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Post by abacus9900 on Feb 15, 2011 19:17:30 GMT 1
She does tend to use the 'B' word a lot.
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Post by speakertoanimals on Feb 15, 2011 21:35:52 GMT 1
O stop being such a total idiot!
YOU claimed that changing the density changes the frequency (it doesn't).
I was never for one minute saying that dropping a photon down a gracvity well didn't change the frequency, or that emitting it from a moving source didn't change the frequency, or that letting it travel through an expanding universe didn't change the frequency.
But what DOESN'T change the frequency, whether it be light or sound waves, is changing the DENSITY of the 'medium', which was your idiotic idea!
Exactly how frequency changes with distance is the hubble law, and if you knew anything at all about it, you would never have started this thread...............
So, let's go back again to your claim -- that sound changes FREQUENCY if it travels through air of a different density. Do you still claim that?
I don't agree with you, so stop claiming I did! Some things can make frequency vary, but bloody DENSITY isn't one of them!
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Post by carnyx on Feb 16, 2011 0:02:07 GMT 1
STA! really! Just LOOK at the OP!
Here you are in full cry:
But here is Hubble;
But how do we KNOW these distances other than by reference to this redshift measurement? And because we only have the one point of view from Earth, we cannot really say!
However, we do know that permeability (mu) and permittivity (epsilon) govern the frequency, and the speed of propagation, of EM waves;
- EM speed (of light c) is proportional to 1/root (mu x epsilon)
- EM frequency is proportion to 1/root (mu x epsilon)
These properties exist in space, and they are affected by magnetic and electrical fields.
So, given the fantastic distances to galaxies, it may well be that EM waves encounter varying values of permittivity and permeability, which could then cause changes in frequency and velocity.
So, the observed redshift may be a function of the net change in these characteristics, rather than the relative velocity of the original emitter.
As this line of thinking must be obvious and thus unoriginal, and so is likely to be raised by a good proportion of student undergraduates ... it is most likely that an academic physicist with an interst in cosmology, with some knowledge of electromagnetic phenomenon, ought to have the refutation to hand, as it were.
(Or, other colleagues and even the odd post-grad could have the answer...)
So, how about it, STA?
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Post by speakertoanimals on Feb 16, 2011 2:47:40 GMT 1
1. The Hubble shift is usually described in terms of the doppler shift, on popular websites, but the actual cause is expansion, not recession. It is used because explaining redshift in terms of space expanding requires an extra explanation, whereas Doppler is familiar to most people from sound.
2. How do you think Hubble discovered the law that bears his name?Because he measured the redshift for objects whose distance he was able to compute using OTHER methods.
3. Other objects? they experience redshifts of the light they receive as well. Imagine light form a very distant object passing through a cloud of hydrogen. The hydrogen absorbs light at the Lyman-alpha line, and where that line is from the point of view of the cloud is in exactly the right place. Now the light continues and meets another cloud, closer to us. From the point of view of the second cloud, the absorption line of the first cloud is redshifted, hence the Lyman-alpha absorption line for the second cloud is at a DIFFERENT point in the spectrum. And so on -- each cloud sees previous Lyman alpha absorption lines as redshifted, hence in a different place to where that cloud will absorb.
Hence when the final light gets to us, we see a whole bunch of Lyman alpha absorption lines, corresponding the to difference in redshift between the source and each individual cloud. The fact that they are in different places says where Lyman alpha Is depends on your point of view -- the clouds hence obviously see light redshifted, and by different amounts to us. Lyman alpha forest, there are so many lines!
WRONG, wrong, wrong, wrong! They determine the SPEED, but NOT the frequency! The frequency of light stays the same, even though when travelling through a medium (like glass) the speed changes, and the wavelength changes, but NOT the frequency!
The cars and walkers and batons example shows that, and any idiot ought to be able to follow it and see that frequency will be fixed, even if speed and wavelength vary.
It's just plain wrong! Only raised by the really dim ones, who can't get it through their thick skulls that refractive index alters speed and wavelength, but NOT frequency!
