The 5 biggest mysteries about the origin of our Universe

From the Big Bang to a prior period of cosmic inflation, our cosmic origins are clearer than ever. Yet these 5 big mysteries still remain.

KEY TAKEAWAYS

• Just 100 short years ago, we hadn’t even discovered the expanding Universe, much less constructed a picture of our hot, dense cosmic origins.

• Over the 20th and 21st centuries, we pieced together the theory of — and the evidence for — the hot Big Bang, including the inflationary state that set it up.

• But even now, in 2025, many mysteries remain about our ultimate cosmic origins. Here are 5 of the biggest unsolved puzzles of all.