Chapter 1: Scientific Method and Big Bang

Question 1

What is a hypothesis?

Answer 1

**An educated guess based on observation. Sometimes only one observation. **

Can be supported or rejected but cannot be proven to be true

Attempts to explain why “why” of something happening

Question 2

What is a theory?

Answer 2

**Summarizes a hypothesis (or group f hypotheses) that explain a set of observations, supported by repeated testing. **

• Considered valid as long as there is no form evidence to dispute it – not guanteed to be true but best we can formulate with current evidence
• therefore can also be rejected or supported
• Explains the “why” of something happening (just like hypothesis)
• Theory is much better formulated and tested than a hypothesis

Question 3

Similarity and Differences between theory and hypothesis

Answer 3

Theory and Hypothesis both attempt to explain the “why” of something.

When enough theory accumuates supporting a hypothesis, it becomes a theory

Therefore, theories are much better formulated and tested than hypotheses

Question 4

What is a law?

Answer 4

A law governs a body of observsations obvservations
Scientific laws DESCRIBE certain scien. observations but they do NOT explain why!
Instead they predict HOW things will happen

• at the time the law is made, no exceptions to it have been found

Question 5

How to tell the difference between a theory and a law?

And why do they typically go hand in hand?

Answer 5

Ask if the statement explains “why” something happens - this is a theory

if it describes “how” something WILL happen, it is a law.

Theory and Law typically go hand in hand becuase we cannot have a full explanation without a why.

Question 6

Explain the law of gravity and theory of universal gravitation to describe why theories and laws often go hand in hand

Answer 6

Law of Gravity (Newton):
predicts the behaviour of an object as it falls but does NOT explain WHY an object falls

Theory of Universal Gravitation (Newton) **
attempts to explain many observsations
that objects on Earth fall with a partiular accelaeration (one of the Law’s of gravity)
* that the earth’s moon and planets follow elliptical orbits (a Law of Planetary Motion)

Therefore, Newton’s Theory of Universal Gravitation provides the “why” that lies behind the Law of Gravity

Question 7

What is the Big Bang theory?

Answer 7

attempts to explain exactly what happened at the start of the Universe.

States that: At the birth of the Universe, time and space were created in a gigantic expansion that emanated from a singularity

Question 8

According to the big bang, what existed before the Big Bang?

Answer 8

There was no time, no space, no matter, no energy -> this was all contained in the singularity

Question 9

What is a singularity (think of a singularity in a black hole)

Answer 9

There is no readily understood definition to offer;
* however it can be said that a singularity is an area in SpaceTime where gravitational force is so high that all known laws of physics breakdown and do not apply
* Thus, we cannot fully understand what happens at a singularity

Question 10

What is unique about the singularity that the Big Big came from? What characteristics do we know to describe the singularity?

Answer 10

Unique because it can not be considered an area in space time because space and time did not exist before the expansion. This singularity can be thought of as the origin of space and time

**Characteristics: **
* infinitely small (ZERO volume) and infinitely dense
* all the matter, energy, space and time in our universe today was concentrated into a point with no spacial dimensions

Question 11

What is a gigantic expansion?

Synonyms for this?

Answer 11

Gigantic expansion AKA Cosmic Inflation: Refers to the initial inflationary period of the universe where universe expanded exponentially within a fraction of a second. in this tiny instant, the universe had a finite beginning (at least if you were inside of it – outside of it there was nothing)

• Was very got and dense during this time.

NOTE: The universe is still expanding but we use the worse cosmic inflation and gigantic expansion to refer to that initial period.

Question 12

Why does gigantic expansion not the same as a gigantic explosion

Answer 12

an explosion needs space to spread into - the expansion created space (and time)

Question 13

While many lines of evidence support the big bang, what are the 3 Pillars of Proof

Answer 13

1. Recession of stars/galaxies (as described by Hubble’s Law
2. The Characteristics of cosmic microwave background (CMB)
3. The abundance of light elements

Question 14

Describe who is Hubble and what are his amazing accomplishements?

