Red shift. How ??

[mistermack]

When you are talking about "speed of change", you really mean acceleration. In classical physics, it is accelerating charges which generate electromagnetic radiation. In a wire carrying AC current, for example, the oscillation involves regular backwards and forwards acceleration, which produces RF waves of 50 Hz. In a classic x-ray machine, the stream of electrons hits a barrier, and undergoes violent deceleration, producing high frequency X-rays.

But in an electron shell, it makes no sense to separate the energy levels and rates. The energy, & thus the frequency of the emitted photon is entirely fixed by the difference in energy levels as the electron makes its quantum jump downwards.

The thing is though, the energy, and frequency, are only fixed in one frame of reference. If the observer has any motion different to the original emitter, the energy and frequency is different.

What I was really getting at, is that a high frequency X-ray, is only a high-frequency X-ray, if you are stationary in the same reference frame that it's emitter was stationary.
Say you observed it in a reference frame that was moving in the same direction, at half the speed of light, you might see it as a normal photon in the green part of the visible spectrum.
How would it differ from any other green photon, apart from being viewed in a different inertial frame?
Surely that attribute of being a high energy x-ray, is only the result of the frame of reference of the observer. Or more accurately, the contrast in motion between the observer and the emitter.

[JimC]

When you are talking about "speed of change", you really mean acceleration. In classical physics, it is accelerating charges which generate electromagnetic radiation. In a wire carrying AC current, for example, the oscillation involves regular backwards and forwards acceleration, which produces RF waves of 50 Hz. In a classic x-ray machine, the stream of electrons hits a barrier, and undergoes violent deceleration, producing high frequency X-rays.

But in an electron shell, it makes no sense to separate the energy levels and rates. The energy, & thus the frequency of the emitted photon is entirely fixed by the difference in energy levels as the electron makes its quantum jump downwards.

The thing is though, the energy, and frequency, are only fixed in one frame of reference. If the observer has any motion different to the original emitter, the energy and frequency is different.

What I was really getting at, is that a high frequency X-ray, is only a high-frequency X-ray, if you are stationary in the same reference frame that it's emitter was stationary.
Say you observed it in a reference frame that was moving in the same direction, at half the speed of light, you might see it as a normal photon in the green part of the visible spectrum.
How would it differ from any other green photon, apart from being viewed in a different inertial frame?
Surely that attribute of being a high energy x-ray, is only the result of the frame of reference of the observer. Or more accurately, the contrast in motion between the observer and the emitter.

You have to have a starting point, which is an observer in the same frame of reference as the emitter. For many purposes, it is the nature of the emitter which is of scientific interest. If there is a known, significant difference in velocities between observer and emitter, then one allows for that in the calculation, and works backwards to establish the frequency upon emission, which is not a vague, relative phenomenon, but an important characteristic which is a vital fact about the emitter.

[Xamonas Chegwé]

When you are talking about "speed of change", you really mean acceleration. In classical physics, it is accelerating charges which generate electromagnetic radiation. In a wire carrying AC current, for example, the oscillation involves regular backwards and forwards acceleration, which produces RF waves of 50 Hz. In a classic x-ray machine, the stream of electrons hits a barrier, and undergoes violent deceleration, producing high frequency X-rays.

But in an electron shell, it makes no sense to separate the energy levels and rates. The energy, & thus the frequency of the emitted photon is entirely fixed by the difference in energy levels as the electron makes its quantum jump downwards.

The thing is though, the energy, and frequency, are only fixed in one frame of reference. If the observer has any motion different to the original emitter, the energy and frequency is different.

What I was really getting at, is that a high frequency X-ray, is only a high-frequency X-ray, if you are stationary in the same reference frame that it's emitter was stationary.
Say you observed it in a reference frame that was moving in the same direction, at half the speed of light, you might see it as a normal photon in the green part of the visible spectrum.
How would it differ from any other green photon, apart from being viewed in a different inertial frame?
Surely that attribute of being a high energy x-ray, is only the result of the frame of reference of the observer. Or more accurately, the contrast in motion between the observer and the emitter.

The frequency (and therefore energy) of photons is affected by relative motion between the emitter and the receiver. Nobody is arguing against that. It is the basis of red-shift.

What you have been claiming though, is that all photons are the same and that it that their energies are determined solely by such relative motion. This is wrong. I can assure you that the lightbulbs in my house are not moving a billion times faster than the local radio transmitter (even after adjustment for time dilation!)

What happens when a bound electron changes energy level and emits a photon is that there is a tiny reduction in the mass of the atom exactly equivalent (using E=mc2) to the energy of the photon emitted. What happens in red shift is that we are NOT talking about the rest mass of the atom - but its relativistic mass, taking into account its relative motion - which affects the energy of the emitted photon.

[mistermack]

You have to have a starting point, which is an observer in the same frame of reference as the emitter. For many purposes, it is the nature of the emitter which is of scientific interest. If there is a known, significant difference in velocities between observer and emitter, then one allows for that in the calculation, and works backwards to establish the frequency upon emission, which is not a vague, relative phenomenon, but an important characteristic which is a vital fact about the emitter.

That's fair enough. I wouldn't say that there is nothing interesting in the original emission. Like you say, if you know or can deduce the velocity of the original body, you can deduce what molecules emitted the radiation. That doesn't really affect my speculation about photons being the same though.
I'm not saying they are, I'm speculating, ''what if they are?''

Say photons were identical cricket balls in space, and instead of different frequencies, they all had different velocities, so they all had different energies. The velocity is a characteristic of the relative motion between the cricket ball emitter, and you. It's not a property of the cricket ball, if there is no ''favoured'' reference frame.
Even though they all have different energies, they are all identical cricket balls.

