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A Level Physics > Module 5: Chapter 20 - Cosmology (the Big Bang) > Flashcards

Module 5: Chapter 20 - Cosmology (the Big Bang) Flashcards

1
Q

What is the Cosmological Principle?

A

The idea that the universe has the same large scale structure when observed from any point within it

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2
Q

What are the 3 assumptions of the cosmological principle?

A

When viewed on a large enough scale:
* The universe is homogeneous
* The universe is isotropic
* The laws of physics are universal

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3
Q

What is an Astronomical Unit (AU)?

A

The average distance from the earth to the sun

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4
Q

What is 1 AU in metres?

A

1.50x10¹¹m

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5
Q

What is a Light-year (ly)?

A

The distance travelled by light in a vacuum in a time of one year

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6
Q

What is a light year in metres?

A

9.46x10¹⁵m

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7
Q

What is a parsec (pc)?

A

The distance at which a radius of one AU subtends an angle of one arcsecond

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8
Q

What is one parsec in metres?

A

3.0857x10¹⁶m

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9
Q

What are the astronomical distances in increasing length?

A

Astronomical Unit, Light-year, Parsec

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10
Q

What are arcminutes and arcseconds?

A

Measurements of angle

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11
Q

What is 1 arcminute in degrees?

A

(1/60)°

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12
Q

What is 1 arcsecond in degrees?

A

(1/3600)°

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13
Q

What is 1 arcsecond in arcminutes?

A

(1/60)°

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14
Q

What is stellar parallax?

A

A technique used to determine the distance to stars that are relatively close to the Earth (less than 100pc) by comparing their apparent positions against distant stars at times 6 months apart

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15
Q

What is parallax?

A

The apparent shift in the position of a relativelyt close star against the backdrop of much more distant stars as the Earth orbits the Sun

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16
Q

What is the equation for distance from stellar parallax?

A

d = 1/p

d = distance, p = parallax angle

d is measured in parsecs and p is measured in arcseconds

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17
Q

What is parallax angle measured in?

A

arcseconds

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18
Q

Why is 6 months the period of time between measurements in stellar parallax?

A

The earth will have rotated half of the way around the sun

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19
Q

Why is stellar parallax limited to stars less than 100pc from the Earth?

A

As the distance increases, the parallax angle decreases, eventually becoming too small to measure accurately

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20
Q

What is the doppler effect?

A

The change in the observed frequency and wavelength of waves due to the relative motion between the emitter and the observer of the wave compared with the observed wavelength/frequency when there is no relative velocity

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21
Q

What is red shift?

A

The lengthening of the observed wavelength that occurs when a wave source is moving away from the observer

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22
Q

What is blue shift?

A

The shortening of the observed wavelength that occurs when a wave source is moving towards the observer

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23
Q

How can you determine if a galaxy is moving towards or away from the earth?

A

By observing the absorption spectrum from distant galaxies, you can recognise the characteristic patterns of lines from different elements, such as helium. You can then compare these spectra to that of those produced in a laboratory on earth and determine whether the pattern of lines has been shifted towards the red or the blue end of the spectrum. Red-shift = relative velocity away, blue-shift = relative velocity towards

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24
Q

What is the doppler equation?

A

Δλ / λ ≈ Δf / f ≈ v / c

λ = source wavelength, Δλ = change in wavelength recorded
f= source frequency, Δf = change in frequency recorded
v = magnitude of relative velocity between the source and observer, c = speed of light

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25
Q

What are 3 uses of the doppler effect?

A
  • Measuring the speed of motorists
  • Measuring the speed of a tennis serve
  • Measuring the relative speed of galaxies
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26
Q

How does speed affect the doppler shift?

A

the greater the relative speed, the greater the doppler shift

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27
Q

How can the doppler effect be used to monitor the speed or motorists or record the speed of a tennis serve?

A

The radar gun will emit microwaves, these microwaves are reflected off the moving object allowing it to act like a source of the microwaves. The doppler shift of the reflected microwaves against the original emitted microwave can be used to determine the speed

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28
Q

What is a receding galaxy?

A

A galaxy moving away from the earth

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29
Q

What is an approaching galaxy?

A

A galaxy moving towards the earth

30
Q

How would a binary star system be shown using redshift data?

A

Binary star systems orbit a common centre of mass. Therefore, one star would be showing redshift as it is moving away from the observer, and one would be showing blue shift as it is moving towards the observer

31
Q

Plot a graph of the effect of the doppler effect (redshift vs blue shift) against velocity for the image below

A
32
Q

What are the 3 types of binary star systems?

