1 THE ACCELERATING UNIVERSE A.Rahman Mohtasebzadeh (9/21/2012)
2 Content Cosmology through ages Necessary Concepts Nobel Prize in Physics (2011) Conclusion
3 Twinkle twinkle little star, how I wonder where you are.. Figure 1
Twinkle twinkle little star, how I wonder where you are.. Egyptian (~1534 BC) 4 Greek (~300 BC) Indian (~200 BC) Chinese (~180 BC) SN185 (Chinese calendar) Persian/Islamic (11 century) (Persian calendar) European (16 century)
5 Redshift Doppler Effect and Redshift Doppler effect causes the wave to be stretched Figure 2
6 Redshift Doppler Effect and Redshift Doppler effect causes the wave to be stretched Figure 3
7 Redshift Doppler Effect and Redshift Doppler effect causes the wave to be stretched Observed wavelength Emitted wavelength In 1916 Vesto Slipher Measured velocities to nearby galaxies, and discovered they were all moving away from us. He studied the spectra of light that is coming from the galaxies. And observed that their lights are stretched.
8 Standard Candle Figure 4
9 Standard Candle Stellar brightness is quantified using visual magnitude scale Hipparchus ranked stars from 1 to 6: 1 being the brightest in the sky, 6 the dimmest (with unaided eye) Now we quantify magnitude: " d % m = M + 5 log$ ' # 10 pc & where m is apparent magnitude, d is distance, and M is the absolute magnitude--the brightness of the object from a distance of 10 parsecs (pc)
10 Standard Candle In 1929, Hubble used brightest stars to measure the distance to the nearest galaxies He assumed that the brightest stars are all the same brightness The faster the galaxy was moving, the fainter the stars!
11 Standard Candle The most distant objects are speeding away from us The error of factor 10! Because he didn t have well measuring equipment Figure 5
12 Standard Candle Figure 6
13 The expanding Universe NOW time (t 1 ) FUTURE time (t 2 ) Figure 7
The expanding Universe 14
15 Einstein s Theory of General Relativity 1905 published equations of general relativity Gravity and acceleration are equivalent Curvature of Space Dynamic Universe (cosmological constant) Figure 8
16 Einstein s Theory of General Relativity Left-Hand Side = Right-Hand Side Curvature = Energy-Momentum G µν + Λg µν = 8πGT µν The Cosmological Constant What can contribute to Energy-Momentum?????? "the greatest blunder of my life" If we weight the universe we can understand it s shape!!
17 Einstein s Theory of General Relativity Figure 9 By measuring all these masses we can measure how much stuff are in the universe
18 Einstein s Theory of General Relativity In the first case, there is enough mass to slow down and stop the present expansion. The universe is not infinite, but has no boundaries (you can picture it as a sphere, you cannot call any point on the surface of the sphere an end). Eventually, the universe will collapse producing what we call Big Crunch. (closed) In the second case, there is not enough mass to stop the expansion. The universe will expand forever and has no boundaries. (open) In the third case, there is exactly enough mass to stop the expansion, after an infinite amount of time. In other words, the universe will expand forever and has no boundaries. (flat) Figure 11
19 Einstein s Theory of General Relativity Ω total amount of stuff in the universe Ω m = matter density Ω Λ = dark energy density Figure 10
20 Three possible cases for the universe If Ω m >1, Ω Λ =0 means the universe is dominant by mass, such a universe decelerates. If 0<Ω m <1, Ω Λ >0 means the universe is dominant by unknown stuff ( dark energy ) and accelerates If Ω m =1, Ω Λ =0 means universe is moving with a constant speed and it s flat.
21 Nobel Prize-Physics 2011 The Supernova Cosmology Project (SCP) was initiated in 1988 by Saul Perlmutter of Lawrence Berkeley National Laboratory (LBNL), USA. Another team leaded by Brian Schmidt of the Mount Stromlo Observatory in Australia and Adam Reiss from University of John Hopkins in Maryland, USA. Saul Perlmutter Brian Schmidt Adam Reiss
22 Supernovae Extremely luminous fireworks in the universe. Happen few once or twice per century in a galaxy, when a star runs out of fuel. Supernova Type Ia In a binary system when when one star feeds the dwarf star with it s fuel, until dwarf star reaches critical mass (1.4 Mass of the sun) or Chandrasekhar limit. For Type Ia supernova, M 19.3 Figure 12
23 Hunting Supernovae Type Ia Figure 13
24 Observation Results Figure 14
25 Observation Results Figure 15
26 Conclusion The study of distant supernovae constitutes a crucial contribution to cosmology. This will lead us to further understanding of our strange universe and will help us answer many cosmological related questions A good foundation for further understanding dark energy and dark matter
27 Resources http://www.physicsoftheuniverse.com/ topics_bigbang_accelerating.html http://atramateria.com/the-shape-of-the-universe/ http://www.spaceandmotion.com/cosmology-historyastronomy-universe-space.htm http://www.youtube.com/watch? feature=endscreen&nr=1&v=qmawnji-sxo http://www.nobelprize.org/nobel_prizes/physics/laureates/ 2011/perlmutter-lecture.html
Thank you! 28