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The possibility of randomness in physics doesnt particularly bother me, but contemplating the possibility that quarks might be made up of something even smaller, just in general, leads me to think there are likely (or perhaps certainly?) thousands of particles and forces, perhaps layers and sub layers of forces, at play that we do not know about. So this got me thinking about quantum mechanics.

I'm no physicist, but I do find it interesting to learn and explore the fundamentals of physics, so I'm wondering: Could the randomness found in radioactive decay as described in quantum mechanics be the result of forces and / or particles too weak / small for us to know about yet resulting in the false appearance of randomness?

Or rather, can that be ruled out?

Qmechanic
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J.Todd
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2 Answers2

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As noted in the comments this is a much studied question. Einstein, Podolsky and Rosen wrote a paper on it, "Can Quantum-Mechanical Description of Reality Be Considered Complete?", published in Physical Review in 1935, and universally known today as the EPR paper.

They considered a particular situation, and their paper raised the question of "hidden variables", perhaps similar to the microstates which undergird thermodynamics. Several "hidden variable" theories have been proposed, including one by David Bohm which resurrected de Broglie's "Pilot Wave" model. These are attempts to create a quantum theory which gets rid of the random numbers at the foundations of quantum mechanics.

In 1964 Bell analyzed the specific type of situation which appears in the EPR paper, assuming that it met the conditions Einstein et al had stipulated for "physical reality". Using this analysis he then showed some specific measurements that are in agreement with any such hidden-variable, classical theory would satisfy a set of inequalities; these are today known as the Bell inequalities. They are classical results.

He then showed that for ordinary quantum mechanics that the Bell inequalities are violated for certain settings of the apparatus. This means that no hidden variable theory can replace quantum mechanics if it also meets Einstein's conditions for "physical reality".

The EPR abstract reads: "In a complete theory there is an element corresponding to each element of reality. A sufficient condition for the reality of a physical quantity is the possibility of predicting it with certainty, without disturbing the system. In quantum mechanics in the case of two physical quantities described by non-commuting operators, the knowledge of one precludes the knowledge of the other. Then either (1) the description of reality given by the wave function in quantum mechanics is not complete or (2) these two quantities cannot have simultaneous reality. Consideration of the problem of making predictions concerning a system on the basis of measurements made on another system that had previously interacted with it leads to the result that if (1) is false then (2) is also false. One is thus led to conclude that the description of reality as given by a wave function is not complete."

In fact, one can run quantum mechanical experiments that routinely violate Bell's inequalities; I'm currently involved in setting one up which will be validated by violating Bell's inequalities. People have been doing this for over 40 years. The main argument against closing this chapter are the various "loopholes" in the experiments. Recently it has been claimed that a single experiment has simultaneously closed all of the loopholes. If that is true, then there are no classical hidden variable theories which can replace regular quantum mechanics unless they are grossly non-local. Einstein certainly would not think that these were an improvement!

Peter Diehr
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    Regarding the claim of having closed the loopholes, see Loophole-free Bell inequality violation using electron spins separated by 1.3 kilometres by Hensen et al. and Strong Loophole-Free Test of Local Realism by Shalm et al. – MvG Feb 24 '16 at 09:59
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    I actually not really read out of it you are answering yes or no to OP – Zaibis Feb 24 '16 at 10:47
  • If you read the two papers noted by MvG you will find that at least one unfalsifiable claim remains. The important thing to note is that every experimental result is consistent with quantum mechanics; Einstein didn't even question this. So there is no need for a hidden variable system; and most of the loopholes are closed. Today we are designing systems which rely on quantum mechanical results that violate the Bell inequities, such as quantum teleportation. – Peter Diehr Feb 24 '16 at 11:08
  • Is there any chance that this can be explained in a way that makes sense to a non-physicist? Intuitively, it certainly seems that there could always be undiscovered factors, but what I've read of QM seems to accept that randomness being inherent to the universe is a proven fact, and your answer seems to agree with this. Can you explain more about these Bell inequalities at a layman's level? –  Feb 24 '16 at 18:52
  • @JonofAllTrades As an other non physicist who followed some seminars about hidden variable theories, quantum mechanics etc last year: the problem is not randomness. The problem is non locality, i.e. the fact that we can act on something here and this will instantly affect something far distant away (see quantum entanglement). You can prove that any hidden variable theory that agrees with quantum mechanics will be non local. I believe de Broglie's theory of the pilot wave was already a non local hidden variable theory which should actually work well. – Bakuriu Feb 24 '16 at 19:27
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    Anyway I remember in these seminars that the speaker showed how we have non locality both if we assume completeness of QM and if we don't. However I don't really see something too wrong about non local hidden variables theories... I mean: QM is non local so it's nothing new. The whole thing seems to be about Einstein premise that we want universe to be local, which simply seems not to be the case, but this only tells us that Einstein was wrong and we should change the notion of physical reality. (But I may have misunderstood/forgot quite a bit of what I heard). – Bakuriu Feb 24 '16 at 19:42
  • @Bakuriu: non-locality violates the non-communication theorem of Special Relativity, which permits non-causal relationships. Einstein definitely did not like this! It also makes it non-classical, for classical physics + special relativity is always causal. The non-local effects of ordinary QM don't permit communication faster-than-light, so they only seem non-causal at first glance. Entanglement is a subtle concept. – Peter Diehr Feb 24 '16 at 19:48
  • @Peter Why is introduction of non-causal relationships such a big deal? From an ontological point of view, there has to be a non-causal layer that causes everything else and physicists are simply exploring downstream of it. – A.S. Feb 25 '16 at 02:48
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    @A.S.: sorry, but I don't even know what the word ontological means. I'm an experimental physicist and engineer, not a philosopher! – Peter Diehr Feb 25 '16 at 02:56
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The answer to your question, despite what commenters are saying, is yes, our observations in physics could be caused by factors that play a part on such an unreachable-small scale we can't detect them yet.

