WWSD

Here is an idea that has been fascinating me for the past two weeks or so. And yes, small round shiney objects also fascinate me...

heregoes:
The universe plays by a set of physical rules that govern every interaction of every particle in it.
At the beginning, the rules were probably the same.

It seems as though the distribution of matter was non-uniform at this time and so the universe had an initial set of conditions.

This distribution could have taken any configuration, but it took configuration A. From that point onward each particle would then be set into a certain path based on its first interaction. Configuration B would have resulted in particles taking other paths and so on. The key is that the paths are set from the beginning.

These paths would lead to the complexity that is the universe today. The paths were set by the initial configuration and have been followed by everything ever since.

Could one, having been able to measure each initial interaction with an superdeedupercomputer at the beginning of the universe, then extrapolate from that to actually predict each event that would take place in the span of all time?

IOW, is everything that happens a result of the initial configuration and does this mean that the initial conditions predetermined the outcome of everything to follow?

Disclaimer: I see no need for purpose or first cause or creatorish type things to have any part of this.

Feather

Well now, that's a tough nut to crack.

Quantum Mechanics seems to indicate that certain "uncaused events" can happen. But this is in actuality just bad language.

Once the Schrodinger Equation is solved for a given system, the "physics" of the system is determined for all time thereafter.

However, the model of determinism you describe has been put forth by various natural philosophers in the past, and most often couched in a Classical picture of the universe. Lagrange stated pretty much your statement: given the state of every particle in the universe (that is its position and the first time derivative of its position, and all the possible forces acting on it) at a given instant it is "possible" to predict the positions (and hence the state of the universe) at every instant in time thereafter.

Quantum Mechanically speaking, it is the expectation values of these things instead that can be predicted (the entirety of "Classical Mechanics of Actual Values" is translated into a sort of "Classical Mechanics of Expectations" in Quantum Mechanics).

But an "expectation value" is just the "most likely value" of a quantity. For example, if you stick a small particle in an infinitely large box and give it certain energies it will be expected to be at the center of the box (but not necessarily), whereas for other energies it can never be at the center of the box. So it is possible to predict where things cannot be exactly under QM.

Moreover, we cannot know the state of the Universe before the so-called Planck Time (it's related to the value of Planck's Constant)--for all we know the laws of physics were totally different then.

Anyway, what this all means is entirely up in the air.

To make a long story short (too late), I don't think it is possible under the current model we have of the universe to make Lagrange's statement with any accuracy.

But, on the other hand, this does not imply that determinism is false. So I don't think the case could be made that the universe is not deterministic, either.

Remember: determinstic != predictable.

Starboy

WWSD, it's been over seventy years since physicists thought that the fate of the universe was determined by classical determinism. As Feather points out, quantum mechanics has changed all that. There is a classic experiment done with light and a two-slit diffractor. As you know when you shine light on a two-slit diffractor it disperses the light into a pattern know as a two-slit diffraction pattern. If the light source is a single frequency of light the pattern is very pronounced and it is easy to compute assuming that light is a wave. This may appear on the surface to be completely deterministic. Shine the light; get the pattern, works every time. Here is the catch. It was discovered that everything is particle (quantized) and everything is a wave, everything, even light (wave/particle duality). If you get a single frequency light source that is dim enough, so dim that only one photon is emitted every second and you place photo detectors where the pattern would form you will notice that the one photon doesn't split up into the pattern, it travels a path and hits just one spot. Each time you send a photon through it lands on a different spot. For the most part it appears to be random. Now this is the interesting part, if you keep sending photons through over time they will build up the same pattern. How can that be? The photon is behaving like a particle and a wave at the same time! On top of that at the particle level the path is not completely determined, for a specific photon, the location that it will hit is not determined, the only thing you can say for sure about a single photon is where it will not hit.

It is this strange behavior at the quantum level that destroys any idea of the universe being completely deterministic. There are probably states the universe can never be in, but the state it will end up in is not classically determined. At the very large scale quantum effects mostly disappear, there are however large scale quantum effects such as super conductivity, laser light, photo electric effect to name a few. There is also some evidence that indicates that quantum effects may be occurring at the galaxy scale. There are alternative theories to dark matter that indicate that gravity doesn’t work the same for very small accelerations.

Starboy

K

Not to mention the fact that the Heisenberg Uncertainty Principle would make it impossible for you computer to specify the exact location and momentum of the particles in your simulation.

Steven Carr

No.

The supercomputer would have to be the size of the universe, and indeed would have to be the universe, if it is going to model *all* of the universe, including its own workings, of course.

WWSD

Thanks guys,

I had been thinking about his all weekend, even at the football game.

Anyway, I did start to wonder how much quantum mechanics would fiddle with my idea.

I rememebered back a few years, like 11 or so, to when I read "In Search of Schrodinger's Cat" and I remembered the idea of virtual particles popping into and out of existence. That sort of pushed my idea over once I realized that reality is so vague (quantum mechanically anyway).

However, I did read a short review of Hawking's latest book. I'd like to read it becasue the review mentioned that Hawking has something to say about determinism and such. Unless, which is often the case, I misread the review and formed some bizarre idea of my own.

Starboy:
There is also some evidence that indicates that quantum effects may be occurring at the galaxy scale.

Do you have a link for this or some other source I could peruse? Sounds really interesting!

Starboy

<a href="http://xxx.lanl.gov/PS_cache/astro-ph/pdf/9805/9805346.pdf" target="_blank">MOND as a Vacuum Effect</a>

If you want more background information check out

<a href="http://www.astro.umd.edu/~ssm/mond/" target="_blank">The MOND Pages</a>

Some of this is heavy duty physics, but it is very interesting.

Starboy

Keith Russell

The supercomputer would have to be the size of the universe, and indeed would have to be the universe, if it is going to model *all* of the universe, including its own workings, of course.

That is not necessarily the case. It depends on the level of 'modelling' that we wish. We often 'model' certain systems using data compression, scale modelling, etc., which do not require a one-to-one correspondence between the model, and the thing (or things) being modelled.

Keith.

Laurentius

Predetermined universe?
When we look back at the whole possible chain of events it may feel as if it can't have been a bit otherwise, but in fact at the moment of each event some alternative could very well have ocurred, within of course the physical boundaries.
I find it amuzing that one may really think it was embedded in the universe's fate that the fall of some asteroid should wipe out the dinosaurs or Pete Sampras should win against Agassi in this edition of the US Open.

AVE

abe smith

Naw; it isn't.