Now this may be totally wrong but if it is I want to know. Okay, for a "Wave" to move it has to wave something correct? I've heard that light is a wave. If there is nothing in space, how does it get to Earth?

I think it waves off another dimension that we can not see or comprehend. Discuss.

Light waves are made up of electric and magnetic fields. Those fields can exist in a vacuum, and therefore so can light. There is no need for another dimension.

Originally posted by James R
Light waves are made up of electric and magnetic fields. Those fields can exist in a vacuum, and therefore so can light. There is no need for another dimension.

That's a very brave statement!

But still, there are measurable factors which determine the speed of light in a medium, permittivity, and permeablity. These same factors have values, ie, are non-zero for a vacuum. Implying what, .........? ;-)

Light does not have a medium, the Michelson-Morley experiment in the 19th century demostrated that the idea of a luminiferous ether was incorrect.

light does have a medium, it is the electromagnetic 'field'.

I tend to see a 'wave of light' as a fluctuation in the electromagnetic field that extends through space.

Of course, just as light acts as a wave, it acts like a particle that we call the photon.

<i>But still, there are measurable factors which determine the speed of light in a medium, permittivity, and permeablity. These same factors have values, ie, are non-zero for a vacuum. Implying what, .........? ;-)</i>

Implying that even a vacuum can carry electric and magnetic fields.

Originally posted by James R
<i>But still, there are measurable factors which determine the speed of light in a medium, permittivity, and permeablity. These same factors have values, ie, are non-zero for a vacuum. Implying what, .........? ;-)</i>

Implying that even a vacuum can carry electric and magnetic fields.

You missed the important part, that free space has measurable parameters. So what are we measuring, exactly? That thought never occurred to you?

If the equation governing the speed came up with the speed of light as we know it when permeability and permittivity hadzero values, then we'd say 'fine' free space is 'empty'. But when these values are non zero, and have a value, albeit diiferent to a 'solid'' medium, you have to ask, doesn't that make a free space a medium too?

Think about it, don't just accept it. Let's be honest, nobody really understands quantum mechanics, we just use the theories to get results.

Originally posted by jcsd
Light does not have a medium, the Michelson-Morley experiment in the 19th century demostrated that the idea of a luminiferous ether was incorrect.

That experiment doesn't disprove a medium , but rather that there isn't an "ether wind".

The medium of free space would have to be frictionless wrt photons, or we'd see stationary photons hanging about, as they'd lose energy to the medium, and eventually stop.

So for an 'ether wind' to provide a measurable deflection of photons in the two paths of light taken in this experiment, photons would have to interact with something.

So this experiment could be said to prove that the medium, or 'ether' if you will is frictionless to photons. An observation born out by the lack of 'stationary' photons,...

Oh, being Devil's Advocate is so much fun!

"
That experiment doesn't disprove a medium , but rather that there isn't an "ether wind"."

The experiment does disprove an ether like medium.

I thought the experiment was more geared toward disproving the notion that C was relative to the observer.

Then why isnt light affected by magnets?

Second question;What keeps a light ray straight?


Third question; Does light lose energy and if it does what happens to that energy?

Fourth question; What determines the rate that electromagnetic fields collapse.

Just curious

So this experiment could be said to prove that the medium, or 'ether' if you will is frictionless to photons. An observation born out by the lack of 'stationary' photons,...It's not about the medium slowing down the light. It's about whether light moves relative to the medium.
Well, a little more than that. The experiment shows that either photons don't move relative to a universal medium, or that the medium is always comoving with Earth, or that lengths are contracted in the direction of the ether wind (enter Lorentzian relativity).

The question that must be asked is: Are ether theories more useful, or can all predictions of such theories be derived more simply without an ether? (And the counter question, of course, is "Does more useful mean right?)

Originally posted by phlogistician
You missed the important part, that free space has measurable parameters. So what are we measuring, exactly? That thought never occurred to you?

If the equation governing the speed came up with the speed of light as we know it when permeability and permittivity hadzero values, then we'd say 'fine' free space is 'empty'. But when these values are non zero, and have a value, albeit diiferent to a 'solid'' medium, you have to ask, doesn't that make a free space a medium too?

