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Post by carnyx on Jan 17, 2011 17:01:37 GMT 1
The concept that EM waves (including light) can self-propagate in a complete void, has always bothered me.
However it is possible to conceive of a 'patch' in an electrical, magnetic (or even a gravitational) field, that has no gradient in any direction, yet it is definitely part of the field. And if so, there is no 'void' anywhere in the universe, and EM waves therefore be described as 'ripples' in the universal EM field.
But then, how could we detect these patches of very low gradient in the EM fields? Do we say instead, that they are not there? And EM waves are self-propagating in a complete void?
Is this belief reinforced by the idea that Maxwell's equations work in the absence of such a 'steady-state' field?
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Post by speakertoanimals on Jan 17, 2011 17:35:17 GMT 1
What tosh!
A 'patch of low gradient' is just a CONSTANT electric field, which is perfecty detectable in that a constant electric field pulls on a charged particle.
What I think the poster meant (if they had understood enough to mean anything), is a region of constant electric potential, where we would have ZERO field.
Well, whoop-de-do, that's just the interior of a faraday cage, a thing experimentalists use all the time to exclude electric and magnetic fields from a region (apart from light, but lets put it in the dark as well!).
In fact, regions of zero field (but non-zero potential) ARE detectable in quantum terms (the Aharonov-Bohm effect)....................
Shame then that all experiments to find the medium have FAILED. And in quantum terms, the fact that em waves can pass through a vacuum are no more mysterious than the fact that electrons can....................
Get over it, or ignore all physics for the last century, you're pretty much flogging a dead horse with this one......................
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Post by carnyx on Jan 17, 2011 19:14:00 GMT 1
STA, yet more tantrums getting in the way?
Let us take two parallel plates, both positively charged. What is the strength of the electrical field at a point in the middle, equidistant from the plates? Is it zero?
In other words, would a particle at that point feel a pull?
Take two bar magnets with their north poles facing each other. What is the strength of the magnetic field at the centerpoint?
Or, are you saying that the definition of a 'field' is the derivative of the property as opposed to the static value of the property at any point?
E.g. is it true that your 'electric field' is a map of the rate-of-change of charge per unit of length, rather than the absolute charge at any point?
( PS re tantrums, you would probably have been one of those who wanted to set fire to Galileo before he was declared 'right'... and now would like to burn his bones, because he is now 'wrong')
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Post by Progenitor A on Jan 17, 2011 19:26:17 GMT 1
The concept that EM waves (including light) can self-propagate in a complete void, has always bothered me. I must say it has never particularly bothered me, but then I have never really though about it. Perhaps the easiest way (for me) to think about it is high-energy waveforms bombing their way through space(such as X-rays, Beta rays, Gamma rays). These are packets of em energy and not having a vacuum actually impedes their progress. Indeed withot a vacuum there is a high probability of the packet losing its kinetic enetgy in a collision, so the best medium for ir (to retain its kinetic energ) is surely a vacuum? Same with an electrical/magnetic wave around a current carrying wire - what is to stop the wave moving away from the wire? If there is a medium (an assembly of things) then that actually impedes the spreading, so a vacuum is the best medium: However it is possible to conceive of a 'patch' in an electrical, magnetic (or even a gravitational) field, that has no gradient in any direction, yet it is definitely part of the field. This, as you are aware, is commonplace. The superposition of em waves of the same frequency and opposing phase produce a 'field of zero gradient - the equivalent of a null field, that is definitely a part of the field. Haven't a clue how you get a 'null' gravitational field though (no-one does) And if so, there is no 'void' anywhere in the universe, and EM waves therefore be described as 'ripples' in the universal EM field. Well yes, anywhere that has a 'null' field could be regarded as simply the superposition of anti-phase waves of the same frequency (or frequencies). And note that if two superimposed waves are anti-phase and very close in frequency, you will get your large 'patch' of zeo-field gradually from the edges building up to a double-peak em field. But then, how could we detect these patches of very low gradient in the EM fields? The detection of null fields, as you are aware, is no problem - the problem is, is it because we have superposition of same frequency anti-phase waves, or simply nothing at all? Do we say instead, that they are not there? And EM waves are self-propagating in a complete void? Quite Is this belief reinforced by the idea that Maxwell's equations work in the absence of such a 'steady-state' field? Indeed that is true of Maxwell - exactly nothing is required As his equations have been used quite a bit I am inclined not to argue with that conclusion |
