Red shift | Scale of the universe | Cosmology & Astronomy | Khan Academy

Created by Sal Khan.

Cosmology & Astronomy on Khan Academy: The Earth is huge, but it is tiny compared to the Sun (which is super huge). But the Sun is tiny compared to the solar system which is tiny compared to the distance to the next star. Oh, did we mention that there are over 100 billion stars in our galaxy (which is about 100,000 light years in diameter) which is one of hundreds of billions of galaxies in just the observable universe (which might be infinite for all we know). Don't feel small. We find it liberating. Your everyday human stresses are nothing compared to this enormity that we are a part of. Enjoy the fact that we get to be part of this vastness!

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[Trowblood]

Laser induced plasma redshift can be shown in the lab.
It always amazed me that with all the intricate equations related to measuring cosmic distance with redshift; any plasma interactions are totally ignored as a factor in the results for redshift.
Then there's the quasars now observed that don't display any redshift.
I guess there's still a lot to learn here.

[daloshea]

Question: why do we assume the photon is intrinsically still connected to it's source after its emission? Is that not comparable to the idea of saying that an object thrown into the air still feels the "throwing" force once it is in the air, which we understand to be incorrect? Just an observation that makes me curious

[EdvardBolaasMusic]

very informative and great videos man, thank you so much for taking the time to make them, props to you friend

[davidgorelle]

Whoa! I think I finally get it. Basically a red shift is the Doppler effect of photons.

[saurabhjoshi]

Couple of questions, so visible light can be red shifted so much that it could turn into microwave or any other invisible spectrum? The galaxies that we see from the telescope, they would be red shifted? Lastly if they are not moving away, and are stationary then how would we perceive it?

[millieegw]

oh my god, thank you so much. I have an exam on this tomorrow and I was freaking out, but now I understand <3

[navedkhan-swhf]

Very nice explanation to the idea, thanks!!!

[Goproflying]

@DeluxeWarPlaya Yes, its the light version of the doppler shift.

[valsarff]

Thank you for this visualization. I now realize that Halton Arp was correct. I already knew there was no CMB, and now I can see the universe is not expanding. The standard model of cosmology is in deep doodoo for sure. The doppler effect works for sound because those waves affect the medium travelled in. But light doesn't do that. Awesome!

[matthiasrandler]

Question:
So if those 2 objects emmited their light at the exact same time, at the exact same distance, relative to the observer, why then would the wavelenght change, when it hits the eye?
The moment it emitted light, it had a fixed position and started to fly away from its source, just as it would happen with a stationairy object. So if the information about its position eventually reaches you, how then would this information know, that its source flies away from you?
Let us assume that an object emits light and from one second to the next the object vanishes. Now the light flies towards you, the observer, even though the object is gone. The information you will receive is based on a particular point in time, space. A fixed position. It doesent matter what the object did after the information flies away from it. Once it starts to fly towards you, it can be gone or fly further away from you, which should not matter at all. Why would it change its wavelenght?
It is in no way, shape or form connected to its source anymore.

[haritadepalli]

I'd say the explanation is still perplexing. The way it was explained at 4:27, the light from the moving object is perceived as if it is originating at its final position when the light reached the observer. Why I am perceiving a future location of the light source, well after it left from its original spot ?

[Trowblood]

Yes! I think I am implying just that.

Despite all the negative output against the universe being electrical in nature; upon checking and reviewing all the evidence it presents; It seems to me that the work of the Thunderbolts group, when it comes to many details, has begun to leave mainstream opinion in the dust.
There is certainly a long history of relativity and people to back its claims but when you check the finer details; the electric universe theory seems leagues ahead in terms of proof.

[wolfshares]

So red shifting can cause light emitting objects to become invisible

[lanog]

Great stuff! I love to review the simple stuff a lot, it seems to help.

[inomis]

Correct me if im wrong please. But i thought The doppler effect applied to light too, The only difference being that its called the doppler effect when the object is moving relative to space, while its known as redshift when the object is standing stil relative to space and it´s space itself that is moving away from us.

[arthistoreebc]

I just love this colorful lesson. :))

[Jesusisyhwh]

It is not redshifting. It is just that the amount of atmosphere that the light has to go through increases and mostly it is the longer wavelengths (such as red) that get through. The rest are absorbed by the atmosphere.

[rbkstudios]

A very important basic question though
How do we know that light received is red shifted?
And if it is, then to what extent


Doesn't this Doppler shift clash with the colour-temperature emission spectra?

[rwh]

@kiensmf I agree the light wave moves through space 'as normal' from a moving source. Instead of 'moving source', think about 'expanding space' similar but different. Due to expansion of the universe (expanding space), ALL light has a 'redshift' (stretched wavelength) because space has expanded during the journey time to the observer.

[CarlMahnke]

But still: How does an expanding space creates a redshift? Normally, a photon doesn't care through how much space it must travel. The distance doesn't affect the wavelength.