The Universe is Deterministic

[Dorfl]

Fusion in the sun, according to Coloumb's law two protons will always repulse each other more strongly the closer they get, Always , so you can't have fusion at the core of the sun, the greater the pressure on the two protons, the harder they push away from each other.

So... how do you get fusion of two protons in the sun?

There is a probability that one or the other will just happen to exist next to the other because of QM. They do not behave like hard little balls they behave like waveforms. So deteministically they can never approach each other. Probablistically they can.

That shows that protons do not behave classically, that you have to use wave-functions to correctly describe how they interact. It doesn't address whether the wave-functions themselves are fundamentally deterministic, does it?

 

[edd]

As I'm sure you know, many events at the quantum level do not have causes as far as we can tell, so I'm puzzled why you would make that statement.

Well, I don't know what makes you say that.


That was a joke.

 

[edd]

Don't forget, QM is the realm of the 'very small'.
What is kind of interesting is how the double slit experiment has been found valid for buckyball molecules of 60 carbon atoms, meaning molecular wt 60 x 12 = 720. That's kind of 'big' in the QM world, isn't it?

It's not immediately obvious how to decide when things should look classical based on mass alone. A top quark has a mass that's over a hundred amu, but you wouldn't say that's out of the quantum realm. The Planck mass in fact is quite macroscopic - there are animals that weigh in the rough ballpark of a Planck mass, probably.
So it's not really so easy to say that's "kind of 'big'".

 

[orange31]

It's not immediately obvious how to decide when things should look classical based on mass alone. A top quark has a mass that's over a hundred amu, but you wouldn't say that's out of the quantum realm. The Planck mass in fact is quite macroscopic - there are animals that weigh in the rough ballpark of a Planck mass, probably.
So it's not really so easy to say that's "kind of 'big'".

Thanks. I know this sounds ridiculous, but say you were able to set up a gigantic version of the double slit experiment but firing bowling balls instead of electrons or bucky balls, and let it go for few weeks, maybe also did those extra steps that people have added on which shift the 'results' to interference or non-interference patterns by if you look for them, etc....

...would bowling balls give an interference pattern?

--------------
As noted above, the original poster's objections is the EPR thing, whether he was aware of it or not!

 

[shuttlt]

Thanks. I know this sounds ridiculous, but say you were able to set up a gigantic version of the double slit experiment but firing bowling balls instead of electrons or bucky balls, and let it go for few weeks, maybe also did those extra steps that people have added on which shift the 'results' to interference or non-interference patterns by if you look for them, etc....

...would bowling balls give an interference pattern?

--------------
As noted above, the original poster's objections is the EPR thing, whether he was aware of it or not!

no

 

[edd]

Thanks. I know this sounds ridiculous, but say you were able to set up a gigantic version of the double slit experiment but firing bowling balls instead of electrons or bucky balls, and let it go for few weeks, maybe also did those extra steps that people have added on which shift the 'results' to interference or non-interference patterns by if you look for them, etc....

...would bowling balls give an interference pattern?

--------------
As noted above, the original poster's objections is the EPR thing, whether he was aware of it or not!

As shuttIt says, no. But the thing about that isn't strictly the mass of a bowling ball but its momentum and the size of the ball. The momentum gives you a wavelength, and the wavelength is much tinier than either the ball or any slits you could possibly hope to build.

 

[sol invictus]

As shuttIt says, no. But the thing about that isn't strictly the mass of a bowling ball but its momentum and the size of the ball. The momentum gives you a wavelength, and the wavelength is much tinier than either the ball or any slits you could possibly hope to build.

That's not the only reason. It's also because it's nearly impossible to prevent the bowling ball from interacting with its environment and decohering. In the imprecise language many people use, the bowling balls almost always get "measured" by interactions with their environment, thereby projecting down to a state that passes through one slit or the other, but not both.

That's why it's hard to put Schrodinger's cat in the state (|dead>+|alive>)/root(2), and why it's hard to make a quantum computer with more than a few qubits.

 

[Ziggurat]

I don't think it's a coincidence either. The evidence is growing stronger and stronger that collapse is nothing more or less than the fact that with lots of particles, the wavefunction is very susceptible to almost instant decoherence. It's nothing more than the fact that (1-e)^{10^23} is a very small number even when e is very close to zero.

