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Transcript of Pasi2010 Bigbang
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Newton’s Static Universe
• Universe is static and composed of an infinite
number of stars that are scattered randomly
throughout an infinite space.• Universe is infinitely old and will exist forever
without any major changes.
• Time and Space are steady and independent
of one another and any objects in existence
within them.
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Newton’s Error
If universe is as how Newton describes,
then why is the sky dark at night?
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Olber’s Paradox
• If space goes on forever with stars
scattered randomly throughout, then in
any line of sight in any direction willeventually run into a star.
• Using this logic, the sky should be the
average brightness of all of these stars;the sky should be as bright as the sun,
even at night.
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But isn’t the sky dark at night…?
Yes, of course - that is what we observe
now and have always observed.
Something is wrong with Newton’s idea of
a static, infinite universe.
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Special Relativity
Time and Space and their rates are
intertwined and depend on the motion ofthe observer (1905).
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General Relativity
Gravity bends the fabric of space time -
the matter that occupies the universeinfluences the overall shape of space
and the rate of time (1916).
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Cosmological Constant
• Represents the pressure that allows the
universe’s expansion to directly balance
gravitational collapse due to the objectsexisting within the universe, thus yielding a
static universe.
• Without this idea of a “cosmological
constant”, Einstein could’ve been the first topredict that the universe is not static.
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Hubble’s Discovery
• Edwin Hubble’sobservations of remotegalaxies, and the
redshift of their spectrallines (1924).
• Hubble noticed that thefurther away the galaxy,the greater the redshift
of its spectral lines.• This linear relationship
is called Hubble’s Law.
http://rst.gsfc.nasa.gov/Sect20/A9.html
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Redshift
• The wavelengths of
the light emitted by
distant objects iselongated as it
travels to earth.
• Longer the light
travels, the more itgets redshifted.
http://rst.gsfc.nasa.gov/Sect20/A9.html
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Hubble’s Law
v = H0dv = recessional velocity of the galaxy
H0 = Hubble constant
D = distance of galaxy to earth
Galaxies are getting farther apart as timeprogresses, therefore the universe is
expanding.
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Hubble’s Constant
• Expansion rate measured using Type1A Supernovae.
• The age of the universe can be derivedfrom Hubble’s constant:
• T0 = d T0 = 1H0d H0
For example, if H0 = 73 km/s*Mpc, thenT0 = 13.4 Billion years old
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Age of Universe
• Currently, after taking into accountdifferences in expansion rate over time
and our movement through space:T0 ~ 13.7± 0.2 byo
• Age of stars: ~13.4 byo± 6%
Therefore, oldest stars are younger thanthe age of universe.
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How the Universe Expands
• The space betweengalaxies expands, not thegalaxies themselves;objects held together by
their own gravity arealways contained within apatch of nonexpandingspace.
• Example: raisins in a loaf
of bread. – As the dough rises, theoverall loaf of breadexpands; the spacebetween raisins increasesbut the raisins themselvesdo not expand.
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Center of Universe?
• There is NO CENTER to the universe
– Expansion looks the same regardless of
where you are in the universe. – Every point appears to be the center of the
expansion, therefore no point is the center.
– The universe is infinite.
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Lookback Time
• The degree ofcosmological redshifttells you how far into
past you are seeing theobject due to the finitespeed of light; this valueis called Lookback time.
• However, these values
are not always certainbecause of theexpansion of universewas not alwaysconstant.
QuickTime™ an d aTIFF ( Uncompressed) decompressor
are needed to see this picture.
http://en.wikipedia.org/wiki/File:Hubble_ultra_deep_field_high_rez_edit1.jpg
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Observable Universe
• Olber’s Paradox is solved:due to the finite speed oflight, the observable
universe does not includethe entire universe.
• Radius of the observableuniverse depends on the ageof the universe and thespeed of light: ~47 billion
lightyears.• Result: Sky is dark at night
with points of light (stars,galaxies, etc.) scatteredthroughout.
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Origins of the Big Bang Theory
• Georges Lemaître (1927) expanded on idea ofexpanding universe, realizing that the universewas smaller yesterday than today, and so on until
a “day that would not have had a yesterday”: themoment of creation. – The moment of creation would be the sudden
expansion that started the expansion of the universeas we know it today.
