single batter, then we might have convenient words for the "rulishness" of such a pitching process. Would something like "acausal fan-out" come anywhere close to depicting what happens when a single photon or electron is put through a double-slit apparatus and contributes to one of many fringes forming on the detection screen?

Another thing to keep in mind is that the word "determine" has a meaning that has been given de facto special status by Heisenberg. He preferred to speak not of the "Uncertainty principle," but the "Indeterminacy principle," and by that expression he meant to indicate that on the atomic scale at least things do not have the determinate positions, momentums, etc. that we are used to on the human scale. We would be better off not to use "determinism" to refer to "acausal fan-out" situations that are yet "rulish." P0M (talk) 07:57, 12 December 2009 (UTC)

How about the article's assertion that there is a perceived problem regarding quantum mechanics because of:

this theory being acausal (in consequence of its inability to provide descriptions of the causes of all actually observed effects) but deterministic in the mathematical sense.

Hitting the average well-informed reader with a statement of this nature is not helpful. What is a "description of the cause" of an observed event supposed to mean? What does "deterministic in the mathematical sense" mean?

I don't want to go over the discussion of what can and cannot be predicted in the double-slit experiment and other experiments with similar features.But if the assertion quoted means what I think it means, then I feel sure that for the general reader a simple example will show in what sense words such as "determinism" are being used.

In discussions about free will and determinism, the argument usually examined involves observations that there being only probabilities involved in certain physical interactions it would be impossible to continue believing that everything that happens today was determined by the initial conditions of the Universe. So for these students of quantum mechanics and its consequences, the quantum mechanical world is free and not deterministic even though they generally would not go so far as to insist that there are, or need to be, ex nihilo events to account for freedom of the will.P0M (talk) 01:03, 13 December 2009 (UTC)

The current text says:

Special relativity has shown that it is not only impossible to influence the past, it is also impossible to influence distant objects with signals that travel faster than the speed of light.

This statement sounds almost solipsistic in the sense that it makes the thought of Albert Einstein the master of how things work in the Universe. Put another way, the statement tacitly posits the existence of "signals that travel faster than the speed of light." In what sense can something be called a "signal" if it cannot be perceived or detected by any apparatus? If it can be detected, then setting up a tachyon beamer on an earthlike planet orbiting some distant star would be at least as useful as the ancient Chinese scheme of constructing signal towers that announced invasions or the like by setting a bright fire after dark.

Maybe the writer was simply trying to deny the possibility of creating any signal that travels faster than light. If that was all that was intended, then why not just say so? P0M (talk) 01:33, 13 December 2009 (UTC)

What is a cause in physics

`Causality' is one of Kant's categories of understanding. These are introduced by him to order observed phenomena, some of them being interpreted as causes, other ones as effects. This may be interpreted as a means to come to understand, or even come to grips with, the relations between the phenomena.

However, in actual practice there most of the time are many causes. You may know this definition: causes are insufficient but nonredundant parts of unnecessary but sufficient conditions. Which of the conditions is considered as the most important one depends on the context. If this context is not well-defined, then speaking in terms of causes will lead nowhere.

In physics some phenomena are considered as `not caused'. For instance, rectilinear motion at constant velocity is considered as such in Newtonian mechanics (since force is zero). In general relativity even nonrectilinear (geodesic) motion is treated as `not caused', gravity being eliminated as a cause. Also in physics causes appear or disappear according to the contexts physicists like best.

The idea of cause seems to be a rather fluid one. This is even so within physics. It seems to me that the Causality (physics) page is a good place to illustrate this fluidity.WMdeMuynck (talk) 23:41, 14 December 2009 (UTC)

