Physical Cosmology, Part I,
Lead: Eberhard Möbius
1/31/2000
Summary by Amy Lovell-Klar:

The Big Bang Theory is the widely accepted model of the universe.

• We may be on the verge of another paradigm shift.

Creation Myths

• We tend to pitch science against religion
• We may not need to be so antagonistic
• Judeo-Christian mythology
  • "Let there be light" fits with today's science
  • One shot universe -- all begins at once.
• Northeast Indian mythology
  • Sedi + Melo -- male and female forces
  • Cyclical -- unity begets duality, duality begets unity
• Guinea mythology
  • Death the Creator (life from death)
  • Cyclical

There are chasms between the different religions and between science and religion. Science's theories and models are self-contained and don't conflict with religion. Stories have meaning to help us determine how we should live.

Science

• As knowledge expands, so do the boundaries of the unknown. New questions come from the answers to old ones.

Theories and Axioms

• Must take axioms as a base for knowledge (e.g. parallel lines)
• Goedel's Theory -- you can't prove the axioms of a theory. Infinite Regress
• What's beyond what we know about our universe?
• We belong to the universe and have to explain ourselves and our experience of the universe.

Observable Universe

• The observable universe only includes light from places that light is reaching us from, i.e. 30 billion light years, radius of 15 billion light years.
  • Beginning of our observation and explanation is within the observable universe.
• To measure is to compare to something we know. Base measurements of universe on size of the earth.
  • Models -- shrink everything by the same ratio to replicate the actual universe
• Galaxies are closer to each other than stars are, relative to their size.
  • Galaxies are moving and will eventually run into each other.
  • Stars in galaxies are so far apart, they won't even hit each other when the galaxies overlap.
• Speed of light -- 300,000 meters per second
  • Light year -- distance light travels in one year
• Center of the known universe -- appears to be Earth from our vantage point.
  • We're probably not in the center in reality, because there is probably more than just the observable universe.
  • Paradigm shifts about the center of the universe
  • Copernican Revolution -- Sun in center to Earth in center
  • Herschel -- mapped stars, Earth appeared in center
  • He wasn't aware of interstellar medium -- fog between stars.
• Beginning of observation outside our galaxy
  • We're not in the center of the galaxy or the universe.

Light as a Time Machine

• Light from the sun is 8 minutes old, from Saturn it's around 80 min. old
• By the time we observe light in the universe, the event or the emission of light has already happened -- we're working with outdated info.
• From the farthest point of the observable universe, info is 15 billion years old.
• We use the "time machine" to watch galaxies form that have been formed for many years. Use this info to understand how comparable galaxies formed.
• Nothing can go faster than the speed of light.
  • Nothing
  • EVER
  • Not even a baseball thrown from a train that is traveling at the speed of light.

Olber's Paradox

• "You can't see the forest for the trees."
• Suppose universe is infinite AND infinitely old. The sky would be completely full of stars and we would burn.

Spectroscopy

• Edwin Hubble used spectroscopy together with Cepheids as distance indicators.
  • Redshifts of Galaxies -- all of them are moving away from us.
  • Farther away galaxies move faster
  • Universe is expanding
• Universe is moving into unknown space -- we get info from light that is farther and farther away.
  • Everything is moving away from the same point at the same ratio of distance to speed.
  • If you calculate backwards you can determine the age of the universe
  • The constant that connects speed and distance in this calculation is called the Hubble constant.

The Big Question

How is the calculation of 10-14 billion years for the age of the universe reconciled with the fact that we can see the oldest galaxies at distances of almost 14 billion light years at the edges of the universe (when they should have been close)?

May 15, 2000