Lecture 9. Cosmology- The Universe As A Whole
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Modern Astronomy Stars & Galaxies Lecture 9 Cosmology Geraint F. F Lewis University of Sydney 2005
Outline The Universe as we know it Cosmological models Observations Ob ti off the th Universe U i The evolution of the Universe The distribution of matter The future of the Cosmos
The Universe as we know it
www-ed.fnal.gov/projects/exhibits
Fundamental Forces Strong: 1
EM: 10-2
Weak: 10-5
Gravity: 10-39
Forces: Unification As the energy of the interactions increases, these force look more like each other. Quantum Electrodynamics: unifies EM & Weak Qua Quantum u C Chromodynamics: o ody a cs EM EM--Weak ea & Strong S o g Currently trying to add gravity
Superstrings?????
Forces: Unification
hyperphysics.phy-astr.gsu.edu/hbase/astro/unify.html
Cosmological Foundations
General Relativity In Einstein’s view, gravity is not really a force! Importantly, gravity is created not only l by b mass, but b t also l by b energy. Remember, Remember mass is energy E=mc2
Cosmology Imagine ag e a universe u e se filled ed with stationary stars. If finely balanced, it remains stationary. A single g star out of p place results in collapse.
Cosmological Constant This worried Einstein as he thought the Universe should be static. He added Λ, the cosmological constant, t t which hi h acts t as antianti tigravity. This acts against collapse, collapse but has negative pressure and appears unphysical! Einstein’s Biggest Blunder!
Cosmology Friedmann & Lemaitre looked at cosmology within the framework of General Relativity. The concluded that, in general, universes must be expanding or contracting. Just how the universe changes with time depends p upon p the energies g in the Universe. When this original work was done, the only energy considered was matter!
Evolution
Too little matter, and the Universe never slows down Too much matter, and the Universe collapses Just right, the expansion slows down forever, but never quite reaches zero
But what does this scale factor mean? It is the change g of separation between a pair of objects.
Evolution
The raisin cake picture encompasses this picture As the cake expands, the distance between raisins increases But for this picture to be accurate, there can be no edges to the cake! Where is the centre of the Universe in this picture?
Geometry
The ratio of the circumference to the diameter of a circle is π=3.141592…. =3 141592 But this is only true in the flat geometry of Euclid What about nonnon-flat geometry??
Open flat, Open, flat closed? Measure π on the surface of the Earth From pole to equator = 10000km Around the equator = 40000km π = 40000/(2£ 40000/(2£10000) = 2
Open flat, Open, flat closed? So,, depending p g upon p the density y in the Universe
Open >π >π: Infinitely large & expand forever Flat = π: Infinitely large & expand forever Closed <π <π: Finite & eventually collapse
Critical density = 1 £ 10-26 kg/m3 = 6 hydrogen atoms / m3
Observing: The redshift
Hubble’s Hubble s expansion Hubble found a relation between distance and velocity V = Ho d where d is the distance to the galaxy and v is its velocity. Hubble’s constant has b been measured d to t be b Ho = 72 km/s/Mpc
Hubble’s Hubble s expansion
Imagine the Earth expands overnight. We might feel squashed in our beds, but when we awake in the morning, all the distances would have increased! What if we lived in the surface?
What is the redshift? The redshift is not a Doppler shift. As the Universe expands, the wavelength of the radiation is also stretched. Mathematically
where z is the redshift and R is the distance between galaxies.
Which universe is ours? The cosmological models make specific predictions on how faint something thi should h ld llook k att a particular ti l redshift. This depends upon the content of the Universe. Universe Observations of distant supernova show that we do not live in a universe containing only matter. matter In fact we live in a universe dominated by Something Else!!!!
