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Author Topic: What is the evidence for the existence of protons and neutrons?  (Read 11814 times)

Offline chiralSPO

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PS: I don't intend to sound hostile--it's just that there have been a number of threads on this forum in the last year or two, in which some members have pointed out repeatedly that quantum can't be correct because it doesn't make any sense--and I'm fatigued of this discussion.

Because I know that you cannot be held responsible for the aggregate behavior of several other people, I apologize if I was too short in my responses on the matter.

Please understand that quantum mechanical models are actually quite good, and are based on reams of evidence. Nobody sat around and theorized, "what if everything was made of waves and couldn't be measured without disturbing the system?" Instead people assumed that they were studying particles in ways that could give definitive answers, and after decades of high-quality experimentation by hundreds of experts across the globe, analysis of the data collected revealed that the world is actually a very strange place on the molecular scale and smaller.

I think reading a history of the development of quantum mechanics might clear up some of the confusion. There are plenty of members here who would be happy to point you in the direction of some good references on the subject.
 

Offline alancalverd

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Quite simply, physics is an attempt to derive predictive mathematical models of what actually happens. The simple Bohr atom doesn't predict what actually happens, so we use quantum mechanics which gives us a much better result.

Thing only go wrong when people anthropormorphise the inanimate and ask unanswerable questions like "why doesn't the electron spiral into the nucleus?" You have to take a much more Zen approach to make sense of physics. Start with the observation that it doesn't, then derive a model that begins with that fact, and before you reach graduation day, you will have derived orbitals, explained stereochemistry, and proved that anthropogenic global warming is bunkum!

Eddington said that the student of physics must become accustomed to having his common sense violated seven times before breakfast. I'd substitute "intellectual vanity" for "common sense" in that sentence, or, as my navigation instructor said "start from where you are, then you won't get lost before you take off".
« Last Edit: 02/09/2015 17:05:48 by alancalverd »
 

Offline mathew_orman

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So they do not spin but do  motion sequences  declared by QM but not able to define or simulate...
 

Offline alancalverd

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We describe and predict what they do, by use of a vector called "spin". It happens that the spin vector of subatomic particles behaves in some ways like the angular momentum vector of a mesoscopic object so it's a very convenient term.
 

Offline mathew_orman

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So there is a vector which descries the motion of an electron which suggests that that temporal position is known and if so then the motion cycle should also be known and animated model would show the electron's motion... But why there is no such visualization available?
 

Offline PmbPhy

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Quote from: mathew_orman
At present time we can created 3D simulations of any structures in motion but not a single atomic structure containing electrons spinning around the nucleus exists...
Quote from: chiralSPO
That's true. Because, as others have pointed out, electrons DON'T spin around the nucleus. Therefore it is a good thing that models based on that assumption fail.
Both of you have used the term "spin" incorrectly and which may have caused some confusion in this thread.

One thing that seems to have caused some confusion in this thread is the use of the term "spin" which refers to an intrinsic property of a particle. What you both spoke of here is orbital motion. The two quantum mechanical quantities having to do with angular momentum are spin angular momentum and orbital angular momentum. Classically spin refers to a body revolving about an axis through it's body while orbit refers to something moving around a point like when the moon orbits the earth. So the Earth "spins" about its own axis and the moon "orbits" around the Earth.

Hans C. Ohanian wrote an article in the American Journal of Physics called What is spin? that you might want to read. It's online at: http://people.westminstercollege.edu/faculty/ccline/courses/phys425/AJP_54(6)_p500.pdf

Ohanian shows that spin ... can be regarded as an angular momentum generated by a circulating flow of energy of the wave field of the electron.

Quote from: mathew_orman
If a neutron, which is a hypothetical particle, has no known force field, it should not be possible to detect it. Also how are neutrons able to stay together so close if the calculated mutual repulsive force is so large?
That's wrong. Neutrons can be detected in other ways since it has mass as well as a magnetic moment. Since it has mass it contributes to the mass of the nucleus but not to its charge. Therefore when an atom is ionized and shot into a magnetic field the atoms with the same number of protons but different number of neutrons will move in different trajectories due to their varying mass and therefore the mass of the nuclei can be measured. The charge of the nucleus tells you how many protons are in the nucleus so once you know that you need to account for the rest of the mass of the nucleus and that's from neutrons.

To see how they were discovered please read the following: https://en.wikipedia.org/wiki/Neutron#Discovery
Quote from: mathew_orman
So they do not spin but do  motion sequences  declared by QM but not able to define or simulate...
If by "they" you're speaking of electrons then an electron has spin by virtue of it contributing to the total angular momentum of an electron as well as it having a magnetic moment.

Quote from: mathew_orman
So there is a vector which descries the motion of an electron which suggests that that temporal position is known and if so then the motion cycle should also be known and animated model would show the electron's motion... But why there is no such visualization available?
In  quantum mechanics its incorrect to think of electrons in motion, so no. That is incorrect. No visualization of an electrons motion is possible because electrons don't have motion in the classical sense of the term, i.e. an electron does not have a position as a function of time.

Mathew - I've noticed that you made a lot of claims about quantum mechanics
 

Offline mathew_orman

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So, using QM one cannot model CRT beam of electrons which could be focused, diverted scanned, expanded and ect. ?
I am not interested in evaluating QM and its is other posters who try explain the problem using QM only to find out that i generates many other questions for which no logical answer exists...
 

Offline chiralSPO

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QM can and does model the behavior of populations (large numbers of) particles, as in a CRT beam. It gives the same answer as classical physics, so people usually use that because the calculation is easier. QM really only gets "funny" when one tries to consider what only one or two particles are doing, especially if one is concerned with what happens on a very small scale (either spatially or temporally).

Think of it this way: a river flows downstream at some velocity that is determined by the depth and width of the river, the change in elevation, and the fluid properties of the water. But if one were concerned about how an individual water molecule is moving, the answer would be very different. Sure, the net movement of water is downstream at a speed of 2 m/s, but each of the molecules is moving at a different speed (all about 10 m/s) and bouncing around off of one another. Almost all of them are moving upstream about half of the time! It would be very difficult to predict or measure the exact path taken by an individual water molecule (especially if we get into the tricky question of how one considers the motion of molecules that are exchanging protons/hydrogen nuclei, as happens quite readily in water). But once a sufficiently large group of molecules is considered, the average or net properties become very classical.
 

Offline mathew_orman

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CRT ray of 16kV, 1mA, 60cm between cathode and anode... What is the resistance, inductance, skin effect, self capacitance, velocity of electrons, power dissipation, radiation effects and etc.?
Where are the models in QM or classical format?
 

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