The Big Bang Theory

    OCR
    GCSE

    The Big Bang theory postulates that the universe began from an extremely hot, dense singularity approximately 13.8 billion years ago and has been expanding ever since. Key evidence supporting this model includes the cosmological red-shift of light from distant galaxies, which demonstrates that recession velocity is proportional to distance. Furthermore, the detection of Cosmic Microwave Background Radiation (CMBR) provides the remnant thermal signature of the early universe, a phenomenon not explained by the competing Steady State theory.

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    Objectives
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    Exam Tips
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    Pitfalls
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    Key Terms
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    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating the universe began from a very small, extremely hot and dense region
    • Credit responses that describe the universe as expanding outwards, rather than exploding into existing space
    • Award 1 mark for identifying CMBR as gamma radiation produced at the Big Bang that has been stretched to microwave wavelengths due to expansion
    • Candidates must link the observation of Red-shift to the conclusion that distant galaxies are moving away from Earth
    • Award 1 mark for stating that the further away a galaxy is, the faster it is receding (Hubble's Law relationship)

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You have correctly identified Red-shift, but you need to explain *why* the wavelength changes (space expanding stretches the light)"
    • "Good recall of CMBR. To improve, specify that it comes from *all directions* and is uniform"
    • "Be careful not to say galaxies are expanding; clarify that the *distance between* galaxies is increasing"
    • "Excellent link between distance and speed. To reach the top band, explain how this supports the Big Bang over the Steady State theory"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating the universe began from a very small, extremely hot and dense region
    • Credit responses that describe the universe as expanding outwards, rather than exploding into existing space
    • Award 1 mark for identifying CMBR as gamma radiation produced at the Big Bang that has been stretched to microwave wavelengths due to expansion
    • Candidates must link the observation of Red-shift to the conclusion that distant galaxies are moving away from Earth
    • Award 1 mark for stating that the further away a galaxy is, the faster it is receding (Hubble's Law relationship)

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When discussing Red-shift, explicitly state that 'wavelength increases' and 'frequency decreases' to ensure maximum credit
    • 💡For Level of Response questions, clearly distinguish between the observation (what is seen) and the deduction (what it implies about the universe's history)
    • 💡Avoid vague terms like 'redder'; use precise terminology such as 'shifted towards the red end of the spectrum'
    • 💡If asked to critique the balloon model, mention that the balloon has a surface/centre while the universe does not

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Describing the Big Bang as an 'explosion' of matter into empty space rather than the rapid expansion of space itself
    • Stating that galaxies themselves are expanding, rather than the space between them increasing
    • Confusing the cause of Red-shift (velocity of recession) with the cause of CMBR (cooling of remnant radiation)
    • Failing to mention that CMBR is detected from all directions in the universe uniformly

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Cosmological Red-shift and the Doppler Effect
    Cosmic Microwave Background Radiation (CMBR)
    Expansion of the Universe from a Singularity
    Hubble's Law and Galactic Recession

    Likely Command Words

    How questions on this topic are typically asked

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