Cosmological time dilation
Cosmological C l i l supernovae are lik like clocks, they brighten and fade in a fixed time. The cosmological equations predict that we should see the distant universe run slowly, a time dilation effect. This has now been observed, providing further evidence that the cosmological models are a good description of the cosmos. cosmos
Putting it all together
Dark Matter • • • •
The Universe is flat f The Universe is 13.7 billion yrs old
Interacts mainly via gravity Not stars, gas, rocks etc Not large black holes Possibl an elementa Possibly elementary particle pa ticle
Dark Energy • • • • •
Not dark matter! Looks like Einstein’s Λ Must be exotic: strings, defects Is beginning to dominate Accelerates the expansion
Accelerated expansion
Running backwards
Running u g the t e Universe U e se backwards, bac a ds, we e see there was a point where the scale factor was zero. Thi marks This k the h Big Bi Bang, Bang B , or start off the h Universe. Currently science cannot answer what caused Currently, this event. But science can describe the universe in detail from 10-43 seconds after the event to the present day!
At the beginning
The smaller the scale factor, the hotter the universe was. was The very early universe was very hot!
The energy from inflation b became particles ti l and d radiation di ti 10-6 secs, protons and neutrons formed 1 sec, protons & neutrons join to make deuterium and helium 3 mins, cooking ceased with the universe 75% hydrogen and 25% helium 300,000 yrs, the Universe is cool enough for electrons to join atoms
There should be a background of radiation left over from this event!!
Background Radiation In 1941, Herzberg saw that molecules in interstellar space were too energetic. H concluded He l d d th thatt they th mustt be b bathed in a radiation of temperature p 2.3K. “a rotational temperature of 2.3k follows, which has of course only a very restricted meaning” Penzias & Wilson confirmed this in 1965 ((and won the Nobel in 1978))
Cosmic microwave background The universe is bathed in cool radiation left over from its energetic start. Some of the snow on tv is this CMB Two important predictions CMB was hotter in the past CMB should not be completely p y smooth
Cosmic microwave background Relativistic cosmology predicts that the temperature of the CMB should scale with the size of the universe. Astronomers have looked at distant molecules in the early universe and have mentioned temperature of the CMB, finding it to be hotter in the past, in agreement with the cosmological model. model www.eso.org/outreach/press--rel/pr www.eso.org/outreach/press rel/pr--2000/pr 2000/pr--27 27--00.html
The CMB
While the CMB has a mean temperature of 2.7K, there should be small (10-5) variations superimposed on it. These variations reflect the distribution of matter in the very early Universe.
Anisotropy
Inflation predicts a very specific pattern on the CMB (red line) Data from COBE and now WMAP have revealed this pattern matches h the h theory! h
In the beginning beginning…
… the Universe was very smooth Inflation results in very small ripples in the matter at the level of 1 part in 10000 (as seen in the CMB) Gravity causes material to flow into denser regions, regions forming the large scale structure of galaxy groups, clusters and superclusters Again need a Universe in a computer
The growth of large scale structure http://v virgo.dur.ac c.uk & http:://www.nbo ody.net
Large Scale Structure Sloan galaxy survey (www.sdss.org)
Surveys of the Universe reveal galaxies y structure predicted p to lie on the foamy from inflation!
Present: 14£ 14£109 yrs
Stars are metal rich More metals made in supernova New stars have less and less hydrogen as they become polluted with metals Mass is getting locked up in white dwarfs, neutron stars and black holes!
Future: 16£ 16£109 yrs
The Milky Way and Andromeda collide and form a single large elliptical
Future: 17£ 17£109 yrs
The Sun dies
Future: 7£ 7£1011 yrs
With the accelerated expansion, galaxies beyond the Local Group fade from view. view The sky outside the Local Group will be black!
Future: 1013 yrs
Nuclear fuel is exhausted Small red stars finally burn out All star light begins to fade All potential raw material for star f formation ti iis llocked k d away in i stellar remnants
Future: 1016 yrs
Stellar interactions finally eject all planets
Future: 1028 yrs
Galaxies finally dissolve, with 90% of stars ejected into intergalactic space The remaining stars spiral into the central black hole
Future: 1032 yrs
Protons decay and matter dissolves into radiation and electrons. electrons
Future: 1067 ! 10100 yrs
Stellar and supermassive black holes evaporate via Hawking radiation Nothing left by a sea of ever cooling radiation The universe is now a cold, dark, lifeless place, a little bit like Canberra.