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Post by Progenitor A on Jan 17, 2011 19:44:56 GMT 1
Let us take two parallel plates, both positively charged. What is the strength of the electrical field at a point in the middle, equidistant from the plates? Is it zero? In other words, would a particle at that point feel a pull? Exactly Take two bar magnets with their north poles facing each other. What is the strength of the magnetic field at the centerpoint? Precisely Or, are you saying that the definition of a 'field' is the derivative of the property as opposed to the static value of the property at any point? Bravo! E.g. is it true that your 'electric field' is a map of the rate-of-change of charge per unit of length, rather than the absolute charge at any point? Again! |
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Post by carnyx on Jan 17, 2011 20:14:37 GMT 1
NM, I like the idea of a Faraday Cage for Gravity. I speculate about a small cave at the centre of the earth. Would one be weightless? And what is the strength of STA's 'gravitational field' here?
(And how will her clock run .... compared to one on the surface?)
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Post by speakertoanimals on Jan 17, 2011 21:02:53 GMT 1
I think you have no idea what electric field is actually defined to be! It certainly has NOTHING to do with absolute CHARGE at a point!
Electric field (like gravitational field) is defined in terms of FORCE.
So, a unit strength gravitational field is one that produces a force of one unit (usually one newton) on a mass of one unit (usually taken to be one kilogram).
Whereas a unit strength electric field is one that produces a force of one unit (again usually newtons) on a charge of size one unit (usually 1 coulomb, which is enormous in physical terms!).
Bugger all to do with rate=of change of charge per unit length, which I suspect is your feeble atempt at the volts per metre description, which is the electric potential.
In short, you're trying to do exactly what you did for gravitational field, and confuse the potential with the field itself, which is utter bollocks. And you did even worse in this case, because rather than even talking about volts per meter, you wittered on about CHARGE instead. Dearie me, people will think you have no idea what you are talking about......................................
And naymissus has no idea either.
Potential isn't field strength and never was, so stop playing silly buggers and confusing people just on the off-chance that you might convince yourselves that you have found me out in an inaccuracy.
Stupid statement number one. A field defined in terms of a force (proper definition) has a value AND a direction. It MAY be expressible as the gradient of a potential, but need not be (conservative forces and all that). The potential isn't the same as the field.
For magnetic fields, your attempted argument falls down even worse, in that the magnetic potential is a vector anyway. So, your pretence that (static) fields can be understood in terms of scalar potentials (or that the scalar potential is what is meant by the field), fails yet again.
If I am midway between two positively charged plates, the force is zero on the simple grounds of symmetry. Ditto two magnets.
Have you never heard of cavorite? H G Wells covered that one, as well as practical problems involved in the manufacture of such a substance. I think HG knew more about actual fields than you though, so maybe you should start with Cavors description of fields, you might learn something...........................
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Post by eamonnshute on Jan 17, 2011 21:11:14 GMT 1
NM, I like the idea of a Faraday Cage for Gravity. If you could shield gravity you could produce a perpetual motion machine. If you had a wheel on a horizontal axis and shielded one side from gravity then the gravity acting on the other side would cause it to rotate for ever. Since this would violate the law of conservation of energy such a shield is impossible. |
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Post by carnyx on Jan 18, 2011 0:20:08 GMT 1
STA, you seem to have blown a gasket with this farrago of contradictions ..
I'll just quote two of your statements;
and now this one;
Therefore, at these midway points, does the field exist? And how do we measure it?
Then I'd like to ask you about the analogous case of a gravity field.
In a small cave at the center of the earth, does the gravitational field exist? If so, how do we measure it ?
