Appearance of the Universe Flashcards
(26 cards)
What Evidence supports a homogeneous isotropic universe?
1 – The Hubble-Lemaître law
2 – The cosmic microwave background radiation
3 – Primordial nucleosynthesis
4 – The age of the Universe
5 – Galaxy number counts
How does the Hubble-Lemaître law support a homogeneous isotropic universe?
The Hubble-Lemaître law has been verified over a large range of scales, and its
accuracy supports homogeneous isotropic cosmologies
How does the cosmic microwave background radiation support a homogeneous isotropic universe?
The Cosmic Microwave Background Radiation (CMBR) is isotropic to a very high
accuracy, and it has a very large energy density (∼ 1 eV cm−3
)
How does the age of the Universe support a homogeneous isotropic universe?
All measurements give consistent values for the age of the universe of 13.7×109 y, supporting models of a homogeneous and isotropic universe
How does Primordial nucleosynthesis support a homogeneous isotropic universe?
By adjusting only the baryon density ρb (∼ 10−28 kg m−3
), given the standard
(Friedman-Lemaître) model for expansion, one obtains an accurate prediction for the
abundances of several light elements (H, He, Li, Be) and their isotopes which is in
agreement with their observed values
When galaxy distribution is separated by redshift layer, what is the most isotropic redshift range?
z>0.06
When galaxy distribution is separated by redshift layer, what is the least isotropic redshift range?
z<0.01
What does a panoramic view of the entire near-infrared sky reveal?
The distribution
of galaxies beyond the Milky Way
What is galaxy number counts?
A statistical technique used to study the evolutionary history of the Universe. It involves counting the number of galaxies above a threshold flux density in a given area of the sky.
What are our initial assumptions when calculating galaxy number counts?
We assume a non-expanding universe
with no curvature and homogeneous, isotropic distribution of matter
What is the luminosity distribution function?
The number of sources per unit volume per luminosity interval
Why do we use the luminosity distribution function?
not all galaxies have the same luminosity
When does our simple calculation of galaxy number counts apply?
to uniformly distributed sources in a non-expanding
flat universe
What does our simple calculation of galaxy number counts not account for?
cosmological redshift and galaxy evolution
When does our simple calculation of galaxy number counts not agree with observations?
large magnitudes (faint objects)
Why might our simple calculation of galaxy number counts not agree with observations at large m?
- evolutionary effects in galaxies
- relativistic phenomenon
What equation do we use to look at the differential number counts of galaxies?
Robertson-Walker metric
What kind of universe does the e Robertson-Walker metric describe?
homogeneous, isotropic, non-flat, expanding universe
Why can we expect n(t) proportional to 1/(a cubed) for a matter dominated universe?
The Cosmological Principle
tells us to assume that sources are uniformly distributed in space-time
How can we deal with the limiting detectable flux from the Differential number counts of galaxies?
use the luminosity distance which objects we may still observe out at r0
Why can Differential number counts of galaxies not be used to determine which cosmological model
the Universe adheres to?
it is extremely difficult to deconvolve the effects of evolution on luminosity from the effects of cosmological expansion
What question did Olbers pose?
why is the sky dark at night?
What is Olbers Paradox?
if the Universe is infinite in extent and
eternal, with stars roughly uniformly distributed throughout space, then every line of sight will intercept a star, so
that the whole night sky should be as bright as the surface of a star
What is the resolution of Olber’s paradox?
- Stars have finite lifetimes and can’t fill their portion of space with light forever.
- The speed of light is finite, so only stars within a finite distance can be observed.
- Above all, the Universe almost certainly has a finite age.