Think about it, don't just accept it. Let's be honest, nobody really understands quantum mechanics, we just use the theories to get results.

The reason the vacuum is assigned values of permitivity and permeability is because condensed matter has different electric and magnetic properties than the vacuum, and it's easier to assign them different values of those properties than to calculate the behavior of different fields in the materials. It's just a matter of convenience and convention.

<b>phlogistician</b>:

<i>You missed the important part, that free space has measurable parameters. So what are we measuring, exactly? That thought never occurred to you?</i>

Here's how it works:

We measure the speed of light in different media (including the vacuum). We then <b>define</b> a value of the permeability of the vacuum. It is important to realise that the value is totally arbitrary; we could set the value to anything we wanted. Setting the value chooses a set of measurement units for electric and magnetic fields. The permittivity is a <b>derived</b> value. To derive it you need to measure the speed of light and define the permeability, then an equation gives you the permittivity.

The permeability need only be defined for the vacuum, because all measurements in other mediums can be expressed as ratios relative to the vacuum values.

So, apart from the fact that the permeability and permitivity of the vacuum must be non-zero (or else Maxwell's equations would not work), the actual values are arbitrary, amounting to no more than a choice of a system of units of measure. We can therefore draw no conclusions about the nature of the vacuum from the mere fac that it has a permeability, apart from the obvious conclusion that it can carry electromagnetic radiation. Certainly, there is no need to postulate an aether.


<b>Greco</b>:

<i>Then why isnt light affected by magnets?</i>

It is. For example, look up the "Faraday effect" on the web, if you're interested.

<i>Second question;What keeps a light ray straight?</i>

According to Einstein, light follows a geodesic in the local spacetime - just like everything else - unless something acts to alter its path.

<i>Third question; Does light lose energy and if it does what happens to that energy?</i>

Light loses energy when it is absorbed by a medium. Its energy is also dependent on the reference frame from which you are viewing it (same as the energy of everything else).

<i>Fourth question; What determines the rate that electromagnetic fields collapse.</i>

I don't understand the question. What do you mean by "collapse"?

Originally posted by Tyger
The reason the vacuum is assigned values of permitivity and permeability is because condensed matter has different electric and magnetic properties than the vacuum, and it's easier to assign them different values of those properties than to calculate the behavior of different fields in the materials. It's just a matter of convenience and convention.

It's not about convenience, the equations speak for themselves. We didn't 'assign' values to free space, we determined them via experimentation. Now, I'm willing to accept that the values are a mathematical artefact because the formula we use is over simplistic, or the way we use maths to describe physical phenomena could be better, but we only ever _determine_ physical constants.

Originally posted by James R


<i>You missed the important part, that free space has measurable parameters. So what are we measuring, exactly? That thought never occurred to you?</i>

Here's how it works:

We measure the speed of light in different media (including the vacuum). We then <b>define</b> a value of the permeability of the vacuum.

And here was me thinking that we take measurements of the speed of light, and then try to derive an empirical formula that best fits the data, and the constants drop out of that, .....

We define our units, and that's that. Like I said in the other thread, I'm willing to accept that non-zero values are artefacts of oversimplified maths, but hand waving over them just won't do.

Surely if we'd happened across the correct formula, the correct units of measurement, and the appropriate mathematical method, these values would be zero for free space? The maths we use is rather linear, and space isn't, get what I'm drivng at?

phlogistician:

<i>And here was me thinking that we take measurements of the speed of light, and then try to derive an empirical formula that best fits the data, and the constants drop out of that, .....</i>

Not in this case. Are you familiar with Maxwell's equations for electromagnetism?

The permittivity (e) and permeability (u) are related to the speed of light by:

eu = 1/c²

As I said before, we measure c (since distance and time units are already specified). We then choose u, which specifies an electromagnetic system of units, then use the equation to get e.

<i>Like I said in the other thread, I'm willing to accept that non-zero values are artefacts of oversimplified maths, but hand waving over them just won't do.</i>

It's not hand-waving. We MUST choose a consistent set of units for the equations to be of any use. In fact, in electromagnetism, there are 3 different sets of commonly-used units: SI units, Gaussian units and Heaviside-Lorentz units. In each system, e and u have different values than they have in other systems. For example, in HL units, both e and u equal 1.

