Download Cosmology

Cosmology
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Past, present and future of the universe
Is space flat or curved?
Where is the center?
What lies beyond our limit of vision?
What is the universe expanding into?
Did the physical laws exist prior to the Big
Bang?
• How old is the universe?
Globular Clusters
• Globular clusters are the oldest stellar
objects observed that can be accurately
dated
• Age of the globular clusters sets the
minimum age for the universe
• The universe is older than these clusters
Where did the big bang occur?
• Everywhere
• It was an explosion of all space and time,
NOT an explosion in space
• Since a singularity exploded and expanded,
and the center of the singularity coincides
with the singularity, the whole universe is
just an enormous center
Space itself is expanding
Cannot really know
• Since we cannot see or find the edge of the
center, we cannot determine the centroid
(center of mass) of the center
• How does one find the center of this room?
• Look at the boundary walls and estimate the
center
• What if one could not see the walls?
Other examples of disorientation
• Inside a tall cornfield
• In a whiteout blizzard
Cosmological redshift
• A wave of EM radiation, as it moves
through the universe, will experience the
same expansion as the universe
• As the wave travels farther and farther, it
expands more and more
• By the time it is observed, it appears
redshifted in proportion to the distance it
has travelled
Background radiation
• The background radiation consists of X-ray and
gamma-ray radiation that arose just after the big
bang
• The wavelength of these shortwave radiations
redshifted (expanded) as the universe expanded
– The cosmological redshift
• The earliest of radiations has redshifted into the
microwave portion of the universe
• The microwave background radiation is the
light from the oldest object in the universe –
the universe itself
Cosmological Constant
• A factor used for adjusting how the universe
expands
• Einstein’s thought it was his biggest blunder
– He introduced the cosmological constant to
make the universe stand still (static universe)
• Distant supernovae now suggest the value is
not zero (like Einstein said!)
• Distant supernovae now suggest that the
universe is accelerating
– Indicate motions that are slower than expected
• We do not know what causes it
Dark matter, dark energy
• Nearly 96% of the universe is invisible
(does not glow like a star or galaxy)
• There may be enough dark matter to
produce the critical density and halt the
expansion of the universe
• Some say that the total of luminous and
dark matter is at the critical density
• The density of the universe determines if it
will expand forever or stop expanding and
collapse back on itself
• Not to worry – we won’t know for billions
of years
• Value of the critical density of the universe
depends on the Hubble constant
• Critical density lies between the collapsing
and expanding forever extremes
Hubble constant
• Somewhere between 50 and 75
• We appear to be at the center of the Hubble
flow
• Observers on all other galaxies also appear
to be at the center of the Hubble flow
• All galaxies appear to be moving away from
us
• Raisin cake analogy
Cosmological principle
• 2 assumptions
• Homogeneity and isotropy
• Homogeneity – one part of the universe is
pretty much like any other part
• Isotropy – looks the same in all directions
• Therefore no edge and no center to the
universe
Olber’s paradox
• Universe is homogeneous and isotropic
• If it is infinite in extent and unchanging in
time, then the universe is uniformly
populated with galaxies filled with stars
• Thus, one’s gaze should fall upon a star
wherever one looked in the night sky and
the night sky should be as bright as a star
However
• The universe is NOT infinite and it is
expanding
• The expansion redshifts the starlight to
longer wavelengths than the visible so
distant stars cannot be seen by our eyes
Cosmological Redshift
End