Transcript Galaxies and the Universe

Galaxies and the Universe
What Are Galaxies?
• Greek galax = milk
• William Herschel, 1783: A disk with the Sun
slightly off-center
What Are Galaxies?
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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
Supercluster
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
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• 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 RelativityGravitational Lenses
What Does The Universe Look Like?
What Does The Universe Look Like?
“The Big Bang”
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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?
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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