Is this a Deterministic Universe

[audioloop]

Thanks Dr, please let me ask this in a slightly different way. If the exact same universe were to be reproduced or started over n times from t=0 i.e. the BB, what are the chances that I would be here typing this in every one? I have heard answers from other Physicists ranging from n to 1 and even 0.

Since I didn't do well in my QM class and it is so long ago, I am unable to judge which answer is most likely and so I wondered what most experts in modern QM think?

I am not looking for a philosophical take or bias, just an understanding of the Physics and QM facts, which perhaps are not sufficiently well understood to be certain of the answer to a question like this?

Physics without philosophical take ? ...:uhh:

 

[Naty1]

Tanelorn:

So my take away is that if the BB happened n times with the same initial conditions we would have universes which are very similar at the top size levels but our particular galaxy would not exist and therefore nothing smaller either.

I would not quite agree, others might. But all this is rather subtle.

The problem is we people cannot produce identical initial conditions; I don't know if nature can and does or not. But if the initial input conditions were precisely identical seems to me the outputs would also be precisely identical. An identical cause produces an identical effect.

To paraphrase, I don't know if nature could reproduce an ensemble of identical systems [in this case identical big bangs n times] but we people can't reproduce anything that yields an identical set of initial states...that is, identical measurements; instead when we try to do that what we get is a statistical set of states/measurements instead of precisely identical ones. Even though we think have performed 'identical state preparations' apparently we haven't really accomplished that.

 

[Tanelorn]

When I said philosophical I meant without religious bias or creation idea bias or any other possible bias.
I just wanted to understand what modern QM Physics has to say.

Audio, I don't see why it is funny to ask a question in the hope of learning something.

Naty, please forget the initial conditions difficulties. As a thought experiment, if I had n Universes all identical in every respect as they were one minute ago, would they still all be identical in every respect one minute later? I just would like to see Yes and No answers from everyone who is reading this.

My view is still no because of the same randomness argument at the QM particle interaction level. Obviously these Universes wouldn't have diverged much in the space of a minute, but over 13.7B years they would.

 

[DrChinese]

1. Space and Time are not like ponderable matter and only provide locations for these particles to exist and interact.

2. I then went on to think that only the immediately preceding Planck time particle state is needed and used to calculate the next Planck time particle state. By this I mean particle location and energy. I thought I had it all worked out, but now you seem to be saying that this is not correct? Is this certain, I hope I don't have to go through all this again :)

1. Spacetime being best described by General Relativity.

2. It might be true or not. The Bohmians take care of this with non-local interactions. Again, there are a variety of interpretations that are generally considered equal in terms of being feasible alternatives. And generally, each requires swallowing a very big pill.

 

[Tanelorn]

Thanks Bill, did you say we know the Universe is fundamentally random and that means every Universe would be different or that we just don't know?

I think that is the most mathematical thing I have ever seen!
http://en.wikipedia.org/wiki/Noether's_theorem

 

[Tanelorn]

I suggest we all agree on the dictionary definitions of these words before continuing.

 

[Pythagorean]

deterministic = one possible future for each state (mathematically, trajectories cannot intersect). There can still be two pasts, just not two futures (so trajectories can merge, but not diverge).

stochastic = many possible futures for each state, trajectories can diverge.

Because if there isn't an underlying deterministic system at work, then what's to cause one outcome to be more probable than another? A probability system without an underlying deterministic system would offer zero predictability, and therefor wouldn't offer much in the way of probability.

That's not true. A probability system need not have uniform distribution of results to be stochastic. It just needs to not be deterministic.

Of course, in any experiment it's impossible to determine whether a system is merely chaotic, has hidden variables, or isn't isolated, or is just probabilistic, so no one really knows whether the universe is deterministic or stochastic. We simply have both deterministic and probabilistic models and sometimes probability is matter of convenience (just model the trends, ignore the chaotic divergence which are technically more informative but not practically useful) but sometimes there's really no other more complete description besides a probabilistic one (i.e. QM).

So all you can really (successfully) ask is... "is it sufficient to model this behavior deterministically?" about specific phenomena.

