<p>Galaxies move <em>through</em> space with velocities of the order of a several 100 km per second; small velocities for small groups (~100 km/s; e.g <a href="https://arxiv.org/abs/astro-ph/0008201" rel="nofollow noreferrer">Carlberg et al. 2000</a>) and large velocities for rich clusters (~1000 km/s; e.g <a href="http://adsabs.harvard.edu/abs/1993ApJ...404...38G" rel="nofollow noreferrer">Girardi et al. 1993</a>).</p>
<p>In addition to this so-called &quot;peculiar velocity&quot;, galaxies also also carried away from each other due to the expansion of the Universe, at a velocity proportional to the distance from each other (the &quot;<a href="https://en.wikipedia.org/wiki/Hubble%27s_law" rel="nofollow noreferrer">Hubble flow</a>&quot;). But this is not a motion <em>through</em> space; rather it is space itself that is expanding (and hence the velocity may exceed the speed of light for sufficiently large distances).</p>
<p>One may define a &quot;global reference frame&quot; with respect to which velocities are measured. Any reference is valid, but it makes sense to use the frame in which all galaxies are, on average, in rest (when the Hubble flow is subtracted)<span class="math-container">$^\dagger$</span>. In this frame, the Local Group that the Milky Way is a part of moves with some <span class="math-container">$620\, \mathrm{km \, s}^{-1}$</span> (as noted in John Duffield's answer above), whereas the center of <strong>the Milky Way has a velocity<span class="math-container">$^\ddagger$</span> of</strong> <span class="math-container">$\mathbf{565 \pm 5 \, km \, s^{-1}}$</span> (<a href="https://ui.adsabs.harvard.edu/abs/2020A%26A...641A...1P" rel="nofollow noreferrer">Planck Collaboration et al. 2020</a>).</p>
<p>What causes this movement of galaxies? Galaxies that are not too far from each (i.e. closer), &quot;feel&quot; each others mutual gravitational forces. A galaxy in a group or cluster moves around in the common gravitational field, but for galaxies that are farther away, the Hubble flow carries them away from each other too fast for them to attract each other.</p>
<p>This movement can be traced back to the tiny quantum mechanical fluctuations in the primordial soup of particles during <a href="https://en.wikipedia.org/wiki/Inflation_(cosmology)" rel="nofollow noreferrer">cosmic inflation</a>, i.e. less than <span class="math-container">$\sim10^{-32}\,\mathrm{s}$</span> after the Big Bang. As time went by, ever-so-slight overdensities grew in amplitude, until they collapsed to form the structure we see in the Universe today. During this collapse, matter grew turbulent, whirling clumps around that eventually became the galaxies that orbit each other.</p>
<hr />
<p><span class="math-container">$^\dagger$</span><sub>Formally, one uses the frame in which the <a href="https://en.wikipedia.org/wiki/Cosmic_microwave_background" rel="nofollow noreferrer">cosmic microwave background</a> is isotropic.</sub></p>
<p><span class="math-container">$^\ddagger$</span><sub>Taking into account our motion around the Galactic center, our Sun (currently) moves through space at <span class="math-container">$369.82\pm0.11\,\mathrm{km\, s^{-1}}$</span>.</sub></p>

CC BY-SA 3.0
2017-09-12T19:33:36.570Z
I'm in awe by the intelligence of you guys. I had to read your response a few times to barely grasp what you are saying. But none nonetheless, I'm going to be researching/learning about everything you are talking about. (which I'm sure that will raise more questions, lol)
Mike
CC BY-SA 3.0
2017-09-13T00:20:04.803Z
@Mike It's less a question of intelligence and more one of experience and study. Most things in life are like that.
jpmc26
CC BY-SA 3.0
2017-09-13T06:31:58.587Z
I second that, @jpmc26!
pela
CC BY-SA 4.0
2017-09-12T18:19:41.650Z
2021-12-29T10:39:32.940Z
2021-12-29T10:39:32.940Z
pela
<p><strong>NO</strong>, if don't want to consider it to be doing so.</p>

<p>Everything in the universe only "moves" when considered from a different frame of reference. From the <a href="https://en.wikipedia.org/wiki/Frame_of_reference" rel="noreferrer">observational frame of reference</a> of the Milky Way galaxy, every <em>other</em> object in the universe is moving, and the Milky Way is stationary.</p>

<p>When I walk to work, what I am actually doing is dragging the surface of the Earth, and everything on it, towards me with my feet, until my office arrives.</p>

