Photon Frequency Shift

[SamBridge]

Something about red/blue shifting seems illusionary, or in a way physically non-nonsensical. If I travel towards a photon that's a light year away with 0 matter and energy in between me and the photon, and a source another light-year away said before the experiment began that the photon is red, when I finally run into it, I will measure it has blue shifted. But, where did it gain the energy? If I knew it gained the energy, how did I not measure it before the amount of time it would have taken light and violate causality? The only way I can think it works is some way of modeling is the energy you put into moving towards the photon is in some way proportional to the relative energy you measure it having, more like running into a brick wall at 20kph rather than 1kph, but, I still can't figure out how that physically works. There's also something weird with a physical mechanism for the frequency increase too. A photon doesn't seem to oscillate in a completely physical way, and when you measure one, you have a quantum eraser effect where the rest of the mathematical model of the photon appears to vanish since you narrowed down its position to a single point. So, how can we even possibly measure a photon's "oscillation over time" like a wave in the water when all definite photon measurements only give you a single point and not multiple points over time and essentially erase the rest of the spacial probabilistic distribution of the photon?

Edited April 16, 2014 by SamBridge

[swansont]

Something about red/blue shifting seems illusionary, or in a way physically non-nonsensical. If I travel towards a photon that's a light year away with 0 matter and energy in between me and the photon, and a source another light-year away said before the experiment began that the photon is red, when I finally run into it, I will measure it has blue shifted. But, where did it gain the energy? If I knew it gained the energy, how did I not measure it before the amount of time it would have taken light and violate causality? The only way I can think it works is some way of modeling is the energy you put into moving towards the photon is in some way proportional to the relative energy you measure it having, more like running into a brick wall at 20kph rather than 1kph, but, I still can't figure out how that physically works. There's also something weird with a physical mechanism for the frequency increase too. A photon doesn't seem to oscillate in a completely physical way, and when you measure one, you have a quantum eraser effect where the rest of the mathematical model of the photon appears to vanish since you narrowed down its position to a single point. So, how can we even possibly measure a photon's "oscillation over time" like a wave in the water when all definite photon measurements only give you a single point and not multiple points over time and essentially erase the rest of the spacial probabilistic distribution of the photon?

 

 

It doesn't gain energy, per se. Energy is not a quantity that stays the same in different frames of reference, i.e. it's not invariant.

 

This is trivially true of classical kinetic energy. Take your example of running into a brick wall. In the wall's frame, you might have 1 unit of KE. But from your frame, the wall (and the entire earth) is moving, having a much larger KE. There is no part of physics that says that the values should be the same in different frames of reference.

[SamBridge]

 

 

It doesn't gain energy, per se. Energy is not a quantity that stays the same in different frames of reference, i.e. it's not invariant.

 

This is trivially true of classical kinetic energy. Take your example of running into a brick wall. In the wall's frame, you might have 1 unit of KE. But from your frame, the wall (and the entire earth) is moving, having a much larger KE. There is no part of physics that says that the values should be the same in different frames of reference.

So what about everything else I said like where the physical mechanism for the energy gain comes from? I understand that if you move towards a photon, you will measure it blue shifting compared to if you measured it while stationary, but what I don't understand is the physical mechanism for how that happens specifically with photons, they aren't exactly brick walls.

Edited April 16, 2014 by SamBridge

[swansont]

So what about everything else I said like where the physical mechanism for the energy gain comes from? I understand that if you move towards a photon, you will measure it blue shifting compared to if you measured it while stationary, but what I don't understand is the physical mechanism for how that happens specifically with photons, they aren't exactly brick walls.

 

There is no energy gain, so there doesn't need to be a mechanism for energy gain.

 

The speed remains constant, but the oscillations will be observed to be happening faster if you're moving toward the photon. It's the Doppler shift, just like in sound.

[Sensei]

Sam, imagine you have boat on water.

1) boat is at rest, and water is waving, f.e. 1 meter wavelength (distance between crests of wave).

2) boat is moving in direction of source of waves, and wavelengths will be shrinking, less than 1 m.

3) boat is moving in direction exactly opposite to source of waves, and wavelengths will be expanding, higher than 1 m.

 

The same happens with sound waves in air. Which is easily noticeable when ambulance is approaching and receding us.

 

 

That's classical Doppler Effect.

 

Add to it constant speed of light, and you will get Relativistic Doppler Effect.

