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I'm presuming that the scientific community pretty much agrees that randomness doesn't exits, and that everything has a cause. Please correct me if I'm wrong, I've heard of quantum mechanics, but as far as I know, it only says that it is impossible to know the electron's position and speed in the same time, because of the uncertainty principle, but I don't think that this makes the electron move randomly.

Now, lets consider big bang. A point starts expanding in size, as the time flows. If there isn't any randomness, it is logical to conclude that matter will position itself in some kind of a predictable pattern, not chaotic shapes as we see today. So, I ask you, how did the universe form as it is today? Is that proof that randomness truly does exits? Does randomness break laws of logic and physics?

Qmechanic
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jcora
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    "I'm presuming that the scientific community pretty much agrees that randomness doesn't exits" Why would you presume that?!? – dmckee --- ex-moderator kitten Apr 25 '12 at 01:32
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    Aside from the wrong presumption, which answers the question, this is a legitimate confusion. Why he downvote? This is a proof that true randomness exists, or as close to one as you're likely to get. – Ron Maimon Apr 25 '12 at 04:11
  • That was my thought as well. The question is based on an incorrect premise, but other than that it's not so bad. Of course people are (mostly) free to do as they wish with their downvotes... – David Z Apr 25 '12 at 06:19
  • I suggest this question to be closed as a duplicate of this one: http://physics.stackexchange.com/questions/317/why-cant-the-outcome-of-a-qm-measurement-be-calculated-a-priori – Anixx Apr 25 '12 at 07:52
  • @Anixx I don't see how the two are asking the same question. They seem different both in focus and in the OPs' levels of understanding. I believe that the standard test is something like 'if the answers on a previous question would also constitute complete answers to this question'. If I take, say, Joe's answer on that question and apply it here, it doesn't seem to answer this question or be at an appropriate level. – Logan M Apr 25 '12 at 11:09
  • Without making any claims for the downvoters I would say that this question "does not show any research effort" just as the downvote tooltip says. I mean google for "real randomness" or similar and see what you get. – dmckee --- ex-moderator kitten Apr 25 '12 at 14:34

2 Answers2

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This is a superb question, because it gets to the core of one of the great debates of 20th century physics - the nondeterministic interpretation of the laws of quantum mechanics (that is, the universe is truly random), vs the "hidden variables interpretation" (that is, the universe is non-random, but the underlying variables that control it can't be measured).

Almost all serious scientists these days accept nondeterminism, usually in the form of the Copenhagen interpretation; so your presumption that "the scientific community pretty much agrees that randomness doesn't exist" is the complete opposite of true.

David Z
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Dawood ibn Kareem
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  • Very succinct. I like it. (Though the Copenhagen interpretation is not the only alternative to hidden variables; perhaps it would be good to use slightly less specific wording.) – David Z Apr 25 '12 at 06:22
  • You're right, of course. But I didn't want my answer to turn into a list of options. I think the OP should get the point, if not from my answer or Logan's, then from the numerous comments pointing out the error of his/her assumption. – Dawood ibn Kareem Apr 25 '12 at 06:29
  • OK, I reworded a little, while trying not to change too much in your post. (If at any point you think that the original version was better or that further changes are needed, do edit accordingly - it is your answer after all :-P) – David Z Apr 25 '12 at 07:01
  • I downvoted this answer because 1)It praises with no purpose a really terrible question 2)It does not meet the question's level 3)It is incorrect. – Anixx Apr 25 '12 at 07:49
  • This is a nice answer. It addresses the heart of the question succinctly, though my answer is more in depth on some tangential issues. – Logan M Apr 25 '12 at 10:53
  • @David, Why do almost all serious scientists these days accept nondeterminism? Is there a simple explanation to this? – Pacerier Jan 01 '13 at 11:42
  • @Pacerier, I think that it is not entirely correct to say that serious scientists "accept" nondeterminism. The more correct version would be to say that serious scientists see no scientifically meaningful difference between the "hidden variables" theory and the "randomness" theory. – Him May 06 '19 at 17:23
  • Since the discovery of quantum mechanics, we have looked for "hidden variables" and they have not appeared. It seems, given our current state of knowledge, that if there are any "hidden variables", they are "hidden" so well as to be beyond observation in any physically meaningful way. If we can't observe them, then they cannot be scientifically studied. This is much the same as how cosmologists generally consider "what lies beyond the observable universe" to be a matter of speculation, and not one of science. – Him May 06 '19 at 17:24
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I think your presumption is entirely incorrect. Quantum mechanics says is that physical observable quantities of systems are given by probability distributions, so there is intrinsic randomness in any quantum mechanical system. The laws of physics, as we know them now, are fundamentally random in some sense.

Your question still makes sense if we ignore that, though. The degree of randomness should be small for large systems. One can ask about why there are anisotropies (deviations from uniformity) in the distribution of matter and energy in the universe. Most people who study this do so in the context of cosmic microwave background radiation, i.e. photons emitted at the big bang. It's probably not possible to study it in the context of, say, ordinary matter, because gravitational effects will cause clumps of matter to get larger over time, forming very dense regions (stars, galaxies) separated by regions which are mostly empty. So gravity actually magnifies anisotropies over time. Keep in mind, though, that galaxies are actually very small compared to the size of the observable universe, and so anisotropies on the galactic scale shouldn't be too surprising.

