Did quantum mechanics kill cause and effect?

Originally posted by Prosoothus
Are you sure that there isn't a reason (a cause) why there are only two kinds of charge (I'm assuming that your ignoring quarks)?
I can't ever be sure that there's no reason -- but we certainly don't know the reason yet. We don't really think there is a reason, and usually let the philosophers tackle it.
And as far as I know, relativity states that time dilation and length contraction is the reason (or cause) behind the principle of invariance of light.
This has been explained to you before. That the speed of light is a constant for all observers is the postulate; it is assumed. Length contraction and time dilation and so on are derived from that assumption. You just have it backwards.

- Warren
 
chroot,

This has been explained to you before. That the speed of light is a constant for all observers is the postulate; it is assumed. Length contraction and time dilation and so on are derived from that assumption. You just have it backwards.

Logically, length contraction and time dilation are deductions from the assumption that light is constant for all observers.

Therefore, length contraction and time dilation must be the causes of the principle of invariance of light, and not the result. Or are you claiming that the speed of light causes time dilation and length contraction??? :bugeye:

Tom
 
Originally posted by Prosoothus
Therefore, length contraction and time dilation must be the causes of the principle of invariance of light, and not the result. Or are you claiming that the speed of light causes time dilation and length contraction??? :bugeye:
Well... I don't know if you and I can agree on the definitions of 'cause' and 'effect' then. If the speed of light is invariant, then length contraction and time dilation also occur. I don't think of either as the 'cause' and the other the 'effect.' They are really the same thing, just said two different ways.

- Warren
 
Originally posted by chroot
hlreed is a crackpot, and was just taking the opportunity to rib him a bit.
Well, I should have known to mind my business... but I felt like posting. I do enjoy watching you smash the crackpots (even when I'm one of them). I think hlreed means well, but yeah.. that doesn't mean he isn't a crackpot. I think it's just that creative people with half-assed logical minds try to apply their creativity to problems that they don't fully understand.. then they gain some "insight" and take themselves way too seriously. Nothing wrong with it as long as you don't take yourself too seriously. I suppose it's okay to be a crackpot as long as you know that's what you're being (IMO). Plus I mean Warren, brother, don't the crackpots help keep you honest? :) Isn't it the killing of crackpots that sets you free?????? lol


Originally posted by chroot

Not that I'm aware of. Can you be more specific?
well, there is no causality regarding which path is chosen right (and I realize I probably mislabeled the experiment and I'm definately not versed enough with this stuff to have a serious conversation about it, I was only trying to make the point that it might SEEM to someone of limited understanding that causality is violated). I'm talking about the experiment where a photon hits a splitting mirror or whatever? Eh, I realize there's probably no real violation.. but it could seem that way given your perspective or lack of understanding.
Originally posted by chroot

Not really. QM does not lead to violations of causality. Period.
I was just trying to nicely say that it's quite counterintuitive. Did you see the article in sciam a month or few ago about quantum computing and entanglement and all that stuff? It was quite interesting and could really get a person with limited understanding going ya know?
 
Originally posted by wesmorris
Well, I should have known to mind my business... but I felt like posting. I do enjoy watching you smash the crackpots (even when I'm one of them). I think hlreed means well, but yeah.. that doesn't mean he isn't a crackpot. I think it's just that creative people with half-assed logical minds try to apply their creativity to problems that they don't fully understand.. then they gain some "insight" and take themselves way too seriously. Nothing wrong with it as long as you don't take yourself too seriously. I suppose it's okay to be a crackpot as long as you know that's what you're being (IMO). Plus I mean Warren, brother, don't the crackpots help keep you honest? :) Isn't it the killing of crackpots that sets you free?????? lol
Sometimes it's quite difficult to find the errors in someone's logic, and sometimes the effort really does teach me a thing or two in the process.
well, there is no causality regarding which path is chosen right
I'm not sure how a photon or electron choosing one slit over another violates causality. A violation of causality would be an electron hitting a detector before it even leaves the source.
I was just trying to nicely say that it's quite counterintuitive. Did you see the article in sciam a month or few ago about quantum computing and entanglement and all that stuff? It was quite interesting and could really get a person with limited understanding going ya know?
...even a person of great understanding. ;)

- Warren
 
chroot

Yet while the laws of physics say systems will tend toward entropy, they do not pick out a direction in time. One recent discovery indicates that the weak interaction (one of the four forces) may violate time-reversal symmetry at the level of one part per billion. This result caused a great deal of interest and follow-up experiments, but in no other instance have scientists observed the violation of time-reversal symmetry. In my opinion, the uniqueness and great weakness of the observed effect serve to underline the actual time-reversal symmetry of the laws of physics.

http://aether.lbl.gov/www/tour/asap/smoot_time3.html


whats that? is it relevant?

and picking up where wes left off... doesnt entanglement have any implications for causality? if a is tweaked and b is instaneously affected, can a still be said to be the cause of b...?
 
