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Sylas
Member (Idle past 5250 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 226 of 309 (193239)
03-22-2005 5:36 AM
Reply to: Message 224 by lyndonashmore
03-22-2005 3:15 AM


Do electrons in a thin plasma act in unison?
lyndonashmore writes:
The force between two electrons 1 metre apart is 2.3x10^-28N. This produces an acceleration of 253m/s^2 ie. 25 times that due to gravity on Earth So why do you doubt that they can act in unison?
Because their mass is so small and their velocity so great that such accelerations are tiny. Gravity is the weakest of the fundamental forces by far.
Consider electrons in a comparatively cool plasma, with a temperature T of somewhere from 300K (room temperature) up to 6000K (surface of the Sun). The electrons will be moving, on average, at around 100,000 m/s to 500,000 m/s. Thus the accelerations Ashmore mentions are far far too small to justify thinking that electrons would move in unison, which is why no such unison effect as Ashmore invokes is actually seen in real life.
An electron hardly notices another electron a meter away.
Macroscopic intuitions about the significance of velocities and distances and accelerations don't work. A meter is a hell of a long way for an electron, but a second is an age.
Cheers -- Sylas
Addendum: Let T be temperature, E be kinetic energy, k be the Boltzmann constant (1.38*10-23 J/K), v be the velocity, m be the electron mass.
Then E = 3kT/2 = mv^2/2, and so v = sqrt(3kT/m) The velocities obtained are not relativistic, so this should be in the right ball park.
This message has been edited by Sylas, 03-22-2005 06:25 AM

This message is a reply to:
 Message 224 by lyndonashmore, posted 03-22-2005 3:15 AM lyndonashmore has replied

Replies to this message:
 Message 227 by lyndonashmore, posted 03-22-2005 8:56 AM Sylas has replied

lyndonashmore
Inactive Member


Message 227 of 309 (193284)
03-22-2005 8:56 AM
Reply to: Message 226 by Sylas
03-22-2005 5:36 AM


Re: Do electrons in a thin plasma act in unison? Yes they do!
Yet more hogwash from Sylas,
In a post on the previous page, I have just shown that the forces between two electrons one metre apart cause the electrons to accelerate at an acceleration of approx 25 times that of the acceleration due to gravity on Earth. Eta_Corinae and Sylas say that that these forces and accelerations are so small that we should ignore them and treat the electron as a ‘free’ particle, one able to go where it likes.
quote:
Because their mass is so small and their velocity so great that such accelerations are tiny. Gravity is the weakest of the fundamental forces by far.
Well folks, would you mind just standing away from your computer screen for one moment, jump up into the air and then come back. Thanks.
Ah! Your back. You see you are not free to go off as you please, the force of gravity brought you back with an acceleration of 10 m/s^-2. Now these sole electrons, one metre apart in space, suffer an acceleration of 25 times that that you just encountered — and yet Sylas and Eta_Corinae say that we can ignore these effects and consider the electron free!
Do you believe them? Hogwash!
Then Sylas says
quote:
Consider electrons in a comparatively cool plasma, with a temperature T of somewhere from 300K (room temperature) up to 6000K (surface of the Sun). The electrons will be moving, on average, at around 100,000 m/s to 500,000 m/s. Thus the accelerations Ashmore mentions are far far too small to justify thinking that electrons would move in unison, which is why no such unison effect as Ashmore invokes is actually seen in real life.
An electron hardly notices another electron a meter away.
Macroscopic intuitions about the significance of velocities and distances and accelerations don't work. A meter is a hell of a long way for an electron, but a second is an age.
Why go to the Sun? Now we are back at our computer screens lets think of the electrons in the wires leading up to our computers. They are at room temperature — the figure Sylas quotes. These electrons too are traveling at 100,000 m/s — just as they are in the plasma around the Sun. These electrons move in unison otherwise our computers won’t work. These electrons in our computer wires travel at about 0.1 mm/s far far below their thermal speeds. All that Sylas has proved above is that there is no way that your computer will work.
I say Sylas is talking Hogwash.
Because you can read this on your fully working computer screen and the temperatures are the same for the electrons quoted by Sylas in the plasma of the Sun (room temp) and the electrons in the wires of your computer then you know Sylas is talking Hogwash when he syas that the electrons cannot move in unison at these thermal speeds.
In fact you can put a voltage of one nano volt (10^-9V) across a wire ten metres long and get a current flowing. The forces acting on these electrons and their accelerations are less than those between my two electrons one metre apart in space. Because a current flows then one knows the electrons are moving in unison. Because these move in unison surely my electrons In IG space can move in unison?
Hogwash Sylas Hogwash!
Cheers
Lyndon.
In case Sylas wants to check the sums.
One nano volt across a wire ten metre long gives an electric field (E = V/d) of 10^-10 V/m.
Force on electron = eE = 1.6x10^-29N giving an acceleration of 17.6 m/s^2. Remember the force on our electrons in IG space 1m apart was 2.3x10^-28N giving an acceleration of 253 m/s^2.

