Chapter 1 - Unit 1 PDF

Preview

Summary

Download Chapter 1 - Unit 1 PDF

Description

Chapter 1: Scientific Theory & Big Bang The Scientific Method  Theory, Law & Hypothesis - Not the same thing!

Hypothesis: educated guess based upon observation; supported or rejected but can't be proven Theory: summarizes a hypothesis that is supported by repeated testing and observation; valid until evidence to dispute it 

Hypothesis > Theory with enough evidence to support it, since both explain why theories better because better formulated and tested

Law: explains a body of observation 

No exceptions found, explains but doesn't describe o

Ex) Newton's law of gravity: explains behaviour of an object as it falls but not why it falls

Theory: Why ||| Law: How

The Big Bang  

Explains what happened at the very beginning of the Universe Singularity: no real, official definition but it is an area in space-time where gravitation force is so high that all known laws of physics break down and do not apply o



Time and space were created in a gigantic expansion at the birth of the universe

Gigantic Expansion: (Not equivalent to gigantic explosion(because explosion would need already existent space)) Think of infinitely small balloon expanding in a fraction of a second and keeps going. Time and space has beginning if you're inside the balloon.

Three Pillars of Proof (observations made, the evidence from the Big Bang): 

Recession of stars/galaxies (as described by Hubble's Law)



The characteristics of cosmic microwave background radiation



The abundance of light elements

Hubble's Law: Edwin Hubble (1889-1953) 

Demonstrated that there were many galaxies in the Universe (not just Milky Way we are currently in)



Proved that the universe is expanding



Showed us how to measure distance in space

Hubble Telescope: huge optical telescope in Earth's orbit

Light's Redshift & Hubble's Law 

An increase/decrease in the frequency of sound, light &other waves as the source and observer move toward/away from one another o





Effect causes the sudden change in pitch such as passing sirens, and redshifts seen by astronomers

Train coming towards you sounds different from going away (apparent change): Doppler Shift/Effect

Light waves similar when moving towards or away (proven by Keeler) o

If towards, wavelength appear to shorten (more to blue spectrum becoming "blueshifted")

o

If away, wavelength appears lengthened (move to red spectrum, becoming redshifted)

Speed of Light 

Fixed, where Hubble observed changes in speed of light (from star) Stars had to be moving away from Earth

o o

Applied to everything he could see, the Universe had to be expanding with the light waves moving through it

Further Away 

Longer it takes to arrive, red-shifted when finally does Red shift used to measure distance of stars or galaxy's from Earth

o

Hubble Law:



v is speed in km/s (obtained from amount of redshift)



d is distance of star/galaxy from Earth in parsecs



Ho is Hubble's constant (Speed of expansion of the Universe, assumed to be constant.. Kind of wrong, but still assume constant!)

Cosmic Microwave Background Radiation 

Extremely hot first seconds and then expanded and cooled. Hot light photons from early, lost energy dropped from visible light to microwave energy range - that constitutes the Cosmic Microwave Background (CMB) that we can still see today o

About the same pattern of distribution throughout all parts of the Universe - last remnants of light/heat energy of Big Bang. Universe temp should be 0K but is 2.767 K

Abundance of Light Elements 

3rd Pillar: ratio of all the various atoms of the three lightest elements: H (75%) He (25%) and Li (trace)

o

ONLY explained if originated from one single ratio of the first subatomic particles of matter (from super-hot environment)

Shape of the Universe 

How will the universe end?



Could be three shapes o

Sphere/positive curvature: would be finite size but without boundary. This model greatly depends upon there being sufficient matter in the universe that gravity can eventually pull things back together

o

Open/negative curvature: 'saddle shaped', infinite and unbounded. Parallel lines eventually diverge, expands forever with expansion rate never approaching zero

o

Flat: you can imagine this kind of universe by cutting out a piece of your balloon material and stretching it out with your hands

______________________ 1. Positive Curvature: like a sphere; "closed" universe: finite in size but without a boundary. Closed in time, eventually stop expanding and then contract in a "Big Crunch" - cyclical event: bang a universe then crunch a collapse and on and on (ball goes up and back down) 2. "Open" or Negative Curvature: saddle-shaped; parallel lines diverge, infinite and unbounded expand forever, expansion rate never approaching 0 (ball keeps going up) 3. Flat: Infinite in spatial extent and have no boundaries, parallel always parallel, always expanding but expansion rate does approach 0 (ball goes up and up but eventually appears to hang there) 

Dark matter affects gravity, it acts in the opposition to gravity and repels matter



Dark energy is the force that seems to control the expansion of space



Right now we seem to be accepting that the universe is almost perfectly flat

Density Parameter - Critical    

- Curvature: insufficient matter around to allow gravity to act and stop expanding; DP < 1 + Curvature: more than enough matter around to allow gravity to pull everything back together DP > 1 (or Ωo > 1) Flat: exactly the 'critical' value of matter around that will prevent the Universe from pulling back together or expanding indefinitely to oblivion DP = 1 (or Ωo = 1)

Affect Gravity? 

Conventional matter: stars, planets, asteroids, comets, etc. (...