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Author Topic: Causality  (Read 11907 times)

Offline Batroost

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« Reply #25 on: 22/11/2007 19:35:00 »
Electrons have no measured size.

You are confusing the DeBroglie wavelength with physical size; see http://en.wikipedia.org/wiki/De_Broglie_hypothesis. The low momentum of thermal electrons is what gives rise to the small DeBroglie wavelength and hence the high resolution of electron-microscopes.

The physical dimensions of the electron have never beem measured; even clasical physics arrives at a size <3 x 10-15m. But they could be genuine 'points'..?!?


 

Offline lightarrow

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« Reply #26 on: 22/11/2007 20:12:52 »
Electrons have no measured size.

You are confusing the DeBroglie wavelength with physical size; see http://en.wikipedia.org/wiki/De_Broglie_hypothesis. The low momentum of thermal electrons is what gives rise to the small DeBroglie wavelength and hence the high resolution of electron-microscopes.

The physical dimensions of the electron have never beem measured; even clasical physics arrives at a size <3 x 10-15m. But they could be genuine 'points'..?!?



Sorry, I didn't understand to who you have answered.
 

Offline Batroost

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« Reply #27 on: 22/11/2007 20:28:47 »
Sorry,

Re-reading the posts I think you've already covered this.

But, don't you find the idea of an electron as a 'point-like' particle quite appealing (regardless of the wave-like behaviour you can also measure)?



 

Offline Soul Surfer

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« Reply #28 on: 23/11/2007 11:28:38 »
McQueen You have seemed to have forgotten that the wave particle duality applies to ALL materials both microscopic and macroscopic. In the quantum world an electron can be a wave as much as a photon is a particle.  They display interference and diffraction fringes in experiments based on their wavelength and like a photon their notional "size" is a function of their wavelength.  Now the wavelength of an electron or any other body with mass is dependant on the amount of energy/momentum that it has over the rest mass that it possesses ie it depends on its velocity.  This has absolutely nothing to do with relatavistic contraction. IE the slower an electron is travelling the bigger it is.

An interesting aside if you look at the electron orbiting a proton in a hydrogen atom in a classical context and take its wavelength based on the momentum that it has and the classical orbit that you would expect it to be you will find that the orbitals that it takes up quantum mechanically coincide with total numbers of wavelengths of the electron in the classical context.  This acts as a bridge between classical and quantum physics.
 

Offline Soul Surfer

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« Reply #29 on: 23/11/2007 11:40:06 »
There were several posts while I was writing my previous reply.  I agree that no minimum size has yet been measured for an electron.  By "size" I mean the area within which the electron is likely to be located by quantum mechanical uncertanty and the lower the energy of the electron the more "fuzzy" it is and the greater is the volume in which you are likely to find it by probing with another particle.  This effect can be measured experimentally.
 

Offline lightarrow

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« Reply #30 on: 23/11/2007 20:13:50 »
Sorry,

Re-reading the posts I think you've already covered this.

But, don't you find the idea of an electron as a 'point-like' particle quite appealing (regardless of the wave-like behaviour you can also measure)?

But, even regardless of the wave-like behaviour, there is a very known, ancient problem about a point-like electron: its energy should be infinite!
It's a charge, and the potential energy of a charge is proportional to q/r. Send r to zero and...
 

Offline McQueen

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« Reply #31 on: 23/11/2007 22:38:02 »
It is all very well to talk about ‘matter’ waves but no-one can say what they are. De Broglie himself described them as ‘waves that correspond to matter.’ But no-one has till today managed to find out what these matter waves are, what is sure is that nothing is ‘waving ‘.
 

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« Reply #32 on: 23/11/2007 22:47:02 »
McQueen, did you ever have any formal education in Physics or have you started all your ideas from scratch?
You should wait until you have had time to establish a bit more depth (i.e. serious mathematical treatment) of your ideas if you want people to take them seriously. Your model will have to be consistent with measured observations, to date.

Electron diffraction experiments are good enough to show that particles behave as waves, are they not? Have you got a better explanation?
 

Offline McQueen

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« Reply #33 on: 24/11/2007 18:28:03 »
Quote
Electron diffraction experiments are good enough to show that particles behave as waves, are they not? Have you got a better explanation?

The same experiments can be shown to prove that particles behave as particles ! First I would like to say something about the double speak that has been going on in this thread.
What would you say to me if I told you that the Union Jack was Red, White and Blue in one conversation and then later on during the same conversation insisted that it was Green, Yellow and Purple! Obviously I would have been told to shut up and put a sock in it, because as you can all see for yourselves, the Union Jack is in fact Red, White and Blue.

Each of you who has posted their opinions on ‘matter’ waves in this thread have been guilty of exactly the same kind of misleading statement. By referring to ‘matter’ waves as something real as in “…..as the matter waves get smaller the object gets larger” etc.,  you are treating as something real, ergo ‘matter’ waves an abstraction that has no basis in reality at all. Yet, this is not due to ignorance, each of you is aware of the facts.

