Superconductivity at room temperature??

[Ziggurat]

I can understand you holding an electron, helium atom or a neutron in a microscopic tweezer but not a photon.
Once the photon comes to rest, it disappears.

ie no rest mass. (or am I mistaken here?)

It's got no rest mass, but the distinction you're trying to draw is not nearly as solid (pun intended) as you suggest. You can, in fact, confine a photon. For example, with a resonant microwave cavity. The standing wave is (a bunch of) trapped photons. It's got some "spread" to its location, but so do electrons, neutrons, and helium atoms. It's just the size of the trap which is different. Photons are more "ephemeral" because there's no number conservation associated with them (so you can create and annihilate them individually), but that's not an issue of wave versus particle characteristics.

 

[Skwinty]

Cool, thanks for all your responses. I must go to bed now as I must go back to work tomorrow after the xmas holidays.

 

[CaveDave]

...
Similarly: in a dry room, take an acrylic disk and put a point charge Q at one point on the circumference. Spin the disk at 1000 rpm; the moving charge will radiate at 1 kHz, enough to pick up (in a near-field sense anyway) in basic lab amplifiers. Now, draw a line of conducting paint around the edge of the disk, and dump the same charge Q on it. It's no longer a point charge, it's a line charge. Spin the disk at 1000 rpm; it's the same amount of charge undergoing the same acceleration, but the oscilloscope now sees no kHz signal.
...

Speaking of the ring example only:

Classically speaking: yes, there are two size scales to consider. First, what is the characteristic wavelength of the radiation? Second, what is the size scale at which the charges stop looking continuous? Look at the case of my spinning disk. Let's make it 10cm diameter and place 1 nC (10^10 electrons) onto it. Spinning at 1000rpm, its radiation would be at wavelengths of 300000 m, but the charges involved look continuous (in the relevant projection) down to 3x10^-11 m. So there's a factor of 10^16 suppressing the classical radiation of this system. My intuition says that QED suppresses it even further, but I could be wrong on that point.
...

Just a minor point, Ben, shouldn't that be 60,000 rpm (or 1000 rps) to create the 1 kHz or 300,000 m numbers?

Or am I confused?

Cheers,

Dave

 

[ben m]

Just a minor point, Ben, shouldn't that be 60,000 rpm (or 1000 rps) to create the 1 kHz or 300,000 m numbers?

Or am I confused?

You're right, thanks. 1000 Hz = 1000 rps.

 

[johanfprins]

As I have last posted, I cannot answer all the many crackpot posts on this thread in a single day and will this proceed with each in seriatum when I have time. I have now come to the following one:

Hey folks,

I have a proposal. The entire discussion of acceleration is relevant to Johan's understanding (or not) of the meaning of the statement "E=0 and B=0 in a superconductor".

Meanwhile, we have left hanging the fact that Johan STILL thinks that this circuit:

ground --- power supply ----------- junction ---------- ground

                                    ___   . . . . . . . . V=3
                                    |    |
                                    |    |  .  . . . . . . V=2
                                    |    | 
                  __________________|    | . .  . . . . . V=1
                 /                       |
________________/                        |_______________ V=0

emits radiation with energy 2qV every time an electron goes through it.

That is a blatant lie and if you have any conscience (which I doubt) you will retract this lie. I have acknowledged that I have not originally done the analysis correct, and spent a lot of time to do it in detail and to post it on my website.

This is confirmed in your "chapter 28" diagram. In figure 28-6, ........

I have also posted on my website that this diagram is not correct, and that people must refer to the erratum. But you are so dishonest that you want to still start an argument about it. I find your attitude despicable; but not surprising since you are not really interested to argue rational science and to gracefully accept it when your opponent concedes that he has made a mistake and corrected this mistake. All you are interested in is to throw aspersions.

I am not going to read new posts but will work my way through them from this one by Ben m until I one day reach the end. People with common sense will then see clearly who has been wrong all along. I will be back when I have time!

 

[excaza]

so, if I'm following correctly it's something like this:

johan: something
someone: this is wrong
johan: I know it's wrong, how dare you be so mean and misleading!?

 

[Cuddles]

People with common sense will then see clearly who has been wrong all along.

We already can. I don't think it's who you think it is.

