3 ms·

> until all of a sudden the most distant stars go dim Why the most distant?

by sampo 12y ago

jacquesm 12y ago
Because if the events move at 0.9c the light still moves at 'c', so the furthest stars (of which there are more than nearby ones) will be the first to show you that something is up. The light from the older events will reach us before the events or the light from later events will reach us. Unless of course the whole thing originates in one of the stars nearby but the chances of that are smaller than that it will happen in a system further away.
- furyofantares 12y ago
  Wouldn't the most likely place for it to start be around halfway between us and the most distant observable stars in whatever direction it starts, then? And then we'd see the sphere of dimming stars increasing in size, while still seeing things behind, in front, or to the sides of the sphere?
  - jacquesm 12y ago
    The part that we can see is so much smaller than what is out there that you'd have to resort to very leaky analogies to try to get the point across. The upper limit to how much larger the universe is compared to the observable (and not the currently observed) universe is somewhere around the 10^20 to 10^25 times larger. Those are hard numbers to grasp but large enough that the chances of an event 'x' taking place outside of the observed universe are larger than inside it.
    - furyofantares 12y ago
      Ah, right, the ones that will disappear are furthest-observed, not furthest-observable... you have to already have been observed to disappear from observance! So, it would be an already-large and rapdily growing sphere intersecting with the sphere of observed stars. edit: Wait, actually, I thought you were saying we CAN (theoretically) observe 10^20+ times as far as we HAVE observed. But re-reading your comment, this sounds wrong: > The upper limit to how much larger the universe is compared to the observable Did you mean to say "the upper limit for how much larger the observable universe is compared to the observed universe"? Or are you actually talking about what might be outside of the observable universe? I figured starting points outside the observable universe were not a consideration for this problem, since they are causally unlinked from us and could not expand into the observable universe faster than it becomes causally unlinked from us as well.
- sampo 12y ago
  Because of 3d geometry, there are a lot more distant stars/galaxies than there are nearby ones. That much I agree. But the most distant galaxies we see, we see them 13 billion years in the past. So this type III civilization turning off starts at the edge of our observable universe would have developed in just 700 million years after the Big Bang. (If we take 13.7 billion years as the age of the universe.) That I find quite improbable. There is a smaller amount of nearer objects than far away objects, but the far away objects are (or we see them as) younger, and the nearby objects are older. There must be some balance between the respective volumes in near and far, and the available time it probably takes for the type III civilization to have developed?

> until all of a sudden the most distant stars go dim Why the most distant?

by sampo 12y ago

> until all of a sudden the most distant stars go dim Why the most distant?

Because if the events move at 0.9c the light still moves at 'c', so the furthest stars (of which there are more than nearby ones) will be the first to show you that something is up. The light from the older events will reach us before the events or the light from later events will reach us. Unless of course the whole thing originates in one of the stars nearby but the chances of that are smaller than that it will happen in a system further away.

furyofantares 12y ago
Wouldn't the most likely place for it to start be around halfway between us and the most distant observable stars in whatever direction it starts, then? And then we'd see the sphere of dimming stars increasing in size, while still seeing things behind, in front, or to the sides of the sphere?
- jacquesm 12y ago
  The part that we can see is so much smaller than what is out there that you'd have to resort to very leaky analogies to try to get the point across. The upper limit to how much larger the universe is compared to the observable (and not the currently observed) universe is somewhere around the 10^20 to 10^25 times larger. Those are hard numbers to grasp but large enough that the chances of an event 'x' taking place outside of the observed universe are larger than inside it.
  - furyofantares 12y ago
    Ah, right, the ones that will disappear are furthest-observed, not furthest-observable... you have to already have been observed to disappear from observance! So, it would be an already-large and rapdily growing sphere intersecting with the sphere of observed stars. edit: Wait, actually, I thought you were saying we CAN (theoretically) observe 10^20+ times as far as we HAVE observed. But re-reading your comment, this sounds wrong: > The upper limit to how much larger the universe is compared to the observable Did you mean to say "the upper limit for how much larger the observable universe is compared to the observed universe"? Or are you actually talking about what might be outside of the observable universe? I figured starting points outside the observable universe were not a consideration for this problem, since they are causally unlinked from us and could not expand into the observable universe faster than it becomes causally unlinked from us as well.
sampo 12y ago
Because of 3d geometry, there are a lot more distant stars/galaxies than there are nearby ones. That much I agree. But the most distant galaxies we see, we see them 13 billion years in the past. So this type III civilization turning off starts at the edge of our observable universe would have developed in just 700 million years after the Big Bang. (If we take 13.7 billion years as the age of the universe.) That I find quite improbable. There is a smaller amount of nearer objects than far away objects, but the far away objects are (or we see them as) younger, and the nearby objects are older. There must be some balance between the respective volumes in near and far, and the available time it probably takes for the type III civilization to have developed?