Download A Sense of Time

A Sense of the Universe
 For medieval astronomer/astrologers the Universe was a small place
o Earth was the center
o Events in the heavens were orderly and designed to benefit humanity
o The only change appropriate was cyclic change - orderly motion of the
sun & planets
 In Europe of the Middle Ages this belief was elevated to the level of religious
dogma
 Copernican revolution (16th and 17th centuries) changed our perception
 Since then observations and increased theoretical understanding demonstrated
that the Universe is:
o Enormous
o Has existed for crazy-long periods of time
o We are not the center of the Universe
 Understanding has increased at breathtaking pace over the last 30 years
o Observational astronomy at wavelengths other than visible light (RadioFrequency, X-Ray, Gamma-Ray, Ultraviolet, ...) has become more
commonplace
 We have begun to appreciate that the Universe is anywhere from an orderly
stage for stately and gentle physical processes to violent cataclysms releasing
energy on a scale to numb the mind of even the most analytic physical
scientist.
 There would be no matter as we know it, no life as we know it, and no
humanity to contemplate these questions, in the absence of violent processes
that would, of themselves, destroy all life within countless light years.
 The development of these ideas has been a truly remarkable odyssey in the
history of human thought
Our Modern Perception of the Universe
 Only in the last 400 years or so have we realized that the earth is not the
"center", and that the Universe is immense.
o The Sun would hold 1.3 million Earths.
o There are 200 billion "Suns" in a galaxy like our own Milky Way Galaxy.
o Astronomers can see billions of galaxies.
o We don't know whether the Universe has an "end" or not; we are not
completely sure even of the full meaning of the question.
 Only in the last 50 years have we realized that the Universe is not static.
o The entire Universe is expanding.
o Events of fantastic violence take place in the Universe.
 In the last half-century we have come to believe that the Universe contains
objects that are truly bizarre as measured in human terms.
o Neutron Stars and Pulsars
o Black Holes
o Quasars
o Exploding and Colliding Galaxies
A Sense of Scale
 If the solar system were the size of a table:
o The Andromedae Galaxy would lie at 10 times the distance to the moon
o The most distant galaxies would lie at 60 times the distance to the Sun.
o Powers of 10 Video
A Sense of Time
 Only in the last 200 years have we begun to appreciate the age of the Universe.
o The Universe is probably 10-20 billion years old.
o Our Solar System is probably 4-5 billion years old.
 If we were to compress the time since the Big Bang into one year, and make
the time of the Big Bang January 1
o The Earth was formed in mid-September.
o The mammals appeared on December 26.
o All human prehistory (from the first known stone tools) and history have
occurred in the last 1/2 hour of New Year's Eve.
 Thus, all of human history is but a fleeting instant on the cosmic timescale.