Introduction. The activity. Part 1 predictions and outcomes. Part 2 a dialogue concerning the origin of the Universe. And so to the Big Bang.

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1 Teacher Notes Introduction And so to the Big Bang. The activity Part 1 predictions and outcomes This introduces Big Bang theory by looking at some of its predictions. The first one was a failed prediction, but the flaw was found to be in the assumptions made in using the data, rather than in the theory. The predicted microwave background radiation and its anisotropy are major successes for the theory. Part 2 a dialogue concerning the origin of the Universe Developed from the original SPU item. This activity requires the students to consider the basic ideas of the Big Bang hypothesis in a novel form that links back to Galileo s dialogues. It can be used as a review activity once the ideas have been discussed or as a starting point for independent work. The dialogue has questions at some key points, for students to provide additional explanation. Appendix A has some guidance for teachers on these points. There are a number of ways in which the dialogue can be used: as a script for three members of the group to read/perform to the rest of the group as a script read in small groups as a passage for individual reading Once the script is read, individual students can use the textbook and other suggested resources to answer the questions posed. This is best performed as an individual activity although students could discuss each other s responses after a suitable period of individual work. This involves more than copying out tired arguments as the students are required to put the arguments in words the character might speak. Some students will enjoy acting out the whole dialogue, including their responses. Some may be interested that Galileo and Shakespeare were born in the same year. Resources How Science Works Textbooks. Sheets of paper (or similar) for summaries. Screen and means of projection of summaries. Student briefing sheets. Comments on the application of HSW ideas in this activity. It is worth noting that there are some scientists who continue to explore the notion that the totality of existence did not begin with the Big Bang speculation about the possibility a multiverse continues, illustrating that robust debate is at the heart of science that dissenting voices are challenged sometimes to the point of mockery, but in the end not always ignored. For those who find the Big Bang inadequate as a complete source of explanation the motivations may be very human aesthetic, religious, or perhaps anti-religious. They may be deep and emotional motivations, rather than objective. Such motivations may be entirely valid if they lead to questioning. A cautious note is that while Big Bang theory has survived some cycles of prediction and test, and is the preferred theory about the Universe, it remains an emerging theory and more observational evidence will be needed before everybody can accept the Big Bang as the end of the story (or as the absolute beginning). Page 1 The Nuffield Foundation, 2008

2 Teacher Notes Appendix A outline answers to questions in the Dialogue These notes are deliberately brief. Longer explanations may be expected from students. 1. The students are expected to give an explanation of red shift. Salviati might try to help out his friends by using an analogy with sound. Note that large red shifts are not due to galaxies moving through space but, rather, due to space itself expanding and taking the galaxies with it. 2. The further galaxies show bigger redshifts and hence are receding more quickly. This can be represented by a rubber band a sort of one-dimensional version of the expanding balloon. Take a nice thick rubber band. Write the letter A on the unstretched band. Write the letter B two centimetres away from A. Write the letter C two centimetres away from B. Now stretch the band. C will move away from A at twice the speed that B does. 3. Answers should provide descriptions of the cosmic microwave background and its discovery. 4. This is an interesting one. Penzias and Wilson s discovery was certainly objective in the sense that they were not out to relating to a particular theory. This does appear to give the Big Bang hypothesis more credibility but if evidence is objective it doesn t matter whether the researcher is seeking to test a theory or not. 5. There are three possible fates of the Universe. It can expand forever at a decreasing rate, it can collapse in on itself or it can stop expanding and freeze at a certain size. The ultimate fate depends on the amount of mass in the Universe. July 2008 Page 2 The Nuffield Foundation, 2008

3 Introduction Did the Universe have a beginning, or has it always existed? It s a question that brings science and religions together. It s a question that has motivated scientists for a long time. The scientific approach is to suggest some ideas that may or may not turn out to be any good. The ideas are tested by using them to make predictions, and then by seeing how the predictions turn out. Many ideas fail. Some survive. Activity Part 1 Predictions and outcomes If the Universe had a beginning then matter and space and time also all have a beginning and that is what we call the Big Bang. The ideas of no matter, no space and no time are pretty incomprehensible but then, they never existed because there was no such thing as before the Big Bang. The idea fits neatly with the observation that the Universe is expanding it may be expanding from its original state of no space. If the Universe had no beginning then expansion is harder to explain but that doesn t mean that it is impossible to explain. In the past, some scientists proposed a theory of this, called the Steady State theory. It has not been as successful as Big Bang theory at making predictions, and most scientists prefer the Big Bang idea. These are some predictions made by Big Bang theory at different times: Prediction The Universe is 3.4 billion years old Outcome Radiation that originated in the very early stages of the expansion of the Universe still exists and should be detectable. It corresponds to radiation that would be emitted by a cold body with a temperature of about 5 K (- 268 C). Hint: Cepheid variables see textbook Hint: Penzias and Wilson see textbook Page 1 The Nuffield Foundation, 2008

4 We see a Universe full of lumpy bits, like galaxies and people and chocolate pudding, separated by a lot of relative emptiness. The strength of the radiation should be different in different directions in the sky. If it was perfectly smooth then it couldn t have led to the unsmooth Universe that we can see. Hint: COBE (and WMAP) see internet Describe the outcomes of the predictions as fully as possible in the spaces provided. Page 2 The Nuffield Foundation, 2008