• This idea wasn’t widely accepted at first: FredHoyle dismissed “this hot Big Bang”, noting thatthere wasn’t any record or remnants. He arguedfor a “steady state” universe.
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Origins of the Big Bang Theory
• George Gamow (1948) suggested that if theuniverse was created with a “hot Big Bang”, then: – Various elements, such as H and He, would be produced for
a few minutes immediately after the Big Bang due to theextremely high temperatures and density of the universe atthis time.
– The high density would cause rapid expansion.
– As the universe expanded, H and He would cool andcondense into stars and galaxies.
– Today, due to continued cooling, radiation left over from the
epoch of recombination, when neutral atoms formed(~380,000 years after Big Bang) should be about 3K.
– Production of H and He during this time instead of just in H-burning in stars would explain why the H:He ratio of theuniverse is higher than what could’ve been produced by
stars alone.
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Evidence for the Big Bang
Theory• Gamow’s theory was revisted in the
1960’s by Bob Dicke and Jim Peebles
of Princeton University. – Believed that this cooled radiation would
be redshifted to the microwave region ofthe electromagnetic spectrum.
– Made a receiver to detect this radiation, butwere unsuccessful.
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Evidence for the Big Bang Theory
• The radiation, so far undetectedby the Princeton team, wasposing a problem for NJ BellTelephone Labs, where Arno
Penzias and Robert Wilsonwere developing a newmicrowave-satellite technologyfor phone calls.
– Puzzled by steady hiss thatthey received no matter wherein the sky they pointed their
antenna. – This faint background noise
they were trying to get rid ofwas exactly what the Princetonteam was trying to detect:evidence of the Big Bang.
http://nobelprize.org/educational/physics/star_stories/overview/index.html
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CMB Radiation
• Intensity of CMB Radiation reveals origins of universe.
– However, difficult to detect intensity from Earth- theatmosphere is opaque to wavelengths 10 m to 1 cm (CMB~ 1 mm).
• COBE (Cosmic Background Explorer) 1989: detectoroutside the atmosphere:
– Measured the blackbody spectrum of CMB radiation to be atT = 2.725 K - consistent with theory.
– CMB radiation almost entirely isotropic; CMB is slightlywarmer in direction of Leo and slightly cooler in direction of
Aquarius.
• WMAP (Wilkinson Microwave Anisotropy Probe) (2002)improved picture of CMB Radiation.
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CMB Radiation
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
• Radiation appears to bemostly smooth, but there areslight variations intemperature that show thatmatter had started to clumpin the early universe -clumps of matter formed thegalaxies and stars seetoday.
• Sound waves in early
universe are recorded in thisradiation; by studying thecharacteristics of thesesound waves, we can findout about the conditions ofthe early universe.
http://www.pas.rochester.edu/~afrank/A105/LectureXVI/LectureXVI.html
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Horizon Problem
• Despite all of the success with the Big BangTheory so far, the horizon problem was stillyet to be solved. – The temperature of the CMB radiation was the ~same no
matter where you look in the sky, indicating that some howinformation linking all parts of the sky was traveling fasterthan the speed of light.
– Also, information from one side of the sky at 100,000 years
old (horizon is 100,000 light years in diameter) differed fromthe other side of the sky by 10 million light years - 100 timesthe diameter of the horizon.
How is this possible?
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Inflation Theory
• Alan Guth (1970s) had a solution:
– The universe must have expanded
exponentially very early for a short periodof time.
– This would account for the clumping of
matter.
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Evidence for Inflation Theory
• Guth predicted that the average densityof the universe should be equal to the
critical density (6 protons/m3
) – This was confirmed by powerful
telescopes.
• Evidence from WMAP shows that the
clumping of matter is consistent with theamount of accelerated expansion duringinflation.
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Big Bang Theory: Timeline of
Universe• Hubble’s Law shows that the universe
has been expanding for billions of years
- the universe is denser the further backin time you look.
• At some point, you reach an infinitely
dense point at which
Tage of universe= 0 Big Bang
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T = 0 seconds to 10-43 seconds
• BIG BANG occurs.
• Something causes infinitely dense point to
expand (into Nothing).• Density of universe is so high that time and
space are curled up and the laws of physics
that we know today do not apply.
