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defining and explaining them to non-experts:
or merging another article's section with this one (give reason) :
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)
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.
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)
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).
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)
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)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.
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.
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.
The article imo needs a major retouch. People (no pun intented) get your terminology straight!!!! :) Thanatos| talk 03:07, 10 December 2009 (UTC)
P0M ( talk) 04:25, 10 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)
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)
I think that Thanatos (why, at age 70, does that name bother me?) is seeing problems with the paragraph that begins:
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:
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:
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)
`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)
The current text has:
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?
P0M ( talk) 22:58, 29 December 2009 (UTC)
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)
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)
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)
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)
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)
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)
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)
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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![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
Do not remove the elements, but rather strike the text as they becomes useless or irrelevant (i.e write
text to be struck) to indicate that this element was verified and found to be alright.
Tasks
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defining and explaining them to non-experts:
or merging another article's section with this one (give reason) :
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)
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.
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)
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).
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)
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)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.
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.
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.
The article imo needs a major retouch. People (no pun intented) get your terminology straight!!!! :) Thanatos| talk 03:07, 10 December 2009 (UTC)
P0M ( talk) 04:25, 10 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)
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)
I think that Thanatos (why, at age 70, does that name bother me?) is seeing problems with the paragraph that begins:
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:
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:
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)
`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)
The current text has:
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?
P0M ( talk) 22:58, 29 December 2009 (UTC)
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)
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)
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)
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)
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)
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)
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)
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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