pasi2010 bigbang

8/10/2019 Pasi2010 Bigbang

http://slidepdf.com/reader/full/pasi2010-bigbang 1/48



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.



Newton’s Error

If universe is as how Newton describes,

then why is the sky dark at night?



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.



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.



Special Relativity

Time and Space and their rates are

intertwined and depend on the motion ofthe observer (1905).



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).



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.



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



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



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.



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



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.



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.



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.



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



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.



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.



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.



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.



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



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.



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



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?



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.



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.



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



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.



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.



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.



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.



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.



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).



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.



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.



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).



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%.



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.



Fate of the Universe

http://www.astro.columbia.edu/~archung/labs/spring2002/lab07.html



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.



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?

pasi2010 bigbang

Documents