Cosmology

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Cosmology
Cosmology From the Big Bang to the Forma;on of Atoms A/Prof Emma Ryan-­‐Weber This presenta;on can be downloaded here: hCp://astronomy.swin.edu.au/~eryan/Outreach/STAV_Physics_2016.pdf Photo Credit: Andrew Hara VCE Physics Unit 1 VCE Physics Unit 1 1. Big Bang Cosmology 2. First par;cles & Big Bang Nucleosynthesis According the opening credits… Our whole universe was in a hot dense state, Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, As every galaxy was formed in less ;me than it takes to sing this song. A frac;on of a second and the elements were made. … It all started with the big BANG! According the opening credits… ✔ Our whole universe was in a hot dense state, Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, As every galaxy was formed in less ;me than it takes to sing this song. A frac;on of a second and the elements were made. … It all started with the big BANG! According the opening credits… ✔ Our whole universe was in a hot dense state, ✔ Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, As every galaxy was formed in less ;me than it takes to sing this song. A frac;on of a second and the elements were made. … It all started with the big BANG! According the opening credits… ✔ Our whole universe was in a hot dense state, ✔ Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, ✔ That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, As every galaxy was formed in less ;me than it takes to sing this song. A frac;on of a second and the elements were made. … It all started with the big BANG! According the opening credits… ✔ Our whole universe was in a hot dense state, ✔ Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, ✔ That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, ✗ As every galaxy was formed in less ;me than it takes to sing this song. A frac;on of a second and the elements were made. … It all started with the big BANG! According the opening credits… ✔ Our whole universe was in a hot dense state, ✔ Then nearly fourteen billion years ago expansion started. Wait... The Earth began to cool, The autotrophs began to drool, Neanderthals developed tools, We built a wall (we built the pyramids), Math, science, history, unraveling the mystery, ✔ That all started with the big bang (Bang)! "Since the dawn of man" is really not that long, ✗ As every galaxy was formed in less ;me than it takes to sing this song. ✗ A frac;on of a second and the elements were made. … It all started with the big BANG! 1. Big Bang Cosmology Time, t=0 seconds: the origin of all space and ;me. All maCer and energy in the Universe was squeezed into a infinitely small space. The Universe itself is infinite, thus there is no edge to this dot. There is nothing outside this dot, not even a vacuum. We don’t know what exactly what happened at this ;me as the laws of physics as we know them have broken down. We have no theory of quantum gravity that would govern these physical condi;ons. However, we do know it must have been DENSE and HOT. Then expansion started. The Planck ;me Temperature Volume of Universe t=10-­‐43 seconds: the Planck ;me. Gravity ‘freezes out’ from the other 3 forces. The Universe con;nues to expand. Like all gases, as it expands, it cools. Time increases Clicker Ques;on What is the Universe expanding into? A. 
B. 
C. 
A vacuum The Universe is not expanding into anything: the fabric of space itself is stretching. The Universe is not undergoing a real expansion because there’s nothing to expand into. Clicker Ques;on What is the Universe expanding into? A.  A vacuum B.  The Universe is not expanding into anything: the fabric of space itself is stretching. C.  The Universe is not undergoing a real expansion because there’s nothing to expand into. Surface of a balloon analogy Just like the 3D Universe, the 2D surface of a balloon •  Has no centre. •  Has no edge. •  At any given ;me, the expansion rate of the surface of the balloon (Universe) is the same everywhere else on the balloon (Universe). Surface of a balloon analogy Cau;on! In the Universe, galaxies are like ants (they don’t expand), not dots. Gravita;onally bound objects are NOT increasing in size due to Hubble expansion (e.g. the Earth, the Solar System, the Milky Way). Measuring the expansion rate 20 seconds A-­‐B = 1cm A-­‐D = 4 cm A-­‐B = 4cm A-­‐D = 16 cm 1 4 Dist. (cm) 16 Measuring the expansion rate A-­‐B 0 Time (s) 20 20 seconds A-­‐B = 1cm A-­‐D = 4 cm A-­‐B = 4cm A-­‐D = 16 cm The expansion rate is the same! dist.
time
3cm
Speed A−B =
= 0.15cm / s
20s
12cm
Speed A−D =
= 0.6cm / s
20s
speed
dist.
