The Universe is Deterministic

[ben m]

Because the 2 that actually end up decaying did so because of some force, they did not "just happen" for no reason. So there was one outcome that was "determined" by some force and the universe is deterministic not non-deterministic. That is if you assume that everything is caused by some force/reason etc..

No---as far as we understand quantum mechanics, it does indeed just happen. Quantum particles are precisely identical---if you have two neutrons, for example, there is quite literally nothing which determines which one will decay first; the decays happen at random. As far as we know, this is not like (say) a bingo drawing---i.e. it's not "since I couldn't keep track of all the balls, I couldn't make a prediction"---but rather is true randomness.

 

[Elf Grinder 3000]

No---as far as we understand quantum mechanics, it does indeed just happen. Quantum particles are precisely identical---if you have two neutrons, for example, there is quite literally nothing which determines which one will decay first; the decays happen at random. As far as we know, this is not like (say) a bingo drawing---i.e. it's not "since I couldn't keep track of all the balls, I couldn't make a prediction"---but rather is true randomness.

You said "there is nothing which determines which one will decay first".

Right you cannot predict with 100% what will decay, but this is not what non-determinism means (the way I think of it).

The decay must happen by some physical "force" - the force is random and you cant determine how it acts but.

You start in state A 10 nuetrino's and you arrive at state B 8 nuetrinos.
There is no way to predict state B given state A.

But isnt it true that ... "there is only one possible state B given state A." This must be true because state B was created from a "physical force"

You just cant predict state B and you never will be able to. But the two statements are differnt.

Example. There are 2 Nuetrino's. A Nuetrino decays if a photon hits the nuetrino dead on. QM might say you cant predict which nuetrino it will hit because you cant "see the photon" because if you did you would have to shine light on it and "ruin" the experiment... But which nuetrino gets "decayed" is certainly determined. It was determined by the event that created a photon. When a photon is set in motion it must act based on physical laws like it goes a certain speed and at a certain vector. Based on those laws it will hit a certain Nuetrino.

 

[Reality Check]

Right you cannot predict with 100% what will decay, but this is not what non-determinism means (the way I think of it).

The thread is not about whether effects (e.g. the decay of a neutron) have a cause (e.g. QM).

It is about whether the universe is deterministric, i.e. whether from a given state of the universe, any future state of the universe is determined from that state by applying the laws of physics. QM says no, e.g. there is no way to predict which of a set of 10 neutrons will decay.

 

[ben m]

But isnt it true that ... "there is only one possible state B given state A." This must be true because state B was created from a "physical force"

You just cant predict state B and you never will be able to. But the two statements are differnt.

Nope, neither of those statements are true. Simple examples:

1) A 211-Bismuth nucleus has two "choices" of how to decay; it can alpha-decay into 207-Tellurium or beta-decay into 211-Polonium. Totally distinct end states from identical initial states. There are many, many examples like this just in nuclear physics, and many more in any other quantum system. I know exactly what the choices are, but I don't know which one way the nucleus is going to go.

But which nuetrino gets "decayed" is certainly determined. It was determined by the event that created a photon. When a photon is set in motion it must act based on physical laws like it goes a certain speed and at a certain vector. Based on those laws it will hit a certain Nuetrino.

You have made a very common error here; the problem is that the usual schoolbook explanation of the Uncertainty Principle ("you disturb the system by scattering a photon off of it") is basically wrong. No, that's not how it works; in this example, the "experiment that created a photon" does not determine exactly precisely where the photon is going---it determines it partially, subject to Heisenberg's Uncertainty and possibly other uncertainties. Beyond that, in a sense, the photon itself doesn't decide where it actually is---i.e. it behaves like a wave---until it's called upon to pick a location, at which point it does so randomly.

 

[Perpetual Student]

State A is the 10 nuetrinos and State B is 8 nuetrinos left. You might not know which one will be left. But this doesnt matter because it does not have to do with determinism - the way we are defining it and the way that the OP probably meant.

