The Observer Effect

[KJW]

8 hours ago, joigus said:

And a koala is also called "koala bear" even though it has nothing to do with bears. It's a marsupial.

I know what a koala is. They used to be in my backyard until they disappeared as a result of urban development.

 

 

8 hours ago, joigus said:

The loss of coherence that connects the quantum domain with the classical domain has to do with interaction, not with the observation of anything. There are planets out there that nobody will ever visit, and electrons, protons, etc, are doing their business giving rise to physics that a potential observer would interpret as classical, because they are in the classical or quasi-classical regime.

Again, it's not about observing, it's about quasi-classical interactions.

I know what quantum measurement is. And I know that they are about interactions and not observation. But there is an aspect that is about observation that goes beyond the objective nature of measurement. When you asked me why we need observers, I said we don't need observers, we are observers, I don't think you understood why I said that. Being an observer does have its consequences. You can't assume that the world would run the same way without observers. Not every manifestation of significance is objectively real. For example, what in the objectively real world is the present? There are no "this is now" markers in spacetime. But as observers, we can't help but see that the present is different to the past and that the future doesn't yet exist. Where is the objective reality in that? I am saying that the collapse of the wavefunction to a single eigenvector is not objectively real and requires a conscious observer to explain. But note that there is another significant issue involved that also needs to be explained, and that is the notion of intrinsic randomness. The many-worlds interpretation explains it, the Copenhagen interpretation does not.

 

 

8 hours ago, joigus said:

I have no doubt now you've picked this up from somewhere, so I've been looking it up.

That's not necessarily true. I do my own analyses beyond what I read.

 

 

8 hours ago, joigus said:

There are better alternatives, but they haven't been considered nearly as seriously as they deserve.

I don't necessarily accept the exact version of the many-worlds interpretation. My view is that something like the many-worlds interpretation is necessary, even if it is a modified version of the original.

 

 

Edited December 4, 2023 by KJW

[studiot]

1 hour ago, KJW said:

I know what a koala is. They used to be in my backyard until they disappeared as a result of urban development.

I notice you carefully avoided the mathematics I picked out for you in @joigus' post.

[KJW]

16 minutes ago, studiot said:

I notice you carefully avoided the mathematics I picked out for you in @joigus' post.

What mathematics are you referring to?  @joigus said:

9 hours ago, joigus said:

Measurement in the formalism of QM selects a basis, not a state from that basis.

which is in complete agreement with what I said.

 

[joigus]

20 hours ago, Luc Turpin said:

You often say in your posts that you are not totally satisfied!!! Can you subtantiate?

Nobody is totally satisfied. There's a little Mick Jagger in me crying out for total satisfaction.

It's the same kind of dissatisfaction that I've seen in the likes of Weinberg, Gell-Mann or G. t'Hooft for example. Although back in those times (before Gell-Mann wrote The Quark and the Jaguar, for example) it wasn't very fashionable to ask that kind of question. My way of putting it is actually from times long, long before I had any inkling that all of these great physicists felt a similar discomfort, and it can be phrased as,

"What is the physical variable that tells me I am in this branching of the universe and not in the other?"

You see, I can accept that there are amplitudes flying about corresponding to the dead cat of which I'm seeing the living version. But there should be a variable of some kind telling you: It's this one.

Entanglement is not enough, because entanglement irreversibly separates the alternatives, but does not confirm either one of them.

15 hours ago, KJW said:

I know what a koala is. They used to be in my backyard until they disappeared as a result of urban development.

Ok. Now I suppose you're either from Australia or a neighbourhood close to a zoo with very poor security.  I meant "observer effect" is a misnomer. Probably a mild one. It's the apparatus that does it. Not consciousness.

13 hours ago, KJW said:

What mathematics are you referring to?  @joigus said:

I'm sure @studiot meant this:

23 hours ago, joigus said:

The interaction Hamiltonian depending on the coordinates of the apparatus had better commute with the observable it's measuring. Otherwise it's just smearing things out. If it does, it can't change the statistical weights. If it doesn't... I've reviewed this over and over and over...

And over. And what's inescapable is that it doesn't change the weights (the diagonal elements of the density matrix). But it does change (and how!) the non-diagonal elements of it. And guess how we call the non-diagonal elements of the density matrix. Yes, you guessed it. "Coherences". And that's no misnomer: It contains all the possible interference terms. If the interaction is "classical enough" (the mechanical action of order many times ℏ ), then the interference terms die out in ridiculously short times.

 

15 hours ago, KJW said:

That's not necessarily true. I do my own analyses beyond what I read.

Duly noted.

[Luc Turpin]

21 minutes ago, joigus said:

 

"What is the physical variable that tells me I am in this branching of the universe and not in the other?"

Than you

Thank you

[KJW]

2 hours ago, joigus said:

18 hours ago, KJW said:

I know what a koala is. They used to be in my backyard until they disappeared as a result of urban development.

Ok. Now I suppose you're either from Australia or a neighbourhood close to a zoo with very poor security.  I meant "observer effect" is a misnomer. Probably a mild one. It's the apparatus that does it. Not consciousness.

