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Type 1a supernovae

a white dwarf steals matter from a companion star, and the white dwarf's mass slowly increases until it exceeds 1.4 M. and explodes

High z supernovae results

1996-indicated the universe wasnt slowing down as expected, but accelerating
1998-results supported this
present day-more results support this

dark energy

some form of repulsive gravity or pressure that is causing the Universe to expand more and more rapidly over time


what year did Einstein propose an anti-gravity cosmological constant to keep the universe in a steady state?


What year did Hubble discover the expansion of the universe?


When did einstein call the cosmological constant the "biggest blunder" of his life?


when did astronomers find evidence for the cosmological constant?

dark matter end to the universe

dark matter dominates cosmic slowdown--acceleration tapers of, ending in a "Big Crunch"

dark energy end to the universe

acceleration gets stronger and eventually rips the universe apart in a "Big Rip"


What % of the universe does dark energy make up?


What % of the universe does dark matter make up?


What % of the universe do atoms make up?


what is Ω total? (Ωbaryons + Ωdark matter + Ωdark energy)

flatness problem

in cosmology, the peculiar circumstance that the early universe must have contained almost exactly the right amount of matter to make space-time flat

Ω should increase rapidly

what should happen to Ω in a closed universe?

Ω should approach zero very rapidly

what should happen to Ω in an open universe?

observable universe

as the universe gets older, light from more and more distant sources makes its way to earth, thus the size of the ______ increases over time

horizon problem

One of the problems of cosmology solved by the inflationary theory: why the Universe has the same average temperature in all directions, even though widely separated regions could never have been in thermal equilibrium with each other since they are beyond each other's horizons.

inflation as a solution

after inflation, the observable universe is so stretched that it appears flat to all measurements--it demands that Ω = 1.

what caused inflation

what doesn't inflation resolve?

what inflation resolves

the flatness problem, the horizon problem, the uniformity of the CMB

open universe

Ω < 1, K = -1

flat universe

Ω = 1, k = 0

closed universe

Ω > 1, k = 1

it will collapse

if the density of the universe is higher than the critical density, what will happen to the universe?

it will expand forever

if the density of the universe is lower than the critical density, what will happen to the universe?

how to determine the fate of the universe

measure H0 and the actual density of the universe

400-800 million years after Big Bang (much earlier than everyone thought they would star forming)

when did galaxies start forming?

Sloan Digital Sky Survey

goal is to measure the brightness of 100 million objects, and map the distances and positions of 1 million galaxies and 100,000 quasars. Still working on this survey today

Big Bang myth

the Big Bang was an explosion of matter into the pre-existing universe


would mean that the most distant galaxies would move away the fastest, less massive galaxies would move away faster, most massive galaxies would be closest to earth, and earth would be located at "ground zero" of the explosion


would mean the most distant galaxies would move away the fastest, there would be no dependence between a galaxy's recessional velocity and its mass, there would be a random distribution of galaxy masses, and every galaxy will see every other galaxy moving away

Hubble's law of redshifts


myth about light

light loses energy as it travels across the universe, the loss of energy creates redshifts, distant galaxies only appear to be moving away from us, therefore the universe would not be expanding

tired light

(1929) Zwicky hypothesized this as an alternative to the idea of an expanding universe wherein light loses energy as it travels (its wrong)

problems with tired light

if light were colliding with something (and slowing down), we should be able to tell, and its hard to imagine a non-expansion process that would redden all wavelengths equally, cant explain CMB, cant explain chemical abundances found in the universe, cant explain the formation of structures in the universe

supernova duration stretching

distant supernovae really do seem to last longer than nearby supernovae, which is what the Big Bang predicts

steady state predictions

the Hubble constant is truly constant (the universe is always expanding at the same rate), the universe had no Big Bang (its infinite in age), no matter how far back in time you go the universe was never zero in size

steady state idea

new matter is created as the universe grows so that the density of the universe remains the same over time, a "creation" or "C-field is responsible for making new matter, the amount of new matter needed isnt large, the jets observed around quasars/neutron stars/black holes could be sites of matter creation


does the old/distant universe look the same as the present/nearby universe?

a hot, dense, opaque blackbody

what did the universe used to be like, as proven by the CMB?


what is the universe like today?

