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Observer effect and Uncertainty principle are the same?


Itoero
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36 minutes ago, Itoero said:

The Observer effect and Uncertainty principle are the same?

No. The observer effect is about how our measurements affect what we are trying to measure. It can apply to almost anything (for example, putting a voltmeter across a circuit changes the behaviour of the circuit). It can also apply to a single measurement, while the uncertainty principle relates two measurements.

The uncertainty principle is about the limits to how accurately we can know something, even with perfect measurements:

"The uncertainty principle has been frequently confused with the observer effect, evidently even by its originator, Werner Heisenberg.[18] The uncertainty principle in its standard form describes how precisely we may measure the position and momentum of a particle at the same time — if we increase the precision in measuring one quantity, we are forced to lose precision in measuring the other.[19] "

https://en.wikipedia.org/wiki/Observer_effect_(physics)

38 minutes ago, Itoero said:

When you try to observe/measure a wave(momentum) it becomes a particle(position).

I'm not sure that is a useful example. After all, particles have momentum (and waves have position). But it does, perhaps, relate to the fact that the uncertainty principle is based on Fourier transforms between the two things being measured.

And not sure why this is in Philosophy as it is purely a matter of physics. 

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20 hours ago, Strange said:
21 hours ago, Itoero said:

-When you try to observe/measure a wave(momentum) it becomes a particle(position).

I'm not sure that is a useful example. After all, particles have momentum (and waves have position). But it does, perhaps, relate to the fact that the uncertainty principle is based on Fourier transforms between the two things being measured.

Agree with you, Strange. I even think that Itoero's expression does not make sense, because it suggests that there is a 'real' wave that at the moment of measurement becomes a 'real' particle. 

And your remark about Fourier transforms: here is a wikipedia article about it.

Quote

In quantum mechanics, the momentum and position wave functions are Fourier transform pairs, to within a factor of Planck's constant. With this constant properly taken into account, the inequality above becomes the statement of the Heisenberg uncertainty principle.

 

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55 minutes ago, Eise said:

Agree with you, Strange. I even think that Itoero's expression does not make sense, because it suggests that there is a 'real' wave that at the moment of measurement becomes a 'real' particle. 

Whether you call it a real wave or particle is your semantic choice. If you want to observe/measure a wave, you stop the wave behavior.

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23 hours ago, Itoero said:

 -When you try to observe/measure a wave(momentum) it becomes a particle(position).

Momentum implies you are discussing deBroglie waves, but QM has Schrödinger waves as well, and it is the waves described by Schrödinger that are the basis of the uncertainty principle (wave functions of conjugate variables are Fourier transforms of each other, as Strange noted earlier). You are mixing two different concepts together, and that's likely to be causing some confusion.

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On ‎28‎/‎10‎/‎2018 at 4:17 PM, Strange said:

The observer effect is about how our measurements affect what we are trying to measure

Like when you use detectors in a double slit experiment. Those detectors detect photons and in doing so, they stop the wave. (observing changes the phenomenon)

Physics is what we say of the universe trough experiments. In those experiments you need to observe stuff (via measuring devices). When you observe something, you change the phenomenon.

It seems that observer effect 'caused' the uncertainty, wave-particle duality...the seemingly randomness...

Also, the observer effect is not necessary  linked to physics. The Hawthorne effect (also an observer effect) is a reaction in which individuals modify an aspect of their behavior in response to their awareness of being observed. In clinical trials to test drugs/supplements/therapies the observer effect can cause placebo-effects. Placebo-controlled studies are a way of testing a medical therapy in which, in addition to a group of subjects that receives the treatment to be evaluated, a separate control group receives a sham "placebo" treatment which is specifically designed to have no real effect.

Wildlife is often very sensitive for the presence of humans. This also an observer effect.

Or for example, you can't know the inside of a tree without 'cutting it down'.

The observer effect occurs in all areas of science.

 

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1 hour ago, Itoero said:

Like when you use detectors in a double slit experiment. Those detectors detect photons and in doing so, they stop the wave. (observing changes the phenomenon)

Good example. And an extreme one where detecting the wave/particle destroys it.

1 hour ago, Itoero said:

Physics is what we say of the universe trough experiments. In those experiments you need to observe stuff (via measuring devices). When you observe something, you change the phenomenon.

But you can (usually) minimise the effect. For example, making sure the impedance of your voltmeter is high enough that it has no significant effect on the circuit. Or...

1 hour ago, Itoero said:

Or for example, you can't know the inside of a tree without 'cutting it down'.

Taking a very small core sample to count tree rings without actually cutting the tree down. This may still have some effect on the tree (and there is the risk of disease) but it is less than chopping it down.

1 hour ago, Itoero said:

It seems that observer effect 'caused' the uncertainty, wave-particle duality...the seemingly randomness...