One of the long-held beliefs among physicists was that physical laws would stay the same under the so-called CPT symmetry. C is charge conjugation (change all + to - and vice versa). P is for parity (basically take the mirror image of everything). T is for time reversal (basically replace t with -t).

When you do all three of these changes at once, physics is supposed to proceed without any changes. In other words, physical laws are symmetric around CPT together.

However, the weak interaction is NOT CPT invariant -- and one of the big symmetries that physicists hoped for was shattered by experiment. All of the other forces are CPT symmetric -- except the weak.

- Warren
 
Quantum mechanics <i>may</i> be acausal when it comes to determining how a wavepacket collapses on measurement. Nobody know if it is or not yet.

A quantum system in a superposition of states will evolve causally to other states unless a measurement is made on the system. When a measurement occurs, however, the wavefunction "collapses" into one of the observable states. The collapse is random - we can't predict in advance which observable state the system will end up in - only the probability of each outcome.

Whether the process of collapse of the wavefunction is deterministic is currently an open question.
 
Originally posted by chroot
However, the weak interaction is NOT CPT invariant -- and one of the big symmetries that physicists hoped for was shattered by experiment. All of the other forces are CPT symmetric -- except the weak.

Sorry to drag this off topic, but when was CPT violation found?

Tom
 
It might not have killed cause & effect, but it surely put a dent in it.

At a philosophical level, Quantum Theory negates the concept of a deterministic universe, which was believable under classical physics. I think most 19th century physicists and philosophers believed in a deterministic universe, but few do today due primarily to the development of Quantum theory. Strict cause and effect laws would suggest a deterministic universe. If the universe is not deterministic, then cause and effect is questionable at best.

The uncertainty principle, the lack of continuous values for physical quantities, and other quantum weirdness strongly imply problems with a cause and effect view of the laws of nature.

At a practical level, it is hard to believe that a process like radioactive decay is a cause and effect phenomenon. It is a random process as indicated by the data associated with it. If the result (effect) is random, it is hard to imagine a cause in the usual sense of the meaning of the word cause. For me, radioactive decay is an experimental example of an effect with no cause.
 
Originally posted by Dinosaur
Strict cause and effect laws would suggest a deterministic universe.
Probablism means that when something happens, the effect is only known in terms of probabilities. Just because the outcome is not predictable does not mean the system is not causal.

I don't see how the probabilism vs. determinism argument has anything to do with causality.

- Warren
 
Originally posted by Prosoothus
chroot,
Isn't randomness a violation of cause-and-effect???
Tom

:eek: I suggest :

Pearl, J. [2000] Causality: Models, Reasoning, and Inference. Cambridge University Press.
 
Chroot:A belief that every effect is due to some cause strongly implies the existence of an algorithm allowing one to predict what will happen as a result of a given action or process (Id est: As a result of a given cause). This certainly suggests that a belief in a strict cause and effect universe implies a belief in a deterministic (in principle) universe.

Until the end of the 19th or the beginning of the 20th century, most scientists and philosophers believed that the future of the universe was in principle predictable at a detailed level. I do not think that anybody believed that it was possible in practice to collect the necessary data and do the necessary calculations.

This belief might have been partially due to theological beliefs. In the scientific community, it was due to belief that at the fundamental particle level, all processes were governed by knowable laws which could be described by precise mathematical equations or algorithms. A belief in the existence of such algorithms seems to be the basis of a cause and effect universe.

The belief in a deterministic universe is no longer accepted by a large segment of the scientific community due to the advent of Quantum Theory. The primary reason for this change in point of view is the statistical or random nature of various Quantum level processes.

Consider the nature of the radioactive decay of a material with a half life of one minute. If you have 1024*10<sup>22</sup> atoms, 512*10<sup>22</sup> will decay in one minute, and another 256*10<sup>22</sup> will decay in the next minute. Half of what is there will decay each minute. It is like flipping a coin for each atom every minute. Heads the corresponding atom decays, tails it doesn’t.

Now what happens if there is only one atom? Half the time it will decay in one minute. 1/4 of the time it will decay in two minutes. 1/8 of the time it will decay in 3 minutes.

The above describes a process that is random. It is also unpredictable in the sense that there is no algorithm for determining which atoms will decay in the next minute. Contrast this with the 19th century view of a many body problem in gravitation or the thermodynamics of a gas. Those problems were unpredictable at a detailed level due to practical problems in applying the proper equations. Other 19th century problems were viewed as unpredictable due to not knowing the pertinent laws, but there was some hope of knowing the laws in the future.

