Dark Matter and Dark Energy
Supernovae taken with the CMB anisotropies constrain us to a Universe in which the flatness is confirmed, but 2/3 due to “dark energy” which is currently accelerating the expansion of spacetime. This may be related to the original cause of inflation, or be a “cosmological constant”. It would be a form of “vacuum energy” (like an anti-gravity). We do not know how to calculate it at the moment (off by 10120 – the single worst #!).
Einstein had put such a force in his equations to keep the Universe static. When Hubble found it was expanding, Einstein said adding the force was his “biggest blunder”. It turns out, saying that may have been his biggest blunder!