See y you next week!
Outline The Universe as we know it Cosmological models Observations Ob ti off the th Universe U i The evolution of the Universe The distribution of matter The future of the Cosmos
The Universe as we know it
www-ed.fnal.gov/projects/exhibits
Fundamental Forces Strong: 1
EM: 10-2
Weak: 10-5
Gravity: 10-39
Forces: Unification As the energy of the interactions increases, these force look more like each other. Quantum Electrodynamics: unifies EM & Weak Qua Quantum u C Chromodynamics: o ody a cs EM EM--Weak ea & Strong S o g Currently trying to add gravity
Superstrings?????
Forces: Unification
hyperphysics.phy-astr.gsu.edu/hbase/astro/unify.html
Cosmological Foundations
General Relativity In Einstein’s view, gravity is not really a force! Importantly, gravity is created not only l by b mass, but b t also l by b energy. Remember, Remember mass is energy E=mc2
Cosmology Imagine ag e a universe u e se filled ed with stationary stars. If finely balanced, it remains stationary. A single g star out of p place results in collapse.
Cosmological Constant This worried Einstein as he thought the Universe should be static. He added Λ, the cosmological constant, t t which hi h acts t as antianti tigravity. This acts against collapse, collapse but has negative pressure and appears unphysical! Einstein’s Biggest Blunder!
Cosmology Friedmann & Lemaitre looked at cosmology within the framework of General Relativity. The concluded that, in general, universes must be expanding or contracting. Just how the universe changes with time depends p upon p the energies g in the Universe. When this original work was done, the only energy considered was matter!
Evolution
Too little matter, and the Universe never slows down Too much matter, and the Universe collapses Just right, the expansion slows down forever, but never quite reaches zero
But what does this scale factor mean? It is the change g of separation between a pair of objects.
Evolution
The raisin cake picture encompasses this picture As the cake expands, the distance between raisins increases But for this picture to be accurate, there can be no edges to the cake! Where is the centre of the Universe in this picture?
Geometry
The ratio of the circumference to the diameter of a circle is π=3.141592…. =3 141592 But this is only true in the flat geometry of Euclid What about nonnon-flat geometry??
Open flat, Open, flat closed? Measure π on the surface of the Earth From pole to equator = 10000km Around the equator = 40000km π = 40000/(2£ 40000/(2£10000) = 2
Open flat, Open, flat closed? So,, depending p g upon p the density y in the Universe
Open >π >π: Infinitely large & expand forever Flat = π: Infinitely large & expand forever Closed <π <π: Finite & eventually collapse
Critical density = 1 £ 10-26 kg/m3 = 6 hydrogen atoms / m3
Observing: The redshift
Hubble’s Hubble s expansion Hubble found a relation between distance and velocity V = Ho d where d is the distance to the galaxy and v is its velocity. Hubble’s constant has b been measured d to t be b Ho = 72 km/s/Mpc
Hubble’s Hubble s expansion
Imagine the Earth expands overnight. We might feel squashed in our beds, but when we awake in the morning, all the distances would have increased! What if we lived in the surface?
What is the redshift? The redshift is not a Doppler shift. As the Universe expands, the wavelength of the radiation is also stretched. Mathematically
where z is the redshift and R is the distance between galaxies.
Which universe is ours? The cosmological models make specific predictions on how faint something thi should h ld llook k att a particular ti l redshift. This depends upon the content of the Universe. Universe Observations of distant supernova show that we do not live in a universe containing only matter. matter In fact we live in a universe dominated by Something Else!!!!