Lyndon Ashmore - bringing cosmology back down to Earth!

This message is a reply to:
 Message 226 by Sylas, posted 03-22-2005 5:36 AM Sylas has replied

Replies to this message:
 Message 228 by Sylas, posted 03-22-2005 9:47 AM lyndonashmore has replied
 Message 230 by Eta_Carinae, posted 03-22-2005 12:11 PM lyndonashmore has not replied

Sylas
Member (Idle past 5250 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 228 of 309 (193311)
03-22-2005 9:47 AM
Reply to: Message 227 by lyndonashmore
03-22-2005 8:56 AM


Re: Do electrons in a thin plasma act in unison? Yes they do!
In a post on the previous page, I have just shown that the forces between two electrons one metre apart cause the electrons to accelerate at an acceleration of approx 25 times that of the acceleration due to gravity on Earth.
What Ashmore ignores is that this acceleration is small by comparison with electron velocities. Ashmore merely repeats his original calculation of 253 m/s2, but has no calculation at all to show that this number represents an acceleration sufficient to make electrons move in unison. He can't of course; and they don't.
The comparison with Earth's gravity can be put in context by seeing that the velocity of electrons in a hot plasma is many times larger than the escape velocity of the Earth, at 1.1*104 m/s. Take a box of rice grains, and Earth's gravity will keep them safely on Earth. Take a box of oxygen atoms, and their velocity is around 500 m/s; well below escape velocity. That's why we have an atmosphere. A box of hot electrons however, will only be retained on Earth because they bind to other particles. The electrons in a plasma move much too fast to be held by Earth's gravity alone.
But the comparison with gravity is irrelevant. We require a meaningful calculation of the significance of accelerations for the case of electrons.
Before I get to the analysis: here is something to give readers some intuition. An electron at room temperature moves around about 105 m/s, and will thus remain within about a meter of another electron for roughly 10-5 of a second, which means a delta-v of only a fraction of a meter per second. The acceleration is thus many orders of magnitude too small to make any appreciable difference.
To be more precise, the potential energy of two electrons at separation r is e2/4πε0r, which at one meter is 2.3*10^-28 J. The kinetic energy of a particle at temperature T is 3*k*T/2, which in a cool plasma is about 2*10-20 J or so. The effect of the electron is thus about eight orders of magnitude too small.
In real physics, we need to calculate effects, and we need to get comfortable with very large and very small numbers without jumping to conclusions based on naive comparisons at radically different scales.
An acceleration of 253 m/s2 sounds good to someone who has not calculated the consequences of this for an electron; but in reality it is roughly eight orders of magnitude too small.
This is another error by Ashmore that a competent high school physics student should be expected to catch.
Cheers -- Sylas
PS. If my computer was a thin plasma spread out over space with one particle every cubic meter or so, then it might make a sensible comparison. But it isn't, and thinking that calculations for velocities and acclerations in wires refute calculations for the actual plasma itself may be his most spectacular error yet.
This message has been edited by Sylas, 03-22-2005 10:23 AM

This message is a reply to:
 Message 227 by lyndonashmore, posted 03-22-2005 8:56 AM lyndonashmore has replied