Not really. And this is where the observer effect differs from the uncertainty principle: both the "randomness" (probabilistic nature) and the uncertainty principle are, as far as we can tell, fundamental aspects of the way the universe behaves.

1 hour ago, Itoero said:

Also, the observer effect is not necessary  linked to physics.

Absolutely. Opinion polls are banned before elections in some countries because they could change the way people vote.

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On 10/29/2018 at 11:12 PM, Eise said:

And your remark about Fourier transforms: here is a wikipedia article about it.

 

I am not even going to try conceptualise this with my knowledge level, just say that hey, I'm on my way, its going to be slow, but I am coming. In the mean time Eise FWIW you just elevated to sitting behind Sean Carrol as inspiration behind my trying to learn the math behind Quantum. And that makes Feynman #3. Just wow.

In quantum mechanics, the momentum and position wave functions are Fourier transform pairs, to within a factor of Planck's constant. With this constant properly taken into account, the inequality above becomes the statement of the Heisenberg uncertainty principle.

That is a beautiful statement in so many ways, most of which I don't understand, but I'm getting a hint at the beauty.

Thank you. It's a statement I am going to hang on to until I understand more than just the aesthetics.

Edited by druS
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4 minutes ago, druS said:

I am not even going to try conceptualise this with my knowledge level, just say that hey, I'm on my way, its going to be slow, but I am coming.

Let me have a go ...

The most well-known (among engineers, anyway) use of Fourier transforms is to transform between the frequency domain and the time domain. What this means is that if we have a signal that varies in time, such as a sine wave, then we can transform it to the list of frequencies that make up the signal. In the case of a single sine wave, this will be a single frequency (the frequency of oscillation of the wave). 

But ... even though we think of a pure sine wave as corresponding to a single frequency (or note, like C#) that is only true if the sine wave is infinitely long (started an infinite time ago and ends an infinite time in the future).

A real sine wave starts when we turn the oscillator on (or play the instrument) and ends some time later. When we analyse what this means in terms of frequency, it turns out that we have to add extra frequencies to represent the fact that there is not signal in the past and none in the future. You can think of this as adding extra sine waves of different frequencies to cancel the signal out at those times.

So, when we do a Fourier transform of a real-world signal we find that it contains many other frequencies. It turns out that for a sine wave of long duration all these other frequencies are closely bundled around the signal frequency and fall off quickly outside that range. For a sine wave that only lasts a short time, there is a wider range of frequencies around the signal frequency.

So, we can either have a signal which is tightly defined in the frequency domain but is extended in the time domain, or we can have a signal that is tightly defined in the time domain but then spreads out in the frequency domain.

We find the same thing when we look at pairs like momentum and position: if you pin one down, the other must be spread out.

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On 30/10/2018 at 7:30 PM, Itoero said:

The observer effect occurs in all areas of science.

Yes +1

and Strange has already dealt with your other examples.

However we should note that the Hesienberg Uncertainty Principle not only limits how accurately we can measure certain pairs of quantities, it also limits how accurately we can calculate them. This applies to pairs. Equations exist that allow accurate calculation of individual quantities, if the other one of the pair is not concerned.

 

The best practical example of HUP I is in spectroscopy and occurs as spectral line broadening. The actual amount of the broadening depends upon the apparatus, but the mechanism can be interpreted in terms of a real world physical process.

The radiation absorbed or emitted is only monchromatic (a perfectly thin line) to the extent that the molecular/atomic energy levels are themselves perfectly defined.
If the energy gap has encertainty  [math]{\Delta E}[/math] then the frequency has an uncertainly


[math]\Delta f \approx \frac{{\Delta E}}{h}[/math]

 

This is seen as a broadening of the perfect spectral line with half line width [math]\Delta f[/math]  leading to an associated uncertainty of time

[math]\frac{1}{{2\pi \Delta f}}[/math]

 

We may interpret this as the time taken for the absorbtion/emission to occur.

 

Note carefully that the HUP provides a theoretical (lower) limit to these values. The measured values will exhibit a range as already stated.

 

 

 

 

 

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On 11/6/2018 at 10:25 PM, Strange said:

Let me have a go ...

 

Awesome work as usual. While I realised that Fourier transforms "peel apart" (non mathematical and egregiously rough perhaps) the source waves in a signal I wouold not have considred the importance of carefully addressing the frequency and time domains. For a sine wave that only lasts a short time, there is a wider range of frequencies around the signal frequency. This makes perfect sense - I just never would have related it to this:.

On 11/6/2018 at 10:25 PM, Strange said:

 

We find the same thing when we look at pairs like momentum and position: if you pin one down, the other must be spread out.

 

At the end of the day starting with Fourier tranforms, using Plank's Constant (I presume as a statement of accuracy?) , deriving (please do correct my clumsiness) an inequality which becomes a statement about the Heisenberg uncertainty principal - this is an incredible act of tautology. I may only catch glimpses of it, but it does help remove some of the fear of the bizarreness of QM.