I started to write a comment here, but you beat me to it since I wiped my own text out before hitting "save."
I started looking around at other websites and was disappointed at what I saw. I remember figuring out the example of the tea kettle and boiling water for a course I was taking at National Taiwan University in the 60s. Prior to that spell of thinking I had maintained a "natural language" idea of cause and effect -- I shoot he dies, etc. I mentioned something about the same kind of idea up near the top of this discussion page (the unarchived part, that is).
I took a look at the Stanford Philosophy page on causality and was disappointed. Their treatment seems to jump into the middle of some argument that they have been having for months or years.
Before I lost what I wrote the last time I had just started to write something about the "butterfly effect" having turned out to be subject to remediation. Experiments were done on nudging the process of "circulation" in (I think it was) the Henon attractor Maybe it was the Lorenz attractor. By interfering physically to change the numbers that would be measured (and the physical factors that would determine the next "calculation") at some location and time, they were able to change the pattern.
I think that Thanatos has been asking for a way to indicate in the English language the kind of situation in which a certain kind of "early half" always produces a single and definite "second half," and the kind of situation in which a certain kind of "early half" produces something like a "fringe hit" in the double slit experiment. One of the German physicist/philosophers (Reichenbach?) wanted a new logic to use one quantum mechanical event descriptions. Maybe he came up with terminology suggestions too.P0M (talk) 02:20, 15 December 2009 (UTC)
Chaos theory and quantum mechanics present examples of "interesting" but difficult questions with respect to causality, which are not sufficiently resolved even within the scientific literature (notwithstanding possible claims to the contrary). Both theories are wrestling with the determinism of classical mechanics, the difference being that the mainstream in physics is that chaos should be deterministic (because classical mechanics allegedly is) and that quantum mechanics is indeterministic (because Bohr and Heisenberg said so).
Weather scientists tried to model weather using equations. In the process of testing how well one particular equation would do, it was accidentally discovered how slight changes in the numbers fed into the mathematical model would produce huge differences in the weather conditions predicted for some later time. The math does not involve any random numbers, and the results produced after some large number of iterations will always be the same providing that exactly the same numbers are fed in at the beginning. Is nature as "deterministic" as are the equations? Maybe the math is inapplicable because nature's quantum characteristics show up somehow at the macro scale of weather. Or maybe the weather system is linked to some "true randomness engine".
Whether quantum mechanics is indeterministic or whether it is deterministic and governed by "hidden variables," the practical result for the observer is something like the electron version of the two slit experiment where the electrons show up one by one on the detection screen but not in any discernible order. Even if their order of appearance is governed by some shrouded factors, as observers in the real world we have to deal with events that are different from each other and appear in a random way. How to differentiate the causal events that appear in a straightforward way (observably identical beginning conditions produce observably identical endings) from those that appear to turn out differently despite having observably identical initial conditions -- that is the big question.P0M (talk) 22:38, 15 December 2009 (UTC)
It would be my advise to start in a page on `Causality in physics' with simpler examples everyone can understand, to show how the notion of causality has been applied in different ways.
It may also be useful to refer to the special application of causality as determinism (which stems from the logical positivist anti-metaphysical idea of explanation as `subsumption under a physical theory', thus circumventing Hume's problem), in which an initial condition is considered to be a cause. Unless the initial condition corresponds to a circumstance able to exert a physical influence (like, for instance, a particle having a certain momentum, enabling the particle to cause on collision a momentum change of another particle) is it highly confusing to equate determinism with causality.WMdeMuynck (talk) 12:16, 15 December 2009 (UTC)
I am not sure that I follow this part. Are you saying that there are many competing ideas of causality and that one of those is "deterministic" in the sense that a "no wild card" equation is taken as a valid or accepted model for the real-world experiment, and under this interpretation any change forced on the physical (e.g., a butane torch applied to the center of an aluminum bar and the resulting temperature readings at representative points on the surface of the bar) would be represented in the theory by changing one of the numbers in the equation and re-solving, and therefore that since the numerical solution to the equation changes in a non-random way one expects the real-world experimental apparatus to change so that the experimental values would correspond to the newly computer theoretical values?
That's one way of blessing the wild products of Mother Nature with the tame results of human thought. That nature should thus appear deterministic is clearly a product of the assertion of its deterministic nature by declaring it accurately represented by an equation.
The "chaos" experiment is a mine field. Suppose one person claims that a system is deterministic and another person rejects this claim. Assume that in this particular case the system is claimed to be "chaotic" but governed by an equation with no random factors. Opponents may claim that experimental departures from calculated values are the result of quantum probabalistic factors, but the supporters of the deterministic explanation could try to explain discrepancies on the grounds of experimental measurement errors.
Is this the kind of thing you have in mind? P0M (talk) 03:52, 16 December 2009 (UTC)
What I was referring to is the Deductive-nomological model, in which deduction is often interpreted as `deduction from initial conditions, using an accepted natural law'. This model has been proposed as an alternative model of scientific explanation/causation to metaphysical explanations based on unobservable forces and other dubious physical influences.
This kind of reasoning was used by Einstein in the EPR experiment, assuming the existence of a measurement result as an initial condition, and considering the fact that this result is obtained during measurement as being caused by the fact that it was already there before the measurement (the possibility of this reasoning is denied by the Copenhagen interpretation because quantum mechanical measurement results do not have values prior to measurement).WMdeMuynck (talk) 12:11, 16 December 2009 (UTC)
Did you mean to write "in which deduction is often interpreted as 'deduction..."? P0M (talk) 21:50, 16 December 2009 (UTC)
So sorry not to have been able to answer sooner. As you probably assumed I should have written: in which `deduction' is often interpreted as `deduction from initial conditions, using an accepted natural law'.WMdeMuynck (talk) 15:30, 27 December 2009 (UTC)
Then you were explaining the word "deductive" in the expression "deductive-nomological model," and not trying to say anything about logic? P0M (talk) 22:34, 29 December 2009 (UTC)
I think that's correct.WMdeMuynck (talk) 13:42, 31 December 2009 (UTC)