People do study CMB anisotropies, and it is a very active area of research. In fact, these anisotropies are actually very small in magnitude. There's still a lot of work to be done here, but the precision measurements that have been done are consistent with what one expects from a quantum mechanical treatment of thermal fluctuations at the big bang (that is to say, quantum mechanical random fluctuations from uniformity at the big bang).

Also, there's no reason to believe that matter was created in all directions equally at the big bang. It's entirely possible to come up with models consistent with general relativity and the big bang which don't have this property. Finally, I question your statement that the galactic-scale structure we see today is chaotic. It exhibits a large number of patterns and has a great deal of structure and uniformity.

On a side note, about randomness, there is a more interesting question in the same vein, which is still open. Why there all matter and essentially no antimatter in the universe, despite the fact that they were created in almost equal quantities at the big bang? The hypothetical answer is CP violation, but all the known sources of CP violation aren't strong enough for the matter density to be what we observe.

Logan M
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  • quantum mechanical treatment of fluctuations is tantamount to saying "pure randomness", so this is just what OP is saying jargon-free. – Ron Maimon Apr 25 '12 at 04:12
  • Nowhere that I can find did the OP say he wanted a jargon-free answer. Even if he did, a certain level of jargon is useful to know, and most of it was clearly explained. I've added an explanation for the particular phrase in question. – Logan M Apr 25 '12 at 10:38
  • Also, I'm not sure what the phrase "pure randomness" means. What makes a particular distribution purely random by your definition? – Logan M Apr 25 '12 at 10:49
  • The point is that "quantum fluctuations" and "pure random" are the same thing. "Pure random" means that some data bits are not determined by anything, but have values that have a probability distribution of some kind. This becomes most meaningful in the infinite limit, it means that a countable infinite sequence of such bits makes a non-constructible real number, that such a number determines the measure of any set in [0,1], breaks AC, etc. Perhaps you don't accept the countable infinite limit, but then pure randomness means undetermined by other bits, its not a property of the distribution. – Ron Maimon Apr 25 '12 at 16:16
  • I don't totally understand what you mean, and I definitely like AC (otherwise how will I know that my rings have maximal ideals?). Personally, I'm of the opinion that random numbers/sequences are essentially abuse of language, but if I translate what you are saying into my language then I think what you call 'pure randomness' is what I would just call randomness, which in my book is a fundamentally physical (i.e. nonmathematical) concept. But in any case I don't think there's any more need for discussion of it here. – Logan M Apr 25 '12 at 23:30
  • A few points: it's enough for all your purposes (I can say this without knowing them!) that all countable rings have maximal ideals. Any uncountable ring becomes countable inside any model of any axiom system, and if it is truly uncountable, you have no intuition. The point is that AC is unacceptable with probability, because it forbids a consistent notion of a "random pick from [0,1]". The distinction here is between "pure random" and "pseudorandom", as in determined by very complicated rules we don't know. Physics includes "pure random" quantum quantities. Math doesn't define "random". – Ron Maimon Apr 26 '12 at 01:59
  • The failure of AC in mathematics that defines randomness is very important. If you don't know this, consider--- I flip a coin infinitely many times and write down a random bit sequence .0110011. This defines a uniformly random pick from the interval [0,1]. What is the probability that this number lands in a Vitali set? This is a paradox. This paradox is removed by either forbidding talk of random picks from spaces with uncountably many elements (the usual convention in mathematics, never actually enforced), or by using Solovay style model of ZF where every subset of [0,1] has Lebesgue measure. – Ron Maimon Apr 26 '12 at 02:03
  • It is definitely not true that any ring I am interested in is countable; take for instance $\mathbb{C}^n$ with the direct product. Most of the explicit examples I'm interested in could be dealt with by countable choice, but for both categorical and practical reasons it it's far easier to just deal with all rings. – Logan M Apr 26 '12 at 07:31
  • Back to probability, I don't think there should be a consistent notion of a "random pick from [0,1]" in the way you are claiming. Such a thing is an abuse of language, as are random bit sequences. A Vitali set isn't an event, so there's no reason to expect it to have a probability. I don't see any paradox with that. It is true that this notion of probability and the physical one are somewhat different, but I don't see a problem with that. If you want to continue this discussion, let's move it to chat, because it's become entirely irrelevant to the topic of the question. – Logan M Apr 26 '12 at 07:36
  • If you pick a random number in [0,1], what's the probability it lands in a Vitali set? This is a perfectly reasonable question, and the process of random picking is made formal by random forcing, so that I adjoin the randomly picked number into the pre-existing model of set theory. I know this is off the main line, but it is annoying to me that mathematicians make the most ridiculous choices, even after being patiently corrected. – Ron Maimon Apr 26 '12 at 09:39