Is there a definition of randomness?

In summary, the concept of "randomness" does not have a formal definition and is often approached philosophically rather than mathematically or scientifically. While there are formal definitions for items used in probability theory, such as random variables and stochastic processes, these do not fully capture the meaning of "randomness". Additionally, the concept of "normal" sequences of digits has some similarities to the folk notion of "randomness", but it is also limited in its ability to provide a clear definition. Ultimately, the predictability of a process depends on the theory being used, and there is no way to determine if there is an unknown, more sophisticated theory that can predict outcomes that currently seem random. The idea of "randomness" is also closely
  • #106
PeroK said:
But, what if there is a physical, theorectical limit to observation knowledge? This could come from a) there being a limit on how accurate a measurement of position could possibly be; and/or b) a limit to the knowledge of two observables - the HUP (Heisenberg Uncertainty Principle) essentially says that the more accurately you know the position of a particle, the less accurately you know its momentum - in any case, you can't know both to an arbitray precision; and/or c) a piece of data that is intrinsically random, such as the spin on an electron, which may be theorectically unknowable.

This ties into my post above. There is no certainty that Quantum Mechanics will one day be replaced by a "deterministic" theory, where the HUP and the instrinsic probabilities disappear. And, unless that happens, then there are clear limits to observational knowledge.

To be more specific, I'm not necessarily saying that randomness exists, but I'm also not saying that it doesn't exist. I definitely don't have privileges that break quantum observation, lol.

And yes, the limits are clear. Assuming that human beings and human logic are the highest point on some hierarchy we imagine exists, thus creating our measurement error in any possible measurement device that we can currently imagine. To be more precise, we will never have a finalized and perfect definition of the physical world, thus we will never have a fully agreed upon definition of what is random.

Zafa Pi said:
Random := The value(s) produce by an objective* physical* process that when repeated yields a sequence that passes randomness tests.
* objective means repeatable by others. * physical means non-algorithmic, like coin flips.

I like this definition of randomness as it is useful for most purposes and clearly delineates physical phenomena from math.

It's theoretical, but I don't think it's fluff. Un-testable by current standards? yes. There is still a humongous debate about whether or not reality is deterministic. I am liking what's going on with Quantum Gravity theory with their quasicrystals and information theoretic notion of reality which takes neither side of the debate. We can only measure phenomena which we can sense (with our senses or some device), and even then, the measurement of that phenomena changes the outcome, plus is very prone to error. Are there dimensions in physical systems which we are not taking into account and could be measured to approximate an outcome, but we simply cannot measure them yet?

I'm not saying that we are in a simulation. That is, I think, too far off topic. But I will give a simulation test example of how randomness can be explained. The problem being that you don't know if physics is the observed result of some higher order algorithm which sits behind the true laws governing the physical system in which the coin is being tossed. You have to take into account "the observer" which is also theoretical, but I mean, if we can't prove randomness exists, then randomness is also theoretical.

Let's take the idea and inverse it.

If you assume that the observer exists, technically any device which senses a physical phenomenon is an observer of that phenomenon whether or not it comprehends what it is sensing. Let's say that I make a program which takes input from a camera, performs a couple of filter operations on the incoming data and creates a 2D space which is scattered with colored points that represent the color edges being sensed in the current frame. So my space has the following dimensions: (x, y), (r, g, b) and the x,y sub-space is filled with points by the edge filter using the r,g,b data from the original video frame. Now let's say that I also populate this space with "observers" which follow some rules that govern their behavior.

What my little simulated observers are sensing are the edge point positions and color that are the result of multiple filters working constantly on some input data. The filter input data is coming from "my reality" or what you refer to as the physical world, whereas the filtered output data is a simplified projection of that raw data. To further complicate things, let's assume that the simulated observers can recall and track edge shapes from the points they observe. They will always ever be observing a filtered 2D projection of a 3D space. Let's also assume that they have some ability to remember patterns and thus predict near-future outcomes like a shape they will see, or where and in what orientation that shape will turn up.