Answer 14

Lived: 1889-1952

• He demonstrated that there are many galaxies in the universe – not just the one we are in
• He proved that the universe is expanding
• He showed us how to measure distances in space
• Hubble thought to have astronomy recognized as belonging to the subject of physics
• after his death the Nobel Prize committee officially made this recognition
• Hubble Space Telescope: NASA installed in 1990 in his honor - many discoveries still being made through this

Question 15

Describe the Doppler effect / Doppler shift

How does this help build toward our understanding of the 1st pillar of proof

Answer 15

When a sound is moving away from you:
wavelengths are stretched (longer)

When a sound is moving towards you:
wavelengths are shorter (compressed)

This results in hearing a different pitch depending on if sound moving away or towards

• Doppler’s discoveries were about soundwaves, but he theorized it would apply to lightwaves as well - helped build toward our understanding of the behaviour of lightwaves

Question 16

What is the behaviour of light wavelengths when light is moving towards vs. away from you

Answer 16

If light moving away from you:
* wavelengths are stretched (red-shifted)

If light moving towards you:
* wavelengths are compressed (blue-shifted)

Question 17

What is red-shifting?

Explain the significance of this

Answer 17

red-shifting occurs when light is moving away and it’s wavelengths are stretched – the light is moving toward the red end of the spectrum

this means it is losing energy, and if enough red-shifting occurs, the light may drop off the visible light spectrum

This is significant becuase red-shifting can tell us if an object is moving towards us or away from us in space, and also provides the explanation for early light red-shifting into microwaves

Question 18

Describe the electromagnetic spectrum, from the most stretched wavelengths to the most compressed

Answer 18

Electromagnetic Spectrum from least to most compressed
radio → Microwave → Infared → Visible → Ultraviolet → x ray → Gamma Ray

The electromagnetic spectrum describes all the possible frequencies of electromagnetic radiation.
* visible light is a type of electromagnetic radiation
* some of them cannot penetrate earth’s atmosphere
* red-shifting occurs when the wavelengths move toward the red end of visible spectrum (wavelengths stretch) and can even stretch into microwave or radio

Question 19

What were the discoveries that led to Hubble’s Law?

Answer 19

• Hubble discovered that galaxies are moving away from us in all directions
• He realized that the faster the light emitting object moving away, the greater the redshift.

Question 20

What is Hubble’s Law? (What does it state, what is the equation)

Answer 20

**Hubble’s Law: **
The velocity at which a galaxy is moving away is directly proportional to it’s distance from Earth

• therefore, an object twice as far away from earth will be receeding twice as fast

Equation for Hubble's Law

v = velocity (speed with direction)
Ho= Hubble’s constant (rate of expansion of Universe)
d= distance from earth

Question 21

What must be taken into account about Hubble’s Equation - Specifically Hubble’s Constant

Answer 21

Hubble assumed a constant rate of expandion of the universe - this has proven to be not true - the rate of the universe is actually increasing

Question 22

How does Hubble’s Law relate to the Big Bang Theory? Why is it the 1st pillar of proof?

Answer 22

• Glaxies receding in every direction implies an expanding universe
• Expanding universe implies there was a starting point (a key idea in BB)
• Implies that if you go back in time, Universe was much hotter and denser (consistent w BB)
• Red-shifting of light moving through space as universe expands (consistent w BB)

Question 23

How can we use Hubble’s equation to calculate distances in Space?

Answer 23

We can simply rearrange Hubble’s equation to caclulate distances in space.

remember that if Ho is innacurate (changes over time) the calculation will be innacurate

Question 24

What is Cosmic Microwave Background (CMB) Radiation?

Answer 24

the remenants of Early light produced by the Big Bang – the leftover radiation from the first light that was able to travel freely in the Universe

Question 25

Explain the Story of Where CMB came from?

Answer 25

• In the early universe, it was so hot and dense and light was constantly being scattered by particles
• eventually cooled down enough for hydrogen to form - the light produced by the BB could travel freely for the first time
• This light stretches and red-shifted as Universe expanded
• Eventually the light lost so much energy it dropped off the visible light spectrum and became microwave radiation (which we not detect as the CMB)

Question 26

When and how was CMB discovered?

