TESU PHYSICS 116 FINAL | QUESTIONS AND ANSWERS | VERIFIED
AND WELL DETAILED ANSWERS | LATEST EXAM
3 Pillars of big band cosmology - CORRECT ANSWER - The hubble
expansion
Big Bang Nucleosynthesis (BBN)
Cosmic Background Radiation (CMBR)
Limitations of Big Bang Science - CORRECT ANSWER - The very early
epoch (less than 10-11 s after Big Bang)
Typical energy was 1 TeV
We do not understand the laws of this epoch
Quantum Gravity - CORRECT ANSWER - Physics that is applied to the very
beginning
Nature of space and time is obscured because of quantum uncertainty
The Big Bang singularity is the mathematical instant
where the Universe started
The Planck Length - CORRECT ANSWER - No Distance is smaller than the
Planck Length!
Heavier black holes have bigger horizon size, and lighter ones have higher
quantum uncertainty; so they cannot be smaller than plank's length
Plank Time - CORRECT ANSWER - The smallest imaginable time is the
Planck time
Time that it takes light to traverse a Planck length
,No distinct time for different observers in plank time because uncertainty is so
high
The Launch of the Universe - CORRECT ANSWER - At the "Planck instant"
everything is chaotic: quantum fluctuations constantly create and annihilate bits
of Planck sized space-time
At least one of these bubbles continued to grow
The Grand Unified Era - CORRECT ANSWER - 10-42 s < t < 10-35 s.
Typical energy: ~10^15 GeV
At this time gravity is encoded in smooth geometry, following the laws of
general relativity
The strong force, the weak force and EM are indistinguishable because of the
enormous temperatures
One unified force; laws are not understood
The Era of Inflation - CORRECT ANSWER - 10-35 s < t < 10-33 s
Inflation: Accelerated expansion of the universe
The total expansion in the inflationary phase was at least 2^100=10^28
Comparable to the factor the universe has grown in 13.8 billion years
TURNED CURVED UNIVERSE TO FLAT UNIVERSE
Expanded quantum fluctuations in the very early universe, into "seeds" that later
grew into the structures
The Primordial Soup - CORRECT ANSWER - Mostly radiation in the early
universe; particle - antiparticle pairs were created but soon annihilated but
easily decayed back to radiation
Baryogenesis - CORRECT ANSWER - 10-33 s < t < 10-11 s
As universe expands and cools, there is a small excess of matter over antimatter
,When Q - antiQ annihilate, small excess of quarks remain and make matters that
we see today
Unknown details
Process for their being matter
The Electroweak Era - CORRECT ANSWER - t~10-11 s Typical energy:
200GeV
From this point, laws of physics are known
Before this time the elementary particles we know were all much lighter than
the typical energy available
Forces were indistinguishable bc force carriers had the same mass
EW era: when forces attained their own identities
The weak force carriers acquired a mass but the photon did not - separate
identity
The Quark-Hadron Phase Transition
Hadrons: proton and neutron - CORRECT ANSWER - t~10-5 s; before this
era, energy was so large that quarks enjoyed asymptotic freedom; (roamed
freely with other leptons and e-)
As energy falls below 300 MeV, quarks formed hadrons
The Reign of Hadrons: Nucleon Soup - CORRECT ANSWER - 10-5 s< t < 1s;
after Q-H transition, all the quarks are bounded
Neutrons can turn into protons by beta decay
Protons can turn into neutrons by inverse beta decay
Inverse B-decay remains as there is enough energy to compensate for larger
mass of neutrons
Endangered Neutrons - CORRECT ANSWER - below 1MeV; e- and e+
annihilate for good to match # e- = # protons. ALSO not enough energy for
inverse B decay
, Neutrons can decay to protons but protons cannot generate neutrons; so
neutrons become an endangered species
Nuclear Fusion Protects Neutrons - CORRECT ANSWER - In the epoch from
1s to 10,000s the temperature cools so the typical energy decreases from a few
MeV to much less (similar to the core of the stars)
Frequent nuclear rxn; He fusion continues
Reaction going both ways??? - CORRECT ANSWER - Nuclear binding
energies are about 8 MeV pr. nucleon so energy is gained when they bind
together. It costs energy to split them apart again
The typical thermal energy in this epoch has fallen below few MeV so most
photons (γ-rays) do not have energy enough to split a nucleus.
The Neutron/Proton Ratio - CORRECT ANSWER - Neutrons did not survive
this epoch
Neutron: Proton = 1:7
25% He, and 75% H by mass in the universe
Most nucleons were created in the first few minutes and they have not changed
since then
4He in the Present Universe - CORRECT ANSWER - Stellar process added
4He, but original condition remains
Dwarf galaxies that are especially poor in oxygen and nitrogen are well suited
to find about universe before star formation (stars create o and N)
Big Bang Synthesis of Metals? - CORRECT ANSWER - Nuclear fusion in
sufficiently heavy stars burn Helium into heavier elements. and the temperature
in the early Universe is sufficient for fusion of Helium into heavier elements.
