What Is Outside the Universe?!

Every second, more of the universe slips out of reach. Not poetically. Measurably.

This is a film about three answers to one of the oldest questions in cosmology: what is outside the universe. The first answer is the everyday one — the observable universe, a 93-billion-light-year sphere centered on every observer. The second is harder — the cosmic event horizon, a one-way membrane past which no signal can ever return. The third is the quietest, and the most final: that "outside" may not be a meaningful word at all.

We walk from the surface of the cosmic microwave background — the wall of light frozen 380,000 years after the Big Bang — out past the event horizon, and into the geometry the Planck satellite measured: flat to one part in 1,400. Flat means infinite. Unless space wraps. We do not know which one we live in. We may never know.

Then the three theories physicists give anyway. Eternal inflation. Conformal cyclic cosmology. The Hartle-Hawking no-boundary proposal. None ruled out.

And finally, the two whispers — the CMB Cold Spot in Eridanus, and the dark flow streaming through Centaurus — that hint, controversially, at something on the other side of a horizon we will never cross.

In 150 billion years, every galaxy outside our Local Group will redshift out of existence. An astronomer in that era will look up and conclude the universe consists of one galaxy. They will be wrong, in a way nothing inside their light cone can ever prove.

We are already living that future. Just earlier.
—
CHAPTERS
0:00 The receding horizon
0:45 The first edge — observable universe
2:10 Faster than light: the Hubble flow
3:30 The second edge — cosmic event horizon
4:50 There is no edge
6:20 Flat geometry, infinite or wrapped
7:30 Three theories physicists give anyway
9:40 The bruise — CMB Cold Spot and dark flow
10:40 A galaxy alone

—

SOURCES
- Planck 2018 Final Results — curvature constraints
- Andrei Linde, Alan Guth — eternal inflation
- Roger Penrose — conformal cyclic cosmology
- Hartle & Hawking — no-boundary proposal
- WMAP / Planck — CMB Cold Spot (Eridanus Supervoid debate)
- Kashlinsky et al. — dark flow

Видео What Is Outside the Universe?! канала Ad_Astrum