Cosmological time dilation
Cosmological C l i l supernovae are lik like clocks, they brighten and fade in a fixed time. The cosmological equations predict that we should see the distant universe run slowly, a time dilation effect. This has now been observed, providing further evidence that the cosmological models are a good description of the cosmos. cosmos
Putting it all together
Dark Matter • • • •
The Universe is flat f The Universe is 13.7 billion yrs old
Interacts mainly via gravity Not stars, gas, rocks etc Not large black holes Possibl an elementa Possibly elementary particle pa ticle
Dark Energy • • • • •
Not dark matter! Looks like Einstein’s Λ Must be exotic: strings, defects Is beginning to dominate Accelerates the expansion
Accelerated expansion
Running backwards
Running u g the t e Universe U e se backwards, bac a ds, we e see there was a point where the scale factor was zero. Thi marks This k the h Big Bi Bang, Bang B , or start off the h Universe. Currently science cannot answer what caused Currently, this event. But science can describe the universe in detail from 10-43 seconds after the event to the present day!
At the beginning
The smaller the scale factor, the hotter the universe was. was The very early universe was very hot!
The energy from inflation b became particles ti l and d radiation di ti 10-6 secs, protons and neutrons formed 1 sec, protons & neutrons join to make deuterium and helium 3 mins, cooking ceased with the universe 75% hydrogen and 25% helium 300,000 yrs, the Universe is cool enough for electrons to join atoms
There should be a background of radiation left over from this event!!
Background Radiation In 1941, Herzberg saw that molecules in interstellar space were too energetic. H concluded He l d d th thatt they th mustt be b bathed in a radiation of temperature p 2.3K. “a rotational temperature of 2.3k follows, which has of course only a very restricted meaning” Penzias & Wilson confirmed this in 1965 ((and won the Nobel in 1978))
Cosmic microwave background The universe is bathed in cool radiation left over from its energetic start. Some of the snow on tv is this CMB Two important predictions CMB was hotter in the past CMB should not be completely p y smooth
Cosmic microwave background Relativistic cosmology predicts that the temperature of the CMB should scale with the size of the universe. Astronomers have looked at distant molecules in the early universe and have mentioned temperature of the CMB, finding it to be hotter in the past, in agreement with the cosmological model. model www.eso.org/outreach/press--rel/pr www.eso.org/outreach/press rel/pr--2000/pr 2000/pr--27 27--00.html
The CMB
While the CMB has a mean temperature of 2.7K, there should be small (10-5) variations superimposed on it. These variations reflect the distribution of matter in the very early Universe.
Anisotropy
Inflation predicts a very specific pattern on the CMB (red line) Data from COBE and now WMAP have revealed this pattern matches h the h theory! h
In the beginning beginning…
… the Universe was very smooth Inflation results in very small ripples in the matter at the level of 1 part in 10000 (as seen in the CMB) Gravity causes material to flow into denser regions, regions forming the large scale structure of galaxy groups, clusters and superclusters Again need a Universe in a computer
The growth of large scale structure http://v virgo.dur.ac c.uk & http:://www.nbo ody.net
Large Scale Structure Sloan galaxy survey (www.sdss.org)
Surveys of the Universe reveal galaxies y structure predicted p to lie on the foamy from inflation!
Present: 14£ 14£109 yrs
Stars are metal rich More metals made in supernova New stars have less and less hydrogen as they become polluted with metals Mass is getting locked up in white dwarfs, neutron stars and black holes!
Future: 16£ 16£109 yrs
The Milky Way and Andromeda collide and form a single large elliptical
Future: 17£ 17£109 yrs
The Sun dies
Future: 7£ 7£1011 yrs
With the accelerated expansion, galaxies beyond the Local Group fade from view. view The sky outside the Local Group will be black!
Future: 1013 yrs
Nuclear fuel is exhausted Small red stars finally burn out All star light begins to fade All potential raw material for star f formation ti iis llocked k d away in i stellar remnants
Future: 1016 yrs
Stellar interactions finally eject all planets
Future: 1028 yrs
Galaxies finally dissolve, with 90% of stars ejected into intergalactic space The remaining stars spiral into the central black hole
Future: 1032 yrs
Protons decay and matter dissolves into radiation and electrons. electrons
Future: 1067 ! 10100 yrs
Stellar and supermassive black holes evaporate via Hawking radiation Nothing left by a sea of ever cooling radiation The universe is now a cold, dark, lifeless place, a little bit like Canberra.
See y you next week!
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