Undefined term

The current text has:

In the D-N view, a physical state is considered to be explained if, applying the (deterministic) law, it can be derived from given initial conditions.

Thanatos brought up the question of when to use "caused" and when to use "determined." One of the reasons for argument may simply be that some terms have not been defined. Does everyone accept the following statement from the article on Determinism?

Determinists believe the universe is fully governed by causal laws resulting in only one possible state at any point in time.

P0M (talk) 22:58, 29 December 2009 (UTC)

necessary and sufficient cause

These terms have meaning, but only if the reader has studied the history of logic. "Necessary cause" does not even have a Wikipedia entry, and the "Sufficient cause" entry is not particularly helpful. Rather than use these terms undefined, it would be better to get the meanings of them incorporated into this article in ordinary language.P0M (talk) 16:39, 25 January 2010 (UTC)

Perhaps a better reference is to the page http://en.wikipedia.org/wiki/Cause, section Necessary and sufficient causes. I tried to create this link but I failed because I was not able to link to the correct section for reasons that transcend my mastery of wiki html.WMdeMuynck (talk) 23:30, 25 January 2010 (UTC)
Done. P0M (talk) 05:21, 26 January 2010 (UTC)
ThanksWMdeMuynck (talk) 10:06, 26 January 2010 (UTC)

A celestial host of butterfly wings

The "butterfly a flapping" image used to popularize the consequences of what was misnamed "chaos effect" depends on a very unlikely premise that is not mentioned -- the premise being that there are no other "butterflies" involved in the total event. And even separating the "total event" out from the rest of the weather system, the weather system from the larger global environment, the global environment from the solar environment, etc. is one of those simplifications that gives us ways to deterministically calculate wrong results. (Wrong because we've got to start with the wrong numbers in that we don't really have all the numbers.)

A more reliable situation would have to be a contrived situation, e.g., a Schrödinger cat apparatus connected to a hydraulic lift apparatus under one corner of Balance Rock. When the rock became unbalanced and rolled a path of destruction to the bay, the hanging judge would look at the inventor and constructor of the diabolical device to hang.

Equations describe situations involving several variables pertinent to a certain kind of physical set-up. For instance, we can describe the pressure of at the base of a column of water, and given the diameter of the water column and the frictional forces operating on the water we can calculate the volume of water per unit of time delivered at the base of the device. As long as nothing changes any of these factors (no detergent is added to the water, nobody moves the whole thing up to the top of K-2, etc.) nothing changes in any of these factors. That's an intentional tautology. What we are interested in, if our basement is getting flooded or if our crops are not getting irrigated, is what has been done to change any of those factors.

So there seem to be two kinds of factors that we are interested in (being a species that delights in dichotomizing things), the balancing factors that all have to be included in a complete description of a phenomenon and the unbalancing factor or factors, factors that frequently can be traced to human interference. Maybe that is why we ask questions like why our homes were destroyed by a tornado on Pentecost. But that is actually not an answerable question unless one has a computer that is doing the same "calculations" as the weather system, no?

