Set 23 Jan 2008.
Due date Wednesday 13 Feb 2008 at 11 am.
You should know that the speed of light, c = 300,000 km/sec
The equation for Hubble's constant, H0, is v = d × H0, where d is the distance and v is the speed.
Make sure your units are consistent and make sense.
Show your work, you will not get credit for simply writing down an answer.
- Consider a galaxy observed to be receding away from us at 18,000 km/sec.
If H0 = 72/km/sec/Mpc, what is the approximate distance to this galaxy?
If H0 were equal to 50 km/sec/Mpc instead, what then would the distance to the galaxy be?
If H0 were equal to 1000 km/sec/Mpc instead, what then would the distance to the galaxy be?
- Consider a galaxy observed to have a recession velocity of 84,000 km/sec.
An independent method of measuring distance finds that this galaxy is 900 Mpc away.
Based only on that measurement, what would you infer the Hubble constant to be?
Now assume that new information has shown that the original distance measurement was in error and that the actual distance is 1,200 Mpc. What now is the estimated value of the Hubble constant?
What would the distance have to be to that galaxy for it to be consistent with a Hubble constant equal to 50 km/sec/Mpc?
- Consider a galaxy measured to a have a redshift, z=0.15
What is the approximate recession velocity of the galaxy?
If the Hubble constant is 72 km/sec/Mpc, how far away is this galaxy?
If further measurements show that local gravitational attraction has caused this galaxy to have an anomalous local velocity of 3000 km/sec towards us, what then is the "real" recession velocity of the galaxy and estimated distance?
- Go to the Cosmology Lab website at Case Westerm
Launch the Applet and pick 5 sets of cosmological parameters.
One of them should be the canonical set: H0 = 72, Omega Matter = 0.3 and Omega Lambda = 0.7, the other four sets can be whatever different non-zero values you choose.
For your five choices, plot the Age, Loockback and Size parameters and print them out.
Comment.
Tell me the current age of the universe for your different choice of parameters.
- Read the short story Loom of Thessaly by David Brin.
In your own words, summarise the plot and conclusion.
Briefly discuss your personal impression of the story and what it tells you.
- Bonus question (2 pts): BOINC runs number of open computing projects.
In particular SETI at home and Einstein at home - the former searches radio data for narrow band extraterrestrial emission, consistent with alien technological civilizations, the latter searches the LIGO gravitational radiation detector database for anomalous events. Both tasks are computing intensive and easily distributed.
For extra credit, sign up for one or the other project, download the code and run it - state your account ID and runtime/units processed for credit.
Last updated 01/08
Back to the top of my home page.