Cosmic Background Northern Illinois University宇宙背景北伊利诺斯大学.pptVIP

WMAP WMAP The Wilkinson Microwave Anisotropy Probe was designed to measure the CMB. Launched in 2001 Ended 2010 Microwave antenna includes five frequency bands. 22 to 90 GHz High angular and frequency resolution L2 Orbit WMAP uses the stable L2 point in the sun-earth system. About 4 times lunar orbit Always faces away from the sun Complete sweep every 6 months WMAP orbits L2 in an elliptical orbit. Onboard propulsion to correct orbit Anisotropy Spatial anisotropy is very small. 0.0002 K fluctuations Absolute temperature measurement includes statistical and systematic error. Coherent errors are the same for all points. Remove error by measuring differences not absolutes Precision Instrument WMAP combines precise frequency and spatial resolution. 20 uK statistical 5 uK systematics 0.3° spatial pixel Back-to-back telescopes provide differential measurements. 140° separation Differential Signal Processing Shape of Space Space can be flat or curved. 3D not just 2D The Riemann curvature parameter determines the direction and extent of curvature. Positive curvature closed Negative curvature open Collapsing Universe Matter contributes to gravitation. Pulls the universe together The orange line represents a universe dominated by high density matter. Few billion years old Eventual collapse Critical Density At critical density the matter is sufficient for a flat universe. Asymptotically reaches maximum size Green curve At lower density gravity cannot stop expansion. Expansion slows but continues Blue curve Dark Energy Dark energy represents energy tied in space itself. This energy drives expansion. Effectively opposes gravity Fraction sets the rate The red curve has a large fraction of the matter as dark energy. Initial Appearance The initial appearance of matter is called the Big Bang. Not really an explosion High density matter and energy Since space is expanding there is no central point. Cooling radiation become the cosmic microwave background. One Second