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How does particle physics explain the doppler effect? (including blue/red shift)
Yes doppler is only about waves but what happens on a particle level?Doppler is a wave phenomenon and has no particular connection to particle physics.
The energy of anything is not invariant. Simply changing reference frames can result in a drastic decrease or increase in the energy of an object or wave. For example, a moving car on a highway has a lot of kinetic energy as viewed from a person standing on the side of the road, but has negligible kinetic energy viewed from another car moving alongside the first.How can photons just change energy?
There is no change in any one photon's energy. Some are observed to have a high energy and some a low energy, but that difference is due to the observer's relative motion.Yes doppler is only about waves but what happens on a particle level?
In dopplerredshift you measure low energy photons on one side and higher energy photons on the other side.
How can photons just change energy?
I don't think that' a valid explanation. You view your own speed due the direct environment (concrete, grass, trees….) the observable speed of the other cars is based on the difference with your speed.For example, a moving car on a highway has a lot of kinetic energy as viewed from a person standing on the side of the road, but has negligible kinetic energy viewed from another car moving alongside the first.
The light emitted from a star is white. Yet we observe blue light on one side and red light on the other. How can photons change energy without inelastic scattering.There is no change in any one photon's energy. Some are observed to have a high energy and some a low energy, but that difference is due to the observer's relative motion.
No, we just choose to use the Earth as the de facto frame of reference when referring to speed and velocity for most of our everyday lives because it is convenient. However the truth is that in our own frame of reference we simply aren't moving and have no kinetic energy. This is a fundamental principle of physics.I don't think that' a valid explanation. You view your own speed due the direct environment (concrete, grass, trees….) the observable speed of the other cars is based on the difference with your speed.
Sure you are. You're asking how a car changes energy because you're asking how a photon changes energy and the two phenomena follow many of the same laws of physics.I'm not asking how a car changes energy.
The idea that photons have one specific energy is only applicable if you choose to measure from a single frame of reference. If you switch to another the photons may not have the same energy. To put it simply, they don't have a specific energy in general. Energy is conserved, but it is not frame-invariant.The light emitted from a star is white. Yet we observe blue light on one side and red light on the other. How can photons change energy without inelastic scattering.
You haven't given an example of a photon changing its energy!The light emitted from a star is white. Yet we observe blue light on one side and red light on the other. How can photons change energy without inelastic scattering.
What makes you think they changed energy? In the frame where the star’s light is white it remains white and has the same energy on all sides. The red and blue shift is due to the Doppler effect on the detector, not a change in energy of the light.The light emitted from a star is white. Yet we observe blue light on one side and red light on the other. How can photons change energy without inelastic scattering.
Which laws? I don't get why you think that's a valid comparison. A photon always travels at c, regardless the energy it has. A car does not.Sure you are. You're asking how a car changes energy because you're asking how a photon changes energy and the two phenomena follow many of the same laws of physics.
How do you know which frame of reference to take?The idea that photons have one specific energy is only applicable if you choose to measure from a single frame of reference. If you switch to another the photons may not have the same energy. To put it simply, they don't have a specific energy in general. Energy is conserved, but it is not frame-invariant.
We don't know why motion does that. The doppler is a description of a phenomenon it doesn't explain the phenomenon. Do you deny this?Observers can measure the energy of light. Is it hard for you to accept the notion that the energy observed depends on the motion of the observer relative to the source?
Why isn't the star taken as frame of reference?Energy is frame dependent, so if you want to claim that the energy changed then you need to identify what reference frame you think that happened.
I still do not see that you have established the starting point of your entire thread here, i.e. the connection between "particle physics" and "doppler effect". Why do you think particle physics can or should "explain" (whatever that word means) the doppler effect?How does particle physics explain the doppler effect? (including blue/red shift)
You're free to choose any one you like. There is no wrong or right choice.How do you know which frame of reference to take?
Sure we do. The energy of what you observe is dependent on your motion because of the way we define energy.We don't know why motion does that.
The Doppler effect is something we observe. It is also something that we can explain.The doppler is a description of a phenomenon it doesn't explain the phenomenon.
When a massive object moves at a speed that's nearly ##c## relative to you, this is what you observe. Very very small changes in the object's speed are associated with very very large changes in the object's energy. It is possible to get so close the speed ##c## that when the energy is increased by orders of magnitude there is a negligible increase in speed.A photon always travels at c, regardless the energy it has. A car does not.
To take for what?How do you know which frame of reference to take?
It can be. There's nothing wrong with that. But since the star is moving with respect to us here on Earth, you will get different measurements for the energy of the starlight if you measure in both frames.Why isn't the star taken as frame of reference?
The Principle of Relativity:Which laws?
It certainly can be, you just have to be clear. In the star’s frame of reference the energy does not change.Why isn't the star taken as frame of reference?
I deny it. Not only do we know exactly why motion does that, the derivation is very basic and well known freshman-level physics.We don't know why motion does that. The doppler is a description of a phenomenon it doesn't explain the phenomenon. Do you deny this?
Then why motion does that?I deny it. Not only do we know exactly why motion does that,
Yes but what does that matter? The speed of a car does not change for different observers.I'll be succinct: do you understand and accept that the speed and therefore the kinetic energy of a car are frame of reference dependent?
Yes it does. Different reference frame will measure different speed! That is what "frame dependent" means!Yes but what does that matter? The speed of a car does not change for different observers.
Yes but what does that matter? The speed of a car does not change for different observers.
Yep. This is why I said we need to start this walkthrough with these foundational physics concepts before even getting into Doppler shift itself.Yes it does. Different reference frame will measure different speed! That is what "frame dependent" means!
Zz.
Start with “In truth, relativity has just a single formula for the Doppler shift ...” here:Then why motion does that?
Obviously it does. It is e.g. 100 kph for observers on the side of the road and 0 kph for observers in the car.The speed of a car does not change for different observers.
Yes but that doesn't explain why motion does that. The 'fact'' that motion can change wavebehavior doesn't explain why it happens.Start with “In truth, relativity has just a single formula for the Doppler shift ...” here:
http://mathpages.com/rr/s2-04/2-04.htm
The geometry and algebra are very straightforward
Not true. The speed of a car is set, regardless of the observers. You need measuring devices to know the speed of a car. When you simply observe speed then the 100 kph is an interpretation without scientific value.Obviously it does. It is e.g. 100 kph for observers on the side of the road and 0 kph for observers in the car.
Yes, it does.Yes but that doesn't explain why motion does that.
There is no uniquely correct reference frame. That is the whole point of the principle of relativity. The roads frame and the vehicles frame are both valid, and the speeds in the respective frames are also both valid.You should try to reduce the observer effect as much as you can...by being in correct reference frame and using correct measuring devices//technology.
When you jump onto a slow-moving train one of the things that can make it easier is if you first run along with the train, matching its motion.Yes but that doesn't explain why motion does that. The 'fact'' that motion can change wavebehavior doesn't explain why it happens.
You mean like one of those radar guns that you point at something and it tells you how fast it's moving? If you stand still as that train approaches you the reading on the radar gun is different than when you don't stand still.You need measuring devices to know the speed of a car.
This reads like a statement along the lines 'Scientists are not as smart as they think they are'. The doppler effect is extremely well known and there is a very simple argument about how the spacing between the peaks and troughs of a wave in a medium and how a moving source or observer will produce or detect those peaks and troughs.The doppler is a description of a phenomenon it doesn't explain the phenomenon.