> ## Content Index
> Fetch the complete content index at: https://www.cascadepbs.org/llms.txt
> Use this file to discover other available public pages before exploring further.

# Dark Energy Is Driving the Universe Apart. We May Finally Know Why.
- URL: https://www.cascadepbs.org/show/pbs-space-time/episode/dark-energy-is-driving-the-universe-apart-we-may-finally-know-why-a5h1to/
- Published: 2026-02-23T21:02:39.000Z
- Updated: 2026-02-23T22:02:11.000Z
- Description: The universe expands faster. “Dark energy” may not be constant after all.
- Author: Cascade PBS Staff
- Tags: PBS Space Time, Season 11, Episode 22, #ZZZ_Episode_7fe2d820-0cb9-465a-bf08-c6a7b8e1b544, #episode, #ZZZ_Show_ae70f836-13b6-4c9d-b61f-99f7b8bc29eb, #v1.16

We’ve known since 1929 that the universe is expanding, and since 1998 that it’s speeding up. The unknown force behind this acceleration is called “dark energy,” assumed to stay constant in density. But new evidence hints it may change over time, possibly explaining why major measurements of the universe’s expansion rate don’t agree.