The Origin & Age of our Universe

1. The Origin & Age of our Universe By Christos N. Hadjichristidis

2. How old is our Universe? • We can roughly tell that our planet is about 4 1/2 billion years old by radiometric dating of rocks. (QUIZ: the oldest earthly rock so far found is 3.8 billion years old, could you explain why one can be sure that the Earth is older?) • But how on Earth can we determine how old is our Universe?

3. Looking at distant objects in the Universe means looking at the PAST • We get an idea about how old objects are in the Universe when we see their light. The speed of light is constant, and distance is a measure of time. So the furthest we look in the Universe the deepest we look at its past. When we see a distant star explosion that occurs billions of light years away, we know that that star exploded billions of years ago.

4. Determining Universe age by looking for old stars in globular clusters • A globular cluster is a dense collection of close to a million stars, all of which formed at roughly the same time so they can serve as cosmic clocks • The fate of every star depends solely on its initial mass. So what should we look for (Corpses of massive or light stars)? • The brightest of white dwarfs is no more luminous than a 100 watt light bulb seen at the moon's distance – so their detection is very hard • Result: The oldest white dwarf observed is about 13 billions years old but big uncertainties due both to the difficulty of accurately determining distances and our incomplete knowledge of stellar evolution. http://imgsrc.hubblesite.org/hu/db/2002/10/videos/b/formats/low_mpeg.mpg

5. A method based upon the idea of an expanding Universe (but we need to learn some tools in order to firstly accept the idea ….. ) • Something you have observed:http://faraday.physics.utoronto.ca/PVB/Harrison/Flash/ClassMechanics/Doppler/DopplerEffect.html • Understanding the Doppler Effect http://www.fearofphysics.com/Sound/dopwhy2.html • Seeing the star light:

6. …..Tools Continued….. • Objects moving away from us emit light that is "redshifted," meaning its wavelengths are shifted from higher energy to lower energy http://www.wwnorton.com/earth/egeo/flash/1_2.swf • Determining large distances: The Cepheid stars yardstick http://imgsrc.hubblesite.org/hu/db/1999/19/videos/c/formats/low_quicktime.mov

7. Hubble’s Discovery

8. …Hubble’s discovery continued • “The red shift of galaxies increases roughly in proportion to the distance from us” • In other words, the more distant the galaxy, the faster it is moving away, and most importantly this is true no matter where exactly in the Universe you are! Thus, despite long-lived beliefs (Aristotelian/Ptolemaic theory) there is nothing special about our place in the Universe. http://observe.phy.sfasu.edu/courses/ast105/lectures105/chapter01/raisin_cake.htm

9. The Big Bang • But, if the galaxies are rushing apart, then they must once have been closer together • http://www.schoolscience.co.uk/flash/bang.htm • http://map.gsfc.nasa.gov/m_or/mr_media2.html Ok, but how does that sound like?

10. Determining the Bing Bang time by using Hubble’s law

11. "Let there be light"; • The early Universe was so hot and dense that atoms were dissociated into their nuclei and electrons. The light was scattered by the free electrons and was not allowed to escape. As universe expanded and cooled, nuclei and electrons combined to form the first atoms and THERE WAS LIGHT.

12. The first Light • Imagine the Universe as a loaf of rising raisin bread, in which the nearly formed galaxies are the raisins. The region in space that ultimately became home to the Milky Way galaxy is moving away from all the other regions... or all the other raisins in the bread. Now imagine that first light that was released simultaneously everywhere in the Universe. Light released within our own region has long since passed us. Light released in regions very far from us, however, is just reaching us now. http://www.gsfc.nasa.gov/gsfc/spacesci/pictures/2003/0206mapresults/COBE-MAP_HDfast.mov

13. Using the CMB to determine the Age of our Universe ? • Distance-Age: The light travels (in vacuum) with a constant velocity of . Thus, when we observe (collect visible light from) a distant object we see it as it was seconds ago. • Redshift-Distance Ruler: Visible light appears reddish . The most distant the object the largest the redshift. But, there is no exact relationship between redshift-distance (current research). Thus, once we have a firm redshift ruler, we can see the CMB ( the first light to escape after the Big Bang) as a redshift. The redshift yields the distance. And the distance (since we know the speed of light) yields the age

14. The Fate of the Universe The fate of the Universe depends on its contents (i.e. how much matter and energy there is: • If there is a lot of matter, then gravity will dominate, slowly reign over the expansion and pulling all matter together back to one point. Some call this the Big Crunch. • If there is not so much matter but rather dark energy -- the force that acts like anti-gravity -- then the Universe will continue to expand until every single speck of matter is pulled infinitely apart from each other. • A more pleasant notion is the situation where the Universe has just the right amount of matter and dark energy to keep it from flying apart or crashing in. http://www.astro.ubc.ca/~scharein/a311/Sim/bang/BigBang.html

15. In Conclusion • Our Universe has probably originated from a Big Bang as supported by both Hubble’s and Cosmic Microwave Radiation Background (first light to break free after the Big Bang) discoveries • We found that the age of our Universe is about 12-13 billion years by: • Looking for the oldest stars, and • Measuring the rate of the expansion of the Universe and extrapolating back to the Big Bang And because a (Greek Orthodox) priest blesses his own beard first, as the saying goes, there is no escape from watching this …..

16. Carlos Frenk's Model Universes Frenk’s work is being supported by The Ogden Trust

17. Indicative Reading List • Books • Hawking, S.W. A Brief History of Time (Bantam Press, Great Britain 1997) • Weinberg, S. The First Three Minutes (Basic Books, New York,1993) • Filkin, D. Stephen Hawking’s Universe (BBC Books, London 1997) • Barrow, J.D. The Origin Of The Universe (Clays Ltd, St Ives plc, London 1994) …and links to the educational resources included in this presentation