Oh, I know what you were saying. I just thought it amusing that you used the example of a koala to someone who not only lives in the country of koalas, but actually had koalas living in their backyard, and therefore has experience of koalas that even other Australians might not have. It is sad that the koalas are on longer around, but I am glad that I was able to experience them for a period of time.

 

[joigus]

26 minutes ago, KJW said:

Oh, I know what you were saying. I just thought it amusing that you used the example of a koala to someone who not only lives in the country of koalas, but actually had koalas living in their backyard, and therefore has experience of koalas that even other Australians might not have. It is sad that the koalas are on longer around, but I am glad that I was able to experience them for a period of time.

 

Ok. Now it's perhaps the time to remind you that my observation wasn't at all about koalas. It was about how something can be named some way (eg, the observer effect) and actually the concept once clarified, not having anything whatsoever to do with the initial conceptual handle that nevertheless survived in the name.

Examples:

Koala bear (not even remotely a bear)

Observer effect (someone actually observing anything not even remotely necessary)

Long live both, koala marsupials and environment-induced decoherence!

 

Edited December 5, 2023 by joigus
minor correction

[studiot]

@Luc Turpin

 

I think this is the time to bring in the correspondence principle and see how it bears (not koalas 😀) on Young's slits.

Have you heard of the correspondence principle ?

[Luc Turpin]

18 minutes ago, studiot said:

 

Have you heard of the correspondence principle ?

No, I have not! But would like to hear about it!

56 minutes ago, studiot said:

@Luc Turpin

 

I think this is the time to bring in the correspondence principle and see how it bears (not koalas 😀) on Young's slits.

 

And all this time, I thought it was a marsupial 😏

[Luc Turpin]

Anyone care to comment? or this is old school as well!

Coming to Grips with the Implications of Quantum Mechanics - Scientific American Blog Network

[studiot]

8 hours ago, Luc Turpin said:

No, I have not! But would like to hear about it!

And all this time, I thought it was a marsupial 😏

 

Put simply The Correspondence Principle basically says that whenever a physical theory is displaced by new theory, the new theory must 'correspond' to the old theory. That is it must match the old theory in those realms of physics that have been tested (by experiment).

Variations/ corollaries of this are RTFM (read the frigging manual) and the so called Domain of Application that every lecturer says at the outset of a series of elctures and everyone promptly forgets about.

So what does this mean for the double slit ?

Well what has been tested ie what actually happens?

That is what do we actually observe and what does it depend on ?

What was the old theory and where does meet and where does it fail the observations ?

And what is the new theory  - obviously in this case the quantum theory - and how does it meet both the conditions the old theory satisfies and those it fails ?

 

Well I contend that too many modern explanations actually degrade the old theory in order to make it look bad.
And of course you have to ask which old theory ?

A wave theory ?

Well there were several levels of wave theory and elementary texts match the simple wave theory of Huygens and Fresnel against quantum statistics.

In fact there are several levels of wave theory, each more exact but more difficult

The first theories due to Grimaldi and Marcus we not of wave interference but wave diffraction.
Grimaldi actually coined the word diffraction.

Undergraduate level Physics today makes a distinction between diffraction and interference.

More advanced work does not. Instead the fully rigorous vector wave theory is based on Maxwell's equations and the boundary conditions associated with the obstacle (in this case the double slit). The boundary conditions are used to calculate a field scattered by the obstacle. The origins of this scattered field lie in currents induced in the obstacle by the incident field. The scattered field is vectorially combined with (allowed to interfere with) the incident field to produce the resultant diffracted field.

This is a very difficult approach, the simplest solutions being the Kirchoff -Sommerfield Integrals.

The normal undergraduate approximation theory is a scalar theory where the Huygens-Fresnel wavelets interfere to produce a new wavefront.

Even this is difficult and produces the Huygens-Fresnel Integral.

An alternative modern treatment involves solving the Helmholtz Equation to find the Gaussian Wave . This can be carried into laser territory.

The problem is that all these methods introduce their own difficulties, for example the backward wave in the Huygens method, which is simply ignored as it is not observed.

 

Bit it was necessary to move on from Grimaldis original (though a nobelworthy effort in 1665) to the nearly accurate version introuced by Young in 1801

 

The intensities and widths of Grimaldis laight and dark zones dod not correspond to observation, in particular the central one was too big.

 

 

[Luc Turpin]

Thanks! I will read this with a pair of fresh eyes tomorrow!

[AIkonoklazt]

On 12/4/2023 at 4:04 AM, Genady said:

When we measure, we could only measure one value. The question of "collapse" is how it causes the multiple simultaneous states to become a definite state corresponding to the measured value.

If we could actually measure all the values (of course, not possible) then there is no collapse. Thus my previous answer of "it's because of the limitation of the measurement," or the limitation of the measuring device, or ultimately just the limitation of the interaction between the measuring device and the "wave" being measured.

[swansont]

13 minutes ago, AIkonoklazt said:

If we could actually measure all the values (of course, not possible) then there is no collapse. Thus my previous answer of "it's because of the limitation of the measurement," or the limitation of the measuring device, or ultimately just the limitation of the interaction between the measuring device and the "wave" being measured.