 

[ben m]

I have also posted on my website that this diagram is not correct, and that people must refer to the erratum. But you are so dishonest that you want to still start an argument about it.

I apologize. I saw the erratum but I thought it was referring to an older version of the diagram. Therefore I thought the printed version was "new" and therefore fair game. Rereading it I see my mistake.

 

[johanfprins]

I apologize. I saw the erratum but I thought it was referring to an older version of the diagram. Therefore I thought the printed version was "new" and therefore fair game. Rereading it I see my mistake.

Thanks. I just wanted to answer your posting #548, but fortunately this posting caught my eye and therefore I will next time proceed from the posts that have been done after your #548.

I apologize for calling you dishonest. I should have known it must be an honest mistake and will be careful to check my facts in future.

 

[johanfprins]

Johan,
After reviewing the posts in this thread, these are the comments you made about a paper which I referenced. http://arxiv.org/abs/0912.4810.
I have read this paper and the author seems to be postulating the same as you, wrt cooper pairs.

Thanks for posting this. I will look at their analysis but doubt that their idea of "vortices" play any role. Furthermore it is a pity that they bring in the concept of an "order parameter" since this usually proves that a person doing so has no insight whatsoever of what really happens on the microscopic scale. It is nothing else but a massive fudge factor.

It is, however, heartening to find that other people are also starting to remove their eye flaps. I am sure that they will not get this paper past the main stream crackpots in charge of superconductor physics.

 

[ben m]

Johan, you have corrected your diagram (in the erratum) to show a potential energy drop of 2qV.

ground --- power supply ----------- junction ---------- ground

                                    ___   
                                    |    |
                                    |    |
                                    |    | 
                  __________________|    | . .  . . . . .  V 
                 /                       |
________________/                        | ..............  0
                                         |
                                         | __________ -V

You show the charge dropping from the "V" level to the "-V" level, a change of 2qV of potential energy. But this charge has to get pushed back up to the V level ... which won't happen with the one-V battery of the diagram above. The battery needs to do 2qV of work to get move this charge from the -V level back to the +V level ... which means that it's a battery whose voltage is 2V to begin with.

In other words, the above voltage scenario---a battery of voltage V pushing electrons through a circuit where they can drop by 2V---again does not conserve energy. Let me fix it for you:

ground --- power supply ----------- junction ---------- ground

                                    ___   
                                    |    |
            battery                 |    |
            has voltage 2V          |    | 
                  __________________|    | . .  . . . . .  V 
                 /                       |
                /                        | ..............  0
               /                         |
 _____________/                          |_______________ -V

That's the voltage landscape that corresponds to your corrected fig. 28-6b. This voltage picture does conserve energy, finally. But look, it's gone back to describing the mainstream Josephson picture:

The energy of the photon emitted is equal to, not double, the net battery voltage times the charge of the charge-carrier.

The V is getting confusing now, let's add a clearer variable name. The above circuit has a battery of voltage B. When a charge q moves through the junction, it emits a photon of energy E = qB. Just like Josephson said. The fact that we observe photons at E = 2eB tells us that q = 2e and therefore that conduction comes from electron pairs.

Your quantity V = B/2 is not the battery voltage, nor the photon energy, nor does it appear to be observable in any way. You seem to be saying "there's V worth of polarization potential plus V worth of Fermi energy", but one way or another this energy needs to be supplied by the battery.

 

[johanfprins]

Not really, but I appreciate your flattery.


You may not have been arguing about that, but your fictional EE was:

And anybody with common sense will know that this statement by my "fictional EE" is not outside the discussion on this thread. Since you do not understand that there can be content in a sentence that "goes without saying" neither I or my fictional EE spoke about anything else but about electronic charge-carriers being accelerated by an applied electric field

Notice the absolute and unqualified nature of your fictional EE's claim. He said "accelerating charges must radiate", and anyone who says otherwise "must be a crackpot".

And he is correct when accelerating charge carriers by an applied electric-field.

He's calling Maxwell a crackpot. If you thought your fictional EE had limited his claim to accelerations "along a ring by an applied electric-field", then you misread his claim.

I wrote it but YOU know better what was discussed!

Ziggurat's counterexample proves that your fictional EE was wrong. You shouldn't take that personally. It's about your fictional EE, not you.

