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itoero
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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?Nugatory said:Doppler is a wave phenomenon and has no particular connection to particle physics.
itoero said:How can photons just change energy?
itoero said: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.Mister T said:There is no change in anyone 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.
itoero said: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.
itoero said:I'm not asking how a car changes energy.
itoero said: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.
itoero said: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.itoero said: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.Drakkith said: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?Drakkith said: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?Mister T said: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?Dale said: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.
itoero said:How does particle physics explain the doppler effect? (including blue/red shift)
itoero said:How do you know which frame of reference to take?
We don't know why motion does that.
The doppler is a description of a phenomenon it doesn't explain the phenomenon.
itoero said:A photon always travels at c, regardless the energy it has. A car does not.
itoero said: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.itoero said:Why isn't the star taken as frame of reference?
The Principle of Relativity:itoero said:Which laws?
It certainly can be, you just have to be clear. In the star’s frame of reference the energy does not change.itoero said: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.itoero said: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?Dale said: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.russ_watters said: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?
itoero said:Yes but what does that matter? The speed of a car does not change for different observers.
itoero said: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.ZapperZ said: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:itoero said: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.itoero said: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.Dale said: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.Dale said: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.itoero said: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.itoero said: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.
itoero said:Yes but that doesn't explain why motion does that. The 'fact'' that motion can change wavebehavior doesn't explain why it happens.
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.itoero said:The doppler is a description of a phenomenon it doesn't explain the phenomenon.
itoero said:Yes but that doesn't explain why motion does that. The 'fact'' that motion can change wavebehavior doesn't explain why it happens.
The Doppler effect is a phenomenon where the frequency of a wave appears to change when the source of the wave is moving relative to the observer. This effect is commonly observed in sound waves, where a moving source will cause a change in pitch perceived by the listener.
The Doppler effect can also be observed in the behavior of particles, such as electrons or photons. When these particles are in motion, they can exhibit a change in frequency due to the Doppler effect. This can be seen in the redshift or blueshift of light emitted from stars, which is caused by the motion of the stars relative to Earth.
The Doppler effect in sound waves is caused by changes in frequency due to the relative motion of the source and observer. In particle behavior, the frequency change is due to the motion of the particle itself. Additionally, the Doppler effect in sound waves is dependent on the medium through which the wave is traveling, while the Doppler effect in particle behavior is not affected by the medium.
The Doppler effect is a useful tool in various fields of scientific research. In astronomy, it is used to study the motion and properties of distant objects in the universe. In medicine, it is used in ultrasound imaging to measure blood flow and detect abnormalities in the body. The Doppler effect is also used in weather forecasting, seismology, and other areas of physics and engineering.
Yes, the Doppler effect can be observed in everyday life. For example, the change in pitch of a siren as an ambulance or police car drives by is a result of the Doppler effect. The change in the sound of a train horn as it approaches and passes by is also due to the Doppler effect. Additionally, the redshift and blueshift of light from moving objects, such as cars or airplanes, can also be observed in everyday situations.