Matter waves (split from Photon is massless why?)

[martillo]

37 minutes ago, studiot said:

Then how do you explain this ?

I don't understand what you are asking me to explain. Please just say it in a more specific way...

[swansont]

1 hour ago, KJW said:

A lot of science is based on indirect measurements based on some theory. For example, in chemistry, do we really have direct knowledge of chemical structure? Perhaps the most direct measurement of a molecule's structure is through x-ray crystallography, but even that involves the theory of x-ray diffraction along with dealing with Fourier transforms

Diffraction is an independently confirmable model.

Most of modern physics is not based on direct measurement. That’s hard to do when things are not visible to the naked eye, even aided. We measure what we can. 

[studiot]

20 minutes ago, martillo said:

I don't understand what you are asking me to explain. Please just say it in a more specific way...

Unlike your formula that I quoted, I don't see momentum mentioned at all.

But most importantly is the statement

"The light quanta would have velocities of slightly different values"

What you are referring to is a modern summary after 30 years of development of the De Broglie - Bohm  theory.

There have been other offshoots , the Yukawa potential and the meson field theory.

 

The factor of 2 that you note is explained in the section following the introductory piece I posted where he discussed radiation pressure an note the relativistic calculation agrees with the electromagnetic value, although momentum is still not explicitly mentioned.

 

 

 

[martillo]

6 minutes ago, studiot said:

But most importantly is the statement

"The light quanta would have velocities of slightly different values"

What you are referring to is a modern summary after 30 years of development of the De Broglie - Bohm  theory.

Yes, that statement called my attention. Do you mean that De Broglie was considering a "light quanta" with a velocity "slightly different" from c? 

That is really astonishing for me. Let me say going through a very wrong way I think...

[KJW]

10 hours ago, studiot said:

Here is a directly measured electron density map of hexamethylbenzene (after Spice 1964)

I think it shows the structure rather well.

 

How is the above a direct measurement of electron density? I've already indicated above that x-ray crystallography is not a direct measurement of molecular structure. Producing a detailed image of the electron density of a molecule is not the same as being a direct measurement.

 

 

10 hours ago, swansont said:

Diffraction is an independently confirmable model.

Most of modern physics is not based on direct measurement. That’s hard to do when things are not visible to the naked eye, even aided. We measure what we can. 

That's exactly my point. If a direct measurement is unavailable, then an indirect measurement based on sound principles is acceptable. Thus, although the phase of a De Broglie wave cannot be measured, the phase velocity of a De Broglie wave can be indirectly measured by measuring the wavelength and frequency of the wave.

 

 

Edited November 18, 2023 by KJW

[joigus]

10 hours ago, martillo said:

Yes, that statement called my attention. Do you mean that De Broglie was considering a "light quanta" with a velocity "slightly different" from c? 

That is really astonishing for me. Let me say going through a very wrong way I think...

I don't think that's what the text means. I think it's a reference to the group velocity. Whenever group velocity is different from phase velocity, we call the medium "disperssive", and that's because every monochromatic component travels at a slightly different speed. v=v(f)

[martillo]

1 hour ago, joigus said:

I don't think that's what the text means. I think it's a reference to the group velocity. Whenever group velocity is different from phase velocity, we call the medium "disperssive", and that's because every monochromatic component travels at a slightly different speed. v=v(f)

No, the text refers to a "light quanta". The text also talks about an associated mass: "...they must have an extremely small mass...".

Here the parts of the text @studiot posted for you to check:

13 hours ago, studiot said:

The text talks about a model for a "light quanta" reconciling the Electromagnetic Wave Theory and Relativity Theory. I think as some mass was associated to the quanta, a velocity "slightly different from c" is needed because in the case of a c velocity the mass would be infinite according to Relativity. I think the small mass comes into place to give a physical reason for the "light quanta" to have momentum and explain the "radiation pressure" @studiot mentions. May be also because the equations E = hf, λ = h/mv and λf = c would give E = mc² for a quanta (photon) with some mass. Interesting but wrong tentative for a photon with mass I think. For a photon with mass unavoidably Relativity Theory must be neglected...

