How We Know What We Know: Observational Evidence
Evidence and models
A scientific picture
A strong cosmological model must explain several different kinds of data at once. Key evidence includes galaxy redshifts, the cosmic microwave background, the abundance of light elements, large-scale structure, and gravitational lensing.
Cross-checking
When many independent observations point to the same explanation, confidence in the model increases.
Examples of observations and what they test
| Observation | What it helps test |
|---|---|
| Galaxy redshifts | Cosmic expansion |
| CMB temperature patterns | Early-universe conditions |
| Element abundances | Early nucleosynthesis |
| Galaxy clustering | Structure formation |
| Gravitational lensing | Mass distribution |
Why the model is trusted
The standard cosmological model is trusted because it explains many unrelated measurements at the same time. No single observation proves everything, but together they form a powerful case.
Which observation is especially linked to the early universe's hot beginning?
The CMB is relic radiation from the early universe.
Correct answer: The cosmic microwave background
What is one reason scientists like models that explain many observations at once?
A model that fits many independent facts is usually stronger.
Correct answer: They are more convincing and less likely to be accidental
Observations are not perfect
Measurements have errors and uncertainties. Cosmologists therefore compare predictions with data statistically, looking for patterns that are unlikely to happen by chance if the model were wrong.
What does gravitational lensing help measure?
Gravity bends light, so lensing reveals where mass is located.
Correct answer: The mass distribution in the universe
Name one type of evidence used in modern cosmology.
Any one major observation type is acceptable.
Correct answer: Galaxy redshifts