Introduction to CosmologyIntroduction to Cosmology

CosmologyCosmology

Scientific study of the origin and Scientific study of the origin and evolution of the universeevolution of the universe

““kosmos” – Greek for “order”kosmos” – Greek for “order” Based on laws of physics, Based on laws of physics,

incorporates chemistry, mathematics, incorporates chemistry, mathematics, and astronomyand astronomy

Foundations of modern Foundations of modern cosmologycosmology

1) General Theory of Relativity (A. Einstein 1) General Theory of Relativity (A. Einstein 1915) – describes gravity in terms of the 1915) – describes gravity in terms of the warping of space-time by the presence of warping of space-time by the presence of mass and energy. mass and energy.

Many predictions have already been Many predictions have already been verified experimentallyverified experimentally

1)1) Precession of perihelion of Precession of perihelion of MercuryMercury

2)2) Bending of starlight around Bending of starlight around sunsun

3)3) Slowing of time in a Slowing of time in a gravitational field gravitational field (gravitational redshift).(gravitational redshift).

4)4) Twisting of spacetime by Twisting of spacetime by rotation of earth (frame-rotation of earth (frame-dragging)dragging)

5)5) Decay of binary pulsar orbit Decay of binary pulsar orbit (through gravity waves, (through gravity waves, whose presence has not whose presence has not yet been directly observed)yet been directly observed)

2) The Cosmological Principle2) The Cosmological Principle

Matter in the universe Matter in the universe is distributed evenly is distributed evenly in all places and in in all places and in all directions all directions (homogeneous and (homogeneous and isotopic), IF YOU isotopic), IF YOU LOOK AT LARGE LOOK AT LARGE ENOUGH SCALES ENOUGH SCALES (about 100 Mpc).(about 100 Mpc).

Forcing the universe to be finite Forcing the universe to be finite and static – enter the and static – enter the “cosmological constant”“cosmological constant”

Einstein’s “greatest blunder”Einstein’s “greatest blunder”

Abbé Georges Lemaître, Abbé Georges Lemaître, father of the “big bang”father of the “big bang” Independently of Hubble, he Independently of Hubble, he

discovered the expansion of discovered the expansion of the universe, and proposed the the universe, and proposed the universe began in the decay of universe began in the decay of a large radioactive atom.a large radioactive atom.

Some religious figures, Some religious figures, including Pope Pius XII, including Pope Pius XII, embraced it as scientific proof embraced it as scientific proof for the Judeo-Christian origin for the Judeo-Christian origin story.story.

Lemaître himself struggled with Lemaître himself struggled with the theological implications of the theological implications of his theory -"As far as I can see, his theory -"As far as I can see, such a theory remains entirely such a theory remains entirely outside of any metaphysical or outside of any metaphysical or religious question."religious question."

George Gamow refined the ideaGeorge Gamow refined the idea

Universe began in Universe began in small, hot, dense small, hot, dense state which has state which has expanded and expanded and cooled over time.cooled over time.

His theory named His theory named “Big Bang” as an “Big Bang” as an insult by Fred insult by Fred Hoyle.Hoyle.

Initial arguments against the big bang theory Initial arguments against the big bang theory included a disbelief that the laws of physics included a disbelief that the laws of physics could possibly be pushed back to the origin of could possibly be pushed back to the origin of the universe.the universe.

There was also an There was also an antireligious antireligious backlash against backlash against the theory, which the theory, which reportedly was part reportedly was part of the motivation for of the motivation for the rival steady the rival steady state model.state model.

Despite Lemaître’s caution, some Despite Lemaître’s caution, some ID proponents still cite the big bang ID proponents still cite the big bang as proof of designas proof of design Hugh Ross argues that the big bang Hugh Ross argues that the big bang

renders "the design of the universe renders "the design of the universe irrefutable." irrefutable."

Noted Intelligent Design proponent Noted Intelligent Design proponent Michael Behe warns that the big bang, Michael Behe warns that the big bang, "although friendly to a religious point of "although friendly to a religious point of view, does not forcibly compel that view, does not forcibly compel that belief."belief."

Tests of the Big BangTests of the Big Bang

1) Observed 1) Observed expansion of the expansion of the universe. Slope = universe. Slope = H, but is difficult to H, but is difficult to determine determine (uncertainties in (uncertainties in velocity and velocity and distance) distance) HST HST Key ProjectKey Project

2) Nucleosynthesis in the first 2) Nucleosynthesis in the first three minutesthree minutes

Predicts percentage of Predicts percentage of light isotopes relative light isotopes relative to hydrogen. Observed to hydrogen. Observed composition matches composition matches theory with great theory with great precision (but restricts precision (but restricts amount of normal or amount of normal or baryonic matter that baryonic matter that can exist relative to can exist relative to light).light).

most elements have been most elements have been created inside starscreated inside stars

““We are star-stuff”We are star-stuff”

– – Carl SaganCarl Sagan

3) Cosmic Microwave 3) Cosmic Microwave Background RadiationBackground RadiationPredicted by George Predicted by George

Gamow in 1948, Gamow in 1948, accidentally accidentally discovered by discovered by Penzias and Wilson Penzias and Wilson in 1965 (1978 in 1965 (1978 Nobel Prize).Nobel Prize).