With descriptions

A
  • Detatched binary - 2 individual stars orbit a common point
  • Semidetatched binary - 2 stars orbit with a mass transfer stream orbit a common point
  • Contact binary - 2 star cores share a common envelope and orbit a common point
33
Q

What is the big bang?

A

The theory that at a moment in the past all the mattter in the Universe was contained in a singularity, the beginning of space and time, that expanded rapidly outwards

34
Q

What is hubbles law?

A

The recessional speed, v, of a galaxy is directly proportional to its distance, d, from the Earth. v ∝ d.

35
Q

What were the 2 observations that led to hubbles law?

A
  • Light from the vast majority of galaxies is red-shifted, therefore they have a velocity away from the Earth
  • The further away the galaxy is, the greater the observed red-shift and therefore the galaxy has a greater recessional velocity
36
Q

What is the equation for hubbles law?

A

v ≈ H₀d

v = recessional speed, d = distance from Earth, H₀ = Hubbles Constant

37
Q

What is hubbles constant, H₀?

A

The gradient of a plot of recessional speed of galaxies against distance from the Earth

38
Q

What is the value of hubbles constant, H₀?

A
  • 2.2x10⁻¹⁸ s⁻¹
  • 67.80 kms⁻¹ Mpc⁻¹
39
Q

What are the units for hubbles constant?

A

Hubbles constant = recessional velocity / distance, therefore the SI units would be s⁻¹. However, cosmologits tend to use velocity in km s⁻¹ and distances in Mpc. Therefore it has an alternative unit of km s⁻¹ Mpc⁻¹

40
Q

What is the exapanding universe?

A

The idea that the fabric of space and time is expadning in all directions and that as a result any point, in any part of the Universe, is moving away from every other point in the Universe, and that the further the points are apart the afaster their relative motion away from each other

41
Q

What does “The universe is homogeneous” mean?

A

Matter is distributed uniformly throughout the Universe (it’s density is the same everywhere) and the same type of structures (galaxies) are seen everywhere

42
Q

What does “The universe is isotropic” mean?

A

The Universe looks the same in all directions to every observer. It follows that there is no centre or edge to the Universe

43
Q

What does “The laws of physics are universal” mean?

A

The theories and models tested on earth can be applied to everything within the Universe over all space and time

44
Q

How is hubbles law evidence for the expanding universe?

A

As light from almost all galaxies observed is red-shifted, it indicates that all galaxies are moving apart from each other. This can be explained by the expanding universe model, which states it is not simply the galaxies moving away from each other, but the actual space itself expanding. This explains why almost all galaxies show red-shift and why the further the points are apart, the greater the relative motion apart

45
Q

What are the 2 key pieces of evidence for the Big Bang?

A
  • Hubbles Law
  • Cosmic Microwave Background Radiation (CMBR)
46
Q

What is Cosmic Microwave Background Radiation?

A

The microwave signal of uniform intensity detected from all directions of the sky, which fits the profile for a black body at a temperature of 2.7K

47
Q

How is CMBR evidence for the Big Bang?

A

The Big Bang theory predicted that when the Universe was young and extremely hot, space was saturated with high-energy gamma photons. The expansion of the Universe means that space itself was stretched over time. This expansion stretched the wavelength of these high-energy photons, so now we observe this primordial electromagetic radiation as microwaves. This expansion has also reduced the temperature of the Universe to 2.7K, treating the Universe as a black-body radiator - the peak wavelength would correspond to about 1mm which falls in the microwave region.

48
Q

How can we estimate the age of the universe?

A

We can estimate the age of the universe by assuming that it has expanded uniformly over time since the Big Bang. We can then use Hubbles law, v ≈ H₀d, and the fact that time = distance/velocity to determine the age of the universe:

49
Q

Why is the estimating for the age of the Universe using hubbles law only a very crude indication of the age of the Universe?

A

It assumes that the Universe has expanded uniformly since the Big Bang, however this is not the case. The expansion of the Universe is accelerating so it is a poor assumption to make

50
Q

Calculate the age of the Universe:

A
51
Q

What is the equation for the age of the universe?

A

Age of the universe ≈ 1/H₀

52
Q

What happened 0 seconds after the Big Bang?

