Following the inflationary epoch after the singularity of the Big Bang, the universe continued to expand, but at a slower rate. The acceleration of the expansion due to dark energy began after the universe was already over nine billion years old (four billion years ago). The weakest of the Standard Model forces, gravity, may provide the solution to this unsolved enigma –the cosmic elephant in the room–in astronomy.
“There’s something a little off about our theory of the universe. Almost everything fits,” reports University of Chicago physicists, “but there’s a fly in the cosmic ointment, a particle of sand in the infinite sandwich” –something is making the universe not only expand, but expand faster and faster over time—and no one knows what the unknown force –cryptically labeled “dark energy”–is that’s causing the universe to expand at an accelerating rate.
“I have absolutely no clue what dark energy is. Dark energy appears strong enough to push the entire universe – yet its source is unknown, its location is unknown and its physics are highly speculative,” said Noble-Prize winning physicist Adam Riess, in an interview with The Atlantic.
Some scientists think the culprit might be gravity—and that subtle ripples in the fabric of space-time that distort the very geometry of space itself and provide a glimpse of our universe less than a trillionth of a trillionth of a second after the Big Bang– could help us find the “particle of sand in the infinite sandwich.”
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