Transcript The Big Bang Theory:

The Big Bang Theory:
Origin & Evolution of the Universe
Newton’s Static Universe
• Universe is static and composed of an infinite
number of stars that are scattered randomly
throughout an infinite space.
• Universe is infinitely old and will exist forever
without any major changes.
• Time and Space are steady and independent
of one another and any objects in existence
within them.
Newton’s Error
If universe is as how Newton describes,
then why is the sky dark at night?
Olber’s Paradox
• If space goes on forever with stars
scattered randomly throughout, then in
any line of sight in any direction will
eventually run into a star.
• Using this logic, the sky should be the
average brightness of all of these stars;
the sky should be as bright as the sun,
even at night.
But isn’t the sky dark at night…?
Yes, of course - that is what we observe
now and have always observed.
Something is wrong with Newton’s idea of
a static, infinite universe.
Einstein’s Relativity
• Einstein overturned part of Newton’s
theory with his theories of special and
general relativity - time and space were
indeed related, as were the objects
existing within them.
Special Relativity
Time and Space and their rates are
intertwined and depend on the motion of
the observer (1905).
General Relativity
Gravity bends the fabric of space time - the
matter that occupies the universe
influences the overall shape of space
and the rate of time (1916).
Implications of Einstein’s Ideas
• Based on the general relativity
equations, the structure of universe is
either always expanding, always
contracting, or always static.
• To agree with the ideas of the time
(Newton’s), Einstein added a
“cosmological constant” which yielded a
static universe.
Cosmological Constant
• Represents the pressure that allows the
universe’s expansion to directly balance
gravitational collapse due to the objects
existing within the universe, thus yielding a
static universe.
• Without this idea of a “cosmological constant”,
Einstein could’ve been the first to predict that
the universe is not static.
Hubble’s Discovery
• Edwin Hubble’s
observations of remote
galaxies, and the redshift
of their spectral lines
(1924).
• Hubble noticed that the
further away the galaxy,
the greater the redshift of
its spectral lines.
• This linear relationship is
called Hubble’s Law.
http://rst.gsfc.nasa.gov/Sect20/A9.html
Redshift
• The wavelengths of
the light emitted by
distant objects is
elongated as it travels
to earth.
• Longer the light
travels, the more it
gets redshifted.
http://rst.gsfc.nasa.gov/Sect20/A9.html
Hubble’s Law
v = H0d
v = recessional velocity of the galaxy
H0 = Hubble constant
D = distance of galaxy to earth
Galaxies are getting farther apart as time
progresses, therefore the universe is
expanding.
Hubble’s Constant
• Expansion rate measured using Type 1A
Supernovae.
• The age of the universe can be derived
from Hubble’s constant:
• T0 = d T0 = 1
H0d
H0
For example, if H0 = 73 km/s*Mpc, then
T0 = 13.4 Billion years old
Age of Universe
• Currently, after taking into account
differences in expansion rate over time
and our movement through space:
T0 ~ 13.78 ± 0.2 byo
• Age of stars: ~13.4 byo ± 6%
Therefore, oldest stars are younger than
the age of universe.
How the Universe Expands
The space between
galaxies expands, not the
galaxies themselves;
objects held together by
their own gravity are always
contained within a patch of
nonexpanding space.
Example: raisins in a loaf
of bread.
– As the dough rises, the overall loaf
of bread expands; the space
between raisins increases but the
raisins themselves do not expand.
Center of Universe?
• There is NO CENTER to the universe
– Expansion looks the same regardless of
where you are in the universe.
– Every point appears to be the center of the
expansion, therefore no point is the center.
– The universe is infinite.
Evidence for Expansion
• The light from remote galaxies and other
objects is redshifted.
• This redshift is called cosmological
redshift because it is caused by the
expansion of the universe, not by the
actual movement of the object (doppler
redshift).
Observable Universe
• Olber’s Paradox is solved: due
to the finite speed of light, the
observable universe does not
include the entire universe.
• Radius of the observable
universe depends on the age
of the universe and the speed
of light: ~47 billion lightyears.
