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Noob physics question: I assume this talks about stars close enough that we can receive their light. Can we say anything about the number of stars & galaxies th

Noob physics question: I assume this talks about stars close enough that we can receive their light. Can we say anything about the number of stars & galaxies that are further away than that?

crazydoggers 6y ago
Good observation... just made another comment about that. You’re asking about the observable universe vs the universe, and it’s an open question. Might be drastically more, or even less. https://en.m.wikipedia.org/wiki/Observable_universe https://en.m.wikipedia.org/wiki/Observable_universe
vermilingua 6y ago
My understanding is that there isn’t much point theorizing about the “outside” universe beyond the horizon of our light cone, because there is no present or future interaction possible between it and us.
- crazydoggers 6y ago
  There’s good reason to theorize about it. Theories might be able to point to or estimate the size even if we can’t directly measure it. For instance if we find evidence of inflation in more fundamental physical processes, we can assume there’s more universe out there than we can see.
permille42 6y ago
My main response to this article is essentially the same question. I think the article is presuming some things to come to this conclusion. The main thing that is being presumed is the "big bang". If you proscribe to believing in the big bang, then the entirety of everything we see is an expansion from a single dense explosion of matter. It is still a valid theory but I myself don't understand the physics of what is observed well enough to be convinced this is true. I believe that they are seeing something similar enough that it could be perhaps a "localized bang" or something like that. The main evidence used as "proof" of the big bang is the observed data seeming to show that the everything in the universe is "dispersing" slowly. That is at least what I've heard claimed.
- permille42 6y ago
  Why in the fuck is sharing some knowledge of what I know about science that leads to people believing there is nothing outside the observable universe downvoted? I can see having a dislike of my opinion and beliefs ( which is not a valid reason to downvote by the way according to what Hackers News itself says... ), but downvoting me when I am attempting to communicate useful information. Come on now.
  - layer8 6y ago
    I didn’t downvote, but you demonstrated a very poor understanding of the big bang, and put forward equally ill-informed conclusions/suspicions based on that. It is not useful.
  - andy_ppp 6y ago
    It’s because opinions are not equal to science and suggesting your opinion without massive corroborating evidence isn’t going to fly here. It’s the same as suggesting climate change isn’t real and COVID is just like flu... these things are made up, not researched science.
  - aSockPuppeteer 6y ago
    I think some read some of paragraph 2 and thought it was heading into religious beliefs or far away from the topic. The last consensus I remember is a Big Bang, rapid expansion, and then slower expansion. There are some other theories but not as popular. It’s a fun topic to dive into. The horizon problem, variable speeds of light, and of course string theory.
  - antonvs 6y ago
    > ... that leads to people believing there is nothing outside the observable universe No mainstream scientific source says this. The observable universe is purely a limit on the distance we can see - a horizon - due to the speed of light and the age of the universe. > The main evidence used as "proof" of the big bang is the observed data seeming to show that the everything in the universe is "dispersing" slowly. That is at least what I've heard claimed. There is much, much more evidence than this. Wikipedia lists observational evidence in 7 categories: https://en.wikipedia.org/wiki/Big_Bang#Observational_evidence https://en.wikipedia.org/wiki/Big_Bang#Observational_evidenc... > If you proscribe to believing in the big bang, then the entirety of everything we see is an expansion from a single dense explosion of matter. This is misleading. The Big Bang is not an "explosion" of the kind we see on Earth, where some matter is pushed apart from a central point by an explosive force. If that were the case, then what we observe would be different. Instead, what we observe has so far only been well explained by the idea that space itself is expanding. In this model, there is no center - there's no location you can point to as where the explosion happened, the expansion happened everywhere equally, it didn't radiate outward from a central point. We have evidence of this omnidirectional expansion, in the form of the cosmic microwave background (CMB) radiation, which is radiation from the early universe that comes from all directions in the sky, because the Big Bang similarly occurred in all directions. Again, this is not what we would observe if it was similar to a traditional explosion. > I believe that they are seeing something similar enough that it could be perhaps a "localized bang" or something like that. If you're thinking of something more like a traditional explosion, no, that is ruled out by the observational evidence.
sandgiant 6y ago
Good question! As most results in extra galactic astrophysics this one also depends on the cosmological model used. The actual paper linked in the article describes it well: "The cosmic optical background (COB) is the average flux of visible light photons averaged over the volume of the observable Universe. It reflects, at least in part, an integral over the cosmological history of star formation occurring in recognizable galaxies, proto-galaxies, and star clusters (Conselice et al. 2016), as well as mass accretion by black holes (BHs) associated with the systems." - https://arxiv.org/abs/2011.03052v2 https://arxiv.org/abs/2011.03052v2 A common problem in astronomy is the lack of ways to measure things (we can't travel to the stars, yet). The special thing about this result is that it is a very direct and independent measurement of the background optical light in the Universe. This means it can be used to put independent constraints on the star formation history, as well as black hole accretion, and perhaps things we haven't even thought about yet. Edit: And all those results are model dependent as everything else.
- fpoling 6y ago
  The article indirectly pointed out that the reason for previous overestimate was model error about solar system light background. The biggest source of uncertainty with the new estimate is modeling of background light of our galaxy. Too bad that we cannot yet send a probe outside it to measure things directly.

