PHYS 182 Lecture Notes - Lecture 3: Electric Field, Vacuum Chamber, Cosmic Microwave Background
PHYS182: Our Evolving Universe
2017-09-12 LEC 3
Reminder: all course information at physics.mcgill.ca
Review of Last Time:
• If space is infinite today, then space is infinite at the Bing Bang
o Paradox: suddenly out of nothing you create infinite space and infinite temperature
o Violates laws of conservation of matter and energy
o However, in an expanding universe, energy is not conserved (i.e. not a paradox), but
getting infinite energy/matter out of nothing is a paradox
§ Theory breaks down
• If “Big Bang” refers to some hot fire ball some 10 billion years in the past, then yes
o But if it refers to the origin of time, then physics can’t answer this question
Note: If you go sufficiently far away, the speed at which the galaxies are moving away is greater than the
speed of light
Q: How does matter look like as the temperature (T) increases?
• As you compress a gas, it heats up à if you go back in time, temperature increases
• ¯T: atoms (e.g. H)
o Atoms have (+) centers and (-) charged electrons around it
o The binding energy (EB) binds the electron to the proton
• At T>EB: Atoms become unstable and electrons can escape à matter becomes a plasma
o Temperature is a form of energy, therefore can compare in this way
Note: The electron is a point particle, an elementary particle not made up of anything else
à But a proton is made up of 3 quarks which are called: u, u, d
• Where u stands for ("up) and d stands for (¯down)
• “gluons” are particles that bind together quarks
• There is a binding energy, BG that binds the gluons
o T>BG: the gluons escape and the quarks are no longer bound together
Going Back in time toward the Big Bang
Time
à
tQCD
tREC
t0
Matter
Quark plasma
Charged plasma:
e- and p-
Recombination
(occurs ~100k
years)
Neutral gas of
atoms
Present
Plasma: light does not travel through plasma in a straight line
Atoms: have no charge, therefore light does travel through atoms in a straight line
• The recombination of plasma into atoms releases light.
• Knowing how much the universe has expanded, you can calculate the frequency of light
• The radiation produced was on the microwave spectrum à now known as the “microwave
background”
• If you scan the sky with microwave telescopes, there is an isotropic cosmic microwave
background (CMB) that stays roughly about ~3 degrees Kelvin
o Confirmation of the theory
Quark soup à plasma of e- and p+ à neutral gas of atoms à structure formation
Document Summary
If big bang refers to some hot fire ball some 10 billion years in the past, then yes: but if it refers to the origin of time, then physics can"t answer this question. Note: if you go sufficiently far away, the speed at which the galaxies are moving away is greater than the speed of light. At t>eb: atoms become unstable and electrons can escape matter becomes a plasma: temperature is a form of energy, therefore can compare in this way. Note: the electron is a point particle, an elementary particle not made up of anything else. But a proton is made up of 3 quarks which are called: u, u, d: where u stands for ( up) and d stands for ( down) Gluons are particles that bind together quarks: there is a binding energy, bg that binds the gluons, t>bg: the gluons escape and the quarks are no longer bound together.
