Belem

Last night, I was working in a response to debunk a friend's claim that the Universe is determinist.

However, suddenly I realised that following my own reasoning the Universe seems to be probabilistic but it is not!

So, I need help. There must be something wrong with my method to analyse this problem.

Here is how I proceed:

This is the especification of a deterministic model:

Y = f (xi, zi,....infinite)

In other words, Y is an event that behaves in a way that is explained or caused by an infinite number of independent variables. We cannot estimate this model because it is IMPOSSIBLE to have all the information. This is how natural events in the Universe are. I mean, everything has a cause, everything is determined by something else.

So, we don't have all the information, we have to build a probabilistic model such as:

Y = f(c, xi, zi,....n, e)

Which means that Y is an event that can be explained only by some relevant independent variables, a constant, and an error term. Why only some variables?, because we don't have all the information, this model is an approximation of reality.

So, we end up with a probabilistic model of natural events in the Universe because we cannot estimate a deterministic model.

Is it true? I mean this conclusion seems to be consistent.

I would like to know if QM assumes that random events are intrinsically random or they just seem to be random because we cannot determine a particle's position and speed at the same time?

Please help me to get out of this mess!

Belem

jpbrooks

I'm really pressed for time at this point, but this issue may involve quantum nonlocality. (I had more to say about this, but I have to leave the computer room now.)

excreationist

jpbrooks:
A simple example of something that is unpredictable to us is radioactive decay. We know that within the half-life, 50% of the atoms would have decayed into something else, but we don't know exactly when a specific atom will decay or whether it will decay in the next half-life or not...
But maybe there are "hidden variables" at work, that cause atoms to decay in a completely deterministic way...
Or maybe probability is involved... e.g. every unit of time (planck time) there might be a 0.000000001% chance that an atom would decay, and if you combine those probabilities, it would mean that there'd be a 50% chance of any individual atom decaying in its half-life.
Or in the parallel universe view of things, all of the possibilities would happen, and the universe "you" and your memories (of the past) are in is just due to chance. The structure of the parallel universes would be deterministic though.

Belem

jpbrooks,

Thanks for the link. I read it but my question remains.

It is very simple.

QM cannot determine a particle's position and speed, so we perceive quantum and macrocosmos events as probabilistic....

Does it mean that a particle NEVER has a position and speed????

Does it mean that the Universe has intrinsic random events (acausal)?

Belem

Exactly, we don't know, but it does not imply that that this event happens. It is not acausal by nature.

VivaHedone

I'm afraid that I know nothing about quantum mechanics whatsoever... but it seems only logical to say that everything must have a cause, even if that cause is hidden from us.

excreationist

Then that leads to the problem of "infinite regression"... if *everything* had a cause, then something caused the big bang, and then something caused that, then something caused that, etc, etc, etc. I think the series of causes would end somewhere. But that's quite off topic.

stretch

Does a deterministic model with an infinite number of variables have any meaning?

Whether or not a deterministic model applies isn't a testable hypothesis.

It seems that you might as well look at the universe as having random components.

Heck, you wouldn't want to put us statisticians out of a job, would you?

Starboy

Belem, before you go any further you must define deterministic. Most people understand deterministic to imply the ability to accurately predict an outcome given a specific set of initial conditions. There are three constraints on this ability:

1) Sensitivity to initial conditions - this results in outcomes that fall along a Gaussian curve. This is interpreted as the outcome contains a random component. No matter how hard you try to recreate the initial conditions for certain physical situations, very tiny initial differences can lead to very large differences in outcome. Such phenomena are referred to as Chaotic.

2) Intractable problems - this occurs when the theory produces an equation that describes the system but it cannot be solved exactly. An example would be the planets in the solar system. It is known as the N body problem and can only be solved exactly for special cases or by approximation. Another example would be the gas in a room. There is a very large number of molecules and they are interacting constantly. The computing power required to compute just a very small part of their interactions is astronomical. By analyzing ensembles of physical states for the gas such problems can be solved statistically.

3) Quantum phenomena - this seems to be a very real phenomenon where it appears that it is only possible to predict the outcome at the quantum scale statistically. The current thinking is that this is not due to a lack of accuracy or the difficulty of computing the outcome but is an actual property of physical systems at the Plank scale. An example of this is photon emission. According to QM, the exact time that a photon will be emitted by and atom cannot be predicted; only the probability of occurrence. When a large number of atoms are observed collectively QM predicts their aggregate behavior to great precision, but at the scale of a single atom all it can predict is a probability.

So if deterministic means “predict everything to great accuracy” then the answer to the question “is the Universe deterministic” at this time is no. But this is not the last word. The basic problem is that the statement “the universe is deterministic” makes a claim about reality. However we can only consider such claims tentatively because we are still exploring reality. The exploration of reality is what science is all about, and it is very much a work in progress.

Starboy

VivaHedone

Yes, the concept of infinity is virtually impossible for our human brains to grasp... but the alternative, an original, first event, without a cause, before which was nothing, seems equally impossible. I tend to go with the 'infinity' view, as it is the limitations of our brains that appear to be the problem, and not any intrinsic logical problem.