LHC@home

Geoffrey Voeth asked

is it possible to stretch a photons wavelength so that it becomes a DC kind of value and if so how would that be possible ?

No, in the redshift the wavelength is multiplied by a finite number and the frequency divded by a finite number. To get DC the wavelength would be infinite and the frequency zero.

That red shift of distant galaxies might not simply be a doppler shift it might also be some sort of decay at work ??

The cosmological red shift may not be caused by motion but by changes in the geometry of space time. For example in some theories the distant galaxiy clusters are not moving away, but instead there is extra space time being squoze in in between. The redshift still happens but whether you choose to call it Doppler or not is more a question of terminolgy than of physics.

This point is vital in the so called inflationary stage of the universe's growth, where the most popular models of the early universe suppose that the 'expansion' was faster than light. As the material objects cannot possibly be moving faster than light, what is meant is that more than 3*10^8 metres of distance was being created every second and squoze in between the existing particles.

Given enough time and space at what point would the red shift turn into a DC value ?

No, if you still receive any signal at all it is still oscillating although slowly. At the exact point where the object is apparently receding at the speed of light (due to new space being created, not motion) the formula looks like it predicts a DC signal, but that is exactly at the cut-off where the light never gets to you anyway.

It is just as well, Maxwell's eqns forbid a DC electromag signal proagating. One of the things that led Einstein to his theories of relativity was when he started to wonder how to keep Maxwell's eqns valid if you are running along beside the crest of a light wave - you'd expect to see a stationary crest, but Maxwell says you never see that.

But good questions. If you'd asked them 101 years earlier you might have beaten our Albert to the publisher... ;-)

River~~

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My knowledge of Physics does not go past Physics 111/112 so the questions I ask probably do seem silly to yall, but light has been interesting to me since I first learned intelligence could be relayed through what seems to be nothingness. One idea I can not get out of my head is that a light wave oscillates between the E field and B field so that it does not exist as both fields simultaneously sort of like the E field represents the potential energy and the B field represents the kinetic similar to what happens in a pendulum.
If this be true then is it possible to intercept the wave when it is only a B field or only an E field ??? Is it possible to intercept the wave when it crosses zero so you see nothing at all ???
When light is polarized which field is being stopped the E or B ???

Just some questions for those more "in tune" with reality.

Thanks;

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My knowledge of Physics does not go past Physics 111/112 so the questions I ask probably do seem silly to yall,

No. Any questions that echo the ones Maxwell, Einstein, and Hertz were asking ~100 years ago cannot be described as silly. And if I know the answers it is not because I worked them out for myself but because I had the advantage of standing on the shoulders of these giants as Newton put it

but light has been interesting to me since I first learned intelligence could be relayed through what seems to be nothingness. One idea I can not get out of my head is that a light wave oscillates between the E field and B field so that it does not exist as both fields simultaneously sort of like the E field represents the potential energy and the B field represents the kinetic similar to what happens in a pendulum.

I thought that till I got to my first undergrad Electromag course. It would follow the behaviour of most waves we know, like a water wave where the up and down motion is max at the midpoint of the displacement, and vice versa. We can represent one as a sine wave and the other as a cosine.

In fact, light is different.

edit: in fact in a standing wave your idea turns out to be true, see next posting. This posting assumes throughout that we are thinking of a wave propagating energy through free space.

For a propagating wave, the E and B fields max out at the same time and space, and cross zero at the same time and space. We can represent both components as sine waves.

There is another important difference: the energy being transferred by any part of the wave is proportional to E x B, and is not carried separately by either E or B. We might crudely consider either E or B to take the place of the displacement in a water wave. Because it does not matter which we choose, by convention engineers and scientists usually consider the E wave, knowing that the B wave is everywhere proportional to it (in a wave in free space at least).

The quantity that takes the place of the up and down motion in a water wave is "simply" the time derivative of the E field (or of the B field) and it does not have a separate symbol or name. It would be written as dE/dt, but more correctly using curly 'd's rather than straight ones (read aloud as "partial d E by d t"), or as E with a dot overhead (read aloud as E dot).

If this be true then is it possible to intercept the wave when it is only a B field or only an E field ???

With a low frequency wave, like microwaves or lower frequency, you can deliberately intercept one or the other component. The E signal maesured by a linear antenna, or the B signal measured by a loop antenna will cross zero at definite times. When we do this we discover that in fact the fields both disappear together, not alternately as you'd expect. We also find that even though we set out to absorb only the E or only the B, that in fact they always disappear together, in accordance with the rule that they are always proportional in free space.