 

[bhobba]

Of course, in any experiment it's impossible to determine whether a system is merely chaotic, has hidden variables, or isn't isolated, or is just probabilistic, so no one really knows whether the universe is deterministic or stochastic. We simply have both deterministic and probabilistic models and sometimes probability is matter of convenience (just model the trends, ignore the chaotic divergence which are technically more informative but not practically useful)

Exactly. Without experimental support its basically a question that's up in the air.

Thanks
Bill

 

[bhobba]

Thanks Bill, did you say we know the Universe is fundamentally random and that means every Universe would be different or that we just don't know?

I am saying so far it hasn't been possible to determine if we are dealing with a fundamentally random universe or a deterministic one because it always seems possible to find an explanation that fits either view eg for QM we have Bohmian Mechanics which is deterministic and the Ensemble Interpretation which is fundamentally random. Either fits the facts - there is no way to differentiate them experimentally. Until there is its not something that can really be decided.

I think that is the most mathematical thing I have ever seen!
http://en.wikipedia.org/wiki/Noether's_theorem

This really is getting off topic and the mods may decide to remove it - it really needs its own thread.

But anyway this is the point I was making. If you understand it its very startling. What could be more intuitive than the laws of physics are the same at any instant of time, where you are or what direction you are facing. It simply shouldn't matter. The startling import of this theorem is its logically equivalent to energy conservation, momentum and angular momentum conservation. You probably say - what - which is the usual reaction of people when they find out about it. It was discovered by mathematics - that is the only tool able to reveal such a deep and profound truth of nature.

But this isn't the thread to pursue it. If you want to go into it deeper read some more about it and start a new thread.

Thanks
Bill

 

[audioloop]

Space and Time are not like ponderable matter and only provide locations for these particles to exist and interact.
:)

A Relational theory of space-time.

Other ones, the continental theories, one of them; geometrodynamics.

 

[audioloop]

I meant without religious bias or creation idea bias.

Fully concur.

 

[Naty1]

Tanelorn: You might find this discussion of interest:

Observation in quantum mechanics

http://en.wikipedia.org/wiki/Quantum_mind%E2%80%93body_problem#Observation_in_quantum_mechanics

What I would add is that it is my limited understanding if two observers at different locations make identical measurements even simultaneously, they can record different results. And their measurements may cause an observed system different perturbations...hence cause different futures for the two system parts...each different than if no measurement were made.
I think this is what is called LOCALITY: nobody has all information, only what is available locally...because stuff further than lightspeed away will not be communicated.

 

[Naty1]

Tanelorn: My last post here.

Chaos: When the present determines the future, but the approximate present does not approximately determine the future.

http://en.wikipedia.org/wiki/Chaos_theory

I am going to start a new discussion
" What does the quantum butterfly effect tell us?"

under Quantum Physics...you might find it interesting...

I never heard of it before.

edit: the quantum butterfly effect is different from the usual macroscopic, not due to different initial conditions. .

 

[Pythagorean]

I think this (so called QM butterfly effect) is still relevant to the thread. Here's a soft nature article on the subject

http://www.nature.com/news/2009/091007/full/news.2009.980.html

I'm fairly ignorant of the QM side here, but the commonly accepted definition of chaos requires it be defined in a deterministic system. Is the QM system here considered deterministic in the evolution of its state trajectories?

 

[audioloop]

I'm fairly ignorant of the QM side here, but the commonly accepted definition of chaos requires it be defined in a deterministic system. Is the QM system here considered deterministic in the evolution of its state trajectories?

Right
http://en.wikipedia.org/wiki/Chaos_theory

Depend on QM interpretation.

 

[Tanelorn]

I am not certain, but most here seem to be saying that we just don't know, one way or the other, if this Universe is truly random.

I think I am effectively asking whether, with a total understanding of all the Physics of the Universe, I can predict with absolute 100% certainty what I will have for breakfast ten years to the day from now, including the number of atoms of each element as well as the exact positions of all included subatomic particles at an instantaneous Planck point in time? And also if I will have indigestion afterwards :)

Everything I thought I knew said that this simple question can never be answered. I didn't realize that it was even something we weren't sure of.


Bill regarding Noether, doesn't this assume a Universe that is not going to change over time? Dark Energy may mean that it does change?