Consider a lava lamp world. It is a closed system except for entropy, and it is kept going by an invariant heater in its base. Being the toy of a tricky inventor, it has a little windmill that can turn to face the wind and can whirl its vanes and operate the pump in its base. What makes it turn? Supposing that we could do the calculations, would there ever be a "cell" in the lava that we could assign a different value to that would not have some effect on the windmill? If there were such a cell and such a change made in it, that would not constitute an uncaused event but an event without a causal impact. That would be like a force exerted that did neither created an action nor created an equal but opposite reaction. But the rules of this world suggest that the only way to get a change in a weather cell that did not have a precedent is changes in other cells would be for the experimenter to act as a stand-in for God and heat or cool that cell from the outside. The system works in a persistent dynamic balance. Or at least we do if we consider only classical physics.P0M (talk) 02:04, 27 January 2010 (UTC)

User: POM, please see your talk page for some comments.WMdeMuynck (talk) 14:35, 29 January 2010 (UTC)

Who ruined this article?

The current version of this article looks like it was written by an amateur with no background in physics. What is the purpose of the paragraph about sheep and human nature? Why is the article written as if Aristotle's ideas about physics were every bit as correct as those of Einstein, as if physics was a collection of mere opinions, rather than facts? Have the postmodernists taken over Wikipedia? Compared with the 2004 version of this article (which doesn't mention Aristotle because his theories are obsolete), the current version is useless for anyone who wants to learn what physics actually says about causality. 71.72.235.91 (talk) 23:20, 24 May 2010 (UTC)

Basic concepts of cause and effect

I have some sympathy with the reversion by User Jomanted, because the text contains a number of valuable observations (like about acausality in quantum mechanics) that could have a more prominent place in the text than it had in the former version. However, much of the addition is about causality in general rather than causality in physics and therefore belongs to the article on causality rather than causality (physics).WMdeMuynck (talk) 07:59, 30 July 2010 (UTC)

Where would you draw the line between causality and causality in physics? I suppose that there are ideas of causality in areas such as history that involve factors for which no physical measurements are even theorized, e.g., that greed caused the conquest of the Americas.
To turn that possible criterion around a bit, are there factors that people call "causal," that are subject to measurements for which operational definitions can be given that involve only inter-subjective objects, and that you would still claim as non-physical? How about something like the number of various denominations of currency in circulation in the world economy at a certain time or within a certain measurement window? P0M (talk) 13:46, 30 July 2010 (UTC)

Grandfather paradox

The article currently says: "For example, the notion that events can be ordered into causes and effects is necessary to prevent causality paradoxes such as the grandfather paradox, which asks what happens if a time-traveler kills his own grandfather before he ever meets the time-traveler's grandmother."

To me, that statement might indeed be defended somehow as being true, but it is not at all obvious what it really says, or what the reasoning behind it is. I believe it ought to be deleted if it cannot be shown to be a true statement. Here are my reasons for believing that it is not a true statement:

The grandfather paradox asks what would happen if time travel were possible and that someone could go back in time and kill his own grandfather. Presumably, absent the grandfather, one or the other of his parents would never have been born, and therefore the time traveler would not have been born. Having not been born, there would be no agent to return through time to kill the grandfather, therefore he would have been born and he would have been able to go back in time to kill his grandfather. So the image is one of feedback chatter.

The paradox depends on the idea of causality, and the idea that what happens first in time will affect what happens second in time. The trouble comes when what happens third in time then produces what happens zeroth in time. We do not like this idea, and our preconceptions tell us that this kind of event sequence is impossible. But it is only a preconception, a prejudice.

"Prevention" of a grandfather paradox actually depends on the impossibility of time travel and/or the impossibility of travel faster than c (which is one of the common ideas of how one might succeed in time travel).

I think that the writer of the sentence in question may have been trying to say that an event initiated at time t=5 cannot causally effect an event or a state at time t=4. Something is not "causal" of something else if it occurs afterwards. Therefore, a grandson born in 2000 cannot kill a grandfather in 1940. Therefore there would not be a paradoxical situation in which the killer ceased to exist before he could have killed. But that argument is essentially tautological.

We can say that we accept the idea of "no time travel" because we like to be able to avoid the possibility of feedback chatter situations even in theory, but there is no logical necessity for such a view. We can say, also, that the fact that we cannot travel faster than c eliminates one of the few plausible explanations for how time travel would be possible. But the fact is that the idea that "the determiner" always falls prior to "the determined" is a view that we take from our everyday experience and generalize to apply to all possible situations. Such set views have hung humans up in the past, denying many of the discoveries of relativity physics and quantum physics.