A
  • Time and Space are created
  • The Universe is a singularity - it is infinitely dense and hot
53
Q

What happened 10⁻³⁵ seconds after the Big Bang?

A
  • The Universe expands rapidly, including a phase of incredible acceleration known as inflation
  • There is no matter in the universe, instead it is full of electromagnetic radiation in the form of high-energy gamma photons
  • The temperature is about 10²⁸K
54
Q

What happened 10⁻⁶ seconds after the Big Bang?

A
  • The first fundamental particles (quarks, leptons, etc) gain mass through a mechanism (that is not fully understood) involving the Higgs Boson
55
Q

What happened 10⁻³ seconds after the Big Bang?

A
  • The quarks combine to forms the first hadrons, such as protons and neutrons
  • Most of the mass in the Universe was created in the first seconds through a process of pair production (high-energy photons transofmring into particle-antiparticle pairs)
56
Q

What happened 1 second after the Big Bang?

A
  • The creation of matter stops after about 1 second
  • The temperature has dropped to about 10⁹K
57
Q

What happened 100 seconds after the Big Bang?

A
  • Protons and Neutrons fuse together to form deuterium and helium nuclei, along with a small quantity of lithium and beryllium nuclei - the expansion of the Universe is so rapid that no heavier elements are created
  • During this stage, about 25% of the matter in the Universe is helium nuclei
58
Q

What happened 380,000 years after the Big Bang?

A
  • The Universe cools enough for the first atoms to form - the nuclei capture electrons
  • The electromagnetic radiation from this stage of the Universe is what can be detected as microwave background radiation
59
Q

What happened 30 million years after the Big Bang?

A
  • The first stars appear
  • Through nuclear fusion within the stars, the first heavier elements are formed
60
Q

What happened 200 million years after the Big Bang?

A
  • The milky way forms as gravitational forces pull clouds of hydrogen and existing stars together
61
Q

What happened 9 billion years after the Big Bang?

A
  • The solar system is formed from the nebula left by the supernova of a larger star
  • After the sun is formed (1 billion years later) the remaining material forms the Earth and other planets
  • Another 1 billion years later and it is estimated that primitive life on Earth begins
62
Q

What happened 13.7 billion years after the Big Bang?

A
  • Around 200,000 years ago the first modern humans evolve
  • The temperature of the Universe is now 2.7K
63
Q

What percent of the universe is matter?

A

4.9%

64
Q

What percent of the Universe is dark matter?

A

26.8%

65
Q

What percent of the Universe is dark energy?

A

68.3%

66
Q

What is dark energy?

A

A hypothetical form of energy that fills all of space and would explain the accelerating expansion of the Universe

67
Q

What is dark matter?

A

A hypothetical form of matter spread throughout the galaxy that neither emits nor absorbs light - could explain the differences between the predicted and observed velocities of stars in galaxies

68
Q

The Big Bang theory initially predicted the universe expanding at a constant rate, however it is actually accelerating, how can this be explained?

A

The concept of dark energy is used to explain the expansion of the Universe. It fills all of space and is the source of energy that tends to accelerate the expansion of the universe

69
Q

What prompted the theory of dark matter?

A

Astronomers studying the doppler shift in light from galaxies found that the velocities of stars in the galaxies did not behave as predicted. It was expected that their velocity would decrease as distance from the centre of the galaxy increases, however they did not. These observations can only be explained if the mass is not concentrated at the centre of the galaxy. However, all the matter we can observe is concentrated at the centre of the galaxies leading to the idea that “dark matter” (which we cannot detect) is spread throughout the galaxy

70
Q

How can the speed of rotation of distant galaxies be determined?

A

You can use the doppler shift of opposite sides of the galaxy (which are rotating in opposite direction) to determine the linear speed of the rotation and therefore determine the angular speed of rotation

71
Q

IMPORTANT QUESTION

This graph shows the wavelength of light emitted from one star in a Binary star system. Calculate the radius of the star’s orbit

When measured in a laboratory on Earth, the wavelength with no doppler shift is 256.28nm
The maximum displacement from the equilibrium position in the line is 0.24nm

A
72
Q

What is the difference between luminous flux, luminous intensity, and luminous Emittance?

A
  • Luminous Flux is measured in Lumens, and is the radiant power emitted by a light source
  • Luminous Intensity is measured in Candela
  • Luminous Emittance is measured in Lux, and is the radiant power emitted by a light source per unit area (flux per area)

A Level Physics (29 decks)

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