 

[audioloop]

I think I am effectively asking whether, with a total understanding of all the Physics of the Universe, I can predict with absolute 100% certainty what I will have for breakfast ten years to the day from now, including the number of atoms of each element as well as the exact positions of all included subatomic particles at an instantaneous Planck point in time? And also if I will have indigestion afterwards :)

Not 100 percent.

Maybe not, maybe you'll die tomorrow, nobody knows.

http://plato.stanford.edu/entries/probability-interpret/

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Probability_interpretations.html.

 

[Tanelorn]

Not 100 percent.

Maybe not, maybe you'll die tomorrow, nobody knows.

http://plato.stanford.edu/entries/probability-interpret/

http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Probability_interpretations.html


.

Exactly, so the universe is too random and complex to ever be able to calculate something like my above simple little breakfast question. Remember I meant someone with total knowledge and complete understanding of all the Physics in the Universe, as well as a computer the size of a planet.

Even creating another Universe and using it as a computer wouldn't work because each time would be different because of the same randomness argument.


Thanks, if every one agrees with you (and me) then I consider the question answered.


And so I am an accident, a lucky roll of the dice.. And no matter how many times the BB happens again (assuming a cyclical universe) none of us will be in them because they will all be different..

 

[audioloop]

perhaps the universe is completely predetermined from the "beginning"
predeterminism or is total chance indeterminism or half and half ?

Universe, etymologically: only one line (latin)
Predeterminism ?



.

 

[Tanelorn]

My tired old brain can't work with these words, better to write down in sentences what you mean.

 

[audioloop]

Thanks, if every one agrees with you (and me) then I consider the question answered.


And so I am an accident, a lucky roll of the dice...

a nice roll...



.

 

[audioloop]

My tired old brain can't work with these words, better to write down in sentences what you mean.

just pondering
totally random or totally determined...


.

 

[bhobba]

I am not certain, but most here seem to be saying that we just don't know, one way or the other, if this Universe is truly random.

It goes further than that. So far all the theories we have are of the type that have deterministic or probabilistic interpretations. Because of that, in principle, it is unknowable.

I think I am effectively asking whether, with a total understanding of all the Physics of the Universe, I can predict with absolute 100% certainty what I will have for breakfast ten years to the day from now, including the number of atoms of each element as well as the exact positions of all included subatomic particles at an instantaneous Planck point in time?

As it stands you have asked a meaningless question because we do not know all the physics of the universe - we have zero idea what new laws that may be discovered will tell us.

But what we do know is this. The laws we do know have initial conditions depending on real numbers and any errors in the knowledge of those initial conditions tends to grow as time goes by so that predictions made without exact knowledge gets greater and greater until it becomes totally unreliable. This is the famous butterfly effect - since a real number requires infinite precision that is impossible to obtain, even if the universe is perfectly deterministic, its useless in practice - you can't predict just about anything with any kind of certainty.

Everything I thought I knew said that this simple question can never be answered. I didn't realize that it was even something we weren't sure of.

Yea - the universe is not only stranger than we imagine, it is stranger than most of us can imagine.

Bill regarding Noether, doesn't this assume a Universe that is not going to change over time? Dark Energy may mean that it does change?

It assumes the fundamental laws of nature, whatever they are (caveat given a bit later) are the same. Fundamental laws mean things like Maxwell's Equations, the laws of QM, Newtons Laws, Relativity and even future laws we may not know about. It's very hard to imagine a law that is not the same regardless of time, where you are, or what direction you are oriented in - its almost by the definition of law - its not really what you would call a law unless it's like that. So basically its really the requirement, more or less, that nature is describable by laws.

That this implies conservation laws like energy, momentum etc is - well shocking. Unless you have come across it before it would be the last thing you would have thought. Its a very very deep fact about nature:
https://www.amazon.com/dp/0918024161/?tag=pfamazon01-20
'Wigner points out that the basis for answering the question posed by him, 'Why is it possible to discover laws of nature?' is explained in every elementary physics text but the point is too subtle, is therefore lost on nearly every reader. The answer, he explains convincingly, lies in invariance principles. As an example, were local Galilean invariance not true it would have been impossible for Galileo to have discovered any law of motion at all. The same holds for local translational, rotational and time-translational invariance. Inherent in Wigner's argument is the explanation why the so-called principle of general covariance is not the foundation of general relativity, which also is grounded in the local invariance principles of special relativity.'

