Universe

• How Do We Know What Happened Before the CMB?
  The CMB is the oldest light we can observe directly, but element abundances and its patterns let cosmologists test models of earlier eras.
• Is the Universe Bounded or Does It Have an Edge?
  The observable universe has a finite horizon, but the whole universe may be finite or infinite; either way, it need not have an edge.
• Is There a Center of the Universe If It Is Finite?
  A finite universe does not necessarily have a center: it may be curved or wrap around without an edge or preferred point in standard cosmology.
• Does Gravity Slow the Expansion of the Universe?
  Gravity from matter and radiation decelerates cosmic expansion, but dark energy now causes the universe’s expansion to accelerate.