He did not since it was not what my fictional EE was talking about

As explained above, your fictional EE made an incorrect claim for which Ziggurat produced a relevant counterexample.

In the context of the discussion on this thread he did not.

Although Ziggurat's counterexample was relevant to the claim made by the fictional EE you quoted, his counterexample may not have been relevant to your argument. If that's the case, then your fictional EE's claim was also irrelevant to your argument.

OK you are funny!

A noble quest. How will you recognize them?

I agree it is easier to recognize those without any common sense like you!

Although I am both flattered and amused that you would group me with such credible scientists, you're over-estimating my contribution. I'm not a professional working on "superconduttion", so my nonsense can't be relevant.

Thanks for informing us that you are really a clown.

 

[johanfprins]

No no no---accelerating "along" a ring? No, we were specifically talking about how charge-carriers can negotiate a curve, a particular type of motion that involves acceleration. When a charge carrier moving at velocity {vx,vy} = {1,0} um/s turns left and ends up moving at {0,1} um/s, that is an acceleration. That is what we are talking about.

It can also first stop and then jump into another direction: there is then no acceleration involved.

That is why the spinning-disk example is relevant---it's an example of an ensemble of charges, all accelerating, that do not emit radiation.

This is not relevant to charge carriers moving around a circle which MUST then radiate EM radiation. The fact that they can do it within a superconducting ring, means that they move without being accelerated. If they did accelerate one would have measured EM radiation.

The defining characteristic of a superconductor is that its charge carriers move WITHOUT BEING ACCELERATED. This is what Onnes discovered in 1911; unless you want to argue that the voltage did not go to zero. If this is the case and the charge-carriers move around a ring without radiating EM waves or scattering, they will keep on accelerating until their speed goes to light speed. This is not observed: In fact they move with a constant speed.

This is the twentieth or thirtieth time: Johan, nobody is insulting you. Several people are saying that you've made physics mistakes, and we are trying to explain those mistakes to you. You are the one leaping to insults. You need to take a long, long, close look at your way of arguing.

You believe that NOBODY has insulted me on this thread? You must be blind!

 

[ben m]

It can also first stop and then jump into another direction: there is then no acceleration involved. This is not relevant to charge carriers moving around a circle which MUST then radiate EM radiation. The fact that they can do it within a superconducting ring, means that they move without being accelerated. If they did accelerate one would have measured EM radiation.

a) Stopping and changing directions is acceleration.
b) The example I gave---a spinning disk---does not involve "stopping and changing directions", it's uniform circular motion, one of the simplest schoolbook accelerations you could possibly think of.

Let's start over. Where, exactly, do you find "acceleration = radiation" in Maxwell's Equations? Please show me.

The defining characteristic of a superconductor is that its charge carriers move WITHOUT BEING ACCELERATED.

No one agrees with you on this "defining characteristic".

If this is the case and the charge-carriers move around a ring without radiating EM waves or scattering, they will keep on accelerating until their speed goes to light speed.

Forget about charge for a second, you need to clear up your understanding of classical acceleration. Take a spinning disk. All of its matter is accelerating all the time. (Do you agree? Please reply.) Does this mean that bits of the disk are increasing in speed all the time?

 

[Ziggurat]

It can also first stop and then jump into another direction: there is then no acceleration involved.

Um... Yes. Yes, there is. When you stop, that's an acceleration. When you jump from a stop, that's an acceleration. You cannot move something in a circle without accelerating. It's not possible.

But I do wonder what you think the velocity of such particles is.

The defining characteristic of a superconductor is that its charge carriers move WITHOUT BEING ACCELERATED.

No, that is not the defining characteristic of superconductors. In fact, it's not even a possible characteristic.

This is what Onnes discovered in 1911

No, he didn't.

unless you want to argue that the voltage did not go to zero.

Onnes didn't measure what we're talking about. And his measurements didn't have infinite precision and accuracy. As I already pointed out, the best you can EVER do with voltage (or any other) measurements is set an upper bound, the measurements themselves can never prove the value is identically zero.

If this is the case and the charge-carriers move around a ring without radiating EM waves or scattering, they will keep on accelerating until their speed goes to light speed. This is not observed: In fact they move with a constant speed.