It is even known that some "different" classes of events in atomic physics can be understood as "the same" class of event running in different temporal directions. So on a limited scale it is possible that events may occur in either direction in time. The "arrow of time" may be related, in the final analysis, to a matter of the probabilities for events and for chains of events. I could arrange a sort of powerful cork gun at the end of a chalk tray at the bottom of a blackboard that would be angled very slightly toward the chalkboard such that when fired this projectile device would fire a blackboard eraser down the chalk tray, eventually striking the blackboard, and rebounding from the blackboard to come flying at the instructor, who might be able to catch it. Properly done, that event would be highly reproducible, and the only chancy thing would be the catching ability of the instructor. The event might be reversed if the instructor threw an eraser at the chalkboard and it hit just right to make it rebound, travel along the chalk tray, and force itself into the projectile firing device. I once accidentally threw an eraser at the blackboard and had it rebound from the blackboard and travel the length of the chalk tray, but the probability of my being able to do so a second time must be very slim. This event and conjecture about it forms a kind of homely example of one way that the statistical probabilities of various chains of events are thought by some (e.g., Brian Greene) to determine the arrow of time.

All this is to say that the "arrow of time" is itself not a sort of conceptual done deal. "Cause comes before effect" is, at best, a matter of definition. Events like the conception and birth of a new human being have conventionally assigned beginnings and endings, and what comes earlier is said to cause what comes after -- because we define the earlier part of a commonly recurring event class as causal. But that methodology really only works when we are dealing with familiar event classes. There are quantum situations wherein the same initial conditions will regularly not produce the same final conditions. What happens to the idea of cause and effect then? Imagine a quantum pachinko game. Pachinko is a game involving indistinguishable metal balls falling on a gridwork of fixed metal pins from which the balls are deflected repeatedly on the way to some exit point at the bottom. It is at least apparently totally random as to results, but making each decision a matter of true quantum probability and having a game involving thousands of potentially different combinations of decision points would result in a rigid experimental apparatus with results that could at best be predicted on a probablistic basis. None of the positions of the balls on their way downward through the maze of pins would seem to "come out of nowhere." "Nothing comes from nothing," as Aquinas long ago observed. But the preceding event could just as easily have been something different. Moreover, the chances of firing one ball from the receiver tray and having it ascend into the hole from which the balls ordinarily descend would be much less than you would want to bet your life on, or even your socks. Even though the possibility is finite, the combination of event after event means the multiplication of low probabilities together to produce even lower probabilities, so that the chances of any broken and splattered egg reassembling are virtually nil. — Preceding unsigned comment added by Patrick0Moran (talk • contribs) 22:33, 7 March 2011 (UTC)

"In classical physics a cause should always precede its effect. In relativity theory this requirement is strengthened{{Why?|date=May 2011} so as to limit causes to the back (past) light cone of the event to be explained (the "effect"); nor can an event be a cause of any event outside the former event's front (future) light cone."

Because special relativity says information, (matter or radiation) cannot be transmitted instantaneously, but is limited to the speed of light, therefore taking some time between cause and effect. — Preceding unsigned comment added by 69.248.118.36 (talk) 13:38, 11 November 2011 (UTC)

