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How does QM Prove that things are undetermine

MasturDbtor
Posts: 45
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7/27/2015 3:14:53 AM
Posted: 1 year ago
undetermined (they really need to make title lengths longer)

Restated How does Quantum Mechanics prove that things in nature are not determined with certainty?

I get how they can prove that things can not be predicted with certainty by human beings or by instruments we may devise. However, every time I read about this in a book it then goes on and just jumps to the conclusion that things in nature literally lack a definite location, with no explanation for this giant leap in logic.

If our perception of reality was limited to staring at a digitized map of the Earth and we could look up the GPS coordinates for any given thing on Earth but there were limitations in how accurate and precise we could be in determining these coordinates that wouldn't mean that in reality all the things on Earth have no definite locations and exist only as probabilities within a certain range of values.

So how does Quantum Mechanics show that this isn't just an inherent limitation in our ability to measure and predict things? How does it prove that this is how nature itself works? It's hard to imagine how they could prove that and books don't usually explain it.

Anyone here familiar enough with Quantum Mechanics to fill in the gaps in these explanations? What would we expect to be different if it was the case that the Universe was purely deterministic BUT that us humans could never measure what was determined with perfect accuracy and precision compared to a Universe that is in and of itself independent of human observation and measurement indeterministic?
MasturDbtor
Posts: 45
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7/27/2015 3:38:38 AM
Posted: 1 year ago
By inherent inability to measure I also mean permanent. I can understand how we can prove that we will never ever be able to determine precision and velocity precisely BUT wouldn't saying that precise position and velocity exist but that physical laws prevent us humans from ever knowing exactly what does values are for any given case be just as consistent with the data as saying these values are, independent of human perception indeterministic? If not then I have yet to stumble upon any explanation in books for how these two possibilities would be told apart.
RuvDraba
Posts: 6,033
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7/27/2015 6:33:11 AM
Posted: 1 year ago
At 7/27/2015 3:14:53 AM, MasturDbtor wrote:
I get how they can prove that things can not be predicted with certainty by human beings or by instruments we may devise. However, every time I read about this in a book it then goes on and just jumps to the conclusion that things in nature literally lack a definite location, with no explanation for this giant leap in logic.

It isn't my field of expertise, MD, so this is just a stab. However the Heisenberg Uncertainty Principle is different from the Observer Effect (where your instruments can affect what you're measuring), and I'll try and explain the differences.

With the Observer Effect, it's true that measurement of one property might change that property or some other. A common example is measuring tyre-pressure: measurement typically lets out some of the air, changing the pressure you're measuring. Measuring current and potential (Volts and Amps) with a multimeter can also change the circuit you're measuring, so you get additional imprecision from the measurement method. But with the Observer Effect, what happens depends on how you measure, whereas with Heisenberg's Uncertainty Principle, it's not.

In quantum experiments, it's observed routinely that certain values come in complementary pairs -- position-momentum, wave-particle, axial spins, duration-energy [https://en.wikipedia.org...]. Due to the wavy nature of matter, each time-dependent value can be calculated as a decomposition of the frequency-dependent properties of the complementary member. This decomposition is called a Fourier transform, which we can think of as layering the amplitudes and phases of different frequencies to build an over-all wave. [https://en.wikipedia.org...] The more precisely we want to define the wave, the more components there must be, which correspond to greater uncertainty in the complementary variable

That sort of calculation is of interest to physicists, theoretical chemists and electrical engineers, but the takeaway point is that these pairs always work together, regardless of how you try to observe them. Like kids on a see-saw behind a fence, one variable manifests more at any time than the other, and as one manifests, you see less of the other.

Why oh why should this be?

There are certain properties of the universe that seem invariant and hence metaphysically fixed: the speed of light, Planck's constant, conservation of energy, momentum and angular momentum, and the wave-particle duality of matter. We might never know why these things are fixed, because we might never be able to peek under the bonnet of our own universe to see how it holds together, but this peculiar relationship is apparently always there (because it scales up above quantum-sized objects), however as objects get bigger, the effect gets less significant and hence harder to observe. So it's not the property which is odd -- it's us. Our brains haven't had to work with this odd relationship for most of our species' development, so we're not great at thinking about it.

It's one of many remarkable things nature does that we only find out about when we really start to look.

I hope that may be useful.
slo1
Posts: 4,364
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7/27/2015 9:43:08 AM
Posted: 1 year ago
At 7/27/2015 3:14:53 AM, MasturDbtor wrote:
undetermined (they really need to make title lengths longer)

Restated How does Quantum Mechanics prove that things in nature are not determined with certainty?

I get how they can prove that things can not be predicted with certainty by human beings or by instruments we may devise. However, every time I read about this in a book it then goes on and just jumps to the conclusion that things in nature literally lack a definite location, with no explanation for this giant leap in logic.

If our perception of reality was limited to staring at a digitized map of the Earth and we could look up the GPS coordinates for any given thing on Earth but there were limitations in how accurate and precise we could be in determining these coordinates that wouldn't mean that in reality all the things on Earth have no definite locations and exist only as probabilities within a certain range of values.

So how does Quantum Mechanics show that this isn't just an inherent limitation in our ability to measure and predict things? How does it prove that this is how nature itself works? It's hard to imagine how they could prove that and books don't usually explain it.

Anyone here familiar enough with Quantum Mechanics to fill in the gaps in these explanations? What would we expect to be different if it was the case that the Universe was purely deterministic BUT that us humans could never measure what was determined with perfect accuracy and precision compared to a Universe that is in and of itself independent of human observation and measurement indeterministic?

It is quite simple in that experiments demonstrate that a particle lacks a definitive location. Part of that is because it appears the particle is a wave when not measuring it and acts like a particle when measuring it.

You can actually make experiments where you shoot one electron or atom for that matter and separate it down two paths. When you don't measure it goes down two paths at the same time (just like a wave would)and when you measure it, it goes down only one of the two paths. (like a particle would)

How do you get two very different results based upon whether you are measuring the electron or not measuring the electron? It is quite the conundrum thus why most schools of QM lack reality or definition of set attributes such as position in the classical sense.

There are attempts such as pilot wave theory which basically states the particle is being pushed via a wave, thus why when not measuring the interference pattern, but the particle rides the wave thus has a deterministic position. There are problems with that interpretation though.

The other indication of non-reality is evident in Bells Theorem. There are tests and if the results are a certain value then it could be that there are "hidden variables" that we don't know of that explain the odd behavior. To date even with more advanced versions of Bell's Theorem results do not indicate hidden variables which would explain there is realism.

Determinism is a different subject than realism although they are related. There is still cause and effect, but what seems as a cause can have an effect on a past event. It gets real crazy.

You ask a good question about why big things don't have the same level of odd behavior. The answer is that as things get bigger the quantum effects get smaller. For example I can in theory shoot a baseball through the double split experiment and show that it is a wave and not a solid object like we think of a base ball. However, I would have to shoot it at such high speed in terms of percentage of speed of light that we don't have the technology to do as such. The baseball has a wave function, but it is such a small wave that it needs to go fast and through a very small slit to get an interference pattern.

We have done the double slit with things as big as collections of atoms or molecules.