Unit 3: Let There Be
Light
NSCI 110, Origins of the Cosmos
Regent University

PowerPoint Overview
▪
Hubble’s Redshift Law
▪
The Doppler Effect
▪
Age of Universe from Hubble’s redshift
▪
Georges Lemaitre & Einstein
▪
Pope’s reaction and then Georges’ Response
▪
Getting scooped on the CMB
▪
Reactions to the CMB

Redshift and Measuring Stars
/

The Doppler Effect of Light
▪
–
The Trumpeter on a Moving Car
▪
We do not notice this effect with light because most visible objects
do not move fast enough to detect a change (with our eyes)
–
𝑓𝑓
=
1 +
Δ𝑣𝑣
𝑐𝑐
𝑓𝑓
0
▪
f is the observed frequency
▪
Δ𝑣𝑣
is the velocity of the receiver relative to the source (it is positive when they are
moving towards each other and negative when they are moving away)
▪
c is the speed of the wave (for the trumpet it would be the speed of sound… for a star it
would be the speed of light)
▪
𝑓𝑓
0
is the emitted frequency of the source

The Trumpet Math▪The Trumpet Player looked like he was playing a ‘C’–This wave has a frequency of 261.33 Hz–The speed of sound is 768 MPH, the car was driving at roughly 35 MPH–What did the observer hear as the car was driving towards him?

Starlight Red/Blue Shifts
Each Element Produces
a Unique Set of Spectral
Lines

More Than Just Hydrogen

More Than Just Hydrogen

Redshift + Star Distances = New Law?

A 2015 Update
The Hubble diagram of galaxies [distance vs. redshift
(velocity)] from a large combined SNIa distance-
indicator sample
The black line (that fits the data so well) represents the
d
(
z
) relation expected for the current cosmology (a flat
universe with mass density 30% and cosmological
constant 70%) and a Hubble Constant of H
o
= 70
km/s/Mpc.
This goes from z = 0.01 (or 140 million light years) to z =
1 (7,000 million light years)

Redshift and Measuring Stars
/
z = 0.14 corresponds to a distance of 1.8 billion light years

Hubble’s Law
▪
𝑣𝑣
=
𝐻𝐻
0
𝑑𝑑
–
Where v is the speed of the galaxy, d is the distance to the galaxy and H
0
is
Hubble’s constant—H
0
would have to have dimensions of inverse time
–
If H
0
is a measure of how fast objects are moving away, at some point in the past
they were touching
▪
If I told you my average speed to Richmond was 90 MPH and I find myself 98 Miles
away, we know I left Regent ~1.09 hours ago
–
From this 2015 paper we see they model H
o
= 70 km/s/Mpc~ 2.3 x 10
-18
s
–
1
𝑀𝑀
0
= 4.4
𝑥𝑥
10
17
𝑠𝑠
~ 13.8
𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏 𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑠𝑠

3 Types of Redshifts
▪
Largest Effect:
–
The Universe’s Expansion
▪
Only seen in closer galaxies:
–
Movement of galaxies relative to each other (a
galaxy moving towards us can have a ‘blueshift’
▪
Tiny Effect:
–
A Gravitational Redshift—light can be shifted itself
from the massive gravity in a galaxy
–
Einstein’s Theory of GR again predicts this
–
“It agrees exactly with the measurements of this
effect”—Dr. Radek Wojtak in 2011 upon seeing new
SDSS data

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- Summer '18
- Dr. Marshall Bowles
- Big Bang, Redshift, Hubble's law, CMB, Georges Lemaître