CC BY-SA 3.0
2017-09-13T11:42:57.667Z
man, no wonder I need coffee when i get to the office..
user230910
CC BY-SA 3.0
2017-09-13T19:17:10.877Z
What about someone else walking to work from the opposite direction? Don't the two of you cancel each other out?
Barmar
CC BY-SA 3.0
2017-09-13T21:31:25.047Z
That's certainly how it feels today. Maybe I need to reset my reference frame. Or find a better office!
Chappo Hasn't Forgotten
CC BY-SA 3.0
2017-09-14T07:56:43.653Z
If you walk to work, you're not just dragging Earth but the whole universe. You're also rotating it by a few millidegrees.
Eric Duminil
CC BY-SA 3.0
2017-09-14T07:58:14.390Z
@Barmar: Both people think that they're stationary, that the universe is moving towards them at 5km/h and the other person is walking towards them at 10km/h.
Eric Duminil
CC BY-SA 3.0
2017-09-14T08:00:07.413Z
@NicholasShanks : `"Does the Milky Way move through space?"` Since the frame of reference is defined, the answer must be **YES**. What you think you're doing when you walk to work is irrelevant.
Eric Duminil
CC BY-SA 3.0
2017-09-14T08:01:54.507Z
@EricDuminil Yes, that's why I qualified it with "if you don't want it to" — and my answer was mostly a somewhat tongue-in-cheek counterpoint to the more technical answers already given.
Nicholas Shanks
CC BY-SA 3.0
2017-09-14T08:12:51.143Z
Einstein is reputed to have asked a ticket inspector, "Does Crewe stop at this train?".
Oscar Bravo
CC BY-SA 4.0
2020-02-07T14:54:02.377Z
I'm stunned that an intelligent person could type that last paragraph, mate.
White Prime
CC BY-SA 3.0
2017-09-13T10:37:24.167Z
2017-09-13T10:37:24.167Z
Nicholas Shanks
<p>Monty Python does not seem very accurate in scientific issues, but this time it does it's job quite well in the Galaxy Song also mentioning the milky ways movement.</p>

<pre><code>Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.

The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.
</code></pre>

<p>And yes, these figures are accurate: (at the time of publish) 
<a href="https://en.wikipedia.org/wiki/Galaxy_Song#Accuracy_of_astronomical_figures" rel="noreferrer">https://en.wikipedia.org/wiki/Galaxy_Song#Accuracy_of_astronomical_figures</a></p>

CC BY-SA 3.0
2017-09-13T14:14:46.803Z
But, just to be a killjoy, it doesn't answer the question.
ProfRob
CC BY-SA 3.0
2017-09-13T14:39:20.223Z
"We're thirty thousand light years from galactic central point.We go 'round every two hundred million years," is a clear "YES" IMHO for the "Milky Way is moving" topic
Ole Albers
CC BY-SA 3.0
2017-09-13T15:51:27.403Z
Of course it isn't. It is a clear statement that the Milky Way is a rotating disc of which we are a part. Rotation and translation (moving thru space) are two entirely different things.
ProfRob
CC BY-SA 3.0
2017-09-14T15:00:08.370Z
True. All the motions mentioned in the song are rotations, except for the expansion of the universe. And giving a single speed for the latter is wrong.
Barmar
CC BY-SA 3.0
2017-09-13T13:24:56.243Z
2017-09-13T13:24:56.243Z
Ole Albers
<blockquote>
  <p>Does the Milky Way move through space?</p>
</blockquote>

<p>Yes it does. </p>

<blockquote>
  <p>I'm very fascinated with space, although I don't have a degree or any formal education, I'm still very in love with everything about it and want to learn constantly. </p>
</blockquote>

<p>Good man Mike. </p>

<blockquote>
  <p>One thing I ask myself is if our galaxy moves through space?</p>
</blockquote>

<p>It does. When we look at the Cosmic Microwave Background Radiation we see a "dipole anisotropy" due to the motion of the Earth relative to it:</p>

<p><img src="https://i.sstatic.net/MsvXR.jpg" alt="enter image description here"></p>

<p><sub>Image courtesy of William H. Kinney's <a href="https://ned.ipac.caltech.edu/level5/Sept02/Kinney/Kinney_contents.html/%22title%22" rel="noreferrer">Cosmology, inflation, and the physics of nothing</a></sub></p>

