NSCI 110_Unit 4_From Dust to Dust.pdf - The Big Bang Regent...

The Big Bang
Regent University

Up Unto This Point
• The universe is very large
– Parallax, Cepheid variable stars, Hubble’s Law
• General Relativity includes the most accurate set of equations ever
written
– Began with several immediate tests: precession of Mercury’s perihelion, 1919
eclipse, redshift of space
• The universe is expanding—it was once together
– What do we expect to see if it was once together?
– It was once in thermal equilibrium—at some point it cooled enough so atoms would
no longer be ionized (Cosmic Microwave Background)
– An astrophysics group was building a machine to measure it and got scooped!

Where do We Go From Here?
• Before the Cosmic Microwave Background
• The first 20 minutes of our universe
• Observations of the first 20 minutes
• Stealing God’s Glory?

Before the CMB
• The CMB: an era when the universe cooled so atoms could form
– What’s smaller than an atom?

Before the CMB
• The CMB: an era when the universe cooled so atoms could form
– What’s smaller than an atom?
• Was the universe ever so hot that nuclei could not even form?
– You can predict the temperature of the universe from the Friedman Equations
– You find that 380,000 years before the CMB the temperature was hot enough to
break apart even nuclei
• At this moment (~1 second after the universe ‘began’)
– The temperature is so hot that no nuclei can even form
– The temperature is also hot enough to convert protons to neutrons

The Delicate Dance
• The universe cools and no new neutrons can form—how many
neutrons and protons exist at this time?
– Can estimate this assuming a Maxwell-Boltzmann Distribution
–
𝑁𝑁
𝑛𝑛
𝑁𝑁
𝑝𝑝
=
𝑚𝑚
𝑛𝑛
𝑚𝑚
𝑝𝑝
3 / 2
𝑒𝑒
−
𝑚𝑚
𝑛𝑛
−𝑚𝑚
𝑝𝑝
𝑐𝑐
2
𝑘𝑘
𝑏𝑏
𝑇𝑇
– When the universe cools enough for nuclei to form, there is 1 neutron for every
5 protons
– Maxwell quote: The only desire which I can have is like David to serve my own
generation by the will of God, and then fall asleep.
• At this temperature, all the neutrons start to decay unless they get
married with a proton forming a nuclei (they only have 15 minutes
to pair up before half of them are gone!)

The Clock is Ticking
• Half of the neutrons will be gone in just 610 seconds
– All of the neutrons would be gone in a single day
• Where can they go?
– 𝑝𝑝 + 𝑛𝑛 → 𝐷𝐷
– 𝐷𝐷 + 𝑝𝑝 →
3
𝐻𝐻𝑒𝑒
– 𝐷𝐷 + 𝐷𝐷 →
4
𝐻𝐻𝑒𝑒
• This epoch is radiation dominated (one billion photons for every
proton or neutron), and it would be extremely rare for 3 baryons to
collide at once so this process can only occur in one proton/neutron
steps

The End of BBN (Big Bang Nucleosynthesis)
• After 20 minutes the whole process is done
– The temperatures are too low to form any nuclei
– The p/n ratio will keep increasing and all unbound n will decay
into protons
• What remains at this time
–