what's outside the universe?

What's beyond the universe's edge, and why it might not need an outside at all. The universe isn't sitting inside anything, and the edge you can see is just a horizon centered on you. The observable universe extends about 46 billion light-years in every direction, but that's only as far as light has had time to reach you since the Big Bang 13.8 billion years ago. Everything beyond that horizon is unreachable, not because there's a wall, but because space itself is stretching faster than light can travel through it. The Big Bang happened everywhere at once, not at a single point, so the universe has no center and no outer edge pushing into empty space. As the mathematician Bernhard Riemann showed in 1854, a space can have limited size without an edge, like Earth's surface, which you can't fall off even though it doesn't go on forever. If the universe closes up on itself the same way, it would need nothing outside to curve into; curvature is measured from the inside. The oldest light (the cosmic microwave background, released 380,000 years after the Big Bang) shows space is flat to within a fifth of a percent, meaning the universe either goes on infinitely or is at least as large as the observable part. Measurements from the BOOMERanG and Planck satellites confirm flat geometry; searches for wraparound patterns found none. Whether the universe is infinite or merely enormous remains unknown, but physics shows it needs no outside and no rim to expand into. Chapters: 0:00 The edge you can see 0:56 The observable universe 2:54 The stretching universe 5:08 Growing into nothing 6:54 Does it go on forever? 8:46 Curved without an outside 9:35 The biggest triangle 10:53 Wrap-around space 12:08 So what's outside? Sources & further reading: Planck satellite: cosmic microwave background measurements: https://www.esa.int/Science_Explorati... Lineweaver & Davis: The Big Bang and the expansion of space: https://www.astronomynotes.com/cosmol... NASA: Universe expansion: https://imagine.gsfc.nasa.gov/feature... Wright cosmology FAQ: https://www.astro.ucla.edu/~wright/co... Riemann: On the hypotheses which lie at the foundations of geometry: https://www.maths.tcd.ie/pub/HistMath... About oh that's why Curious people of any age and background who want to finally understand how an everyday thing actually works, and laugh on the way. One everyday thing at a time, explained properly. Subscribe for more: https://www.youtube.com/@oh-thats-why... #universe #physics #outside