# Is the empty space between galaxies different than the empty space within galaxies **URL:** \ **Category:** Factual Questions\ **Created:** [April 25, 2015, 3:46pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518 "2015-04-25T15:46:54Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [April 25, 2015, 3:46pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/1 "2015-04-25T15:46:54Z")
Is the empty space between stars within a galaxy any different than the empty space between galaxies? I’m assuming there are more random particles and radiation within the galaxy, is anything at all (radiation, particles, etc) going to be seen or felt between galaxies? ---
**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:** [April 25, 2015, 5:03pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/2 "2015-04-25T17:03:37Z")
Nowhere in space is a perfect vacuum: There are always a handful of stray atoms here and there. But there are fewer of them between galaxies than within galaxies. ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [April 25, 2015, 5:13pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/3 "2015-04-25T17:13:21Z")
Science has passed it by to some extent, but I’m reminded of Poul Anderson’s [_Tau Zero_](http://en.wikipedia.org/wiki/Tau_Zero) ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 25, 2015, 5:13pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/4 "2015-04-25T17:13:29Z")
Every galaxy seen through a telescope is viewed by the photons that traveled through empty space to reach us. Neutrinos hardly interact with anything. Gazillions are passing through you every moment. They flood the universe, everywhere. Cosmic rays reach us across vast distances. On a more macro scale, individual stars and planets can break loose and go off on their own. They are extremely rare by comparison, although collectively they add to what we would think of a large number. Between galaxy space is similar to within galaxy space, just far, far more attenuated. ---
**Author:** ![Ornery\_Bob](https://avatars.discourse-cdn.com/v4/letter/o/da6949/32.png) [@Ornery\_Bob](https://boards.straightdope.com/u/Ornery_Bob)\ **Post date:** [April 25, 2015, 6:30pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/5 "2015-04-25T18:30:29Z")
I was between galaxies once… almost ran out gas. ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [April 25, 2015, 7:34pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/6 "2015-04-25T19:34:22Z")
> [@Exapno\_Mapcase](#): > > Every galaxy seen through a telescope is viewed by the photons that traveled through empty space to reach us. > > Neutrinos hardly interact with anything. Gazillions are passing through you every moment. They flood the universe, everywhere. > > Cosmic rays reach us across vast distances. > > On a more macro scale, individual stars and planets can break loose and go off on their own. They are extremely rare by comparison, although collectively they add to what we would think of a large number. > > Between galaxy space is similar to within galaxy space, just far, far more attenuated. So if hundreds/thousands of years from now an alcubierre drive or something similar was created it would not preclude intergalactic travel? ---
**Author:** ![DSeid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dseid/32/20194_2.png) [@DSeid](https://boards.straightdope.com/u/DSeid)\ **Post date:** [April 25, 2015, 8:03pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/7 "2015-04-25T20:03:45Z")
Whatever dark matter turns out to be there is [more of it in the space contained within and immediately around galaxies](http://www.universetoday.com/119848/scientists-map-the-dark-matter-around-millions-of-galaxies/) than in the larger spaces between galaxies. > [@](#): > > The new maps confirm current theories that suggest galaxies will form where large concentrations of dark matter exist. The new data show large filaments of dark matter where visible galaxies and galaxy clusters lie and cosmic voids where very few galaxies reside. > > “Our analysis so far is in line with what the current picture of the universe predicts,” said Chihway Chang from the Swiss Federal Institute of Technology (ETH) in Zurich, a co-leader of the analysis. “Zooming into the maps, we have measured how dark matter envelops galaxies of different types and how together they evolve over cosmic time.” ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 25, 2015, 10:57pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/8 "2015-04-25T22:57:59Z")
> [@Wesley\_Clark](#): > > So if hundreds/thousands of years from now an alcubierre drive or something similar was created it would not preclude intergalactic travel? What does one have to do with the other? ---
**Author:** ![Wesley\_Clark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wesley_clark/32/20581_2.png) [@Wesley\_Clark](https://boards.straightdope.com/u/Wesley_Clark)\ **Post date:** [April 26, 2015, 12:11am UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/9 "2015-04-26T00:11:58Z")
> [@Exapno\_Mapcase](#): > > What does one have to do with the other? I was curious if FTL travel ever becomes possible if it would work for intergalactic travel. ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [April 26, 2015, 4:15pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/10 "2015-04-26T16:15:59Z")
There is a question of scale in terms of intergalactic space. When astronomers speak of how the galaxies are\* ‘moving away from each other at an increasing rate’\* they are not hurtling thru intergalactic space the way stars in galaxies are rotating around the galactic core. The space between galaxies is itself expanding, so the apparent distance between them appears to be increasing. Think about it too long and your head hurts… ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [April 26, 2015, 4:23pm UTC](https://boards.straightdope.com/t/is-the-empty-space-between-galaxies-different-than-the-empty-space-within-galaxies/718518/11 "2015-04-26T16:23:22Z")
> [@Wesley\_Clark](#): > > I was curious if FTL travel ever becomes possible if it would work for intergalactic travel. To the extent an alcubierre drive is based on physical principles, then certainly it would work in intergalactic space. To the extent it is based on what in today’s world is essentially magic, same answer. Again, nothing fundamental is different about intergalactic space.