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##### Cosmic Acceleration

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**Cosmic Acceleration**• The evidence • What it could be • Why each options is interesting/confusing • Planning the next steps**The evidence**• - Supernovae • - CMB • - Clusters**The evidence**• - Supernovae • - CMB • - Clusters**Cosmic acceleration**Using supernovae (exploding stars) as cosmic “mileposts”, acceleration of the Universe has been detected. Supernova**Acceleration of the universe**The Hubble law at great distances depends on the variations of the Hubble “constant” H with time.**Cosmic acceleration**Accelerating matter is required to fit current data Preferred by data c. 2003 Amount of acclerating matter (“Dark energy”) “Ordinary” non accelerating matter Supernova Amount of gravitating matter**Cosmic acceleration**Accelerating matter is required to fit current data Kowalski, et al., Ap.J.. (2008) Preferred by data c. 2008 Amount of acclerating matter (“Dark energy”) “Ordinary” non accelerating matter BAO Supernova Amount of gravitating matter**Cosmic acceleration**Accelerating matter is required to fit current data Kowalski, et al., Ap.J.. (2008) Preferred by data c. 2008 Amount of acclerating matter (“Dark energy”) “Ordinary” non accelerating matter BAO Supernova Amount of gravitating matter (Includes dark matter)**The evidence**• - Supernovae • - CMB • - Clusters**The evidence**• - Supernovae • - CMB • - Clusters**The Edge of the Observable Universe:**As we look back in space we look back in time. We see: Light traveling from far away =from distant past Here & Now Long ago (about 14 Billion years) the Universe was so hot and dense it was opaque: The edge of the observable universe**Properties of the Edge of the Observable Universe:**Similar to surface of Sun at time of emission • Today: • Only 2.726K above absolute Zero • “Microwave Radiation” (The “Cosmic Microwave Background”: CMB) • 1,000,000 times weaker than ambient radiation in a pitch dark room. Here & Now**Observing the Microwave Background, Past, present and**future:**Time**The History of the Universe New Image of the “Last Scattering Surface” from NASA’s WMAP satellite released Feb 11 2003 High Energy & Temp**Note: we are really on the inside looking out**WMAP map of the “edge of the observable universe” plotted as a sphere**WMAP**• Characteristic oscillations in the CMB power Inflation Temperature Power “Active” models Adapted from Bennett et al Feb 11 ‘03 Angular scale I.1 Successes**The predicted “cmb power” curves are different for**different models of the universe. Only curves with specific parameter choices fit the data. http://space.mit.edu/home/tegmark/movies.html**Cosmic acceleration Using supernovae (exploding stars) as**cosmic “mileposts”, acceleration of the Universe has been detected. Preferred by modern data Amount of “antigravity” matter “Gravitating” non accelerating matter Supernova Amount of gravitating matter**The evidence**• - Supernovae • - CMB • - Clusters**The evidence**• - Supernovae • - CMB • - Clusters**Dark matter require to explain galaxy rotation curve data**“Cluster data” measures something similar**Cosmic acceleration (newest data)**Using supernovae (exploding stars) as cosmic “mileposts”, acceleration of the Universe has been detected. Preferred by modern data Amount of “antigravity” matter “Gravitating” non accelerating matter Supernova Amount of gravitating matter**Cosmic acceleration**Accelerating matter is required to fit current data Preferred by data c. 2003 Amount of w=-1 matter (“Dark energy”) “Ordinary” non accelerating matter Supernova Amount of “ordinary” gravitating matter**Cosmic acceleration**Accelerating matter is required to fit current data Kowalski, et al., Ap.J.. (2008) Preferred by data c. 2008 Amount of w=-1 matter (“Dark energy”) “Ordinary” non accelerating matter BAO Supernova Amount of “ordinary” gravitating matter**Cosmic acceleration**Accelerating matter is required to fit current data Kowalski, et al., Ap.J.. (2008) Preferred by data c. 2008 Amount of w=-1 matter (“Dark energy”) “Ordinary” non accelerating matter BAO Supernova Amount of “ordinary” gravitating matter (Includes dark matter)**Dark Energy and Inflation**Here for inflation Preferred by modern data Amount of “antigravity” matter “Gravitating” non accelerating matter Supernova Amount of gravitating matter • Accelerating “Dark Energy” is what makes U=1 (required to give consistency with inflation) • Acceleration or (required for inflation) is possible (+) • Dark Energy *very* poorly understood (-/+)**Dark Energy and the fate of the Universe**Preferred by modern data Amount of “antigravity” matter “Gravitating” non accelerating matter Supernova Amount of gravitating matter In the presence of dark energy, the simple connection between open/closed/flat and the future of the universe no longer holds**95% of the cosmic matter/energy is a mystery. It has never**been observed even in our best laboratories Ordinary Matter (observed in labs) 5% Dark Matter 25% Dark Energy (accelerating) 70%**95% of the cosmic matter/energy is a mystery. It has never**been observed even in our best laboratories Ordinary Matter (observed in labs) 5% Gravitating Dark Matter 25% Dark Energy (accelerating) 70%**Problems with cosmic acceleration**• Shouldn’t the pull of gravity slow down the expansion? • The challenge is much greater when one knows the “foundations” of particle physics. Extremely difficult to accommodate acceleration**Cosmic Acceleration**• The evidence • What it could be • Why each options is interesting/confusing • Planning the next steps**What could cause the acceleration?