Question

Discuss the possibility that star velocities at the edges of galaxies being greater than expected is due to unknown properties of gravity rather than to the existence of dark matter. Would this mean, for example, that gravity is greater or smaller than expected at large distances? Are there other tests that could be made of gravity at large distances, such as observing the motions of neighboring galaxies?

a) Gravity is greater than expected; other tests involve cosmic microwave background radiation
b) Gravity is smaller than expected; other tests involve gravitational lensing
c) Gravity is greater than expected; other tests involve galactic red shifts
d) Gravity is smaller than expected; other tests involve the behavior of dark matter

Answer 1

If star velocities at galaxy edges are explained by unknown properties of gravity, this implies gravity is stronger at large distances. Researchers also utilize gravitational lensing and cosmic microwave background radiation to test gravity on a cosmic scale, helping to comprehend the universe's structure and the role of dark matter.

Step-by-step explanation:

Galactic Star Velocities and Gravity

The observations that stars at the edges of galaxies move faster than expected led scientists to hypothesize the existence of dark matter. If, alternatively, this phenomenon is due to unknown properties of gravity, it would imply that gravity's influence is stronger than presently accepted theories predict, especially at large distances. However, the discovery of such anomalous gravitational behavior would necessitate a revision of our current understanding of physics.

Additional tests to understand gravity at large distances include studying the gravitational lensing effect, which can reveal the presence and distribution of mass (including dark matter) that distorts the path of light from distant sources. Observations of the cosmic microwave background radiation can also provide clues about the gravitational effects on the early universe's temperature fluctuations.

Investigations into the red shifts observed in galactic light can help scientists understand the expansion rate of the universe and infer the mass distribution that affects this expansion, including the role of dark matter. These methods collectively contribute to a better understanding of the large-scale structure of the universe and the fundamental nature of gravity.