Labs / Astronomy
Expanding Universe
Space itself is stretching, carrying the galaxies apart. Slide the scale factor to run the expansion forward and back, then click any galaxy to see how far away it is, how fast it is fleeing, and how its light gets stretched toward red. Notice that the farther a galaxy sits, the faster it recedes — that steady ratio is the Hubble constant.
d —v —z —H —
What to try
- Click a nearby galaxy, then a distant one. Which has the larger redshift z, and why?
- As you push the scale factor higher, do the absorption lines slide toward red or toward blue?
- Pick three galaxies at different distances. Does the implied Hubble constant H come out the same for all of them?
- Crank H₀ up. What happens to a distant galaxy’s recession speed — can it approach the speed of light?
- Run the scale factor below 1 into the past. Do the galaxies crowd together toward a single point?