I strongly urge you if you are interested in actually understanding why the world is as it is, to get that book and study it closely.

Now for the caveat. Noethers theorem depends on the laws of nature being in a particular form called a least action principle. All the laws of nature so far known are like that and it would be a bit shocking if any was found that isn't, but it is an assumption.

Thanks
Bill

 

[Tanelorn]

Thanks Audio and thanks Bill. If the book you mention is mathematical I would likely not appreciate it. Advanced Math is like an alien foreign language to me unfortunately.

Thankfully the Universe knows what to do next after each Planck time slice even if it isn't aware of it.

 

[Naty1]

Thankfully the Universe know what to do next after each Planck time slice...

This is another wide ranging subject...search these forums for discussions of "time" if interested.

Note there is no consensus evidence time is discrete...nor continuous...and some suggest the question is meaningless! A minimum Planck time is but one way to consider time...one possible perspective. One model is continuous [relativity]; the other is discrete [quantum mechanics]...quantum gravity may be be neither


http://arxiv.org/abs/gr-qc/0604045
Unfinished revolution
Carlo Rovelli

...Roughly speaking, we learn from GR that spacetime is a dynamical field and we learn from QM that all dynamical fields are quantized. ... the conceptual foundations of classical GR are contradicted by QM and the conceptual foundation of conventional QFT are contradicted by GR: In conventional QM, time is treated as an external parameter and transition probabilities change in time. In GR there is no external time parameter… a notion of proper time is associated ….[with] each timelike worldline; yet in quantum theory there are no physical individual trajectories… only transition probabilities between observables….

...the physical variable measured by a clock is a nontrivial function of the gravitational field. Fundamental equations of quantum gravity might therefore not be written as evolution equations in an observable time variable. And in fact, in the quantum–gravity equation par excellence, the Wheeler-deWitt equation, there is
no time variable t at all...

 

[Tanelorn]

thanks Naty, well a Planck time slice is so thin that there is little difference between continuous and quantized in the macro world. It is probably is only important in the realm of QM.

 

[bhobba]

Advanced Math is like an alien foreign language to me unfortunately.

Unfortunately as far as UNDERSTANDING fundamental natural laws, and revealing its underlying beauty and simplicity math is necessary. If there is anything physics has shown us its that those laws are written in the language of math.

Two books at your level I would suggest are Feynman - The Character of Physical Law and Brian Cox E=MC^2 (I have that book as an audio-book because being a member of an audio-book club I get so many free as part of the membership and it really is surprisingly good - explaining many things including Noethers famous theorem)
https://www.amazon.com/dp/0679601279/?tag=pfamazon01-20
https://www.amazon.com/dp/0306818760/?tag=pfamazon01-20

You can also watch Feynman online:


Another excellent thing to read is Wigners famous essay:
http://www.dartmouth.edu/~matc/MathDrama/reading/Wigner.html

Thanks
Bill

 

[audioloop]

my farewell.

there are various "flavors" of determinism, or rather, degrees of determinism

Fatalism -> Predeterminism -> Adequate Determinism.

the high regularity of events in the world, assures that nature is not entirely indeterminate, ...at least.

dear tanelorn, your next breakfast is assured !

.

 

[Tanelorn]

Thanks audio!

Bill one thing that would really help with maths like that is a companion. ie A full description in words of everything that each equation says and why it is being used. It wouldn't be hard yet mathematicians for some reason don't do it. Not everyone can or wants to learn this much math.

 

[MathematicalPhysicist]

I agree, every time you think you have found first cause you can always ask what caused that?
First cause and final effect therefore do not exist, just like a place at infinity cannot.

If there is no first cause nor last effect then we must deduce that causality is an illusion, or that there is a first cause which is also its last effect, we just haven't yet arrived at it.

Circle is the name of the game.

 

[Tanelorn]

If there is no first cause nor last effect then we must deduce that causality is an illusion, or that there is a first cause which is also its last effect, we just haven't yet arrived at it.

Circle is the name of the game.

MP, thanks for the reply!

Wait for it...

What caused this circle in the first place? lol