Cosmology Flashcards
What is the Doppler principle for radial velocities?
The apparent change in wavelength of a source due to it’s radial velocity with respect to the observer.
What is red shift?
When light from distant galaxies is shifted to longer wavelengths.
What do the letters and symbols mean in the Doppler equation?
λ = observed wavelength λ0 = stationary wavelength v = radial velocity of object c = speed of wave (speed of light)
Why is blueshift possible for galaxies in the local group?
As they may be attracted to us therefore they are moving towards us rather than away from us (e.g. Andromeda)
What does Hubble’s Law state?
Except for a few nearby galaxies, the recession velocity of a galaxy is proportional to it’s distance from us.
How can astronomers use the value of the Hubble constant to determine the age of the universe and what is assumed?
-v = Hd
-v/d = H
-d/v = 1/H
-t = 1/H = age of the universe.
Assumption - universe is expanding at a constant rate
What is CMB?
Cosmic Microwave Background Radiation - microwave signals seen everywhere in the Universe. Significant as may be proof for the Big Bang - gamma photons from the bang red shifted and seen today as CMB radiation.
How was CMB discovered?
Bell telecommunication engineers detected a uniform ‘noise’ i all direction.
What is the main observational evidence that the universe is expanding?
Red shift (galaxies moving away from us.
What is dark matter?
‘Missing mass’ around galaxies which prevents them from collapsing in on themselves.
What is dark energy?
In early Universe, the rate of expansion was less, meaning something must be increasing it - Dark Energy - open universe.
What are the main arguments in favour of the Big Bang?
- CMB
- Relative abundance of elements
What are other theories for the beginning of the Universe?
Steady State theory - Universe has been expanding forever
Why are cosmologists unable to agree on one model?
As there is evidence for all and we can never be sure - not enough evidence.
What are the two different theories for the future of the Universe?
Open Universe - will expand forever
Closed Universe - gravity will stop expansion and will collapse in on itself- big crunch