Radioactive decay and other quantum processes seem to deny the possibility of ever being predictable. Such processes seem to be governed by some capricious laws outside the realm of cause/effect relationships.

Oddly enough, for huge numbers of atoms, the behavior seems consistent and predictable, leading us to believe that deterministic laws are governing our classical world. A very accurate clock can be based on radioactive decay. The classical world of our senses which seems to be deterministic is built on the statistical Quantum world. The apparent cause/effect nature of it cannot be extrapolated to the Quantum world.

The quantum world underlying our classical world is whimsical, capricious, subject to statistical laws. Not deterministic and subject to cause effect laws. Two of the most brilliant minds of the 20th century made statements like the following.
Bohr: If you are not confused by Quantum Theory, you do not understand it.

Feynman: Do not ask how it can be like that. Nobody knows how it can be like that.
The classical world of our senses acts like a cause/effect world. Our minds have been conditioned by several millions years of evolution in the classical world of our senses. That conditioning has been very important to our survival. Such minds cannot be comfortable with the notion of a world governed by capricious laws.
 
Dinosaur, everything you said was correct. and thanks for the long exposition about how the quantum world is not deterministic.

i m pretty sure chroot knows all this.

you are talking about probabilism vs determinism. this has nothing to do with causality. quantum mechanics is still causal.

the propagation of a wave function takes place within it s light cone. therefore causality is preserved. no quantum event, no matter how random or unpredictable it is, occurs before it s cause.
 
Lethe: The bolded (by me) part of your post is correct, but see caveat below.
the propagation of a wave function takes place within it s light cone. therefore causality is preserved. no quantum event, no matter how random or unpredictable it is, occurs before it s cause.
Any event with a cause must occur after the cause, but this statement assumes the existence of a cause. Do all random quantum events have causes?

One must be careful with certain statements. For example, all seven headed men have 14 eyes is logically valid, but does it inmply the existence of men with 14 eyes?

Suppose some experiment recorded activity relating to a particular radioactive nucleus until it decayed. Could the cause of the decay be identified?

I have never read anything about a cause for radioactive decay, but I do not claim to have read everything on the subject. I have never read anything about causes for various other random quantum phenomena. For example, when there is a 25% chance of a quantum entity passing though a polarity detector, is there a known cause for why it made it through or did not make it though?

It seems to me that an identifiable cause would make an event predictable. Various quantum events are described as random, implying unpredictability.

I am not an expert in Quantum Theory, although I think I understand better than a lot of those who post at this forum. I do not claim to know more than all of you, but would prefer not to name names in this post.

I would like to hear from anybody who has knowledge of the existence or nonexistence of causes for any random quantum event.
 
Dinosaur: OK, i see your point now.

so first, just so everyone is clear on this: when there is a cause and an effect, the cause always precedes the effect. this is what is meant when we say causality is preserved in quantum theory.

but your point: does every quantum event have a cause? if not, then can we really say that quantum theory is causal?

it s a good point.

i m also not an expert on quantum theory. i want to think about this a bit. right now, i m inclined to say that there is a cause for all quantum events. just that some are not measurable. when we calculate decay rates for particles, we do it with perturbative quantum field theory. in this theory, virtual guage bosons appear in the vacuum to catalyze the particle s transformation. we can say that quantum fluctuations, in a very rough sense, due to heisenberg s uncertainty principle, are the cause of the particle s decay. insofar as you can think of virtual particles really existing, i think you can say that the quantum event has a cause.
 
Originally posted by Tom2
Sorry to drag this off topic, but when was CPT violation found?

Tom

probably chroot meant parity violation? quite an interesting thing, the discovery that the weak force breaks parity symmetry.

after they discovered this fact, theoretical physicists hoped very much that CP (charge conjugation + parity inversion) would be preserved. but nope. the weak interaction also violates CP. not very much (unlike P, which it violates maximally), but enough to notice.

now physicists are hoping that CPT won t be violated. as i understand it, this one will be difficult to measure (because how to you invert time in the laboratory?). a lot of nice theories will be thrown out if CPT is violated (like SUSY (supersymmetry), but then, there is no experimental observation of SUSY yet, so who cares, right? well lots of people really really believe in SUSY. and they care.) but as far as i know, CPT violation has not yet been found. they re looking though.

anyway, chroot s comment works just fine. just change CPT to P. or CP.
 
Lethe your knowledge is requested in the "Chiral Condensate" postings. We have no clue what we're talking about quite frankly. Thanks. :bugeye:
 
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