Edited November 18, 2023 by martillo

[martillo]

12 hours ago, studiot said:

But most importantly is the statement

"The light quanta would have velocities of slightly different values"

What you are referring to is a modern summary after 30 years of development of the De Broglie - Bohm  theory.

There have been other offshoots , the Yukawa potential and the meson field theory.

So you have been interested about some "offshoots"...

May be someday you could be interested in taking a look at my rather radical alternative try...

May be not. Too radical, forget it.

 

Edited November 18, 2023 by martillo

[studiot]

39 minutes ago, martillo said:

So you have been interested about some "offshoots"...

May be someday you could be interested in taking a look at my rather radical alternative try...

 

It is important to have a clear idea of where you want to go.

 

This discussion started off as a discussion about the validity of Relativity.

 

DeBroglie- Bohm theory is about Quantum theory, not Relativity.

 

Your hypothesis should be posted in the usual way in speculations, not in this thread.

 

Then it can be properly examined and discussed.

Since it has beecome important here is the full page 1 of the 1924 paper

A pdf of the full paper can be found at

https://www.pwein.at/physics/Lectures/Famous-Papers/Phil-Mag-47-446-1924.pdf

 

Please note just how humbly he writes.

the key points are

1) He is using Einstein's notion of 'quanta' and Einstein's terminology (he also later refers to Einstein's use of 'fields')

2) He sets out to explore the possibilities of reconciling the quantum notion with the wave theory.

He ends up finding that a great many experimental observations can be explained by his approach, but owns that not all of them can.

Pilot waves and Matter waves come in the 1927 paper and the Nobel prize for this work in 1929

Quote

Wikipedia

He won the Nobel Prize in Physics in 1929 "for his discovery of the wave nature of electrons". In his later career, de Broglie worked to develop a causal explanation of wave mechanics, in opposition to the wholly probabilistic models which dominate quantum mechanical theory; it was refined by David Bohm in the 1950s.

 

[martillo]

9 minutes ago, studiot said:

It is important to have a clear idea of where you want to go.

 

This discussion started off as a discussion about the validity of Relativity.

 

DeBroglie- Bohm theory is about Quantum theory, not Relativity.

 

Your hypothesis should be posted in the usual way in speculations, not in this thread.

 

Then it can be properly examined and discussed.

No, forget it, I'm not ready to discuss my hypothesis in the forum at the moment. I tried in the past to discuss for instance the equation of force F = dp/dt in the forum and gave me too much troubles, discussing with several ones at the same time, several days without sleeping appropriately... Do you remember? We discussed a lot in that thread: 

I'm not ready to have another discussion like that for now. May be in the future something could surge.

 

36 minutes ago, studiot said:

Since it has beecome important here is the full page 1 of the 1924 paper

A pdf of the full paper can be found at

https://www.pwein.at/physics/Lectures/Famous-Papers/Phil-Mag-47-446-1924.pdf

I will take a look. 

 

 

[swansont]

5 hours ago, KJW said:

That's exactly my point. If a direct measurement is unavailable, then an indirect measurement based on sound principles is acceptable. Thus, although the phase of a De Broglie wave cannot be measured, the phase velocity of a De Broglie wave can be indirectly measured by measuring the wavelength and frequency of the wave.

If the quantity has no physical significance, how is it a measurement? 

[KJW]

5 minutes ago, swansont said:

If the quantity has no physical significance, how is it a measurement? 

The same could be said about any quantum wavefunction because we are in fact talking about the quantum wavefunction of a free non-zero mass particle.

 

Edited November 18, 2023 by KJW

[studiot]

5 hours ago, KJW said:

How is the above a direct measurement of electron density? I've already indicated above that x-ray crystallography is not a direct measurement of molecular structure. Producing a detailed image of the electron density of a molecule is not the same as being a direct measurement.

I'm sorry I don't see my answer to your question any more.

