Is there such a thing as randomness?

[Leros]

I have hard time understanding how something can be truly random. Do we call things random because we don't have a working model for the process?

 

[NikolaeVarius]

I guess technically, you can't call most things in life Random because everything is just a combination of many factors. Theoretically, we could make a coin flip heads every time, if we could replicate every single time, the exact conditions that are requiremed for the coin to land on heads. Right now we don't have the computing power to calculate this, and so for all purposes, it is random.

However, you can call the movements of particles random because we can't measure in what way they will move, in accordance with the uncertainty principle.

Of course, this is just a guess originating from my limited knowledge

 

[Leros]

Originally posted by: tenshodo13
However, you can call the movements of particles random because we can't measure in what way they will move, in accordance with the uncertainty principle.

Is that just a cheap way of saying we don't know yet so lets just call it random?

 

[f95toli]

It depends. Sometimes "random" simply means "unpredictable".
In other cases -such as radioactive decay (see the other thread)- the process is (to the best of our knowledge) truly random; i.e. there is no way even in principle to predict when an atom will decay. The latter is usually called a stochastic process.

 

[BrownTown]

I don't think you could really say from my knowledge of physics. Even something like nuclear decay could easily be completely non-random. The forces involved might not be understood, or even measurable yet, but that doesn't mean they aren't still there. OF course you always get into the argument like "if everything is any effect of an earlier casue then what started it all to begin with". Personally I find it useless to try to think about such things. IF you find it to be a fun mind game than more pwoer too you, but the fact is that we DONT know, so your specualtion is really based more on religious/dogmatic princples and not a basis in reality.

 

[Jeff7]

Originally posted by: Leros

Originally posted by: tenshodo13
However, you can call the movements of particles random because we can't measure in what way they will move, in accordance with the uncertainty principle.

Is that just a cheap way of saying we don't know yet so lets just call it random?

The uncertainty principle means that we can't know the EXACT properties of an atom, because measuring it changes it. If you take a picture of something and use a flash, you put energy into the surface you're imaging, which changes its properties.
If you're dealing with a single particle, bouncing a photon or electron off of it will cause it to move slightly. So how fast is it moving then? Hit it with another photon to find out where it moved to, and how fast it got there - oops, you just changed its speed again.
We can determine how probable it is that a particle will be at a certain position, or have a certain speed, but it's currently impossible to get exact data on small particles.

If there existed a way of obtaining information on particles without interacting with them, perhaps the uncertainty principle would go away. I don't see that happening anytime soon, if ever.
Hell, even the transporters in Star Trek had Heisenberg Compensators.

 

[mozirry]

if you choose a card out of a deck at random, it means you are choosing a card without any attached variables

 

[Leros]

Originally posted by: mozirry
if you choose a card out of a deck at random, it means you are choosing a card without any attached variables

Surely there is some kind of chemical process in the brain that we could use to predict which card the person would choose.

 

[PowerEngineer]

Originally posted by: BrownTown
I don't think you could really say from my knowledge of physics. Even something like nuclear decay could easily be completely non-random. The forces involved might not be understood, or even measurable yet, but that doesn't mean they aren't still there. OF course you always get into the argument like "if everything is any effect of an earlier casue then what started it all to begin with". Personally I find it useless to try to think about such things. IF you find it to be a fun mind game than more pwoer too you, but the fact is that we DONT know, so your specualtion is really based more on religious/dogmatic princples and not a basis in reality.

Einstein argued against quantum physics using this same rationale, so I'd say you are in great company. In the end, however, the proponents of quantum physics were able to prove that there were true limits to what we could know about quantum processes like nuclear decay. It's a stunning result.

Here's a clip on the double slit experiment which describes the particle-wave duality that leads to randomness.

 

[PhatoseAlpha]

Not with 100% certainty. Heisenberg again. A little uncertainty here meets up with some there, and the uncertain results of their interactions meet up with more uncertainty. Add up all those little uncertainties, and then start realizing that it's a long chain with lots of uncertainties giving uncertain reactions.

Modern Quantum theory has completely killed true determinism and Laplace's dream of the world calculator. Get right down to it, not only is there true randomness, it's all there is. Probability makes it appear as if there is order, but there is only uncertainty. Heck, after dealing with the EPR paradox, even a perfect scope which doesn't disturb anything can't get an accurate measurement.

In short, the universe is random.

 

[StopSign]

When a stray bullet shot from the other side of the map hits my head in CS:Source, I call that true randomness.

 

[Xdreamer]

There is no randomness as far as man is concerned. We cant understand it. IF there were, would we know?

 

[StopSign]

Would we know what?

 

[alimoalem]

to those that believe in God, no, there is no randomness. God is all knowing and knows where every one of His atoms are and what they're doing.

to those that don't believe in God, then yes, there is such a thing as randomness. there are some things that we (as humans) will never understand or know

 

[Blouge]

>there is no way even in principle to predict when an atom will decay

You mean there is no way to predict the outcome according to YOUR principles.