Answer 26

in 1965 as “noise” in a very sensitive microwave radio receiver - was first thought to be pigeons nesting in the antenna.

Question 27

Relate CMB to the BB? How does it support the BB as the second pillar of proof?

Answer 27

Existance of CMB
* exactly what would be expected if the universe had originated from a hot, dense state and then expanded and cooled over billions of years.
* the only explanation that makes sense is that it is the remenants of early light produced by the BB initial expansion

Uniformity
* The CMB is remarkably uniform in all directions - supports the early uni as homogenous and isotropic (consistent w BB)

Temperature
* CMB has a temperature of about 2.7K, suggesting the Uni has cooled from its initally hot and dense state (consistent w BB)

Question 28

Was ALL early light red-shifted into microwaves? If so, where did the light we see today come from?

Answer 28

Yes, all the early light produced by the BB eventually shifted into microwaves as the Universe expanded, leaving a period of “dark ages” until the universe had cooled enough for star formation to begin and other sources of light to be produced

Question 29

What is meant by “adundance of light elements”

How does this support the BB as the 3rd pillar of proof?

Answer 29

This refers to the specific ratios of the various atoms of the lightests elements:

75% - Hydrogen
25% - Helium
Trace lithium

Relating to BB:
*Big Bang nucleosynthesis theory predicts the percentages of hydrogen (about 75%) and helium (about 25%) in the universe, with trace amounts of lithium
* they can be explained ONLY if they originated from one single ratio od the first subatomic particles of matter than can be formed from a super-hot environment
* the only way to get that one critical ratio is through a unique event like the BB

Question 30

Why is knowing the shape of the universe important?

Answer 30

answers many questions like:
how will the universe end?

Question 31

What are the three possible shapes of the universe?

Summarize their characteristics and the “fate of the universe” associated with each.

Answer 31

1. Sphere (Positive Curvature, Closed Universe)
* finite in size but without boundaries
* parallel lines would eventually meet
* would eventually stop expanding and start collapsing in on itself in a “Big Crunch”
* Total Density > Critical Density
* suggests creation of universes is cyclical

2. Saddle-Shaped (Negative Curvature, Open Universe)
* infinite
* expansion rate continues to increase forever
* parallel lines diverge
* Total Density < Critical Density
* “Big Freeze”

3. Flat Universe (No Curvature, Open)
* infinite in sptial exent
* parallel lines remain parallel
* expansion continues forever but expansion rate approaches 0
* Total Density = Critical Density

Question 32

Define critical density

Answer 32

the amount of matter that will result in a perfectly flat universe

Question 33

What determines the shape of the universe? Why?

Answer 33

• overall density of the universe
• amount of matter and energy the universe contains

because there affect space curvature and the shape of the universe refers to the geometry of the curvature of space time.

Question 34

How do we measure the shape of the Universe?

Answer 34

**we compate the total density of the universe to the critical density. **

We use a Density parameter (Ω):

Ω = 1 for critical density

Ω > 1 for positive curvature
* total density is greater than critical density
* the universe contains more than enough matter to pull evrything together and stop the expansion, evenetually collapsing in a “Big Crunch”

Ω < 1 for negative curvature
* total density is less than critical density
* there is not enough matter to stop the expansion, universe continues expanding at ever increasing rate until “Big Freeze”

Ω = 1 for flat Universe
* total density = critical density so the universe is flat.
* Uni contains the critical amount of matter that prevents it from pulling back together OR from expanding into oblivion

Question 35

What is the actual shape of our universe?

Answer 35

Through comparing total and critical density, scientists discovered the universe is almost flat with slight negative curvature

this means we are close to the critical density but the expansion rate is increasing

for the purposes of this course we will say it is flat

Question 36

Define the types of matter in our Universe and the % they make up

Answer 36

1. Conventional Matter
* stars, planets, etc
* less than 5%

2. Dark Matter
* matter we can not see because it gives off no electromagnetic energy, but we know it exists because we can detect its gravitational attractional to conventional matter
* 27% of the universe

3. Dark Energy
* a mysterious force that acts in opposition to gravity - repels matter
* possibly 70% of universe

Question 37

What would happen if there were ONLY conventional matter or ONLY Dark Matter?

