Lecture 7 Flashcards
what did vesto slipher do and when
measured redshifts of other galaxies (and velocities)
Andromeda in 1913
25 more in 1917
how did slipher measure redshifts
spent weeks measuring individual galaxy spectra, identified patterns of lines in them from known elements, finding redshifts
what did Edwin Hubble and Georges lemaitre do?
combined Hubbles measurements of galaxy distances with silphers measurements of galaxy velocities
found more distant galaxies travelled faster
how did the Hubble parameter measurements change over time since 1929
they became more accurate over time
in recent times value of the parameter has not changed much but the scatter and uncertainty has
what does Hubbles law imply
the universe is expanding
are galaxies moving?
no, the space between them is expanding
since the universe is NOT expanding into anything, what is actually happening
space is internally getting larger, this stretches light on its path, the expansion is uniform there is no centre
how does gravity effect expansion/vice versa
expansion is a gravitational effect
galaxies stars and planets do not get larger
anything that is gravitationally bound together stays together (clusters and galaxies)
what are peculiar velocities
components of velocities that deviate from hubble flow
on average what is happening to galaxies due to expansion
moving apart but some can move towards each other (andromeda and the Milky Way)
what does the Hubble space telescope do
measures cepheids out to 25 Mpc using 800 cepheids, this is 5 times further than previous measurements
why is their a conflicting measurement of H0
measured h0 to be 72 via the Hubble space telescope, 68 from earlt universe such as CMB , it is either 68 or 72 so there is a tension
what is tired light
an alternative proposed to the universe expanding - suggested that light gradually lost energy as it travelled
explain the specifics of tired light
lower energy light meant redder photons which could explain Hubbles law, could happen if light interacts with other light very slightly
why is tired light wrong
would have been detectable within our galaxy and In distant radio and optical source behaviour
what are the two possibilities for the past if the universe is expanding
matter was all denser - big bang
matter has been gradually created during expansion - steady state model
who created steady state model
fred Hoyle, Hermann bondi, thomas gold
explain the steady state model
theory adding a new source called c-field to relativity that gradually generated new matter
generated at 1 atom per cubic meter every 100k years so not detectable
einstein explored similar but didn’t publish
perfect cosmological principle - universe would look the same at any point in space or time
why was the steady state theory ruled out
despite being fully realised and mathematical cosmological model, based on relativity with a small tweak. it was ruled out with observations
what happened after steady state was ruled out
creators kept working on it, updated model had periods and regions of expansion and contraction
not taken seriously
over view of the Big Bang
early matter was denser and hotter, near uniform with no structures
it occurred everywhere in space at once
it is a process/era not a point
what is the CMB
a microwave signal that is uniform across the sky
if interpreted as a black body then temperature about 3 kelvin
had to work carefully to remove other known signals
exactly as big bang predicted
why are most gasses transparent
photons are scattered by the free electrons
how do you get plasma and what is it
hot gas, free elections and protons, scatters photons so it is opaque
