Define the Big Bang theory .

The Big Bang theory states that around 14 billion years ago , the universe began from a very small, extremely hot and dense region, then underwent a giant explosion and has been expanding and cooling ever since.

What does the balloon analogy show about the expansion of the universe?

Points on the balloon's surface (representing galaxies) all move further apart by the same amount as the balloon inflates, because space itself is expanding between the galaxies, not because the galaxies are moving through space.

What happens to the density of galaxies as the universe expands?

The density of galaxies falls , because the galaxies move further apart from each other as space expands between them.

What are the two main pieces of evidence supporting the Big Bang theory ?

Galactic red-shift and Cosmic Microwave Background (CMB) radiation .

Define Cosmic Microwave Background (CMB) radiation .

CMB radiation is electromagnetic radiation, in the microwave region (wavelength of around 1 mm), that remains from the early, hot, dense universe and has a generally uniform temperature of about 2.73 K .

Why was CMB radiation not discovered until 1964 , even though the Big Bang happened billions of years earlier?

Microwaves are absorbed by the Earth's atmosphere, so the radiation could not be detected until space flight allowed telescopes to be sent into orbit above the atmosphere.

As the universe expanded over the last 14 billion years, the wavelength of the radiation from the Big Bang ______ , shifting it from the gamma end of the spectrum into the microwave region.

As the universe expanded over the last 14 billion years, the wavelength of the radiation from the Big Bang increased , shifting it from the gamma end of the spectrum into the microwave region.

True or False? The CMB radiation is at a completely uniform temperature everywhere in the universe.

False. The CMB is mostly uniform at 2.73 K but has minuscule temperature fluctuations (around 0.00001 K), reflecting slight differences in the density of galaxies across the universe.

Define the Doppler effect (Doppler shift).

The Doppler effect is the change in the observed frequency and wavelength of waves that occurs when a wave source moves relative to an observer.

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

The wavelength decreases (λ – Δλ) and the frequency increases .

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

The wavelength increases (λ + Δλ) and the frequency decreases .

In the Doppler shift equation, Δλ means ' ______ '.

In the Doppler shift equation, Δλ means ' change in wavelength '.

Define reference wavelength , λ 0 .

The reference wavelength is the unshifted wavelength of light emitted by a source, measured in metres (m), used for comparison against the observed (shifted) wavelength.

True or False? The Doppler shift value, Δλ / λ 0 , has units of metres.

False. Δλ and λ 0 both have units of metres, so they cancel in the fraction; the Doppler shift has no units .

Redshift is the phenomenon of the wavelength of light appearing to increase when the source moves away from an observer.

Blueshift is the phenomenon of the wavelength of light appearing to decrease when the source moves towards an observer.

What happens to the frequency of light from a source that is redshifted?

The frequency decreases , since an increase in wavelength corresponds to a decrease in frequency.

The Doppler effect affects all types of waves, including ______ .

The Doppler effect affects all types of waves, including light .

How does the red-shift of distant galaxies compare with that of nearby galaxies, and what does this show?

Light from distant galaxies is red-shifted more than light from nearby galaxies. This shows that the greater the distance to a galaxy, the greater the redshift, and so the faster it is moving away from Earth.

How does galactic red-shift provide evidence for the Big Bang theory ?

Since more distant galaxies show greater redshift, all galaxies are moving away from Earth and from each other, faster at greater distances. This indicates the universe is expanding , as expected if it originated from a single point.

Why does the expansion of the universe cause light travelling through space to become redshifted?

As space expands, light waves travelling through it are stretched , increasing their wavelength, which is observed as redshift.

True or False? A galaxy's light shifts towards the blue end of the spectrum as the galaxy moves away from Earth.

False. A galaxy moving away from Earth causes its light's wavelength to increase , which is redshift (a shift towards the red end of the spectrum), not blueshift.

IGCSEPhysicsEdexcelPhysics (Modular)Unit 2Flashcards9. AstrophysicsCosmology

Cosmology (Edexcel IGCSE Physics (Modular): Unit 2): Flashcards

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FrontThe Big Bang Theory
Define the Big Bang theory.