Matches a blackbody Matches a blackbody of T = 2.7 K (and is of T = 2.7 K (and is very isotropic!)very isotropic!)

Misconceptions about Big BangMisconceptions about Big Bang

1)1) It did not occur at a single point in It did not occur at a single point in space-time but describes the early space-time but describes the early evolution of space-time as a whole.evolution of space-time as a whole.

2)2) It does not say what happened It does not say what happened before the universe, nor does it before the universe, nor does it explain why (or even how) the explain why (or even how) the universe was born, just how it universe was born, just how it evolved from a hot, dense state.evolved from a hot, dense state.

Friedmann-Robertson-Walker Friedmann-Robertson-Walker models (aka, what shape is the models (aka, what shape is the universe?)universe?)

So which shape is the So which shape is the universe?universe?

ΩΩ = = ρρ / / ρρcriticalcritical

= 1 (flat)= 1 (flat)< 1 (open)< 1 (open)>1 (closed)>1 (closed)

0.02 < 0.02 < ΩΩ < 2 < 2

The early universe is The early universe is described by particle physicsdescribed by particle physics

Anyone got a “TOE”?Anyone got a “TOE”?

Problems with original Big Problems with original Big Bang modelBang model1)1) Why is CMB so Why is CMB so

smooth?smooth?

2)2) Why is universe so Why is universe so close to being flat?close to being flat?

3)3) Where does Where does structure come from?structure come from?

4)4) Where are the Where are the magnetic magnetic monopoles?monopoles?

Enter Inflation!Enter Inflation!

In 1981, particle In 1981, particle physicist Alan physicist Alan Guth sought a Guth sought a solution for the solution for the magnetic magnetic monopole monopole problem and problem and ended up ended up revolutionizing revolutionizing cosmology!cosmology!

Our “universe” is but one small Our “universe” is but one small piece of the original Big Bangpiece of the original Big Bang

Solves all four problems:Solves all four problems:

1)1) Our visible universe Our visible universe evolved from a small evolved from a small “smooth patch”“smooth patch”

2)2) Predicts Predicts ΩΩ=1=1

3)3) End of inflation plants End of inflation plants “seeds” for structure “seeds” for structure formation.formation.

4)4) Dilutes magnetic Dilutes magnetic monopoles (hard to monopoles (hard to find)find)

Another success: Another success: age of universe can be determined by:age of universe can be determined by:

Hubble constantHubble constant Abundances of radioactive isotopes in Abundances of radioactive isotopes in

very old starsvery old stars Cooling times of white dwarfsCooling times of white dwarfs Models of stellar evolution compared Models of stellar evolution compared

to old starsto old stars

All agree with @ 13-14 billion yearsAll agree with @ 13-14 billion years

Another fly in the ointment!Another fly in the ointment!

The expansion is not The expansion is not slowing down, but slowing down, but is accelerating!is accelerating!

Presence of Presence of something like something like Einstein’s Einstein’s cosmological cosmological constant (called constant (called “dark energy”)“dark energy”)

Most precise CMB measurements Most precise CMB measurements (WMAP) results agree with (WMAP) results agree with “Concordance cosmology”“Concordance cosmology”

ΛΛCDM: accelerating, CDM: accelerating, ΩΩ = = 11 universe with @ 70% universe with @ 70% dark energy and @ dark energy and @ 25% cold dark matter 25% cold dark matter and @5% “normal” and @5% “normal” mattermatter

So far results are So far results are consistent with inflation consistent with inflation as well.as well.

“ “The field of cosmology has a grand history The field of cosmology has a grand history of pushing back the boundary between of pushing back the boundary between physics and metaphysics. Decades ago, physics and metaphysics. Decades ago, who would have thought that the origin of who would have thought that the origin of relative abundances of the different relative abundances of the different chemical elements would be considered the chemical elements would be considered the subject of physical calculation rather than subject of physical calculation rather than metaphysical speculation! I have no doubt metaphysical speculation! I have no doubt that we will find more opportunities to push that we will find more opportunities to push the boundary back even further.” the boundary back even further.”

- Andreas Albrecht (1994)- Andreas Albrecht (1994)

Big questions we might be Big questions we might be able to answerable to answer Will the Big Bang (and general relativity) Will the Big Bang (and general relativity)

hold up to improved observations and hold up to improved observations and experiments?experiments?

What particle makes up dark matter?What particle makes up dark matter? What is dark energy? What is dark energy? Will the acceleration of the universe cease?Will the acceleration of the universe cease? Which model of inflation best fits Which model of inflation best fits

observations?observations? What is the TOE? What is the TOE?

Big questions we may never Big questions we may never be able to answerbe able to answer What caused the Big Bang to occur? What caused the Big Bang to occur? Do we live in a multiverse?Do we live in a multiverse? Why are the constants of nature what Why are the constants of nature what

we observe?we observe?