They will never be able to fully predict where and when in their reality, the points that represent my hand will show up, because they don't know my hand exists as a hand. The idea of what a hand is supersedes them, since they don't have hands or bodies. A hand is only represented in their space as a recognizable set of points with specific relationships in 2D+Color+Edge space, which occur in some positions at some rotations, etc. The physics of how a CCD camera works, how the edge filter algorithm works, and how my own decision making process works are all impossible to know for these observers because their observable reality is a product of these perception filters used to create their reality space. Their reality is a projection of my reality that is further filtered before they can even perceive it. These are the observational limits of their perception as set forth by filtering (projection) process.

It is to say, I can accurately predict where the points that represent my hand will show up in their space and in roughly which configuration those points will be, because I am an outside observer of their reality and I can perceive the extra dimensions which affect that reality, but they cannot (imposed measurement limit). No matter how intelligent these lower dimensional observers are, the best they can ever do is create a statistical observation of where my hand might show up with some certainty quantifier. They might even make up equations like the Heisenberg Uncertainty Principle to formally define this and try to explain the phenomenon as random because it saves them the time of trying to imagine something that eludes them about their own perception of what they believe to be reality.

I'm not saying that this microcosmic example is true for our perception of reality, I'm saying that we never stand a chance of knowing if randomness truly exists or not. Perhaps it's just an artifact of the laws that govern the physical space we exist in, which could be generated by a higher-dimensional space in which other laws apply.

It is proven that each perception of reality is not the same as other's perceptions. The Pauli exclusion principle perhaps is a clue that either we are not seeing the same data, or that we are seeing the same input data, but through the chained filters of our "perceptive ability" and the distinct point of view through which we perceive the space. No two measuring devices can exist in the same physio-temporal position, thus no two perceptions of the same data will ever result in the same final input which is then processed by the perceiver. This is yet another filter, the entire process taking time to actually happen. In a very real way, the perceptive filter of our reality is represented physically by a sense organ or device. What we see is what we get. Are we all inside of a higher dimensional reality which, upon perception, collapses into a lower dimensional representation of that reality?

That brings us to the idea of fractals. A fractal is a projection of a higher dimensional space onto a lower dimensional plane. Point by point at any scale or n-dimensional rotation, can be calculated up to the currently working infinity limit, which is rendered in the projection as negative space. When projection happens, one or more dimensions must be collapsed into another dimension on the plane of interception/observation. When your eye perceives light, it generates signals which are rendered in your brain as a 2D projection. If you have two eyes, you have a higher sense of depth. This is a perception of a dimension of physical space which we call depth. This third perceived dimension helps us further define and comprehend the data we are perceiving inside of the space in which we exist.

Is it hard to imagine that the factors operating in a coin toss elude our limits of perception given the limited physical representation of reality at which we interact and observe? No... and that's why we have statistics. Statistics smooth for "randomness" by counting, summing, and the like, in order to account for the error in our ability to recognize data as an ordered pattern due to those perceptive limits.

This is really a great question! Thanks for the inspiration. I'm loving this forum, I feel like I've been missing out on talks like this IRL.
 
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  • #107
I wonder if it would be meaningful to throw-in the idea of some Godel-like results, if we view a theory as a collection of axioms together with rules of inferences. Then there will always be some non-random events ( not provable within the system).
 
  • #108
stevendaryl said:
it seems to me that @andrewkirk gave the most scientifically relevant answer. A process is random or not relative to a theory for predicting it.
PeroK said:
Randomness in QM is different, because you have perfect information. You have an ensemble of electrons that are spin-up in the z-direction; you measure their spin in the x-direction and you get spin-up 50% and spin-down 50%.

The theory of QM predicts this and suggests that there is no further information that could possibly be available to you (hidden variables) that would allow you to predict when an electron will be spin-up and spin-down.

Tossing a coin is random because you have inexact information about the experiment.
QM states that measurements are random variables, and it also states that the evolution of the state of an electron (and S/G device) obey a deterministic law.
What ever theory one proposes it is a subjective decision (with consensus) which physical instruments and processes are modeled by the theory.

