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The Hubble Constant

Physics: Cambridge International GCSE Supplement, topic 6.2.9

The Hubble Constant

The Hubble Constant

The Hubble Constant

  • The Hubble constant (H0) links a galaxy’s speed and distance.
  • It is defined as the ratio of the speed at which the galaxy is moving away from the Earth to its distance from the Earth.
Current estimate

Current estimate

  • The formula to calculate it is H0=dvH_0 = \dfrac{d}{v}
  • vv is the speed the galaxy is moving away (m/s)
  • dd is the distance of the galaxy (m)
  • The current estimate of the Hubble constant is about 2.2 × 10-18 per second.
The age of the Universe

The age of the Universe

  • The equation dv=1H0\dfrac{d}{v} = \dfrac{1}{H_0} represents an estimate for the age of the Universe.
  • This suggests that, if galaxies are moving apart now, they must once have been much closer together.
  • This is strong evidence that all matter in the Universe was once at a single point, which is the idea behind the Big Bang theory.

Test yourself on The Hubble Constant

  • What does the Hubble constant represent?

  • Which equation defines the Hubble constant?

  • What is the approximate current value of the Hubble constant?

  • What does Hubble’s law suggest about the origin of the Universe?

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