William III Universe - CCPhysics.US · Universe Tenth Edition Chapter 26 Exploring the Early...
Transcript of William III Universe - CCPhysics.US · Universe Tenth Edition Chapter 26 Exploring the Early...
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UniverseTenth Edition
Chapter 26
Exploring the Early Universe
Roger Freedman • Robert Geller • William Kaufmann III
26‐1 How the very young universe expanded enormously in a brief instant of time
26‐2 How the fundamental forces of nature and the properties of empty space changed during the first second after the Big Bang
26‐3 How the physics of subatomic particles affected the evolution of the early universe
26‐4 As the early universe expanded and cooled, most of the matter and antimatter annihilated each other
26‐5 Which chemical elements in today’s universe are remnants of the primordial fireball (??? – jh)
26‐6 How the first stars and galaxies formed in the early universe
26‐7 What steps scientists are taking in the quest toward an all encompassing “theory of everything”
By reading this chapter, you will learn
The First Three Minutes
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Planck Epoch• No Physics exists to describe the cosmos previous to
this time: 10‐43 seconds (unless M‐theory bears out)
• Impossibly high temperatures (1032K), inconceivably
tiny universe (10‐35m) at the end of this brief epoch
• All four fundamental forces—strong, weak,
electromagnetic, and gravity‐–were expressed as
one.
– Unified by the high energy/temperature into a single force
Particles, the Four Forces and the Standard Model
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Forces Due to Particle Exchange Well, it’s not momentum…
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The CERN Particle Collider
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Discovery of the Higgs Particle
Unification of the Four Forces
Spontaneous Symmetry: High Energy State ‘Rolls Downhill’
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String Theory
• A step towards a ToE or SupergrandUnified Theory
• Stems from the transition from continuum Physics to
quantum Physics at the turn of the 20th C
• Starting in the ‘80’s the notion arose that strings were
a better model for the basic constituents of matter
• Feynman diagrams describing Standard Model
interactions are too convoluted to incorporate these extra
dimensions
• “Branes” are introduced to explain interactions, but they
need more dimensions
Dimensions
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Other Dimensions
• Flatland, a Romance in
Many Dimensions
– Edwin Abbott Abbott, 1885
– A square and his wife in
Flatland
• An introduction to greater
dimensions
M‐Theory
• String theory required 9+1 dimensions
• However, this produced 5 equally valid variations!
Unacceptable!
• A lesser known theory, Supergravity, postulated 10+1
dimensions
• Merging the two ideas resolved the 5 variations
• However, the addition of the 11thdimension caused the
strings to weave into Membranes
• A theory of the “trigger”
• Multidimensional Universe or multiverse
• Gravity is the weakest force because it stretches between branes and is diluted
• Intersection of branes initiates a BB
• So time didn’t have to begin with the BB
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Lisa Randall
• Astrophysicist at Harvard
• Leading ‘Brane’
proponent
• Warped Passages:
Unraveling the Universe's
Hidden Dimensions
• See also David Deutsch,
Hugh Everett…
How the Universe Got Its Spots
Jenna Levin and others
propose a more
topological description of
cosmology than M Theory
Wearehere
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Inflationary Epoch
• As the name implies, a period of enormous expansion
• The Universe grew from 10‐28 m to 1016 m
• To put this in perspective, think of the size of a proton
compared to a parsec!
• The Universe cooled, as any expanding system of particles
would, then reheated shortly after inflation ended.
– The energy used to ‘push’ the Universe outward was released as heat
A Note About Inflation
• Proposed by Alan Guth of MIT in the early 1980s, Inflation does a good job
of explaining the Universe as we see it today
• During this era the early Universe expanded faster than the speed of light
– Not a violation of SR since nothing is actually moving > c
• It solves the flatness problem, the horizon problem, and the monopole
problem
– Flatness: why (total energy density of the universe) is so close to crit
– Horizon: why the CMB varies so little (isotropy)
– Monopoles: N or S magnetic pole w/o the other
• BICEP2 MAY have found Primordial B‐mode polarization
• CMB photons polarized by intense gravitational waves
rapid inflation at 10‐38s, earlier than thought
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Polarized Light
Polarization of the Cosmic Microwave Background
Where Inflation Comes From
• Current theory holds that a different value of the cosmological constant, inflation , was present during this epoch
• This formed an inflaton field, a type of scalar field– You can think of a scalar field like gravity near the ground—the
higher you go the more potential for falling fast you have
• Invoking a scalar field is common in theoretical physics, and perfectly legal, but it doesn’t make a theory true. For that, real evidence is required
• And from observation, the Universe is in a period of inflation now, with the current scalar field being dark energy (whatever that is)
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The Observable Universe With and Without Inflation
How Inflation Fixes Flatness
• The Flatness problem: the ratio of the current energy density () of the Universe to the critical density is 1
• Doesn’t seem like much, but when you allow for expansion and run the clock backwards, the ratio differs from 1 (perfectly flat) by one part in 1060!