Replies to this message:
 Message 239 by lyndonashmore, posted 03-23-2005 6:50 AM Sylas has replied

Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 229 of 309 (193378)
03-22-2005 11:52 AM
Reply to: Message 224 by lyndonashmore
03-22-2005 3:15 AM


Please go and take a plasma physics/basic EM course.
I am not getting any work done here But....
The force between two electrons 1 metre apart is 2.3x10^-28N. This produces an acceleration of 253m/s^2 ie. 25 times that due to gravity on Earth So why do you doubt that they can act in unison?
Agreed on the numerical values. But as a comparison an electron at the Bohr radius of a Hydrogen atom has an acceleration of 10^23 m s^-2.
253 m s^-2 is absolutely trivial.
They cannot be acting in unison when the accelerations are so tiny.
Your whole problem here is that you don't understand plasmas and are trying to treat an extremely extremely dilute plasma as a magnetohydrodynamic system. This cannot be done.
Secondly, yes i do know about Debye lenghth and suprisingly an electron interacts with other electrons within a sphere of radiius equal to the Debye length. In IG space the Debye length is 20km so the number of electrons each individual electron acts with is 3.5x10^13 I believe.
The Debye length is a measure of the screeening BUT it is also the characteristic distance at which you go from treating the plasma as a continuous system to small scale indivdual particle behaviour.
In other words when the Debye length is of the order kilometeres then you cannot apply the fluid approximation inherent in your use of the equations.
These have to be treated as individual scattering events unknown to the other electrons. Which is EXACTLY what you expect for electrons a metre apart and the incoming photons of wavelengths small compared to km.
Think man, you have photons of wavelengths of say 5 x 10^-7m interacting with electrons a metre apart - you cannot treat the electron/photon system as anything but a scattering event of themselves.
Thirdly you and many more are expending a lot of time on Ashmore's paradox. Remember this is a 'novelty' to pour scorn on the BB. It is there to point out that whenever a BB'er states the age of the universe it is equal in magnitude to m/hr for the electron, a metre length of space according to the BB expands by hr/m for the electron each second. This is nonsense because in the BB they are not supposed to be related.
Its a very unlikely coincidence in the BB, thats all. But in my theory you expect this sort of numerical coincidence because my expression for H is H = 2nhr/m and 'n' is about 1.
For the thousandth time it is unit dependent. You call this a paradox long before you invoke the density which only restores it if the density is approx. 1/m^3.
Problems include:
Only the farthest IGM has this low a density. All nearby space and cluster medium has a much greater density ruining your equivalence.
Where is the patchiness in the CMB due to this?
How do you get this thermalised to give a black body WHEN all these plasmas are so dilute that the electrons do NOT have a Maxwell distribution because they are so far apart collisions cannot bring them into equilibrium.
Work out the mean free paths and collision times. The times for these dilute plasmas to get into equlibrium necessary for any hope of achieving a blackbody emission are immense.
P.S. is your home town really near Preston?
I am from Burnley originally though my family is actually from Preston a generation before me.

This message is a reply to:
 Message 224 by lyndonashmore, posted 03-22-2005 3:15 AM lyndonashmore has not replied

Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 230 of 309 (193396)
03-22-2005 12:11 PM
Reply to: Message 227 by lyndonashmore
03-22-2005 8:56 AM


