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![Page 1: The measurement of q 0 If objects are observed at large distances of known brightness (standard candles), we can measure the amount of deceleration since.](https://reader036.fdocuments.in/reader036/viewer/2022062722/56649f315503460f94c4bffa/html5/thumbnails/1.jpg)
The measurement of q0
• If objects are observed at large distances of known brightness (standard candles), we can measure the amount of deceleration since this governs the size of the universe
• At z=0.5 (d=6000 Mpc), difference in observed brightness of a “standard candle” between a flat matter-filled universe and an empty matter-filled universe is 25% - universe will be larger if it is empty and thus the objects will be further away and fainter.
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• Best standard candle is Type Ia supernova• Observed scatter in their intrinsic brightness is 15% and
thus if we could measure their brightness at z=0.5, we could measure q0
• Two research groups obtained large amounts of telescope time to do this and they detected 42 Type Ia SNe up to z=0.8.
• Their results published in 1998 showed that the distant SNe are 25% dimmer than nearby SNe.
• This means that over the 8 billion years that the light has been travelling towards us, the change in the rate of expansion of the the universe must have increased not decreased.
• The universe is accelerating!
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The only way to explain these results is to introduce the cosmological constant
Best model fit to the changing apparent brightness mB with redshift z gives (for k=0)(matter)=0.25+/-0.09 at the current epoch; and thus =0.75.
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The CMB
An image of the Universe at 380,000 years old
(Cosmic Microwave Background)
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Universe is hotElectrons are freeLight scatters off electrons
Universe is coolere- and p+ form hydrogenLight travels freely
The History of the Universe
Until ~380,000 years after BB
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Why Microwave?
• Universe was ~ 3000° K at 380,000 yr
• Full of visible light (~1μm)
Universe is expanding
• Causes light to change wavelength
• Visible light becomes microwaves (~1cm)
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The History of CMB observations
1965
1992
2003
Discovery
COBE
WMAP Gra
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COBE RESULTS
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COBE angular resolution ~ 10 deg
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frequency spectrum
T=3.725+/-0.001 K
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BOOMERANG
LAUNCH IN EARLY 2000
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BOOMERANG mapped 2.5% of the sky at a resolution 35 x COBE
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April 2000: BOOMERANG map of the CMB fluctuations
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Measurement of the peak-to-peak spacing of the anisotropies shows that they have scales of ~ 1 degree. This corresponds to 0.88 < Omega < 1.12, indicating the universe is very close to having a flat geometry.
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BOOMERANG power spectrum - Fourier transform of the data, showingthat the angular scale is close to 1 degree.
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Combination of Supernovae and BOOMERANG results
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The WMAP Satellite
WMAP=Wilkinson Microwave Anisotropy Probe
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Launch June 2001
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What WMAP saw
Graphic from WMAP website
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Zooming the colour scale…
1 in 1000
Graphic from WMAP website
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Removing the effect of our motion through the galaxy
Graphic from WMAP website
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An image of the Universe at 380,000 years old!
Graphics from WMAP website
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A characteristic scale exists of ~ 1 degree
Graphics from WMAP website
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Statistical properties
• Spherical harmonic transform
• ~Fourier transform
• Quantifies clumpiness on different scales