Transcript The Big Bang Theory - Physics@PennState!

The
Big Bang Theory
Elizabeth Walsh
A Static Universe
• In the early 1900s, the accepted view held was
that the universe was static, which never
changes; it has always been the same and always
will
• Albert Einstein was one of the largest supporters
of this belief
• When the idea of an expanding universe was
proposed, Einstein spoke out: “This circumstance
irritates me. To admit such possibilities seems
senseless.”
Hubble’s Discoveries
• However, not everyone was convinced that the
universe was never changing
• In 1929, astronomer Edwin Hubble, at the Mt.
Wilson Observatory in California, found that the
velocity of a star appeared to be proportional to
its distance from the Earth
– The further the star from the Earth, the faster it
appeared to move away from the Earth
– This concluded that the universe is expanding and the
galaxies are moving away at high speeds
Einstein’s Mistake
• Looking to gain a greater understanding of the
universe, Einstein turned to his theory of
general relativity- the current description of
gravitation in physics
– His surprising discovery found that the universe
would have to be expanding and contracting
• Hubble’s findings, paired with Einstein’s
theory supported the idea of an expanding
universe
Georges Lemaitre
• Georges Lemaitre was a Belgian Cosmologist and
Catholic priest
• Used Einstein’s laws of gravitation as a basis to
claim that the universe must be expanding
• He published a solution to equations of general
relativity in 1927 in regards to the expanding
universe
• Stated that the expanding universe was not static
– but without evidence he had little support
• His model soon became known as the “Big Bang
Theory”
The Big Bang Theory
• Combination of two approaches to the
universe: astronomical and cosmological
• Describes the development of the universe
prior to its current existence
• All matter and space in the universe was
originally compressed into a tiny dot, called
the singularity, which expanded and all the
matter instantly filled what is now our
universe
Evidence for the Big Bang
• Lemaitre used Hubble’s findings to support his
theory
– If the galaxies are currently moving forward, at
one point they must have been all together
– Once there was a primordial atom that contained
all the matter in the universe
• Lemaitre also used the concept of entropy everything is moving towards greater disorder
– to support his theory
Following the Discovery
• Much debate followed his theory - some
supported the idea while others chose to take
on a “steady state” theory
– The universe is constantly expanding, but the
average density remains constant
• Debate ended when Arno Penzias and Robert
Wilson found evidence for cosmic background
radiation – residue of the big bang
• The expansion of the universe is now viewed
as one of the greatest scientific discoveries
Impact of the Big Bang Theory
• The Big Bang Theory sparked discussion and
encouraged further studied into the universe
• This theory is used as a way to estimate the
age of the universe (within a large range)
• It also lead to questions relating to the
universe expansion – Will it expand forever?
What happened before the big bang?
“Never in all the history of science has there
been a period when new theories and
hypotheses arose, flourished, and were
abandoned in so quick succession as in the last
fifteen or twenty years.”
– Willem de Sitter, 1931
References
• Big Bang Theory is Introduced. (n.d.). PBS. Retrieved February 26, 2014,
from http://www.pbs.org/wgbh/aso/databank/entries/dp27bi.html
• Georges Lemaitre, Father of the Big Bang. (n.d.). Georges Lemaitre, Father
of the Big Bang. Retrieved February 26, 2014, from
http://www.amnh.org/education/resources/rfl/web/essaybooks/cosmic/p
_lemaitre.html
• Strickland, J. (2008, June 18). How the Big Bang Theory Works.
HowStuffWorks. Retrieved February 25, 2014, from
http://science.howstuffworks.com/dictionary/astronomy-terms/big-bangtheory.htm
• The Expanding Universe (Cosmology: Ideas). (n.d.). The Expanding
Universe (Cosmology: Ideas). Retrieved February 26, 2014, from
http://www.aip.org/history/cosmology/ideas/expanding.htm