Lecture 8 Flashcards
A finer-scale temperature scale for all-sky maps of the CMBR reveals
a dipole pattern
if you remove the dipole variation
time progresses, space missions accrue and image resolution improves
We can model the intrinsic CMBR variations using
spherical harmonics
We compute the angular power spectrum (formula)
Cl = <|a^2(lm)|>
predicted power spectrum that gives
best fit to observed data points
the shape of the predicted curve is very sensitive to ‘ingredients’ of cosmological model and values of the model parameters
prior to decoupling the universe consists of a
baryon-photon fluid
fluctuations in the CMBR imply that there were tiny differences in
gravitational potential at the epoch of recombination
gravity tries to collapse the
fluid and radiation pressure tries to expand it
the fluid sloshes around in the potential wells and sets up
acoustic oscillations in the fluid
acoustic oscillations implies a
pressure or sound wave
when decoupling occurs,
oscillations ceases and their pattern was frozen in to the CMBR pattern we observe today.
this generates a series of acoustic peaks corresponding to oscillations that were just at the right size to be at maximum compression or maximum rarefaction when the photons decouple.
the sound horizon
the physical scale of the oscillations is determined by how far sound waves could have travelled before decoupling
the particle horizon
is the limit of the region with which an observer can be in casual contact
its the proper size of the observable universe.
particle horizon (formula)
s(hor) = 2c/Ho Ω^(-1/2)(m0) (1+z(CMBR))^(-3/2)
sound horizon =
s(hor,s) = 0.25Mpc
