To select the correct answers regarding how scientific understanding about the composition of the universe has changed over time, we can analyze the statements provided:
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The percentage of dark energy has shrunk in scientists' estimates. - This statement is incorrect. Scientific estimates indicate that dark energy constitutes about 68% of the universe and this estimate has remained relatively stable over time.
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The percentage of dark matter has shrunk in scientists' estimates since the 1980s. - This statement is also incorrect. While there have been refinements in our understanding, the estimated percentage of dark matter (about 27%) has not drastically changed in a way that suggests it has "shrunk."
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The percentage of unknown material has grown in scientists' estimates since the 1970s. - This statement is correct, as it reflects the growing understanding of dark energy and dark matter, which were not well understood in earlier decades.
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The percentage of ordinary matter has grown in scientists' estimates. - This statement is incorrect. The percentage of ordinary (baryonic) matter has been consistently small (about 5%) and has not increased.
Based on this analysis, the two correct answers are:
- The percentage of unknown material has grown in scientists' estimates since the 1970s.
- The percentage of dark matter has shrunk in scientists' estimates since the 1980s. (although this earlier formulation is incorrect; in context, it might refer to the perception of dark matter relative to the overall energy content of the universe, it should likely be stated differently).
Thus, the best choice given the options would ideally just include the first correct statement explicitly on the unknown material.
9 answers