Re: Do electrons in a thin plasma act in unison? Yes they do!
Ah! Your back. You see you are not free to go off as you please, the force of gravity brought you back with an acceleration of 10 m/s^-2. Now these sole electrons, one metre apart in space, suffer an acceleration of 25 times that that you just encountered — and yet Sylas and Eta_Corinae say that we can ignore these effects and consider the electron free!
Do you believe them? Hogwash!
No you are pulling the hogwash! In particle physics accelerations like you are talking about are effectively zero. As I pointed out earlier an electron orbiting a proton at the Bohr radius is undergoing an acceleration of 10^23 m s^-2.
These electrons too are traveling at 100,000 m/s — just as they are in the plasma around the Sun. These electrons move in unison otherwise our computers won’t work. These electrons in our computer wires travel at about 0.1 mm/s far far below their thermal speeds. All that Sylas has proved above is that there is no way that your computer will work.
Either you are now lying for effect or you really are this dumb about physics? It's hard to tell.
What part of a LOW density about IG plasmas do you not get?
You cannot, IF YOU ARE HONEST, compare a IG plasma with n=1/m^3 with a metal with an electron density of say 10^23 m^3.
Don't you get it - a 23 orders of magnitude difference??????????????
In case Sylas wants to check the sums.
One nano volt across a wire ten metre long gives an electric field (E = V/d) of 10^-10 V/m.
Force on electron = eE = 1.6x10^-29N giving an acceleration of 17.6 m/s^2. Remember the force on our electrons in IG space 1m apart was 2.3x10^-28N giving an acceleration of 253 m/s^2.
AaaaaaaaaaaaaaaH!!!!!!!!!!!!!!!!
The Debye length in a metal is of the order of the 10^-12 m. Of course they behave in unison - BUT a plasma 10^23 times less dense when the Debye length jumps to a kilometer then you cannot.
Lyndon, in all seriousness you are a chap who has gotten hold of a bunch of formulae you don't fully understand and have just sat down with your calculator and cranked out some numbers without understanding where and when such formulae apply. What results from this is not physics, it's not groundbreaking, IT'S JUST WRONG!!!
PS
If you are so adamant in this then submit it to ApJ or MNRAS or Physics Letters or some such journal.
See what happens.
And don't scream they would be biased - after all Halton Arp and Geoff Burbidge still get stuff in there.

This message is a reply to:
 Message 227 by lyndonashmore, posted 03-22-2005 8:56 AM lyndonashmore has not replied

Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 231 of 309 (193399)
03-22-2005 12:13 PM
Reply to: Message 225 by Admin
03-22-2005 5:03 AM


Er
I called his model bullshit, not him personally. His model is bullshit and I think at times he has been disingenuous in this thread. He went into deflect mode and poison the Sylas well mode pretty early on.

This message is a reply to:
 Message 225 by Admin, posted 03-22-2005 5:03 AM Admin has not replied

lyndonashmore
Inactive Member


Message 232 of 309 (193443)
03-22-2005 2:34 PM


reply to simon and garfunkel
What we are forgetting here gentlemen, is that overall, plasma is neutral. For every horse there is a mare, for every man there is a woman and for every little electron there is a positive charge. Plasma is overall electrically neutral. Fact.
So whilst our little electrons are doing their whizzing about as per the laws of Sylas and Eta_Carinae there is another law at work. That of ‘things like to be electrically neutral’. Fact.
So if our should our little electron should whiz where it wants to whiz, the law of ‘things like to be electrically neutral’ comes in to play and says Hold on, I don’t care what Sylas and Eta_Carinae say, I’m not having any of this plus and minus stuff. You! Little electron, get back over here!
To put this in ‘Physics speak’ the paths of the electrons veer to keep the plasma electrically neutral.
This is why electrons in plasma oscillate — even in sparse plasma.
When an electron is displaced (by absorbing a photon), it moves forwards, say. The plasma was neutral. In dense plasma it will pass some positive charges which (being more massive) are reluctant to move. Now there are more electrons in front of it making this region negative and fewer electrons behind it making this region positive. Restoring forces bring it back but its momentum carries it past this point and restoring forces act but this time in the opposite direction. The electron performs SHM. In sparse plasma, like IG space, they don’t pass other electrons but space charges are set up and the same thing happens. If the plasma was neutral and the electron moves forwards then this ‘hole’ must now be overall positive — you get the idea.
In this way, the whole plasma can oscillate if resonance occurs. The frequency of oscillation of the plasma (bulk) is the same as that for the individual electrons. We know this frequency for IG space and it is less than 30Hz.
The oscillations are superposed on top of the random thermal motion of the electron — like the ac currents in our computers (which is working very well Sylas)
At least now Sylas and Eta_carinae (who are singing from the same song sheet) are talking about forces etc even though they say they are small. Before they denied that they existed.
This morning, Eta_Corinae was whinging saying that when the energy of the incoming photon was greater than the Kinetic energy of the electron, we should get inverse Compton effect. I agreed and pointed out that I had already done the sums on this. This is how the peak of the CMB curve came about. I show mathematically on my site that this watershed, where the energy of the incoming photon is equal to the average KE of the electrons of the plasma in IG space, produces the peak in the CMB curve.
Pretty good test of my theory. Theory passed it with flying colours.
What did Sylas and Eta_Corinae sing from their same songsheet?
Hello darkness my old friend.
Cheers Lyndon
PS Burnley eh, You can’t be all bad then.
(PS)^2 To publish in ApJ one has to pay to be published. Galilean Electrodynamics is free. Why should I publish in the ‘vanity press’?
(Actually that was unkind because I did send it to ApJ and the Editor was very kind and got someone to do a quick peer review. The points made were pertinent and helpful and I went away and sorted them out. No sarcastic comments from either of you two, but it is a much better paper because of it because from then on the sums worked out. On resubmitting it they decided not to accept. Fair enough.
As for the . MNRAS!)
Lyndon