And god knows why you think electric and magnetic fields are going to effect the refractive index of nearly empty space...........
And even if they did, it would not effect the frequency. I suggest you read AGAIN the cars and walkers with batons example, and see if you can finally get the BASICS of wave propagation into your head, and stop claiming that you have some up with some simple question that no one can answer -- it has been answered, just you seem to be too dim to understand the answer.
WHY do you think refractive index changes the frequency? You kep saying it does, I have explained why it can't, yet you keep on insisting..................
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Post by robinpike on Feb 16, 2011 8:52:40 GMT 1
STA, there is one thing that I'm not quite clear on about the expansion of space.
My understanding is this: We don't see expansion of space locally because, although space locally is expanding, gravity has a greater effect and keeps the earth the same distance from the sun, and gravity keeps the stars in the milky way the same distance from the center of the galaxy - the effect of gravity not being influenced by whether space locally is 'thinner' now than it was previously.
How ever light is 'part of space', therefore the reason why light that is travelling through expanding space is red shifted, is because the light is part of space and gets stretched too, giving it a lower frequency.
So a couple of questions:
1) If we had some perfect reflectors that enabled us to reflect some light in a circle of travel continously without absorbing any of them, would we - if we observed them for long enough - notice the photons slowly become red shifted?
2) Light is continually being emitted and absorbed here on earth, for example infra-red photons at the center of the earth in the form of heat. So each time an infra-red photon is emitted and absorbed at the center of the earth, while it is travelling that very small time through space - the space itself is undergoing expansion (albeit very slowly) and therefore has by a very small amount also caused the light to be red-shifted. So, over millions of years, will this not effectively remove energy from the center of the earth?
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Post by carnyx on Feb 16, 2011 9:45:23 GMT 1
@sta#48
For EM waves;
F = 1/root( (epsilon + Cepsilon) x (mu +Lmu) )
C= 1/root (epsilon x mu)
Discuss.
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Post by speakertoanimals on Feb 16, 2011 14:44:32 GMT 1
Discuss what? I suggest you stick to trying to understand: v = f lambda, because so far, you AIN'T GOT IT. I ask you again, WHY are you still convinced that if refractive index changes, so does frequency? You might like to look at this educational resource from the Rensselaer Polytechnic Institute (Rensselaer is America’s oldest technological research university): www.rpi.edu/dept/phys/Dept2/APPhys1/optics/optics/node7.htmlwhich says that: So there we have it -- wavelength and speed change, but NOT frequency................................
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Post by carnyx on Feb 16, 2011 17:53:51 GMT 1
STA
You are still hung-up on the analogy rather that the substantive proposition.
I agreed back in #34 that the sound-in-air analogy broke down, because in a gas the density and pressure are in lockstep ... and for the more subtle reason that sound waves in a medium have an inertial property, i.e. we are dealing with the movement of mass, and so conservation of momentum will have a part to play in keeping the frequency constant.
But EM waves do not travel in a mass medium, and so do not have this inertial quality. If follows that the frequency of EM waves is not constrained by inertial considerations, and by other mass-related properties of the medium, such as temperature, pressure, density, elasticity, local speed of sound.
But for EM waves traversing the cosmos we know that there is such a thing as the permittivity and permeability of free space, which are inductance per meter and capacitance per meter respectively.
We know that the product of capacitance and inductance govern frequency, as any electrical engineer will tell you . l And according to Maxwell, the product of capacitance per metre and inductance per meter of free space .... govern the speed of propagation of EM waves in space!
Now IF in deep space the permittivity OR permeability values are not exactly uniform, we ough to see a change in frequency as the EM waves pass through, AND speed cahnges as welll!
Sadly we have no means of directly measuring if the effective inductance OR capacitance of space is constant over these huge distances, or indeed any way of measuring any changes in speed over the distances either .... but it would be interesting to do a few back-sums to work out by how much they would need to be changed, to account for the Red Shift phenomenon
If there are any electrical engineers out there .. feel free to comment! ...