• Inflation fixes this by essentially flattening all the ‘bumps’ in the Universe, much like inflating a balloon smoothes out all the wrinkles
is currently very close to zero; 0 means flat
Inflation Solves the Flatness Problem
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Horizons: The Isotropy Problem
• Think of a horizon as the furthest distance than can be
seen for which there is time for light to travel
• If an event happens in one region that would affect
another region, then there must be sufficient time for
the effect to travel that distance
– Re: a light cone!
Light Cones
• A way to plot space and time
• It tells you how much information you can have at a certain time, limited by the speed of light
• The x‐y plane represents space and the z axis represents time– Now is 0, past is ‐, future is +
• Not far in the past (white arrow) only nearby events can be known
• Events that happened long ago (gold arrow) can be known even if they were far away
The Isotropy Problem
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Run the clock backwards. It turns out that, given the
short time scales involved, there was insufficient time for
energy to travel from one region to another, a necessary
condition for a near‐uniform temperature
Planck
But why was there variation?
• High temperatures imply uniformity
• Heisenberg’s Uncertainty Principle prohibits absolute uniformity,
because that means there’d be no limit on detail in data
• Therefore, in a quanta sized early universe there must be Quantum
Fluctuations
Particle Epoch• Quarks cool and form more massive particles
– Two up and one down = p+
– Two down and one up = N• Interactions abound
–mN > mp so more p+ than N• Heavy decays to lighter
– 6p+ for 1N • Too hot for nuclei to form• Universe has cooled to 109K by end of era
– The “Freeze Out”; baryons cease to perish in the high temperature
• As for electrons…
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Virtual Pairs: more Heisenberg
Pair Production and Annihilation
Inflation: From Virtual to Real Particles
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Nucleosynthesis Era
• Universe cools to 3000K
• 1s < 3 min
• Atoms form (ionized):
– N half‐life ~ 15 minutes
– By 3 minutes, 14p for 2N
• Some neutrons had decayed into protons, so p+:N , 6:1 becomes 7:1
• 2p+ + 2N = He
– So out of 16 nucleons, 1 He for 12 H
– Hydrogen, including deuterium (75% by mass)
– Helium (25% by mass)
– Lithium (109 < He)
Nucleosynthesis In the Early Universe
Atom Epoch• 3 min < t < 380,000 years
• Universe cools enough for electrons to attach to atoms
– Down to 18 K by end of era
• Universe becomes transparent, photons free to travel
– The “Last Scattering”
• CMB starts now
– ½ of 1% of radio noise is CMB
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The Growth of Density Fluctuations, the outgrowth of Quantum Fluctuations
Dark Matter/Energy• Horizons and Flatness are inter‐
related
• The geometry of the Universe is
determined by the amount of
dark energy
• Left: the scale of the CMB
fluctuations in the WMAP picture
indicate curvature
– Open if the fluctuations < 1/2o
– Flat if ~1o, closed if > 1o
• Ultimately determines the fate of
the Universe
If the Universe is flat, the angle is 1o
If it is curved inward (closed) the angle is > 1o
If it is curved outward (open) the angle is < 1o
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Using Simulations to Constrain the Matter Density of the Universe
These values (the ones I suggested last PPT you DON’T memorize) can affect the accuracy of our lookback time calculations
A Cold Dark Matter Simulation with Dark Energy
Stelliferous Era
• From about 380,000 years after the Big Bang until now– Galaxies at about 1 billion A.B.B
• Average temp = 3K
• The era of stars, galaxies, and us
• Top down vs. bottom up– Did massive clouds of gas form first, generating the stars (top down)
or did stars form first, collecting into galaxies (bottom up)?
– Probably a combination• Where gas was dense enough, stars formed first
• Where gas was rarefied, dark galaxies formed, later yielding stars
• Era will continue until the year 100 trillion A.B.B
Youngest object ever imaged @ 800MYr A.B.B
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The First Stars
“Bottom Up” Galaxy Formation: Observation
“Bottom Up” Galaxy Formation: Simulation
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A Galaxy Under Construction
The Universe at 2 GyrOld
A Timeline of Light in the Universe
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The History of the Universe
Your text was published before the BICEP evidence was in. Alan Guthmay get the Nobel Prize for this if polarization is confirmed
The Future:
• The most likely* outcome will be the open Universe– AKA The Big R.I.P.