0.15cm / s
=
= 0.0375s −1
4cm
0.6cm / s
=
= 0.0375s −1
16cm
Rate of Expansion =
Rate of ExpansionA-B
Rate of ExpansionA-D
1 4 Dist. (cm) 16 Speed =
A-­‐B 0 Time (s) 20 Predict the speed of galaxies dist.
time
3cm
Speed A−B =
= 0.15cm / s
20s
12cm
Speed A−D =
= 0.6cm / s
20s
Speed =
speed
dist.
0.15cm / s
=
= 0.0375s −1
4cm
0.6cm / s
=
= 0.0375s −1
16cm
Rate of Expansion =
Rate of ExpansionA-B
Rate of ExpansionA-D
What the? This means that galaxies that further apart should be travelling away from each other at greater speeds! Hubble’s Observa;ons In the 1920s Edwin Hubble observed the speed and distance of galaxies external to our own Milky Way. Hubble’s Law & constant Hubble found that more distance galaxies were receding faster and concluded that the Universe is expanding at a constant rate, now known as Hubble’s constant, H0=22 km/s /Mega light-­‐year. velocity=H0 x distance Hubble’s observa;ons of the expanding Universe provide EVIDENCE for the BIG BANG. © 2014 Pearson Educa;on, Inc. How old is the Universe? Hubble's constant can be used to es;mate the age of Universe. [length][;me]-­‐1[length]-­‐1 Hubble’s Constant, H0 = Current rate of Expansion = 22 km/s /Mega light-­‐year 1 Mega light-­‐year = distance travelled by light in 1 million years The speed of light Age$~$1/H0 =
10 6 !light&years!
22"km/s
=
!" ! !!"#$%!×!!×!" ! !"/!
!!!!"/!
3×10!! !years!×!km/s
!!!!!!!!!!!=
!
22!km/s
!!!!!!!!!!!!= 1.36!×!10!" !years
~ 14 billion years Current best cosmological measurement is 13.8 billion years Clicker Ques;on If we use a telescope to look 13.8 billion light years away we will see remnant radia;on from the Big Bang? A. 
B. 
Yes No Clicker ques;on answer The answer is no, because the edge of our observable Universe (the big bang) is actually 46 billion light-­‐years away. How can that be, if nothing can travel faster than the speed of light? It’s because space between us and the big bang has stretched “faster than the speed of light”. These defini;ons of distance & ;me are not the same as those defined by Special Rela;vity. © 2014 Pearson Educa;on, Inc. Light-­‐years: works well for “close” objects A light-­‐year is the distance light travels in one year. The speed of light is 3x105 km/s Thus 1 light-­‐year = 365.25 x 24 x 60 x 60 [s] x 3x105 [km/s] = 9.5x1015 km The Andromeda galaxy is located 2 million light-­‐years from the Milky Way. These photons we have captured depict Andromeda as it was 2 million years ago (as human life was emerging on Earth). Space hasn’t stretch much over this short cosmic ;me/distance. Space-­‐;me diagram How does expansion affect distance measurements? For example, a supernova explodes in a nearby galaxy and the light takes 400 million years to reach the Milky Way. How far away is the galaxy? Lookback ;me Distances between faraway galaxies change while light travels. Unambiguous to think in terms of lookback 2me rather than distance. The two galaxies are separated by 400 million years in lookback ;me. © 2014 Pearson Educa;on, Inc. How big is the Universe? The Cosmological Horizon marks the limits of the observable universe. It is a horizon in %me rather than space. Since looking far away means looking back in ;me, there must be a limit – the beginning of the universe! Our past light cone defines our cosmological horizon The Big Bang Here & now 13.8 billion years in lookback ;me (≠ 13.8 billion light years in distance) The current distance from Earth to the edge of the observable universe is 46 billion light years. Can we observe the Big Bang? No, the furthest we can see photons is to a ;me lookback ;me of 13.7995 billion years. This is the cosmic Microwave Background. Gravity Waves We can’t see photons beyond the opaque screen of the cosmic microwave background, but in theory GRAVITY WAVES can travel uninterrupted through this screen. The first observa;on of gravity waves was announced by the LIGO consor;um on 11th Feb 