The fact that people like Hertz discovered this experimentally and that Maxwell produced the maths that predicted the same thing was the most important thing in proving that radio waves are the EM waves predicted by Maxwell's equations.

The propagation speed was the most important factor that caused people to extend Maxwell's eqns to light as at that time it was impossible to measure the E and B fileds of light.

...
When light is polarized which field is being stopped the E or B ???

Like in the example of the different shaped antennae, whichever is being stopped will take out the other one as well.

By convention, when you see a piece of polaroid with a line on it to indicate polarization direction, that line is drawn parallel with the E that is transmitted.

This means that the line must also be parallel with the B that is absorbed, but most people find it confusing to remember both facts, and choose to remember only that the conventional orientation of a polarizing filter is parallel to the maximum E transmission.

When you use polaroid shades to eliminate glare, this works as the E field perpendicular to the shiny surface is refelcted less than than the parallel component. Working from Maxwell's eqns it can be shown that the partially polarizing effect of the surface must be an electrical rather than a magnetic effect.

The major source of glare is from horizontal surfaces, so the polaroid lenses are aligned to transmit vertical E.

The polarizing effect is only produced by non-conduction surfaces - polaroid sunglasses will not protect you from glare from a pool of mercury for example. This is also predicted by Maxwell's eqns (and 30 years ago I could do the maths from memory, I can't now), and constitutes further evidence in favour of treating light as an EM wave.

On the other hand, the behaviour of bi-refringent crystals (calcite etc) where the crystal reacts differently to light of different circular polarization can be shown from Maxwell's equations to be a magnetic rather than an electrical effect.

So, like the fact that we can choose to design a radio antenna as a magnetic (loop) device or as an electrical (linear) one, at light frequencies we still have the fact that for some interaction the B field is more useful to think about, and for others the E field.

This has always reminded me of wave-particle duality - both realities are always present, but one or the other is more useful at different times when humans try to grok what is going on. The duality is in our heads, not out there in the universe.

In more complex mathematical theories the E and B fields are both part of the same "tensor", so it is not surprising that they behave in the same way sometimes. In tensor algebra Maxwell's equation is a single equation, and what we know as his four equations are effectively just components of it.

And no, I am not going to try to explain tensor algebra - I understood one corner of it for about six months in 1979, in the time between postgrad lectures and the postrad exams. If you think vectors are harder than scalars, well tensors are like vectors of vectors and the difficulty seems to be exponential...


Feel free to keep asking - I will answer only when / if I am in the mood so please don't be offended if you get no reply, or a much delayed one.

R~~

River~~

In a standing wave, energy goes nowhere. Radio hams will have seen this if they have ever tried to transmit when the antenna cable is plugged in to the rig but not plugged in to the antenna at the far end, or is shorted out somewhere along the way.

The positions of the zeros of the current and voltage in a standing wave in a cable are a quarter wave apart. Likewise if you make a standing wave in free space (maybe use a laser cavity without its usual filler) you'd see E and B interspersed, as you originally expected.

However the point here is that the energy is going nowhere. In fact the pedulum is a very good analogy as there too the energy goes nowhere, just jiggles between two modes in the same general area.

So in fact you have produced a vivid analogy, but of a different situation to the one you intended. Any insights you get from the pendulum analogy may turn out to be useful in designing laser cavities, but not in considering a propagating wave in free space.


You may wonder how the two cases can both be true - where in one case the peaks have to coincide and in the other they interleave. Well the first thing to notice is that the peaks that coincide are moving at the speed of light, whereas the interleaved peaks are stationary, so there is already a major difference.

The more mathematical explanation is that when we consider the standing wave as an addition of two propagating waves, we have to invert one and only one of the two fields. This is because the direction of travel is given by a "handed" rule. It then follows automatically that where the E field maxes at +E for both waves, the B field maxes at +B for one wave, and at -B for the other, hence cancellation.

