Doppler Effect on Light: Understanding Red and Blue Shifts in Galaxies

In summary, the Doppler effect is a change in the frequency of light when it is being emitted or received.
  • #1
mach990
5
0
Hi, I'm new to these forums. I just had a question about the Doppler effect on light (red and blue shifts of light). I've read how it is supposed to work, but I also read in a book that the speed of light is constant in all moving frames.

So if you've got a galaxy moving towards you, and it's throwing out photons towards you, all of which traveling at c, shouldn't there be no doppler effect because relative to one another, they're all traveling 186,000 miles a second, and would all reach you at the same time anyways? The analogy in the book (I think it was Hyperspace by Michio Kaku) said something about cars traveling at 99% the speed of light, and a train traveling at the speed of light, but to the car it would seem the train is still speeding ahead at 100% the speed of light, and not 1% the speed of light...

OR is it simply that if they're both going the speed of light, the effect can apply?

Bear with me, I am probably missing something obvious or just plain not understanding :biggrin:

Thanks for any replies. (And I hope this was the right category to put this in!)
 
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  • #2
From what I understand.

If you're in a vehicle traveling very close to the speed of light, time inside the vehicle will go normally, but outside the vehicle time will be slowed down, from an observer inside the vehicle.

I would love for someone that knows a bit more about this to give a proper explanation, I'm very confused as well hehe.
 
  • #3
Hi there,

The Doppler effect as nothing to do with the speed of light contanst. It simply says that if you are moving toward a light source, the frequency of the light will increase.

Whether the light is blue, red or purple, it all travels at the speed of light. The only difference is the distance between two peaks. As a matter of fact, the only difference between radio wave, micro wave, visible light, X-rays/gamma-rays lies in this distance between peaks.

Cheers
 

1. What is the Doppler Effect on Light?

The Doppler Effect on Light is a phenomenon in which the wavelength of light changes when an object emitting light is moving towards or away from an observer. This causes a shift in the color of the light, known as a red or blue shift.

2. What causes red and blue shifts in galaxies?

The red and blue shifts in galaxies are caused by the relative motion between the galaxy and the observer. If the galaxy is moving away from the observer, the light will appear more redshifted, indicating a longer wavelength. If the galaxy is moving towards the observer, the light will appear more blueshifted, indicating a shorter wavelength.

3. How does the Doppler Effect on Light help us understand the movement of galaxies?

The Doppler Effect on Light allows us to measure the relative motion of galaxies by analyzing the red and blue shifts in their light. By comparing the observed shifts to the expected shifts based on the galaxy's distance from Earth, we can determine the speed and direction of its movement.

4. How is the Doppler Effect on Light different from the Doppler Effect on sound?

The Doppler Effect on Light and the Doppler Effect on sound are similar in that they both involve a change in wavelength due to relative motion. However, the speed of light is much faster than the speed of sound, so the effect is much more pronounced for light. Additionally, the Doppler Effect on sound is perceived as a change in pitch, while the Doppler Effect on Light is perceived as a change in color.

5. Can the Doppler Effect on Light be used to determine the age of a galaxy?

No, the Doppler Effect on Light alone cannot be used to determine the age of a galaxy. However, it can provide valuable information about a galaxy's movement and evolution, which can be used in conjunction with other data to estimate its age.

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