Here is my simple theory: A coin flip is a two valued uniform r.v.
Most would agree that a "fair" coin flipped from the Eiffel Tower or in a wind tunnel is a physical device that is modeled by the theory. I now define that processes/result as random. And most would agree, though some would say random due to ignorance. I find this silly since saying there is information (but inexact) is math or philosophy not physical (no way to test). Same goes for determinism in general.
Any other r.v. can be generated by the coin flip. Flip it a 100 times and you have have a number from [0,1] chosen uniformly. Take functions of that to get any other continuous distribution. With an average of two flips of the fair coin you can get any other two valued r.v., e.g. 1 with probability 1/π, 0 with probability 1 - 1/π.

Now this may too slow in practice, but so what it's a definition of random. What the OP asked for.
Now, what if someone asks if the results of a S/G apparatus (above) are random. Well what does the consensus say, is it distinguishable from coin flipping? If not then it's random, if it is how so.
 
  • #109
PeroK said:
The theory of QM predicts this and suggests that there is no further information that could possibly be available to you (hidden variables) that would allow you to predict when an electron will be spin-up and spin-down.
Unless you have/apply ALL the information in the universe?
 
  • #110
entropy1 said:
Unless you have/apply ALL the information in the universe?
One problem is that "all the information in the universe" may not be well defined. Especially if the universe is infinite.
 
  • #111
PeroK said:
One problem is that "all the information in the universe" may not be well defined. Especially if the universe is infinite.
Ok. Suppose we know ALL there is to know about the universe, EXCEPT the outcome of the spin-measurement of our electron. Would that imply that we THEN could calculate what the outcome will be? (Almost the same question, I realize)
 
  • #112
entropy1 said:
Ok. Suppose we know ALL there is to know about the universe, EXCEPT the outcome of the spin-measurement of our electron. Would that imply that we THEN could calculate what the outcome will be? (Almost the same question, I realize)
I don't believe that is a well defined question. But, to take it at face value, I don't know. There is nothing in physics that demands that we would know the outcome in advance. And QM suggests that we couldn't necessarily know the outcome.

Just to be clear: it's the assumption that ultimately all uncertainty can be, theoretically at least, swept away that I believe is wrong.
 
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  • #113
I was wondering, if variable A is random, it is said we cannot predict its outcome. However, can't we really? We can't for a single instant, however we can or should very well for the distribution of a set of generated outcomes; that is the principle of probability theory, right? Maybe this is contrary to situations where we can predict a single outcome, but not a distribution, like when I drive through town and I can predict when I will go right or left, but not what the ratio between right or left will be. Anyway, in case of our variable A, the distribution of outcomes should be pretty predictable, right?
 
  • #114
entropy1 said:
Ok. Suppose we know ALL there is to know about the universe, EXCEPT the outcome of the spin-measurement of our electron. Would that imply that we THEN could calculate what the outcome will be? (Almost the same question, I realize)

According to quantum mechanics, no. There is nothing in the far reaches of the universe or in the details of subatomic particles that would allow you to predict the result of a measurement, in general. (There are certainly cases where the result is predictable, but in many cases, it is not.)
 
  • #115
stevendaryl said:
According to quantum mechanics, no. There is nothing in the far reaches of the universe or in the details of subatomic particles that would allow you to predict the result of a measurement, in general. (There are certainly cases where the result is predictable, but in many cases, it is not.)
So 'who/what' is 'deciding the outcome' then?
 
  • #116
entropy1 said:
So 'who/what' is 'deciding the outcome' then?

Quantum mechanics doesn't say anything about what or who decides the outcome. So if you need an answer, then you have to have some theory that goes beyond quantum mechanics.

To say it's random is the same thing as saying that nothing decides the outcome.
 
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  • #117
stevendaryl said:
To say it's random is the same thing as saying that nothing decides the outcome.
So, if there is no decision, maybe both outcomes are real, right? Depending on the interpretation? And maybe both are real given a certain probability? (for my understanding)
 
  • #118
If randomness could be defined then it's not random.
Sort of a non sequitur
 
  • #119
rootone said:
If randomness could be defined then it's not random.
Sort of a non sequitur
I defined random in post #108. How does that definition make it not random?
 
