Isotropic Universe-3

Isotropic Universe These lab activities have evolved over years of use in Clemson University’s Department of Physics and Astronomy general astronomy laboratory. Contributors include Tom Collins, Mark Leising, Neil Miller, Peter Milne, Grant Williams, Donna Mullenax, Jessica Crist, Keith Davis, Amber Porter, Lea Marcotulli, and David Connick. Please direct all questions, complaints, and corrections to David Connick (dconnic@clemson.edu) who is responsible for all errors and omissions. Introduction In this lab you will explore the notion of an isotropic universe through the scientific method. This lab is different from previous lab activities as instead of completing a worksheet during the lab meeting you will be collecting data outside of the lab time and will turn in a written report. This lab report is worth 15% of your total grade in this lab course. Recall that one important principle for scientists to make progress in Astronomy is the Cosmological Principle. One way to state the cosmological principle is that the physical laws and the properties of the universe are the same everywhere and in all directions. Two properties of the universe that would result from the cosmological principle is that the universe is homogeneous and isotropic. A homogeneous universe is one that has the same composition and properties in all locations while an isotropic universe will appear the same in all directions. It is easier for us to test the isotropic nature of the universe from our location on earth and that is exactly what you will do in this lab. The Scientific Method This is the process by which we develop explanations of the natural world and test them. Generally, the process includes: 1) A problem or question to be addressed 2) A hypothesis (or “educated guess” as to what is happening, usually based on some theory, and consistent with previous measurements or experiments) 3) An experiment or observation to test a prediction of the hypothesis 4) An analysis of the experimental data collected 5) A conclusion, either that the data supports your hypothesis or the data does not support your hypothesis. What changes to the hypothesis or the experimental process need to be made for future experiments? For the purposes of this lab you will be given instructions for the various parts of the scientific method. You will need to outline your process in detail for your report. Your report should have the following sections that address the steps of the scientific method. Contact the instructor if you have any questions about what the final report should look like. Introduction 1-2) Your question is whether or not the universe is isotropic. Before you begin making any scientific observations you should form your own hypothesis about the universe being isotropic.

Try to develop your hypothesis based on your current knowledge and casual observations without the use of tools. It is not important if this experiment supports or does not support your hypothesis but it is important that you clearly state your hypothesis before beginning. Your hypothesis should include a numerical consideration of what it means to look the same in multiple directions. Seeing the exact same thing in every direction is an unreasonable expectation, what do you consider to be reasonably ‘the same’ and why? Procedure 3) You will perform 3 short experiments to collect data and test your hypothesis. An outline of each experiment will be given and you must fill out the details and outline them in your report. a) The first set of data will come from naked eye observations using a tube to limit your field of view. i) You can use a toilet paper tube, paper towel tube, a rolled up piece of paper in a tube shape or another tube of your choice. You will need to calculate the field of view of your tube using the instructions in the “Field of view” document. ii) Once you have your tube you should make 3 observations of the sky in different directions. You will need to know what direction you are looking so it is recommended you use a star viewing app to find a target star to look towards with each observation. Count the number of stars you see within the field of view of your tube for each observation. b) The second set of data will come from the Starry Night program. i) Set the field of view (FOV) in Starry Night to the same field of view that your tube had. ii) Using your target star or another method look in the same directions you did with the naked eye observations. iii) Record the number of stars within the field of view in the Starry Night program for each viewing direction. c) The final set of data will come from the Hubble Deep Field images. i) We cannot choose where the Hubble telescope took deep field images but we do have two deep field images taken in different directions in the sky. ii) Analyze the images in the “Hubble Deep Fields” file while thinking about what they tell you about the isotropic nature of the universe. iii) Collect data about these images by counting objects in parts of the images or intelligently estimating the total number of objects in each image. iv) Remember to compare these images you will need to collect data in the same field of view for each image. Data and Analysis 4) You will need to analyze the 3 sets of data you collected during the observation part of the lab. a) Your data should be nicely organized in clearly labeled tables with all relevant sources included. b) You should make a thorough analysis of your data. i) Does each set of data show the same trends or do they disagree?