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A-Level Physics > Cosmology > Flashcards

Cosmology Flashcards

1
Q

What is the astronomical unit (AU)?

A

The mean distance from the centre of the earth to the centre of the sun

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2
Q

What is the value of 1 AU?

A

1.496 x 10^11 m

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3
Q

What is a light-year?

A

The distance travelled by light in one year

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4
Q

What is the value of a light year?

A

9.46 x 10^15 m

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5
Q

What is a parsec?

A

The distance at which a radius of 1 AU subtends an angle of 1 arcsecond

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6
Q

What is 60 arcminutes equal to?

A

1 degree

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7
Q

What is 60 arcseconds equal to?

A

1 arcminute

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8
Q

What is 1 arcsecond equal to?

A

1/3600 degrees

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9
Q

What is the value of 1 parsec?

A

3.1 x 10^16 m

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10
Q

What is stellar parallax?

A

The apparent shifting in position of a nearby star against a background of distant stars when viewed from different points on earth, during the earths orbit about the sun

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11
Q

What is the equation for the parallax angle?

A

p = 1/ d

p = parallax angle (arcseconds)
d = distance to nearby star (parsec)

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12
Q

What is the rule for the parallax angle equation?

A

It is only accurate for stars up to 100 pc away

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13
Q

What is the Cosmological principle?

A

The universe is isotropic, homogeneous and the laws of physics are universal

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14
Q

What does isotropic mean?

A

The universe is the same in all directions to every observer

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15
Q

What does homogeneous mean?

A

The matter is uniformly distributed, the universe has a uniform density

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16
Q

If a wave source is moving, what can happen to the waves?

A

They can become stretched or squashed

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17
Q

What happens if the wave source is moving towards the observer?

A

The wavefronts will appear squashed

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18
Q

What happens if the wave source is moving away from an observer?

A

The wave fronts will appear stretched

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19
Q

What happens to the wavelength and frequency of a wave in front of the source?

A

The wavelength decreases and the frequency increases

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20
Q

What happens to the wavelength and frequency of a wave behind the source?

A

The wavelength increases and the frequency decreases

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21
Q

Does the actual wavelength change when a wave appears stretched or squashed?

A

No - it is only the wavelength received by the observer that has appeared to have changed

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22
Q

What is the Doppler effect?

A

The apparent shift in wavelength occurring when the source of the wave is moving

23
Q

What is blue-shift?

A

If the galaxy is moving towards the earth then the absorption lines will move towards the blue end of the EM spectrum because the wavelengths appear shorter/ squashed

24
Q

What is red-shift?

A

If the galaxy is moving away from the earth then the absorption lines will move towards the red end of the EM spectrum because the wavelengths appear stretched

25
Q

What is the doppler effect equation?

A
26
Q

What is Hubbles law?

A

The recessional velocity of a galaxy is almost directly proportional to its distance from earth

27
Q

What is Hubbles law equation?

A
28
Q

The further away a star is from earth, the ______ it is moving away from us

A

Faster

29
Q

What is the latest estimate for the Hubble constant?

A

67.4 +- 0.5 km s^-1 M pc^-1

30
Q

What does distant galaxies having a greater red-shift represent?

A

The greater the distance from the earth, the greater the red-shift of the galaxy. This means the further away the galaxy, the faster it is moving away from earth. This shows how the universe is expanding

31
Q

What are the 2 key pieces of evidence to support the big bang theory?

A
  • Hubbles law
  • Microwave background radiation
32
Q

How does Hubbles law support the Big Bang theory?

A

Shows the universe is expanding through the red shift of light from distant galaxies

33
Q

How does microwave background radiation show the universe has expanded?

A

When the universe was extremely hot and young, space was saturated with high-energy gamma ray photons. The expansion of the universe means that space itself stretched over time. This expansion stretched the wavelength of these high-energy photons, so we now observe this primordial EM radiation as microwaves

34
Q

How does the temperature of 2.7K show the expansion of the universe?

A

The microwave background radiation has a general temperature of 2.7K. The universe was extremely hot and dense when it was young. Expansion of space over billions of years has reduced that temperature to around 2.7 K. The universe may be treated as a black body radiator - at this temperature the peak wavelength would correspond to about 1mm, in the microwave region of the spectrum

35
Q

What does space-time do?

A

Connects the 3 dimensions of space to a 4th, time/

36
Q

How do you calculate the age of the universe?

A

time = 1/ H0

H0 = hubbles constant

37
Q

What are the time marks in the evolution of the universe?

A
  • The Big Bang
  • 10^-35 s
  • 10^-6 s
  • 10^-3 s
  • 1 s
  • 100 s
  • 380 000 years
  • 30 million years
  • 200 million years
  • 9 billion years
  • 13.7 billion years
38
Q

What happend at The Big Bang?

A

Time and space are created. The universe is a singularity - it is infinitely dense and hot

39
Q

What happend at 10^-35 s?

A

The universe expands rapidly, including a phase of incredible acceleration known as inflation. There is no matter in the universe - it is instead all EM radiation in the form of high-energy gamma photons. The temperature is about 10^28 K

40
Q

What happend at 10^-6 s?

A

The first fundamental particles (quarks, leptons etc) and their antiparticles come into existence and gain mass. There is slightly more matter than anti-matter

41
Q

What happend at 10^-3 s?

A

The quarks combine to form the first hadrons such as protons and neutrons. Most of the mass in the universe was created within the first second through pair-production

42
Q

What happend at 1 s?

A

The creation of matter stops, once the temperature has dropped to about 10^9 K

43
Q

What happend at 100s ?

A

Protons and neutrons fuse together to form deuterium and helium nuclei, with a small quantity of lithium and beryllium. During this stage, about 25% of the matter in the universe is helium nuclei

44
Q

What happend at 380,000 years?

A

The universe cools enough for the first atoms to form. The nuclei capture electrons. The EM radiation from this stage of the universe is what can be detected as microwave background radiation

45
Q

What happens at 30 million years?

A

The first stars appear. Through nuclear fusion the first heavy elements begin to form

46
Q

What happend at 200 million years?

A

Our galaxy, the milky way, forms as gravitational forces pull clouds of hydrogen and existing stars together

47
Q

What happens at 9 billion years?

A

The solar system forms from the nebula left by the supernova of a large star
- About 1 billion years after the sun forms, the remaining material forms the earth and other planets
- About 1 billion years after the earth forms, primitive life is believed to have begun on earth

48
Q

What happens at 13.7 billion years?

A

200,000 years ago the first modern humans evolve. The temperature of the Universe is 2.7K

49
Q

What is dark energy?

A

A type of energy that permeates the whole universe and opposes the attractive gravitation force between galaxies via the exertion of a negative pressure

50
Q

What is dark energy used to explain?

A

Why the universe is expanding

51
Q

What percentage of all energy in the universe is dark energy?

A

68%

52
Q

What is dark matter?

A

Matter which cannot be seen and does not emit or absorb EM radiation

53
Q

What is dark matter used to explain?

A
  • The velocity of an object within a galaxy is expected to decrease as its moves from the galaxies centre
  • This is the case for smaller mass systems but not the case in larger mass systems eg. entire galaxies
  • This means mass is not concentrated in the centre of galaxies - it is spread out
  • However, all observable mass of a galaxy is observed to concentrate in the centre of galaxies
  • Therefore, there must be another type of matter that cant be observed - this is known as dark matter
54
Q

What percentage of mass in the universe is thought to be dark matter?

A

27%

A-Level Physics (23 decks)

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