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is about 90 thousand millions ly in diameter This is the diameter of the observable universe. We don't know if the universe is infinitely big, but all signs (e

is about 90 thousand millions ly in diameter This is the diameter of the observable universe. We don't know if the universe is infinitely big, but all signs (e.g. the flatness of space as far as we can measure it) point to it being infinite, or very very much larger than our observable sphere. I don't understand why I'm constantly having to inform smart people of this very basic fact. Is there something wrong with the way we teach astronomy? Can you help me spread the word?

akvadrako 10y ago
Your "fact" didn't support the grandparent's argument, so now amount of teaching will get him to accept it. His other fact is also pointless - it doesn't matter how old the universe is now; the idea is that most Boltzman brains will form in the future.
- jbmorgado 10y ago
  1st. It's not an argument, it's science and what your parent just said violates general relativity (read the lengthly answer given in the thread). 2nd. The great grandparent asked: "So why are we not Boltzmann Brains ourselves?" and that's what was being answered. I hope that this teaching will get you to accept it...
  - Analog24 10y ago
    It does not actually violate general relativity. You can read the response to the post you reference for some more details.
    - jbmorgado 10y ago
      Please explain what "doesn't violate relativity" since from your other response you don't seem to be understanding what is being discussed here.
      - Analog24 10y ago
        You made the original claim that it violates relativity so why don't you take your own advice and be more explicit. The current accepted size of the observable universe is ~90 billion light years in diameter. If you were referring to some other statement that you think violates relativity then feel free to clear things up. if you're upset about people making assumptions about your comments then (calmly) address those and clarify your point(s). Don't make aggressive and pejorative assumptions of your own.
        jbmorgado 10y ago
        If you don't know what I was referring to, then why where you so sure that "it doesn't violate relativity" then? The statement was made about the infinite size of the Universe and the OP (along the way) was talking about the observable Universe. He is mixing the extent of the Universe with the spatial dimensions of the Universe (so, the better word here is actually space). It is still an open debate if the dimensions of the Universe (space) are infinite (although what we knows seems to point that way), but the extent of the Universe is not infinite, if it was, that would violate relativity (or the standard model as I explained along the thread).
lucozade 10y ago
Could you expand on the "all signs" bit please? I was under the impression that there was little to no evidence of anything much outside the observable universe.
- solipsism 10y ago
  Read about measurements of the flatness of space. To the precision we're capable of measuring, it appears completely flat. Then picture us as ants on a surface that appears flat as far as we can see. Are we on an infinitely sized surface? Either we are, or it's a sphere but the surface is curved but so slightly that it appears flat. This implies the sphere is much bigger than our observable area. Note, we're assuming the universe doesn't just end we arbitrary boundaries. It either is infinite or it curves back on itself.
jbmorgado 10y ago
> ""90 thousand millions ly in diameter" This is the diameter of the observable universe. We don't know if the universe is infinitely big, but all signs (e.g. the flatness of space as far as we can measure it) point to it being infinite, or very very much larger than our observable sphere." Our observable sphere is nowhere near 90 thousand million ly in diameter since that would violate relativity. Our observable sphere in ly is always smaller than the age of the universe in years (so ~14 thousand million years). Also, what you said is no fact, basic or not, it's just some misconception you have about cosmology so you should stop spreading that word since you are misinforming people you talk to. In a nutshell: A Universe that begins in a singularity cannot have an infinite diameter and while it's true that we do calculate the size of the Universe by assuming the expansion rate right after the Big Bang and that rate might be wrong, it still cannot be infinite without violating the major principles of physics and the all big bang theory.
- Analog24 10y ago
  There is a difference between the size of the observable Universe now and the size when the light was emitted. It does not violate relativity to state that objects that were 14 billion light years away when the light we see from them left are now much farther away due to expansion. Furthermore, your reference to relativity is also incorrect. The expansion of the Universe is not caused by objects moving away from each other, which would be limited by the speed of light. The expansion of the Universe is actually an expansion of space itself, which is not limited by the speed of light. You should look up the "metric expansion of the universe". In general, relativity is known to be incomplete on a cosmological scale. The situation is much more complicated due to the existence of dark energy and dark matter. You should read about the Lambda-CDM model if you want to learn more about the state of modern cosmology.
  - jbmorgado 10y ago
    > "Furthermore, your reference to relativity is also incorrect. The expansion of the Universe is not caused by objects moving away from each other" I never said that and in fact I explained that the issue here is the metric of the universe expanding, not the particles moving away from each other. > "is a difference between the size of the observable Universe now and the size when the light was emitted" Nope, I also never said that. Seriously just go read what I actually wrote instead of writing whatever goes in your mind with no regard for what is actually being discussed.