Like you said, the velocity of the cricket ball would be interesting, as it tells us the absolute velocity of the emitter, relative to us. But it doesn't really affect the fact that they are all identical balls, just with different emitters. If copper emitted cricket balls of a certain speed, and we knew the velocity of the emitting body, those identical cricket balls would tell us if they were emitted by copper.

By the way, I'm just speculating, not claiming anything. I like to get a mental picture of what's happening, if I can.

[Xamonas Chegwé]

All photons are the same. But they don't have different velocities, just different frequencies, and hence different energies. All photons travel at c in a vacuum and at slightly lower speeds in other media. The higher their energy, the less they are slowed by interaction with molecules in air/water/glass/etc. - hence rainbows.

[JimC]

All photons are the same. But they don't have different velocities, just different frequencies, and hence different energies. All photons travel at c in a vacuum and at slightly lower speeds in other media. The higher their energy, the less they are slowed by interaction with molecules in air/water/glass/etc. - hence rainbows.

The last sentence is the wrong way round. Higher frequency (and thus higher energy) photons are slowed down more as they enter a transparent material from air or a vacuum, and as a consequence, are refracted through a greater angle. Violet light bends the most, red light the least.

[mistermack]

All photons are the same. But they don't have different velocities, just different frequencies, and hence different energies. All photons travel at c in a vacuum and at slightly lower speeds in other media. The higher their energy, the less they are slowed by interaction with molecules in air/water/glass/etc. - hence rainbows.

The last sentence is the wrong way round. Higher frequency (and thus higher energy) photons are slowed down more as they enter a transparent material from air or a vacuum, and as a consequence, are refracted through a greater angle. Violet light bends the most, red light the least.

To be absolutely pedantic, the ''they don't have different velocities'' bit isn't right, either. They have different velocities, since they have different directions, but move at the same speed.
But we all do that. I try not to, but it slips in all the time. But since everybody does it, everybody knows what you mean.

[Xamonas Chegwé]

All photons are the same. But they don't have different velocities, just different frequencies, and hence different energies. All photons travel at c in a vacuum and at slightly lower speeds in other media. The higher their energy, the less they are slowed by interaction with molecules in air/water/glass/etc. - hence rainbows.

The last sentence is the wrong way round. Higher frequency (and thus higher energy) photons are slowed down more as they enter a transparent material from air or a vacuum, and as a consequence, are refracted through a greater angle. Violet light bends the most, red light the least.

I knew that. I just had a forget...

To be absolutely pedantic, the ''they don't have different velocities'' bit isn't right, either. They have different velocities, since they have different directions, but move at the same speed.
But we all do that. I try not to, but it slips in all the time. But since everybody does it, everybody knows what you mean.

To be even absolutelyer pedantic, they don't all have different velocities. Photons moving parallel to one another have identical velocities - vectors are identical if the have equal magnitude and direction, regardless of position in space.

[mistermack]

To be even absolutelyer pedantic, they don't all have different velocities. Photons moving parallel to one another have identical velocities - vectors are identical if the have equal magnitude and direction, regardless of position in space.

Yeh but, to be INFINITELY pedantic, that can't happen, because to be parallel in the real world, the alignment would have to be infinitely accurate.
Unless the direction that a photon takes goes in quantum increments, I suppose.

[Xamonas Chegwé]

To be even absolutelyer pedantic, they don't all have different velocities. Photons moving parallel to one another have identical velocities - vectors are identical if the have equal magnitude and direction, regardless of position in space.

Yeh but, to be INFINITELY pedantic, that can't happen, because to be parallel in the real world, the alignment would have to be infinitely accurate.
Unless the direction that a photon takes goes in quantum increments, I suppose.

Wrong. Photons have integer spin and are not limited by the Pauli exclusion principle, so can be superimposed infinitely - ie. a large number of photons can occupy the same quantum state in the same place with an identical trajectory. That's what lasers are, basically.

[mistermack]

To be even absolutelyer pedantic, they don't all have different velocities. Photons moving parallel to one another have identical velocities - vectors are identical if the have equal magnitude and direction, regardless of position in space.

Yeh but, to be INFINITELY pedantic, that can't happen, because to be parallel in the real world, the alignment would have to be infinitely accurate.
Unless the direction that a photon takes goes in quantum increments, I suppose.

Wrong. Photons have integer spin and are not limited by the Pauli exclusion principle, so can be superimposed infinitely - ie. a large number of photons can occupy the same quantum state in the same place with an identical trajectory. That's what lasers are, basically.

I think you've used ''can'' when ''could in theory'' would be more accurate.

Nothing is perfect or infinite in reality.

Collimated light is light whose rays are parallel, and therefore will spread minimally as it propagates. The word is related to "collinear" and implies light that does not disperse with distance (ideally), or that will disperse minimally (in reality). A perfectly collimated beam, with no divergence, cannot be created due to diffraction.

Of course, the word parallel could be viewed as a comparative term, not necessarily implying infinite perfection.
Depends how far you take these things. That's why I said, ''to be infinitely pedantic''.
A real pedantic could always say, ''well, they're not parallel then'' if they diverged an inch over a billion light years.

[mistermack]

When I first posted about the red shift, the bit that was giving me trouble was the way in which time dilation cancels out the motion differences between observers and light, so that the observer always experiences the same speed of light.
I couldn't see why it didn't do the same thing for the frequency of light. If I was a mathematician, I guess it would be pretty obvious, from the equations, but I ain't.

What gave me a better mental picture, is the fact that time dilation is the same, regardless of the direction of motion. So travelling away from the source of the light would have the same time effect as towards it, whereas it would have the opposite effect, on the observed frequency.
That makes it obvious that time dilation couldn't have the same effect on frequency as it does on speed.
ie exactly cancelling out the effect of relative motion.