Lyndon Ashmore - bringing cosmology back down to Earth!

Replies to this message:
 Message 233 by Eta_Carinae, posted 03-22-2005 3:06 PM lyndonashmore has replied
 Message 236 by Sylas, posted 03-22-2005 10:44 PM lyndonashmore has not replied

Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 233 of 309 (193449)
03-22-2005 3:06 PM
Reply to: Message 232 by lyndonashmore
03-22-2005 2:34 PM


Don't lie about what I said.
I might have said forces were negligible, which they are, but I didn't say they didn't exist.
By the way - you cannot neglect displacement current which is what you are doing.
The charge neutrality is lost because it is so diffuse.
THAT is why the fluid approx. CANNOT apply. The length scale of charge separation becomes large compared to the volume under discussion.
****LYNDON , please buy a textbook on astrophysical plasmas and save yourself all this heartache. You are applying the WRONG equations in the WRONG regime ****
**** I do not believe you submitted this to ApJ and got any feedback that was anything but scathing - I AM GOING TO CHECK THIS since I know the people there ****

This message is a reply to:
 Message 232 by lyndonashmore, posted 03-22-2005 2:34 PM lyndonashmore has replied

Replies to this message:
 Message 234 by lyndonashmore, posted 03-22-2005 3:24 PM Eta_Carinae has replied

lyndonashmore
Inactive Member


Message 234 of 309 (193453)
03-22-2005 3:24 PM
Reply to: Message 233 by Eta_Carinae
03-22-2005 3:06 PM


Re: Don't lie about what I said.
You are off again Eta.
Check away. When the world is saying that the universe is expanding at a rate of hr/m and didn't realise it until Ashmore told them, it is of interest to real scientists.
What is up with this board?
Why can we not have a pleasant, fun, intelligent discussion?
banter is good and enjoyable.
But this?
Check away and then come back and tell us what you found out.
We are ALL waiting
In fact, might I suggest that you do not come back until you can report on your findings?
Cheers,
Lyndon

Lyndon Ashmore - bringing cosmology back down to Earth!

This message is a reply to:
 Message 233 by Eta_Carinae, posted 03-22-2005 3:06 PM Eta_Carinae has replied

Replies to this message:
 Message 235 by Eta_Carinae, posted 03-22-2005 3:38 PM lyndonashmore has not replied

Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 235 of 309 (193459)
03-22-2005 3:38 PM
Reply to: Message 234 by lyndonashmore
03-22-2005 3:24 PM


