Big Bang and Steady State Theories - Past exam questions (6 mark) (1) * Scientists believe that the Universe is expanding. Describe how careful observation of electromagnetic radiation from distant galaxies as well as from the whole of space gave evidence supporting the Big Bang Theory. (6) (2) *b While the origin of stars is well understood, there is still much debate about the origin of the Universe. Two major theories about the origin of the Universe are the Big Bang and the Steady State theories. Some evidence supports both theories. Other evidence supports only one theory. By considering the evidence, discuss why one of these theories is preferred by most scientists. (6)
Examiner comments (1) Full marks could be obtained by a clear description of the observation of red-shift of light from galaxies together with either an appreciation of its significance in terms of an expanding universe or some detail about the process. This should lead to a brief description about how this supported the Big Bang theory. This should then be coupled with an understanding of the significance of another observation; cosmic microwave background radiation. Candidates were not asked to describe the Big Bang or Steady State theories in detail and many candidates devoted a large part of their answer in doing so. Some candidates used much of the available response area by effectively writing out the question again. Some common inaccuracies were to write about planets expanding or moving away and galaxies being red-shifted (rather than the light from those galaxies). Nevertheless, candidates have clearly found this topic interesting and many displayed a very detailed understanding. Results Plus: Examiner Comments This is a level two answer. There are some correct details about red-shift and CMBR; even though the candidate has described red-shift as a theory rather than an observation. In order to be in level three the candidate would have needed to explain that the red-shift is caused by the galaxies moving away from us and have written more detail about CMBR (for example that it is observed in all directions).
Examiner Comments (2) To gain full marks here, candidates would have to state what both pieces of evidence were and give an explanation of each of them, link this evidence to the appropriate theories and explain which theory was most likely on the basis of the evidence. This was answered confidently by many candidates and there were some excellent examples of candidates gaining full marks for well-presented discussions. It was encouraging to see that the topic is well understood. Marks were lost by some candidates because they described the two theories themselves rather than describe the evidence and its relevance. Results Plus: Examiner Comments There was good discussion of evidence but not linked to the theories. This acheived level 2, QWC appropriate, four marks.
Results Plus: Examiner Comments No marks were awarded here. Theories discussed but no evidence considered.
Mark scheme Question Number (1) QWC * Indicative Content A description to include some of the following facts: observation of visible light led to discovery of red-shift. galaxies are moving away from each other CMBR detected in radio telescopes space telescopes (such as COBE) gave more detail of CMBR Big Bang and Steady State theories were proposed distances to galaxies could be determined Big Bang could explain red-shift Steady State could explain red-shift The description gives some of the following details: red-shift means lower frequency / longer wavelength red-shift was greatest for the most distant galaxies red-shift means universe is expanding Big Bang / Steady State can explain an expanding universe only Big Bang could explain CMBR CMBR is residual radiation (6) Mark
from the Big Bang The description gives some of the following reasons for scientists beliefs observation of increasing red-shift with distance is a reason to believe in expanding universe Level 0 No rewardable material 1 1-2 a limited description of either red-shift or CMBR, e.g. light from galaxies was red-shifted OR Red-shift is evidence for Big bang. the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy 2 3-4 a description giving full detail of either red-shift or CMBR OR some detail of both red-shift and CMBR, e.g. light was seen to be shifted towards a longer wavelength. This means that the galaxies are moving away from each other. the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy 3 5-6 a detailed description of how both red-shift and CMBR give supporting evidence for the Big Bang theory, e.g. light was seen to be shifted towards a longer wavelength. This means that the galaxies are moving away from each other so the Universe must be expanding. This is evidence for the Big Bang theory. Cosmic Background Radiation coming from all directions provides further evidence for the Big Bang. the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors
Mark scheme Question Number (2) QWC * Indicative Content Mark A discussion linking some of the following points red shift linked to movement both theories have expanding Universe redshift support both CMB linked to ageing Universe Big Bang ageing, SS not CMB supports Big Bang only because only Big Bang has single origin (6) Level 0 No rewardable material 1 1-2 a limited discussion stating both pieces of evidence or limited detail about either red shift or CMB e.g. change in wavelength /red shift shows galaxies / stars moving away the answer communicates ideas using simple language and uses limited scientific terminology spelling, punctuation and grammar are used with limited accuracy 2 3-4 a simple discussion including both pieces of evidence and simple detail about either red shift or CMB e.g. a change in wavelength shows galaxies / stars moving away the answer communicates ideas showing some evidence of clarity and organisation and uses scientific terminology appropriately spelling, punctuation and grammar are used with some accuracy 3 5-6 a detailed discussion describing both pieces of evidence and drawing a conclusion e.g. a change in wavelength shows galaxies / stars moving away and CMB shows Universe has been changing with time and redshift supports both theories, CMB supports only Big Bang because Steady State has constant Universe the answer communicates ideas clearly and coherently uses a range of scientific terminology accurately spelling, punctuation and grammar are used with few errors