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PHYS 180 Fall 2021

Final Essay

I would like you to pick a topic you are interested in and which builds on the materials presented in the class, and write an essay about this article. Here are some suggested topics:

1. The Three Dark Matter Problems

Reading: L. Krauss, The Fifth Essence

Reading: J. Silk, The Big Bang

Goal: Describe the observational and theoretical evidence for dark matter in the Universe. What are the three dark matter problems? How solid does the evidence for dark matter appear to you? What could the dark matter be and how could one look for it?

2. Dark Energy

Reading: M. Turner, Dark Energy and the New Cosmology, arXiv:astro- ph/0108103.

Reading: R. Kirshner, The Extravagant Universe (Princeton Univ. Press, Princeton, 2002).

Goal: Why do cosmologists now believe that about 70% of the energy of the universe is in a mysterious component called ”dark energy”? What are the key characteristics of dark energy? What is the key diﬀerence between dark energy and dark matter?

3. Nucleosynthesis

Reading: S. Weinberg, The First Three Minutes (Basic Books, New York, 1993).

Goal: Describe how the light elements which constitute the baryonic matter in the Universe are formed. Why are no heavy elements formed in the early Universe? Where do heavy elements originate? Why is nucleosynthesis a strong observational pillar of big bang cosmology? What can we infer about the density of baryonic matter in the Universe?

4. Black Hole Evaporation

Reading: S. Hawking, A Brief History of Time (Bantam Books, 1998).

Goal: Discuss in a bit more detail than was covered in class why black holes can evaporate when quantum eﬀects are taken into account.

5. The Arrow of Time

Reading: P. Davies book, Chapter 3.

Goal: The equations of Physics do not distinguish between moving forwards iin time and moving backwards. Why do we perceive the two as diﬀerent?

6. String Theory and the Fabric of Space-Time

Reading: B. Greene, The Elegant Universe

Goal: Address the question of what String Theory says about the structure of space-time on the smallest scales? How is it diﬀerent from our view coming from General Relativity?

7. History of the Development of Quantum Mechanics

Reading: T. Hey and P. Walters, “The Quantum Universe”

Goal: Describe how key experiments led to an overturn of our classical picture of matter, replacing it with the quantum paradigm.

You could pick an article from a recent issue of Nature or Scientiﬁc Amer- ican which looks interesting to you Nature is a high impact journal in which physicists and astronomers like to publish their latest discoveries at a level which is not too technical. You should be able to access Nature via your McGill VPN.

In science, the art is always to be able to present results concisely. Hence, there is a page limit on the essay. The essays will be graded on the basis of content and structure. A good essay should tell a story: you start with an introduction in which you motivate the work which you report on, you end with the conclusions of the work, and in between you present the key points which let the authors reach their conclusions.

* Page limit: 8 pages.

* Level: what you would feel comfortable presenting in class. Thus, assume that the reader knows everything that was covered in class. Your job is to present the results of the article at a level which builds on what was presented in class.

* Due date: Sunday, Dec. 19 2021.