The Expanding Universe: Redshift and the Big Bang Theory

#BigBang #Redshift #ExpandingUniverse #EdwinHubble #Cosmology #science #universeexploration #GalaxyDistances #CepheidVariables #CosmicHistory

This is part of my intro Astronomy class I taught at Willam Paterson University and CUNY Hunter.

What you’re about to watch is a captivating journey into the mysteries of the Big Bang and the concept of redshift, as I explore one of the foundational pillars of cosmology. In this lecture, I delve into Edwin Hubble’s groundbreaking discoveries and extend them to the cosmological redshift-distance relationship.

Starting with a revisitation of Hubble’s initial exploration of nearby galaxies, I expand on his discovery of the expanding universe. You’ll learn about the cosmological principle, which states that the universe is homogeneous and isotropic on the largest scales, meaning it looks the same in every direction and no place is special. This principle is a cornerstone of modern astronomy and cosmology.

I will show you the evidence for redshift and explain why it supports the theory of the universe’s expansion. Redshift, the change in light’s wavelength as objects move away from us, provides a measure of this expansion. Through a deep dive into historical data and modern techniques, I’ll help you understand how astronomers measure galaxy distances and their velocities, leading to the realization that our universe is expanding.

You’ll take a closer look at the work of Vesto Slipher, who measured the redshift of spiral nebulae, leading to the discovery that most galaxies are moving away from us. By measuring distances to these galaxies using standard candles—Cepheid variables, whose luminosity relates to their period of variation—Hubble demonstrated a linear relationship between distance and recession velocity, now known as Hubble’s Law.

I’ll show you how redshift is calculated and explain how it ties into the Hubble parameter, the rate of the universe’s expansion. I will also cover the intricate process of measuring these phenomena, from using large telescopes to painstakingly collecting spectra over many nights.

I’ll describe the challenges faced by early 20th-century astronomers, the contributions of key figures such as Henrietta Swan Leavitt, and the technological hurdles they overcame. You’ll understand the significance of Hubble’s measurement of a 500 km/s/Mpc expansion rate, and how subsequent calibration refined this to the modern value closer to 72 km/s/Mpc.

I will touch on contemporary research, including recent measurements and the tension between direct and indirect measurements of the Hubble constant. This segment underscores the ongoing scientific endeavor to understand the universe’s expansion rate.

Lastly, I will elaborate on the concept of the expanding universe, explaining how light’s journey across spacetime demonstrates this expansion. You’ll discover the fascinating implications of this, such as the realization that the Big Bang occurred everywhere in the universe at once, a concept that defies common sense but is supported by robust observational evidence.

Join me as I unravel the intricacies of the universe’s expansion, the role of redshift, and the vast scale of cosmic history. This lecture is not just a glimpse into the past but a gateway to understanding the dynamic and ever-expanding cosmos.

[phdupont]

Dr. Kendall, I just wanted to drop you a note with my eternal thanks for placing this fantastic trove of information online and available to all. Your dedication of time, effort and knowledge is a beacon of light in the darkness. You’re a genuine quasar of informational dispersion, right here on our little blue marble in spacetime.

[Choofalong]

OH MY GOD! The old version of this video is the first I EVER watched of yours! Looking forward to this one. What's another hour together after the last 200 or so I've already seen?

Keep it up man, very much appreciate the effort you put in.

EDIT: swear not stalking, just enjoy your content: G'day, from Down Under!

[DevanMccallister]

Great information video. I listen to your videos when I go to sleep @ night. And no, that’s not a bad thing lol

[wrighty]

Good to hear you give Humason some recognition. Most just mention Hubble.

[frederf]

Quick Q: emission proper distance (A), reception proper distance (B), light travel distance (Z) is A<Z<B? Is it some other ordering? Is Z some approximate fraction of B/A like sqrt(1/2) or 1/e? Does it depend on the particular age?

[jcw]

Hopefully you will provide insight into the issue of "Dark Matter" as well as the phenomenon labelled "gravity" from the large scale to the smallest imaginable. These are the greatest mystery on my small mind.

[vanessacherche]

cool to see the data of things i've heard about. great lecture :)