Ultralarge Ultrasmall PCES 5.31 PARTICLE PHYSICS & - PowerPoint PPT Presentation

Ultralarge �� Ultrasmall PCES 5.31 PARTICLE PHYSICS & COSMOLOGY The energies needed to probe the unification of the forces are beyond our reach- at 10 16 times higher than at CERN! They only ever existed once- right after the big bang. The physics at such energy scales (energy here in temperature units, with 1 eV ~ 11,600 K) is shown along with the time when the universe was at this temperature. Note the unification of Strong & Electroweak forces at 10 28 K, & the unification of weak & EM to make electroweak at 10 16 K (the CERN LHC works at this energy). We believe gravity unifies Somehow with the others at ~ 10 33 K. In the very early universe can we probe this physics

PCES 5.32 Cosmic Distance & Time Scales When we look out to great distances we also look back in time. So we need to measure large distances – this not easy. Cepheids play a crucial role- these giant pulsating stars have a pulsation period simply & accurately related to their luminosity. They can be seen ABOVE: Close-up of NGC 4603- some out to ~ 10 8 light yrs with NGC 4603, @ 108 million lt. yrs Cepheids are identified in boxes modern telescopes- we know their real luminosity because some Cepheids are near enough to have their distances measured in other ways (parallax, etc). At much greater distances one relies on supernovae, whose luminosity is known fairly accurately from their spectra. These are so bright they can be seen as far as the farthest galaxies. From all this work we find that the radius of the visible universe is ~ 14 billion (1.4 x 10 10 ) light years, & the age of the universe is thus ~ 1.4 x 10 10 yrs LEFT: Supernova in HST deep field- note difference between 1996-7.

PCES 5.33 Theories of the Early Universe Theories of the early universe try to combine ideas about string and/or particle physics with gravity theory. This is hard without a proper quantum theory of gravity. There are very strong theoretical reasons for a modified Big Bang which begins with the Size of early universe plotted against time quantum tunneling of all of spacetime from a ‘false vacuum’ state into the present universe (in a way reminiscent of the nucleation of a new phase) followed by An extremely fast expansion, or ‘inflation’ (above), and finally a long period of Hubble expansion, still going on. The idea of inflation is due to Guth. The timeline of the v e timeline of the very early ry early universe c universe can onl n only be surmis y be surmised ed theoretically, from theoretically, from the standard the standard model of high-energ del of high-energy phy y physics (cf sics (cf Alan Guth (1947-) slides 5.21-5.27). On slides 5.21-5.27). On sl slide 5.30 the ti ide 5.30 the timeline meline of this of this expansion is expansion is shown – own – as the univ the univers erse rapidly rapidly expa expanded nded it cooled, & after the v it cooled, & after the various arious forces & orces & particles particles were produced, nuclei were produced, nuclei beg began to n to be synthesized about 1 be synthesized about 1 sec after the Big ec after the Big Bang. Initially this involved protons ng. Initially this involved protons and el and electrons, but thes ectrons, but these collided to form e collided to form He & He & Li nuclei. T Li nuclei. This stopped after 3 minutes is stopped after 3 minutes when the therm when the thermal energ l energy was too low, was too low, producing the initial concentrations of H, He, a producing the initial concentrations of H, He , and Li nuclei i nd Li nuclei in the primitiv n the primitive univ e univers erse. For a For a long ti long time after this after this the pri the primev eval soup of photons al soup of photons, el electrons, neutrinos, & ectrons, neutrinos, & lig light nuclei nuclei c cooled f oled from om m many billio billions ns of of degr degrees down to down to a a fe few t w thousa ousand. At t nd. At this is Point, between 372,000 - Point, between 372,000 - 387,000 yrs after the Bi 87,000 yrs after the Big Ban g Bang, a r , a remarkab markable le tra transforma sformation occurred tion occurred - the univ he univers erse bec became transparent (next pag transparent (next page) ) Cosmic Abundance of early nuclei

