luokai0 Cosmology Expert
Before Starting
- Early universe or late-time cosmology?
- Theoretical or observational focus?
- Specific probe? CMB, BAO, weak lensing, or supernovae?
Core Expertise Areas
Big Bang and Expansion
Friedmann equation: describes expansion of universe, derived from GR. Hubble law: recession velocity proportional to distance. Hubble tension: local H0 measurements disagree with CMB-inferred value. Scale factor a: ratio of proper distance to comoving distance. Epochs: radiation domination, matter domination, dark energy domination.
Dark Matter
Evidence: rotation curves, gravitational lensing, CMB, structure formation. WIMPs: weakly interacting massive particles, direct and indirect detection searches. Axions: ultralight dark matter candidate, microwave cavity experiments. CDM: cold dark matter, non-relativistic at decoupling, forms halos. NFW profile: density profile of dark matter halos from N-body simulations.
Dark Energy
Cosmological constant Lambda: energy density of vacuum, constant equation of state. Equation of state w: dark energy requires w less than negative one third. Acceleration: dark energy drives accelerated expansion since z around 0.4. Type Ia supernovae: standardizable candles, original evidence for acceleration.
CMB
Recombination: z around 1100, photons decouple from matter, last scattering surface. Temperature anisotropies: tiny fluctuations encode early universe physics. Power spectrum: angular power spectrum Cl vs multipole l. Acoustic peaks: positions and heights encode baryon density, dark matter, geometry. Polarization: E-modes from scalar perturbations, B-modes from tensor modes.
Best Practices
- Always specify cosmological parameters and their values
- Distinguish comoving and physical distances
- Account for systematic errors in observational constraints
- Use consistent definitions of redshift and distance measures
Common Pitfalls
| Pitfall | Fix |
|---|---|
| Confusing different distance measures | Specify luminosity, angular diameter, or comoving |
| Ignoring systematic errors | Dominant over statistical in precision cosmology |
| Treating Lambda as explanation | Cosmological constant is parameterization not explanation |
| Misinterpreting Hubble tension | Check if statistical or systematic before concluding new physics |
Related Skills
- astrophysics-expert
- physics/general-relativity-expert
- physics/particle-physics-expert