• Result: Sky is dark at night
with points of light (stars,
galaxies, etc.) scattered
throughout.
Origins of the Big Bang Theory
• Georges Lemaître (1927) expanded on idea of
expanding universe, realizing that the universe was
smaller yesterday than today, and so on until a “day
that would not have had a yesterday”: the moment
of creation.
– The moment of creation would be the sudden expansion
that started the expansion of the universe as we know it
today.
• This idea wasn’t widely accepted at first: Fred Hoyle
dismissed “this hot Big Bang”, noting that there
wasn’t any record or remnants. He argued for a
“steady state” universe.
Evidence for the Big Bang Theory
• Gamow’s theory was revisted in the
1960’s by Bob Dicke and Jim Peebles of
Princeton University.
– Believed that this cooled radiation would be
redshifted to the microwave region of the
electromagnetic spectrum.
– Made a receiver to detect this radiation, but
were unsuccessful.
Evidence for the Big Bang Theory
• The radiation, so far undetected by
the Princeton team, was posing a
problem for NJ Bell Telephone
Labs, where Arno Penzias and
Robert Wilson were developing a
new microwave-satellite
technology for phone calls.
– Puzzled by steady hiss that they
received no matter where in the
sky they pointed their antenna.
– This faint background noise they
were trying to get rid of was
exactly what the Princeton team
was trying to detect: evidence of
the Big Bang.
http://nobelprize.org/educational/physics/star_stories/overview/index.html
CMB Radiation
• Detection of this radiation, called Cosmic
Microwave Background radiation, won
Penzias and Wilson the Nobel Prize for
Physics in 1978.
• CMB radiation can be detected by your
tv as well - 1% of static seen on a
channel that your tv doesn’t receive is
from the birth of the universe.
CMB Radiation
• Intensity of CMB Radiation reveals origins of universe.
– However, difficult to detect intensity from Earth- the
atmosphere is opaque to wavelengths 10 m to 1 cm
(CMB ~ 1 mm).
• COBE (Cosmic Background Explorer) 1989: detector
outside the atmosphere:
– Measured the blackbody spectrum of CMB radiation to
be at T = 2.725 K - consistent with theory.
– CMB radiation almost entirely isotropic; CMB is slightly
warmer in direction of Leo and slightly cooler in
direction of Aquarius.
• WMAP (Wilkinson Microwave Anisotropy Probe) (2002)
improved picture of CMB Radiation.
CMB Radiation
• Radiation appears to be mostly
smooth, but there are slight
variations in temperature that
show that matter had started to
clump in the early universe clumps of matter formed the
galaxies and stars see today.
• Sound waves in early universe
are recorded in this radiation; by
studying the characteristics of
these sound waves, we can find
out about the conditions of the
early universe.
http://www.pas.rochester.edu/~afrank/A105/LectureXVI/LectureXVI.html
Horizon Problem
• Despite all of the success with the Big Bang Theory so far, the horizon
problem was still yet to be solved.
–The temperature of the CMB radiation was the
~same no matter where you look in the sky,
indicating that some how information linking all
parts of the sky was traveling faster than the
speed of light.
–Also, information from one side of the sky at
100,000 years old (horizon is 100,000 light years
in diameter) differed from the other side of the sky
by 10 million light years - 100 times the diameter
of the horizon.
How is this possible?
Inflation Theory
• Alan Guth (1970s) had a solution:
– The universe must have expanded
exponentially very early for a short period of
time.
– This would account for the clumping of
matter.
Evidence for Inflation Theory
• Guth predicted that the average density
of the universe should be equal to the
critical density (6 protons/m3)
– This was confirmed by powerful telescopes.
• Evidence from WMAP shows that the
clumping of matter is consistent with the
amount of accelerated expansion during
inflation.
Extent of Inflation
Today, evidence and theory show that:
• At T = 10-35 sec, universe d = 10-24 cm
• Between T = 10-35 sec and T = 10-32 sec,
the universe expanded exponentially by
a factor of 1050..
• For the briefest moment, the universe
expanded faster than the speed of light.