This isn't an oversimplification. Maxwell's equations are an accurate description of all classical electromagnetic phenomena.

<i>Surely if we'd happened across the correct formula, the correct units of measurement, and the appropriate mathematical method, these values would be zero for free space?</i>

No. As I explained before, the equations are such that the values cannot ever be zero. The simplest choice we can make is a system of units where all three values are equal to 1. We know the correct formulas. There is no correct system of units. A system of units is arbitrary; one is as good as another. Units are chosen for convenience.

<i>The maths we use is rather linear, and space isn't, get what I'm drivng at?</i>

Not yet.

Originally posted by James R
<b>phlogistician</b>:
<i>Fourth question; What determines the rate that electromagnetic fields collapse.</i>

I don't understand the question. What do you mean by "collapse"?

Well, how does light propagate? Doesnt it depend on an electric field expanding then collapsing producing a magnetic field that then collapses to produce an electric field? I just wonder what determines the rate of expansion and collapse of the fields.

Am I making sense? If not please ignore the question.

I looked up the faraday effect and it says that light rotates when exposed to strong magnetic fields, if that is the case then if I wear polaroid glasses and observe light near strong magnetic fields such as those around power transformers or radio antennas then I sould see light distorting, dont you agree?

Greco:

<i>Well, how does light propagate? Doesnt it depend on an electric field expanding then collapsing producing a magnetic field that then collapses to produce an electric field?</i>

Hmm... close, but not quite right. A light wave consists of magnetic and electric fields that oscillate. They do it in phase, meaning the electric field is strongest when the magnetic field is strongest. When the electric field is zero, so is the magnetic field.

Both of the fields have defined directions, and the two fields always point at right angles to each other. So, if we look at just the electric field, for example, the field starts at zero, increases in one direction, decreases back to zero, increases in the opposite direction and then goes back to zero and starts again. The magnetic field does the same thing, only in a direction perpendicular to the electric field.

<i>I just wonder what determines the rate of expansion and collapse of the fields.</i>

The rate of oscillation is given by the <b>frequency</b> of the light wave, which corresponds to its colour.

<i>I looked up the faraday effect and it says that light rotates when exposed to strong magnetic fields, if that is the case then if I wear polaroid glasses and observe light near strong magnetic fields such as those around power transformers or radio antennas then I sould see light distorting, dont you agree?</i>

No, because sunlight is pretty much unpolarised to start with. Your sunglasses tend to reduce the overall amount of light coming through, by blocking out light polarised in certain directions. By the way, the direction of polarisation of light is the same as the direction that the electric field oscillates in.

Originally posted by James R
phlogistician:

eu = 1/c²

As I said before, we measure c (since distance and time units are already specified). We then choose u, which specifies an electromagnetic system of units, then use the equation to get e.



Except for media we can determine specific values for permittivity, by measuring it's capacitance.

So this single dimension has a value in it's own right, it is not merely the product of permeability and permittivity that is of consequence.

Sure, but the units of capacitance are determined by our choice of u in the vacuum.

Originally posted by James R
Light waves are made up of electric and magnetic fields. Those fields can exist in a vacuum, and therefore so can light. There is no need for another dimension.

Scientists talk about space bending or warping doesnt that imply that space has structure? How can nothing have structure? They also mention that light or any EM wave will follow any space curvature. Does that mean space geometry determine EM wave travel and if so what kind of geometry is that?

>>Light does not have a medium, the Michelson-Morley experiment in the 19th century demostrated that the idea of a luminiferous ether was incorrect.

One interpretation is that the field we are immersed in is inertial, therefore the aether is inertial, therefore it affects light to the same degree in any direction.

To understand this see electrodynamic spin gravity papers, available from a link in this section.

Originally posted by James R
Sure, but the units of capacitance are determined by our choice of u in the vacuum.

But the cpacitance of a fixed system has a fixed value, so all you are saying is that if we choose U, then that changes the dielectric value for the system, according to whatever units we decide to use.