• The actual density of the Universe is less than the critical density– /c ~ 1– *Actually too small to ever measure accurately for proper
prediction• The Universe will expand forever• Three Foreseeable Epochs (after the Stelliferous
Era):– The Time of Degeneracy: 1014 years– The Time of Black Holes: 1032 years– The Time of Photons: 10100 years
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Key Ideas
• Cosmic Inflation:A brief period of rapid expansion, called
inflation, is thought to have occurred immediately after the
Big Bang. During a tiny fraction of a second, the universe
expanded to a size many times larger than it would have
reached through its normal expansion rate.
• Inflation explains why the universe is nearly flat and the
2.725‐K microwave background is almost perfectly isotropic.
Key Ideas
• The Four Forces and Their Unification: Four basic forces— gravity,
electromagnetism, the strong force, and the weak force— explain all the
interactions observed in the universe.
• The Standard Model accurately describes all the known particles in nature and
their observed interactions (except for gravity).
• The weak force and electromagnetic force became unified into a single force called
the electroweak force at higher energies than those typically found in today’s
universe. This unification has been observed in high‐energy particle accelerators.
• Grand unified theories (GUTs) are attempts to explain three of the forces (strong
force, weak force, and electromagnetic force) in terms of a single force. This has
not been observed, and particle accelerators fall far short of having the energy to
directly probe the high energy where this unification is predicted to occur.
Key Ideas• A supergrand unified theory (AKA Theory of Everything) would explain all
four forces (including gravity) at extremely high energies as a single force act‐
ing similarly on all the particles in nature. String theory attempts to make this
unification, and it would describe the quantum nature of gravity. Supergrand
unification is hypothesized to occur before the Planck time (t = 10−43 seconds
after the Big Bang).
• Spontaneous Symmetry Breaking: As the universe expands and cools, the
unified forces break into separate forces. Starting around the Planck time,
gravity became a distinct force through a spontaneous symmetry breaking.
During a second spontaneous symmetry breaking, the strong nuclear force
became a distinct force. A final spontaneous symmetry breaking separated
the electromagnetic force from the weak nuclear force; from that moment
on, the uni‐ verse behaved as it does today.
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Key Ideas• Particles and Antiparticles: Heisenberg’s uncertainty principle states
that the amount of uncertainty in the mass of a subatomic particle
increases as it is observed for shorter and shorter time periods.
• Because of the uncertainty principle, particle‐antiparticle pairs can
spontaneously form and disappear within a fraction of a second. These
pairs, whose presence can be detected only indirectly, are called virtual
pairs.
• The collision of two high‐energy photons can produced a real particle‐
antiparticle pair. In this process, called pair production, the photons
disappear, and their energy is transformed into the masses of the
particle‐antiparticle pair. In the process of annihilation, a colliding
particle‐antiparticle pair disappears and two high‐energy photons appear.
Key Ideas• The Origin of Matter: Just after the inflationary epoch, the
universe was filled with particles and antiparticles formed from
numerous high‐energy photons. The particles also
annihilated to produce a state of thermal equilibrium
between the particles and the photons.
• As the universe expanded, its temperature decreased. When the
temperature fell below the threshold temperature required to
produce each kind of particle, annihilation of that kind of
particle began to dominate over production.
Key Ideas
• Nucleosynthesis:Helium could not have been produced until the
cosmological redshift eliminated most of the high‐energy photons.
These photons created a deuterium bottleneck by breaking down
deuterons before they could combine further to form helium.
• Density Fluctuations and the Origin of Stars and Galaxies:The
large‐scale structure of the universe arose from primordial density
fluctuations.
• The first stars were much more massive and luminous than stars in the
present‐day universe. The material that they ejected into space
seeded the cosmos for all later generations of stars.
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Key Ideas
• Galaxies are generally located on the surfaces of roughly spherical
voids. Models based on dark energy and cold dark matter give
good agreement with details of this large‐scale structure.
• The Frontier of Knowledge:The search for a theory that unifies
gravity with the other fundamental forces suggests that the
universe actually has 11 dimensions (ten of space and one of time),
seven of which are folded on themselves so that we cannot see
them. The fundamental objects in our universe may be very small
strings, rather than point‐like particles.