Oh Boy!
Because you ahve ignored almost every point brought up as to why you cannot use the equations you are doing and that your coincidence/paradox is nothing but a unit choice game and when you interject the electron density it is then a game of pick a regime of the astrophysical plasmas out there.
***FINAL TIME ****
You cannot treat a diffuse plasma as anything but particle scattering events. PERIOD!!
You can whine about this BUT you would be laughed out of every astronomy & physics department in the world for using the equations you are using in the context you are applying them to.
Every treatment of diffuse astrophysical plasmas rests on the fact that it CANNOT be a macroscopic fluid because it is so diffuse. The displacement current cannot be neglected, the particles are NOT in thermal equlibrium because the Universe isn't old enough for them to get there.
WHY don't you write a letter to Don Osterbrock, Dopita & Sutherland and all the other authors of the standard astrophysical textbooks that they have it all wrong.
Also pen letters to the literally tens of thousands of authors of papers in the astrophysics and atmospheric physics and plasma physics and space physics communities who have written papers using equations you discard and that they should all along have been using the macroscopic fluid equations of magnetohydrodynaics?????????????
Please do this and see the response.
*********************************************
By the way, who at ApJ did you send it to?

This message is a reply to:
 Message 234 by lyndonashmore, posted 03-22-2005 3:24 PM lyndonashmore has not replied

Sylas
Member (Idle past 5250 days)
Posts: 766
From: Newcastle, Australia
Joined: 11-17-2002


Message 236 of 309 (193549)
03-22-2005 10:44 PM
Reply to: Message 232 by lyndonashmore
03-22-2005 2:34 PM


The scale of an electron
Some of Lyndon’s errors arise from failing to handle scale properly.
I’ll respond to this in two ways. The first is a simple units example, to help give a feel for what it means to move from one scale to another, aimed at about secondary level. The second is a more technical analysis for a plasma, which involves some more advanced level concepts, but mathematically still very simple.
What is it like to be an electron? (elementary level)
In physics we deal with very large and very small numbers, and systems that differ enormously in scale.
Our normal day to day intuitions work fine on the scale of meters and seconds. We can easily picture walking a kilometer, or handling a grape about a centimeter wide. But distances in the solar system, or in an atom, are outside our experience.
We do things minute by minute. A second is a pretty convenient time measure for us. An hour might be better; because we have problems thinking easily in times less than a second. We can plan a year in advance, or time rapid events in seconds. But time scales of a strobe light, or of millenia, are outside our normal experience.
In physics, we use different units to handle things at different scales, which can help intuitions. For example, small distances can be measured in Angstroms or microns; large distances in light years or MegaParsecs. Alternatively, we use normal units, but then we have to get used to very large or very small numbers. An Angstrom is 10-10 m, and a MegaParsec is about 3*1022 m.
If we were electrons, what units might we like to use?
Electrons are small. They would rather think of distances in Angstroms than in meters. This is still far bigger than an electron; so for an electron an Angstrom is a bit like a kilometer is for us. Electrons move pretty quickly, so they cover an awful lot of Angstroms in a second. They like to think in terms of femptoseconds. (10-15 seconds). A slow electron (corresponding to a kinetic energy of about room temperature) is moving at around 1 Angstrom per femptosecond, so these are units that match an electron’s experience rather better.
In a plasma, average electron speeds are around 5 Angstroms per femptosecond (at the surface of the Sun) up to hundreds of Angstroms per femptosecond or more (in the ionized IG medium).
What about forces on electrons? Lyndon Ashmore has noted that one electron at a distance of 1 meter from another electron experiences an acceleration of about 253 m/s2. He’s quite correct with the number; but fails to appreciate what that number means at the scale of an electron. Electrons would rather think in units closer to their own experience.
The acceleration on an electron from another electron one Angstrom away is 253 Angstoms/femptosecond2. (Yes, this is the same number, but the units are different and the electrons are much closer.)
But another electron a meter away is 10000000000 Angstroms away, and the resulting acceleration is 2.53*10-18 Angstroms/femptosecond^2. This is near enough to zero, as far as an electron is concerned.
As a thought experiment, Lyndon proposes we think about jumping on Earth. When we jump, we move at a few meters per second, and the escape velocity at Earth’s surface is 1.1 * 104 m/s. So for us, Earth holds us tightly.
In electron units, the escape velocity becomes 0.11 Angstroms per femptoscond. An electron can jump at a couple of Angstroms per femptosecond, so when an electron jumps it blasts off into space without any trouble at all Earth’s acceleration is just too small to hold it. The only thing that holds an electron is bumping into molecules of air along the way. Molecules are a big deal for electrons, and they can catch and hold it far better than Earth’s gravity can manage.
All of this is intended to help give an intuition for life at the scale of an electron. Ashmore’s analogies are presented at the wrong scale, and he does not calculate whether the forces and accelerations he describes can actually hold an electron. In thin plasma, an electron moves like a free particle; unlike electrons in glass which are tightly bound to the rigid crystal lattice.
Calculating the real effects (technical)
Analogies don’t suffice for a proper analysis of the photon electron interactions invoked in Ashmore’s tired light model. We need some actual calculations. For this, I’ll use SI units.
The question is whether electrons in a plasma can act as free particles, interacting with each other one by one in isolated interactions. Plasma in which the electrons are free particles, interacting one by one, is called good plasma. I’m using terminology from page 192 of Cosmology: The Origin and Evolution of Cosmic Structure, by P. Coles and F. Lucchin (John Wiley, 2002).
The scale at which the plasma can be considered as neutral unity is called the Debye radius. Below this scale it is isolated particles interacting with each other as individuals. If the Debye radius is much greater than the mean distance between particles, then we have a plasma in which thermal energy dominates over the energy of Coulomb interactions, and the particles interact with each other individually.
The Debye radius of a plasma is given by λD = sqrt(ε0kT/4πne2). Constants used are as follows:
kBoltzmann constant1.38*10-23 J/K
ε0Permittivity of free space8.854*10-12 C2/Jm
eElectron charge1.6*10-19 C
πpi3.14159