5 Part 2 A dialogue concerning the nature of the Universe Introduction In the year 1632 Galileo published his Dialogue on the Two Chief World Systems. Galileo presented the competing models of the Solar System through the words of two speakers. Simplicio defended the geocentric (Earth-centred) view of Ptolemy whereas Sagredo supported the Copernican model. A third character, Salviati, represented an intelligent man trying to decide between the two theories. Here we have a possible dialogue between a modern day Simplicio and Salviati about a more recent theory. Activity Taking one of the parts, read the Dialogue Concerning the Origin of the Universe (below), in a small group or as a class performance. Add explanations, as if you were Salviati, at the numbered points (1 to 5) in the Dialogue. Use the textbook or other sources to help you. Dialogue Concerning the Origin of the Universe Scene: Inside a pub. Simplicio and Salviati are sitting at a table beside a window. Rain is spotting against the window from a grey November sky. The two friends have met for lunch. They have known each other for years. Simplicio is a solicitor, Salviati an engineer. Simplicio is complaining that his wife made him watch a television programme about the Big Bang rather than the film he was looking forward to. They are expecting Sally, Simplicio s wife, to join them later. Simplicio: Just because Sally s brother is one of you lot, some sort of techy -nerd, she made me watch some absolute nonsense about the Universe. Salviati: And the programme was nonsense because.....? Simplicio: Because there was no sense in it. I should write a letter of complaint. Salviati: Complaining about what, exactly? Simplicio: Complaining about the rubbish that s shown on the television. Obviously. Salviati: But you haven t told me what this rubbish is. Simplicio: Right then. As it happens I have a good memory for detail, it goes with my job. This is what I remember. What are you doing? Salviati: Getting out a notebook. I haven t got a good memory for detail so if I m going to try to convince you about these ideas I need to take notes. Simplicio: You don t get out very much do you? Salviati: Come on, this will be fun. Simplicio: That ll be fun spelt d..u..l..l I suppose. Page 3 The Nuffield Foundation, 2008

6 Salviati: Come on, I ve only got another two hours off. Simplicio: Excellent. Two more hours wasted on this nonsense. So, as far as I remember the programme, this is the theory, according to Professor No Mates or whatever he was called. One day there was nothing. Nothing but empty space. And then all of a sudden Bang there was this explosion and the Universe started sort of filling up. Salviati: You ve got that wrong. There was no space before the Big Bang. Time, matter and space were all created together. Simplicio: So that makes it better does it? Seems even more dodgy now. Anyway this thing happened about fourteen million years ago. Salviati: Fourteen billion years ago. Simplicio: Same thing. Salviati: It s lucky you re not an accountant. Simplicio: Billions or millions. Doesn t really matter, does it? Its not going to change my mortgage. Anyway, the whole thing started with a huge sort of explosion. But it was just energy. Very hot. And then it kept expanding and getting cooler. After about years atoms started forming, is that right? Salviati: Yes, go on. Simplicio: Well, that s about it. Professor what s-his-name seemed less interested in the next bit. He said gravity got in on the act and atoms clumped together to form stars. These clumped together to form galaxies and groups of galaxies. And that s it. Next step formation of the Solar System, evolution of life on Earth culminating in the near perfect specimen of humanity you see before you. And mobile phones. Salviati: You don t understand evolution but that s another issue. Did the programme not say anything about Supernovae and why near perfect specimens such as yourself have heavy elements in them? Simplicio: He prattled on about us all being stardust but by that time I d assumed he was bonkers anyway. Salviati: OK. So what exactly don t you accept? Simplicio: I don t think I accept any of it. Not only does it all sound nonsense, I can t see the point of it. (Looking up as his wife, Sally enters) Hi Sally, you re just in time to hear me having a moan about the state of the Universe. I m explaining why I hated that programme last night. Sally: I thought it was quite good, but I didn t understand too much. Simplicio: Well, our friend will explain all. Salviati: Yes, but what are your problems? Simplicio: First. Its impossible. You can t just create matter out of nothing. Salviati: Oh yes you can. Simplicio: But there s no proof. We don t see galaxies flying away from each other. Salviati: Well actually we do... 1 Page 4 The Nuffield Foundation, 2008

7 Sally: Well perhaps we can observe this red-shift, but does this show that more distant galaxies are moving away from us more quickly than nearer galaxies. Simplicio: Hang on, why should further galaxies be moving more quickly? Salviati: Let me try to answer both questions... 2 Sally: OK, so more distant galaxies are moving away more quickly, but this doesn t mean that there was a Big Bang where s the evidence for that? Simplicio: I know isn t that something about microwave ovens? Salviati: No. Not microwave ovens. Microwaves. Simplicio: Same thing. We ve got a microwave in our kitchen. Sally: No we haven t, we ve got a microwave oven. They produce microwaves. Simplicio: Who cares. So is there any evidence for a Big Bang? Salviati: Yes. Listen.. 3 Sally: I don t understand why you think its so important that Penzias and Wilson made this discovery without knowing what it was. Salviati: Well, it gave independent support to the theory. You can t argue that Penzias and Wilson were trying to prove anything. Simplicio: Would it have mattered if they were trying to prove anything? Salviati: Reasonable point surprising from you. This is what I think.. 4 Sally: So what s going to happen now? Simplicio: I m going to get another drink. Sally: No, I mean, what s the future for the universe. Salviati: Well, there s a question... 5 Sally: Thanks. I feel sort of clearer know. Simplicio: Thanks. I d feel depressed if I thought it mattered. Page 5 The Nuffield Foundation, 2008