MOND myth

MOdified Newtonian Dynamics; "inventing" dark matter to explain observations like the rotation curves of spiral galaxies is troubling to some astronomers--we might not understand gravity as well as we could, and therefore have no need for dark matter

MOND gravity theory

(1981) says that all stars in a galaxy should orbit at the same speed, and no dark matter is required. Mordehai Milgrom observed this. Explains galactic rotation curves, but isnt good at explaining things like the "bullet cluster"

evidence for dark matter

motions of galaxies in clusters, rotation curves of galaxies, hot x-ray emitting gas in galaxy clusters, gravitational lensing by galaxy clusters

gravitational lens

When massive objects bend space and time enough to create multiple images of an object located behind them.

evidence for Big Bang

expanding universe, nucleosynthesis, CMB


The building up of heavier elements from lighter ones by nuclear fusion (occurs in stars and during supernovae explosions).


left over cooled photons from the Big Bang

Fritz Zwicky

(1930's) deduced that there must be some kind of unseen matter whose gravity holds the galaxies in clusters.


how much mass is not observed/"missing?"

mass to light ratio (M/L)

the measure of how much unseen matter is present compared to the visible luminous matter

galactic rotation curves

Plot of speed around center of galaxy

evidence for dark matter

motions of galaxies in clusters, rotation curves of galaxies, hot x-ray emitting gas in galaxy clusters, gravitational lensing by galaxy clusters


make up everyday matter, are combinations of 3 quarks (protons, neutrons)

dark matter

a hypothetical form of matter that is believed to make up 90 percent of the matter in the universe. doesnt interact with light.


how much of all matter is unlit (and only detected via gravity)?


how much matter is made of something as yet unknown?


MAssive Compact Halo Objects, baryonic matter living in the halo of our galaxy that we dont easily see. Ex: brown dwarfs, dead stars, and massive black holes


neutral particles with high energies but almost zero mass, there should be lots of them leftover from the Big Bang

Homestake Gold Mine

neutrino "telescope"

Super Kamiokande

neutrino "telescope"


Weakly Interacting Massive Particles, a new kind of non-baryonic particle. Ex: supersymmetric particles, axions, kaluz-klein dark matter

4-pico seconds

when did "primordial soup" form after the Big bang?

1-micro second

when did protons and neutrons form after the Big Bang?

3 minutes

when did nuclei form after the Big Bang?

400,000 years

when did atoms form (recombination) after the Big Bang?


Cosmic Background Explorer

"clumpiness" problem

the Universe today is clumpy; if the ultra-smooth CMB is linked to todays universe, shouldnt there be some clumpiness in the CMB? otherwise, where did the galaxies come from?

John Mather and George Smoot

discovered the blackbody form and anisotropy of the CMB

3000 K

at what temp. does hydrogen recombine?

z = 1000

if hydrogen recombines at 3000 K, at about what redshift did decoupling occur?


a flammable, poisonous gas on Earth and in interstellar clouds that can be used to detect CMB

clumps seem to be bigger

measuring Ω with the CMB-- Ω > 1

clumps seem to be uniform

measuring Ω with the CMB-- Ω = 1

clumps seem to be smaller

measuring Ω with the CMB-- Ω < 1


rapid expansion of the early universe will drive compression waves, or _____, through the universe, which we can measure by studying the bumps in the CMB

harmonic overtones

by studying the relative intensity of these, we can work backwards to determine the properties of the universe at decoupling


Event in the early universe when atoms first formed, and after which photons could propagate freely through space.

elements in the Universe

Hydrogen, Deuterium, Tritium, Helium-3, Helium-4, Lithium-7, Beryllium-7


hydrogen was built into deuterium-->deuterium was destroyed in a reverse reaction-->universe cooled over time, and more deuterium survived long enough to form helium-->a bit of helium formed lithium. Couldn't really build any elements more complex than lithium because the universe had cooled so much that nuclear reactions began to slow

3 minutes after Big Bang

when did nucleosynthesis stop?

15 minutes after Big Bang

when were the Universe's elemental abundances fixed?

Big Bang nucleosynthesis

observed chemical abundances in early stars/galaxies constrain Big Bang models, so depending on the conditions of the early universe, different chemical abundances will result

Population I

youngest stars, most stars in Milky Ways disk, stars like our sun that are abundant in metals


anything other than H and He

Population II

older stars with low metal abundances, globular cluster stars

Population III

the first generation of stars, contain virtually no metals, only a few have been observed


Ωbaryon = ? , as indicated through Big Bang nucleosynthesis?

spectral lines

careful analysis of ________ in distant galaxies leads to measurements of H, D, He, and Li in the early universe.

expand forever

if Ω = 0.04, what will be the fate of our universe?


has the universe's chemical makeup changed much since 3 minutes after the Big Bang? (yes/no)

Wilson and Penzias

(1964) discovered CMB


around 400,000 years AB, the Universe cooled enough to allow protons and electrons to come together to form hydrogen atoms, making the universe transparent for the first time

dipole discovery

a red shifted side and blue shifted side in the CMB, due to the motion of the earth with respect to the CMB. proved that the CMB was not in the earths atmosphere, and allowed astronomers to measure the speed of the Milky Way through space

Big Bang theory

claims that nearly all of the matter in our universe (neutrons, protons, H, He...) was created in the first 3 minutes after the Big Bang.

the four forces

strong nuclear force, electromagnetic force, weak nuclear force, gravity (in order of strength from strongest to weakest)

