# Quantum Mechanics : !?

Discussion in 'Physics & Math' started by The God, Jun 1, 2017.

1. ### Write4UValued Senior Member

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question;
Is there a difference in *wave function collapse" and a "physical collapse" of say, a building?

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3. ### The GodValued Senior Member

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This was also one of the points...

The observation or measurement is complete only when signal (transmitted or source) is received back by the observer.

In such distant cases we observe or measure based on light emitted by these objects, while in certain closer cases we send a probe signal and receive it back after it interacts with the object.

So when actually collapse happens? In the case when we are just observing the light emitted by these objects, collapse appears meaningless. We can all appreciate that when we send a signal for observation or measurement, then this signal may interact and may change the state of object. For example a laser photon sent to observe or measure the electron spin, can effect electron state. What is so quantum mechanical about it? Send a huge comparable boulder to observe the moon, it's state may change. It may collapse if impact is ooh lala..

Last edited: Jun 2, 2017

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5. ### Write4UValued Senior Member

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Why? The collapse of the wave function just follows the "rules", regardless of distance.

It would be remarkable if it did not.

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7. ### SeattleValued Senior Member

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I don't consider that it is a quantum system. It is made of particles but it doesn't act like a quantum system. You can use "quantum system" math on it but it doesn't return anything useful.

8. ### SeattleValued Senior Member

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I think what is being argued regarding the collapse of waves is in the category of "interpretation". What accurately predicts is the math and when you get a specific answer the waveform collapses.

Beyond that who knows what actually is going on. Is it a wave, as in a water wave that collapses when you touch the water, is it an "informational" wave only. I think there is no answer is there since none of this has been proven or we wouldn't be talking about it?

The key is that what we are talking about is within the context of a small, low energy system. When higher energy comes into contact with that system the state "collapses" and you get whatever you get.

There is no point talking about actions that take place on a quantum level and now applying that to the macro world.

The only interpretation that is probably currently valid is the "shut up and do the math" interpretation.

9. ### danshawenValued Senior Member

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Schroedinger evidently thought he could apply it to his cat and a decaying radioactive atom. Is the Earth and an electron so different?

How about the Earth and a pi meson? We could rig it so that when the pi meson decays, Trump pushes the button and the Earth's wave function collapses. Who would know, I mean, if they didn't actually observe it? Not Trump, unless he read about it in the fake news or something.

Good example of a bad example of quantum processes. Yes, as you say, 'silly'. Trump would not hesitate for the pi meson to decay. He would simply devise a conspiracy theory to prove that it already had, that and the FBI had been listening when it happened.

Just another statistical quantum glitch. Very deniable.

Last edited: Jun 2, 2017
10. ### The GodValued Senior Member

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You need to really work hard to know more abt QM, this post of yours is quite vague bordering to complete ignorance about the subject.

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11. ### The GodValued Senior Member

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For Schrödinger and for De Broglie after 1929....NO.

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12. ### The GodValued Senior Member

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It's half a century of posts, still none could associate collapse with some kind of physical aspect.

SF should hire some experts to contribute anonymously, but not like that Scneibster.

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13. ### exchemistValued Senior Member

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Take a look at my response to Seattle then. I have a quick and non-rigorous go at illustrating what I think QM will say for an Earth-sized object.

You will - if I've got this right after so many years - have billions of virtually identical eigenstates superimposed in a "wave packet", "collapse" of which by interaction with a measuring instrument will make essentially no difference, as the uncertainty in properties of the object due to QM effects will be so tiny.

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14. ### QuarkHeadRemedial Math StudentValued Senior Member

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Err, ahem. The correct term chaps is "superposed". Roughly speaking it means that if the state of a quantum system is $\Psi$ - a vector - then it can (almost) always be resolved as $\Psi =\psi_1 + \psi_2$ (say), also vectors

Note that it is the state itself that is subject to superposition, not its eigenstate under the action of an operator, as exchemist (inadvertently?) implied

15. ### exchemistValued Senior Member

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Yes you are right of course. That's what comes of not using this stuff day to day. Thanks.

