Okay, you are telling me people at different distances see different colors!

This is the story of a color, a color that has travelled a distance, say a million light years. What about it?

By chance, if you are a keen observer, you would’ve noticed that each time an ambulance or a police car passes before you something about its siren change as it races further down the road. The sound gets less loud and it loses its shrillness compared to what it was when it was near you. What you have noticed is know as the Doppler Effect. Yes, its real science not just something you just feel.

What’s the science behind the Doppler Effect?

Doppler Effect is a phenomena that comes in effect when we deal with sound waves or even electromagnetic waves. I think an example was a great wat to start talking about the effect. You can now comprehend the latter effortlessly.

Waves have 3 main mechanical properties:

1. Amplitude: Height of the Wave
2. Wavelength: Length of the Wave
3. Frequency: Wavelength/second (kind of like velocity)

These three terms will come in handy afterwards. Referring to the example itself, shrillness is analogous to the frequency of the sound.

Higher the frequency, more shrill the sound is.

As mentioned, the sound loses its shrillness as it goes further from you. This means the frequency decreases. As wavelength ∝ 1/frequency, the same would follow the increase in its wavelength.

Acoustic Doppler Effect

Now imagine the exact converse for the ambulance with the siren coming towards you. The shrillness of the sound would increase as it approaches you.

It’s frequency increases and wavelength decreases

The same thing happens with light, follow below

Now, refer to the picture below

Scientifically elaborate picture of electromagnetic spectrum.

Closely notice the fact that that higher is the wavelength of the wave, the more red it becomes. Vice-verse is true for violet. The extremes of the color spectrum you see up there makes up only a 0.0035 percent of the entire electromagnetic spectrum. Just keep that in mind presently.

One more fact that relates to the same is:

The more blue the wave is, more energy the wave has, less wavelength the wave has.

The converse is true for red: less energy, less wavelength, more frequency.

Now put into effect, the great Doppler Effect. If a light from far away is reaching you, say 100 million lightyears, it would become more red, because its wavelength increases and frequency decreases. Here, the cause behind this is similar to that of sound, easy to understand.

Imagine a galaxy, 100 million lightyears far away from you is racing away from you at a speed close to speed of light. It emits light towards you similar to every object in this universe. Assume it was Blue in color.

The conditions are similar to that of an ambulance, it is racing away from you and it emits something in form of waves.

Ambulance : Sound :: Galaxy : Light

In the latter one, exact same things happens, the wavelength increases and frequency decreases.

Now, the catch here is the increase in wavelength is not a spontaneous process. The increase is infinitesimally gradual. A person 50 million light years away from the Galaxy would not see complete red, he/she/they would see probably a yellow or an orange galaxy.

This was the Cosmological Doppler Effect, simply explained

Now, why is the Galaxy racing further from you and what happens to the rest of the electromagnetic spectrum?

The answer to this question you may find in the next story, or you curiosity!!

Thanks for reading till here, awesomely high-five 🙌🙌. Have a great day ahead!!