ASTR100 (Spring 2008) Introduction to AstronomyCosmological Inflation

Prof. D.C. Richardson

Sections 0101-106

Inflation

What aspects of the universe were originally unexplained

by the Big Bang theory?

An early episode of rapid inflation can solve all three mysteries!

Mysteries Needing Explanation

1. Where does structure come from?2. Why is the overall distribution

of matter so uniform?3. Why is the density of the

universe so close to the critical density? That is, why does the universe have

such a flat geometry?

Inflation can make structure by stretching tiny quantum ripples to enormous size.

Inflation can make structure by stretching tiny quantum ripples to enormous size.

These ripples in density then become the seeds for all structure in the universe.

How can microwave temperature be nearly identical on opposite sides of the sky?

Regions now on opposite sides of the sky were close together before inflation pushed them far apart.

The overall geometry of the universe is closely related to total density of matter and energy.

Density = Critical

Density > Critical

Density < Critical

Inflation of universe flattens overall geometry, causing total density of matter plus energy to be very close to critical density.

How can we test the idea of inflation?

Patterns of structure observed by WMAP tell us the “seeds” of the universe.

Observed patterns of structure in universe agree (so far) with what inflation should produce.

In excellent agreement with observations of present-day universe and models involving inflation and WIMPs!

“Seeds” Inferred from CMB

Overall geometry is flat. Total mass + energy has critical density.

Total matter is ~ 26% of total. Ordinary matter ~ 4.4% of total. Dark matter is ~ 22% of total.

Dark energy is ~ 74% of total. Universe is 13.7 billion years old.

Why is the darkness of the night sky evidence for the Big

Bang?

Olbers’ Paradox

If universe were

1) infinite;

2) unchanging;

3) everywhere the same;

then, stars would cover the night sky.

Olbers’ Paradox

If universe were

1) infinite;

2) unchanging;

3) everywhere the same;

then, stars would cover the night sky.

The night sky is dark because the universe changes with time.

As we look out in space, we can look back to a time when there were no stars.

The night sky is dark because the universe changes with time.

As we look out in space, we can look back to a time when there were no stars.

Cool fact: if you tune your TV set between channels, a few percent of the "snow" that you see on your screen is noise caused by the background of microwaves…

Is there life beyond the Earth?

The Drake Equation

Number of civilizations with whom we could potentially communicate

= NHP flife fciv fnow

NHP = total number of habitable planets in galaxy;

flife = fraction of habitable planets with life;

fciv = fraction of life-bearing planets with civilization at some time;

fnow = fraction of civilizations around now.

We do not know the following values for the Drake equation:

NHP : probably billions.

flife : ??? hard to say (near 0 or near 1).

fciv : ??? it took 4 billion years on Earth.

fnow : ??? can civilizations survive long-term?

Looking for deliberate signals from E.T.

SETI

We’ve even sent a few signals

ourselves…

Earth to globular cluster M13: Hoping we’ll hear back in about 42,000 years!

Your computer can help! SETI @ Home: screensaver with a purpose.

How difficult is interstellar travel?

Pioneer plaque Voyager record

Current Spacecraft

Current spacecraft travel at <1/10,000 c; 100,000 years to the nearest stars.

Are We Alone?

I hope not!

ASTR100 (Spring 2008) Introduction to AstronomyCourse Review

Prof. D.C. Richardson

Sections 0101-0106

Our Cosmic Address

Our Cosmic Origins

Our Cosmic Motion

Chapter Summaries

1. Our Place in the Universe2. Discovering the Universe for

Yourself3. The Science of Astronomy4. Making Sense of the Universe5. Light: The Cosmic Messenger6. Formation of Planetary Systems7. Earth and the Terrestrial Worlds8. Jovian Planet Systems9. Asteroids, Comets, and Dwarf

Planets

Chapter Summaries

10. Our Star11. Surveying the Stars12. Star Stuff13. The Bizarre Stellar Graveyard14. Our Galaxy15. Galaxies and Cosmology16. Dark Matter, Dark Energy, and

the Fate of the Universe17. The Beginning of Time18. Life in the Universe

Latest Material (Ch. 12–14)

Star Stuff Star birth. Stellar evolution (low-mass vs. high-mass). Planetary nebulae, massive star supernovae.

The Bizarre Stellar Graveyard White dwarfs, neutron stars, black holes. Novae, white dwarf supernovae, pulsars. Gamma ray bursts (skipped).

Our Galaxy Structure, star-gas-star cycle, formation. Galactic center.

Latest Material (Ch. 15–17)

Galaxies and Cosmology Galaxy types, distances, evolution. Hubble’s Law. Quasars and other Active Galactic Nuclei.

Dark Matter, Dark Energy, and the Fate of the Universe Dark matter: nature, evidence. Structure formation. Fate of the universe, dark energy.

The Beginning of Time The Big Bang, evidence, inflation.

Final Exam

Fri May 16, 8 am – 10 am, this room. Don’t be late! And DON’T miss the exam!! Special needs: go to Shoemaker, same time.

Chapters 1 through 17 inclusive. Most weight on chapters 12–15. No notes, calculators, cell phones, etc.

Worth 120 points (~22%)… 48 × 1-2/3 for multiple choice. 4 × 10 for short answer (night sky, planets, stars, galaxies).

5-pt bonus!