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16. ### DinosaurRational SkepticValued Senior Member

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There are Posters here who assign some mystical effect due to intelligent observers. For example River Post #10
Relating to the statement from some post
Quantum Level events occurred billions of years ago when there were no observers.

Another example is from the Quark Head Post 19 (see below).

From my Post 15
From Quark Head Post 19
The semantics of your above remark indicates that observation or measurement by an intelligent observer is required to “collapse the wave function.”

Actually, the so called collapse occurs when some quantum level process has an effect at the classical level.

The notion that measurement by an intelligent observer is required is due to the remarks of some expert being misinterpreted by a technical writer for some publication directed at folks with little knowledge of Quantum Theory.

Also from Quark head Post #19
The above refers to my remark
From the POV of probability theory.

The possible locations of a photon are a set of mutually exclusive values: If the photon observed at location A it cannot be elsewhere at the time of the observation. The sum of the probabilities for all locations is one.

The possible values of a dice throw are 36 mutually exclusive values. If a dice throw is observed to be a 9, it cannot be any of the other 35 possible values at the time of the observation. The sum of all the probabilities is one.​

The probability analysis of mutually exclusive events is applicable to both of the above, although calculating probabilities for photon locations & various quantum level events are far more difficult than dice throw calculations (& sometimes not even possible in practice).

From a probability POV, There is an excellent analogy between dice throws & photon locations.

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17. ### Confused2Registered Senior Member

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A while back rpenner posted a link (I think this is it) which might give some insight into QM
http://www.scottaaronson.com/democritus/lec9.html

18. ### QuarkHeadRemedial Math StudentValued Senior Member

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No, not unless its location is measured. The "possible locations" of any subatomic entity is given by an operator acting on the state function, in this case the position operator,. This operator has a continuous spectrum of eigenvalues, which exist in eigenspace - a projection from state space to a different vector space. If these eigenvalues are not determined, then the position of a quantum entity is unknown

In other words, in the quantum world, there appears to be no such thing as an "actual eigenvalue" or if you prefer a "real world".

19. ### river

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Which is exactly what the sub-atomic should be .

Qauntum is where creativity of energy is .

Quantum is not about the real world , because the real world has coalesced into the macro physical objects .

Galaxies etc. You know the rest .

Quantum is where creativity of energy and the results are expressed in the macro-world.

20. ### arfa branecall me arfValued Senior Member

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Why has IBM made its quantum chip and API available to the public?
--https://en.wikipedia.org/wiki/Quantum_computing
It wants as many people as possible to have access to the technology. Quantum logic in terms of connecting gates together is a foot in the door, you won't need a degree in physics.

The computer has been built, IBM is positioned to release its 17 qubit processor, and industry will be looking for quantum programmers. To be one you need to understand how to connect unitary reversible gates together in a "meaningful" way.
The rules, as it were, for connections are defined in user guides. The rule of thumb with all this is that you need to understand this new programming language in terms of logic gates, where the logic is unfortunately not Boolean, nor classical; you get to connect together some awesomely weird shit. Booyah!

One could also consider just how new the territory is; there are algorithms nobody knows about yet--you could be the first!

Last edited: Jun 4, 2017
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21. ### DinosaurRational SkepticValued Senior Member

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From my Post #53
From QuarkHead Post #55
Your above remark seems absurd.

It claims that until a measurement is made it could be at location A and at location B at the same time.

Perhaps you do not understand what mutually exclusive means.

22. ### DinosaurRational SkepticValued Senior Member

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From Write4U Post 41
I have objected to the collapse semantics in Posts to many Threads.

The wave function is an abstract mathematical entity. The semantics of collapse in every other context of which I am aware relates to some physical object like a bridge or building.

The use of the term in Quantum Theory

23. ### DinosaurRational SkepticValued Senior Member

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Mea Culpa: I was interrupted & made Post 59 too soon.

The use of the word collapse in Quantum Theory is misleading. The semantics suggest some physical object collapsing.