How does Dark energy control the rate of expansion of the Universe

Answer 37

if there were only conventional matter, there would be so little density that we might as well turn off the lights - distances between stars would quickly become so great that we would only be able to see our sun

if there were only dark matter, this might be enough to slow the expansion and pull things back together into a big crunch

however, we know that the rate of expansion is still increasing
this is explained by Dark Energy , which seems to be the factor that controls the expansion of space.

Question 38

What does it mean if dark energy exactly counterbalances the kinetic energy of the big bang? Is this currently the case?

Answer 38

this would mean we are at the critical value of 1 for density parameter - flat universe.

since the expansion rate is increasing, we are close to flat with slight negative curvature

Question 39

What methods are used to determine the age of the universe?

Answer 39

Several methods are used to estimate the universe’s age, including:

**Radioactivity: **Measuring the age of old stars by the decay rates of radioactive elements.
Hubble’s Expansion Constant: Using the expansion rate of the universe to estimate how long it has been expanding.
Cosmic Microwave Background Radiation: Analyzing the CMB data to model the early universe’s conditions and estimate its age.

Question 40

How do we use radioactivity to determine the age of the universe? What estimates of age of universe have been made using this method?

Answer 40

Certain elements have components that are radioactive (break down at fixed rates to form other components and energy)

Steps:
* observe the compositions of gases around old stars
* know exact radioactive processes required to produce these gas compositions from the very first elements in BB
* know all the time factors involved in breaking down one component to yield others

Therefore, the discovery of old stars helps estimate a minimum age of the universe

estimates brtween 11.5 and 17.5 billion years old
one star was found and dated at 13.2 billion years, so universe must be older than that

Question 41

How can we use Hubble’s Constant to determine the age of the Universe?

What discoveries for the age of Universe were made using the Hubble Space Telescope?

Answer 41

Hubble’s constant is the rate of expansion of the universe. Since the rate of universe is actually increasing, refinements have been made to H (primarily based on shape/density parameters)

We can use equation to determine age of most distant light sources.

In 2002, Hubble Space Telescope found some white dwarf stars, a prime candidate for dating.
All stars in this cluster gave dates between 12 and 13 billion years.
Considering it would have taken less than 1 billion years to cool sufficiently to form a star:
Universe must be between 13 and 14 billion years old.

Question 42

What are white dwarfs and why are they prime candidates for dating to estimate age of universe?

Answer 42

White Dwarf: remenents of stars that have consumed all their fuel

to have gone through whole life cycle of a star, they must be very old, thus prime candidate for dating

Question 43

How can the Cosmic Microwave Background Radiation be used to determine the universe’s age?

What estimate has been made of the universe’s age based on this?

Answer 43

CMB signals offer the most accurate view of conditions of the early universe. A model of the universe can be developped (which includes many assumptions) back to the time when BB produces the first photons.

Assuming right model has been made, Universe is 13.80 + or - 0.04 billion years

Question 44

What is the current estimated age of the universe based on the latest models and observations?

Answer 44

The most accepted current estimate of the universe’s age, primarily derived from the CMB data and refined by other observations, is about 13.80 billion years. This estimate combines the evidence from the universe’s expansion rate, the background radiation, and the oldest observed stars.

Question 45

What alternative theory does Neil Turok propose regarding the Big Bang and the universe’s expansion?

Answer 45

Neil Turok, a mathematical physicist at the Perimeter Institute of University of Waterloo, suggests that the Big Bang was not a unique event but one of many such occurrences in an endless cycle of expansion and contraction:

Cyclical Universe Model: Turok proposes that the universe consists of** two infinitely extensive sheets, separated by a thin layer of energy. Periodic instabilities cause these layers to collide, generating energy sufficient for a new Big Bang.**
This theory challenges the traditional view of a singular Big Bang and proposes a perpetual universe without a beginning or end.

Theory is new and still under construction