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Post by speakertoanimals on Feb 16, 2011 18:44:33 GMT 1
Nope -- you have misunderstood the WHY of frequency being constant, go back to my cars and walkers example.
You were the one who kept claiming that speed changes with density (it doesn't for sound, yet I fail to see an actual admission that you were totally incorrect!), so don't try and castigate me for picking on that. Because you WERE reasoning from that, and if where you started from was false, then we can discard anything that comes after.
It all boils down to -- PERHAPS there is some magic, unspecificed property of space between us and distant galaxies that can shift frequency.............wibble, wibble perhaps em fields do it.............
And that's IT, as far as your supposed great idea goes! Except there WASN'T an idea there to be had, people already tried other explanations, and they couldn't get apparent recession speed going as distance (so, WHY should it go so nicely if its all a fairly accidental, local property that does the shifting?). Whereas for expansion, the point is that it is NOT local, it involves the whole universe, which is why we get the SAME redshift versus distance patternm, wherever we look. It always goes like that, because that is what the universe as a whole is doing.
Another TERRIBLE analogy, in that in the circuit case, we are talking about tuned circuits and resonance.
You are also confusing electric permitiviity with capacitance. It is related to the force between unit charges a unit distance apart, NOT capacitance. It hence comes into calculations for the capacitance of parallel plates, because the force needed to move a charge from one to the other is related to the voltage, and the force is related to the permitivitty.
Hence the permitivitty is talking about forces, the fact that it turns up in the capacitance of a pair of paralle plates is coincidental. You don't have a capacitor without the plates! Which aren't a vacuum.........
Back to capacitance -- the force between charges obviously depends on how easy it is for the electric field to reach out across the gap between them. Hence it is no surprise that it relates to travelling electric and magnetic fields, with NO free charges or anything else lying about.
And as regards circuits -- trying to use them to get all surprised about Maxwells equations is nonsense, because the laws that govern cuircuits are just a special consequence of Maxwells equations.
Except they're NOT uniform in actual materials like glass, we don;t see a change of frequency there, so there is no logical or even sane reason for thinking we should see a change when we are talking about much smaller changes in almost vacuum. It is total and utter nonsense, whichever way you come at it!
After all, goes against all logic if BIG changes in permitivitty and permeability produce NO change in frequency, yet you somehow claim that miniscule changes will............................
I expect a final admission that you were wrong when you kept claiming I was wrong as regards density and frequency.....................
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Post by Progenitor A on Feb 16, 2011 18:47:33 GMT 1
We do know that em waves (or particles) are affected by gravitational forces. It can be shown that a light wave (or stream of particles) coming to us from a distant galaxy will, on average experience a shift toward the red end of the spectrum.
As STA has so kindly advised us , gravitational fields do change the frequency of light (in fact I would propose that they do not, but for the sake of this argument will assume that they do) then the sum of gravitational fields passed through during the progress of light from a distant galaxy toward us, may account in a not wholly insignificant measure toward the observed red shift
It is self-evident that the furhter away a galaxy or star, the more pronounced the red shift will be due to the encountered gravitational fields during its passage
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Post by speakertoanimals on Feb 16, 2011 18:56:33 GMT 1
Repeated bollocks from earlier in the thread!
When light enters a gravity well, it gets blueshifted, but it gets redshifted back again when it climbs out to get to us. Hence no net effect, unless (as I said several times before), we are somehow uphill wrt the entire rest of the universe.
Stop these silly games NM, its obvious to everyone that repeating points that have already been explained is just you messing about.
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Post by carnyx on Feb 16, 2011 22:34:46 GMT 1
STA
I think you don't have it right with regard to the permittivity, or permeability, of free space.
For other posters, Permeability (mu)is the measure of resistance encountered when forming a magnetic field, and Permittivity (epsilon) is the measure of resistance encountered when forming an electric field.
They both have positive values, even in space;
Maxwell's famous equation C= root(1/Mu x Epsilon) says it all.
He is telling us that the permittivity and permeability of space itself sets the limit on the speed of light.
And, if we wanted to send information faster than the speed of light, we just have to drop the permeability OR permittivity values in our channel off communication, to be less than the free-space values.