Variables, with sample values, are:
Temperature (room)T = 300 K
Temperature (cool plasma)T = 3000 K
Temperature (hot plasma, IG medium)T = 106 K (and more)
Electron density (IG medium)n = 0.5 m-3
The Debye radius for the IG medium at 106 K and density 0.5 m-3 is 2.76 * 104 m. Estimates of the IG medium are usually hotter, and less dense, so this is a low value for the Debye radius.
The Debye radius is more than four orders of magnitude larger that the mean distance between particles in the plasma, which means that the energy of Coulomb interactions with other electrons is much less than the thermal energy. That is; the electrons move in the plasma like free independent particles. They interact with other electrons on a one by one basis. Unified motions of the plasma, including plasma waves, only occur at a much larger scale, and give a negligible contribution to the motions of an individual particle. The plasma waves are only seen when you average over many billions of particles, and so Ashmore’s notion of individual electrons being in simple harmonic motion is another error.
Cheers -- Sylas
PS. Added in edit. I have corrected the value given originally for Debye radius. Previously it was given for density n = 0.25, which is 31 km. Now it is 27.6 km for n = 0.5. The Debye radius with n = 1 is about 20 km.
This message has been edited by Sylas, 03-23-2005 12:51 AM

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Replies to this message:
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Eta_Carinae
Member (Idle past 4365 days)
Posts: 547
From: US
Joined: 11-15-2003


Message 237 of 309 (193552)
03-22-2005 10:52 PM
Reply to: Message 236 by Sylas
03-22-2005 10:44 PM


Hey I was saying that all along.
Cannot use magnetohydrodynamics when the fliud approx. breaks down when the mean free path gets large. i.e. when the Debye length is 13 orders of magnitude greater than the incoming photons wavelength.

This message is a reply to:
 Message 236 by Sylas, posted 03-22-2005 10:44 PM Sylas has not replied

NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 238 of 309 (193553)
03-22-2005 10:54 PM
Reply to: Message 236 by Sylas
03-22-2005 10:44 PM


Re: The scale of an electron
Great post! Thanks Sylas.
I love that kind of stuff. (can you spell N e r d ? )

This message is a reply to:
 Message 236 by Sylas, posted 03-22-2005 10:44 PM Sylas has not replied

lyndonashmore
Inactive Member


Message 239 of 309 (193633)
03-23-2005 6:50 AM
Reply to: Message 228 by Sylas
03-22-2005 9:47 AM