 

[SamBridge]

 

There is no energy gain, so there doesn't need to be a mechanism for energy gain.

 

The speed remains constant, but the oscillations will be observed to be happening faster if you're moving toward the photon. It's the Doppler shift, just like in sound.

See, that conflicts with something that you yourself said while ago in some other topic, which is that you can't actually physically model a photon that way, and it's because of the property I already described which you also described at a previous point. When you measure a photon, you are not observing millions of atoms over time like a wave, you're observing a single point of a collapsed wave function and you shouldn't have any knowledge of exact position or energy outside of a mathematical model generated by some computer, it's not the same as matter on the macroscopic scale and you yourself said that, I know you have a different explanation that makes more sense, or at least one that doesn't contradict other things you said.

Prior to measurement, sure, you can measure a photon's probability as a time evolution oscillation or a wave packet, but that probability model itself isn't doesn't work the same way as macroscopic substances, and I know you know that and that's why I never understand why you keep doing this, I don't know if you're just screwing with me or what.

 

Sam, imagine you have boat on water.

1) boat is at rest, and water is waving, f.e. 1 meter wavelength (distance between crests of wave).

2) boat is moving in direction of source of waves, and wavelengths will be shrinking, less than 1 m.

3) boat is moving in direction exactly opposite to source of waves, and wavelengths will be expanding, higher than 1 m.

 

The same happens with sound waves in air. Which is easily noticeable when ambulance is approaching and receding us.

 

 

That's classical Doppler Effect.

 

Add to it constant speed of light, and you will get Relativistic Doppler Effect.

 

Or you could pull out the equivalence principal and model it as a photon moving into a higher gravitational field, or, more contracted space, and that compensates for the pre-measurement frequency gain that way. Either way, there's a still a gap with the physical mechanism to patch up the apparent crack between relativity and quantum mechanical models that so far is not explained in this topic. If source says they emit a red photon at a certain time, I'm just taking that on pure faith, I have no measured information about the photon that I haven't encountered yet, so I can't know that it's actually "oscillating faster" until I get to it. It might at first make sense to physically model it like any other Doppler effect but when you start considering quantum mechanical models as well, the result isn't as clear.

Edited April 18, 2014 by SamBridge

[swansont]

 

See, that conflicts with something that you yourself said while ago in some other topic, which is that you can't actually physically model a photon that way, and it's because of the property I already described which you also described at a previous point. When you measure a photon, you are not observing millions of atoms over time like a wave, you're observing a single point of a collapsed wave function and you shouldn't have any knowledge of exact position or energy outside of a mathematical model generated by some computer, it's not the same as matter on the macroscopic scale and you yourself said that, I know you have a different explanation that makes more sense, or at least one that doesn't contradict other things you said.

Prior to measurement, sure, you can measure a photon's probability as a time evolution oscillation or a wave packet, but that probability model itself isn't doesn't work the same way as macroscopic substances, and I know you know that and that's why I never understand why you keep doing this, I don't know if you're just screwing with me or what.

 

I would much prefer that you quote me (or better yet provide a link) rather than summarize what you think I said, because there's a decent chance the two are not the same thing, or there is a missing bit of context in one discussion that doesn't apply to the other. if I was feeding you wrong information, others here would call me on it, just as they've pointed out errors of mine in the past.

[SamBridge]

 

I would much prefer that you quote me (or better yet provide a link) rather than summarize what you think I said, because there's a decent chance the two are not the same thing, or there is a missing bit of context in one discussion that doesn't apply to the other. if I was feeding you wrong information, others here would call me on it, just as they've pointed out errors of mine in the past.

I'm not going to bother looking through a year of topics, you know what you know, and I know you know your description isn't fully accurate according to your own past explanations. Sometimes I said stuff that I know isn't 100% is current but could do for the situation and no one called me on it, so that doesn't really mean anything if no one calls you on it, you're not even considering the fact that people wouldn't question you because they'd assume you're correct. I know you know that you can't model a photon just like any macroscopic substance, and I'm sure most others with knowledge in the field like some of the staff members would agree but simply didn't bother to say it because they don't want to argue with someone else who's a staff member. Your description contradicts what you specifically said, you specifically said it wasn't the thing you just said it was in this topic, it specifically doesn't physically work like that according specifically to what you said. This is just a case of you not taking the topic seriously, nothing more.

