Why Do Galaxies have a Redshift Proportional to Distance?

We know that the universe in expanding because of the fact that galaxies are observed to be rushing away from us in all directions. How do we know this to be true?
This is the fourth of the videos in my new series of Cosmology. I'm going through Dr. Barbara Ryden's textbook "Introduction to Cosmology". If you follow along, you'll get a full upper-division undergraduate course in Cosmology. I used this textbook at William Paterson University.
This course will cover the current state of the science of Cosmology. To follow along, it'll be a good idea for you to ge to know your calculus. Here are the topics of this video:
Introductory Cosmology
Chapter 02: Fundamental Observations
Section 03: Redshift is Proportional to Distance
Some things covered:
Nearly all Galaxies Show a Redshift...
Does cosmic redshift happen by chance?
Does the redshift violate the cosmological principle?
How can we quantify the expansion of spacetime?
What are the Hubble Time and Distance?
How does measuring the rate of expansion give us the age of the universe?
What is the Steady State Model?
Why does the Big Bang win over the Steady State?
What's beyond the cosmic horizon?
NGC 1068: ned.ipac.caltech.edu/cgi-bin/...
2MASS J18082002−5104378: The brightest (V = 11.9) ultra metal-poor star : www.aanda.org/articles/aa/ful...
The First Stars: A Low-mass Formation Mode: ui.adsabs.harvard.edu/abs/201...
GOODS: www.stsci.edu/science/goods/
Textbook: / introduction-to-cosmology
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/ @jasonkendallastronomer

[@Truth_Teller_101]

The best teachers are those who have a genuine passion for the subject, and I haven't seen cosmology so eloquently discussed in such an easy to understand way since Carl Sagan.

[@Namelis1]

Hi. This is an uniroinic, backhanded compliment explaining how pleasant it is to sleep through this lecture.

[@Choofalong]

I REALLY enjoy getting into the actual formulas and do some maths!
Such a pleasure to see it, as opposed to all the "popular" channels that seem to be scared to show any numbers at all

[@pedrojorge1912]

I love these videos from Professor Kendal, I feel like I've unlocked so much from the universe from his lessons!

[@KF1]

Great remake. Lemaitre was a badass

[@agxryt]

Vesto Slipher sounds like a bad ass Jedi Knight

[@Isuzu81]

Redshift is also proportional to age. The younger universe was expanding, but has it slowed down?

[@astronomy-channel]

I know what’s at the edge!!

[@JasonKendallAstronomer]

Bono?

[@astronomy-channel]

Yes a bono theory that explains the shape of the universe!

[@abighairyspider]

Halton Arp

[@JasonKendallAstronomer]

Arp was shown to be incorrect a long time ago. For those following at home, Arp came up with some amazing observations that tried to show that cosmological redshifts can't work given some quasar's proximity to galaxies, as well as "streamers" and other things. However, later Hubble Space Telescope imagery and now JWST images show that all the "anomalies" were actually due to the low resolving power of ground-based telescopes, and Arp's own selection effect of being really good at finding photogenic colliding galaxies. Now we know that most galaxies undergo mergers, and that quasars suffuse the cosmos, making line-of-sight conjunctions seem to be significant, when in point, they are not. SDSS quasar surveys, as well as direct imaging of quasars' surrounding galaxies have put to rest Arp's quest to deny cosmological redshift.

[@astronomy-channel]

don't red dwarfs live trillions of years Jason???

[@JasonKendallAstronomer]

Yes, but, the universe isn't trillions of years old, so none have become "black dwarfs" yet.

[@Fat_Tony_Capaldi]

Excellent lesson. Keep them coming brother!

[@JasonKendallAstronomer]

Thanks! Will do!

[@Fat_Tony_Capaldi]

1100 views, and only 59 likes? Smash the like button for this guy!