If you send a photon through a double slit, you get one dot on your detector screen. How is that a limitation of the screen?

[AIkonoklazt]

Just now, swansont said:

If you send a photon through a double slit, you get one dot on your detector screen. How is that a limitation of the screen?

You can only get a dot if you use a detector screen. That's all you could get.

"What other thing could we even use to detect?"  Nothing, I suppose. This "collapse," is a limitation.

[swansont]

9 minutes ago, AIkonoklazt said:

You can only get a dot if you use a detector screen. That's all you could get.

"What other thing could we even use to detect?"  Nothing, I suppose. This "collapse," is a limitation.

The screen will fluoresce wherever a photon strikes it. You get one dot because there’s one photon.

How do you propose to get more than one dot? Is the limitation the detector, or the collapse?

[AIkonoklazt]

11 minutes ago, swansont said:

The screen will fluoresce wherever a photon strikes it. You get one dot because there’s one photon.

How do you propose to get more than one dot? Is the limitation the detector, or the collapse?

If, as I've mentioned earlier, we can do the absolute impossible and measure all values of this wave instead of one, then it's not going to be a dot.

How? You can't. It's impossible.

(Can we end up wit a cat that's both dead and alive? Not really. That's the limitation of a cat and the rig that's supposed to kill it.)

[swansont]

17 minutes ago, AIkonoklazt said:

If, as I've mentioned earlier, we can do the absolute impossible and measure all values of this wave instead of one, then it's not going to be a dot.

How? You can't. It's impossible.

So what’s the point of this little exercise?

 

[AIkonoklazt]

Just now, swansont said:

So what’s the point of this little exercise?

 

We measure things we can measure.

Just because there are things outside of measurement doesn't make the measurement pointless.

[swansont]

57 minutes ago, AIkonoklazt said:

We measure things we can measure.

Just because there are things outside of measurement doesn't make the measurement pointless.

I don’t think anyone said the measurement is pointless. It’s science. We’re limited to what we can measure. If it can’t be measured or detected, it’s not in the realm of science.

[AIkonoklazt]

3 hours ago, swansont said:

I don’t think anyone said the measurement is pointless. It’s science. We’re limited to what we can measure. If it can’t be measured or detected, it’s not in the realm of science.

Yes, you asked me "what's the point" and that was all I could say to it.

Plenty of scientists came up with non-verifiable theories because they're about non-verifiable things that's beyond human reach. (One thing being black holes being "dark matter stars" and another being white holes are results of dimensional collisions- Forgot who coughed up that one, maybe Tegmark)

[joigus]

8 hours ago, AIkonoklazt said:

If, as I've mentioned earlier, we can do the absolute impossible and measure all values of this wave instead of one, then it's not going to be a dot.

We can't "measure the wave." We can use the postulated wave to predict the measurements. The measurements are those dots on a screen.

In fact, there is a theoretical principle, called "gauge invariance" --of which we're pretty certain-- that says there's a big chunck of this wave we cannot know in any way. Some people say it's junk, or a redundancy, etc.

And black holes are not "dark-matter stars", but that's another story.

[studiot]

10 hours ago, Luc Turpin said:

Thanks! I will read this with a pair of fresh eyes tomorrow!

 

There has been lots of, probably confusing, argument about quantum interpretation, calculation and 'measurement' .

A fundamental question that need to be addressed before any of this can be done concerns the wave function.

Consider a photon or electron just poddling along.

It has a wave function Ψ_a ,

Now let the particle interact with the rest of the universe.

What is the wave function now ? Let's call it Ψ_b

Is Ψ_b the same as Ψ_a or is it a new wave function ?

If the wave function for the part of the universe that it interacts with is Ψ_c , can Ψ_b be constructed from some combination of Ψ_a and Ψ_c ?

In other words when there is an interaction does a new wave function appear which now includes the 'observer' in the quantum system ?

 

10 hours ago, swansont said:

The screen will fluoresce wherever a photon strikes it. You get one dot because there’s one photon.

How do you propose to get more than one dot? Is the limitation the detector, or the collapse?

Please note this extremely important comment from swansont. You only get one dot.

Moreover this one dot 'contains' all the quantum of energy of the one photon or electron.

This is not wave behaviour.

(The italics were mine, the bold was swansont.)

We will see why this is important when we fully examine the mechanism of the double slit from both classical and quantum points of view.

 

But I keep saying, and I hope you can now begin to see, that the double slit experiment is difficult and complicated for an good intructory explanation of QM.

Here is an excellent short extract from a Cambridge University text, Optical Physics by Lipson and Lipson whcih introduces QM via the PhotoElectric Effect, which is much simpler and more understandable.

 

[Genady]

2 hours ago, joigus said:

We can't "measure the wave."

Exactly. Just like we can't measure the number \(\pi\).

[studiot]

11 minutes ago, Genady said:

Exactly. Just like we can't measure the number π .

But, just like the number pi we can do calculations involving the wave function.

😀