Download General Theory of Relativity

Rachel Thackeray
Max Weiss PHYS 1040 MWF 10:00-10:50
Group Presentation Paper
General Theory of Relativity
The general theory of relativity was established by Albert Einstein in 1916. This theory
generalizes (imagine that it is the general theory and it generalizes something) the special theory
of relativity. Newton’s law of universal gravitation is also used in explaining Einstein’s theory.
General relativity also introduced physical cosmology (also known as the principle of
covariance), stating that the physical laws apply the same regardless of where you are in the
Universe. This theory explained Newton’s mystery of where gravity came from.
General relativity describes gravity to be caused by massive objects affecting the spacetime by curving it. This part of Einstein’s theory was confirmed in 1919 during an eclipse. The
curve shown in the pictures of the eclipse matched Einstein’s theory; this started the proof which
still continues to come today. The photographs showed gravitational lensing, “The bending of
light by gravity. Can be used to detect extrasolar planets,” (Understanding Our Universe). During
this total solar eclipse, light from the sun bent around the moon. This shows that gravity does
indeed bend space-time. We are currently using gravitational lensing to discover dark matter
galaxies and especially to try to find Earth-like planets around stars similar to our Sun in located
in the habitable zone. We have not found extraterrestrial life yet, but due to Einstein’s
explanation of gravitational lensing we are coming closer to it.
Einstein added the cosmological constant to general relativity in 1917. Einstein, as many
other scientists, wanted the Universe to be static. It was what could be seen at this time and, this
would have allowed for an easier explanation. However, easy doesn’t always work. The
Universe was found to be continuously expanding by Hubble in 1929 and Einstein withdrew the
constant claiming it as his, “Biggest Blunder”.
Many people today still think that Einstein’s theory of general relativity will falter. This
may be true, but it hasn’t occurred yet. We are constantly putting it to the test as we discover
more and more massive objects. Extremely massive objects are believed to be the key to finding
a loophole in Einstein’s theory. Despite these beliefs general relativity has recently been put to
the test and prevailed. A quickly spinning newton star (a pulsar) was found, the most massive yet
with 2.04 times more mass than our Sun. This pulsar is creating gravitational waves, just like
Einstein’s theory said it would.
While I do not understand much about Einstein’s theory of general relativity, and I
probably couldn’t tell you much about it if you asked I know a couple visual examples which
have helped me understand a tiny bit more. One of these examples requires use of a trampoline.
If you and a ball occupy a trampoline together, both of you will create a curve in the trampoline.
Your curvature will be larger because your mass is larger than that of the ball’s. This is
comparative to general relativity because it shows how more massive objects create more of a
change in the space-time continuum.
Another example I use to understand general relativity uses airplanes. I’ve heard
countless times that if you follow a straight line that will be the fastest route. However this
principle does not work for airplanes flying long distances. This principle does work for foottravel because we do not cover enough ground to truly walk on a curve. Geodesics show how
airplanes follow the curvature of the Earth. If you were to fly in a “flat” line you would crash
into the Earth’s surface. To get to your destination you are flying in a straight line, but the line is
not flat, but it is curved.
Works Cited
http://en.wikipedia.org/wiki/General_relativity
http://www.dummies.com/how-to/content/einsteins-general-relativity-theory-gravity-as-geo.html
http://astro.berkeley.edu/~jcohn/lens.html
Understanding Our Universe
http://www.princeton.edu/~achaney/tmve/wiki100k/docs/Physical_cosmology.html
http://www.wired.com/thisdayintech/2009/05/dayintech_0529/
http://cosmology.carnegiescience.edu/timeline/1917
http://www.newscientist.com/article/mg21428664.000-pulsar-heavyweight-champ-challengeseinstein.html#.UpWzSsSUTgN
http://wordpress.mrreid.org/2010/09/09/geodesics/