• All four forces in nature were unified.
• This is time is called the Planck Time.
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Separation of Forces
After the Planck time, the temperature
had decreased 1032 K and gravity was
the first force to separate.The remaining three forces were still
united - these are the conditions that
particle physicists today try to replicate.
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T = 10-35 to 10-32 seconds
• Inflation caused the size to the universe
to increase exponentially by a factor of
1050.• This time is called the inflationary
epoch.
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After Inflation Stops
• Matter is created: – Photons collide and produce pairs of elementary
particles such as electrons and positrons, andquarks and antiquarks.
– Pair production continues until one of particlecould no longer be produced - pair annihilationhappens - result: symmetry breaking.
– Reason for slight excess of matter over antimatter
is because of an unknown reaction known asbaryogenesis, in which conservation of baryonnumber is violated.
– Pair Production occurred until T = 6E9K, but pairannihilation happens independent of temperature.
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Particle Production in Early Universe
• As the size of the universe increases and thetemperature decreases, the particles producedare of decreasing energy.
• The fundamental forces and parameters ofelementary particles at the time that symmetrywas broken are the same as they are today.
• The time between the birth of the universe and t= 10-11 is rather unknown, but we can speculatewhat is happening based on other observations;beyond this time is less speculative as these areconditions that particle physicist try to replicate.
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T = 10-6 seconds
• Temperature has cooled enough for baryons(Protons, Neutrons) to form.
• Like the leptons, baryons form in pair production.
• Once the temperature has decreased past thepoint at which baryons can no longer beproduced, pair annihilation occurs again, leavinga slight excess of baryons over antibaryons.
• Also, at this temperature, all particles are nolonger moving relativistically, so the universebecomes dominated by the higher energyphotons (radiation-dominated universe).
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T = few minutes
• Temperature ~ 1 GK, density ~ that of air.
• Neutrons combine with protons makingdeuterium and helium nuclei, and some
protons remain independent (hydrogennuclei).
• Called Big Bang nucleosynthesis.
• Temperature is still too high to form atoms as
they would be ionized immediately.• The universe would appear opaque during all
this time because photons and matter wouldbe interacting due to high temperatures.
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T = 379,000 years
• Universe is now cool enough that matterenergy is greater than radiative energy, thusallowing atoms to form.
• Radiation is decoupled from matter andphotons are free-streamed throughout space- origin of CMB radiation.
• This time is known as the epoch ofrecombination.
• Universe is now matter-dominated.
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T ~ 400 million years
• Since epoch of recombination, slightly denser
regions attracted matter nearby and the first
stars begin to form.• Regions continue to acquire matter and other
objects like galaxies and gas clouds form.
• Universe begins to look like how we know it
today (still expanding and still cooling).
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Matter in the Universe Today
• Evidence gathered from WMAP shows that all
of the matter in the universe is composed of
three types of matter: – Cold dark matter
– Hot dark matter
– Baryonic matter
– Cold dark matter accounts for ~82% of all matterand hot dark matter and baryonic matter combined
account for the remaining ~18%.
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Nature of Expansion Today
• Evidence of Type 1a supernovae and CMBradiation show that the expansion is accelerating,driven by dark energy.
• Dark energy comprises ~72% of all energy and
permeates all space.• It is likely that this dark energy has always been
throughout the universe, but when the universewas younger and much smaller, gravity was
stronger than dark energy.• This acceleration could be described by
Einstein’s cosmological constant.
• Today, dark energy is still very misunderstood.
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Fate of the Universe
http://www.astro.columbia.edu/~archung/labs/spring2002/lab07.html
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Research Today
• Today, particle accelerators such as the LHCare trying to replicate conditions just after theBig Bang so that we understand how the
universe formed.• Currently, all cosmic evolution after
inflationary epoch can be modeled anddescribed pretty accurately, but the time
before this (10-15 sec) is basically unknown;understanding this time remains one of thegreatest mysteries in physics.
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Remaining Questions
• What is dark matter?
• What is dark energy?
• Can dark energy and matter be detected andstudied in labs?
• What happened from the birth of theuniverse, at the instance of the Big Bang, until
the end of the inflationary epoch?• What caused the Big Bang?
• What is the ultimate fate of the universe?