This even has precedent: before Einstein we couldn't tell what was causing the seemingly erratic movement of microscopic objects. See animation (source):

enter image description here

His description of what we now call Brownian Motion correctly described the motion of the blue ball as a result from constant bombardment of the much smaller red balls. While this doesn't seem helpful at first, the laws of thermodynamics and rules of probability help use derive useful macroscopic quantities of motion at the cellular level, such as how far the blue ball will be from it's starting center after a certain amount of time.

Perhaps, yes, little tiny Planck-length scale balls are bombarding the inside of all nuclei causing the emissions we now describe with the weak force. However, what you are suggesting is not doing physics. In this field, if you can't observe your prediction, you cannot expect others to take it as a de facto model of nature.

While you might be right about the cause of QM phenomena being these tiny, difficult to measure interactions, without any sort of proof you are just doing math (and without the math, you're just doing science fiction). This has been one of the leading criticisms we hear again and again about string theory.

user1717828
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    I would like to reiterate OP's point is not falsifiable: randomness found.. be the result of forces and / or particles too weak / small for us to know about yet. This is always a possibility, but since it's not falsifiable it is not physics. – user1717828 Feb 24 '16 at 04:06
  • Well, I think most will dissagree with me on this, and hence I dont claim to be a physicist per se, but, without knowing the math, I often formulate physical representations of the physics in my mind, and it seems to me that if I can hypothesize behavior, and then observe correlating behavior on two opposite extremes, for example the way gravity works on the simplest most fundamental level under normal crcumstances, and then the way it affects objects near a black hole, if my hypothesis physically matches the behavior observed at both extremes, ... – J.Todd Feb 24 '16 at 07:23
  • ... then I could potentially be very sure of it being accurate, even without direct observation. That seems like physics to me; despite not being able to observe such small/weak particles / forces directly with present technology, if a hypothesis can line up with observable behaviors of physics at both of two opposite extremes than we could determine the hypothesis to be highly likely, even though we cant test/observe it directly in an experiment. – J.Todd Feb 24 '16 at 07:23
  • What you are suggesting is a good start; I recommend that you read Galileo's "Two New Sciences", which is in the form of an extended dialogue between three people. – Peter Diehr Feb 24 '16 at 12:08
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    What? This completely ignores the theoretical and experimental demonstrations of the violation of Bell inequalities. – DanielSank Feb 24 '16 at 18:04
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    @DanielSank Hi. Well. I truly don't understand why have you said that. Where does he ignores it? The experiment you said indeed does indicate that there cannot be local determinism in quantum mechanics. Fine! But how about non-local determinism? How about quantum non-equilibrium theories? This experiment does not rules out non-determinism. The word "local" is quite important and cannot be ignored. I think this answer is nice: It is saying: "Always trust experiment", and also saying: "Without experiment, one is just doing math". – Physicist137 Mar 29 '17 at 23:29
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    @Physicist137, yea, I never understood either the downvotes or the agreement with Bell-Inequality-Shoutout-Guy. It was responses like this that made me realize Physics.StackExchange is "science by popularity" and caused me to stop participating. – user1717828 Mar 30 '17 at 00:41