Of course if they could be zero, or one could be negative and so they cancelled each other out .... then the speed of transmission would be infinitely fast.
But to the matter in hand, IF the permeability OR the permittivity in a patch of free space were to be changed in any way, the local speed of light would be changed.
And, this differential change woud have the effect of making this patch of space anisotropic, which opens the possibility of frequency change via Raman scattering. As we are dealing with stupendous distances, Raman scattering may be worth looking at as a possible candidate for an alternative explanation for red shift.
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Post by speakertoanimals on Feb 16, 2011 23:01:15 GMT 1
Which is actually totally meaningless, and a mere consquence of our units system!
A sensible arrangement would be -- light fastest in a vacuum, put stuff there and it gets slower, hence we could call lightspeed in a vacuum one, and related everything else to that.
Saying -- if they could be made zero, we could have faster-than light travel, if just a daft tautology. Because obviously, if there was no 'resistance' to growth of a field, it means that changes in that field propogate at infinite speed, which means light propagates at infinite speed.
Trying to change the sign of permitivitty would just be saying that like charges would attract, rather than repel, which would lead to electrostatic forces being more like gravity. Would also mean that unlike charges would repel, and heigh-ho, all atoms would fall apart as all electrons were sent to the great negative charge dump at one side of the universe, whilst all the protons ran off to the great positive charge dump at the other side.
Hence all these statements about what if we could change them are nonsense.
which opens the possibility of frequency change via Raman scattering.
Except Raman scattering isn just what happens when light scatters inelastically off MATTER. And scattering would have the teensy problem that the scattered light would no longer be travelling from the source to us, hence we couldn't SEE it.
So, bollocks suggestion number 19 million after a desperate google search for some process involving light and frequency change.
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Post by carnyx on Feb 16, 2011 23:29:04 GMT 1
STA
...Permeability of free space = 0?
"In SI units, permeability is measured in the henry per metre (H m−1), or newton per ampere squared (N A−2). The permeability constant (μ0), also known as the magnetic constant or the permeability of free space, is a measure of the amount of resistance encountered when forming a magnetic field in a classical vacuum. The magnetic constant has the exact (defined)[1] value µ0 = 4π×10−7 ≈ 1.2566370614...×10−6 H·m−1 or N·A−2)."
Maxwell says the speed of light = root (1/permeability of free space x permittivity of free space)
But STA says Maxwell is talking bollocks ..... so we can add him to the list, too . Then we have the obvious ignorance of the properties of materials with a negative refractive index.
And that babbling about Raman?
STA is NO physicist .....
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Post by speakertoanimals on Feb 17, 2011 13:41:45 GMT 1
Where do you think I said that?
Earlier I was talking about relative permeability -- a material versus a vacuum, and then you take
ratio = 1 + X,
where X is then zero by definition for a vacuum.
Nope, you're the one who was trying to claim that Maxwell and lightspeed was at variance with tuned circuits.................
Okay, you can get weird stuff going on in specific carefully designed materials - but we were talking about out in space, NOT in such materials. So whilst you might be able to get really freaky stuff going on in some specific material over some small volume, this is not the behaviour across intergalactic space that you were proposing -- which would cause the weird problems I mentioned.
So, take some copper conducting elements an arrange then carefully in a special array, and you can get weird effects with microwaves, but this is hardly the universal effect that we would need to explain redshift, and witihout all the fiddly bits of copper anyway, just (almost) empty space.
You were the one who brought it up, as a possible explanation for red-shift. Except even an idiot should be able to see that the fact that we can SEE distinct images of distant objects means that the light from those objects has not suffered any significant RANDOM deviation from the shortest-path from the object to us (I say random because gravitational lensing is a non-random, systematic deviation of the light). Whereas scattering, as the name implies, is a random process. Hence any light that was scattered would be scattered out of the path of the very light that forms the image, hence we see yet again that your suggestions are total bollocks.
AsI said, looks like you just googled to try and find SOME physical process that changed frequency, and Raman scattering was the nonsense you came out with.
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