First, many physicists are opposed to the use of the ideas of cause and effect -- not out of any prejudice against either of them, but because they claim it is just not the most appropriate way to think about changes in nature.
The first statement above is really about how physicists think about things in their daily lives. If you've been watching Nova, Brian Greene just said it on TV: The equations work forwards and backwards and there is no indication given by the equations of which way things should go in time. What we observe most frequently are situations in which the experimenter becomes a part of the "cause and effect" relationship. Newton says f=ma. The experimenter can increase the force exerted by the rocket motor and the spaceship will accelerate. The experimenter can jettison some ballast from the spaceship and the acceleration of the spaceship will increase. The experimenter can direct the spaceship tangentially through the atmosphere of some planet and the spaceship will decelerate. The equation, by itself, doesn't say how the spaceship will behave. It could accelerate or decelerate. It could gain mass or lose mass. Forces applied to it could increase in one direction or decrease in the opposite direction, and more than one or two force vectors could be created by outside actors.
Quantum mechanics describes situations where A → B but also where A ← B. Of course one can say that in the first case A causes B, and in the second case B causes A. But it can also be viewed as the same event going in different directions in time.
It is quite clear that when one is talking about two events then there is a time gap between the two of them. Samantha is on the space station and observes that her husband Sam has just bet the family's entire wealth on a washed up nag with a split hoof. No matter how fast she moves she can't get to the race track to prevent the bet before it happens. Even her options if she should learn of the impending bet a little ahead of time are limited -- because it takes a finite amount of time at light speed for her phone message to reach her husband. The best a God invoked return to classical physics could do for her would be to cut the lag between cell phones to 0. But if she made that call at the same time Sam was putting their money down, it still would not prevent disaster.
One hopeful question is, "What would happen if she could move even faster than the speed of light?" Neutrino communications?
Another hopeful question is, "What if there are wormholes that lead from here and now to here and then?" If time is not a construct, not something that comes into existence as eggs splatter and stubbornly refuse to let Humpty Dumpty be put back together again, if time is a fabric of out of space and time space-time, then moving from one part of that fabric to another part of that fabric by way of wormholes in that four dimensional fabric could be possible.
Once one admits the possibility of some way of getting behind oneself in time, then the paradox exists. Our minds do not know how to deal with the idea of feedback chatter in space and time. "Jason ate the poison pill.→ Feeling the initial effects of the poison, Jason went back in time and substituted a hummingbird egg for the poison pill.→ Jason ate the hummingbird egg, and because he felt no ill effects he did not go back in time to switch out the poison pill. So Jason ate the poison pill.→....." Two entirely different scenarios follow from Jason's eating the poison pill and his not eating the poison pill. What happens to the chains of events that follow from each alternative? In one "universe" the ambulance taking Jason to the hospital collides with the future President and horrible results follow. In another "universe" Jason invents sustainable hydrogen fusion and saves us from global Venusization. It's much easier to sleep peacefully at night if we do not admit the possibility of time travel even by wormhole.
But it is self-delusory to say, "We cannot have that kind of thing going on, so we must impose the law that cause always comes before effect in time."
The whole argument is flawed in another way because it assumes that if one maintains one initial set of conditions throughout several runs of an experiment the final result is always the same. The clear result of quantum mechanics is that initial conditions produce a wilder zoo of later conditions the smaller the actors are. If human decisions depend in some significant part on events that happen at the atomic or near-atomic scale, then the third time through the loop Jason might be distracted and not notice symptoms of toxicity in time to push the button on his time machine. End of Jason, end of sequences messing up time-lines.
The main problem with the article is that it claims that one thing about the way causation works in the universe is caused by a distaste for infinite loops.P0M (talk) 17:03, 11 November 2011 (UTC)

Oh God! This is terrible!

I really don't know where to start with fixing it. Actually, I do. I'm going to remove the whole "Basic concepts of cause and effect" to start. Lucaswilkins (talk) 05:49, 11 December 2012 (UTC)

I plan to add more about how physical causality differs from other theories. I need my reference manager though. Lucaswilkins (talk) 06:14, 11 December 2012 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Causality (physics)/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

The idea of causality in physics is very important -- it is one of those principles that is so thoroughly built into the foundation of physical law that no-one would consider a theory in which it is violated! Nevertheless, the article as is is a bit unfocused. It needs to define causality clearly in the beginning, for example, and basically be a little more comprehensible to the reader. Terms like "light cone" could be introduced a little more gently. Perhaps better connections to other articles in physics could be made. Wesino 00:57, 29 November 2006 (UTC)

Last edited at 00:57, 29 November 2006 (UTC). Substituted at 11:05, 29 April 2016 (UTC)

Causality

In my Quantum Field theory (relativity + quantum mechanics) classes,

Causality means that an effect can not occur from a cause which is not in the the back (past) light cone of that event. Similarly, a cause can not have an effect outside it's front (future) light cone.

Nothing more, nothing less. No association wtih about uncaused events, Newton's second law, etc. In quantum field theory, it means that the commutator of two events is 0 if the separation is spacelike/elsewhere rather than timelike.

I removed superfluous text. Jmv2009 (talk) 08:26, 12 June 2016 (UTC)

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