         O n t h e T r a c k o f M o d e r n P h y s i c s Big Bang The Belgian priest Georges Lemaître was the first to propose, in 1927, that the Universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant galaxies. Two years later, Edwin Hubble made systematic measurements of the red shift. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance. The light that is reaching us has been stretched out as the universe has stretched, so light that was once visible now is reaching us in the form of microwaves Gamma Rays X-RaysUltraviolet Visible InfraredMicrowavesRadio, TV Electromagnetic Wavelength (metres) A microwave map of the whole sky made the Cosmic Background Explorer (COBE) Differential Microwave Radiometer (DMR).  0 >1  0 <1  0 =1 size time Open Universe looks like a horse saddle  +  +  <180 o Flat Universe  +  +  =180 o Closed Universe looks like the surface of a sphere  +  +  >180 o The fossil radiation When the temperature of the primordial plasma was low enough to allow electrons stick to nuclei, the Universe become transparent for light and the radiation decoupled started to wander around the Space. In the adiabatic expansion this radiation cooled down. Now its temperature is 2.73 K, corresponding to microwaves. In 1964, Penzias and Wilson, two engineers of Bell Telephones, working on communication with a satellite, observes a strange noise. They got Nobel prize for it in  y 1s100s 1000s 10 6 y 10 9 y y Birth of the Sun Today 2.73 K Forming of the galaxies Electromagnetic decoupling 3000 K 4  10 8 K Nucleosynthesis 2  10 9 K Evolution of the temperature of the Universe Time evolution of the Universe for different mass density parameter  0 which measures the ratio between the density  of the studied universe and a particular density, called the critical density  c. (about 6  kg/m 3 ). What is the geometry of the Universe? The density of matter inside the Universe determines its geometry: for a high density we will obtain a closed universe with a positive curvature, but with a density lower than the critical density, we will obtain an open universe. Some scientist say that time-space is closed, and folded inside like the Swiss cheese. But recent observations show that it is flat, or better, cubic. Moreover, the Universe accelerates its expansion and we do not know why! “If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.” Georges Lemaître “This is the most beautiful and satisfactory explanation of creation to which I have ever listened.” Albert Einstein Our Universe started somewhat 14.5 billion years ago. It took less than one millionth of a second to make disappear heavy quarks, one hundredth of a second to make protons and three minutes to make hydrogen and helium but 300,000 years to decouple the light from the matter. If You observe a picture like this on Your TV, do not change the channel. This can be a hidden massage from distant civilizations, and for sure 1/3 of this noise comes from the Big Bang fossil radiation. COBE in 1990 and WMAP in 2003 showed not only that Universe started as a ball of wriggly plasma but also that it is flat to the most remote corner. Georges Lemaître ( ) from 1935 was a canon of the cathedral in Malinas. Mikołaj Kopernik ( ) from 1510 was a canon of the cathedral in Frombork.