Re: Do electrons in a thin plasma act in unison? Yes they do!
Nah! Not having this. You see Silas you haven't done your sums. Any Child in Kindergarten knows that have to do your sums first. You see, when you say:
quote:
To be more precise, the potential energy of two electrons at separation r is e2/40r, which at one meter is 2.3*10^-28 J. The kinetic energy of a particle at temperature T is 3*k*T/2, which in a cool plasma is about 2*10-20 J or so. The effect of the electron is thus about eight orders of magnitude too small.
Now I gave an example of a voltage of one nanovolt (10^-9V) across a wire 10m long still produced a current event though the wire was at room temp. Sylas told us that at room temp the average KE of the electrons is 2x10^-20J. Well in our wire, a voltage of one nanovolt means that every coulomb that travels from one end to the other gains 1x10^-9 Joule of energy. Our little electron has 1.6x10^-19 Coulombs, so it gains 1.6x10^-28Joule of energy electrically. This is less than the potential energy of our two electrons one metre apart in space and he ridicules this. You see it is eight orders of magnitude too small too. So what Sylas is still proving is that your computer and all sorts of other things cannot work — but they do! Sylas is wrong.
He also goes on about the time of interaction between our two electrons, but this does not apply here cos Eta_Corinae and I were discussing whether the forces were negligible. If one includes time for the interaction then you have to look at what happens when our electron leaves the field of one charge and enters another. In fact, if you bring dynamics into it the forces acting on our electron are zero at equilibrium separation and increase as it is displaced — as I have been saying all along!This is why you get oscillations superposed on top of their thermal motion.
Nope, as I said, it wasn’t a good post at all. You see you have to do your sums first otherwise you end up with egg on your face.

Lyndon Ashmore - bringing cosmology back down to Earth!

This message is a reply to:
 Message 228 by Sylas, posted 03-22-2005 9:47 AM Sylas has replied

Replies to this message:
 Message 240 by RAZD, posted 03-23-2005 7:52 AM lyndonashmore has replied
 Message 243 by Eta_Carinae, posted 03-23-2005 12:24 PM lyndonashmore has not replied
 Message 247 by Sylas, posted 03-23-2005 4:16 PM lyndonashmore has replied

RAZD
Member (Idle past 1395 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 240 of 309 (193642)
03-23-2005 7:52 AM
Reply to: Message 239 by lyndonashmore
03-23-2005 6:50 AM


Re: Do electrons in a thin plasma act in unison? Yes they do! not.
lyndonashmore writes:
If one includes time for the interaction then you have to look at what happens when our electron leaves the field of one charge and enters another.
where it gets accelerated towards the next electron (while it is accelerated towards our specific electron) until they pass their nearest point of approach when the acceleration values slow them back down ... and you have the electron adjusting it's {path\speed\vector} in speed and direction {forwards & backwards}, {up and down} and {side to side} based on the {net sum of all these interactions with even the most distant electrons that hardly register a calculatable acceleration} ... but there is no net stopping force here.
ashmore also assumes a static field of electrons rather than a field where each electron is busily pursuing it's own career regardless of the others. they have a variety of speeds and energies (which brings up the question of how you can distinguish between an electron accelerated by a photon ATL interaction and one with that same energy without the interaction), so the electron is just as likely to be pulled faster by the nearest neighbor as it is to be pulled slower.
like I said before: it depends on constantly losing energy for this scenario to work: other electrons need to cause a net braking force (they don't) and then they need to be able to lose their energy that they gained in the braking action to be reset for the next photon.
think of a high speed small rock whizzing through the solar system at 4 times the speed needed to escape the gravity well: it's path will be altered but it will not be captured. regardless of whether your computer is on your desk or in your lap or how high you can jump.
This message has been edited by RAZD, 03*23*2005 07:54 AM

we are limited in our ability to understand
by our ability to understand
RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

This message is a reply to:
 Message 239 by lyndonashmore, posted 03-23-2005 6:50 AM lyndonashmore has replied

Replies to this message:
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