[Foucceedo]

http://video.google.com/videoplay?do...4618&q=quantum


Is there still no explanation as to how an observed collapsed the wave function?

[HOTgirlsXXL]

Exactly what do you mean? It's quite easily explained by wave-particle duality, and the act of observing is what collapses the wavefunction.

I'd quite happily give a full explanation, but you ask so many stupid questions that I don't think it's worth the time before work.

[cheapphenonline]

http://video.google.com/videoplay?do...4618&q=quantum


Is there still no explanation as to how an observed collapsed the wave function?

That movie just made my head hurt, how the feck can just observing it make it behave differently :\

[intisgunkas]

If you observe something, then it's been interacted with (either directly or indirectly). Electrons will not produce an interference pattern through a double slit if one sets up counters across each slit - in other words, if you attempt to observe individual electrons passing through the gaps, then they exhibit particle properties. Remove the counters and just observe the screen, and the interference pattern will return.

It's best to just not think of things like electrons being particle and/or waves - they're neither. The correct term is quantum entity - they exhibit different behaviour, depending on how one observes them.

[cheapphenonline]

If you observe something, then it's been interacted with (either directly or indirectly). Electrons will not produce an interference pattern through a double slit if one sets up counters across each slit - in other words, if you attempt to observe individual electrons passing through the gaps, then they exhibit particle properties. Remove the counters and just observe the screen, and the interference pattern will return.

It's best to just not think of things like electrons being particle and/or waves - they're neither. The correct term is quantum entity - they exhibit different behaviour, depending on how one observes them.

its pretty crazy if you think about it tho that just observing can casue this. i think we are being played with by the maker lol we getting too close to the truthe must be lol.

[intisgunkas]

Observing something isn't just a case of "sitting back and looking". You only see something because light has been reflected off the object towards your eyes - that light also interacts with the object. In the case of a table, the mass and size of the table is so large that the amount of momentum imparted by the light to it is, to all intents and purposes, nothing. However, in the case of an electron, it would have a huge effect (or it would if the wavelength of light was sufficiently small enough to be useful for detecting individual electrons).

In short: to observe something means that some form of an interaction has to take place.

[Dstyeglm]

its pretty crazy if you think about it tho that just observing can casue this.

As far as I understand it, we're not really 'causing' anything though are we? By measuring it we're just looking at it in a different way and so the observed result looks different. I suppose you could liken it to looking at the same object from different angles. It's a gross oversimplification, but yeah...

Would I be right in reaching this conclusion?

[Hoglaunccoolf]

What specifically about the interaction is responsible for the wavefunction collapsing Neeyik? As opposed to shining some photons on the experiment and seeing nothing happen to the interference pattern.

[intisgunkas]

Before when I mentioned placing detectors at the slits to cause the interference pattern to disappear, one can do this by taking advantage of the fact that moving charged particles emit electromagnetic waves or produce a magnetic field; either way, utilising this causes an interaction back to the electrons. In effect, it's a bit like saying "treat it like a wave and it will behave like one; treat it like a particle and it'll happily oblige".

[Foucceedo]

Observing something isn't just a case of "sitting back and looking". You only see something because light has been reflected off the object towards your eyes - that light also interacts with the object. In the case of a table, the mass and size of the table is so large that the amount of momentum imparted by the light to it is, to all intents and purposes, nothing. However, in the case of an electron, it would have a huge effect (or it would if the wavelength of light was sufficiently small enough to be useful for detecting individual electrons).

In short: to observe something means that some form of an interaction has to take place.

So, you are saying that when people look at objects they interact with them through light, but by themselves light does not inter'act with those objects?

If light has been reflected off the object SPECIFICALLY to our eyes?

[intisgunkas]

What specifically about the interaction is responsible for the wavefunction collapsing Neeyik?

The interaction is essentially taking the wavefunction equation, plugging in some values for the variables and then getting the result. "Collapsing" just means resolving.

So, you are saying that when people look at objects they interact with them through light, but by themselves light does not inter'act with those objects?

The light does interact with the object - that's what reflection is. If it didn't happen then we wouldn't see the object.

[Foucceedo]

The interaction is essentially taking the wavefunction equation, plugging in some values for the variables and then getting the result. "Collapsing" just means resolving.


