Most scientists think that the Universe began with a huge explosion called the Big Bang. A ball of matter smaller than an atom but at an incredibly high density and temperature exploded, producing a fireball what was the of matter and space. Bang? It is thought that the Big Bang happened BIG around 14 billion (thousand million) years ago. Redshift If you imagine that time reduced to just one year, a human lifetime would amount to less than one fifth of a second! Ever since the Big PKS 2000-330 Bang, the matter that was created has been D In 1982, the most distant known A B C moving apart at great speeds, a fact discovered object in the Universe s e s by the American astronomer Edwin Hubble in a e r c n i the 1920s. e c n a t s i When he looked at the light emitted by distant D galaxies for the spectral lines characteristic of particular chemical elements, Hubble found that Quasar 3C273 A B C D each line had moved towards the red end of the Three billion light years away spectrum, where the light has longer wavelengths. This implied that the light waves Edwin Hubble had been stretched during their journey. Not 1889–1953 only that, but the further away the galaxy, the The spectrum of radiation from distant Pleiades Cluster greater the movement of the lines – or ‘red galaxies shows peaks at wavelengths which are 400 light years away A B C D shift’, as the phenomenon is called. It was clear characteristic of various elements, especially to Hubble that this effect could only happen if hydrogen. If a galaxy is moving away from us, these characteristic peaks occur at longer the galaxies were moving away from us at wavelengths – in other words they are shifted great speed. towards the red end of the spectrum.This is The A B C D the ‘red shift’ – an example of the Doppler Eight light minutes away The General Relativity Theory of the great Effect.The faster the galaxy is moving, the suggests that it is not greater the red shift. In the diagram,A, B, C the galaxies themselves that are moving but the Ultraviolet Visible light Infra-red and D represent four peaks seen in the spectrum of stars and galaxies. space in between them – the space–time Wavelength of radiation increases continuum – that is expanding. Hard as it may be to imagine, the galaxies are being forced apart rather as currants in a cake mixture are moved apart as it rises. This gives us a way of understanding what happened at the beginning of the Universe. It is not that all matter started squashed together at one point in space and then moved outwards to fill up the rest of space. Instead, all matter was created squashed up because all of space was squashed up – there The General Relativity Theory suggests that it is was no other space outside. At the moment of not the galaxies themselves that are moving but the Big Bang, time began and space started to the space in between them – the space–time expand. As it did so, it carried all matter with it. Albert Einstein continuum – that is expanding 1879–1955 more TheBIGBang Further Information Particle Physics and Research Council If you would like to know more about the Big Bang theory and cosmology, the The Particle Physics and Astronomy Research Council following resources may help. (PPARC) is the UK Government-funded body that exists World Wide Web sites to support research in basic science: Particle Physics BBC Science Astronomy www.bbc.co.uk/science/space/ Space Science origins/bigbang/index.html This support is provided by funding UK researchers Cosmology links and by ensuring that they have access to world-class http://www.damtp.cam.ac.uk/ facilities in the UK and overseas.The Council pays cosmos/Public/index.html the UK’s subscription to the science programmes of the European Laboratory for Particle Physics (CERN) DAMTP www.damtp.cam.ac.uk/user/gr/ and the European Space Agency (ESA). public/bb_home.html PPARC recognises the importance of its science in assisting wealth creation; in post-graduate training; and in MAP motivating young people towards an interest and career map.gsfc.nasa.gov/m_uni.html in science generally. Books Russell Stannard Our Universe – A Guide to What’s Out There Kingfisher1996

Stuart Clark The Encyclopedia of Stars and Atoms Particle Physics and Astronomy Andromeda Oxford 1994 Research Council Robert Snedden Particle Physics and Science Horizons – Space Astronomy Research Council Belitha Press 1995 Polaris House North Star Avenue Swindon Wiltshire SN2 1SZ Tel:+44 (0) 1793 442000 Fax: +44 (0) 1793 442002 Particle Physics and Astronomy Email: [email protected] Research Council PPARC also publishes information on a variety of topics related to physics and astronomy, to help increase public Acknowledgments: awareness of the UK’s achievements in Photos supplied by: , CERN, ESA, Hulton Deutsch, Lucent Technologies, NASA, Popperfoto, ROE, Exploring the origins of our science and technology. Find out more by Science Museum, UMIST. visiting the PPARC World Wide Web site: Design and production Joint Reprographics Service www.pparc.ac.uk Version May 2004 Universe BIGBang OR STEADY STATE?