Which suggests that the Copenhagen interpretation, though effective from a practical standpoint, is wrong. So while Cynic seems to be either confused about aspects of QM or unable to express his opinions with clarity (or maybe both), simply telling him that standard quantum mechanics is probabilistic isn't really the whole story.

And I don't think it's true that we never model collapse accurately. Mesoscopic systems that maintain coherence are becoming more and more common.

If they're maintaining coherence, then they aren't collapsing. That's the whole point of maintaining coherence. So no, I think that statement stands: we never model collapse.

That's what a quantum computer is, after all. So I think experiment has already pushed back the edges of what constitutes a measurement, and I suspect that will accelerate.

Yes: we'll model bigger and bigger systems that evolve for a period of time without collapse, then we stop modeling them and collapse happens. Pushing back what happens before collapse doesn't really change that.

Well, either you think measurement devices are made of particles that obey the known laws of physics, or you don't and you think there's some new and mysterious law of physics that applies to voltmeters but not electrons.

Which is it?

I suspect the former, but cannot disprove the latter. Moreover you've misstated the latter possibility: it need not be new laws of physics which apply to voltmeters but not electrons, it could be new laws of physics which become significant for voltmeters but not for electrons (for example, small nonlinearities in QM).

 

[sol invictus]

Which suggests that the Copenhagen interpretation, though effective from a practical standpoint, is wrong.

In internet discussions I try to be precise and focus on comments that were actually made. Cynic's claim (the one at issue for this sub-topic) wasn't that the CI is wrong, it was that it isn't probabilistic. That's simply false, as can easily be verified by a glance at any QM text.

So while Cynic seems to be either confused about aspects of QM or unable to express his opinions with clarity (or maybe both), simply telling him that standard quantum mechanics is probabilistic isn't really the whole story.

And I didn't stop with that. The next obvious question is, can the CI be wrong in a way which makes QM deterministic but preserves locality? Answer: no, Bell proved that impossible.

If they're maintaining coherence, then they aren't collapsing. That's the whole point of maintaining coherence. So no, I think that statement stands: we never model collapse.

But they don't always maintain coherence, and one can both probe that process experimentally and model it theoretically (that's what "decoherence" is, and there's a lot of theoretical work done to model it).

I suspect the former, but cannot disprove the latter.

And you can't disprove the existence of magic non-local elves that mischievously alter our results so that they always conform to QM, either.

 

[Ziggurat]

...would bowling balls give an interference pattern?

If you did the experiment correctly, it should. But given the fact that the de Broglie wavelength of a bowling ball is so many orders of magnitude smaller than the diameter of the ball, which essentially forms your minimum slit widths, the deflection angles from going through a slit are going to be amazingly small. So the required size of your interferometer to get any halfway-decent signal would be ridiculously large. I haven't plugged the numbers (I have vague memories of seeing someone else having gone through them), but I think we may be talking something galaxy-sized.

 

[Ziggurat]

But they don't always maintain coherence, and one can both probe that process experimentally and model it theoretically (that's what "decoherence" is, and there's a lot of theoretical work done to model it).

Decoherence isn't the same thing as collapse, though. And it gets modeled statistically assuming random perturbations because you can't model the perturbations explicitly.

 

[shuttlt]

If you did the experiment correctly, it should. But given the fact that the de Broglie wavelength of a bowling ball is so many orders of magnitude smaller than the diameter of the ball, which essentially forms your minimum slit widths, the deflection angles from going through a slit are going to be amazingly small. So the required size of your interferometer to get any halfway-decent signal would be ridiculously large. I haven't plugged the numbers (I have vague memories of seeing someone else having gone through them), but I think we may be talking something galaxy-sized.

Aren't we also talking about having to get a bowling ball (diameter approximately 12.5cm) to pass through a slit somewhat smaller than 12.5cm without touching the sides?

 

[Ziggurat]

Aren't we also talking about having to get a bowling ball (diameter approximately 12.5cm) to pass through a slit somewhat smaller than 12.5cm without touching the sides?