An important difference: the Universe expands so the 4He nuclei must collide
before their density is too dilute
AND WELL DETAILED ANSWERS | LATEST EXAM
3 Pillars of big band cosmology - CORRECT ANSWER - The hubble
expansion
Big Bang Nucleosynthesis (BBN)
Cosmic Background Radiation (CMBR)
Limitations of Big Bang Science - CORRECT ANSWER - The very early
epoch (less than 10-11 s after Big Bang)
Typical energy was 1 TeV
We do not understand the laws of this epoch
Quantum Gravity - CORRECT ANSWER - Physics that is applied to the very
beginning
Nature of space and time is obscured because of quantum uncertainty
The Big Bang singularity is the mathematical instant
where the Universe started
The Planck Length - CORRECT ANSWER - No Distance is smaller than the
Planck Length!
Heavier black holes have bigger horizon size, and lighter ones have higher
quantum uncertainty; so they cannot be smaller than plank's length
Plank Time - CORRECT ANSWER - The smallest imaginable time is the
Planck time
Time that it takes light to traverse a Planck length
,No distinct time for different observers in plank time because uncertainty is so
high
The Launch of the Universe - CORRECT ANSWER - At the "Planck instant"
everything is chaotic: quantum fluctuations constantly create and annihilate bits
of Planck sized space-time
At least one of these bubbles continued to grow
The Grand Unified Era - CORRECT ANSWER - 10-42 s < t < 10-35 s.
Typical energy: ~10^15 GeV
At this time gravity is encoded in smooth geometry, following the laws of
general relativity
The strong force, the weak force and EM are indistinguishable because of the
enormous temperatures
One unified force; laws are not understood
The Era of Inflation - CORRECT ANSWER - 10-35 s < t < 10-33 s
Inflation: Accelerated expansion of the universe
The total expansion in the inflationary phase was at least 2^100=10^28
Comparable to the factor the universe has grown in 13.8 billion years
TURNED CURVED UNIVERSE TO FLAT UNIVERSE
Expanded quantum fluctuations in the very early universe, into "seeds" that later
grew into the structures
The Primordial Soup - CORRECT ANSWER - Mostly radiation in the early
universe; particle - antiparticle pairs were created but soon annihilated but
easily decayed back to radiation
Baryogenesis - CORRECT ANSWER - 10-33 s < t < 10-11 s
As universe expands and cools, there is a small excess of matter over antimatter
,When Q - antiQ annihilate, small excess of quarks remain and make matters that
we see today
Unknown details
Process for their being matter
The Electroweak Era - CORRECT ANSWER - t~10-11 s Typical energy:
200GeV
From this point, laws of physics are known
Before this time the elementary particles we know were all much lighter than
the typical energy available
Forces were indistinguishable bc force carriers had the same mass
EW era: when forces attained their own identities
The weak force carriers acquired a mass but the photon did not - separate
identity
The Quark-Hadron Phase Transition
Hadrons: proton and neutron - CORRECT ANSWER - t~10-5 s; before this
era, energy was so large that quarks enjoyed asymptotic freedom; (roamed
freely with other leptons and e-)
As energy falls below 300 MeV, quarks formed hadrons
The Reign of Hadrons: Nucleon Soup - CORRECT ANSWER - 10-5 s< t < 1s;
after Q-H transition, all the quarks are bounded
Neutrons can turn into protons by beta decay
Protons can turn into neutrons by inverse beta decay
Inverse B-decay remains as there is enough energy to compensate for larger
mass of neutrons
Endangered Neutrons - CORRECT ANSWER - below 1MeV; e- and e+
annihilate for good to match # e- = # protons. ALSO not enough energy for
inverse B decay
, Neutrons can decay to protons but protons cannot generate neutrons; so
neutrons become an endangered species
Nuclear Fusion Protects Neutrons - CORRECT ANSWER - In the epoch from
1s to 10,000s the temperature cools so the typical energy decreases from a few
MeV to much less (similar to the core of the stars)
Frequent nuclear rxn; He fusion continues
Reaction going both ways??? - CORRECT ANSWER - Nuclear binding
energies are about 8 MeV pr. nucleon so energy is gained when they bind
together. It costs energy to split them apart again
The typical thermal energy in this epoch has fallen below few MeV so most
photons (γ-rays) do not have energy enough to split a nucleus.
The Neutron/Proton Ratio - CORRECT ANSWER - Neutrons did not survive
this epoch
Neutron: Proton = 1:7
25% He, and 75% H by mass in the universe
Most nucleons were created in the first few minutes and they have not changed
since then
4He in the Present Universe - CORRECT ANSWER - Stellar process added
4He, but original condition remains
Dwarf galaxies that are especially poor in oxygen and nitrogen are well suited
to find about universe before star formation (stars create o and N)
Big Bang Synthesis of Metals? - CORRECT ANSWER - Nuclear fusion in
sufficiently heavy stars burn Helium into heavier elements. and the temperature
in the early Universe is sufficient for fusion of Helium into heavier elements.
An important difference: the Universe expands so the 4He nuclei must collide
before their density is too dilute