Fred Hoyle

Support for Big Bang Theory 1915–2001 was discovered in 1964, while using a horn radio antenna in Holmdel, N.J. to isolate, identify and measure sources of Hubble’s discoveries of an expanding Universe noise in the led a Russian-born scientist, George Gamow, to atmosphere, Bell Labs argue in the late 1940s that there must have scientists Arno Penzias been a point when the Universe started to (right) and Robert Wilson expand. Soon after Gamow published his idea, discover faint cosmic radiation the English astronomer gave a radio from the farthest reaches of talk in which he dismissed the theory as ‘some sort of big bang’. Although Hoyle had meant the known space. phrase to be insulting, it stuck, and from then on, George Gamow as far as most people were concerned, Gamow’s idea was called the Big Bang theory of the COBE (Cosmic 1904–1968 beginning of the Universe. Background Explorer) For almost 20 years, arguments raged between Satellite revealed tiny Big Bang the believers in the Big Bang theory and Hoyle’s temperature differences supporters, who believed in the rival ‘steady- that reflect early state’ theory, in which the Universe has always existed in much the same way as we see it now, variations in the density Supporters g with no beginning. Strong evidence for the Big of matter, the seeds of Bang, and a tough challenge to the steady-state galaxies. theory, came from the new branch of science called . It was discovered in the 1930s that galaxies emitted radio waves, but the first map of the sky’s radio sources was made in the 1950s by Boomerang is a balloon-bourne Martin Ryle, the radio astronomer. millimetre-wave robotic If Hoyle’s steady-state theory was correct, Ryle telescope, built to observe should have found an even distribution of structure in the Cosmic galaxies through space. But he didn’t. The Microwave Background further Ryle looked into space with his receiver, the more sources of radio waves he found. Since radiation. It takes both the light and the radio waves from distant advantage of the wind galaxies have taken billions of years to reach us, pattern that circulates we see them as they were in the distant past. around the Antarctic Ryle was detecting galaxies that were closer in continent to run a long Martin Ryle time to the Big Bang. The fact that there were duration flight, arriving more of them suggested that the Universe had close to its launch site. 1918–1984 been much denser then than it is now. This was tremendous support for the Big Bang theory. Then, in 1964, two American scientists, Arno Penzias and Robert Wilson,made a discovery A new development is the Very that finally tipped the balance in favour of the Small Array, designed Big Bang theory. They were using a radio to help build up a more- antenna to look for interference to satellite broadcasts when they accidentally picked up detailed microwave microwave radiation coming from all areas of picture of the early the sky.This is the same form of energy that we Universe. It will consist use (at a much greater strength) to cook with of 15 small horns and in microwave ovens. The radiation had a reflectors, each temperature equivalent to 2.7 degrees Kelvin – connected to an less than three degrees above absolute zero, the extremely sensitive coldest temperature possible. One of their receiver, and will be colleagues, Robert Dicke, guessed very quickly constructed among the Arno Penzias that they had found the remains of the vast conventional telescopes b 1933 amount of heat energy released at the time of already operating at the Robert Wilson the Big Bang – the lingering afterglow of Teide Observatory, in Tenerife. creation.This would make it quite clear to the b 1936 reader what the modern view of cosmology is. more utrons d ne fus an e to ns ge to th ro e P r

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i E e le cl ct u ro n 10 ns um fa eli 10 sten d h seconds to hydrogen an The first detailed, all-sky picture of the infant universe. The WMAP image reveals 13 billion+ years old temperature fluctuations (shown as colour differences) that correspond to the seeds that grew to become the galaxies. Encoded in the patterns are the answers to many age-old questions, such as the age and geometry of the Universe. We can’t say anything about the conditions in the Universe before about 10 -43 seconds, but by 10-35 seconds the lightest particles, Early observations with the COBE satellite, quarks and leptons, launched in 1989, showed conclusively how Time elapsed had appeared. uniform the background radiation was, but more (in seconds) Particles were detailed data seemed to show for the first time from Big Bang to now constantly being created and small variations in this cosmic radiation.The annihilated at results indicated that ‘ripples’ had formed in the 10 -12 seconds and it was only at substance of the Universe within 300,000 years 10-6 seconds that quarks formed of the Big Bang. These findings appear into neutrons and protons. to back up physicist Alan Guth’s ‘inflationary Some of those particles were model’ of how the Universe formed. According annihilated, but the remainder gradually joined up to form to Guth’s idea, during the rapid expansion, or the atoms we find now in inflation, of the Universe that followed the Big our Universe. Bang,‘imperfections’ might have spread through space as matter began to appear, where previously there had been only energy. Each of these imperfections might have been a focal point around which stars and galaxies formed, condensing together under the force of their own gravity.

The COsmic Background Explorer (COBE) satellite looked for radiation from the very edge of space for clues to the origin of the Universe.

More evidence that the Big Bang happened neutrons fu nd se comes from a closer look at the elements that s a tog on et t he astronomers have detected in the regions of ro r P space where new stars are forming. The first stages of the Big Bang took place in a small fraction of a second, when the Universe was only a million billion billion billionth of a centimetre

Q s across. Within a billion billionth of a second it u n a o r t k o s r had swelled to many times the size of a star and fo p rm nd i s a consisted of an incredibly dense sea of particles nto neutron c r i called quarks and leptons. By the time it was e le at c a hundred millionth of a second old, the single in u g t n he igh unified force that was present at the birth of lium er l and oth the Universe had already branched into the four forces familiar to scientists: strong, electro- Quarks magnetic, weak, and gravitational. Leptons Neutrons & Protons The End of the Universe? Until recently, astronomers believed that gravity was slowing the expansion of the Universe.What would then happen to the Universe would depend on the amount of matter in the Universe. If there turned out to be enough matter, then its current expansion would slow down and stop. In that case, we would be living in a Universe destined to collapse in the far distant future.This scenario is known as the “Big Crunch” - in which galaxies and stars would eventually be compressed into a hot dense gas at a temperature of over a billion E i degrees.The alternative would be that the le le c c Universe is destined to expand forever - leading to tr nu o a cold, dark Universe filled with dead stars. ns m fa liu st he Then in 1998, astronomers announced that en t and o hydrogen observations of remote supernovae seemed to show that the expansion of the universe is actually speeding up. If that is so, there must be some form of unknown dark energy in the Universe powering this acceleration. Since 1988, observations of the seconds cosmic microwave background and more accurate estimates of the total amount of matter in the Universe have strongly supported the idea that we live in an accelerating Universe with far too little matter to cause a big crunch. However, we are far 20 from understanding what the mysterious dark 10 energy actually is.