Edwin Hubble, Doppler Shift, and the Expanding Universe

So we've made it all the way to the 20th century with the history of astronomy. Plenty had to happen to get us to that point, but the most amazing stuff is yet to come! Shortly after Einstein did his best work, a guy named Edwin Hubble demonstrated that what we thought was the entire universe was actually just one little island of stars out of billions of other galaxies. And that's just the tip of the iceberg! The universe is also expanding! What does all this mean for cosmology? Let's find out.

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[fahad_hassan_]

Criminally underrated channel, you deserve more than a billion subscribers!

[tomisoetan]

Thanks so much for this professor Dave! In all honesty I was avoiding this video because I saw it in my recommendations and I thought it would be complex and hard to understand. You explained it all brilliantly and make me excited to learn more about this! I’ll surely be checking out the rest of this series and be doing some reading on this. Have a great day and keep doing what you’re doing please!

[laptopreviews]

Can't wait for upcoming episodes.. I kinda like space....

[johugr]

Thanks for your clear explanation Professor Dave. I have a couple of questions as a non scientist. The further away we are looking the further back in time. So how do we know that those galaxies have not slowed up since? If the universe expansion was slowing would you not expect to see older galaxies moving away faster? Also accepting that the universe is expanding, the greater the distance the galaxy the greater the difference in its "direction of travel" from our own. Presumably this is covered for in the maths?

[christianlundmand]

Love it! One correction though: The spectra shown as emission spectra are actually absorbtion spectra.

[EleanorPeterson]

5:50 - Was anybody else waiting for the universe to pop?

[muhammedzahir]

Wow, thanks professor Dave, this really helped me a lot. Thank you so much.

[samjordan]

Professor Dave. Thanks for all your fab videos. I am a high school ( secondary school ) physics teacher in the UK. I think they are great. You always seem to pitch it just right. Accessible yet but with some nice high brow details for the more inquisitive!

[eigentlichtoll]

4:23 It should be made clear, that redshift and blueshift can be caused for different reasons. Those are, as far as we know, Doppler effect, gravity and expansion of space.

[davidhine]

Hubble's Constant can be easily calculated using ONLY the speed of light (C) and Pi 2 X a megaparsec X C, divided by Pi to the power of 21 = 71 K / S / MPS. This equation comes from the "Principle of Astrogemetry"

[jaydoubleli]

at 4:50 how were the Expected values of each galaxy's spectra obtained?

[maitland]

This is really good, and I'm going to show it to my students. I have a teeny critique, which is that when you say "emission spectrum" you show an absorption spectrum, no?

[fallendown]

... i am speachless... Good job Houble

[kingvsj]

Hey hi professor! Can it be that the universe just like other elements has a tendency to become stable. And its expanding in order to make itself stable relative to all the integrated particles present in it?
BTW UR VIDEOS ARE ASWM!

[mr.Mohit]

respected sir
can you please upload the notes they are beneficial for us.

thank you sir

[I-AM-A-NERD]

the Doppler shift, like the Dopler effect

[ekojar]

If Light and sound has a shift effect when it's moving, Does spacetime and gravity also have shift effect? Like how light gets lower and sound becomes lower pitched, does spacetime stretch and gravity get weaker when spacetime is moving away? I feel like the answer to the expansion of the universe lies somewhere in that along with something I have been thinking about. Surface area of atoms or matter. When I think of the early universe, I picture an endless sea full of salt grains. The grains being all atoms. When 2 grains of salt combine together, there are two sides that are now essentially pushing space out of the way, and now the space has nowhere to go, no cracks to fill, so all this extra space goes out and around causing everything to separate further from its neighbors.

[simon]

How did Hubble realise that the redshifts correlate with not only speed but also distance? I mean didn't we start measuring distance of the galaxies only after assuming such correlation? I can imagine that he used mere brightness as as an indicator... but since then we observed "quasars" which are very bright and also have very high redshifts ... and we ASSUMED that according to Hubble's Law they must just be very HUGE distant galaxies...

I mean is there a chance that Hubble was wrong? (Not to mention how Einstain's Relativity theory should technically make light immune to the Doppler effect - yeah I know that we can just try to think that space itself stretches... but really - it's already a "stretch", don't you think? ;P)

Im just curious if there are any additional evidence for the Hubble's Law :)

[stan]

I just cannot wrap my head around the ideas that: 1. Gravitational attraction between the Milky Way and Andromeda can be greater than the "force" (for lack of a better word) that is supposedly causing all other galaxies to move away from each other. 2. The idea that any object (i.e. a Galaxy) can be accelerating at an exponential rate AWAY from anything else. I am admittedly uneducated in these matters, but as far as I know, there is no phenomena here on earth that is comparable to that, and the only way something can accelerate at an exponential rate is when it's being drawn TOWARD something else. 3. The idea that no matter which galaxy you might be looking out from, every other galaxy would still appear to be moving away from you at an exponential rate. That just doesn't make sense to me. 4. Why isn't this "force" that is causing galaxies to move away from each other so rapidly also causing galaxies themselves to be ripped apart? Can you possibly explain these things in a way I might understand? Thanks!

[dalegriffiths]

Sorry but they are absorption spectra and not emission spectra
Otherwise nice video