Galaxies and the Universe

What Are Galaxies?• Greek galax = milk• William Herschel, 1783: A disk with the Sun

slightly off-center

What Are Galaxies?

• 19th Century: “Spiral Nebulae”• Nearby? Maybe Solar Systems in Formation?• 1920: Galaxies are Stars• 1920’s: Galaxies are like the Milky Way• Biggest single increase in our mental picture

of the Universe in human history

Where Are We in our Galaxy?

• The visible Milky Way suggests our galaxy is a flat disk

• Surrounding other galaxies is a spherical halo of Globular Star Clusters

Galaxies and Globular Clusters

The Milky Way’s Globular Clusters

The Milky Way As We See It

Anatomy of a Galaxy

Spiral Arms

In Microwaves, We Can See the Hub of the Galaxy

Mapping the Neighborhood

Mapping the Neighborhood

Mapping the

Galaxy: Not There

Yet

Mapping the

Galaxy: Not There

Yet

The Local

Group

Downtown: The Virgo Cluster: 50 m.l.y

The Local

Super-cluster

The Coma Cluster

350 m.l.y.

Large-Scale Structure

of the Universe to 500 m.l.y.

Travel to the Stars?• Kinetic Energy = 1/2 Mv2

• What does it take to get a 1000-ton spaceship to 10% of the speed of light? (43 years to Alpha Centauri)

• M=106 kg, v = 3 x 107 m/sec• KE = 1/2 x 106 x 9 x 1014 = 4.5 x 1020 joules• Equals U.S. Energy Production for 4.5 years• Once you get there, you have to stop.

Relativity• Speed of Light is Independent of Source• Michelson and Morley, 1887 - Speed of

Light Independent of Observer• “One of the Most Unexpected Results in

the History of Science” - Isaac Asimov• Conclusion: Speed of Light is the Same for

All Observers• Implication: Space and Time Must Change

to Keep Speed of Light Constant

Why the Speed of Light is a Speed Limit

• Energy of a Moving Object in Relativity:

E = mc2 -------------------------------------------------------------------------------

1 - v2/c2

• One consequence: as v approaches c, Energy goes to infinity

• Also, as we approach c, Energy goes up very fast

Fuel Economy of a Starship• At 0.1 c, energy is 0.7% greater than

Newtonian formula• At 0.5 c, 24% greater• At 0.9 c, 3 x greater• At 0.99 c, 12 x greater• At 0.999 c, 43 x greater• Each extra 9 more than triples the energy• Getting our 1000 ton ship to 0.9 c takes 1.1 x

1023 joules = U.S. energy use for 1100 years

Another Consequence of Relativity- Gravitational Lenses

What Does The Universe Look Like?

What Does The Universe Look Like?

“The Big Bang”• Edwin Hubble, Recession of Galaxies, 1929• Red-shift increases with distance• Cosmic Microwave Background, 1965• Estimated Age of Universe: 12-15 b.y.• “Big Bang” originally a derisive term, coined

by Fred Hoyle

As Far Out as We Can See - Ten Days With the Hubble Telescope

A New Name for the “Big Bang?”(Sky and Telescope, 1995)

• The Big Boot• God’s Log-On• Fred Withair Day (“Nobody ever named

anything else after me, so why not?”)• What Happens If I Push This Button?• You’re Never Going To Get It All Back In

There Again

90% of the Universe is “Missing”

• Outer Stars in Galaxies revolve faster than expected

• What holds clusters of galaxies together?• Conclusion: There must be a lot of invisible

mass in the Universe• Not really “missing”, just non-luminous

Astronomers Are Not As Upset As One Might Expect

• MACHO’s (Massive Compact Halo Objects): faint stars, brown dwarfs, planets

• Cool non-luminous gas• Massive Neutrinos?• WIMP’s (Weakly Interacting Massive

Particles)• Magnetic monopoles• Exotic objects: strings, mini-black holes

Fine Tuning the Universe• Density– Much greater and the Universe would already

have collapsed in on itself– Much less and stars could not have formed

• Nuclear Forces– Fusion impossible– Fusion too easy

• Anthropic Principle– Cosmology has to be able to explain why we exist

Fine Tuning the Universe• It just came out that way• It has to be that way for reasons we haven’t

yet discovered• Maybe there are an infinity of universes but

only those with certain parameters develop intelligent life (Multiverse)

• Engineered or designed

Fine Tuning the Universe• Designer?• Doesn’t Explain Anything• If the Designer can create a Universe, why is c

= 300,000 km/sec instead of 400,000?• If Designer had to have c = 300,000 km/sec,

why? What (who?) dictated that, and why?• Who says Designer is anything pictured by any

religion?

Misinterpreting Relativity• There are no absolutes– Speed of light is absolute– It may not be possible to be absolutely right but it

is very easy to be absolutely wrong

Where Will It All End?

• Trillions of years: Star formation ends• 10-100 trillion years: Stars stop radiating• 1015 – 1020 years: Planetary orbits decay• 1032 – 1041 years: Protons decay?• Heat Death?• Big Crunch?• Big Bounce?

What Does Cosmology Imply for Philosophy?

• Nothing• At Least, Not Yet• It Is Hopelessly Premature To Try To Create A

Philosophy Based on Cosmology– We can say what the fate of the Universe will be

based on specific assumptions– We are a long way from knowing the assumptions

are complete or correct

• If you support your philosophy with science, be prepared for science to prove it wrong