<p>See <a href="https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy" rel="noreferrer">Wikipedia</a> for more:</p>

<p><em>"From the CMB data it is seen that the Local Group (the galaxy group that includes the Milky Way galaxy) appears to be moving at 627±22 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 276°±3°, b = 30°±3°.[82][83] This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction).[84]"</em></p>

<p>627 km/s is quite fast. See <a href="https://astrosociety.org/edu/publications/tnl/71/howfast.html#6" rel="noreferrer">this article</a>, which says it's 1.3 million miles an hour. The speed of light is just under 300,000 km/s or 670 million miles per hour, so the Milky Way is moving through the Universe at circa 0.2% of the speed of light. Also see <a href="https://physics.stackexchange.com/a/25929/76162">the CMBR</a> physics answer by ghoppe which talks about the CMBR reference frame, which is in effect the reference frame of the universe.   </p>

<blockquote>
  <p>Or does it stay in a single location? If it does move, what causes it to move?</p>
</blockquote>

<p>I'm afraid I don't know why it's moving. Perhaps it's because the Universe is full of things moving in fairly random directions. Like a gas.  </p>

<blockquote>
  <p>Hopefully the question makes sense, if not I can elaborate.</p>
</blockquote>

<p>It certainly makes sense to me! </p>

<p><strong>Edit 13/09/2017</strong> : as Dave points out in the comments, there are other motions, including the motion of the solar system around the galaxy, which is circa 514,000 mph. (See the Wikipedia <a href="https://en.wikipedia.org/wiki/Galactic_year" rel="noreferrer">Galactic Year</a> article). And the motion of galaxies isn't neat and tidy either. </p>

CC BY-SA 3.0
2017-09-12T19:29:09.543Z
Awesome response! There's a ton for me to look-up and read about. I really appreciate your time/explanation.
Mike
CC BY-SA 3.0
2017-09-12T19:31:27.240Z
My pleasure Mike. I try!
John Duffield
CC BY-SA 3.0
2017-09-12T20:59:14.560Z
"Why is it moving?" It would be an incredible coincidence if it were perfectly still. There are uncountable numbers of objects in the universe exerting gravitational attractions in different directions. They would have to exactly balance out the for the galaxy not to move.
Barmar
CC BY-SA 3.0
2017-09-12T21:13:43.753Z
@Barmar : good point. Why didn't I think to say that? Duh!
John Duffield
CC BY-SA 3.0
2017-09-12T23:15:03.863Z
Well, at least everything *continues* to move (how it all started to is still up for debate I suppose ;) because stuff is still hot. When everything gets cold, absolutely nothing will move anymore.... supposedly: [heat death of the universe](https://en.wikipedia.org/wiki/Heat_death_of_the_universe). To put it simply as I understand it, eventually once all the atoms in the universe equalize in temperature, no work can be done anymore because there will be no potential energy left anywhere to do any work. Or something like that.
Mazura
CC BY-SA 3.0
2017-09-12T23:15:33.493Z
"there exists the view that the mechanical movement of the universe will run down, as work is converted to heat, in time because of the second law [of thermodynamics]."
Mazura
CC BY-SA 3.0
2017-09-13T09:58:49.190Z
@Barmar: From "A brief history of time" : `Newton realized that, according to his theory of gravity, the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point?` and `We now know it is impossible to have an infinite static model of the universe in which gravity is always attractive.`
Eric Duminil
CC BY-SA 3.0
2017-09-13T14:02:31.493Z
I think this answer is confusing, because the graphic shows motion of the solar system, rather than motion of the galaxy, and the solar system moves relative to the center of mass of the galaxy.  Then the answer discusses the motion of the local group, but the Milky Way moves relative to the center of mass of the local group.  See the article http://iopscience.iop.org/article/10.1086/527428/meta especially the caption of Fig. 3, for more information.
DavePhD
CC BY-SA 3.0
2017-09-13T16:59:50.840Z
@DavePfD : noted Dave. I've edited my answer to include something on that.
John Duffield
CC BY-SA 3.0
2017-09-14T08:08:04.347Z
_"627 km/s is quite fast. See this article, which says it's 1.3 million miles an hour."_ One might think that in Physics.SE, it would be sort of assumed that the reader knows how to convert km/s to miles/hour. Especially when 627 m/s is 1.4 mi/h, not 1.3, so the article probably uses other data.
JiK
CC BY-SA 3.0
2017-09-16T20:14:08.913Z
@Barmar Given the amount of advanced mathematics used in the study of physics, and the fact that the word "uncountable" has a specific mathematical meaning that almost certainly doesn't apply in this case, it might make sense to clarify whether you are asserting that the set of objects (planets, stars, motes of dust etc.) acting on the influence of gravity in the universe has equal cardinality with the set of real numbers or not.
Todd Wilcox
CC BY-SA 3.0
2017-09-12T18:49:05.520Z
2017-09-13T16:59:08.633Z
2017-09-13T16:59:08.633Z
John Duffield
<p>Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?</p>