R~~

Being no physics major I really find it interesting that what you say is so believable. There are other questions I have also...probably only limited by my imagination...My math does not really go past high school algebra/trig...So please do not get too heavy in math. I understand that men have studied trying to find some kind of "Ether" sort of like there are sound waves in air that EM waves are nothing more then a disturbance of the Ether. Possibly the EM wave itself is the Ether they look for the reason you do not normally see it is that it is in a kind of equilibrium??? Also the speed of light represents some kind of equilibrium point...possibly one dimension is missing with light...the dimension of time ???? Can you please comment on this too. Is it possible to use light one photon at a time...like could you make a radar that sends out a single photon which bounces off a mirror someplace or is one photon too small to see with our instrumentation or to difficult to produce ?
On the question of universal Entropy...how does entropy affect EM waves ?
My questions are very disjointed I know I have no direction in my learning at this time.Totally informal & Undirected, I guess you might say Philistine...Philistinian this does more for me then for you.
Thank You for your time.

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Im still at school and im rubish at explaining stuff so im sure river will be able to clarify/correct me.

The idea of a light ether is from the time of maxwell but as it was found to be flawed. although it was probably a detailed theory with much more maths, the basics of what you described are correct, light travelled in this ether and energy was transfered from one bit of the ether to the next and so on between where it was emited and where its was absorbed, alot like a sound wave. the key problem with theories based on the ether is that they all suggested that we would be travelling through the ether at a finite speed and so by messuring the time it takes for a beem of light to travel the same distance vertically and horizontally, our speed through the ether could be calculated, its sorto hard to describe without a picture.however whatever experiment was carried out, we were always found to be at rest w.r.t the ether, even if the experiment was carried out in a moving car. But that simply doesnt work because if your at rest with respect to something, your either both stationary or both travelnig at the same speed, however you cant be traveling at the same speed as the ether wich is traveling at the same speed as the car which is moving away from you!
the solution to this probelm was special relativity, in which the a particle of light is moving away from you at C even if youre moving towards it in the car.

im not sure what you meant by equilibrium position, but the only time ive heard it consider that is when talking about objects traveling faster than light, however i think its more a mathmatical trick as alot of the equations of specail relativity contain terms like (c^2-v^2)^(1/2) where
if V<C it gives real solution(s)
if V=C it gives 0 (one real solution)
if V>C it gives imaginary solutions

the way i understand entropy is the amount of potential energy in a system, which unless in an equilibruim position will tend to decrease, as an EM wave consists of only one part, entropy is not usually considers, i may however be wrong as so far i have learnt only the basic mathmatics behind entropy and not its physical implecations

dealing with single photons brings up all sorts of quatum mecanicas which i dont understand yet so i think i wont even take a guess as to why single photons arnt used to investigate light

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Your responses are quite clear to me even though I do not understand very much about what is being said. I wish I had more formal education in my background.

About the measurement of time : It is possible to travel either way along the other dimensions of space like the X/Y/Z axises but with time you only travel in a single direction so I was just wondering if time was a real thing or in reality, possibly, we are simply measuring something else when we use time like Entropy. But then that must be silly too because Entropy never goes backward either. I understand Entropy to be the natural tendency of everything to go from order to disorder and even if you try to bring order about you can not do so without increasing the entropy.
Entropy is responsible for everything that happens. Without the differences in shift between order and disorder nothing would ever happen.
Is any of this understanding correct ?

Also, the sun is slowly increasing in intensity so in a few hundred million years the surface of the Earth will be too hot to sustain human or any other life as we know it and this time is much shorter than one billion years as we hear normally on TV.
Humanity/life in general, is doomed long before the Sun ends its life and becomes a red giant.

if the ether is expanding and we are moving in it then there will be no relative velocity between the ether and ourselves so it would not be a measrable thing to see us move through it.
I sometimes imagine there is absolute vacuum outside our known universe and it seems normal to me that our universe would expand into that vacuum and no special dark forces are needed to keep the universe accelerating into its expansion and eventual heat death.

I can imagine we are a small hot universe imbedded within an incredably cold and dark one with occasional eruptions of big bangs like seemes to have created our own. But in no way do I see or can imagine the presence of any divine intervention in the workings of anything. It seems to me that with the laws of physics just about anything can happen without any intelligence guiding things.
I can not imagine a physics major maintaining any real belief in any kind of God as religious folks think of him.
We all are just sort of the condensations of the physical reality and we shall come and go possibly oscillating between life and death through all eternity.
Each life being totally isolated from the previous.

When I look at you I see myself at some other place and time and when you look at me you see yourself at some other place and time and that is all there really is to the universe.

Not trying to sound too silly here but it must sound silly to you folks.
The average person shakes there head and pushes me into the nuthouse when I talk this way in person.

Thanks for your comments and answers, they help me to think straighter.

gmvoeth

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