To claim that no way exists at all is presumptuous and unscientific. It's especially arrogant when you do this just to avoid admitting ignorance. Just like the ancients needed Thor or Zeus to explain thunderbolts, you need Randomness to explain atomic decay.

Whether something is random is a matter of faith or opinion, not a matter of fact. It's impossible to prove that something is unpredictable or random. It's not scientific. For the statement "X is unpredictable" to be scientific theory, it needs to be falsifiable. It can never be falsified because you can never rule out the possibility that the mechanism IS predictable but just not understood.

>God is all knowing and knows where every one of His atoms are and what they're doing.

FYI, I think that means you don't believe in free will. (I don't either.)

>to those that don't believe in God, then yes, there is such a thing as randomness

Sorry, but I'm not buying into either of these things.

 

[PhatoseAlpha]

AFAIK, as it stands nuclear decay is currently understood to be dependent upon vacuum energy. Vacuum Energy is a quantam effect, therefore subject to Heisenberg uncertainty, therefore unknowable, therefore random.

 

[Blouge]

"therefore unknowable, therefore random"

You don't understand something, so it must be random. Or maybe it's because of The Gods.

Great logic there.

 

[f95toli]

Originally posted by: Blouge
"therefore unknowable, therefore random"

You don't understand something, so it must be random. Or maybe it's because of The Gods.

Great logic there.

Well, quantum mechanics is a probabilistic theory and as far as we know QM is correct. Hence, to the best of our knowledge there IS such as thing as true randomness.

There is an important technical point here: namely that "randomness" in QM has nothing to do with "lack of knowledge", it is so to speak a natural consequence of the theory (the most famous example of this is of course the uncertainty relation).

That said you are of course right that there is no way to "prove" this; but then it is by definition impossible to prove anything in science so that is not surprising. All we can say is that the predictions of QM have been thoroughly tested in countless experiments and so far it has passed every test.

 

[PhatoseAlpha]

Originally posted by: Blouge
"therefore unknowable, therefore random"

You don't understand something, so it must be random. Or maybe it's because of The Gods.

Great logic there.

Unknowable != Not understood
Unknowable means it cannot be known. Even if you have a perfect detector, with no error whatsoever, absolutely perfect, you still can't know it.

Quantum Mechanics and Heisenberg Uncertainty are very clear on this. It is not lack of human understanding, or lack of equipment, or lack of anything - some things are simply impossible to know.


You have a box. Something might come out of it. Something might not. Due to the fundamental nature of the universe, it is impossible to know what, if anything, is in that box. If not random, what would you call it?


Determinism is dead. Has been since Quantum theory was discovered. Is there a possibility that Quantum theory is wrong? Sure, but if you're going to casually discard one of the most highly tested theories in all of science with the "It could be wrong" thing, you have no business being involved in any form of scientific discussion whatsoever. Laplace's universe calculator ain't gonna happen.

Go read up on Quantum Mechanics.

 

[WildHorse]

On the one hand you have the established orthodoxy of science and the idea of random probabilities.

On the other hand you have Jung & his proposed idea of synchronicity, no randomness, plus the world's many mystical traditions that teach the same.

I think that fundamentally, these two ideas presently stand in opposition.

A higher understanding will need to eventually be found through which these may be reconciled. Maybe that will involve new concepts that will leave the old dichotomy behind, and "dis-solve" the problem.

 

[CSMR]

Originally posted by: Leros
I have hard time understanding how something can be truly random. Do we call things random because we don't have a working model for the process?

Hello. We call something random when we don't know what it is and when our thinking is ordered in terms of probabilities. Economic theory has some good notions of what probability means. It expresses the subjective beliefs of a rational but ignorant person. (Although there are some ambiguities when the unknown events influence preferences.) Kreps' "Notes on the theory of choice" gives a good survey of this work.

 

[CSMR]

Originally posted by: alimoalem
to those that believe in God, no, there is no randomness. God is all knowing and knows where every one of His atoms are and what they're doing.
to those that don't believe in God, then yes, there is such a thing as randomness. there are some things that we (as humans) will never understand or know

Well I believe in God and think that (subjective) randomness is a good notion. As for objective randomness no-one has defined such a notion although many claim to believe in it. If you want to connect objective randomness and God then you would have to say what it means first.

I think when Einstein said God does not play dice he was expressing his belief in objective laws of physics and denying that these laws could be probabilitic in nature: denying objective probability. Which brings us on to...

Originally posted by: f95toliWell, quantum mechanics is a probabilistic theory

Yes

and as far as we know QM is correct.

How can you call a probability correct? What would it mean for "the particle will be seen here with a 60% chance" to be right?

