User talk:Sbyrnes321

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I disagree with you revert at Fourier transform infrared spectroscopy in Conceptual introduction[edit]

I really understand what you mean but the problem is that viewing a Michelson interferometer as a wavelength filter is not right at all. In fact, that is how a spectrometer works. More over the usual mistake about the Michelson interferometer is to compare it to a spectrometer which it is not. You must know that all wavelengths are passing through a Michelson interferometer and that what you see on one of the output ports is the sum of the interference pattern of each wavelength for a certain optical path difference. I know that the way a Michelson interferometer works is not easy to understand but it may be better to avoid false description (I am sorry for my poor english). This is a description taken from Michelson interferometer : "The Michelson interferometer's detector in effect monitors all wavelengths simultaneously throughout the entire measurement, increasing the integration time and the total number of photons monitored"

Oh, I already wrote a message at Talk:Fourier_transform_infrared_spectroscopy#Conceptual_introduction ... I will copy this message and we can keep talking there :-)

An invitation, not a request[edit]

You might be interested in making some animations on the Casimir effect. In particular, you could make either a spaghetti plot or a sequence of captures of either the position or velocity of a one dimensional wave (by the uncertainty principle you can never see both). The probability distribution can be obtained from Quantum field theory in 1D (still under construction). My instincts tell me that the Casimir effect will occur if regularization includes only 5 or 10 modes.

I do most of my work on Wikiversity for two reasons: (1) I have more freedom to express myself, and (2) I would like to see an evolution from Wikpedia the encyclopedia to Wikipedia/Wikiversity/Wikibooks the encyclopedia/bookstore that includes editable books on all sorts of subjects from all sorts of viewpoints. --guyvan52 (talk) 15:02, 13 October 2014 (UTC)

Clebsch–Gordan coefficients for SU(3)[edit]

Hi, I have created and developed a page on Clebsch-Gordan coefficients for SU(3) group. This is my first edit. It will be really great if you take a look at it and propose some improvements if necessary.Arkadipta Sarkar (talk) 16:58, 20 November 2014 (UTC)Arkadipta Sarkar

Sorry, I don't know anything about that topic. (I used to understand it to some extent, but I've forgotten it long ago!) Maybe you should ask instead at Wikipedia talk:WikiProject Physics?
I don't have the energy to read it carefully BUT, superficially, it looks to me like a very polished and professional article. It doesn't look like somebody's first-ever wikipedia article. Impressive! :-D --Steve (talk) 03:53, 21 November 2014 (UTC)

Electron Holes[edit]

Hi, We seemed to be in disagreement on Electron holes.

You state that the holes and the electron can move in the same direction but according to the reference you give "Introduction to Solid State Physics' C. Kittlel - I only have the 5th edition - in the the 5th edition look at page 218 figure 10 in the caption it clearly states "the electron and holes drift velocities are in opposite directions".

In your explanation of the electron and holes moving in the same direction " like a bubble in water" - it's impossible to explain how a LED or semiconductor laser emits light. or at least I would be interested to see how you explain the operation of a LED.

I hope we can come to some agreement on this issue.

Best wishes. — Preceding unsigned comment added by (talkcontribs) 06:27, 8 December 2014 (UTC)

Did you read the rest of that section?
If Kittel says "the electrons and holes drift velocities are in opposite directions", he presumably means the conduction-band electrons, not the electrons near the top of the valence band (which is what the wikipedia article is talking about). That is my strong suspicion. But I don't have the 5th edition to check the full context. If you disagree with me, and feel that "electrons" is not short for "conduction-band electrons" in that sentence, then can you quote a few sentences before and after, and explain the context better?
Conduction-band electrons drift in the opposite direction to holes like you say. :-D --Steve (talk) 13:04, 8 December 2014 (UTC)

Thanks for responding

Yes you're right the caption in Kittel 5th edition specifically refers to holes having a drift velocity opposite to the conduction bad electrons - I think also my point about the LEDs not working is not valid because although the electrons and holes are moving in the same direction they have opposite mass therefore opposite momentum and thus cannot not recombine because that would violate the conservation of momentum.

Although all of this applies really just at zone centre where the electron mass is negative when the electron acquires some momentum its mass becomes positive and it changes direction - that's one way of looking at Bloch Oscillations. Your analogy of the river of with the bubble implies a net flow of negative charge in a p-type semiconductor towards a negative electrode and that is not the case. However, no analogy is perfect and the bottom line is that I'm OK with leaving your description in - because it does bring out the point about the electrons and holes in the valence band moving in the same direction at least at zone centre.

