Monday, March 17, 2008

Announcements:

Assignments:

Chapter 11 - General Relativity

General relativity deals with accelerated reference frames and the curvature of spacetime as a result of gravity.
Equivalence principle - All physical experiments yield identical results in an accelerated reference frame as they do in a gravitational field.  (i.e. No experiment can distinguish between an accelerated lab in zero gravity or a stationary lab on Earth.)
Gravitational lensing - the gravitational attraction due to a massive object (a star, black hole, or galaxy) can bend light much like a lens refracts light.
    Diagram showing gravitational lensing caused by a galaxy.
    Other examples and class notes from a lecture on general relativity at Berkeley.
Based on observations from astronomy, there is evidence that the universe is expanding at an accelerated rate.  NASA's WMAP website
Color image of the microwave background of the universe from WMAP.
The "discovery of the blackbody form and anisotropy of the cosmic microwave background radiation" is so important in physics that it received a Nobel prize last year (Mather and Smoot, 2006)
The shape of the universe:  closed, flat, or open?
Euclidean geometry deals with the three familiar coordinate directions for 3D objects:  x, y, z
A fourth dimension of space is one that is orthogonal (perpendicular) to the first three, which is difficult to visualize.
In terms of relativity, time is generally considered to be the fourth dimension.
Dark matter and dark energy. - One of the most fantastic discoveries in the past 20 years is that matter as we know it constitutes only about 4% of all the "stuff" of the universe!  We still have much to learn and discover about our universe!


 Chapter 12 - Extraterrestrial Life and Pseudoscience

This chapter addresses the really big questions of "Where did we come from?", and "Are we alone in the universe?"
SETI is the Search for Extraterrestrial Intelligence, and has been active mostly through private funding via the SETI Institute which was founded in 1984.
Planets beyond our solar system are being discovered on nearly a weekly basis now.  As of 3/15/08, 228 exoplanets have been identified.
    These planets cannot be seen directly, but their existence can be inferred by observing a periodic wobble (astrometry) or dimming (photometry) of a parent star, or by observing a periodic shift in the emission spectrum of a star from red to blue and back again (doppler spectroscopy).
The number of planets in our galaxy that likely have intelligent life that could communicate with us is found from:  N = n1*f1*f2*f3*n2*f4*f5*f6
where:
    n1 = number of stars in our Milky Way galaxy:  ~400 billion
    f1 = fraction of these stars that are single stars (as opposed to binary or tertiary stars):  ~0.5
    f2 = fraction of single stars that are like our sun (not too big or too small):  ~0.1
    f3 = fraction of sunlike stars that have planetary systems:  0.1 to 1.0
    n2 = number of Earthlike planets in each planetary system:  0.1 to 1 or more
    f4 = fraction of planets where life has arisen or will arise:  0.01 to 1.0
    f5 = fraction of planets where intelligence develops: 0.000001 to 0.01
    f6 = fraction of those planets with intelligent life that could communicate with us:  probably less than 1 ppm
Conclusion:  While there are perhaps millions or even billions of planets in our galaxy where life has developed, it is unlikely that we will have the opportunity to communicate with intelligent life on another planet due to the great distances and relatively short lifetime of technological societies compared to planet lifetimes.

Pseudoscience often masquerades as science, but is not grounded in empirical evidence. 
    Examples include: astrology, UFOs, creationism, ESP, fortune-telling, witches and ghosts, etc.