Lensing Properties
Image Information
H₀ Measurement
About Strong Lensing
Strong gravitational lensing by a massive galaxy creates multiple images of a background quasar. Each image travels a different path through curved spacetime, experiencing different gravitational time delays.
The time delay Δt between images depends on:
- Geometric delay: Differences in physical path length
- Shapiro delay: Gravitational time dilation near the lens
- Time-delay distance: D_Δt ∝ 1/H₀
By measuring time delays between brightness variations in different images, we can infer H₀. This provides an independent measurement complementary to the CMB and supernova methods.
Instructions
- Adjust the lens mass to change the Einstein radius
- Move the source position to see image positions change
- Watch how time delays vary with geometry
- Vary H₀ to see its effect on predicted time delays
- Compare "measured" vs "inferred" H₀