ASTR 1200Announcements

Websitehttp://casa.colorado.edu/~wcash/APS1200/APS1200.html

Last Lecture on Thursday.

Final Exam Wednesday Dec 17 1:30-4:00In Benson 180

Josh will hold review 5:30-6:30 here (Benson180)On Monday (15th)

A Modern Hubble Diagram

Galaxies are Flying ApartGalaxies remain same size. They just get farther apart.

Effect is the same no matter which position you occupy

Expanding Universe

Early Universe

Current Universe

The volume of the universe isincreasing.

The Age of the Universe

Hdv

vH

d

1 vtd Notice: At time zero, d = 0

All galaxies are at zero distance!

The universe has zero volume!

when t=1/H

Feeding a Quasar

Accretion disk is formed of starsand clouds that wander too near thebig black hole.

Tidal forces rip them apart.They settle into an accretion disk.

When there’s no material falling in,the quasar goes quiet.

Jets

The Cosmic Web

Structure of the Universe

Where is the center of the Universe?

Where are the edges?

What happens if you fly to the edge and stick your finger through?

Newtonian Universe must be infinite.

Cosmological Principle: The Universe is Everywhere the Same(when averaged over grand scale)

Classical Universe

• Euclidean Geometry

• Infinite in Extent

• Matter may or may not be everywhere

• Universe infinitely old – always been here, always will be

• Expansion still possible• 2 x ∞ = ∞

Cosmological Principle

• Cosmological Principle applied to expanding Euclidean Universe

• New matter must be formed of nothing to keep density everywhere the same.

Olber’s Paradox

If universe is infinite with stars everywhere,then there an infinite number of stars.

Any line of sight will eventually intersect thesurface of star. Sky would be as bright as thesurface of the Sun.

Well it isn’t. So why not?

Universe Must Change

Answer to Olber’s Paradox:

Universe must change:

Space: ie the stars stopThis was the answer until mid 20th Century

Time: Universe hasn’t always been here, so can’t see forever.Discovery of Big Bang leads us to this answer.

General Relativity

• GR provided an answer

• The presence of matter warps space in on itself.

• Space is actually DEFINED by the presence of the matter in it!!!

• Solves the edge problem

• But geometry is no longer Euclidean

Geometry of Universe

Space Curvesin on itself

There’s no pathout!

Curved Space

There is no “edge” but the volume is finite.Surface of Earth has no end,but it is finite.

Expands and falls back

Universe starts as pinprick

Expands.

But its below escape velocity.

Hits maximum size.

Then shrinks

The End is the “Big Crunch”

Negatively Curved Universe

Its warped so it cannot close back on itself.

Is infinite in extent.

Open vs ClosedUniverse is either open or closed.

If closed: Positive CurvatureFinite MassFinite LifetimeFinite Volume

If open: Negative CurvatureInfinite MassInfinite VolumeInfinite Lifetime That’s INFINITY Folks!!!

Astronomers have prejudice in favor of closed universes.

All measurements have been inconclusive. We live near the edge!

Critical Density

• Whether Universe is open or closed depends on the average DENSITY of matter.

• Above 10-29 g/cc the universe is closed

• Below 10-29 g/cc the universe is open

• We are very close to that density

• Coincidence?

crit is about 1 atom per liter

History and Fate of Universe

Universe is one of these (maybe).

Best Guess Size

• Diameter of Universe is about 1024 times larger than the part we can see.

• That makes the volume 1072 times larger.

• But still finite

• How big is 1072 ?

Heat Death of Universe

• If universe is open, then it will last forever• But stars will all burn out 1014 years• Protons decay 1031 years• Orbits will decay into black holes at center

of the galaxies 1060 years• Giant black holes evaporate 10100 years

• Nothing left but redshifting photons

More on Infinite Universe

• If Cosmological Principle holds and universe is infinite, there’s infinite mass.

• Infinite Planets• Infinite Earth-like planets• Infinite planets just like

you.• Infinite You’s

• Far away: About 1181010 meters away

The Origin of it All?