  • #120
Zafa Pi said:
I defined random in post #108. How does that definition make it not random?
Isn't a coin flip from the Eiffel Tower random because the effect (the yieling of the result) and the cause (the flipping of the coin) have such a complicated relationship (chaoticly), that the relationship can't be described, not conceived and not even traced back that FAPP there IS no relationship between cause and effect?
 
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  • #121
andrewkirk said:
In short, QM is a probabilistic theory because it makes probabilistic predictions. But that 'probabilistic' is a property of the theory, not of the universe.
If we have probabilistic definitions of events in QM, doesn't that then imply that we can't make predictions? (on that field)
 
  • #122
PeroK said:
In your case, you can hypothesise that QM might be replaced - frankly, anyone can do the hypothesising - but the critical question is how your exact, non-probabilistic theory could explain the observed phenomena. What are its key elements that would allow it to do that? And, moreover, what experimental or theoretical justification is there to get your theory going in this or that direction?
I would say for instance: all X-spin directions of all the electrons in the universe add up to 0, for instance. So, one electron's spin is fixed by all the other electrons, and theirs on their turn also. There is however no way to verify that, but maybe it is possible to build a theory around it and get circumstantial evidence, I don't know.
 
  • #123
entropy1 said:
If we have probabilistic definitions of events in QM, doesn't that then imply that we can't make predictions? (on that field)
No. It doesn't imply that. It just implies that we cannot make predictions using quantum mechanics alone.
 
  • #124
andrewkirk said:
No. It doesn't imply that. It just implies that we cannot make predictions using quantum mechanics alone.
What else would be required then?
 
  • #125
entropy1 said:
What else would be required then?
A larger theory, that is compatible with QM within certain constraints that are satisfied by most experiments done to date.
 
  • #126
entropy1 said:
Isn't a coin flip from the Eiffel Tower random because the effect (the yieling of the result) and the cause (the flipping of the coin) have such a complicated relationship (chaoticly), that the relationship can't be described, not conceived and not even traced back that FAPP there IS no relationship between cause and effect?
It's random because no one can predict the outcome of a flip better than 50/50. Chaos is a math concept, a coin flip is physical
 
  • #127
andrewkirk said:
No. It doesn't imply that. It just implies that we cannot make predictions using quantum mechanics alone.
This is your answer to:
entropy1 said:
If we have probabilistic definitions of events in QM, doesn't that then imply that we can't make predictions? (on that field)
Then entropy1 says:
entropy1 said:
What else would be required then?
and you reply
andrewkirk said:
A larger theory, that is compatible with QM within certain constraints that are satisfied by most experiments done to date.
Do you think it is possible that some grander theory than QM will avoid random (see post #108) outcomes for measurements for spin? Not even super determinism will accomplish that. However, super determinism, as a theory, does say there are no probabilities.
 
  • #128
Zafa Pi said:
Do you think it is possible that some grander theory than QM will avoid random (see post #108) outcomes for measurements for spin? Not even super determinism will accomplish that. However, super determinism, as a theory, does say there are no probabilities.

The question is mixing up the two different meanings of "random". A theory may be deterministic, so that there are no intrinsically random events, but it may be practically impossible to predict some events, and so that they would appear random. But "appearing random" would be a matter of how much computational power you want to put into predicting future outcomes. I suppose that past a point, prediction would be impossible in practice.
 
  • #129
Zafa Pi said:
It's random because no one can predict the outcome of a flip better than 50/50. Chaos is a math concept, a coin flip is physical
I mean, is being random the result of the decoupling of cause and effect? (and maybe the definition, as you suggest)
 
  • #130
stevendaryl said:
The question is mixing up the two different meanings of "random". A theory may be deterministic, so that there are no intrinsically random events, but it may be practically impossible to predict some events, and so that they would appear random. But "appearing random" would be a matter of how much computational power you want to put into predicting future outcomes. I suppose that past a point, prediction would be impossible in practice.
I have only one definition of random (given in post #108), it applies to a physical process. A theory may state that certain things are random variables.
I agree that a deterministic theory may say there are no r.v.s and as a consequence no random events, merely a lack of knowledge, but then as you say prediction would be impossible in practice.