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Post by Progenitor A on Jan 18, 2011 9:53:00 GMT 1
Carnyx
I think that it is disgraceful that you, after all these years running your own cutting edge electronics design company , have no idea what an electric field is!
I bet, after all your experience that you thought an electric field was generated by charges (at a point or otherwise)!
Shame in you.
Were you confidence -tricking your customers you bastard!
See! Fancy not knowing that! What on earth was going on during all those years of College and industrial work!
Well, I bet that you thought that vm-1 was the rate of change of potential over distance didn't you (either the average or derivative)?
So did I actually - i had no idea that it was simply the electric potential!
Good job she is here isn't it? There are people like me not knowing that potential (unit V) = potential gradient (dv/ds)! In other words whenever we measure the potential we know the potential gradient! Remarkable!
How did we manage?
Was it you or me?
Doesn't matter one supposes
Well you certainly deserve chastisement here! I mean she would never confuse the potential gradient dv/ds with the potential V such as in the equation V=dv/ds, would she?
Oh! Just a minute! She has just done that hasn't she? It must be you and I that are getting confused!
Trouble is with you and I, is that we think that a potential V and potential gradient dv/ds are alternative measurements of the same field and that one can be derived from the other. That's where the likes of inferiors like you and me go wrong!
Wow! And there was you and me thinking that electric potential V was just one measurement of an electric field, and dv/ds another measurement of the same field! Who'd have thought there were two fields depending on how we measure it!!
Am I glad I came here!
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Post by Progenitor A on Jan 18, 2011 10:11:33 GMT 1
NM, I like the idea of a Faraday Cage for Gravity. If you could shield gravity you could produce a perpetual motion machine. If you had a wheel on a horizontal axis and shielded one side from gravity then the gravity acting on the other side would cause it to rotate for ever. Since this would violate the law of conservation of energy such a shield is impossible. You will have to expamd upon this if I am to understand what you mean. Why would the wheel rotate? As far as shielding a gravitational field is concerned, imagine a spherical body with the same mass as the earth, except that the mass is concentrated into a thin shell with the remainder of the interior of the sphere being empty space. On the outside surface of the sphere, a man would feel the same gravitational attraction as on the surface of the earth, but inside the sphere there would be zero gravity and he would just float about. |
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Post by eamonnshute on Jan 18, 2011 10:36:43 GMT 1
You will have to expamd upon this if I am to understand what you mean. Why would the wheel rotate? Because gravity would pull down on one side of the wheel but not the other. The gravity from the shell would indeed be zero on the inside, but you would still feel the gravity from other objects outside the shell, so it is not shielding. |
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Post by Progenitor A on Jan 18, 2011 11:25:15 GMT 1
You will have to expamd upon this if I am to understand what you mean. Why would the wheel rotate? Because gravity would pull down on one side of the wheel but not the other. But on the side of the wheel that did experience gravity, gravity would act uniformly to the front and rear, Why would it rotate? Yes I agree that the interior is not shielded from gravity from other objects but it is certainly a null field of its own gravity - the gravity inside cancels out |
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Post by eamonnshute on Jan 18, 2011 11:39:22 GMT 1
But on the side of the wheel that did experience gravity, gravity would act uniformly to the front and rear, Why would it rotate? Imagine you are looking along the (horizontal) axis of the wheel, and the part of the wheel to the right of the axis is shielded from gravity. The left side of the wheel is being pulled by gravity, so it will rotate anti-clockwise. |
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Post by carnyx on Jan 18, 2011 12:44:41 GMT 1
I should like to pursue the idea of a force-field ( electric, magnetic, or gravitational) that exists yet cannot be detected. It seems that, as such fields are detectable only if the force has a direction i.e. it is a vector quantity. But say in the equidistand points between charged plates there is no direction; hence no resultant vector .... It seems that such 'flat' fields can exist undetected. However, a local disturbance of this flat field will produce local gradients, which can be detected. And we could say that such disturbances will propagate across this field.
So it may well be that EM radiation is actually a propagating sympathetic disturbance in the universal electric, and magnetic, force-fields, and not in 'nothing' .....
It follows that space is not 'empty' at all.
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