A student describes a model in which the Universe expands but its average density stays constant because matter is continuously created.
Which identifies the model and explains why matter must be created?
Big Bang; expansion would otherwise increase the density.
Steady State; expansion would otherwise decrease the density.
Big Bang; expansion would otherwise decrease the density.
Steady State; expansion would otherwise increase the density.
94 exam-style questions on Edexcel GCSE Physics 7.2 The Universe and red-shift, covering 7.2.1 Big Bang and Steady State theories, 7.2.2 Evidence for the Big Bang, 7.2.3 The Doppler effect and red-shift, 7.2.4 Red-shift as evidence for an expanding Universe, and 7.2.5 The CMB and the accepted model. Each one has a worked solution and a mark scheme showing where the marks go.