Originally published at: http://boingboing.net/2016/10/14/more-than-2-trillion-galaxies.html
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You misread the article. Astronomy gets confusing because it involves time travel: the farther out you look, the farther back in time you are seeing. “The observable universe”, which they talk about in the article, is basically “the universe since almost the beginning of time.” Given big enough telescopes and enough time to look everywhere, we could see 2 trillion galaxies, but most of those are galaxies from the early days of the universe. Which have since merged into today’s more modest population of ~200 billion galaxies.
Also, the number of stars now existing is not raised by this new count of visible-but-no-longer-existing galaxies. Sorry.
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Wait. That’s a little confusing.
Even if those galaxies have already merged, we still can’t see what they’ve become yet. It’s not like all those ancient galaxies are parts of ones much closer to us now.
So it’s kind of like looking at the population of humanity.
You could express it in terms of how many people are alive right now ~7 billion. Or you could express it in the # to have ever lived including now: ~107 billion including us now.
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We can’t see what became of those specific galaxies, but we can infer what happened to them in aggregate. Astronomers assume, reasonably, that the galaxies we see at each distance from us (ie, at each epoch of the past) are typical of all galaxies at that time in the past, and as long as we get our distances right, we can assemble a complete overview of the history of the universe from as far back in time as you can see, to the near-present of just a few million years ago.
So we look at distant galaxies at the outer limits of what we can see wirh current telescopes, and see 10x more galaxies per unit volume than today, and they are all small galaxies on the order of the magellenic clouds or smaller. Look closer, and the tiny galaxies give way to fewer and bigger galaxies. We infer that the many little galaxies merged into fewer bigger galaxies.
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Wow I’m going to have to rethink my vacation plans.
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Reading this I had one of those weird mental moments where I wondered…
If the universe wrapped-around, like an old Atari game…
and you could fly out one side to fly in the other…
we’d be seeing the nearer universe, as well, from the opposite direction past that boundary.
Could we tell? Would we recognize the chaos of all these galaxies from the opposite direction?, perhaps even superimposed over more iterations of the same scene?
Yes, I understand there’s no aether or whatever to limit it. It would be obvious if it were like two mirrors facing one another, but time itself would be a limiting factor, would it not?
I need coffee…
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My question is - how does this affect our estimates of Dark Matter/Energy? Or does it have no affect. I think I know the answer, but hopefully someone smarter will fill me in.
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I know that it matters regarding things like the expansion of the universe, but I think a lot of what created the need for it was the rotation and perhaps the lensing of galaxies themselves, wasn’t it? If I recall correctly, it was observations of individual galaxies, and their behavior not matching their perceived mass, that was the original need for dark matter.
… but I am despairingly ignorant in these matters. Perhaps someone with actual knowledge will reply.
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I had my mind blown at a local planetarium when the facilitator decided to show off the software they use to map the universe. Usually they just do looped videos, or special talks, so this was kind of neat.
Starting at earth, he zoomed out a bit to show the solar system. Then our local area in the Milky Way. Then a bit more. And more. And there, finally was the whole galaxy. It was massive. Just so massive.
Then he zoomed out to our local neighborhood galaxies. And zoomed out a bit more. And a bit more. Through all of this, the camera was panning and rotating, but here were just more and more and more galaxies.
By the end, there was basically these two massive cones of galaxies spraying out from a center point, the Earth, snug in the Milky Way. Due to the fact that most of the matter in a spinning galaxy is confined to a plane, it is hard for us to track things parallel to the plane of our galaxy’s rotation. But the implication was clear; the universe is really, really big. Like, mind-boggling big.
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Sorry to be boring, but The universe has a horizon beyond which it is not possible to see. In practical terms, this is the distance at which we are seeing the light from the moment, a few hundred thousand years after the Big Bang, when the universe became transparent. We recieve that light as microwaves (because of red shifting) and call it the cosmic background radiation.
Look out there with an optical telescope and you see zilch because all the light has shifted into the radio specrum. There’s also a somewhat closer limit to seeing anything useful with an optical telescope because past a certain distance, you are looking into the past before the formation of stars, at which point the universe looks very boring.
The good news is that we can’t yet see that far with our current best telescopes, so we keep building bigger ones.
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But we base that on how far we can see, right? It isn’t like we see a big black wall out there.
My insane thought is what if we aren’t seeing as far as we think, but dealing with a curvature effect, seeing the view in iterations from different perspectives because of the wraparound I mentioned. If we were, would we recognize those areas of the universe we are seeing from behind, or from other angles?
What is nuts is billions of years in the future, as the universe is expanding away from us, there will be a point in time where someone in our galaxy won’t be able to see anything other than our local galactic cluster.
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Hmmm. That doesn’t seem right. At some point, all of the other galactic clusters might be receding quickly enough that no new light from them will ever reach Earth, but there will still be light in-transit from other galactic clusters that will eventually reach us, sent a lot earlier.
And eventually, even that will dwindle, but it should be asymptotically approaching zero as time goes on, never actually reaching zero.
Watch the video, I think it explains it. This assumes that space time keeps expanding at the current rate. IIRC basically things will be so far away, and space time expanding so quickly, that light from far away will never reach us again because space is expanding faster than light. So it would be like an RC car running at 9.9mph and the tread mill at 10mph, slowly increasing speed. The car will never move fast enough to reach the other end of the tread mill.
Stuff that is already far away and we can see now will eventually wink out when the expansion vs speed aligns.
That’s not to say that newer galaxies haven’t formed in the spaces where those old galaxies were, or drifted in on arms of galaxy clusters. It’s not likely to be void-space where they once were.[quote=“Mister44, post:10, topic:87431”]
how does this affect our estimates of Dark Matter/Energy?
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@aLynHall has it correct. Dark Energy is a mathematical equation written to explain why galaxies appear to be moving away from eachother at an accelerating speed. We don’t know the source for this inflation, so Dark Energy is invoked.
Dark Matter is the equation to explain why the edges of spiral (or rotating) galaxies appear to be rotating so fast. It requires a lot of gravity to pull them along at such a speed, but the observable matter doesn’t account for enough mass to match this gravitational tug, hence Dark Matter is invoked.
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[quote=“Glaurung, post:2, topic:87431”] Which have since merged into today’s more modest population of ~200 billion galaxies.
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Thanks, Obama!
#MakeTheUniverseGreatAgain
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Well, there’s the “we’re all inside a black hole” and “the universe as a simulation” thought experiments if you are inclined to further boil the ol grey matter…
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As a kid I was fascinated with black holes. This was the mid 80s and we didn’t really know much about them really. But being a curious kid I wanted to know where the Big Bang “got all that stuff” AND where did the stuff sucked up by a black hole go. I figured well maybe black holes span universes. Turns out – decades later – some folks think the 12yo me may have been onto something. My current weird idea is that somehow universes have been evolving like life on earth has, each with some slight change that somehow makes it a better one. But I don’t think they “mate” and it doesn’t look like there’s a survival of the fittest thing, so I think my idea is not going to be picked up by Popular Science anytime soon.
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