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T H E E X PA N D I N G U N I V E R S E
A S S E E N W I T H T H E V E R A C . R U B I N O B S E R VAT O RY
T H E E X PA N D I N G U N I V E R S E A S S E E N W I T H T H - - PowerPoint PPT Presentation
T H E E X PA N D I N G U N I V E R S E A S S E E N W I T H T H - - PowerPoint PPT Presentation
T H E E X PA N D I N G U N I V E R S E A S S E E N W I T H T H E V E R A C . R U B I N O B S E R VAT O RY Keith Bechtol University of Wisconsin-Madison Apparent Recession Speed Distance The first Hubble Diagram (1929) Apparent
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Distance Apparent Recession Speed
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The first Hubble Diagram (1929) Distance Apparent Recession Speed
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Distance Apparent Recession Speed
Expansion rate today ~ 70 km s-1 Mpc-1 (modern measured value)
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Two contributions to an apparent wavelength shift
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Relativistic Doppler Effect
Two contributions to an apparent wavelength shift
Tells us relative velocity between emitter and observer
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Relativistic Doppler Effect Cosmological Redshift Tells us relative velocity between emitter and observer Tells us relative size of Universe when light was emitted
Two contributions to an apparent wavelength shift
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Relativistic Doppler Effect Cosmological Redshift Tells us relative velocity between emitter and observer Tells us relative size of Universe when light was emitted
Two contributions to an apparent wavelength shift
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Before
Image credit: DES
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Before After supernova
Image credit: DES
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Before After
Type Ia supernovae are explosions of known intrinsic luminosity
(1) Observed flux → distance → light travel time from when supernova exploded (2) Redshift → size of Universe when supernova exploded supernova ~1036 Watt
Image credit: DES
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Distance Apparent Recession Speed
Expansion rate today ~ 70 km s-1 Mpc-1
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Distance Apparent Recession Speed (Age of Universe) (Size of Universe)
Expansion rate today ~ 70 km s-1 Mpc-1
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Distance Apparent Recession Speed (Age of Universe) (Size of Universe)
Expansion rate today ~ 70 km s-1 Mpc-1
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Distance Apparent Recession Speed (Age of Universe) (Size of Universe)
Slope tells us the matter-energy density of the Universe
(current value is equivalent to ~6 protons per cubic meter) Expansion rate today ~ 70 km s-1 Mpc-1
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Distance Apparent Recession Speed (Age of Universe) (Size of Universe)
The inverse of the slope tells us the approximate age of the Universe
(~14 billions years) Expansion rate today ~ 70 km s-1 Mpc-1
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Distance Apparent Recession Speed (Age of Universe) (Size of Universe)
The inverse of the slope tells us the approximate age of the Universe
(~14 billions years)
T H E R AT E O F E X PA N S I O N H A S C H A N G E D T H R O U G H O U T C O S M I C H I S T O RY
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Expansion Rate
CMB (age ~ 380,000 yr) Now (age ~ 13.8 Gyr) z = 1 (age ~ 6 Gyr)
Size of Universe
Image adapted from David Kirkby
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M a t t e r
- d
- m
i n a t e d Dark Energy! Expansion Rate
CMB (age ~ 380,000 yr) Now (age ~ 13.8 Gyr) z = 1 (age ~ 6 Gyr)
R a d i a t i
- n
- d
- m
i n a t e d
Expansion rate controlled by matter-energy components
Size of Universe
Image adapted from David Kirkby
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(Dark) Matter Radiation Dark Energy
𝝇 ~ a-4 w = +1/3 𝝇 ~ a-3 w = 0
𝝇 ~ const. w = -1
Now (age ~ 13.8 Gyr) z = 1 (age ~ 6 Gyr) CMB (age ~ 380,000 yr)
Size of Universe Energy Density
Image adapted from David Kirkby
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(Dark) Matter Radiation Dark Energy
𝝇 ~ a-4 w = +1/3 𝝇 ~ a-3 w = 0
𝝇 ~ const. w = -1
Now (age ~ 13.8 Gyr) z = 1 (age ~ 6 Gyr) CMB (age ~ 380,000 yr) Dark energy density equivalent to ~4 protons per cubic meter
Size of Universe Energy Density
Image adapted from David Kirkby
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All Matter Radiation Dark Energy Atoms
Now (age ~ 13.8 Gyr) z = 1 (age ~ 6 Gyr) CMB (age ~ 380,000 yr)
Size of Universe Fraction of Total Energy Density
Image adapted from David Kirkby
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All observations from the present day to ~1 second after the Big Bang can be explained by a “simple” cosmological model…
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However, this model has five distinct lines of evidence for new physics:
Dark Matter Dark Energy Massive neutrinos Inflation Matter-antimatter asymmetry
All observations from the present day to ~1 second after the Big Bang can be explained by a “simple” cosmological model…
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Type Ia supernova occur roughly once per century in a large galaxy like the Milky Way…
Image credit: HSC
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Type Ia supernova occur roughly once per century in a large galaxy like the Milky Way… Legacy Survey of Space and Time (LSST) will monitor >10 billion galaxies over 10 years, yielding a sample of ~1 million type Ia supernovae across billions of years of cosmic time
Image credit: HSC
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What is the Universe expanding into? It’s more appropriate to think of cosmic expansion in terms of the typical physical separation between galaxies increasing, and the density of matter decreasing Are we at the center of the Universe? No more than anyone else; there are no preferred positions (homogenous) or directions (isotropic) Can galaxies recede faster than the speed of light? Yes, Special Relativity does not apply to apparent recession speed due to cosmic expansion Can we see galaxies receding faster than speed of light? Yes, because the expansion rate has changed over time How large is the observable Universe? Because space is expanding, the observable part of our Universe has a radius of more than 14 billion light years Is the Earth / Solar System / Milky Way expanding? No, gravitationally bound objects remain in equilibrium How will the Universe end? Cold, dark, and lonely, according to the current cosmological model
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References
“Misconceptions About the Big Bang” Charles H. Lineweaver & Tamara M. Davis, Scientific American, 2005 Scientifically curious audiences “Introduction to Cosmology” Barbara Ryden Undergraduate level textbook “Modern Cosmology” Scott Dodelson Graduate level textbook