# 2 Trillion Galaxies? **URL:** \ **Category:** Factual Questions\ **Created:** [October 14, 2016, 11:45am UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502 "2016-10-14T11:45:16Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [October 14, 2016, 11:45am UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/1 "2016-10-14T11:45:16Z")
Some scientists have recalculated the estimated total number of galaxies in the universe and arrived at the number 2 trillion:eek:. This is ten times the previous best estimate and they say 90% of these galaxies are too far away or faint to be seen. Could this explain the previously unaccounted-for missing (or dark) matter? The article I read didn’t address this. ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [October 14, 2016, 11:50am UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/2 "2016-10-14T11:50:09Z")
I read it was between 1 trillion and 2 trillion. Pretty wide range, eh? And I believe that’s just the observable universe. Does that mean the night sky will become lighter faster, as the light from these stars eventually reaches us? ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [October 14, 2016, 12:25pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/3 "2016-10-14T12:25:02Z")
The missing mass idea is mostly based on the rotational behavior of individual galaxies. How many galaxies there are doesn’t affect that part of the analysis at all. That’s a purely galaxy local effect. Another component of the missing mass puzzle is the “organization” large superclusters of galaxies have. Finding out more about these hard to see galaxies might provide more information regarding this and how dark matter is involved. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 14, 2016, 12:46pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/4 "2016-10-14T12:46:00Z")
> [@](#): > > The missing mass idea is mostly based on the rotational behavior of individual galaxies. How many galaxies there are doesn’t affect that part of the analysis at all. That’s a purely galaxy local effect. Well, partly. There must be some dark matter within galaxies, to explain their rotational curves. But there’s also cosmological evidence for dark matter, which predicts a greater proportion than the galactic rotation curves do. Ergo, there must also be a significant amount of dark matter outside of galaxies. ---
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [October 14, 2016, 1:20pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/5 "2016-10-14T13:20:58Z")
> [@Jackknifed\_Juggernaut](#): > > I read it was between 1 trillion and 2 trillion. Pretty wide range, eh? And I believe that’s just the observable universe. Does that mean the night sky will become lighter faster, as the light from these stars eventually reaches us? No, because the universe is expanding, which results in cosmological redshift (moving light out of the visible range) and some galaxies simply being too far for the light to ever catch up to us. The night sky technically gets darker over time because further galaxies end up too far away for us to see, though most of the light humans can see is actually from local stars so it’s not really observable. ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [October 14, 2016, 2:02pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/6 "2016-10-14T14:02:40Z")
Heh, just the other day I was watching a documentary on Netflix wherein scientists are speculating that the universe is much _smaller_ than previously thought. They went on to suggest that what they observe as distant galaxies may be just reflections of closer, near by galaxies. On the surface, this all sounds a bit woo, but the idea has enough merit behind it that they are actually building a satellite specially designed to hash this theory out. (If they haven’t already, not sure how old the documentary was) ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 14, 2016, 2:26pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/7 "2016-10-14T14:26:43Z")
Do you remember the name of the show? I can’t think of anything planned to be launched to look for a smaller universe. Normally though they’re looking for other data (luminosity of Cepheids, parallax distances etc.) and then seeing how that fits the predictions of their model. ---
**Author:** ![Grrr](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/grrr/32/146_2.png) [@Grrr](https://boards.straightdope.com/u/Grrr)\ **Post date:** [October 14, 2016, 2:55pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/8 "2016-10-14T14:55:53Z")
I believe it was Edge of The Universe. Don’t ask me which episode though. (There’s only three) ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 14, 2016, 6:44pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/9 "2016-10-14T18:44:59Z")
That was ruled out a long time ago, based on the data from the MAP satellite, and that was far from MAP’s primary mission. How old was this documentary? ---
**Author:** ![Nansbread1](https://avatars.discourse-cdn.com/v4/letter/n/6a8cbe/32.png) [@Nansbread1](https://boards.straightdope.com/u/Nansbread1)\ **Post date:** [October 15, 2016, 2:34pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/10 "2016-10-15T14:34:49Z")
> [@Pantastic](#): > > No, because the universe is expanding, which results in cosmological redshift (moving light out of the visible range) and some galaxies simply being too far for the light to ever catch up to us. The night sky technically gets darker over time because further galaxies end up too far away for us to see, though most of the light humans can see is actually from local stars so it’s not really observable. If the light from far away galaxies has not reached us then how can hubble see it or if hubble cant see it then how do we know they are there to add to the total ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 15, 2016, 2:49pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/11 "2016-10-15T14:49:14Z")
We don’t see galaxies whose light has not yet reached us. What makes you think we did? ---
**Author:** ![Jackknifed\_Juggernaut](https://avatars.discourse-cdn.com/v4/letter/j/9de053/32.png) [@Jackknifed\_Juggernaut](https://boards.straightdope.com/u/Jackknifed_Juggernaut)\ **Post date:** [October 15, 2016, 3:12pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/12 "2016-10-15T15:12:17Z")
> [@Pantastic](#): > > No, because the universe is expanding, which results in cosmological redshift (moving light out of the visible range) and some galaxies simply being too far for the light to ever catch up to us. The night sky technically gets darker over time because further galaxies end up too far away for us to see, though most of the light humans can see is actually from local stars so it’s not really observable. Does this mean that the universe is expanding at a rate faster than the speed of light? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 15, 2016, 7:49pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/13 "2016-10-15T19:49:47Z")
When you get far enough away, yes. But that “far enough away” is the key, there. The “rate of expansion of the Universe” is not actually a speed; it’s a frequency. Things that are further away are receding proportionately faster, so for any given expansion rate, no matter how small, there’s always some distance beyond which the expansion is faster than light (of course, the slower the expansion rate, the greater that distance is). ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [October 16, 2016, 9:07pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/14 "2016-10-16T21:07:15Z")
I was going to make a longish post explaining this result and some of the misconceptions herein, but Phil Plait did it [a whole lot better](http://www.slate.com/blogs/bad_astronomy/2016/10/14/there_are_two_trillion_galaxies_in_the_universe.html) than I could. ---
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [October 17, 2016, 2:36pm UTC](https://boards.straightdope.com/t/2-trillion-galaxies/768502/15 "2016-10-17T14:36:17Z")
> [@Nansbread1](#): > > If the light from far away galaxies has not reached us then how can hubble see it or if hubble cant see it then how do we know they are there to add to the total We can’t see light that hasn’t reached us, I’m not really sure what’s confusing about that. We don’t know that there are other galaxies outside of the observable universe, since we can’t observe them. There’s decent evidence that the universe looks like what we can see outside of the area we can see because we don’t see any evidence of change at the edge, but that’s more speculation than observation. No one is adding things that we’re not observing to the total, the comment you replied to was saying that if they’re there they’re not part of and aren’t going to be part of the total.