Hubbles Law - 13c - Intro to Astronomy Sessions

Describing Hubble's Law as a pattern between redshift velocities and galaxy distances. This was the first observational evidence that our Universe is expanding.
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Please note that this was designed as an introductory survey of astronomy course, mostly for non-science majors, and does simplify many of the topics accordingly. I encourage people who are just getting into astronomy to use this as a jumping off point for more in depth studies. I've tried to edit out specific references to my course (regarding assignments, tests, etc.) but I might have missed some. Finally, scientific fields are constantly advancing, with new data and studies resulting in our ideas being continually improved. This means some of the ideas presented here may soon be out of date, so I again encourage people to continue to investigate whichever topics are of particular interest to you.
Opening Image Credit: www.nasa.gov/feature/goddard/...

[@NalitaQubit]

This explains Hubble’s Law very eloquently. Thank you for your excellent way to teach. You are a priceless educator.

[@homiesmol935]

Does the hubble law assume that the acceleration of the expansion of the universe is constant? Would we get different hubble constants (different slopes) as we observe further back in the past? If so, how do we measure distances using redshift taking the acceleration of the expansion of the universe into account?
Thanks for the amazing video!

[@PhysicistMichael]

For galaxies that are not super far away (within a billion light years or so) or equivalently have redshifts (v/c) quite a bit less than one, any acceleration of the Universe will not have had a large enough effect to throw off our numbers a lot.
However, Hubble's constant is a bit misnamed in that it's not constant over cosmological time (it is constant in the sense that it doesn't depend on what direction you're looking in). At much greater distances, you need to incorporate a specific model for the Universe (what is the matter and energy content) to determine the distances. An empty universe, a universe with just a little or a lot of matter, or with other contents (like Dark Energy) will have different dynamics described by the Friedmann equations (a solution to the equations for General relativity for a universe with no special locations or directions). I'll mention some of these properties in an upcoming video in this series, but the details are more complicated than I could get into for this intro course.
Note that these different models for the Universe also make different predictions about how the brightness of galaxies and the angular size of different galaxies on the sky should vary. So this give us more information to test which models of the universe might actually be correct.
Thanks for the great question!

[@homiesmol935]

@@PhysicistMichael Thank you for the thorough explanation!

[@NalitaQubit]

Are you an Everettian?

[@PhysicistMichael]

I try to apply proper skepticism towards any ideas I'm presented with, meaning I try to withhold accepting ideas until there is sufficient evidence to support it, and then my acceptance is tentative. And the gold standard of evidence is for the proposed model to predict a new phenomenon that is subsequently detected.
If you're referring to whether I accept the many worlds interpretation of quantum mechanics, I'm not convinced (I also am not convinced that it is wrong). It seems like it COULD answer some questions about quantum mechanics, but I'm not aware of any new predictions that it is able to make that differ from a number of other QM interpretations. In this kind of situation I think the appropriate response is to keep working on both this idea and competing ones to identify points where we can test disagreements between the models.

[@NalitaQubit]

Fair enough. Thank you, professor.