akvadrako 10y ago

Your "fact" didn't support the grandparent's argument, so now amount of teaching will get him to accept it. His other fact is also pointless - it doesn't matter how old the universe is now; the idea is that most Boltzman brains will form in the future.

jbmorgado 10y ago
1st. It's not an argument, it's science and what your parent just said violates general relativity (read the lengthly answer given in the thread). 2nd. The great grandparent asked: "So why are we not Boltzmann Brains ourselves?" and that's what was being answered. I hope that this teaching will get you to accept it...
- Analog24 10y ago
  It does not actually violate general relativity. You can read the response to the post you reference for some more details.
  - jbmorgado 10y ago
    Please explain what "doesn't violate relativity" since from your other response you don't seem to be understanding what is being discussed here.
    - Analog24 10y ago
      You made the original claim that it violates relativity so why don't you take your own advice and be more explicit. The current accepted size of the observable universe is ~90 billion light years in diameter. If you were referring to some other statement that you think violates relativity then feel free to clear things up. if you're upset about people making assumptions about your comments then (calmly) address those and clarify your point(s). Don't make aggressive and pejorative assumptions of your own.
      - jbmorgado 10y ago
        If you don't know what I was referring to, then why where you so sure that "it doesn't violate relativity" then? The statement was made about the infinite size of the Universe and the OP (along the way) was talking about the observable Universe. He is mixing the extent of the Universe with the spatial dimensions of the Universe (so, the better word here is actually space). It is still an open debate if the dimensions of the Universe (space) are infinite (although what we knows seems to point that way), but the extent of the Universe is not infinite, if it was, that would violate relativity (or the standard model as I explained along the thread).

lucozade 10y ago

Could you expand on the "all signs" bit please? I was under the impression that there was little to no evidence of anything much outside the observable universe.

solipsism 10y ago
Read about measurements of the flatness of space. To the precision we're capable of measuring, it appears completely flat. Then picture us as ants on a surface that appears flat as far as we can see. Are we on an infinitely sized surface? Either we are, or it's a sphere but the surface is curved but so slightly that it appears flat. This implies the sphere is much bigger than our observable area. Note, we're assuming the universe doesn't just end we arbitrary boundaries. It either is infinite or it curves back on itself.

jbmorgado 10y ago

> ""90 thousand millions ly in diameter" This is the diameter of the observable universe. We don't know if the universe is infinitely big, but all signs (e.g. the flatness of space as far as we can measure it) point to it being infinite, or very very much larger than our observable sphere." Our observable sphere is nowhere near 90 thousand million ly in diameter since that would violate relativity. Our observable sphere in ly is always smaller than the age of the universe in years (so ~14 thousand million years). Also, what you said is no fact, basic or not, it's just some misconception you have about cosmology so you should stop spreading that word since you are misinforming people you talk to. In a nutshell: A Universe that begins in a singularity cannot have an infinite diameter and while it's true that we do calculate the size of the Universe by assuming the expansion rate right after the Big Bang and that rate might be wrong, it still cannot be infinite without violating the major principles of physics and the all big bang theory.

Analog24 10y ago
There is a difference between the size of the observable Universe now and the size when the light was emitted. It does not violate relativity to state that objects that were 14 billion light years away when the light we see from them left are now much farther away due to expansion. Furthermore, your reference to relativity is also incorrect. The expansion of the Universe is not caused by objects moving away from each other, which would be limited by the speed of light. The expansion of the Universe is actually an expansion of space itself, which is not limited by the speed of light. You should look up the "metric expansion of the universe". In general, relativity is known to be incomplete on a cosmological scale. The situation is much more complicated due to the existence of dark energy and dark matter. You should read about the Lambda-CDM model if you want to learn more about the state of modern cosmology.
- jbmorgado 10y ago
  > "Furthermore, your reference to relativity is also incorrect. The expansion of the Universe is not caused by objects moving away from each other" I never said that and in fact I explained that the issue here is the metric of the universe expanding, not the particles moving away from each other. > "is a difference between the size of the observable Universe now and the size when the light was emitted" Nope, I also never said that. Seriously just go read what I actually wrote instead of writing whatever goes in your mind with no regard for what is actually being discussed.