# The Doppler Effect- According to Quantum Mechanics

• andmir92
In summary, the conversation discusses the relationship between quantum mechanics and the Doppler effect, as well as the limitations of the quantum model in explaining certain phenomena. The individual also seeks recommendations for resources to learn about quantized energy absorption, and asks for advice on learning differential equations and calculus in relation to quantum mechanics.
andmir92
I am just beginning to learn about quantum mechanics and I have already come up with a question regarding it. I know that light is absorbed by an electron at once and I know about the doppler shift. Yet is light emitted at once, or gradually? If at once, how could the wavelength be shifted because of the receding or approaching speed of a planet, and therefore, individual atoms (I know it can be shifted by gravity, but that's besides the point, I think)? If it gets emmitted gradually, then why (I mean, why is it absorbed at once and emmitted gradually)?
Can anyone offer any suggestions for books or website articles that specifically address quantized energy absorbtion? And as I am just starting and do not know anything about differential equations and calculus, should I try to learn it from a school textbook, wait until I take the class, or read a book that might explain it in easier terms (I am a sophmore in high school)?

Thank You

The Doppler effect is a macroscopic phenomena, and you are trying to fit it in a quantum model. Don't. Quantum physics doesn't deal with questions like "is the photon emitted at once" or "does the electron jump instantaniously between energy levels". That is taking the model too literally. Unlike classical physics, QP doesn't try and explain what "actually happens"..

When it comes to Doppler the only reasonable explanation is that the emitted wave is stretched or compressed when continuously emitted by a, relative to observer, moving source.

If you're looking for a detailed explanation of how an atom absorbs light, I'm sorry to say you'll probably be disappointed. The quantum model goes no deeper than to say that the atom absorbs the photon and an electron increases it's energy level accordingly. The model is mainly mathematical, I believe.

It's a good question. There must be a quantum mechanical explanation of the doppler effect. I can't think what it is at the moment though.

## 1. What is the Doppler Effect?

The Doppler Effect is a phenomenon in which the perceived frequency of a wave, such as sound or light, changes when the source of the wave is in motion relative to the observer. This results in a shift in the wavelength and frequency of the wave.

## 2. How does the Doppler Effect work according to Quantum Mechanics?

According to Quantum Mechanics, the Doppler Effect is explained by the change in the energy levels of particles due to their motion. When a source of a wave is moving, the energy levels of the particles emitting the wave shift, resulting in a change in the frequency and wavelength of the wave.

## 3. What is the difference between the classical Doppler Effect and the Quantum Mechanical Doppler Effect?

The classical Doppler Effect only takes into account the motion of the source of the wave, while the Quantum Mechanical Doppler Effect also considers the motion of the observer. This is because in Quantum Mechanics, particles can also act as waves, and their motion affects the frequency and wavelength of the wave.

## 4. How is the Doppler Effect used in Quantum Mechanics?

The Doppler Effect is an important tool in Quantum Mechanics for studying the behavior of particles and waves. It is used to study the motion and energy levels of particles and to make predictions about their behavior in different situations.

## 5. Can the Doppler Effect be observed in everyday life?

Yes, the Doppler Effect can be observed in everyday life. It is most commonly observed with sound waves, such as the change in pitch of a siren as an ambulance passes by. It can also be observed with light waves, such as the redshift of stars and galaxies due to their motion away from us.

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