Cosmology Flashcards
(11 cards)
What do observations of galaxies outside the local group show
That light is shifted to longer wavelengths (redshift). This is caused by galaxies receding from us
Redshift formula
¥(observed) -¥0/¥0(emitted)= v/c where v is the radial velocity of the source and c is the speed of light..
Essentially, percentage change in wavelength, or percentage redshift, is equal to the percentage radial velocity of the speed of light. 20% redshift means a galaxy is receding at 20% light speed.
What evidence confirms the expanding universe
Redshift means that distant galaxies are moving away from us, implying the universe is expanding.
What is Hubble’s Law
V(radial velocity of recession) = Ho(Hubble constant)d(distance from Earth). Essentially V and D are directly proportional with the Hubble Constant as the constant. This is also the gradient of a v-d graph.The currently accepted value is 68 km per second per Megaparsec.
For every Megaparsec away from Earth, radial velocity increases by 68km/s
How can the Hubble Constant be used to estimate the age and size of the universe?
As age =(roughly) 1/H0, we can invert this value to get Hubble time - 4.6x10 to the 17 seconds. 14 billion years - the age of the universe.
If we multiply this by the speed of light ( as distance = speed x time’, we get Hubble Length, the distance travelled by light in Hubble Time, I.e. the size of the Universe
How do we convert the Hubble constant to Hubble time
The Hubble constant is 68 km/s/Mpc, which has two units of distance in. If we convert km to Mpc then we arrive at a small value with the unit “per second”. We do this by writing it as (70km/s)/ 1Mpc. This can be rewritten as (70/number of km in an Mpc)second to the -1. We then invert this to find Hubble time, and use it to find Hubble length
Basically number of km in a an Mpc over 70
How does the expansion of the Universe support both the Big Bang theory and the Steady State theory?
Because both depict a model of an expanding universe, which we have proved through the redshift of distant galaxies, showing they are moving away from us.
What is the major evidence in favour of the Big Bang theory?
Quasars - only found with high redshifts, implying they are very far from us, and existed in the early universe, supporting the evolutionary nature of the Big Bang theory
Cosmic Microwave Background(CMB) - the faint microwave radiation found in all parts of space. It implies a very hot and dense universe at the start, supporting the Big Bang theory.
The Hubble Deep Field image - Shows thousands of old galaxies, with the eldest looking smaller, dimmer and more irregular. This implies the evolution of the universe, and contradicts the steady state theory in which the universe is always the same
What is the significance in the fluctuations in the CMB detected by the Wilkinson Microwave Astronomy Probe and the Planck mission?
The CMB is not the same everywhere, we can detect small temperature changes which can tell us things.
1. These fluctuations match predictions with the Big Bang models.
2. They show that the Universe is slightly older than previously thought
3. The universe is 25% dark matter
What is the significance and possible nature of dark matter and dark energy?
Dark matter does not emit or absorb light, so we can’t see it. We detect it because of its gravitational effects on galaxies. It is significant because it holds galaxies together, and makes up 25% of the universes mass-energy. It could be made of unknown particles not yet detected
Dark Energy is the mysterious force driving the expansion of the universe, a kind of anti-gravity.
It is significant because it explains why the universes expansion is speeding up. It makes up 68% of the universes mass-energy. It could be a property of space itself!
Therefore in total dark energy and dark matter account for nearly 95% of the universe.
What are the current models for the future evolutionary paths of the universe
- The rate of expansion decreases until the universe remains a constant size.
- The rate of expansion decreases until the universe collapses in a ‘Big Crunch’
- The rate of expansion remains constant - a ‘coasting universe’
- The rate of expansion will constantly increase due to dark energy