Electroweak Theory

theory uniting electromagnetism with the weak nuclear force

Grand Unified Theories (GUTs)

theory uniting electroweak with the strong nuclear force

Theory of Everything (TOE)

seeks to united gravity with the GUT. has not been done yet

Proton-proton process

(1938) discovered by Hans Bethe, the fusion reactions by which stars convert hydrogen to helium, usually occur in stars the size of the Sun or smaller

particles surviving

the earliest universe was dominated by light (radiation). at first the universe was so hot that any particles that happened to form were immediately destroyed, but as the universe expanded/cooled, the radiation lost energy. so, particles could survive for longer and longer periods of time

quantum gravity era

current physics cant explain it, but its when matter, light, and energy coexisted in a kind of primordial soup. all four forces were united. ended with symmetry breaking.

symmetry breaking

a process in which gravity "froze out" of the cooling primordial soup. ended the quantum gravity era

the grand unified era

during this era, the electromagnetic, strong, and weak forces were united. gravity was distinct. this era ended when the strong nuclear force "froze out" of the mixture

inflationary era

when the universe went through a stunning growth spurt--got 1 googol times bigger WOW! no one is sure why it happened.

quark era

when free quarks roamed the universe, interacting with protons and other particles in violent matter/antimatter reactions. during this era, electromagnetism and the weak force seperated, so the four forces were distinct

hadron era

when the universe cooled enough that free quarks condensed together to form hadrons (like mesons and baryons)

Lepton era

when all antimatter had been wiped out in reactions with matter, and protons greatly outnumbered baryons


hadrons and leptons.


made of quarks, interact via strong force


not made of anything smaller, interact via weak force


carry forces between the fermions

a few seconds after the Big Bang

when was the amount of matter in the universe basically fixed?


quantum gravity era-->grand unified era-->inflationary era-->quark era-->hadron era-->lepton era (QGIQHL)


what is the rate of expansion determined by?

escape velocity

the minimum velocity needed to escape a gravitational field, outward energy vs. inward gravity

Friedmann equation

"escape velocity" for the universe

closed universe

k = 1, parallel lines will converge

flat universe

k = 0, parallel lines will never meet

open universe

k = -1, parallel lines will diverge


in which universe could you see the back of your own head if you could look out far enough into space?

critical density

the density of a flat universe


the age of the universe is given by 1/H0


age = 1/H0 is only true in a totally empty universe. in fact, the gravity between all the stuff in the universe should be slowing down the expansion of the universe

the true age is less than 1/H0

if the universe is slowing down, how does the true age of the universe compare to 1/H0?


fate of closed universe

expands forever (barely)

fate of flat universe

expands forever

fate of open universe

cosmological constant

________ this could make an open or flat universe expand even faster, or make a closed universe into an open universe

Henrietta Leavitt

(1868-1921) one of the Harvard College Observatory "calculators" (along with Annie Jump Cannon). Discovered that there is a relationship between the period of a Cepheid variable star and its luminosity.

cepheid variable stars

stars whose luminosity varies ("variable stars") in a regular, predictable, periodic way.

period-luminosity relation

if you know the period of a Cepheid variable star, then you can determine its average luminosity!

cosmological distance ladder

radius of the earth-->distance to the moon-->distance to the sun-->parallax of stars-->"spectroscopic parallax"-->star clusters-->cepheid variables-->supernovae in galaxies-->Hubbles law of redshifts

Edwin Hubble

he discovered that galaxies are moving away from each other. Found Hubble constant which can give the age of the universe

scale factor

A mathematical quantity that describes the changing separation of two points as the Universe expands

the expansion of the universe

what are redshifts caused by?


when the universe expands, light waves also expand to longer wavelengths (when wavelengths stretch between two points, so does space) causing a redshift

"R dot"

the velocity at which the universe is expanding


(276-194 BC) a mathematician, geographer, and the third librarian of Alexandria, devised an early leap-year calendar, and wrote On the Measurement of the Earth

William Herschel

(1738-1822) discovered infrared light, made telescopes, discovered Uranus

Caroline Herschel

William Herschel's sister who discovered 8 comets, many nebulae, and was one of the first women elected into the Royal Society

John Herschel

William Herschel's son who carried on his fathers work to chart nebulae in the southern hemisphere

1 pc

3.26 light years

Freidrich Struve

discovered stellar parallax when he measured a parallax from Vega, which was the first distance measurement ever made to an object outside our solar system

Freidrich Bessel

man who measured another parallax, which was the second distance measurement ever made to an object outside our solar system


machine whose mission was to map the motions of 120,000 stars. Shutdown in 1993, but mapped lots of stars


Global Astrometric Interferometer for Astrophysics. Its a Planned European Space Agency satellite, which will measure the positions and Doppler shifts of 1 billion stars with crazy precision. Scheduled for launch in 2013

globular clusters

spherical groupings of tens of thousands of stars. contain so many stars that they can be seen at much larger distances than single stars. About 150 are known in the Milky Way

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