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Cards in this collection (24)

Define the Big Bang theory.
The Big Bang theory states that around 14 billion years ago, the universe began from a very small, extremely hot and dense region, then underwent a giant explosion and has been expanding and cooling ever since.
What does the balloon analogy show about the expansion of the universe?
Points on the balloon's surface (representing galaxies) all move further apart by the same amount as the balloon inflates, because space itself is expanding between the galaxies, not because the galaxies are moving through space.
What happens to the density of galaxies as the universe expands?
The density of galaxies falls, because the galaxies move further apart from each other as space expands between them.
What are the two main pieces of evidence supporting the Big Bang theory?
Galactic red-shift and Cosmic Microwave Background (CMB) radiation.
Define Cosmic Microwave Background (CMB) radiation.
CMB radiation is electromagnetic radiation, in the microwave region (wavelength of around 1 mm), that remains from the early, hot, dense universe and has a generally uniform temperature of about 2.73 K.
Why was CMB radiation not discovered until 1964, even though the Big Bang happened billions of years earlier?
Microwaves are absorbed by the Earth's atmosphere, so the radiation could not be detected until space flight allowed telescopes to be sent into orbit above the atmosphere.
As the universe expanded over the last 14 billion years, the wavelength of the radiation from the Big Bang ______, shifting it from the gamma end of the spectrum into the microwave region.
As the universe expanded over the last 14 billion years, the wavelength of the radiation from the Big Bang increased, shifting it from the gamma end of the spectrum into the microwave region.
True or False?
The CMB radiation is at a completely uniform temperature everywhere in the universe.
False.
The CMB is mostly uniform at 2.73 K but has minuscule temperature fluctuations (around 0.00001 K), reflecting slight differences in the density of galaxies across the universe.
Define the Doppler effect (Doppler shift).
The Doppler effect is the change in the observed frequency and wavelength of waves that occurs when a wave source moves relative to an observer.
What happens to the wavelength and frequency of waves in front of a moving source?
The wavelength decreases (λ – Δλ) and the frequency increases.
What happens to the wavelength and frequency of waves behind a moving source?
The wavelength increases (λ + Δλ) and the frequency decreases.
In the Doppler shift equation, Δλ means '______'.
In the Doppler shift equation, Δλ means 'change in wavelength'.
Define reference wavelength, λ₀.
The reference wavelength is the unshifted wavelength of light emitted by a source, measured in metres (m), used for comparison against the observed (shifted) wavelength.
State the Doppler shift equation used to find the speed of a galaxy.
$\frac{λ - λ_{0}}{λ_{0}} = \frac{Δ λ}{λ_{0}} = \frac{v}{c}$
Where λ = observed wavelength (m), λ₀ = reference wavelength (m), Δλ = change in wavelength (m), v = velocity of the galaxy (m/s), c = speed of light (m/s).
A star has a reference wavelength of 435 × 10^-9 m. A distant galaxy emits the same light at 485 × 10^-9 m. Using $v = c \times \frac{λ - λ_{0}}{λ_{0}}$ with c = 3 × 10⁸ m/s, calculate the galaxy's speed relative to Earth.
$v = (3 \times 10^{8}) \times \frac{(485 \times 10^{- 9}) - (435 \times 10^{- 9})}{435 \times 10^{- 9}}$
$v = 3.4 \times 10^{7} m/s$
The galaxy is moving away from Earth (its light is redshifted).
True or False?
The Doppler shift value, Δλ / λ₀, has units of metres.
False.
Δλ and λ₀ both have units of metres, so they cancel in the fraction; the Doppler shift has no units.
Define redshift.
Redshift is the phenomenon of the wavelength of light appearing to increase when the source moves away from an observer.
Define blueshift.
Blueshift is the phenomenon of the wavelength of light appearing to decrease when the source moves towards an observer.
What happens to the frequency of light from a source that is redshifted?
The frequency decreases, since an increase in wavelength corresponds to a decrease in frequency.
The Doppler effect affects all types of waves, including ______.
The Doppler effect affects all types of waves, including light.
How does the red-shift of distant galaxies compare with that of nearby galaxies, and what does this show?
Light from distant galaxies is red-shifted more than light from nearby galaxies. This shows that the greater the distance to a galaxy, the greater the redshift, and so the faster it is moving away from Earth.
How does galactic red-shift provide evidence for the Big Bang theory?
Since more distant galaxies show greater redshift, all galaxies are moving away from Earth and from each other, faster at greater distances. This indicates the universe is expanding, as expected if it originated from a single point.
Why does the expansion of the universe cause light travelling through space to become redshifted?
As space expands, light waves travelling through it are stretched, increasing their wavelength, which is observed as redshift.
True or False?
A galaxy's light shifts towards the blue end of the spectrum as the galaxy moves away from Earth.
False.
A galaxy moving away from Earth causes its light's wavelength to increase, which is redshift (a shift towards the red end of the spectrum), not blueshift.

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