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New measurements of the sky's blackness

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Re: New measurements of the sky's blackness

#21

Post by permille42 »

joering2 wrote: post #17
permille42 wrote: post #14

Um. What? Is this the new "the earth is flat"? Space is infinite. I believe it goes on forever in every direction. Whether you can see whatever is out there from here in no way proves that it isn't...

We have no proof Universe is infinite, but we can also argue that the building blocks of Universe - atoms? - cannot come in unlimited quantity. At least it sounds more reasonable that way. Unless of course we are all in a symultation and our whole Universe takes up half a sq. inch of a silicone chip.

This is my point. We have no evidence either way, so it seems strange to me to blindly claim "this is everything".

Re: New measurements of the sky's blackness

#22

Post by permille42 »

crazydoggers wrote: post #16
permille42 wrote: post #14

Um. What? Is this the new "the earth is flat"? Space is infinite. I believe it goes on forever in every direction. Whether you can see whatever is out there from here in no way proves that it isn't...

That’s not known. This article refers to the observable universe which is bound by the speed of light. Whether the universe is infinite or not is an open question. It might be finite but unbounded. Spacetime geometry is complicated.

Neither the title nor the summary say anything about the "observable universe". They make broad claims beyond that. The detail of the article in no way mentions that there could very well be infinite duplicates of what we see out there beyond observable distance.

Re: New measurements of the sky's blackness

#23

Post by crazydoggers »

permille42 wrote: post #22
crazydoggers wrote: post #16

Earlier quoted context omitted.

That’s not known. This article refers to the observable universe which is bound by the speed of light. Whether the universe is infinite or not is an open question. It might be finite but unbounded. Spacetime geometry is complicated.

Neither the title nor the summary say anything about the "observable universe". They make broad claims beyond that. The detail of the article in no way mentions that there could very well be infinite duplicates of what we see out there beyond observable distance.

Because this is an article that’s using the layman terminology. The scientists involved surely understand the difference. In fact read the Wikipedia article and you’ll see the old estimate of 2 trillion for the observable universe.

https://en.m.wikipedia.org/wiki/Observable_universe

Re: New measurements of the sky's blackness

#24

Post by ObjectiveZen »

permille42 wrote: post #14

Um. What? Is this the new "the earth is flat"? Space is infinite. I believe it goes on forever in every direction. Whether you can see whatever is out there from here in no way proves that it isn't...

Perhaps space is infinite, but that doesn’t necessarily mean there is infinite matter.

Re: New measurements of the sky's blackness

#25

Post by ObjectiveZen »

permille42 wrote: post #21
joering2 wrote: post #17

Earlier quoted context omitted.

We have no proof Universe is infinite, but we can also argue that the building blocks of Universe - atoms? - cannot come in unlimited quantity. At least it sounds more reasonable that way. Unless of course we are all in a symultation and our whole Universe takes up half a sq. inch of a silicone chip.

This is my point. We have no evidence either way, so it seems strange to me to blindly claim "this is everything".

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.

Re: New measurements of the sky's blackness

#26

Post by crazydoggers »

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?

Dark energy and dark matter are separate concepts. Dark energy refers to a factor that increases the expansion of the universe, ie a cosmological constant.

Dark matter on the other hand is matter we can’t detect currently, but we theorize is there from its gravitational effects.

There’s a lot of other data like galaxy rotation rates, CMB, gravitational lensing, etc that effect dark matter estimates. I’m not sure how much of the current estimate is based on larger observable universe structure, so it’s an interesting question.

Re: New measurements of the sky's blackness

#27

Post by maga »

crazydoggers wrote: post #26
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?

Dark energy and dark matter are separate concepts. Dark energy refers to a factor that increases the expansion of the universe, ie a cosmological constant. Dark matter on the other hand is matter we can’t detect currently, but we theorize is there from its gravitational effects. There’s a lot of other data like galaxy rotation rates, CMB, gravitational lensing, etc that effect dark matter estimates. I’m not sure how…

I understand that, I mean the matter-energy balance in the universe at the moment accounts 5% to ordinary matter, 26% to dark matter and the rest to dark energy. Since we now assume there are less stars, hence, ordinary matter, but the galaxies are still accelerating at the same rate, doesn't that mean the dark energy accounts for more than the estimated 69%?

Re: New measurements of the sky's blackness

#28

Post by permille42 »

ObjectiveZen wrote: post #25
permille42 wrote: post #21

Earlier quoted context omitted.

This is my point. We have no evidence either way, so it seems strange to me to blindly claim "this is everything".

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 seriously thinks that eventually there is just a wall in space or that it wraps around?

Wrapping around makes zero sense in 3-dimensional space.

Re: New measurements of the sky's blackness

#29

Post by sandgiant »

kkaranth wrote: post #9

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?

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

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.

Re: New measurements of the sky's blackness

#30

Post by tsimionescu »

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.

Well, stars whose light has never even reached us are likely out of our light hypercone, so they might not exist in the scientific sense (i.e. Their existence or non-existence is completely unprovable and has no consequences, even in principle).
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