It was definitely there this morning.

 

I will try to recreate it for you, since you are obviously unaware of 50 years of experimental Chemistry. though it will not be as comprehensive since i put o lot of apparantly wasted effort into it.

[swansont]

1 hour ago, KJW said:

The same could be said about any quantum wavefunction because we are in fact talking about the quantum wavefunction of a free non-zero mass particle.

 

Indeed. The wave function isn’t physical, and we do not measure it.

[KJW]

1 hour ago, studiot said:

you are obviously unaware of 50 years of experimental Chemistry

I'm familiar with chemistry. That's why I chose an example from chemistry. It seems to me that you don't understand the point I'm making.

[studiot]

14 minutes ago, KJW said:

I'm familiar with chemistry. That's why I chose an example from chemistry. It seems to me that you don't understand the point I'm making.

What I pity your mind is made up before you have seen the evidence.

So I will not bother with all that explanatory work I did again but just refer you directly to this department of industry paper

 

Quote

https://pubs.acs.org/doi/10.1021/ed079p1141

This paper gives a simple pictorial introduction to the interpretation of electron densities to obtain information about bonding. The electron density of a molecule can be readily calculated using ab initio or density functional theory methods and it can also be obtained experimentally by X-ray crystallography. Unlike an orbital model of a molecule, the electron density is a physical observable.

 

[KJW]

13 minutes ago, studiot said:

What I pity your mind is made up before you have seen the evidence.

So I will not bother with all that explanatory work I did again but just refer you directly to this department of industry paper

As I said, I'm familiar with chemistry.

 

Edited November 18, 2023 by KJW

[studiot]

40 minutes ago, KJW said:

As I said, I'm familiar with chemistry.

 

So familiar that you didn't ask where the picture I posted came from.

In fact it was a scan of a photgraphic plate record of an actual measurement made in the early 1960s.

Today we would probably uise different techniques for making the record.

I further suppose that you would say that all the mineralogist and metallurgists in the world, beavering away examining their specimens on their polarising microscopes are not doing direct measurements.

I had prepared a discussion of the equivalent X ray technique for molecules, called the rotating crystal method.
Including scans of photgraphic plate records of such experiments.

[KJW]

3 minutes ago, studiot said:

So familiar that you didn't ask where the picture I posted came from.

Correct.

Although I haven't seen an electron density map of hexamethylbenzene before, I have seen electron density maps of other compounds, so I did know what I was looking at with your picture.

 

3 minutes ago, studiot said:

In fact it was a scan of a photographic plate record of an actual measurement made in the early 1960s.

Hmmm, perhaps I spoke too soon. The direct image from x-ray crystallography is an arrangement of spots of various intensities. A Fourier transformation of these intensities yields a Patterson function (a convolution of the electron density with its inverse) due to the "phase problem". So how does one obtain a photographic plate image of the electron density? Specifically, what is performing the Fourier transformation? In particular, how is the "phase problem" being solved?

 

3 minutes ago, studiot said:

I further suppose that you would say that all the mineralogist and metallurgists in the world, beavering away examining their specimens on their polarising microscopes are not doing direct measurements.

I didn't use those as examples as I'm not very knowledgeable of those fields.

 

[martillo]

20 hours ago, studiot said:

Wouldn't the image be a graphic of scanning electron tunneling microscopy on the molecules? Not a x-ray crystallography...

Edited November 18, 2023 by martillo

[KJW]

9 minutes ago, martillo said:

Wouldn't the image be a graphic of scanning electron tunneling microscopy on the molecules? Not a x-ray crystallography...

It's definitely from x-ray crystallography. Note that only the carbon atoms are showing because hydrogen atoms are rather insensitive to x-rays. Neutron diffraction would be better if one needs to explore bonding to hydrogen atoms.

[studiot]

15 minutes ago, martillo said:

Wouldn't the image be a graphic of scanning electron tunneling microscopy on the molecules?

