The Hot Big Bang
-
Upload
tara-henderson -
Category
Documents
-
view
37 -
download
1
description
Transcript of The Hot Big Bang
![Page 1: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/1.jpg)
The Hot Big Bang
Monday, November 17 Pick up corrected Problem Set 6 (average score = 84);
Recitation 4:30 pm today, McPherson 4054
![Page 2: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/2.jpg)
Hot Big Bang Model:
Universe began expanding a finite time ago from a very dense, very hot initial state.
DenseDense = particles packed close together. HotHot = particles moving rapidly.
![Page 3: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/3.jpg)
Hot Big Bang Model (continued):
As space expanded, the universe became lower in density and colder.
Expansion of space has been continuous since the “Big Bang”
(start of expansion).
![Page 4: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/4.jpg)
Idea of expanding space: Alexander Friedmann (1922).
Observation of expansion: Edwin Hubble (1929).
Coining of phrase “Big Bang”: Fred Hoyle (1949).
Who invented the Big Bang Theory?
Idea of initial dense “primeval atom”: Georges Lemaître (1931).
![Page 5: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/5.jpg)
“BigBig BangBang” is a misleading name.
Galaxies are not flying through space like shrapnel after an explosion.
They’re moving apart along with expanding space.
The textbook laments that the name isn’t “Expanding Space Theory”.
![Page 6: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/6.jpg)
I lament that it isn’t “Horrendous Space KablooieHorrendous Space Kablooie”.
![Page 7: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/7.jpg)
There are some special times during the expansion.
t = 0: Expansion starts.
t ≈ 3 minutes: Protons & neutrons combine to form nuclei (Big Bang Nucleosynthesis).
![Page 8: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/8.jpg)
t ≈ 400,000 years: Protons & electrons combine to form hydrogen atoms. Universe becomes transparent.
Photons decoupledecouple from matter.
free protons & electrons
hydrogen atoms
![Page 9: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/9.jpg)
Until t ≈ 400,000 yr, protons, electrons, He nuclei, & photons interacted frequently. Thus, they
all had the samesame temperature.
Today’s inhomogeneous universe is full of things with differentdifferent temperatures.
![Page 10: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/10.jpg)
The very early universe had a very high
temperature.
![Page 11: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/11.jpg)
t ≈ 13.7 billion years: Intelligent life in at least one location in the universe.
More special times.
t ≈ 750 million years: Formation of first stars and galaxies.
![Page 12: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/12.jpg)
nucleo-nucleo-synthesissynthesis
trans- trans- parencyparency
11stst stars & stars & galaxiesgalaxies
3 min3 min 400,000 yr400,000 yr 750 million yr750 million yr
![Page 13: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/13.jpg)
What evidenceevidence supports the Hot Big Bang Theory?
Before the 1920s, everyone on Earth thought the universe was not expanding.
Scientists generally don’t accept radical new theories without strong proof.
![Page 14: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/14.jpg)
Flashback: Top 3 pieces of evidence for the Hot Big Bang.
1) Dark Dark night sky → Finite age for universe.
2) RedshiftRedshift proportional to distance → Homogeneous & isotropic expansion.
3) Cosmic Microwave Background Cosmic Microwave Background → Universe was hot & dense enough to be opaque.
![Page 15: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/15.jpg)
Other bits of evidence for the Hot Big Bang.
4) ¼ helium + ¾ hydrogen¼ helium + ¾ hydrogen → Universe was hot & dense enough for Big Bang Nucleosynthesis.
5) Age measurementsAge measurements of stars & planets are less than the Hubble time 1/H0 .
6) Large scale structure Large scale structure looks like that in simulations of an expanding universe.
![Page 16: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/16.jpg)
About the large scale structure: We knowknow what density fluctuations were present
when the universe became transparent.
In a static universe, the fluctuations would grow exponentiallyexponentially.
![Page 17: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/17.jpg)
In an expanding universe, gravitygravity is trying to make the dense regions collapsecollapse,
expansionexpansion is trying to pull them apartpull them apart. Growth is slow.Growth is slow.
linear growth
power law
exponential
![Page 18: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/18.jpg)
Structure seen in a simulationsimulation:
![Page 19: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/19.jpg)
Structure seen in realityreality:
![Page 20: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/20.jpg)
Hot Big Bang explains:
Redshift & distribution in space of galaxies (t = 0.75 →13.7 billion years).
Existence of Cosmic Microwave Background (t ≈ 400,000 years).
Production of 4He, & a little 7Li, by Big Bang Nucleosynthesis (t = 3 → 15 min).
![Page 21: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/21.jpg)
Gosh! We understand what the universe was like when it was a
few minutes old!
1) At t < 1 minute, things get more speculative.
2) Cosmologists love to speculate.
![Page 22: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/22.jpg)
The Large Hadron Collider at CERN (between France & Switzerland)…
…is nicknamed the “Big Bang Machine”. Why?
![Page 23: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/23.jpg)
The LHC will accelerate protons until they have a kinetic energy of 2 2 × 10× 10-6 -6 joulesjoules.
This is a lotlot of energy for one proton (mc2 for a proton is 2 × 10-10 joules).
In the early universe, the temperature was high. All All particles had lots of kinetic energy.
![Page 24: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/24.jpg)
The particle energy produced by the LHC will be comparable to the particle energy
1010-13 -13 secondsseconds after the Big Bang.
Once they actually get it working.
![Page 25: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/25.jpg)
quantum foam Planck length Planck time
quantum gravity theory of everything loop quantum gravity
M-theory grand unified theory
baryogenesis electroweak unification quark-hadron transition
If you like to speculate about the very early universe (t < 3 minutes),
then section 11.2 is for you!!
None of these topics will be on the final exam.
![Page 26: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/26.jpg)
“…long words Bother Me.”
I will continue to concentrate on things that are observable (stars, galaxies, CMB) and events that have directly observable
consequences (BBN and helium-4).
![Page 27: The Hot Big Bang](https://reader035.fdocuments.us/reader035/viewer/2022062221/568137ec550346895d9fa474/html5/thumbnails/27.jpg)
Wednesday’s Lecture:
Reading:
Chapter 11
Density of the Universe