• Good Question

• Perhaps a bubble in a hyper-universe

• Perhaps its “unknowable”

• But it appears Universe started as a very tiny bubble. How small, we don’t know.

The “Planck Era”

• When quantum fluctuations exceed the radius of the universe our theories are definitely inadequate.

• R < 10-35m• t < 10-44 seconds• Density of Universe > 1093 g/cc• T > 1032 K

• Then it starts to expand and cool….

The Inflationary Universe

• Idea: Vacuum of space-time created with excess energy folded upon itself

• At t=10-37s, T=1028K, starts to relax

• From 10-37 to 10-33s it expands by the creation of new space.

• Universe expands from 10-28m to 0.1m

• That’s 10cm in 10-33s = 1032m/sv = 3x1023 c !!!

How Can It ExpandFaster than Light?

• Einstein’s Law says nothing can travel faster than light.

• Particles in the inflationary universe aren’t traveling.

• More space comes into existence between them.

• Before inflation could see whole universe.

• Since then, can only see a small part.

Big! Very, Very Big

Because of inflation, universe gets muchbigger A factor of 1026!

Means now, universe is 1026 times largerthan we can see.

Rvisible = 1026m

Runiverse = 1052m We are connected to only one part in 1078

of the volume

Maps of Microwave Background

The size of lumps andblobs set before inflation.

Indicate residual gravity fromparts of the universe we canno longer see.

Strong evidence that inflationis on the right track.

The Annihilation Era

• After inflation settles down and resumes normal expansion

• So hot that matter and anti-matter are in equilibrium.

• For every 100,000,000 antimatter particles, there are 100,000,001 matter particles.

• Basic Asymmetry From Planck era is not understood, but it’s why we’re made of matter.

.001 Seconds

• Jump from 10-33s to 10-3s

• T = 1012K

• Neutrons and Protons now have cooled so that can annihilate with anti-neutrons and anti-protons.

• Leave mostly photons and an occasional particle of matter.

1 Second

• Electrons and Positrons have cooled to point where they are no longer in equilibrium. T=1010K

• Create photons.

• One matter particle in hundred million is left.

• Those are today’s electrons.

Era of Nucleosynthesis

• T = 109 K• t = 100s• Hydrogen and Helium form from neutrons

and protons.• Tiny amounts of Li and Be are created.• No carbon: density too low for triple alpha

• This is when the initial elements form

The Plasma Era

• From 100s to 100,000 years universe is a soup of ionized hydrogen and helium

• But its expanding and cooling• Ends at 100,000years when the

temperature falls below 3000K.• Hydrogen and Helium nuclei combine with

electrons to form neutral atoms• At that moment, universe becomes

transparent

Sky Aglow

• At moment of de-ionization, sky is glowing as blackbody at 3000K (M star)

• Photons released are no longer re-absorbed• They travel into the universe and are travelling

today

• But they redshift.• Now 1000 times longer wavelength than then

(makes them microwaves)

The Cosmic Microwave Background

• Microwave Antenna at Bell Labs – 1965• Penzias and Wilson

• Microwaves coming from sky, but not Earth. Uniformly

• Predicted as part of a “Big Bang” by Gamov in the early 1950’s

• Inescapable proof of the “Big Bang”• Killed all steady state theories• Now we’re studying it.

At 100 Million Years

• No Galaxies yet – or perhaps protogalaxies

• Gas mostly smooth through universe

• Clumps cause gravitational spots that create even greater density fluctuations.

• Size:

• Remember: Dark matter dominates

Primordial Density Enhancements Grow

• Now (12.4Billion years) we have structure

• Galaxies and clusters

Recap

History and Fate of Universe

Universe is one of these (maybe).

Dark Energy

• Expansion of Universe is Accelerating!!!

• Implies New Inflationary Era (Why Now?)

• Acceleration takes energy

New Cosmology

• 70% of mass is Dark Energy (E=mc2)• 25% of mass is Dark Matter• 3.5% of mass is in Intergalactic Medium• 1.5% of mass is regular matter in galaxies

• Together they add to exactly critical density.• We’re right on the edge of open/closed

• Universe is either finite and very big, or infinite.