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.

• 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!

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.

The CMB

An image of the Universe at 380,000 years old

(Cosmic Microwave Background)

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

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

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COBE RESULTS

COBE angular resolution ~ 10 deg

frequency spectrum

T=3.725+/-0.001 K

BOOMERANG

LAUNCH IN EARLY 2000

BOOMERANG mapped 2.5% of the sky at a resolution 35 x COBE

April 2000: BOOMERANG map of the CMB fluctuations

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.

BOOMERANG power spectrum - Fourier transform of the data, showingthat the angular scale is close to 1 degree.

Combination of Supernovae and BOOMERANG results

The WMAP Satellite

WMAP=Wilkinson Microwave Anisotropy Probe

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Launch June 2001

What WMAP saw

Graphic from WMAP website

Zooming the colour scale…

1 in 1000

Graphic from WMAP website

Removing the effect of our motion through the galaxy

Graphic from WMAP website

An image of the Universe at 380,000 years old!

Graphics from WMAP website

A characteristic scale exists of ~ 1 degree

Graphics from WMAP website

Statistical properties

• Spherical harmonic transform

• ~Fourier transform

• Quantifies clumpiness on different scales