By the way, I have also worked on Quantum Cascade lasers - give my regards to Frederico - let him know I've moved from Scotland to Australia. — Preceding unsigned comment added by (talkcontribs) 06:51, 9 December 2014 (UTC)

Oh cool! I edited the text to hopefully make it clearer in the future. I agree with everything you say. I will say hi to Federico from you. Thanks again, --Steve (talk) 13:33, 9 December 2014 (UTC)

The page on Group Velocity[edit]


I made the edit on the page on Group Velocity yesterday. . Thank you for cleaning up what I wrote! I do have one thing to say, which is that the modulus of the wave packet remaining constant doesn't really mean anything, does it? The actual wave is the real part of the exponential, and at a given space time point, the vibration of the system has a value which is somewhere intermediate between that on the wave packet envelope, because of the vibration within it. That vibration is given by the vibration moving at the phase velocity within the wave packet, in the first order approximation. Thanks,

Aritrop (talk) 18:39, 18 February 2015 (UTC)

Oh, you're right. It's obvious to me how to interpret the absolute value, but it would not be obvious to readers. I just edited to rephrase. Is it better now? I'm sorry that I reverted that aspect of your edit, I didn't realize what the problem was. :-D --Steve (talk) 18:58, 18 February 2015 (UTC)


Now it seems exactly how I had wanted to put it. You wrote it much better than how I tried conveying the same thing. Thanks a lot!

And how would you interpret the absolute value?

The way you put it now just seems the easiest way to understand group velocity, to me.

Aritrop (talk) 19:25, 18 February 2015 (UTC)

Thank you!!
Normally when you have waves represented as complex numbers, the absolute value squared of the wave is related to its power. (That is a bit vague; the details depend on the type of wave I think.) Also, I was just imagining File:Wave_packet.svg with the absolute value being "obviously" (in my head) equal to the envelope. :-P --Steve (talk) 19:49, 18 February 2015 (UTC)

Hi Steve,

So you meant the energy travels at the group velocity and so the power of the wave is constant in time? I don't really recall how the power propagates for a general system, but I'm sure what you said makes sense, and it can be shown that the energy is transmitted at the group velocity, assuming of course that there is no distortion. Anyway, i feel it is best the way it's written now, for the understanding of how the group velocity emerges in conjunction with the phase velocity.

Aritrop (talk) 20:03, 18 February 2015 (UTC)

For example, in a wave on a string / spring, there is potential energy and kinetic energy, and energy converts back and forth between them as the wave oscillates. So the wave "passes through zero", but the energy is still there. You don't need to do a time-average in that example.
Energy usually travels at the group velocity, but not always ... after all, there are examples where group velocity is faster than the speed of light :-P --Steve (talk) 20:19, 18 February 2015 (UTC)


Sorry I made an edit just now in the previous comment. I think it is an interesting exercise to check that the power actually gets transmitted at the group velocity for normal systems, and I have not done that exercise yet. Aritrop (talk) 20:22, 18 February 2015 (UTC)

If (1) the energy is around the location where the wavepacket is, (2) The wavepacket moves at the group velocity, then therefore (3) The energy must travel at the group velocity.
I think the weird examples that I just mentioned where group velocity is faster than light involve very lossy waves, so the wave is rapidly shrinking everywhere and it's hard to guess how the energy is flowing. --Steve (talk) 20:38, 18 February 2015 (UTC)

Thanks for letting me know. Does it seem like I exhibit nascent traits of a quack? Aritrop (talk) 00:47, 21 February 2015 (UTC)

I don't know what you mean by "quack". I think the group velocity article has definitely improved as a result of your efforts, so thanks again for that. --Steve (talk) 01:45, 21 February 2015 (UTC)

Well, I was looking through the criteria that Warren Siegel gives for identifying quacks, and I was curious if the grandiose way in which I made my first edit did portray some of those characteristics. I'm assuming you're fairly familiar with the conspiracy theory mongering paranoid delusional section of mankind that says and does crazy things. If this sounds crazy and irritating, don't bother to reply, because it's probably all that. Aritrop (talk) 03:22, 21 February 2015 (UTC)

Don't worry, see WP:BOLD. --Steve (talk) 15:59, 21 February 2015 (UTC)

total energy of the universe[edit]

That's rigth [1], "According to present understanding" is implicit in every statement of every science article, but I still disagree with the example. I have many friends who are professional physics, and cosmology, to most of them (I guess all!), is just mystics. Every statement of every science article can be (at least in principle) verified by anyone, but we do not even know how to compute exactly the total energy of the universe, perhaps we do not even know the exact meaning of that expression. So why do not say something like "Conservation of energy in the Milky Way is conserved, but this statement does not immediately rule out the possibility that energy could disappear from the Sun while simultaneously appearing in another distant star"? Of course it is not completely clear how to evaluate exactly the total energy of the Milky Way, but the statement is not that problematic. By the way, I do not know whether there is a continuity equation in quantum electrodynamics; entanglement and Einstein-Podolski-Rose paradox surely create problems - maybe they can be solved some way or another, I do not know... I feel that the right idea is that quantities are conserved under their respective appropriate conditions. Everything works just only under appropriate conditions. Cheers. (talk) 01:15, 1 August 2015 (UTC)

OK, I think I see what you mean. I just changed the example to within Earth, and avoided the phrase "total energy of the universe" - [2] - do you think it's OK now? --Steve (talk) 12:25, 1 August 2015 (UTC)
Yes, I think it is much clearer now, thank you! (talk) 13:00, 1 August 2015 (UTC)