Question about Uncertainty

[gib65]

Do the electrons collapse back into a point on the target screen because they are in affect being measured?

 

Well, they are interacting with the target screen, and this brings about the collapse. If this results in something observable, then you could call it a measurement. From what I understand, all measurement is a form of interaction, so all measurement brings about the collapse, but I'm not so sure that measurement (human observation) is the only condition under which things collapse.

 

If so' date=' I also don't understand how the electron knows where to collapse.

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Therein lies the most perplexing feature of quantum mechanics. The consensus is that this is non-deterministic. Some tried to fight this notion with the idea of "hidden local variables" but this was eventually disproved (I'm not sure how). You can still take a deterministic position, but you'd have to go off into metaphysics to uphold this view which would place you outside the ring of science.

 

if the electron wave did not collapse' date=' would the target screen show the imprint of the entire "interference pattern" all at once, just getting stronger and stronger over time?

[/quote']

 

I think you've got the right idea, but seeing as how this is not the way nature actually works, who's to say what you would actually observe.

[Membrain]

Therein lies the most perplexing feature of quantum mechanics. The consensus is that this is non-deterministic. Some tried to fight this notion with the idea of "hidden local variables" but this was eventually disproved (I'm not sure how).

Hmm, dang. Can anyone confirm this?

 

To re-explain:

 

Here's a page with some images:

http://en.wikipedia.org/wiki/Double-slit_experiment

 

1. First, let's do this one electron at a time. Actually we only need to talk about one electron.

 

2. The electron goes through the double slits and is like a wave interacting with itself, yes?

 

3. When the self-interfering waves hit the target screen they show up as a single point.

 

4. There appears an "interference pattern" on the target screen made up of the accumulating points.

 

So my confusion comes from some apparent consistencies.

 

A: The electron seems to behave in at least one consistent way in that the self-interfering waves create a consistent "interference pattern". By this I mean, that after an electron goes through he slits, and a period of time passes where the electron has dissipated, the next electron comes, and when it passes through the slits it sets up the same interference pattern as the previous electron.

 

B. This implies that the waves from each slit are created at the same time for every electron, with the same "energy" (or whatever you want to call it) for each wave, in such a way as to accurately create the interference pattern. Because if the electron did something different, it would create a different interference pattern, yes?

 

C. Since the artists rendering of the self-interfering waves seems to show the waves bulging out towards the front, wouldn't that mean that the waves would collapse consistently at those most forward points? By that I mean, the waves to the left-most and right-most would never reach the target screen because the center "bulge" would always collapse the wave first.

 

That's about it. Another question is: if all the waves (for a single electron) "touched" the target screen at the same time, doesn't it make sense that the collapse points would appear random since you have all the waves collapsing at the exact same time?

 

Again, if the waves coming through the slits are consistent, and if they interact with the target screen at exactly the same time, wouldn't the apparent random collapse points make sense?

 

Perhaps I'm repeating myself too much, but I want to get as much out there as I could. Thanks!

[gib65]

I think you might be misunderstanding what the wave actually is. It's not an "energy" wave as you called it. The electron doesn't become the wave and visa-versa. The wave is a representation of the probable locations of where the electron is. The best way to think of it is as a conceptual or mathematical tool that tells us where we can expect to find the electron when we try to measure its location. It's not actually there like a mechanical wave. What this means is that the electron has no definite location before the collapse of the wave. We call this "superposition". It's important to note that, although you'll hear superposition being defined as "being in more than one place at the same time", the most accurate way of understand it is "having equal probabilities of being measured in one place versus other places" (and even then, the probabilities aren't always equal).

 

So, to answer your question, the bulge of the wave does not always determine where the electron will strike the plate. Even though it hits the plate first, there isn't really a "something" that's hitting it. If you look at the diagram, you'll see that the bulge is just as much a wave peek as other points along its circumference. This tells you that the electron has equal chances of being at the bulge as all the other points. Just because the bulge hits the plate first (conceptually/mathematically) means nothing insofar as where the electron will ultimate be found when measured. However, where the two waves interfere, the probability augments, and so you get double the probability of the electron being found at those points - hence, the interference pattern.

[Membrain]

I think you might be misunderstanding what the wave actually is. It's not an "energy" wave as you called it. The electron doesn't become the wave and visa-versa. The wave is a representation of the probable locations of where the electron is. The best way to think of it is as a conceptual or mathematical tool that tells us where we can expect to find the electron when we try to measure its location. It's not actually there like a mechanical wave. What this means is that the electron has no definite location before the collapse of the wave. We call this "superposition". It's important to note that, although you'll hear superposition being defined as "being in more than one place at the same time", the most accurate way of understand it is "having equal probabilities of being measured in one place versus other places" (and even then, the probabilities aren't always equal).

Got it, thanks. That's interesting. So we know we have an electron in a specific location as we fire it from the gun (I'm assuming), and we have the same electron in a specific location on the target screen, but between those two locations the location of the electron is probabilistic?

 

I could visualize that.

[Dims]

since we can't accurately measure sub-atomic wave/particles we have to take a probabilistic, statistical approach which leads to scientists being "uncertain" as to what the sub-atomic particles are doing at any one time. The sub-atomic particles are not themselves "uncertain"; they have a definite existence within reality, we just can't measure them with certainty.

No, it cant be so. If subatomic particles would have definite parameters, then we could determine them indirectly. But we can't. Several fact say, that there are not us, who don't know particle parameters,but it is nature itself, who does not know it.

 

It seems to me, that it should be clear just on phylosophical basis.

 

Look.

 

We are going deeper and deeper in our researching nature. Sooner or later we should come to decomposing the existance itself. We should come to level, at wich we see everything.

 

What is existance? It is some relation with object and subject, or between two objects. One exists for another means, that some property of one is true for another. But the world is material. So, this relation should be materialized. And it is materialized: any relation is interaction. If there is no interaction, then it should be no relation.

 

Now, in QM we came to this state of knowledge. We see the material of relations itselfes. The interactions are mediated with some particles. So, the relations also. The only sense of state is what result it can give in interaction.

 

To clarify: I think scientists think that to assert a determinacy about sub-atomic particles is something that is unmeasurable, and that it is only "philosophical" to talk about it.

But don't forget, that unmeasurability is principal. Some things can not be measured neither directly nor indirectly, neither now, nor later. Any suggestions about such things are neither useful nor harmful and etc. Can you offer some sense in what such things are EXIST?