My key objection is (are?) the words "in practice" and "intrinsically". They are unnecessary, superfluous, and misleading. When flipping a coin from the top of the Eiffel Tower or in a wind tunnel there is no information that would predict the result. Some might object and say: if one knew the position and velocities of all the entities in the air, the the position and force from the thumb, etc. the result could be predicted. I say it is a pipe dream to say that information exists. Certainly you can't prove that it does, all one can do is hypothesize its existence based on a nonexistent theory below the Planck scale. As Griffiths said, God doesn't even know.
All is random, and the Law of Large Numbers keeps us sane. :bang:
 
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  • #131
entropy1 said:
I mean, is being random the result of the decoupling of cause and effect? (and maybe the definition, as you suggest)
In a coin flip what are the cause and effect? After you answer that tell me what decoupling means.
 
  • #132
Zafa Pi said:
In a coin flip what are the cause and effect? After you answer that tell me what decoupling means.
What are cause and effect is a matter of preference I think; you could say that the tossing device is the cause and the effect is the read-out (heads/tails).

With "decoupling" I mean that there is, practically at least, no discernable relation between the cause and the effect - this would be randomness, that is, for the effect/readout.
 
  • #133
Zafa Pi said:
Some might object and say: if one knew the position and velocities of all the entities in the air, the the position and force from the thumb, etc. the result could be predicted.
With no identifyable relation between cause and effect, I mean the correlation between cause and effect is just as random as the toss is, regardless of in-principle possible relations. But maybe this is circular - dunno. Probably.
 
  • #134
Zafa Pi said:
My key objection is (are?) the words "in practice" and "intrinsically". They are unnecessary, superfluous, and misleading. When flipping a coin from the top of the Eiffel Tower or in a wind tunnel there is no information that would predict the result.
Well, I disagree completely. To say that something is in practice unpredictable has a clear meaning, and it’s a different meaning from a theory being stochastic, or probabilistic.
 
  • #135
entropy1 said:
What are cause and effect is a matter of preference I think; you could say that the tossing device is the cause and the effect is the read-out (heads/tails).
So you don't think the breeze or the topography of the ground are part of the cause? Right up until the coin settles down.
entropy1 said:
With "decoupling" I mean that there is, practically at least, no discernable relation between the cause and the effect - this would be randomness, that is, for the effect/readout.
I wonder where that decoupling takes place? If the coin weren't flipped there would be no result.
 
  • #136
Zafa Pi said:
If the coin weren't flipped there would be no result.
Yeah, that would be the null hypothesis.
 
  • #137
stevendaryl said:
Well, I disagree completely. To say that something is in practice unpredictable has a clear meaning, and it’s a different meaning from a theory being stochastic, or probabilistic.
Well I disagree that we disagree. I do agree with what you said.
Our difference is semantic. Saying that a coin flip is in practice unpredictable carries no more information than saying it is unpredictable, and what I call random (see #108). I think the "in practice" is a red herring and adds confusion. Determinists say it is due to lack of knowledge and that is "not even wrong".

QT says that measurements are random variables - stochastic, very different than above. But in QT or probability theory the word random or intrinsically random do not appear and not defined. And that's why they should be tossed out in that context.
 
  • #138
Zafa Pi said:
QT says that measurements are random variables - stochastic, very different than above. But in QT or probability theory the word random or intrinsically random do not appear and not defined. And that's why they should be tossed out in that context.
If randomness is not defined, how do you predict anything that is random or derived from it?
 
  • #139
entropy1 said:
If randomness is not defined, how do you predict anything that is random or derived from it?
You only quoted part of my post. I did define it. Please read my other posts before you reply.
 
  • #140
Zafa Pi said:
You only quoted part of my post. I did define it. Please read my other posts before you reply.
I did read them. I must say I'm a little confused. Does QM only take place around the Eiffel tower? Or must all QM related experiments be reducible to Eiffel tower coin tosses?
 

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