Noob physics question: I assume this talks about stars close enough that we can receive their light. Can we say anything about the number of stars & galaxies that are further away than that?

crazydoggers 6y ago

Good observation... just made another comment about that. You’re asking about the observable universe vs the universe, and it’s an open question. Might be drastically more, or even less. https://en.m.wikipedia.org/wiki/Observable_universe https://en.m.wikipedia.org/wiki/Observable_universe

vermilingua 6y ago

My understanding is that there isn’t much point theorizing about the “outside” universe beyond the horizon of our light cone, because there is no present or future interaction possible between it and us.

crazydoggers 6y ago
There’s good reason to theorize about it. Theories might be able to point to or estimate the size even if we can’t directly measure it. For instance if we find evidence of inflation in more fundamental physical processes, we can assume there’s more universe out there than we can see.

permille42 6y ago

My main response to this article is essentially the same question. I think the article is presuming some things to come to this conclusion. The main thing that is being presumed is the "big bang". If you proscribe to believing in the big bang, then the entirety of everything we see is an expansion from a single dense explosion of matter. It is still a valid theory but I myself don't understand the physics of what is observed well enough to be convinced this is true. I believe that they are seeing something similar enough that it could be perhaps a "localized bang" or something like that. The main evidence used as "proof" of the big bang is the observed data seeming to show that the everything in the universe is "dispersing" slowly. That is at least what I've heard claimed.

permille42 6y ago
Why in the fuck is sharing some knowledge of what I know about science that leads to people believing there is nothing outside the observable universe downvoted? I can see having a dislike of my opinion and beliefs ( which is not a valid reason to downvote by the way according to what Hackers News itself says... ), but downvoting me when I am attempting to communicate useful information. Come on now.
- layer8 6y ago
  I didn’t downvote, but you demonstrated a very poor understanding of the big bang, and put forward equally ill-informed conclusions/suspicions based on that. It is not useful.
- andy_ppp 6y ago
  It’s because opinions are not equal to science and suggesting your opinion without massive corroborating evidence isn’t going to fly here. It’s the same as suggesting climate change isn’t real and COVID is just like flu... these things are made up, not researched science.
- aSockPuppeteer 6y ago
  I think some read some of paragraph 2 and thought it was heading into religious beliefs or far away from the topic. The last consensus I remember is a Big Bang, rapid expansion, and then slower expansion. There are some other theories but not as popular. It’s a fun topic to dive into. The horizon problem, variable speeds of light, and of course string theory.
- antonvs 6y ago
  > ... that leads to people believing there is nothing outside the observable universe No mainstream scientific source says this. The observable universe is purely a limit on the distance we can see - a horizon - due to the speed of light and the age of the universe. > The main evidence used as "proof" of the big bang is the observed data seeming to show that the everything in the universe is "dispersing" slowly. That is at least what I've heard claimed. There is much, much more evidence than this. Wikipedia lists observational evidence in 7 categories: https://en.wikipedia.org/wiki/Big_Bang#Observational_evidence https://en.wikipedia.org/wiki/Big_Bang#Observational_evidenc... > If you proscribe to believing in the big bang, then the entirety of everything we see is an expansion from a single dense explosion of matter. This is misleading. The Big Bang is not an "explosion" of the kind we see on Earth, where some matter is pushed apart from a central point by an explosive force. If that were the case, then what we observe would be different. Instead, what we observe has so far only been well explained by the idea that space itself is expanding. In this model, there is no center - there's no location you can point to as where the explosion happened, the expansion happened everywhere equally, it didn't radiate outward from a central point. We have evidence of this omnidirectional expansion, in the form of the cosmic microwave background (CMB) radiation, which is radiation from the early universe that comes from all directions in the sky, because the Big Bang similarly occurred in all directions. Again, this is not what we would observe if it was similar to a traditional explosion. > I believe that they are seeing something similar enough that it could be perhaps a "localized bang" or something like that. If you're thinking of something more like a traditional explosion, no, that is ruled out by the observational evidence.

sandgiant 6y ago

Good question! As most results in extra galactic astrophysics this one also depends on the cosmological model used. The actual paper linked in the article describes it well: "The cosmic optical background (COB) is the average flux of visible light photons averaged over the volume of the observable Universe. It reflects, at least in part, an integral over the cosmological history of star formation occurring in recognizable galaxies, proto-galaxies, and star clusters (Conselice et al. 2016), as well as mass accretion by black holes (BHs) associated with the systems." - https://arxiv.org/abs/2011.03052v2 https://arxiv.org/abs/2011.03052v2 A common problem in astronomy is the lack of ways to measure things (we can't travel to the stars, yet). The special thing about this result is that it is a very direct and independent measurement of the background optical light in the Universe. This means it can be used to put independent constraints on the star formation history, as well as black hole accretion, and perhaps things we haven't even thought about yet. Edit: And all those results are model dependent as everything else.

fpoling 6y ago
The article indirectly pointed out that the reason for previous overestimate was model error about solar system light background. The biggest source of uncertainty with the new estimate is modeling of background light of our galaxy. Too bad that we cannot yet send a probe outside it to measure things directly.