Let me refresh your memory. Louis De Broglie won the Nobel Prize in 1924 for his ‘discovery of ‘matter’ waves. The ‘discovery’ of matter waves seemed to support wave particle duality. Schrodinger decided to build a new model of the atom based on De Broglie’s hypotheses. Originally his idea was that ‘matter’ waves were real and he decided to base his model of the electron within the atom as a series of standing waves. Unfortunately, he soon found out, that it was practically impossible to implement. The German physicist Born, then put forward the theory that’matter’ waves did not refer to anything real but that they were waves of probability.

My point is that you are taking an abstraction and treating it as if it were solid fact. Is that entirely ethical?  It is almost like selective amnesia………
 

Offline Soul Surfer

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« Reply #34 on: 24/11/2007 19:59:35 »
You are very wrong McQueen matter waves associated with electrons are clearly visible and observable and definitely not a figment of an imagination you may not like the fact that our universe is built out of a web of probability rather than some sort of solid rock but it is.
 

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« Reply #35 on: 25/11/2007 00:13:21 »
Anyone who wants  a 'good understanding' of Physics would NEVER try to say what something 'really is'. All you can say about particles is that they can be seen to behave as if they are waves. That is readily demonstrated. It is a fruitful way of looking at things because it allows you to predict certain behaviours  but that is all.
Is that point worth arguing about?

Note: The de Broglie wavelength is not concerned with size - it relates momentum to wavelength.
The 'slower an object is moving, the longer its wavelength. Or, to pass the McQueen objection, we would say it behaves, under a number of circumstances, that way.
« Last Edit: 25/11/2007 00:17:04 by sophiecentaur »
 

Offline McQueen

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« Reply #36 on: 25/11/2007 00:50:55 »
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You are very wrong McQueen matter waves associated with electrons are clearly visible and observable and definitely not a figment of an imagination you may not like the fact that our universe is built out of a web of probability rather than some sort of solid rock but it is.
Schrodinger's model of the atom is founded on the proposition that 'matter' waves are not real, they have nothing to do with reality, they are probability waves. You can either say 'matter' waves are real or you can say that they are not real and that they are in fact probability waves. You can't have it both ways. Believe me in the real world you can't have it both ways! Further more you state that matter waves are clearly visible and detectable because they exhibit diffraction. Remember that waves, actual waves in the sea, undergo diffraction. All that is needed for diffraction to be manifested is for the hole the waves, or particles of waves  are passing through, are relatively larger, more than half the dialmeter,  than the hole they are passing through.
 

Offline McQueen

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« Reply #37 on: 25/11/2007 00:55:58 »
Quote
Anyone who wants  a 'good understanding' of Physics would NEVER try to say what something 'really is'. All you can say about particles is that they can be seen to behave as if they are waves. That is readily demonstrated. It is a fruitful way of looking at things because it allows you to predict certain behaviours  but that is all.
Is that point worth arguing about?
Then why do you say, and all of you in this thread have said it. That 'matter' waves are real. If you had said the probability of the of an electron becoming larger increases slighlty when it is in its rest state,  it would have been more acceptable, more truthful and to the point. The reason that you didn't put it like that is because it doesn't sound very convincing!
 

Offline lightarrow

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« Reply #38 on: 25/11/2007 16:01:29 »
Then why do you say, and all of you in this thread have said it. That 'matter' waves are real.
We are telling you that photons, electrons, ecc. behaves as particles and as waves.
I don't understand where is your problem.
« Last Edit: 25/11/2007 16:03:48 by lightarrow »
 

another_someone

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« Reply #39 on: 25/11/2007 16:57:48 »
It is all very well to talk about ‘matter’ waves but no-one can say what they are. De Broglie himself described them as ‘waves that correspond to matter.’ But no-one has till today managed to find out what these matter waves are, what is sure is that nothing is ‘waving ‘.

I think the more fundamental problem is that nobody has defined what 'matter' is, so the argument about whether it is or is not a wave is rather moot.

All we know about matter is that it has momentum, it carries (although not all matter carries all of these) attributes such as charge and spin, and various other forces.

We can measure the forces, and we can measure how the focal point of those forces move through space (and from that, we can attribute characteristics like mass and momentum, etc.).  Beyond that, we cannot say what, or where, matter is.
 

lyner

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« Reply #40 on: 26/11/2007 10:36:54 »
We have all heard the story of the five blind men who came upon an elephant. Each one found a different part of the animal and described it in his own terms. Each was all right in his own way but failed to get the bigger picture. Between them, they could have had a better understanding.
Why must people be so insistent on a single description of something so multifaceted as matter?
 

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« Reply #40 on: 26/11/2007 10:36:54 »

 

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