The Big Bang theory is one theory for the origin of the Universe - Edexcel - GCSE Physics - Question 4 - 2021 - Paper 1

Light from distant galaxies exhibits a redshift phenomenon, where the wavelengths of light are stretched as the galaxy moves away from us. This redshift indicates that these galaxies are receding, supporting the theory that the Universe is continuously expanding. The greater the distance to the galaxy, the higher the redshift, which correlates with the expansion.

Similarity: Both theories describe an expanding Universe.
Difference: The Big Bang theory posits that the Universe had a definite beginning, whereas the Steady State theory suggests that the Universe has no beginning and maintains a constant density through continual creation of matter.

Using Figure 4, the estimated velocity of the galaxy that is 15 Mpc away from the Earth is approximately 1050 km/s.

To calculate the gradient, we can use the formula: $ext{gradient} = \frac{\Delta y}{\Delta x}$. By analyzing the graph, the gradient is calculated to be approximately 70 km/s per Mpc.

The gradient represents the rate at which galaxies are moving away from Earth. However, various factors such as dark energy, changes in the rate of expansion, and local gravitational effects can influence this rate, leading to only an estimate of the age of the Universe rather than an exact measure.