4 ms·

Is there an "edge" in the sense that, if you lived there and looked in your telescope in one direction, you see galaxies, but if you turned it around, you'd see

Is there an "edge" in the sense that, if you lived there and looked in your telescope in one direction, you see galaxies, but if you turned it around, you'd see nothing?

jethkl 4y ago
An equivalent reformulation: is there a point where most of everything is behind you? [edited]
- nsxwolf 4y ago
  I'm confused. Are you saying it's hard to believe my question is serious?
  - jethkl 4y ago
    Not at all! I had the same question. Sorry for any misunderstanding, I edited my comment.
fknorangesite 4y ago
There is a fundamental limit to how far we can (and will ever be able to) see, but as far as we know, it is galaxies forever in every direction.
- Supermancho 4y ago
  We can only see a finite distance. QED as far as we know, we don't know it is galaxies forever in any given direction.
  - fknorangesite 4y ago
    The evidence strongly indicates a flat, infinite, isomorphic universe. You are correct of course that we do not and cannot know, but anything else would require extraordinary evidence to the contrary.
    - ipaddr 4y ago
      Flat universe theory sounds like flat earth theory in the 14th century. How could the earth be round at that point? It would take extraordinary evidence to the contrary. That doesn't mean flat earth theory was true.. just that everyone accepts that answer now.
    - opportune 4y ago
      Wouldn’t this evidence also be consistent with being “not near enough to the edge to perceive an edge”? And also consistent with that, because of the expansion of the universe we will never be able to get a signal from the “edge” to know anyway? My problem with an infinite isomorphic universe is that it implies infinite mass. I don’t know enough about cosmology or other physics to understand all the implications, but to me it seems like it would make models of the early universe janky - ie why would it not just immediately collapse in on itself?
    - AnimalMuppet 4y ago
      Strongly indicates? I question that. As I understand it, the standard cosmology includes inflation, which stretched out the "full" universe to much larger than the observable universe. This also made the observable universe very, very close to flat, which makes it almost impossible to observe the difference between "flat" and "not flat, but very close to flat in the observable part of the universe". So if you think there's evidence that strongly indicates "truly flat", I'd like to hear what it is. Ditto for evidence that strongly indicates "infinite" as opposed to "finite, but considerably larger than the observable portion". [Edit: If you want to say that inflation is a just-so story, I'm not sure I will disagree. And if you say that inflation looks like it was specifically designed to be untestable, I could probably agree with that, too. But those are different from saying that you have sufficient evidence to rule out inflation.]
      - fknorangesite 4y ago
        https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy... > We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe. https://wmap.gsfc.nasa.gov/universe/uni_shape.html https://wmap.gsfc.nasa.gov/universe/uni_shape.html
- nsxwolf 4y ago
  So there's infinite mass? I thought the Big Bang implied a finite mass. Or is the Big Bang not a thing anymore?
  - fknorangesite 4y ago
    > So there's infinite mass? Sure, why not? > I thought the Big Bang implied a finite mass. What makes you say that? How so?
suzzer99 4y ago
Yeah this is what I don't understand. In order for this not to be true, space would have to be curved back in on itself like the surface of a balloon. Meaning you could eventually wind up back where you started. But do we know for sure this is how the 3D space in our universe works?
fnordpiglet 4y ago
There is no edge, no. In some theories Space warps around on itself, but it would be more like a möbius strip. But the edge of our observable universe is just when the Big Bang happened, and before that we can’t detect any light, so it looks like an edge. If you were there the universe would looks much the same as it does from our own vantage as it’s self similar.
- petters 4y ago
  Why a Möbius strip? That would imply that if I travelled around the universe and back to Earth, everything would be like it had been reflected in a mirror.
  - fnordpiglet 4y ago
    Why do you say that? But, as to why a a strip, because you appear to walk in a straight line but end up at the same point. It could have been a sphere too, but you have more dimensions to move in, and they aren't nearly as cool.