**1) A “cosmological constant” (see “special topic” on p698) 2) A new batch of “potential dominated matter”. Can think of the current era as “starting a new period of inflation”. 3) We must develop a new theory of gravity which can account for the data without needing acceleration (in the above, we assume Einstein’s General Relativity is correct). 4) Some other misinterpretation of data? (Getting less and less likely as more data comes in)**What could cause the acceleration?**1) A “cosmological constant” (see “special topic” on p698) 2) A new batch of “potential dominated matter”. Can think of the current era as “starting a new period of inflation”. 3) We must develop a new theory of gravity which can account for the data without needing acceleration (in the above, we assume Einstein’s General Relativity is correct). 4) Some other misinterpretation of data? (Getting less and less likely as more data comes in)**What could cause the acceleration?**1) A “cosmological constant” (see “special topic” on p698) 2) A new batch of “potential dominated matter”. Can think of the current era as “starting a new period of inflation”. 3) We must develop a new theory of gravity which can account for the data without needing acceleration (in the above, we assume Einstein’s General Relativity is correct). 4) Some other misinterpretation of data? (Getting less and less likely as more data comes in)**What could cause the acceleration?**1) A “cosmological constant” (see “special topic” on p698) 2) A new batch of “potential dominated matter”. Can think of the current era as “starting a new period of inflation”. 3) We must develop a new theory of gravity which can account for the data without needing acceleration (in the above, we assume Einstein’s General Relativity is correct). 4) Some other misinterpretation of data? (Getting less and less likely as more data comes in)**Cosmic Acceleration**• The evidence • What it could be • Why each options is interesting/confusing • Planning the next steps**Each of the above explanations has its problems:**• A “cosmological constant”: Requires a value 10-120 the • “natural value”. Hard to know how that could come about.**Each of the above explanations has its problems:**• A “cosmological constant”: Requires a value 10-120 the • “natural value”. Hard to know how that could come about. • A “horizon” forms around us as the acceleration continues. • We will never see any object cross the horizon (just a bit larger than the currently observed universe) • Perhaps the universe is truly finite?**Each of the above explanations has its problems:**• A “cosmological constant”: Requires a value 10-120 the • “natural value”. Hard to know how that could come about. Much like a black hole horizon • A “horizon” forms around us as the acceleration continues. • We will never see any object cross the horizon (just a bit larger than the currently observed universe) • Perhaps the universe is truly finite?**Each of the above explanations has its problems:**• A “cosmological constant”: Requires a value 10-120 the • “natural value”. Hard to know how that could come about. Much like a black hole horizon • A “horizon” forms around us as the acceleration continues. • We will never see any object cross the horizon (just a bit larger than the currently observed universe) • Perhaps the universe is truly finite? Long list of amazing implications!**Each of the above explanations has its problems:**2) A new batch of “potential dominated matter”. Requires a new elementary particle with mass10-33 times the electron mass. Tough to fit that into current theories.**Each of the above explanations has its problems:**3) We must develop a new theory of gravity which can account for the data without needing acceleration (in the above, we assume Einstein’s General Relativity is correct). Pretty much every attempt to do this has produced a problematic theory (i.e. mathematically inconsistent).**Each of the above explanations has its problems:**4) Some other misinterpretation of data? So far the most compelling suggestions have all been ruled out.**American Association for the Advancement of Science**…at the moment, the nature of dark energy is arguably the murkiest question in physics--and the one that, when answered, may shed the most light.**“Basically, people don’t have a clue as to how to solve**this problem.” - Jeff Harvey “Right now, not only for cosmology but for elementary particle theory, this is the bone in our throat.” - Steven Weinberg “… would be No. 1 on my list of things to figure out.” - Edward Witten ‘This is the biggest embarrassment in theoretical physics” - Michael Turner “… Maybe the most fundamentally mysterious thing in basic science.” - Frank Wilczek