A "force" causes #4 and #7 of the 10 nuetrino's to "decay". But since everything happens for a reason - something must have caused the 2 nuetrinos to decay. And something caused the force so it was determined by the previous force.

So although QM says you cannot predict with 100% accuracy which 2 or 3 etc.. nuetrinos will decay. This does not show that the universe is not deterministic.

Because the 2 that actually end up decaying did so because of some force, they did not "just happen" for no reason. So there was one outcome that was "determined" by some force and the universe is deterministic not non-deterministic. That is if you assume that everything is caused by some force/reason etc..

You are missing the point here. First, I am discussing free neutrons (not neutrinos), which have a mean lifetime of less than fifteen minutes.
So, let's try this:
If I were to place two free neutrons in a mechanism that will explode and kill you depending on which neutron decays first, QM does not allow for any way to "determine" the outcome. You have a 50/50 chance -- end of story. Consequently, the universe cannot be deterministic.

 

[sol invictus]

Let's place 10 unstable particles (e.g.: neutrons) with a half-life of a few minutes in a row before us so that we can number them 1, 2, ... 10. Call this situation "state A." Now there is no science that can tell us which of these particles will decay first, second, or third, etc. It is my understanding of QM that it is not true that our sceince is not yet adequate for the task; it is actually the case that there is absolutely no underlying basis for the order of decay. After a few minutes when (about) half of the 10 particles have decayed, we can call this "state B."
We know that State A can give rise to several states other than B in the same time frame. How then can there be any case for the universe being deterministic?

If states C, D, E, etc. occur as well as B.

 

[martu]

If I were to place two free neutrons in a mechanism that will explode and kill you depending on which neutron decays first, QM does not allow for any way to "determine" the outcome. You have a 50/50 chance -- end of story. Consequently, the universe cannot be deterministic.

You assume too much - maybe we'll never know what determined the outcome but that is no reason to assume that no cause exists.

 

[sol invictus]

You assume too much - maybe we'll never know what determined the outcome but that is no reason to assume that no cause exists.

It's not as simple as make an "assumption".

The set of possible "causes" is extremely tightly constrained by Bell's theorem. Any theory (with a few sensible conditions, like locality) that predicts that some particular neutron decayed first must also make predictions that satisfy Bell's inequality. But Bell's inequality is not satisfied by the world.

 

[martu]

It's not as simple as make an "assumption".

The set of possible "causes" is extremely tightly constrained by Bell's theorem. Any theory (with a few sensible conditions, like locality) that predicts that some particular neutron decayed first must also make predictions that satisfy Bell's inequality. But Bell's inequality is not satisfied by the world.

Feel free to show that Bell's assumptions are justified.

 

[martu]

Bugger forgot the quote I meant to add, Bell discussing Bohmian mechanics which implies non locality as one example:

in this theory an explicit causal mechanism exists whereby the disposition of one piece of apparatus affects the results obtained with a distant piece.

Bohm of course was well aware of these features of his scheme, and has given them much attention. However, it must be stressed that, to the present writer's knowledge, there is no proof that any hidden variable account of quantum mechanics must have this extraordinary character. It would therefore be interesting, perhaps, to pursue some further "impossibility proofs," replacing the arbitrary axioms objected to above by some condition of locality, or of separability of distant systems.

Bell, J. S., 1987, Speakable and Unspeakable in Quantum Mechanics

 

[sol invictus]

Feel free to show that Bell's assumptions are justified.

The assumptions (necessary to prove that determinism is inconsistent with experiment) are, roughly speaking:

(1) "reality": that one unique result is obtained when a measurement is made

(2) "locality": that an action here does not instantaneously affect things over there.

Assumption (2) is justified by relativity and quantum field theory. (1) is not justified by anything, and it's probably not true.

Bugger forgot the quote I meant to add, Bell discussing Bohmian mechanics which implies non locality as one example:

Yes, that violates (2) and is inconsistent with relativity.

