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6.2.3Space Physics

THE Universe — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 9 parts Lesson 20 of 24 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Lesson summary

6.2.3 The Universe — IGCSE Physics Notes — IGCSE PHYSICS notes: Describe the Milky Way and the scale of the Universe using the light-year, and the evidence for the Big Bang from redshift, the CMBR and the Hubble constant.Milky Way — the galaxy containing the Solar System, one of …

  • Other galaxies
  • Definition
  • Observation
  • Conclusion
  • Redshift evidence
  • Stretching

Part 1 of 7The Milky Way and the Universe

Milky Way
  • Milky Way the galaxy containing the Solar System, one of many billions of galaxies in the Universe.
Galaxy
  • Galaxy a collection of billions of stars.
Diameter
  • Diameter the Milky Way is about 100 000 light-years across.
Other galaxies
  • Other galaxies they are much further away, from millions to billions of light-years.

Part 2 of 7The light-year

1Definition
  • Definition the distance travelled by light in space in one year.
2Value
  • 1 light-year is about 9.5 × 1015 m.
3Meaning
  • Meaning light takes 100 000 years to cross the Milky Way.

Part 3 of 7Redshift (Extended)

Observation
  • Observation light from distant galaxies has a longer observed wavelength, shifted towards the red end.
Cause
  • Cause the galaxies are moving away from us (recession).
Pattern
  • Pattern the further away a galaxy is, the greater its redshift and the faster it recedes.
Conclusion
  • Conclusion the Universe is expanding.

Part 4 of 7Big Bang theory (Extended)

Idea
  • Idea the Universe began from a single point about 13.8 billion years ago.
Redshift evidence
  • Redshift evidence expansion traced back leads to a very small, hot, dense beginning.

Part 5 of 7Cosmic microwave background radiation (Extended)

CMBR
  • CMBR microwave radiation observed from all directions in space.
Origin
  • Origin it was produced shortly after the Big Bang.
Stretching
  • Stretching it has been stretched into the microwave region as the Universe expanded.
Role
  • Role it is further evidence for the Big Bang.

Part 6 of 7Hubble constant and age (Extended)

Recession speed
  • Recession speed found from redshift.
Distance
  • Distance found from the brightness of a supernova.
Hubble constant
  • H₀ = v / d, the ratio of the speed of recession to the distance, about 2.2 × 10-18 per second.
Age of the Universe
  • Age of the Universe about d / v = 1 / H₀, assuming a constant rate of expansion.

Part 7 of 7More from the specification

1
Cosmic microwave background radiation
  • Cosmic microwave background radiation detecting uniform thermal background radiation across deep space provides an observational means to validate Big Bang models.
2
Nebula and star formation
  • A cloud of gas and dust, mostly hydrogen, collapses under gravity to form a protostar, which becomes a star when fusion starts.
3
Nuclear fusion
  • Hydrogen nuclei fuse into helium in the core, releasing energy because the products have a slightly smaller mass,
  • which is converted to energy.
4
Stellar life cycle
  • A star of the Sun's size stays in the main sequence and becomes a red giant,
  • then a white dwarf;
    • a much more massive star becomes a red supergiant and ends in a supernova leaving a neutron star or black hole.
5
Scale of the universe
  • The Earth orbits the Sun in the Milky Way galaxy, whose centre is a very large distance away, measured in light-years.
6
Element formation
  • Heavier elements form in fusion reactions in massive stars and are spread by supernovae.
7
Stable
  • Returns to its original position when tilted slightly.
8
Galactic redshift
  • Shift of galaxy spectral lines to longer wavelength due to recession.
9
White dwarf
  • Small, hot, dense core left by a low-mass star.
10
Background radiation
  • Radiation that is always present in the environment.
11
Planetary nebula
  • The shell of gas ejected by a red giant.
12
Fusion
  • Joining of light nuclei into a heavier one.
13
Reaction
  • The partner force acting on the other object.
14
Nebula
  • Cloud of gas and dust in which stars form.
15
Helium
  • Product of the fusion of hydrogen in stars.
16
Spectrum
  • Range of colours in white light.
17
v = H0d
What the symbols mean: v = recession speed of the galaxy (km s−1) · H0 = Hubble constant (km s−1 Mpc−1) · d = distance (Mpc)

Key terms

TermMeaning
Milky WayThe galaxy that contains the Solar System.
Light-yearThe distance light travels in one year, 9.5 × 10^{15} m.
RedshiftIncrease in the wavelength of light from a receding source.
CMBRMicrowave radiation from all directions, left over from the early Universe.
Hubble constantH₀ = v / d, the ratio of recession speed to distance.

Avoid these mistakes

1
Treating the light-year as a unit of time — it is a unit of distance.
2
Saying the Big Bang was an explosion at a place in space — it was the expansion of space itself.
3
Saying redshift means light turned red — it means the wavelength increased.
4
Using H₀ as the age — the age is 1 / H₀.

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