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How Big is the Universe?

2012-02-11 · Hank · watch on YouTube · Science & nature · explainer learning

Hank explains why physicists think the universe has no edge: the observable universe is just our horizon, the universe expands without expanding into anything and has no centre, and it may be infinite; any edge would be forever beyond our sight.

What is said

00:00:00 — Intro ('No edge'): today's video is that the universe has no edge; the observable universe, a sphere centred on each observer

  • ★★★ Hank says today's video is about the fact that the universe does not have an edge, starting with the observable universe. — 00:00:00
  • ★★ Hank says the observable universe is what we can conceivably see, since photons must travel to us; it is a sphere centred on the observer, so each of us is its centre. — 00:00:00

00:00:34 — The observable ocean analogy; 'everything there is' is a poor definition; the universe as an evenly dense, expanding mass of stuff

  • ★★ Hank compares the observable universe to the observable ocean: a horizon seen from the beach doesn't mean there is nothing beyond it. — 00:00:34
  • ★★ Hank says defining the universe as everything makes an outside impossible but is a poor definition; really it is an evenly dense, ever-expanding mass of stuff we can study. — 00:00:34

00:01:03 — Expanding but not into anything: the Big Bang was not an explosion, there is no centre, space itself stretches, the Big Bang happened everywhere

  • ★★★ Answering the common objection that an expanding universe must expand into something, Hank says it isn't expanding into anything; the Big Bang was not an explosion with more stuff in the middle. — 00:01:03
  • ★★★ Hank says there is no centre: after the Big Bang everything was evenly spaced and remains so apart from gravitational clumps; expansion means the fabric galaxies exist in is stretching. — 00:01:33
  • ★★ Hank says the physical place where the Big Bang started would be everywhere. — 00:01:33

00:02:02 — The universe may be infinite (current data suggests so) or finite with an edge beyond what we can see

  • ★★★ Hank says scientists aren't sure whether the universe is infinite, though current data suggests it is, so it may be both infinite and expanding; some infinites may be larger than others. — 00:02:02
  • ★★ Hank says the universe might instead be finite, with an edge somewhere beyond where we can see. (hedged) — 00:02:02

00:02:40 — Beyond what we can see there is certainly more; Hank's Tumblr died, please re-follow

  • ★★★ Hank concludes that beyond what we can see there is certainly more, and if there is an edge we will never see or know it. — 00:02:40
  • ★★ Hank says his Tumblr died and asks people who followed him there to follow him again. — 00:02:40 · Tumblr

00:03:10 — Leftover Tour de Nerdfighting CDs; sign-off to John; end screen: subscribe to SciShow; 'edge of glory'

  • ★★ Hank offers the few leftover Tour de Nerdfighting CDs, which he had at the tour, because he doesn't want to throw the extras away. — 00:03:10 · Tour de Nerdfighting
  • ★ Hank tells John that even though John doesn't seem to find the universe appropriately interesting, he still likes him a lot. (playful) — 00:03:10
  • ★★ On the end screen Hank says this video is what SciShow is all the time, with nicer production values, and suggests subscribing at youtube.com/SciShow. (hedged) — 00:03:10 · SciShow

Humor (significant)

  • Hank begins his usual greeting to John and is cut off by the outburst. — 00:00:00 > «Today I would like to talk to you and... No edge.»
  • After Hank says nothing can be outside everything, the outburst comes again, eerily. — 00:00:34 > «No edge! That one was creepy.»
  • Hank says the universe may be both infinite and expanding. — 00:02:02 > «No edge! I know! I'm right there with you, dude.»
  • The end screen, after the SciShow plug, closes on a sung edge pun. — 00:03:35 > «I'm on the edge of glory and I'm hanging on a moment with you.»

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