 

[Tumbleweed]

When you guys figure out when and why a radioactive particle decays, could you then work on why light has no acceleration and why it instantaneously goes the speed it does? And why c? Why not c+ 1? And "just because" won't cut it! That's akin to saying "magic"

 

[martu]

The assumptions (necessary to prove that determinism is inconsistent with experiment) are, roughly speaking:

(1) "reality": that one unique result is obtained when a measurement is made

(2) "locality": that an action here does not instantaneously affect things over there.

Assumption (2) is justified by relativity and quantum field theory. (1) is not justified by anything, and it's probably not true.

Yes, that violates (2) and is inconsistent with relativity.

Well then this must mean that QM is inconsistent with relativity. Non local interaction is assumed* there isn't it?

* probably not the correct word, maybe required instead?

 

[Tumbleweed]

Doesn't the speed of light in a sense make the Universe partially deterministic? After all, ALL observers can agree beforehand what that speed will be in an experiment, and the experiment, when done, will not give random results as collapsing a wave function does, thus determining all predicted answers to be correct; it is c

 

[martu]

When you guys figure out when and why a radioactive particle decays, could you then work on why light has no acceleration and why it instantaneously goes the speed it does? And why c? Why not c+ 1? And "just because" won't cut it! That's akin to saying "magic"

It is massless and nothing can go faster than c hence c+1 is nonsensical. Why c? The geometry of 4 dimensional spacetime results in a maximum speed for any universe where causality is not violated. Observations say causality isn’t violated in our universe so, well you can work the rest out yourself. Why is it the value it is? No idea, maybe this value was ‘set’ at the big bang (or not long after) and different starting parameters at the BB would result in different values of c??

 

[Tumbleweed]

Does QM say that the speed of light is NOT a certainty and if an experiment is done enough times there is a scintillian of a chance the speed will not be c? If so that takes the certainty out of everything and reduces reality to mere statistical probability.
And if what I choose to do here most definitely effects reality there, doesn't that then make me God -like in a random- like way since my chioce is by definition random?

 

[Tumbleweed]

It is massless and nothing can go faster than c hence c+1 is nonsensical. Why c? The geometry of 4 dimensional spacetime results in a maximum speed for any universe where causality is not violated. Observations say causality isn’t violated in our universe so, well you can work the rest out yourself. Why is it the value it is? No idea, maybe this value was ‘set’ at the big bang (or not long after) and different starting parameters at the BB would result in different values of c??

So you are saying it has to be something so why not c. But when I am going 60 MPH there is a physics reason behind it. Same with 100mph. So what is the physics reason for c? And still ,why the instantaneousness. How does no mass explain that?

 

[ben m]

Does QM say that the speed of light is NOT a certainty and if an experiment is done enough times there is a scintillian of a chance the speed will not be c? If so that takes the certainty out of everything and reduces reality to mere statistical probability.
And if what I choose to do here most definitely effects reality there, doesn't that then make me God -like in a random- like way since my chioce is by definition random?

Quantum uncertainty doesn't mean "Any old thing can happen"---it means something very specific about how a wavefunction can be broken down into a set of eigenfunctions; an observation forces it to leap (randomly) into one of these available eigenfunctions.

"going faster than light" is never on the list of possibilities, so it never happens.

 

[martu]

So you are saying it has to be something so why not c. But when I am going 60 MPH there is a physics reason behind it. Same with 100mph. So what is the physics reason for c? And still ,why the instantaneousness. How does no mass explain that?

Ok c was set at the Big Bang. If the Big Bang had been slightly different c would be (perhaps slightly) different. Does that answer your question?

Can you show me an equation for acceleration that does not include the mass of the object involved?

 

[ben m]

Doesn't the speed of light in a sense make the Universe partially deterministic? After all, ALL observers can agree beforehand what that speed will be in an experiment, and the experiment, when done, will not give random results as collapsing a wave function does, thus determining all predicted answers to be correct; it is c

Nobody ever said nothing was predictable. The specific thing that QM says is unpredictable is which eigenfunction a wavefunction chooses to drop into when measured. That's it. If you take an electron and measure its spin twice, for example, it is 100% certain (within experimental error) that the second measurement gives the same result as the first.