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New measurements of the sky's blackness

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Re: New measurements of the sky's blackness

#51

Post by simonh »

pvorb wrote: post #11
tsimionescu wrote: post #7

Earlier quoted context omitted.

This is more about the invisible stars and galaxies, the ones too far to actually count, but whose lights just gives a faint glow to the darkness.

This depends on your definition of visible. If you think of visible as some form of light reaching a man-made object, then GPs statement is still true.

I would argue that any reasonable definition of visible includes being able to resolve features. In support of this, many dictionary definitions include words like 'accurate', 'clear' and 'obvious', while it's antonyms include 'unclear', 'indistinct' and 'obscured' and not just 'invisible'.

Re: New measurements of the sky's blackness

#52

Post by ksherlock »

ljlolel wrote: post #47
ivalm wrote: post #8

Earlier quoted context omitted.

I don’t think so. For astrobiology we are mostly looking for life in our galaxy, this study looks at presence of very far away galaxies. For purposes of communication those galaxies are forever out of reach as they are at such high red shifts they are escaping from us faster than speed of light.

"escaping from us faster than speed of light." ?????

https://en.wikipedia.org/wiki/Expansion_of_the_universe

The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not expand "into" anything and does not require space to exist "outside" it. As the spatial part of the universe's spacetime metric increases in scale, objects move apart from one another at ever-increasing speeds. To any observer in the universe, it appears that all of space is expanding while all but the nearest galaxies recede at speeds that are proportional to their distance from the observer – at great enough distances the speeds exceed even the speed of light.

Re: New measurements of the sky's blackness

#53

Post by Keysh »

maga wrote: post #20

Does this mean there is "more" dark energy since we still have all the effects of extra matter but less visible matter?

No, because only about 10% of normal (baryonic) matter is actually in the form of stars. The rest is mostly in the form of hot, dilute gas in intergalactic space.

The idea that about 5% of the total mass-energy budget of the universe is in the form of baryonic matter is well-determined by cosmological observations (including the relative amounts of hydrogen and helium formed in the Big Bang). It if turns out we've overestimated the amount of baryonic matter in stars by a factor of two, that just means that 95% of the baryons are in the hot intergalactic medium instead of 90%.

Re: New measurements of the sky's blackness

#55

Post by dang »

permille42 wrote: post #32
permille42 wrote: post #18

Earlier quoted context omitted.

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…

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.

Would you please stop breaking the site guidelines? You've been doing it repeatedly (e.g. https://news.ycombinator.com/item?id=25819408). That's not cool.

https://news.ycombinator.com/newsguidelines.html

Re: New measurements of the sky's blackness

#56

Post by pvorb »

tsimionescu wrote: post #48
pvorb wrote: post #43

Earlier quoted context omitted.

Isn't this like saying that aliens do not exist, because we never received any signal from them? Of course you can see it like that, but does it really change the probability of their existence? I think there's a difference between what we know and what actually exists.

Well, if the aliens exist outside our light hyper-cone (that is, by definitio, any kind of information from them has never reached and will never reach any piece of information we create) then it is the same. However, if any aliens have lived or will live anywhere in the visible universe, then that is something we could at least in theory confirm our deny at some point, so it is not the same. It's also important to r…

You introduced "will never" to this argument here. Neither me nor parent comments said that being visible today or in the past has anything to do with being visible in the future.

I would argue that science is about a core of what is considered proven and thus is true, as well as topics that are currently discussed and a large amount of knowledge that still has to be discovered. And I think these galaxies that are invisible today might be in the latter category - if they exist at all. But I wouldn't rule out their existence unnecessarily. In a few years, due to advances in technology, it could be possible to "discover" (or rather estimate) far more galaxies than what is proposed in this study.

Just because mankind in the middle ages had never seen Pluto doesn't mean it didn't exist back then.

Re: New measurements of the sky's blackness

#57

Post by permille42 »

dang wrote: post #55
permille42 wrote: post #32

Earlier quoted context omitted.

