Summary
Observations of distant galaxies show that space itself is expanding. This expansion implies that the universe was smaller, denser, and hotter in the past, pointing toward a finite beginning of physical reality.
Observation / Fact
Astronomical measurements reveal that distant galaxies are receding from one another in all directions. The farther a galaxy is, the faster it appears to be moving away.
Why This Is Non-Trivial
The recession is not galaxies moving through space, but space itself stretching. This means the expansion applies universally and cannot be localized to a region or explosion within space.
What It Implies
Reversing this expansion mathematically leads to a boundary condition where distances approach zero. This indicates a temporal origin of space itself, not merely a rearrangement of preexisting matter.
Related
- Hubble–Lemaître Law
- Cosmic Redshift
- Past Temporal Finitude