Chapter 1: Scientific theory and the Big Bang

hypothesis

educated guess based on observation, can be supported or rejected but not proven true

scientific theory

summarizes a hypothesis, explains a set of observations and supported by repeated testing, explains why something happens

law

governs a body of observations, predicts how they happen but not why

singularity

an area in space-time where gravitational force is so high that all known laws of physics break down and do not apply

gigantic expansion

refers to the rapid increase in size of the universe following the Big Bang, leading to the formation of galaxies and cosmic structures.

three pillars of proof for the Big Bang theory

1. recession of stars/galaxies described by Hubble’s law

2. the characteristic of cosmic microwave background radiation

3. the abundance of light elements

what did Edwin Hubble demonstrate (3)

• multiple galaxies in the universe

• the universe is expanding

• how to measure distance in space

Doppler shift/effect

when an object is approaching, sound waves are compressed. when the object is moving away where the sound waves are lengthened

explain red shift and how it proves the Big Bang theory

• Doppler effect → if light moves away from observer, the wavelength lengthens and moves into the red-spectrum/becomes red-shifted (approaching → blue-shifted)

• the greater the shift, the faster the object is moving

  • Hubble observed that stars and galaxies were all moving away from us by measuring their red shift

Hubble Law

v = H₀d

• v = speed in km/s

• d = distance of star/galaxy from earth in parsecs

  • H₀ = Hubble constant

Hubble constant

the speed of expansion of the universe, assumed to be a constant

cosmic microwave background

hot light photons from early periods of the universe lost energy and dropped from visible light range to microwave energy range, representing the last remnants of light/heat energy of the Big Bang’s initial expansion

abundance of light elements

the ratio of the three lightest elements: hydrogen (75%), helium (25%) and lithium (trace)

the abundance can only be explained if they had originated from one single ratio of the first subatomic particles of matter formed from a super-hot environment (Big Bang)

closed universe

• universe has a positive curvature, or a sphere shape.

• is finite in size but without a boundary, end up where you started

• are closed in time, will eventually stop expanding and contract in a big crunch

• depends on their being sufficient matter that gravity can pull things back together

  • production of universes is a cyclical event → bang then crunch

open universe

• have negative curvature, or are saddle shaped

• infinite and unbounded, expanding forever with expansion rate never approaching zero

• parallel lines eventually diverge

flat universe

• infinite in spatial extent with no boundaries

• parallel lines always parallel

  • expand forever but expansion rate approaches zero

density parameter - universe with negative curvature

less than 1, insufficient matter that allows gravity to stop expansion

density parameter - universe with poistive curvature

greater than 1, more than enough matter for gravity to pull everything back together

density parameter - universe with flat universe

=1, is the critical value of matter to prevent universe from pulling back or expanding

conventional matter

stars, planets, asteroids, comets

less than 5% of universe

dark matter

no electromagnetic energy, but can detect its gravitational attraction to conventional matter

about 27% of matter in universe

dark energy

acts in opposition to gravity by repelling matter

about 70% of matter in universe

controls the expansion of space by countering kinetic energy of Big Bang expansion

what shape is the universe right now?

at critical value where density parameter = 1

is almost flat (with slight negative curvature)

how to figure out age of universe

• observe compositions of gases around stars

• knowing exact radioactive processes required to produce these gas compositions from first elements created by Big Bang

  • knowing all the time factors involved in breaking down one component to yield others

estimated age of universe

11.5-17.5 billion years

from white dwarf star → 13-14 billion

from cosmic microwave background radiation → 13,8 billion years

white dwarf star

remnants of stars that consumed all their fuel and cooling off - is very old, a good candidate for dating

sandwich model of universe

proposed by Neil Turok, the universe consists of two infinitely extensive sheets separated by a thin layer of energy

this energy layer becomes unstable once in a while, gravity starts pulling things together and layers bounce together

at point of contact, sufficient energy is generated to produce a Big Bang

until next point of contact, universe continues to expand