The measurement of q 0

1. 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.

2. 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!

4. 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.

5. An image of the Universe at 380,000 years old The CMB (Cosmic Microwave Background)

6. The History of the Universe Universe is hot Electrons are free Light scatters off electrons Until ~380,000 years after BB Universe is cooler e- and p+ form hydrogen Light travels freely

7. 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)

8. Graphic from WMAP website

9. The History of CMB observations 1965 Discovery COBE 1992 Graphic from WMAP website 2003 WMAP

10. COBE RESULTS

11. COBE angular resolution ~ 10 deg

12. frequency spectrum T=3.725+/-0.001 K

13. BOOMERANG LAUNCH IN EARLY 2000

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

15. April 2000: BOOMERANG map of the CMB fluctuations

16. 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.

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

18. Combination of Supernovae and BOOMERANG results

19. The WMAP Satellite Graphic from WMAP website WMAP=Wilkinson Microwave Anisotropy Probe

20. Launch June 2001

21. What WMAP saw Graphic from WMAP website

22. Zooming the colour scale… 1 in 1000 Graphic from WMAP website

23. Removing the effect of our motion through the galaxy Graphic from WMAP website

24. An image of the Universe at 380,000 years old! Graphics from WMAP website

25. A characteristic scale exists of ~ 1 degree Graphics from WMAP website

26. Statistical properties • Spherical harmonic transform • ~Fourier transform • Quantifies clumpiness on different scales