PCES 5.34 Radiation-Matter Decoupling: the Microwave Background The sud The sudden tr tran ansp spar arenc ency o of the universe after nearly the universe after nearly 300,000 yrs came fr 300,000 y s came from om the de the decoupling o coupling of matter and f matter and photons. The basic idea is shown at right. In the early hot photons. The basic idea is shown at right. In the early hot universe, all the H, He, and Li universe, all the H, He, and Li were ionized - were ionized - a ‘plasma of a ‘plasma of nuclei and electrons. However as nuclei and electrons. However as they c they cool they ev ool they even entually tually boun und into an d into an exp expanding gas o ing gas of neutral atoms. The plasma neutral atoms. The plasma was opaque to photons – was opaque to photons – the hey s y scatter catter o off the char the charged ged Photon propagation before and after decoupling particles – particles – but th ut the neutral gas e neutral gas was almost transparent. Thus was almost transparent. Thus roughly 300,000 y oughly 300,000 yrs after the Big Bang, the radiat s after the Big Bang, the radiation decoupled fr ion decoupled from the om the matter, and has been matter, and has been traveling almost freely ever since, through and around the H, He, and Li. traveling almost freely ever since, th rough and around the H, He, and Li. The expansion of the universe, since then, has cooled both these photons, & the condensed gas, down to 2.7 K - the universe is full of photons at this temperature. In the late 1940’s it was realised by Gamow & Alpher that this ‘microwave background’ ought to exist in the universe, and that it would constitute a relic of the conditions in the early universe, at the time of decoupling. This work was mostly ignored at that time. A Penzias R Wilson (1933-) The discovery of the ‘microwave background’ by Penzias & Wilson in (1936-) 1964, using a new microwave detector they had developed, thus provided dramatic evidence for the Big Bang, & stimulated a new era in cosmological research. Since 1964 tw o important themes in ‘cosmology’ (the study of the properties & evolution of the universe at these cosmic scales) have been the changing constitution of all the matter in the universe (starting w ith nucleosynthesis in the early universe, follow ed by nucleosynthesis in stars – see pp. 5.11-5.17), & the changes in large-scale structure. This latter study brings together particle physics & general relativity, in the new field of relativistic astrophysics.

FLUCTUATIONS in the MICROWAVE BACKGROUND PCES 5.35 Beginning in the late 19 ginning in the late 1950 50’s, the rem ’s, the remarkable s rkable self-t lf-taugh aught Soviet theori t Soviet theorist Ze st Zeldovich ldovich pioneered a large ioneered a large part of rel part of relativistic a ativistic astrophy trophysics, ex sics, exploring ing the role o the role of general relativity general relativity in high-energy phenomena such as super in high-energy phenomena such as supernov novae ae, black black holes holes, & t , & the early universe. Among hi early universe. Among his many contrib s many contributions wa utions was the prediction that s the prediction that quantum quantum fluctuations in the energ fluctuations in the energy density of density of the early universe, the early universe, around the around the ti time of ra e of radiation-m diation-matter tter deco decoupl upling, would determine the ng, would determine the later distrib later distribution of m tion of matter in the univers tter in the universe – – thes hese s small fluctuations all fluctuations would act as ‘s would act as ‘seeds eeds’ for the latter or the latter collaps collapse of matter into g e of matter into galaxies. alaxies. YB Zeldovich Remarkably, this would lead ot arkably, this would lead ot a a ‘filam ‘filament-like’ nt-like’ structure for the structure for the (1914-1984) distrib distribution of g tion of galaxies in the univ alaxies in the univers erse. Moreov . Moreover , er , one would be able to s one would be able to see e the initial fluctuations the initial fluctuations even now, because they wo even now, because they would be ‘froz uld be ‘frozen’ n’ into the into the microwave background at microw ave background at the tim the time of decoup of decoupling. ling. Predictions of mass distribution from Zeldovich theory Much w ork since then has confirmed Zeldovich’s basic ideas. Observations of the distribution of galaxies both now & in the distant past (back to w hen the galaxies first formed, revealed by deep space photos of supernovae & galaxies), show the predicted pattern of voids & filaments. Fluctuations in the microw ave background, mapped in great detail, confirm the inflationary universe picture The WMAP observation of the microwave background – the blow- Mass distribution in universe, up shows the polarisation Results from the COBE observations including dark matter