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Comment by mirimir | Hacker News Reader

IANAP, but I think so. I vaguely recall that early inflationary expansion was very fast. Like several times the speed of light.

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Belated edit: More like ~10^81 times the speed of light.

> According to the theory of inflation, the Universe grew by a factor of 10 to the sixtieth power in less than 10 to the negative thirty seconds, so the "edges" of the Universe were expanding away from each other faster than the speed of light [0]

It seems that the universe was on the order of ~1 meter in diameter then.[1] So the "'edges' of the Universe were expanding away from each other" at ~10^90 meters per second.

0) http://curious.astro.cornell.edu/physics/109-the-universe/co...

1) https://www.forbes.com/sites/startswithabang/2017/03/24/how-...

Edit: Upon reflection, I get that "~1 meter in diameter" makes no sense. Maybe just say that the "edges" were ~1 meter apart.

> Belated edit: More like ~10^81 times the speed of light.

I have no grounding in physics on which to place this hunch but... doesn't this sound like a wee fudge factor to make the Big Bang theory fit evidence?

I am reminded of the concept of "aether" and "land bridge theory" where people had a workable hypothesis except for the niggly little problem that the hypothesis was contraindicated by some of the evidence.

I wonder about that too.

So the universe is expanding at greater than 10^90 m/s now, since the expansion is accelerating?

No, "inflation" refers to a specific episode in the very early history of the universe. Or rather, in some models of this.

Much slower expansion continued and continues today, and if you look really carefully is slightly accelerating not decelerating right now.

m/s, or comparing to the speed of light, isn't really a great way to measure this. Points far away from us are moving away, and faster the further you go; we know of no limits to this.

No, not really. One theory is that eventually things will slow and then collapse again. https://en.wikipedia.org/wiki/Big_Crunch

Taken to the extreme, this expansion and collapse has been happening over and over again in a cyclical fashion. https://en.wikipedia.org/wiki/Cyclic_model

The shape of the universe currently prevents this. For what we can tell the universe is flat, which means at no point will it collapse on itself, unless something major changes. That said, major changes have happened, around 8 billion years ago expansion appears to have sped up.

I'm no expert (so correct me if I'm wrong), but from what I'm read, flat, concave, and convex universes are all possibilities and they would all look flat to us because our measurements take place on such a small scale.

Our measurements occur across billions of light-years. By comparing redshift agaist the standard candles we measure relative speeds of vastly distant objects. And given the speed of light, we are also measuring what those speeds were billions of years ago. It is a very big ruler.

We've measured the flatness of the universe on the scale of the cosmic microwave background, which is essentially as big a ruler as could possibly exist.

https://map.gsfc.nasa.gov/mission/sgoals_parameters_geom.htm...

https://wmap.gsfc.nasa.gov/universe/uni_shape.html

Those darn flatspacers

Space itself is expanding. At small scales, it isn't really that "fast" (gravity can/does overcome the effects within our galaxy and the Local Group). However, at large scales, it can exceed the speed of light (google "Hubble volume") so at some point, light emitted from sources outside this range will not longer reach us because the space between here and there expanded faster than light travels.

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