Gregory's Server@ZachWeinersmith except doesn't the fact that light has a measurable speed and does not move infinitely fast suggest the universe is curved?
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 @doctroid @ZachWeinersmith then why does light have a measurable speed from our perspective? @quirk @ZachWeinersmith Nothing can have infinite speed. That would mean an action here has immediate consequences infinitely far away. The universe doesn't work like that. @doctroid @ZachWeinersmith Einstein's theory of relativity describes time dilation as someone near the speed of light experiences time differently from an observer on earth; a few minutes for them could be a few hours for us. If you were to travel at the speed of light, you'd think your trip was instantaneous, while a great deal of time would have passed on earth. Speed = distance / time, if you divide by 0 you get ∞. We don't observe this, so light must be bending in our universe of space time. @quirk @ZachWeinersmith As someone with a doctorate in physics, I can tell you your understanding is incorrect. For one thing, nothing prior to the last sentence has anything to do with curvature, so the last sentence doesn't follow. And we do observe light behaving in exactly the way you describe, curvature or no curvature. @doctroid @ZachWeinersmith your argument from authority notwithstanding, general relativity does tell us that, from the perspective of light, it travels instantly. From our perspective, it does not. We understand this as time dilation. So how do you account for the fact that light does have an observable speed limit in our universe from all perspectives other than light? Or has this theory been superseded?  @oblomov @ZachWeinersmith except for the fact that, as light travels through space, its vector is being changed from the straight line at infinite speed it wants to travel at to a vector where we observe it travelling at 299 792 458 m/s, which is the universal speed of light. It's folly to dismiss this interaction when determining the shape of the universe, as this may give us a clue as to both the size and shape of the universe. |
@quirk @ZachWeinersmith No, light speed has nothing to do with space curvature.
Yes, a gradual expansion would *eventually* give you curvature so small it's indistinguishable from flat. But you need the expansion to be rapid for it to have flattened early enough in the history of the universe.
It would still not be absolutely flat, it could be open or closed, but on such a huge scale (vastly larger than the observable universe) you couldn't tell it isn't flat.