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## Cosmology & The Big Bang Theory

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**Cosmology &The Big Bang Theory**Dr Alex Calverley**Cartesian coordinates**Polar coordinates**Special relativity**General relativity**In 1915...**In 1917... Using the GR metric from the last slide Friedmann solved the equation in 1922 to get...**k > 0**k < 0 k = 0**Demonstrating the relationship between comoving(i.e.**coordinate) distances and physicaldistances a = 1 today (a0), and a(t) < 1 at earlier times**However, in 1927...**If D(t) is the proper distance between two objects at time t and D0 is the proper distance now, then: and Then combining these So Lemaîtrehad predicted**EVIDENCE FOR THE BIG BANG THEORY (1)**An expanding universe where the recessional speed is proportional to the distance away**In 1948...**George Gamow predicts the ratio of light elements due to Big Bang Nucleosynthesis Ralph Alpher and Robert Herman predict the glow from the Big Bang will still be visible in the microwave spectrum with a temperature of about 5 K**EVIDENCE FOR THE BIG BANG THEORY (2)**A near perfect blackbody spectrum at T ≈ 2.7 K, suggesting the Universe was once much hotter anddenser**EVIDENCE FOR THE BIG BANG THEORY (3)**BB Nucleosynthesiscan explainthe observed ratios of lightelementsin pristine primordial gas**In 1999...**The Universe’s expansion is accelerating! Need an extra component to the Friedmann equations called Dark Energy – which acts just like Einstein’s Λ term!