- #71
DrRocket
- 113
- 2
Pythagorean said:Well, this is frustrating. You've basically repeated many of the posts I've already made in this thread as if they were counterarguments.
I've done research in acoustics, and currently do research in chaos theory (i.e. nonlinear dynamics). I've also taken a full degrees worth of physics classes and some probability theory for my master's study. I said exhaustive sample space, not probability space. If you still don't know what I mean, and refuse to look in your texts on probability, I can break it down for you, but I'm hoping you were replying with animosity, thinking I was an ignorant armchair philosopher and didn't really consider what I may have meant at the moment.
I understand probability theory pretty well and it is quite frankly you who do not know what you mean. Trying to somehow appeal to authority with veiled references to unspecified degrees is not going to work. I will see all of your degrees and raise you a couple. Degree comparisons are not germane in any case. Let's stick to content.
Go ahead and break it down if you like. This should be interesting.
No animosity involved. As to anything else, I will simply form my opinion based on the content of our posts, or lack thereof.
Pythagorean said:In acoustic (experimental acoustics if that clears things up.. we're actually looking at real data) the word random has a statistical basis. The definition is based on a lack of information. When I used "white noise" I obviously meant the acoustics definition, which is physically defined: it has a flat power spectral density. That's not the point though. The point is that I can use a random number generator to simulate the white noise. I was demonstrating the usefulness of a definition of random in probability theory as it applies to science. This is just one example.
The definition in terms of a flat power spectral density it NOT physically defined, but rather mathematically defined -- via the statement that the power spectral density is constant. That is a statement about Fourier transforms. It is not physical, and in fact is not physically possible. It is an idealization that makes for simplicity in some calculations.
Just precisely how are you "demonstrating the usefulness of a definion of random in probability theory"? Remember that a random variable is nothing more and nothing less than a function that is measurable in terms of the sigma algebra of your probability space -- fpr the function to be measureable the inverse image of an open set must be a member of the sigma algebra (aka a measurable set). So, just how have you demonstrated the usefulness of this concept ?
Pythoagorean said:In chaos theory, on the other hand, the discussion tends to be more philosophical. The point being that seemingly random events do actually have a cause and that apparent randomness can be traced back to a sensitivity to initial conditions. This definition of randomness is about causation. It's not an assertion as to whether all events can be random or not, it's the study of particular events that seem random, but aren't (and the study of determining whether certain events truly are random or are not).
Chaos theory has NOTHING to do with random processes. In fact, what are normally called chaotic systems are in fact completely deterministic -- as reflected in the sensitivity to initial conditions in some cases. Moreover, there are all sorts of things going under the title of "chaos theory" some not worthy of the name "theory" at all. For a good, rigorous discussion, in the context of topological dynamics one might refer to Bob Devaney's book An Introduction to Chaotic Dynamical Systems, but it is rather tangential to the discussion at hand. In fact I have no idea why you bring up this red herring.
What is heavens name is "the study of particular events that seem random, but aren't" ? Have you ever read a book on topological dynamics, or maybe ergodic theory ? You are spouting nonsense.
Try Devaney's book.
Pythagorean said:Of course, I think it's somewhat cavalier to talk about causation and randomness in quantum mechanics without talking about quantum field theory, which I'm guess none of us are well versed in.
Speak for yourself. If you want to bring in quantum field theories go right ahead. But it adds nothing to the discussion, save to eliminate direct reference to the Schrodinger equation.
There is and was nothing cavalier about the reference at all. It is quite germane.
Pythagorean said:Anyway, back to my point, which you eagerly missed. The statistical/probability definitions of random are useful to us in the sciences and are weakly connected to causation, as long as we acknowledge that our sample space is limited (i.e. not exhaustive).
I did not "eagerly miss" anything. What is your point ? This makes no sense. I suggest that you go back and review your own probability books, and in particular the definition of "sample space" and "probability space". Try Probabilty by Loeve, which is the classic text or Stochatic Processes by Doob.
Pythagorean said:A concrete example to help you with the assertion:
When I try to change the environment in different ways to produce different outputs on the microphones in my acoustic array, I can't possibly find (or practically setup) every possible combination of inputs. Everything I can possibly do has no affect on the noise. The noise remains. I don't say "eureka!" the noise is random (uncaused)! I say, "well, within the sample size I was able to attain, I can't find any causes of the noise".
Which has nothing to do with random processes. Your inability to adequately set up and shield your electronics from outside electromagnetic fields or from outside acoustic signals, or both, has nothing to do with causality. It may have something with your personal inability to locate the source of the noise, but that is completely unrelated to the question of whether a cause of the noise exists.
"Random" and "uncaused" are not the same thing. Shot noise and ordinary electromagnetic interference are caused. In fact one of the sources of noise in electronic systems is the cosmic background radiation, the discovery of which earned Wilson and Penzias a Nobel prize. I would not call that uncaused (see "Big Bang"). I think many would characterize it as random in some sense -- it matches blackbody radiation, which as a quantum effect can reasonably be called random.
You seem to have somehow confused an inability to locate a source with some unstated question involving random processes. Perhaps what we have here is some sort of random thought.
Pythagorean said:If we can find a cause for something, we model it based on its dependent variables (the cause) and we no longer have a need for random data generation. That's how it's connected to causation. But this definition (lack of information) is not based on causation.
It is quite possible to know the cause of something ans still not have at hand a "model based on its dependent variables". That is precisely the situation with "white noise" or "shot noise" in communication theory. It would also apply to black body radiation, wherein one can predict the spectrum but not every bump and wiggle in the received signal.
Pythagorean said:Which becomes confusing in discussions, since there is also the qualitative definition of randomness that pertains to actual causation, regardless of information. But notice, that if a system is truly random in this way, then it is also a matter of a lack of information. There's no information to be had about causation. Just the observation, statistically recorded (i.e. bose-einstein statistics and fermi-dirac statistics). i.e. Quantum Mechanics.
All you have demonstrated here is that you don't understand quantum mechanics, whether that be ordinary quantum mechanics or quantum field theories. This is just meaningless juxtaposition of words.
This is getting silly. I'm done.