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.

Would you please stop breaking the site guidelines? You've been doing it repeatedly (e.g. https://news.ycombinator.com/item?id=25819408 ). That's not cool. https://news.ycombinator.com/newsguidelines.html

Fuck you

Re: New measurements of the sky's blackness

#58

Post by perl4ever »

permille42 wrote: post #28
ObjectiveZen wrote: post #25

Earlier quoted context omitted.

Did you not blindly claim space is infinite? That seems the stranger assumption. If I’m standing in a forest counting all the trees I can see, I’d certainly take into account that there are some trees I can’t see, but I wouldn’t assume there exists an infinite forest of trees.

You're right. The earth is clearly flat and that is a sensible assumption if you haven't left your local area or been in space or seen a picture from space. Or not. Flat earthers are quacks. It is the same principle essentially. It is illogical to think "hey if I keep walking that way I'll hit a wall eventually". That is why flat earthers are quacks from the beginning. The same principle applies to space. What quack…

The universe appears to be fairly flat, but according to: https://en.wikipedia.org/wiki/Shape_of_the_universe

...if the universe was like a "3-torus", it could be both flat and finite: https://en.wikipedia.org/wiki/Three-torus

If you ever played the classic game "asteroids", you might remember how everything wrapped around at the edges of the screen. A 3-torus would be like that, only in 3D.

On the other hand, one could imagine the universe as a 3-sphere, which I believe would mean it would be both locally curved and finite in volume. https://en.wikipedia.org/wiki/3-sphere

There are also other possibilities, like something analogous to a Klein bottle with an extra dimension.

There are a bunch of possibilities for "flat and finite" as well as "positively curved and finite" that I can't begin to visualize.

There is even supposedly such a (hypothetical) thing as a negatively curved, (commonly described as saddle shaped) yet finite universe.

But regardless, the current belief about the real universe is that it is at least very close to flat, but not known to be finite or infinite.

Re: New measurements of the sky's blackness

#59

Post by mncharity »

detritus wrote: post #50
iso1631 wrote: post #41

Earlier quoted context omitted.

Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns—the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the…

I never unserstood that ridicule - I always thought it was an apt-description of the levels of ignorance we can honestly presume for ourselves. Refreshingly honest of Rumsfeld, if anything.

> I never unserstood that ridicule

Perhaps try the response with a different issue and respondent swapped in?

Q: There are reports there is no evidence of a direct link between [...]

Vaccination-autism policy advocate: Reports that say that something hasn't happened are always interesting to me, because as we know, there are known knowns; [...] But there are also unknown unknowns—the ones we don't know we don't know. And if one looks throughout the history of our country and other free countries, it is the latter category that tends to be the difficult ones.

Q: The real situation is worse than the facts show? (later NATO press event)

UFO-abduction policy advocate: The message is that there are no "knowns." [...] Absence of evidence is not evidence of absence.[1]

[1] https://www.nato.int/docu/speech/2002/s020606g.htm

Re: New measurements of the sky's blackness

#60

Post by drran »

perl4ever wrote: post #58
permille42 wrote: post #28

Earlier quoted context omitted.

You're right. The earth is clearly flat and that is a sensible assumption if you haven't left your local area or been in space or seen a picture from space. Or not. Flat earthers are quacks. It is the same principle essentially. It is illogical to think "hey if I keep walking that way I'll hit a wall eventually". That is why flat earthers are quacks from the beginning. The same principle applies to space. What quack…

The universe appears to be fairly flat, but according to: https://en.wikipedia.org/wiki/Shape_of_the_universe ...if the universe was like a "3-torus", it could be both flat and finite: https://en.wikipedia.org/wiki/Three-torus If you ever played the classic game "asteroids", you might remember how everything wrapped around at the edges of the screen. A 3-torus would be like that, only in 3D. On the other hand, one co…

Asteroids game is not a physical model. Did you ever played with GPT2 text generator? Your theory would be like that.
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