Explain why the Steady State Theory is no longer accepted as a model for the origin of the universe.

Edexcel A-Level Physics (9PH0) — 7.2 Capacitors · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Scientists have proposed different theories to explain the origin and evolution of the universe. The Big Bang Theory is currently the accepted model, but the Steady State Theory was once considered a competing explanation.

Model answer (5 marks)

The Steady State Theory proposes that the universe has always existed, is the same everywhere and at all times, and that new matter is continuously created as it expands.

However, the cosmic microwave background radiation (CMBR) is detected uniformly in all directions. The Steady State Theory cannot explain this background radiation.

Observations of distant galaxies show that the universe looked different in the past – the red‑shift of galaxies and the evolution of star types indicate change over time. This contradicts the idea that the universe is unchanging.

Because the Big Bang Theory accounts for the red‑shift, the CMBR and the observed evolution of the universe, it is the more accepted model.

Examiner tips

  • Use the exact phrases from the mark scheme – e.g. "uniformly in all directions" for CMBR. Show the logical sequence: Steady State → predicts no CMBR → CMBR observed → contradiction. Mention red‑shift and evolution of stars as evidence for change. Conclude with the Big Bang being better supported.

Common mistakes

  • Confusing the Steady State Theory with the Big Bang – e.g. saying the Steady State predicts a CMBR. Omitting the observation that the universe has evolved (e.g. red‑shift). Using vague language like "the universe is different" without specifying evidence.

Mark scheme (5 marks)

  1. The Steady State Theory suggests the universe has always existed / the universe is the same at any time and any place / matter is continuously created as the universe expands
  2. Cosmic microwave background radiation (CMBR) is detected in all directions / all around us
  3. The Steady State Theory cannot explain / does not account for CMBR
  4. Observations show that different types of stars / the universe looked different in the past / the universe has evolved over time
  5. The Big Bang Theory accounts for all the experimental evidence (red-shift and CMBR), so it is the more accepted / better-supported model

Key terms in this question

Steady State Theory

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