Is there an "edge" in the sense that, if you lived there and looked in your telescope in one direction, you see galaxies, but if you turned it around, you'd see nothing?

jethkl 4y ago

An equivalent reformulation: is there a point where most of everything is behind you? [edited]

nsxwolf 4y ago
I'm confused. Are you saying it's hard to believe my question is serious?
- jethkl 4y ago
  Not at all! I had the same question. Sorry for any misunderstanding, I edited my comment.

fknorangesite 4y ago

There is a fundamental limit to how far we can (and will ever be able to) see, but as far as we know, it is galaxies forever in every direction.

Supermancho 4y ago
We can only see a finite distance. QED as far as we know, we don't know it is galaxies forever in any given direction.
- fknorangesite 4y ago
  The evidence strongly indicates a flat, infinite, isomorphic universe. You are correct of course that we do not and cannot know, but anything else would require extraordinary evidence to the contrary.
  - ipaddr 4y ago
    Flat universe theory sounds like flat earth theory in the 14th century. How could the earth be round at that point? It would take extraordinary evidence to the contrary. That doesn't mean flat earth theory was true.. just that everyone accepts that answer now.
  - opportune 4y ago
    Wouldn’t this evidence also be consistent with being “not near enough to the edge to perceive an edge”? And also consistent with that, because of the expansion of the universe we will never be able to get a signal from the “edge” to know anyway? My problem with an infinite isomorphic universe is that it implies infinite mass. I don’t know enough about cosmology or other physics to understand all the implications, but to me it seems like it would make models of the early universe janky - ie why would it not just immediately collapse in on itself?
  - AnimalMuppet 4y ago
    Strongly indicates? I question that. As I understand it, the standard cosmology includes inflation, which stretched out the "full" universe to much larger than the observable universe. This also made the observable universe very, very close to flat, which makes it almost impossible to observe the difference between "flat" and "not flat, but very close to flat in the observable part of the universe". So if you think there's evidence that strongly indicates "truly flat", I'd like to hear what it is. Ditto for evidence that strongly indicates "infinite" as opposed to "finite, but considerably larger than the observable portion". [Edit: If you want to say that inflation is a just-so story, I'm not sure I will disagree. And if you say that inflation looks like it was specifically designed to be untestable, I could probably agree with that, too. But those are different from saying that you have sufficient evidence to rule out inflation.]
    - fknorangesite 4y ago
      https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy_Probe https://en.wikipedia.org/wiki/Wilkinson_Microwave_Anisotropy... > We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe. https://wmap.gsfc.nasa.gov/universe/uni_shape.html https://wmap.gsfc.nasa.gov/universe/uni_shape.html
nsxwolf 4y ago
So there's infinite mass? I thought the Big Bang implied a finite mass. Or is the Big Bang not a thing anymore?
- fknorangesite 4y ago
  > So there's infinite mass? Sure, why not? > I thought the Big Bang implied a finite mass. What makes you say that? How so?

suzzer99 4y ago

Yeah this is what I don't understand. In order for this not to be true, space would have to be curved back in on itself like the surface of a balloon. Meaning you could eventually wind up back where you started. But do we know for sure this is how the 3D space in our universe works?

fnordpiglet 4y ago

There is no edge, no. In some theories Space warps around on itself, but it would be more like a möbius strip. But the edge of our observable universe is just when the Big Bang happened, and before that we can’t detect any light, so it looks like an edge. If you were there the universe would looks much the same as it does from our own vantage as it’s self similar.

petters 4y ago
Why a Möbius strip? That would imply that if I travelled around the universe and back to Earth, everything would be like it had been reflected in a mirror.
- fnordpiglet 4y ago
  Why do you say that? But, as to why a a strip, because you appear to walk in a straight line but end up at the same point. It could have been a sphere too, but you have more dimensions to move in, and they aren't nearly as cool.