Lecture 2: History of the Universe: Basic Outline PDF

Lecture 2: History of the Universe: Basic Outline  History of the Universe We can understand the history of the universe from very early times through to the present, JUST BY APPLYING THE LAWS OF PHYSICS THAT WE KNOW However there are are few things we haven’t yet sorted out –...

Lecture 2: History of the Universe: Basic Outline  History of the Universe We can understand the history of the universe from very early times through to the present, JUST BY APPLYING THE LAWS OF PHYSICS THAT WE KNOW However there are are few things we haven’t yet sorted out – When did the first stars and galaxies form? – What is dark matter and dark energy? – Is there life on other planets? – We have detected gravity waves! What will they tell us?  Time 300,000years Few minutes Inflation Credit: Stargazing Live, BBC, Open University, NASA Time Few hundred million years Few billion years Credit: Stargazing Live, BBC, Open University, NASA Time 9 billion years 10 billion years Credit: Stargazing Live, BBC, Open University, NASA Time Today Credit: Stargazing Live, BBC, Open University, NASA Time 20 billion years Finally, universe cold & dark Credit: Stargazing Live, BBC, Open University, NASA  t=380,000 years, z~1100 Dark Energy – Ordinary matter – the stuff existed but was we are made of (baryonic matter) unimportant Dark matter – 5 times as much as ordinary matter WMAP measures the temperature of the early universe à Density of matter  t=380,000 years, z~1100 Redshift: ratio of size of the universe now to the size then Dark Energy – Ordinary matter – the stuff existed but was we are made of (baryonic matter) unimportant Dark matter – 5 times as much as ordinary matter WMAP measures the temperature of the early universe à density of matter The universe has been expanding since its beginning (we don’t understand why) That expansion is now accelerating Due to ‘dark energy’ (we don’t understand what it is) Data that determines the most likely model For the expansion of the universe © 2014 Pearson Education, Inc. Figure 23.17 Evolution of the Universe: 4 possible models © 2014 Pearson Education, Inc. Figure 23.17 Evolution of the Universe: 4 possible models © 2014 Pearson Education, Inc. The universe has been expanding since its beginning (we don’t understand why) That expansion is now accelerating Due to ‘dark energy’ (we don’t understand what it is) Expansion means that the size and volume of space is increasing An analogy for the expansion - baking a loaf of bread  Evolution of the dark matter in the universe Denser regions collapse under gravity (dominated by dark matter) © 2014 Pearson Education, Inc. Karatsov  Stars form in the densest regions from clouds of dust, gas and molecules, live their lives, and recycle new elements into the interstellar medium Credit: Anna Frebel History of the universe scaled to 1 year  Human civilisation is just a few seconds, and a human lifetime a tiny fraction of a second  Eppur si muove “and yet it moves” (Allegedly uttered by Galileo before the Inquisition - ‘it doesn’t matter what you believe, here are the facts’) You may have a sense of being stationary, but in fact you are moving at enormous speeds through space 6 different ‘motions’ – some accelerating and some ‘virtual’ Motion 1: rotation of the Earth Period: 1 day  Motion 2: orbiting the Sun Rotational motion and orbital motion in the same directions Average speed 107,000 km/hr Motion 3: the Sun moves with respect to the local stars The Sun moves with respect to the other stars in the local neighbourhood, at about 70,000 km/hr, Motion 4: it rotates around the Milky Way every 230 million years à 800,000km/hr  Our motion around the Galaxy measures mass Most of the mass in the galaxy is not in stars, but in dark matter. Motion 5: Milky Way in the Local Group Motion 6: Local Group moving towards the Virgo Cluster Putting it all together – nothing stays still! Local Group moving towards Virgo Cluster, etc  How do we determine our ‘final velocity?’ With respect to the Cosmic Microwave background, we are moving at 369km/sec in the direction of the constellation of Leo in the southern sky. X  Distance – and big numbers Astronomical Unit: average distance between the Earth and the Sun – 150 million kms = 150,000,000 kms = 1.5 x 108 kms (scientific notation) 2024 Sem 2 From the Solar System to the Cosmos 29  Scientific notation Any very big or very small number can be written in scientific notation (and should be!) Comprises (1) a decimal between 1-10 (2) a power of 10 Multiplication, division and powers are now easy But if you need to add and subtract, make sure you expand the numbers out. 2024 Sem 2 From the Solar System to the Cosmos 30  Distance – and big numbers Astronomical Unit: average distance between the Earth and the Sun – 150 million km = 150,000,000 km = 1.5 x 108 km (scientific 1 notation) Light-year: distance light travels in a year 2024 Sem 2 From the Solar System to the Cosmos 31 1 light-year = (speed of light) x ( 1 year) ! km $ = # 300, 000 & × (1yr ) " s % ! km $ ! 365days $ = # 300, 000 & × (1yr ) × # & " s % " 1yr % ! km $ ! 365days $ ! 24hr $ ! 60 min $ ! 60s $ = # 300, 000 & × (1yr ) × # &×# &×# &×# & " s % " 1yr % " 1day % " 1hr % " 1min % 2024 Sem 2 From the Solar System to the Cosmos 32 1 light-year = (speed of light) x ( 1 year) ! km $ = # 300, 000 & × (1yr ) " s % ! km $ ! 365days $ = # 300, 000 & × (1yr ) × # & " s % " 1yr % ! km $ ! 365days $ ! 24hr $ ! 60 min $ ! 60s $ = # 300, 000 & × (1yr ) × # &×# &×# &×# & " s % " 1yr % " 1day % " 1hr % " 1min % 2024 Sem 2 From the Solar System to the Cosmos 33 1 light-year = (speed of light) × (1 year) " km # " 365 days 24 hr 60 min 60 s # = $ 300,000 %×$ × × × % & s ' & 1 yr 1 day 1 hr 1 min ' =9,460,000,000,000 km = 9.46 x 1012 km Parsec: distance unit professional astronomers use (about 3 light-years) defined later on 2024 Sem 2 From the Solar System to the Cosmos 34  Looking back in time The speed of light is finite – but pretty fast! = 3 x 108 m/sec Mostly this speed only matters when we look out into space When we look at distant objects we are looking back in time The further away we look, the further back we look in time Limit: the universe is 13.8 billion years old – can we see right back to the beginning? 2024 Sem 2 From the Solar System to the Cosmos 35  The observable universe GN-z14 13.5 billion light years, so Limit of observable universe 300 million years old, as we see it - Cosmic Microwave Background - 13.8 billion light years 2023 Sem 2 From the Solar System to the Cosmos 36  Mass is measured by the motion of one object around another By measuring the velocity of an object orbiting the Sun, and its distance, we can weigh the Sun. (upcoming weeks lectures) 2024 Sem 2 From the Solar System to the Cosmos 37  Measurement of time is based on Earth’s year The longest time we consider is the age of the universe – 13.8 billion years = 1.38 x 1010 years The shortest time we consider is the first time in the history of the universe when we believe that physics, as we understand it today, was applicable – 10-43 seconds 2024 Sem 2 From the Solar System to the Cosmos 38