The point is, that all of these physical constants are not in isolation, each one has a relationship with another. It is not their value, that is of interest, but rather their relationships. Saying we set an abitrary value for one (U) and saying that value is meaningless rather misses the point that they all interact. Tweak one value, they all change.

Now, if it was possible that the values could be tweaked so U was zero, then would that not be a more 'common sense' value to describe vacuum? Could that be done, ......?

[ [/B][/QUOTE] No, because sunlight is pretty much unpolarised to start with.

Okay so far, so if if I pointed a laser at an oscillating strong EM field and looked at the laser beam with polarised glasses I should be able to see the laser oscillating at the rate of the EM field oscillations, is that correct?

If the answer is yes, next question is, why cant a magnetic field bend a light beam instead of just rotating it. Isnt that what happens inside a CRT? I understand that the beam is made up of electrons but dont moving electrons create EM fields?

<b>phlogistician</b>:

<i>But the cpacitance of a fixed system has a fixed value, so all you are saying is that if we choose U, then that changes the dielectric value for the system, according to whatever units we decide to use.</i>

It doesn't change the physical characteristics of the system, of course. It only changes the numerical values given to them.

<i>The point is, that all of these physical constants are not in isolation, each one has a relationship with another.</i>

Yes, and the basic choices you need to make to uniquely determine a system of units are values of c and u (in vacuo), as I said.

<i>Saying we set an abitrary value for one (U) and saying that value is meaningless rather misses the point that they all interact. Tweak one value, they all change.</i>

I didn't say it was meaningless. I said the choice of u in a vacuum is arbitrary (except that it can't be zero).

<i>Now, if it was possible that the values could be tweaked so U was zero, then would that not be a more 'common sense' value to describe vacuum? Could that be done, ......?</i>

No. As I said before, Maxwell's equations only hold for non-zero values of u.


<b>Greco</b>:

<i>Okay so far, so if if I pointed a laser at an oscillating strong EM field and looked at the laser beam with polarised glasses I should be able to see the laser oscillating at the rate of the EM field oscillations, is that correct?</i>

No, because the wavelengths of the oscillations are too small, and the frequencies are too high for your eye to see the oscillations. You'd need some other kind of detector - such as a photomultiplier tube.

<i>If the answer is yes, next question is, why cant a magnetic field bend a light beam instead of just rotating it. Isnt that what happens inside a CRT? I understand that the beam is made up of electrons but dont moving electrons create EM fields? </i>

The light for a CRT is created when electrons hit the phosphor coating of the screen, depositing energy, which gets converted to light. The steering of the beam involves steering the electrons. Electrons are charged particles, and so are affected by both electric and magnetic fields. Light photons, on the other hand, are uncharged.

Originally posted by James R
It doesn't change the physical characteristics of the system, of course. It only changes the numerical values given to them.



Hoorah! We're there! The formula for determining the relationship between the values is fixed by the physical system. The units are arbitrary, but the value of u will never be non-zero for a vacuum, no matter what units we choose, no matter what arbitrary values we choose for c.

Does it make sense that _nothing_ has an attribute with a value?

So, does the fact that _nothing_ has a speed limit of c make sense? Nope, just something we accept, but we don't understand it.

Doesn't matter how arbitrary we think the values are, the implications are significant.

phlogistician:

<i>Hoorah! We're there! The formula for determining the relationship between the values is fixed by the physical system. The units are arbitrary, but the value of u will never be non-zero for a vacuum, no matter what units we choose, no matter what arbitrary values we choose for c.</i>

:)

That's what I've said all along.

<i>Does it make sense that _nothing_ has an attribute with a value?</i>

Well, it also makes sense to say that two points in empty space are separated by a distance of 3 kilometres, or that the speed of light in empty space has a non-zero value, so it's not really that surprising that we can associate certain values with "empty" space. But it is a jump from there to draw the conclusion that empty space is a medium.

<i>So, does the fact that _nothing_ has a speed limit of c make sense?</i>

Space doesn't have a speed of limit of c. Objects travelling in space have a speed limit of c. That has more to do with the objects than the space.

<i>Doesn't matter how arbitrary we think the values are, the implications are significant.</i>

That's where we differ, isn't it?