is a-causality necessary for randomness?

San K

What is the relationship between a-causality and randomness?

Let's look at the argument below:

For something to be (truly/inherently) random there cannot be a cause.

Because, if there is a cause then the cause can be studied and the result/output can be predicted and hence there would no randomness.

True Randomness means something that cannot be predicted.

We can predict whether will be an interference pattern or not, however we cannot predict the location of any individual/single photon/electron on the screen.

We can, in principle, predict the results of a roll of a dice (or toss of a coin) if we took into account all the factors such initial forces on the dice during the toss, effect of air molecules etc. Since the roll of a dice has a cause its predictable.

bhobba

An observation causes a quantum system to change state - we just can't predict what that state will be - but 100% for sure it caused it to change state - the change was not a-casual.

In classical 100% deterministic systems chaotic behaviour abounds meaning since it is impossible to know with 100% accuracy the initial conditions there will always be some imprecision in knowledge that will grow to the point prediction is meaningless.

Thanks
Bill

VortexLattice

This seems a tad philosophical but... at the very least, it seems like you could have a perfectly reasonable "cause" for a "random" process, but the cause is necessarily hidden. I think that's the same as Hidden Variable Theory, which is I guess wrong because of Bell's Theorem, but I don't know exactly why.

JPBenowitz

This isn't true. Nothing is truly random, even quantum mechanics. Although QM may seem completely random it isn't, it's just that we can never acquire the necessary information to determine precisely how the system will evolve.

Zarqon

This is not known. All we can say is that we measure what appears to be a truly random phenomena when we measure quantum states. Although there exists deterministic explanations these are just speculations and have not been proven. At this point it is still an open question on whether the universe is really random or deterministic.

bhobba

What can be said is a process that passes all tests for randomness may be truly random but of course we can never know if its the result of some deterministic process that has not been discovered yet and that process just happens to mimic randomness - tests for true randomness are pretty good these days and only some very sophisticated algorithms can actually pass it. If you believe nature just happens to be that 'good' - well it is a logically valid position - but I do not ascribe to it. Occams razor would suggest if we know of no underlying deterministic process and it passes randomness tests then the simplest explanation is it really is random.

And as far as we can tell today QM is utterly and truly random eg random number generators based on thermal noise which is quantum in origin I am pretty sure pass every known test for randomness that even some reasonably sophisticated pseudo generators fail - although pseudo generators do exist that do pass those tests.

Thanks
Bill

Maui

Shouldn't 'truly random' be regarded as the approximately 50/50 distribution of outcomes of hundreds of trials? If you toss a coin 222 times and it lands on tails approximately 111 times, it means it is truly random because nothing unobservable can be said to be affecting its 50/50(1 of 2) possibile outcomes. Does anyone object to this definition?

Electrons and other fundamental particles do not obey the 50/50 statistics so they cannot be truly random. For reference, just look at the interference pattern from single electrons in a double slit experiment. I don't see how we could observe a newtonian(-like) universe based on a truly random quantum foundation. It would fall apart immediately, wouldn't it?

San K

Each of the fringes has a fixed probability of the electron/photon landing up on it, I thought.......for a given experimental setup (slit width and distance, electron distances etc).

So conceptually the 50/50 i.e. fixed probability (totaling to 1), concept applies.

Maui

The subtlety lies in the fact that the fringes are formed by the accumulation of thousands of single dots(landings). It's as if the electron travels as a wave through the slits but lands on the detection screen as a particle. After many many landings accumulate, we get the interference pattern and this is anything but random. It's so much more on the holistic side, that calling it random seems to require a re-definition of "randomness".

audioloop

unpredictability does not imply the lack of a cause, we cant confound determinism with predictability (or indeterminism with unpredictability)
a-causality have to do with indeterminism but indeterminism does not have a relationship with randomess.

by the way there are deterministic theories without being computable i.e. nopredictable outcomes and indeterministic process can produces a non-random sequence of outcomes.

JPBenowitz

My position isn't necessarily that QM isn't "truly random" but what it means to be truly random. For instance we cannot know both the position and momentum of a particle precisely because observing it changes it; in other words the very act of observation constrains the observer to how much information can possibly be extracted from any given system. Because of this information constraint we cannot know precisely the initial conditions of any system to predict a precise outcome. Does this mean that the universe is intrinsically deterministic? Not necessarily because no observer could possibly compute the future--the future remains completely hidden. The universe isn't exactly deterministic or truly random in this sense.

JPBenowitz

Randomness is really just chaos. Where predicting the outcome in a chaotic system requires hefty computation. True Randomness is where a chaotic system cannot have a predicted outcome because of a fundamental computational limit.

audioloop

another confusion,
Chaos involves deterministic process i.e. no random.

A deterministic system will have an error that either remains small (stable, regular solution) or increases exponentially with time (chaos). A stochastic system will have a randomly distributed error*, these systems are deterministic, meaning that their future behavior is fully determined by their initial conditions, with no random elements involved**.


*Casdagli, Martin. "Chaos and Deterministic versus Stochastic Non-linear Modelling", in: Journal Royal Statistics Society: Series B
**Kellert, Stephen H. (1993). In the Wake of Chaos: Unpredictable Order in Dynamical Systems. University of Chicago Press.
Lorenz, Edward N. (1963). "Deterministic non-periodic flow". Journal of the Atmospheric Sciences 20 (2): 130–141

JPBenowitz

That's literally what I am saying. Randomness is really just a deterministic system with an error that increases exponentially. True Randomness is when that error exceeds all computational possibilities on a fundamental physical level.

Zarqon

You have to be careful with your statements. I don't think this has been shown at all. It might work like that but you can't make a statement saying it's certain that it does work like that because it has not been proven (and if you think it has been proven could you find some sources for your claim?).

bhobba

Indeed.

Thanks
Bill

JPBenowitz

You are correct I do not think it has been proven. Which is precisely why I am going to explore this avenue. I'll get back to you on what I find :)