Is the majority of dark matter baryonic or nonbaryonic?

Question

BlackTom AI · Accepted Answer

To tackle the question, let's lay out the key context about dark matter composition in the universe.
Option a: 'We have no clue.' This is not accurate given current cosmological evidence. Precise measurements of the cosmic microwave background, large-scale structure, and nucleosynthesis constrain the nature and amount of dark matter, making a blanket statement of having no clue inconsistent with data.
Option b: 'Nonbaryonic.' This is the supported view. Observations show that the total matter density is about five times the density of baryons, with dark matter making up roughly 27% of the universe and baryons only about 5%. Big Bang nucleosynthesis limits the baryon density to a small fraction of the total, and the gravitational effects attributed to dark matter cannot be explained by ordinary matter alone. These lines of evidence point to dark matter being nonbaryonic.
Option c: 'Baryonic.' If dark matter were mostly baryonic, the baryon density inferred from primordial element abundances would account for a much larger fraction of the matter content than observed, conflicting with nucleosynthesis constraints and with microlensing searches that limit massive compact objects as the primary dark matter component. Thus this option conflicts with established cosmological measurements.
In summary, the combination of cosmic microwave background data, large-scale structure, and Big Bang nucleosynthesis constrains the baryon density to be too small to account for all dark matter, leading to the conclusion that the majority of dark matter is nonbaryonic. The other options misinterpret the evidence or rely on outdated or incompatible assumptions.

Is the majority of dark matter baryonic or nonbaryonic?单项选择题

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