 

The STM can indeed be used to measure electron densitiy, but I left university 10 years befor they were invented so my pics are from an earlier technique in the days before we had massive computer backup.

Fourier analysis took months the old fashioned way so more direct methods were used such as the Weissenberg technique.

 

42 minutes ago, KJW said:

Hmmm, perhaps I spoke too soon. The direct image from x-ray crystallography is an arrangement of spots of various intensities. A Fourier transformation of these intensities yields a Patterson function (a convolution of the electron density with its inverse) due to the "phase problem". So how does one obtain a photographic plate image of the electron density? Specifically, what is performing the Fourier transformation? In particular, how is the "phase problem" being solved?

See above. You are correct that the phase problem is insoluble without either massive computer support or some jiggery pokery.

A Photographic plate can also perform a material fourier transform in the exposure and developing processes.

Note also that many of the so called diffraction methods are (were?) actually reflection methods including the X ray rotation method.

The point about the mineralogist that is replicated when you rotate the Xrays or the crystal is that as you do so only certain planes are active at any given angle of rotation so measurement of this activity against angle give useful structural information.

Another piece of jiggery pokery is to artificially introduce heavy nuclei into the structure at known positions to act as markers.

Finally neutron scattering can also provide useful structural information although the techniques are many times more difficult.

Googling Oxford Universities pages on the techniques will yield many better (and colour) images than mine.

 

Just as a matter of interest I think this whol argument about direct measurement is a red herring.

Any measurement can be called non direct, it just depends upon how far you take it.

For example

If I connect my modern digital multimeter into a circuit and 'directly' measure the current, I am not really measuring the current at all. I am measuring voltage.

If I connect my old fashioned analog meter into that circuit and measure voltage, I am not really measuring voltage at all. I am measuring current.

But then I could take this argument one stage further.

I am not measuring current or voltage at all, I am measuring an illuminated pattern of lines/dots on a screen on one hand and a needle deflection on the other

and I could go on and on down this rabbit hole.

But nobody does in reality.

 

 

[martillo]

33 minutes ago, studiot said:

Just as a matter of interest I think this whol argument about direct measurement is a red herring.

Any measurement can be called non direct, it just depends upon how far you take it.

So returning to the initial discussion about the phase velocity of the "matter wave" of massive particles...

I arrived to the two approaches that could give the phase velocity v_p in terms of the linear velocity v of the particles:

Relativistic approach: v_p = c²/v

Non-relativistic approach: v_p = v/2

(v_g = v)

Independently of which one would be better in whatever case, if v is measurable then v_p is measurable.

The phase itself is not observable and not measurable but its velocity is measurable.

The phase velocity is related to the energy and the momentum of the wave/particle: p = E/v_p.

Edited November 18, 2023 by martillo

[KJW]

32 minutes ago, studiot said:

A Photographic plate can also perform a material fourier transform in the exposure and developing processes.

Is this some form of holography?

 

32 minutes ago, studiot said:

Just as a matter of interest I think this whole argument about direct measurement is a red herring.

Any measurement can be called non direct, it just depends upon how far you take it.

For example

If I connect my modern digital multimeter into a circuit and 'directly' measure the current, I am not really measuring the current at all. I am measuring voltage.

If I connect my old fashioned analog meter into that circuit and measure voltage, I am not really measuring voltage at all. I am measuring current.

But then I could take this argument one stage further.

I am not measuring current or voltage at all, I am measuring an illuminated pattern of lines/dots on a screen on one hand and a needle deflection on the other

and I could go on and on down this rabbit hole.

But nobody does in reality.

I tend to agree with this. But ultimately, I was simply justifying the statement that phase velocity can be obtained from the measurements of wavelength and frequency.

 

[martillo]

1 hour ago, KJW said:

I tend to agree with this. But ultimately, I was simply justifying the statement that phase velocity can be obtained from the measurements of wavelength and frequency.

Which formula do you apply to obtain v_p with λ and f?

By the way, seems f is not measurable...

Edited November 18, 2023 by martillo