Which statement about motion in the universe is not true?
Your speed of rotation around Earth’s axis is faster if you live near the equator than if you live near the North Pole.
Except for a few nearby galaxies, all other galaxies are moving away from us.
The mysterious dark matter is the fastest-moving material in the universe.
Some stars in the Milky Way Galaxy are moving toward us and others are moving away from us.
The Correct Answer and Explanation is:
Correct Answer:
The mysterious dark matter is the fastest-moving material in the universe. — This statement is not true.
Explanation
Dark matter is a hypothetical form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter. Scientists estimate that dark matter makes up about 27% of the universe. However, contrary to the statement, dark matter is not the fastest-moving material in the universe. In fact, dark matter is believed to be relatively slow-moving, or “cold,” which is why it clumps together under gravity to form the scaffolding for galaxies and galaxy clusters.
The idea of “cold dark matter” is central to modern cosmology. “Cold” here means that the particles move slowly compared to the speed of light. This allows dark matter to remain gravitationally bound and help in the formation of large-scale structures in the universe. If dark matter were moving very fast (as in the “hot dark matter” model, like neutrinos), it would not cluster effectively, and galaxies might not form in the way we observe.
In contrast, other statements about motion in the universe are true:
- Earth’s rotation speed is indeed faster at the equator (~1670 km/h) than at the poles, due to the larger circumference traveled in the same time.
- The expanding universe means almost all galaxies (except a few gravitationally bound ones) are moving away from us — a discovery made by Edwin Hubble.
- Star motions in the Milky Way vary: some stars are approaching Earth (blueshifted), and others are receding (redshifted), based on their individual orbits and velocities.
Thus, the claim about dark matter being the fastest-moving material is incorrect and contradicts well-supported astrophysical theories
.