 

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  • 3 months later...

Apologies for re-awakening this thread, especially as it is likely to be a short input.

My studies have progressed. I understand the relevance of Plack's constant now, though I am a long way from pulling Fourier transform into my mathematical understanding. And I have tested in my education when I will offered the transforms -  it will take time.

On 11/6/2018 at 10:11 PM, druS said:

In quantum mechanics, the momentum and position wave functions are Fourier transform pairs, to within a factor of Planck's constant. With this constant properly taken into account, the inequality above becomes the statement of the Heisenberg uncertainty principle.

That is a beautiful statement in so many ways, most of which I don't understand, but I'm getting a hint at the beauty.

I stand by that last statement. There is a lot of talk of "aha" moments when you choose to study STEM subjects. I'm not talking "aha", I am talking literal beauty. Like Mozart or Rembrandt. God I envy those who do understand it. It will take me years, all I can say is that I am on the journey.

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5 minutes ago, druS said:

I stand by that last statement. There is a lot of talk of "aha" moments when you choose to study STEM subjects. I'm not talking "aha", I am talking literal beauty. Like Mozart or Rembrandt. God I envy those who do understand it. It will take me years, all I can say is that I am on the journey.

It might help to bear in mind that Heisenberg is a special case or subset of a much larger class of inequalities of the format


[math]AB \ge \Upsilon [/math]


Where [math]\Upsilon [/math] is some constant.

In particular the units/dimensions of the constant, upsilon,  needs to be consistent with the units of A and B.

The use of Planck's constant enables this in Heisenberg.

Other constants appear in the Cauchy-Schwarz inequality and the triangle inequality, which  are more general examples of the same principle.

 

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2 hours ago, Itoero said:

HUP is about the relation between 2 measurements which are subject to the observer effect. Agreed?

No.

This seems to be at the core of your misunderstanding. The HUP has nothing to do with the observer effect. It is a statement about the relationship between those values, whether you measure them or not. 

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30 minutes ago, Strange said:

whether you measure them or not. 

It is more than that it is a strong statement of the circumstances under which you can't measure them, no matter what you do.

 

itoero.

It is my belief that the simplest and easiest route to understanding the HUP lies via spectroscopy.

Let us say you want to measure the frequency (and therefore the energy)  of spontaneous emission of EM radiation from some atom.

But this emission takes a finite time.
This time to emit appears as a slight blurring or spreading of the emission spectrum.

This real (and observable) effect cna be calculated according to the HUP.

But since the observer is observing in passive or receiving mode only, he does not / can not affect the emission which comes before he starts observing.

 

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14 hours ago, Itoero said:

HUP is about the relation between 2 measurements which are subject to the observer effect. Agreed?

No. And you should have known that nobody here that knows his/hers physics agrees with you. It was pointed to you many times, that the HUP has nothing to do with our methods of measurement. And this was done by real physicists, and a few others, who cited several reliable sources. 

Explain to us how you, at least principally, could overcome the limits of frequency spread in wave mechanics due to Fourier transformation. (Do not forget, the uncertainty principle is valid for any wave phenomenon, not just QM).

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23 hours ago, studiot said:

It might help to bear in mind that Heisenberg is a special case or subset of a much larger class of inequalities of the format


ABΥ


Where Υ is some constant.

In particular the units/dimensions of the constant, upsilon,  needs to be consistent with the units of A and B.

The use of Planck's constant enables this in Heisenberg.

Other constants appear in the Cauchy-Schwarz inequality and the triangle inequality, which  are more general examples of the same principle.

 

Studiot, you'll have to be patient with me. Very.

I have a long way to go before I am grappling with this math. I can tell you that I need to work on inequalities.

OTOH These conversations are most definitely having an impact on my choices in study. I have a building list of topics I require to be covered that sits actually quite outside the standard study choices.

Thanks for this.

 

Dru

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19 hours ago, Strange said:

No.

This seems to be at the core of your misunderstanding. The HUP has nothing to do with the observer effect. It is a statement about the relationship between those values, whether you measure them or not. 

Yes but those values only exist when you measure them, you can't invent those values. HUP is only visible when you measure a particle And measurements are subject to the observer effect.

The hup is a constraint. If phenomena did not change when measured/observed then there wouldn't be a constraint. When you measure the momentum of a particle then you alter it's energy, you change the phenomenon….But if there was no observer effect then you could measure  the momentum without altering its energy and without changing the phenomenon. If there was no measurement/observer effect then particles don't know they are measured and you could measure momentum and position as precise as possible. Without measurement/observer effect, measuring doesn't alter the particle so you can repeat the measurements.

Edited by Itoero
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5 minutes ago, Itoero said:

If there was no measurement/observer effect then particles don't know they are measured and you could measure momentum and position as precise as possible.

That is your error. HUP says that momentum and position together are not precise, not just that we cannot measure them precise.

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