Nearly 400,000 years after the Big Bang, electrons and protons formed the first hydrogen atoms, and the Universe became transparent.
The photons that were released at that time form the cosmic microwave background that we observe today.
The cosmic microwave background reveals three surprising features of our Universe:
1. In its infancy, the Universe was remarkably homogeneous, but there were tiny fluctuations already in place.
2. The spatial geometry of the Universe is flat, even though this is an unstable state and there is not enough matter in the Universe to make it flat.
3. Most of the matter in the Universe is composed of unknown particles.
These observations lay the foundation for the current standard model of cosmology, in which the Universe initially underwent a growth spurt called inflation and is now filled with dark matter and dark energy.
I present a brief history of the Universe, focusing on the evidence for inflation, dark matter, and dark energy in the cosmic microwave background.
I then address the unanswered questions inherent in the standard cosmological model:
What caused inflation?
What is dark matter?
And what is the dark energy that will dominate the Universe's future?