2016 was due to two blackholes merging 1.1 billion years ago. Gravity waves from the big bang have NOT been detected yet. In 2014 scien;sts using the BICEP2 telescope claimed to have detected these waves, however the signal was contaminated by dust in the Milky Way. The Big Bang Here & now 2. First par;cles & Big Bang Nucleosynthesis Let’s go back now and take a more detailed look of what happened between t=0 and t=380,000 years. Recall, at the Planck ;me, t=10-­‐43 seconds, Gravity froze out from the other 3 fundamental forces. Par2cle era: Amounts of maCer and an;maCer nearly equal (roughly 1 extra proton for every 109 proton– an;proton pairs!) Era of nucleosynthesis: At t=0.001 seconds all the remaining an;maCer is annihilated and Helium nuclei fuse. Era of nuclei: At t=3 minutes fusion stops. Universe became too cool to blast helium apart. Era of atoms: At t=380,000 years. Atoms are formed and the Cosmic Microwave Background radia;on released. Par;cle Era Heisenberg Uncertainty Principle (you cannot know the exact energy of a system at every point in ;me) AND Energy-­‐Mass can be exchanged E = mc2 Photons can be converted into par;cle–an;par;cle pairs and vice versa. An electron & positron can spontaneously appear from the vacuum of space, but can only exist for 6x10-­‐22 seconds. © 2014 Pearson Educa;on, Inc. Big Bang Nucleosynthesis Up un;l t=2 seconds the Universe was s;ll so hot (T>1010 K, or >1 MeV) that electrons, protons, positrons and neutrons were all in thermodynamical equilibrium: neutrons could convert into protons are vise versa. At t=2 seconds (T<0.8 MeV) neutrons & protons are no longer in thermal equilibrium, no new neutrons are created and the Fusion of Helium begins. © 2014 Pearson Educa;on, Inc. A powerful predic;on From sta;s;cal mechanics equa;ons, the Big Bang theory predicts: 75% H, 25% He (by mass). Neutrons have a mean life;me of 15 minutes © 2014 Pearson Educa;on, Inc. Why didn’t Carbon (and other elements) form in the Big Bang? Carbon forms through the rare Triple-­‐alpha process (collision of 3 He-­‐4 nuclei) There’s no enough ;me in the 3 minutes following the Big bang for the Triple-­‐alpha process to occur. A}er 3 minutes the Temperature falls below that needed for nuclear fusion. Carbon (and all the other elements heavier than Helium) are created inside of stars (stellar nucleosynthesis). The first stars switched on their nuclear reac;ons ~500,000 years a}er the big bang. Stars today con;nue to generate new elements. Clicker Ques;on Which of these abundance paCerns is an unrealis2c chemical composi;on for a star? A.  70% H, 28% He, 2% other B.  95% H, 5% He, less than 0.02% other C.  75% H, 25% He, less than 0.02% other D.  72% H, 27% He, 1% other Clicker Ques;on Which of these abundance paCerns is an unrealis2c chemical composi;on for a star? A.  70% H, 28% He, 2% other B.  95% H, 5% He, less than 0.02% other C.  75% H, 25% He, less than 0.02% other D.  72% H, 27% He, 1% other Why? Because you can increase Helium through fusion in a star, but you can’t decrease the amount of Helium. There is a minimum of 25% Helium in every star. Era of Nuclei A}er Big Bang Nucleosynthesis finished the Universe was filled with a plasma of Hydrogen and Helium Nuclei (plus very small amounts of Lithium & Beryllium), free electrons and photons. We s;ll can’t observe this era directly as the Universe was s;ll so dense that no photon could possibly make it way out of this plasma without colliding into or scaCering off another par;cle. This situa;on remained the same for 380,000 years. Transi;on to the Era of Atoms © 2014 Pearson Educa;on, Inc. The Cosmic Microwave Background The whole sky glows at a mean temperature of 2.73 Kelvin or 2 mm (in the microwave) Thermal Spectrum Observa;ons show a perfect thermal radia;on spectrum at temperature 2.73 K. Expansion of the Universe has stretched the wavelength of the thermal radia;on from that ;me by ~1000 ;mes to the microwave part of the electromagne;c spectrum. © 2014 Pearson Educa;on, Inc. The Cosmic Microwave Background Planck Satellite all-­‐sky map of the Cosmic Microwave Background RadiaNon The CMB is a snapshot of the oldest light in our Universe, imprinted on the sky when the Universe was just 380,000 years old. It shows ;ny temperature fluctua;ons that correspond to regions of slightly different densi;es, represen;ng the seeds of all future structure: the stars and galaxies of today. Growth of stars & galaxies The expansion of space pulls everything apart. Gravity pulls maCer together Models show that gravity of dark maCer pulls mass into denser regions—the universe grows lumpier with ;me. Red regions are 0.0002 Kelvin hoCer than blue regions. MaCer is denser in blue regions Next Slide: Time evolu;on of a 3.3 Mly region. The movie transi;ons from the dark maCer density field to gas temperature (blue: cold, green: warm: white: hot) and then the colour scale shows increase in chemical elements in the Universe. The explosion are due to gas falling into on accre;on disks of supermassive black holes. Clicker Ques;on What observa;onal evidence do we have that the Universe started with the Big Bang? A. 
Hubble’s observa;ons that more distant galaxies appear to recede faster and therefore the universe is expanding. B.  The observa;on of primordial gas consists of 75% Hydrogen and 25% Helium. C.  The observa;on of the cosmic microwave background radia;on. D.  All of the above Clicker Ques;on What observa;onal evidence do we have that the Universe started with the Big Bang? A. 
Hubble’s observa;ons that more distant galaxies appear to recede faster and therefore the universe is expanding. B.  The observa;on of primordial gas consists of 75% Hydrogen and 25% Helium. C.  The observa;on of the cosmic microwave background radia;on. D.  All of the above One last piece of the puzzle Mysteries that need to be solved. 1) 
What caused the ;ny temperature/density fluctua;ons in the cosmic microwave background? 2) 
Why is the overall distribu;on of cosmic microwave background radia;on so uniform? An early episode of rapid infla2on can solve these mysteries! Infla;on Infla;on is a period of rapid expansion that is theorized to have occurred at about t=10-­‐38 seconds – during the par;cle era. Tiny quantum ripples are flung to enormous distances during infla;on. These ripples in density then become the seeds for all structures in the universe. © 2014 Pearson Educa;on, Inc. Cosmological Horizon Under normal circumstances, two points on the opposite side of the sky should not be causally connected…. otherwise there could be grave consequences! Infla;on also solves the problem of how these two points of cosmic microwave temperature know about each other. Infla;on Regions now on opposite sides of the sky were close together before infla;on pushed them far apart. © 2014 Pearson Educa;on, Inc. © 2014 Pearson Educa;on, Inc. Opportuni;es at Swinburne Inspire
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Closing credits All maCer & Energy squeezed into one point will be hot & dense! ✔ Our whole universe was in a hot dense state, ✔ Then nearly fourteen billion years ago expansion started. Wait... … ;me=1/H0 = 14 billion years Evidence: 1.  Galaxies recede at increasing speed with increasing distance 2.  75% H 25% He ✔ That all started with the big bang (Bang)! 3.  Cosmic microwave background radia;on at T=2.7 K …. ✗ As every galaxy was formed in less ;me than it takes to sing this song. ✗ A frac;on of a second and the elements were made. The first galaxies start to light up about 200 Helium Fusion stops at 3 minutes. million years a}er the Heavier elements are made in stars Big Bang. Download This presenta;on can be downloaded here: hCp://astronomy.swin.edu.au/~eryan/Outreach/STAV_Physics_2016.pdf 

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