The light does interact with the object - that's what reflection is. If it didn't happen then we wouldn't see the object.

So why does it matter if WE look at it? Everything else looks at it and it behaves like a wave, but when WE look at it - it doesn't?

[Biassasecumma]

I figure I'm missing something here - IIRC (from a few decades and concussions ago) the double slit experiment was to demonstrate the interference pattern between the photons passing through both slits. The strange thing - IMO, of course - is that single photons still show an interference pattern. Is this correct? I'm on 56k so it's still d/loading [yawn].

[edit] watched it - similar to how I recall it, so by observing the action of the photon, we're basically 'forcing' it to make a call on how it's going to act?

As an aside - as has been said, in order to observe or measure something, there has to be some interaction with it to alter the properties of the observing medium. Easiest thing to consider is an electrical meter - in order to move the needle there is a small parasitic drain (called the "burden") which is the energy required to move the needle.

In the above question, as I understand it, we're not looking at the table, rather we're 'looking' at the image conveyed by the photons emitted by the table that hit our retinas, causing an electrical signal to pass to our brain where it's joined by many others and our brain interprets it as a 'table'.

[edit] My brain hurts!

[intisgunkas]

So why does it matter if WE look at it? Everything else looks at it and it behaves like a wave, but when WE look at it - it doesn't?

How do you know it behaves like a wave for everything else observing it? Quantum entities exhibit behaviour concordant with however it is being observed, regardless as to who is doing it.

I figure I'm missing something here - IIRC (from a few decades and concussions ago) the double slit experiment was to demonstrate the interference pattern between the photons passing through both slits. The strange thing - IMO, of course - is that single photons still show an interference pattern. Is this correct?

Yes, that's correct - individual quantum entities will "build up" an interference pattern over time.

[loyalgagora]

This is the first time I've heard of this experiment, but after looking at it, this is how I have come to understand it:

When an electron/quantum particle is fired, it travels as a wave of probabilities - i.e. a wave where the particle has a probability of being anywhere on the wavefront, with the most probability being in the direction of travel and the probability decreasing as you deviate from the direction of travel. When this wave hits the double slits, it will form an interference pattern of probabilities, and when this pattern hits the screen, an actual position for the electron is determined according to the probability patterns. This explains the interference pattern observed on the screen.

The important thing to understand is, the actual position of the electron is ONLY determined (calculated there and then according to the probability function of the wave) when it is observed (this can be when it hits the screen, or when it is monitored by a detector) before it is observed, it remains simply as a wave of probabilities. After it is observed, the wave disappears and the particle materialises. From then on, the particle will will travel to its destination knowing exactly where it is, hence behaving like a particle. This explains why observing the wave/particle before it hits the screen will remove the interference pattern.

Does this make any sense to anyone?

[intisgunkas]

Yes, that's right, although some of your terminology isn't quite as it should be - for example, it doesn't travel as a wave of probabilities. An expression, called the wavefunction, does describe the probabilities of a quantum entity of having a certain position, momentum, etc but this isn't in itself the wave. The electron is described as having wave behaviour simply because if one treats it as being a wave (properties given by de Broglie) then it is easy to describe the viewed interference pattern.

[Kvkcgktl]

Wow this is interesting, I didn't know that by just observing electrons we can change how they behave.

[fujitsusi]

Is this similar to "spooky action at a distance" that Einstein describes? I'm not a physicist or anything and I can't watch the video on my work computer.

[Foucceedo]

Yes, that's right, although some of your terminology isn't quite as it should be - for example, it doesn't travel as a wave of probabilities. An expression, called the wavefunction, does describe the probabilities of a quantum entity of having a certain position, momentum, etc but this isn't in itself the wave. The electron is described as having wave behaviour simply because if one treats it as being a wave (properties given by de Broglie) then it is easy to describe the viewed interference pattern.

I don't understand the observation part still...


It doesn't make sense. if electron A travels through hole A and leaves A mark on the board when it is being observed (same for B), BUT when it is not observed, it does NOT leave A (or B) mark on the board...

[BegeMoT]

If a tree falls in a forest and no one is around to hear it, does it make a sound?