Welcome to Physics 107 Ideas of Modern Physics Physics for Future Presidents 1
What scares us? Radioactivity in the basement Being hit by lightning Terrorist dirty bomb Return of the Ice Age Global warming The energy crisis All out nuclear holocaust horrible world war Asteroid impact destroying Earth The LHC at CERN creating a black hole Ejection of Earth from solar system by Jupiter gravity A wandering star disrupting the solar system The Sun exploding into a Red Giant Brett Favre The Universe collapsing like a cold souffle 2
Did an asteroid impact kill the dinosaurs? Asteroid Itokawa, seen from probe: http://antwrp.gsfc.nasa.gov/apod/ap070422.html Visit APOD for great Astronomy Pictures of the Day! Barringer Crater, Arizona Artist rendition of Chicxulub impact site 3
Impact sites world wide http://rst.gsfc.nasa.gov/sect18/sect18_1.html#18-2 We see impact craters on the Moon and on other planets. This map of recognized impact sites reveals a history of visitors to Earth. Barringer Crater, Arizona 4
Close to home A Wisconsin impact site: Glover Bluff Wisconsin, U.S.A. N 43 58' W 89 32' 8 km radius < 500 million years http://www.unb.ca/passc/impactdatabase/images/ glover.htm So in a sense it can happen here! 5
Chicxulub Impact the culprit? Chicxulub impact in the Yucatan Peninsula is one of the largest short-term natural events known in the geologic record (of nuclearcomparative magnitude in excess of 100 trillion tons of TNT equivalent). It occurred 65 million years ago and led to a 200-300 km (>150 mi) wide and 16 km (10 mi) deep depression. It has been proposed that this event had a catastrophic influence on the biosphere, ending the age of the dinosaurs. 6
Sensing with gravity The Mexican na+onal petroleum company, Pemex, had discovered in the 1950s an unusual layer of broken while drilling the northern coast of Mexico's Yucatan Peninsula. A magne+c survey revealed later a large circular structure centered near the town of Chicxulub. The structure is confirmed with measurements of the variation of local gravity. Gravity is magical and universal. hgp://pubs.usgs.gov/fs/ fs- 0239-95/fs- 0239-95.pdf. hgp://science.jrank.org/pages/47689/ gravity- measurement- interpreta+on- anomalies.html Gravity anomaly map hgp://miac.uqac.ca/miac/chicxulub.htm 7
Videos: bombs and deep impacts Hiroshima http://www.youtube.com/watch?v=x9lwvimjqt0&nr=1 Deep Impact movie trailer: http:// www.youtube.com/watch?v=flgskv2p-ow Deep Impact (more) http://www.metacafe.com/watch/yt-1xliw_pct-y/ deep_impact_1998_meteor_hits_earth_16x9_hd/ This movie is maybe scarier! http://www.youtube.com/watch?v=oclnvh82-kk Browse orbits of near Earth objects: http://neo.jpl.nasa.gov/orbits/ 8
SO what IS out there? Christmas 2009 a smallish visitor missed Earth by 1 percent of the radius of the Earth s orbit. http://neo.jpl.nasa.gov/ca/ 9
Stuff found just within 60 days http://neo.jpl.nasa.gov/risk/ Observations have errors. It is not possible to immediately predict the motions so an impact probability is computed for each object. 10
What can one conclude? First thing to know in the number of objects as a function of object size. There are many small objects (meteorites) than large objects but these burn up in the atmosphere. For a given size, estimate the impact probability based on observation and assumptions. For example, 1 million objects each with an impact probability of 1 in 100 million per year leads to a mean expected rate of 0.01 per year or 1 every 100 years. For a given size, model the interaction with the Earth and the consequences. 11
When might we become extinct? http://rst.gsfc.nasa.gov Christmas visitor size is rather common and relatively harmless. Sigh of relief, but. 12
By the way It is not entirely clear that an impact killed the dinosaurs. Yet. Also, it seems unlikely our technology could avert a disaster. Something big enough to affect the Earth carries a lot of inertia and energy and requires deployment of something of similar scale. Simply effectively intercepting a post launch phase little ICBM is difficult! Food for thought. The Earth is 4.5 billion years old. There have been about 4500 one in a million year events already. 13
Science and policy How do we address fears of natural (and artificial) disaster? Keep our heads on. Study the problems and assess the risks. Be quantitative about consequences and probabilities. Follow up more data, more observations help solidify understanding. Then act to mitigate the consequences, if possible, when a real risk is identified. 14
Science and the citizen How do you address fears of natural (an artificial) disaster and other questions involving science? You can t always leave questions to experts for they could be working for the dark side (big media, big oil, big tobacco, big drug companies, big government, some other government ) or you simply might believe or not like their answers! (Think about the debates about climate change and energy sources.) Your generation has unprecedented access to information. Sift and winnow. Educate yourself and question authority. 15
The role of physics Physics is about fundamental natural laws that govern such things as space, time, and the motion and interaction of objects. Physics is also about the nature of matter (elementary particles, atomic nuclei, atoms, molecules, solids, liquids, gases, planets, stars, galaxies) and immaterial energy in the universe (light, gravitational waves, and other traveling force fields. The goal of physical science is to understand everything. Everything physical that is. We are pretty close, and yet so far 16
Physics for Future Presidents Let s learn just a little about physics and what it teaches in the context of contemporary issues. Along the way, we will meet some magical things and demystify some things. In its full glory, physics is a best expressed in the language of mathematics. We will not use much math, only enough to get a sense of the quantitative nature of questions and answers. 17
Logistics See course website at www.physics.wisc.edu for details. M,W Lecture: one chapter per week, attendance required A weekly paper (one page, two references) is required on your choice of discussion or internet research topics from text or alternate topic approved by the TA. Due in electronic drop box at LEARN@UW Thursday 8 AM. F work session: attendance required 1) work multiple choice questions in text and hand in bubble sheet answers 2) presentations of best two student papers of the week M,T Discussion: attendance required review of concepts and formula, presentation and discussion of preassigned discussion topics (graded) 18