No, you would use a slit slightly bigger than the bowling ball, or the ball won't go through. To get a sense of the size of the interferometer you'd need, consider the ratio of the slit size (a bit bigger than the ball) to the de Broglie wavelength (much smaller than an atom). The interferometer should be at least the same ratio bigger than the slit size. So, really really freakin' huge.

 

[Cynic]

Cynic's claim (the one at issue for this sub-topic) wasn't that the CI is wrong, it was that it isn't probabilistic.

I've been quiet because I'm still thinking about all the questions I'm getting owned on here. But just to be perfectly, crystal clear (if that is possible):

My claim is that ontologically (that is, in reality) the universe cannot be shown to be either deterministic or non-deterministic. The Copenhagen Interpretation and, from what I can tell, every other interpretation or aspect of quantum mechanics specifically addresses epistemology, not the reality.

But anyway, I'm out for the weekend, during while I'll mediate on this some more.

 

[shuttlt]

No, you would use a slit slightly bigger than the bowling ball, or the ball won't go through. To get a sense of the size of the interferometer you'd need, consider the ratio of the slit size (a bit bigger than the ball) to the de Broglie wavelength (much smaller than an atom). The interferometer should be at least the same ratio bigger than the slit size. So, really really freakin' huge.

I made a bunch of assumptions that should throw the figure orders of magnitude off on the low side, but I came up with 417,000km as the size of the interferometer.

 

[LordoftheLeftHand]

As other posters have said, pick one:

1. Hidden variables (the world is deterministic)
2. Locality (one object can not effect another faster than the speed of light)

At most only 1 of these can be true.

 

[Ziggurat]

I made a bunch of assumptions that should throw the figure orders of magnitude off on the low side, but I came up with 417,000km as the size of the interferometer.

I decided to check the numbers myself, and got something significantly larger. The de Broglie wavelength should be h/p, where h is Planck's constant (not hbar) and p is the momentum. Let's suppose we've got a 6.6 kg bowling ball (in the right ballpark for a bowling ball, will keep our figures round) traveling at 1 m/s, that gives a de Broglie wavelength of 10^-34 meters. Keeping things nice and round, we'll say the slit is about 10 cm, so the ratio of slit/wavelength is about 10³³. If we keep this same ratio for interferometer/slit, we get 10³² meters = 10²⁹ km, or about 10¹⁶ light years. So actually, larger than the visible universe.

 

[sol invictus]

My claim is that ontologically (that is, in reality) the universe cannot be shown to be either deterministic or non-deterministic. The Copenhagen Interpretation and, from what I can tell, every other interpretation or aspect of quantum mechanics specifically addresses epistemology, not the reality.

If that's the approach you'd like to take I think you're in the wrong forum. Science is just a bunch of models. Those models either match experiment or they don't, but you're always free to assume "reality" is something else. It could all be someone's dream, after all.

The challenge for you is to find a model for the world which is deterministic but not in conflict with experiment. That's a very, very difficult challenge because of Bell's inequality (and the experimental results that demonstrate that it's violated). I suggest you do some reading on that topic, as it is by far the most powerful tool available to address the question in the OP.

 

[shuttlt]

I decided to check the numbers myself, and got something significantly larger. The de Broglie wavelength should be h/p, where h is Planck's constant (not hbar) and p is the momentum. Let's suppose we've got a 6.6 kg bowling ball (in the right ballpark for a bowling ball, will keep our figures round) traveling at 1 m/s, that gives a de Broglie wavelength of 10^-34 meters. Keeping things nice and round, we'll say the slit is about 10 cm, so the ratio of slit/wavelength is about 10³³. If we keep this same ratio for interferometer/slit, we get 10³² meters = 10²⁹ km, or about 10¹⁶ light years. So actually, larger than the visible universe.

I thought I was on the low side.

 

[arthwollipot]

Tangential (and somewhat semantic) question - my statement was that quantum events are stochastic, not random. Is there actually a difference? Dictionaries usually use the word "random" as part of the definition of "stochastic" but my impression was that "stochastic" wasn't quite the same thing. I was using it to mean, basically, "unpredictable" - in that a quantum event (like nuclear decay) was not something where you could predict in advance when it was going to happen. I'm not sure that's quite the same thing as "random".