Short Answer
The near-perfect uniformity of the CMB despite regions not yet in causal contact is the best answer.
Astrophysics questions often combine observation with first-principles physics. The winning move is to connect the measurement being made, such as luminosity, spectrum, redshift, or orbit, to the physical model behind it.
Regions of CMB separated by more than ~2° had not had time to exchange information, yet appear identical — solved by inflation fast-tracking causal contact.
Why This Answer Is Correct
This is a Hard-level question in Astrophysics & Cosmology. The prompt is really testing whether you can connect the concept to its defining physical relationship instead of picking a nearby-but-wrong term.
Good astrophysics reasoning always asks what the telescope actually measured and what physical quantity that measurement traces.
Choices At A Glance
- A. Inability to see beyond the cosmic horizon
- B. The near-perfect uniformity of the CMB despite regions not yet in causal contact
- C. Black hole horizons
- D. Galaxy formation at low redshift
When similar options appear on an exam, eliminate the ones that break the core law, use the wrong units, or confuse a definition with a consequence.
Topic Snapshot
Topic: Astrophysics & Cosmology
Difficulty: Hard
Best next move: Re-state the governing law in your own words, then solve one more example from the same topic before moving on.