IMO the best way to think of a probibalistic theory is to see it as a particular expression of uncertainty about the world. "Accepting" the theory means aligning one's probability estimates with that of the theory. The theory cannot be called "correct" because that is not defined for probabities. It could however be "reasonable" to hold a certain probability or range of probabilities and align ones beliefs with a probabilistic theory given supporting data. But not "correct".
Note there is a fundamental difference between this and a non-probibalistic predictive theory. Even though we may never know whether they are true or not the theory itself (the set of predictions) can be correct.

 

[f95toli]

Originally posted by: CSMR
How can you call a probability correct? What would it mean for "the particle will be seen here with a 60% chance" to be right?

First of all, in the majority of cases where we use QM to calculate a quantity the expectation values are very sharply peaked, i.e. the part of the variance that is due to "quantum noise" is very small; ususally much smaller than the noise that is due to e.g. thermal fluctuations. Hence, from a practical point of view the uncertainty is rarely a real issue. Even in the field of quantum computing there are single-shot methods that can measure the state of a qubit with nearly unit visibility.

Secondly, the time evolution is a QM system can be complettely deterministic (i.e. there is no "randomness" in the propagator of the density matrix); it is only when we try to MEASURE a observable of that system that the probabilistic nature of QM becomes apparant. Hence, there are lots of systems where we have in a sense "full control" as long as we leave it alone; a trivial example is measurements of Rabi oscillations or Ramsey fringes; there is no way to observe them directly since we can only measure one point at a time (since the measurements itself causes the system to collapse) . However, by repeating our measurement many times and measuring at various times we can "build up" the curves. The expectation values of the level populations are therefore ina sense deterministic observables.
Hence, while we can't "observe" it continuosly we can still know where the system will be at a given time. This is why it is possible to e.g. use shaped microwave pulses to manipulate the state of an atom or molecule in NMR in a determinstic fashion.

Finally, and this is the most important point.
While we can't e.g measure anything "exactly" there are still many things you CAN measure. The mean and the variance of an observable are the most obvious example.
However, in many systems we can also measure higher order moments meaning it is possible to study various correlation functions. A good example is a Hanbury-Brown and Twiss-type experiments which are not only interesting for fundamental studies but also has some practical applications when it comes to e.g. characterizing single photon sources.
The same type of experiments can be used to demonstrate violations of Bell-type inequalities, these violations are important since they give importat support for the idea that QM is fundamentaly correct.

 

[Blouge]

Unknowable means it cannot be known. Even if you have a perfect detector, with no error whatsoever, absolutely perfect, you still can't know it.

Yes, it's frustrating, isn't it - being perfect and still not being able to know something!

You have a box. Something might come out of it. Something might not. Due to the fundamental nature of the universe, it is impossible to know what, if anything, is in that box. If not random, what would you call it?

I would call it "ignorance". I don't know what's in the box, but whoever manufactured it or closed it last does know. It's not random.

Determinism is dead. Has been since Quantum theory was discovered.

You couldn't be more wrong. Did you know Einstein was a determinist? Oops, I forgot, you're much smarter than Einstein.

Did you know that Bohm created a deterministic theory that matches QM exactly in its predictions?

From http://en.wikipedia.org/wiki/Determinism,
"It is... possible to augment quantum mechanics with non-local hidden variables to achieve a deterministic theory that is in agreement with experiment. An example is the Bohm interpretation of quantum mechanics"

Is there a possibility that Quantum theory is wrong?

Of course: it is undoubtedly wrong as it stands because it does not mesh with general relativity. The clearest evidence that it's not ultimate answer to everything, is that you don't see all of the theoretical physicists in the unemployment line. Thinking that you have the ultimate scientific knowledge, and that something you can't explain must be "random", is an arrogant and common mistake made throughout history. Brownian motion was once thought to be a random motion of small particles, until Einstein explained how it's the result of collisions with atoms. It's unpredictable (by us), and seemingly random, yet perfectly deterministic and reasonable.

QM might be random. If that's your belief, that's fine. It's a good crutch for arrogant people who feel they need to know everything - whatever they can't know or understand can just be labeled "random". It's also a good belief for people whose spirituality depends on whatever contemporary cracks exist in the scientific edifice. It's also a good tool for bewildering young QM students. Unfortunately, because the belief cannot be falsified it is purely a religious one and it has absolutely nothing to do with science.

The truth is that the universe is not random at all. In reality, each and every particle is touched by His Noodly appendeges: http://www.venganza.org/

From http://www.venganza.org/about/open-letter/,
"But what our scientist does not realize is that every time he makes a measurement, the Flying Spaghetti Monster is there changing the results with His Noodly Appendage. We have numerous texts that describe in detail how this can be possible and the reasons why He does this. He is of course invisible and can pass through normal matter with ease."

Ramen.

 

[PhatoseAlpha]

You couldn't be more wrong. Did you know Einstein was a determinist? Oops, I forgot, you're much smarter than Einstein.

You know, I didn't actually know about Bohm. But since you're making personal attacks now, I'm done with this conversation.