Nonsense. Circular motion at uniform speed requires perpetual acceleration. a = v²/r. Surely you're familiar with that equation, aren't you?

 

[Skwinty]

See my post 514.

I would be interested to know the veracity of the math link at the end of this post.

Here is a snippet.

It's also possible to question whether the equations of electrodynamics really do imply that an accelerating charge necessarily radiates. Surprisingly, this is still an open question for the classical theory. The difficulty is in knowing how to correctly account for the influence of a charged particle on itself. Remember that two electrons repel each other with a force (statically) proportional to the reciprocal of the square of the distance between them. This is traditionally understood in terms of each particle interacting with the field of the other particle. The intensity of each electron's field increases to infinity as the distance goes to zero (assuming point-like particles), so the force with which an electron is repelled increases to infinity as it approach the location of an electron - but therein lies a conceptual difficulty. According to this description, each electron is located in a place where there is an infinite force of repulsion against electrons!



We can try to deal with this in various ways. For example, we might simply declare that an electron does not interact with its own field, it interacts only with the fields of other particles. If we take this approach we must then explain why a charged particle resists changes in its state of motion more strongly than an uncharged particle of the same inertial mass. The traditional account of accelerated charges tell us that this "radiation reaction" force applied through the particle's motion supplies the energy that is radiated away in the form of electromagnetic waves. The origin of this force is usually taken to be the interaction of the particle with its own field. Thus if we declare that charged particles do not interact with their own fields we need a different explanation for radiation reaction. One well-known candidate is the Wheeler-Feynman absorber theory, according to which the excess resistance of a charged particle to changes in its state of motion is due to advanced waves emanating backwards in time from an all-encompassing array of absorbers in the future, whose waves are excited by the retarded waves emanating forwards in time from the particle.



We could also point out that although the force of repulsion on a charged particle from its own field is infinite, it is equally infinite in all directions, so the infinite forces cancel out, leaving no net force on the particle due to its own field - at least if the particle is in uniform motion. Then we can further suppose that the acceleration of a charged particle causes it to bias this singularity as it overtakes its own field, thereby incurring a net force. This same disturbance of the field results in radiation, so we can see the expected correlation between radiation and reaction. However, this approach leads to some highly non-intuitive conclusions. For one thing, the equation of motion based on this premise seems to imply that a uniformly accelerating charge does not radiate at all. (This is sometimes called hyperbolic motion, because the worldline of the particle is a hyperbola in spacetime, asymptotic to a particular pair of light rays.) Even more disquieting, we find that the equations of motion for a free charged particle possess "run-away" solutions, in which the particle rapidly accelerates toward the speed of light. In effect the particle is surfing on its own field.

 

[ben m]

See my post 514.

I would be interested to know the veracity of the math link at the end of this post.

For starters, the author of Mathpages.com is not a crackpot; this is basically mainstream physics. This topic is radiation reaction, which has had a complex history that I don't know very well. I can't tell (from a scan, not a detailed read) if the author's discussion is leaving us with the current state of thinking or cutting off at some midcentury confusion point.

 

[Skwinty]

Thanks Ben, I am especially intrigued by

"In effect the particle is surfing on its own field."

 

[ben m]

Thanks Ben, I am especially intrigued by

"In effect the particle is surfing on its own field."

So am I. I've never heard of this solution, if indeed it exists, and as I said I'm not familiar with the details of classical radiation reaction---neither the historical development nor the present state of affairs. It's annoying that the author does not provide references, and I don't have time to go textbook-mining to figure out what he means.

 

[Skwinty]

I had a quick google and this came up, so perhaps it's not to goofy footed.

http://apl.aip.org/resource/1/applab/v90/i20/p204103_s1?isAuthorized=no

The author theoretically demonstrates a gel-free electrophoretic ratchet under a nearly unidirectional traveling electric field whose wavelength is much longer than the transverse dimension. Because of length scale separation, a charged particle can migrate synchronously or asynchronously with the field as if it was surfing on the wave. The author shows, with a dynamical phase portrait, that if the wave speed is slower than the characteristic electrophoretic velocity, a suspension of charged particles can be trapped into distinct particle bands synchronizing with the field. A tunable sieving capability of this ratchet provides the potential for continuous fractionation and characterization of colloidal suspensions.