v = H o d Hubble s Law: Distant galaxies move away fastest Velocity (v) is proportional to Distance (d):

Transcription

1 Hubble s Law: Distant galaxies move away fastest Velocity (v) is proportional to Distance (d): v = H o d The Hubble Constant was measured after decades of observation: H 0 = 70 km/s/mpc Velocity (km/s) Distance (Mpc) This allows us to calculate the age of the universe!

2 The Age of the Universe! Imagine a galaxy at a distance d, moving away at speed v! At some time in the past (t) it was in the same place as our galaxy.! This time is the age of the universe.! t = d / v! But from Hubble s law we know that: v = H o x d! So the age of the universe is:! t = d / (H o x d) = 1/H o! H o =70 km/s/mpc! t = 1/H o = about 14 Billion Years

3 The Big Bang! The further back in time we go, the closer the galaxies are! So the density was higher in the past.! At some point, when all the galaxies were together, the density would have been enormous!! The initial explosion of matter is called: The Big Bang! However, the Big Bang, was not an explosion which occurred in one place: it was everywhere. The Big Bang Theory attempts to explain the origin of the Universe using the laws of physics and observations. As time goes by, the Universe cools down, and goes through different phases, like steam cooling to become water, then ice.

4 The Universe Began Hot then cooled down

5 Early Universe Story Part 0: The Mysterious Origin... The Universe s first instant was very hot and dense Before a time of seconds, our present laws of physics cannot explain the Universe!! Perhaps a Theory of Everything someday will. Another mystery: what happened before the Big Bang? Perhaps there was no before : time began then. But some cosmologists are trying to explain what could have caused the Big Bang

6 Early Univ. Part I: The First Matter In the beginning, there were photons of high energy Some of this energy become matter (E=m c 2 )! The universe went from being radiation dominated to being matter dominated. Both matter and anti-matter were produced. When matter touches anti-matter both annihilate! photon

7 After the annihilations, there was slightly * more matter than anti-matter. (& we don t know why!) This mass consisted of protons, neutrons and electrons...that became atoms that became...us! To understand how this matter formed we need to reproduce conditions like those at the Big Bang. We can create such high temperature environments by colliding particles together at high energy. *only % more!

8 Particle accelerators help us understand the conditions that occurred during the Big Bang SLAC: Stanford, CA

9 The LHC discovered the Higgs particle... resulting in a Nobel Prize (2013) Large Hadron Collider, Europe

10 Part II: The First Elements (Nuclei)! Today, the Universe is made up of:! Hydrogen (H) & Helium (He) -- 99%! Lithium (Li) & Deuterium (D, and isotope of H)! Heavier elements like: C, N, O! We know that the heavy elements are made inside stars by nuclear fusion.! Stars can also make He, but not as much as is found in the universe! Where did the Primordial He & Li come from?

11 Primordial Nucleosynthesis! The early (primordial) universe was as hot as the inside of a star!! So hot that atomic nuclei were made (synthesized) by nuclear fusion.! This is called primordial nucleosynthesis! New elements (like Li & He) can be made.! This happened a few minutes after the Big Bang.! Observations have confirmed that the ancient universe contains these elements... as predicted by the Big Bang Theory. Some primordial reactions

12 Part III: The First Atoms! The early universe was a hot plasma (ionized)! Electrons floated freely, and collided with photons of light.! Light could not travel far; the universe was opaque.! 380,000 years after the Big Bang, it had cooled to 3000 K! Electrons joined protons to form the first Hydrogen atoms Ionized H Neutral H! The universe become transparent.

13 ! When the first atoms formed, light was free to travel through space.! The Big Bang Theory says we should still see this light today.! But the expansion of the universe would have stretched these light waves out...into microwaves.! So, the universe should have a Cosmic Microwave Background! It should have a temperature of just 3 K.

14 Looking Back Towards the Early Universe The farther out we look in space the farther back we look in time. CMB

15 Cosmic Microwave Background! In the 1960 s, two researchers (Penzias and Wilson) were calibrating horn antenna! (a type of telescope sensitive to microwaves)! They detected a static hiss which was not instrumental They found a bird s nest in their antenna. And removed it.

16 Cosmic Microwave Background! To their surprise, the static remained.! It came from every part of the sky.! So it could not be from our solar system! It had a black body spectrum with a temperature of just 3 K. They had discovered the Cosmic Microwave Background predicted by the Big Bang Theory They won the Nobel Prize in Physics in 1987!

17 Predictions of the Big Bang Theory! Like any good theory, the Big Bang Theory makes predictions which must be confirmed by observation.! The Big Bang Theory predicts: 1. The universe is expanding 2. A Cosmic Microwave Background (CMB) 3. The abundances of light elements (H, He, Li...) These predictions have been confirmed by observations. But...

18 Challenges to the Big Bang Theory! The microwave background came from the early universe! It was observed to be very smooth! This was a problem.! How could a smooth early universe turn into the clumpy universe we have today, with clusters and superclusters of galaxies? To explore this mystery, NASA launched the Cosmic Background Explorer satellite (COBE)

19 COBE Satellite! COBE observed the C.M.B., the echo of the Big Bang! It measured the temperature of this light to be: 2.7 K (from Wien s Law)! This matches theoretical predictions of the Big Bang Model

20 COBE Satellite! COBE also took a picture of light coming from the origin of the universe! The light was clumpy : it shows bright and dark spots.! This proves the early universe isn t completely smooth Map of the CMB over the entire sky

21 Cosmic Microwave Background (CMB) 2010 data! Newer observations revealed the CMB in more detail.! The brighter spots come from regions of higher density! These regions can eventually grow to become clusters of galaxies!

22 newest data from Planck sat. (2014)

23 The largest structures in the universe are walls of galaxy clusters. They are over 1 Million Light Years across. anim.