Edited April 18, 2014 by SamBridge

[Sensei]

 

I would much prefer that you quote me (or better yet provide a link) rather than summarize what you think I said, because there's a decent chance the two are not the same thing, or there is a missing bit of context in one discussion that doesn't apply to the other. if I was feeding you wrong information, others here would call me on it, just as they've pointed out errors of mine in the past.

 

I think so he was talking about that we know nothing about photon until it's absorbed, and when it's absorbed, it's gone from the system.

[SamBridge]

 

I think so he was talking about that we know nothing about photon until it's absorbed, and when it's absorbed, it's gone from the system.

Exactly, so how do you constantly measure physical oscillations over time like waves in the water? As soon as its observed you get a quantum eraser effect, my moving towards the photon shouldn't have any impact on the photon at all while its traveling, and that's why there's no measured energy gain in the photon from an outside frame. It simply does not make physical sense to model it as if you're on the beach, neither the ocean nor its waves spontaneously disappear when one wave takes the time to hit the shore. In fact, even after a single wave hits the shore, the energy continues dispersing through the rocks.

Edited April 18, 2014 by SamBridge

[Sensei]

I will explain you how to measure Doppler Effect.

 

Imagine we have laser with well know frequency (so also energy/momentum/wavelength is known).

And container with atoms which are reacting for this frequency.

If we will place laser on vehicle, airplane or rocket. And laser will be pointing to container with above atoms. We can see transition.

Then when we will start moving it in direction to/from container, transition will stop happening - frequency will be higher or lower than needed for transition to happen.

 

In the case of external source of photons, such as Sun or star, we have to rely on well known absorption/emission spectral lines to calibrate

 

Similar method was used in measurement of gravitational shift, but laser was pointing down and it was failing down.

[swansont]

 

I think so he was talking about that we know nothing about photon until it's absorbed, and when it's absorbed, it's gone from the system.

 

What does that have to do with anything, or contradict anything I've said here? If you are moving toward the photon, you will measure a higher frequency when you measure the frequency, i.e. when it's absorbed. You can easily measure this with a narrow transition — atoms moving toward or away from the light are shifted toward or away from resonance, depending on how you've set it up. You can see how the absorption/transmission is affected.

[SamBridge]

 

What does that have to do with anything, or contradict anything I've said here? If you are moving toward the photon, you will measure a higher frequency when you measure the frequency, i.e. when it's absorbed. You can easily measure this with a narrow transition — atoms moving toward or away from the light are shifted toward or away from resonance, depending on how you've set it up. You can see how the absorption/transmission is affected.

But what is the physical process that accounts for the relative energy gain occurring considering that quantum mechanical models are widely different than models of waves on a beach? You move towards a photon, an atom absorbs it and gets into a higher energy state than if it were stationary, but you still have the quantum eraser effect, so what physical phenomena do you model to account for the seeming mix of quantum and classical properties? Classical relativistic doppler shift definitely doesn't answer all the questions.

 

I will explain you how to measure Doppler Effect.

 

Imagine we have laser with well know frequency (so also energy/momentum/wavelength is known).

And container with atoms which are reacting for this frequency.

If we will place laser on vehicle, airplane or rocket. And laser will be pointing to container with above atoms. We can see transition.

Then when we will start moving it in direction to/from container, transition will stop happening - frequency will be higher or lower than needed for transition to happen.

 

In the case of external source of photons, such as Sun or star, we have to rely on well known absorption/emission spectral lines to calibrate

 

Similar method was used in measurement of gravitational shift, but laser was pointing down and it was failing down.

I'm talking about a single photon though, a laser is many many photons or even charged particles which would only make the ambiguity of the situation easier to brush off as a classical notion. As I said, from a classical stand-point it could at first make sense, but the problem with that is the fact that photons aren't completely classical, there's phenomena that don't act like waves on the beach, you don't run into the rest of an individual photon over time, as soon as its definitely absorbed and not just decohered, it collapses to a measured point, the rest of the proposed physical component of the photon is subject to the quantum eraser effect whereby the probability of its spacial distribution instantaneously disappears with the determining of its exact properties and it no longer has any wave-like nature. Originally, it would have made sense to me, but after reading through a debate and looking at particle physics, Swan and the rest of the internet made it really clear that photons don't work completely like waves on a beach.

Edited April 19, 2014 by SamBridge