CC BY-SA 3.0
2017-09-12T20:41:54.613Z
Check out the articles about [Galaxy Clusters](https://en.wikipedia.org/wiki/Galaxy_cluster) and the [Great Attractor](https://en.wikipedia.org/wiki/Great_Attractor), they may be of interest to you.
RomaH
CC BY-SA 3.0
2017-09-12T21:07:12.153Z
Only if you want to use something besides our galaxy's origin as your frame of reference. You could structure any maths to accurately describe our galaxy as the ONLY stationary one. It just isn't very modest to do so.
Raven
CC BY-SA 3.0
2017-09-12T23:30:40.843Z
"Through space" is not a thing. Space doesn't have locations. Motion is always relative to something else, like another galaxy, or the Cosmic Microwave Background, or whatever. You've already received some answers for the relative motion, see below.
Florin Andrei
CC BY-SA 3.0
2017-09-13T03:39:31.957Z
It's hard to think about something that has locations. Very interesting to think about. Thanks!
Mike
CC BY-SA 3.0
2017-09-13T07:22:54.097Z
I have a term that you might be interested in to Google: laniakea
PlasmaHH
CC BY-SA 3.0
2017-09-13T07:48:49.760Z
In Soviet Union, space moves through Milky Way!
el.pescado - нет войне
CC BY-SA 3.0
2017-09-13T15:20:45.103Z
@el.pescado  and in several other reference frames :-)
Carl Witthoft
CC BY-SA 3.0
2017-09-13T19:52:36.383Z
@PlasmaHH - I looked up laniakea and came across an amazing Youtube video. Very very interesting, thank you mentioning it. You know, deep thinking about the universe, Milky Way, and other universes I wonder if we will be able to see the end or edge of space. I understand space most likely has no end, but crazy to think what things would look like if you could have an outside view of the over-all peak of what all this is.
Mike
CC BY-SA 3.0
2017-09-15T06:15:30.727Z
I think it's worth mentioning that not only does it "move", but it'll also [collide with the Andromeda galaxy](https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision) (our neighbor).
r41n
CC BY-SA 3.0
2017-09-15T14:30:28.533Z
I would advise a tall glass of skepticism when watching videos on YouTube. A good portion (though certainly not all) of them will be... inaccurate.
Reinstate Monica -- notmaynard
CC BY-SA 3.0
2017-09-15T23:35:44.017Z
It sounds like you have just embarked on your journey to understanding the cosmos. There is a lot of high quality, easily accessible material to help you learn, no matter how little you know. Three good things that jump to mind are Stephen Hawking's book "A Brief History of Time", Brian Greene's book/videos "The Fabric of the Cosmos" and Neil deGrasse Tyson's reboot of the "Cosmos" series (available on Netflix!).  Really, that's just the tip. Plenty of videos have been made by Nova/PBS, BBC, National Geographic, Discovery, Science Channel, etc. Numerous books, suitable for laymen, also exist.
bubbleking
CC BY-SA 3.0
2017-09-16T17:15:29.997Z
the answer is "Very much so ...."
Fattie
CC BY-SA 4.0
2022-07-08T17:06:08.960Z
Motion is relative, so the question "Does the Milky Way move through space?" is technically not a valid question because it does not specify relative to what. Like any object, in the frame of itself it does not move.  In any other frame, it does move.  However, in the specific case of galaxy motions there is a special frame which is used by cosmologists to study and understand galaxy motions, and that is the frame of the Microwave Background. The mean of galaxy motions over very large scales is insignificant in this frame of reference.
eshaya
<galaxy><universe><milky-way>
Does the Milky Way move through space?
Mike
# Does the Milky Way move through space?

(Asked by: username_0 on 2017-09-12)

Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?

**Tags:** galaxy, universe, milky-way

> **Comments:**
> **username_1**: Check out the articles about [Galaxy Clusters](https://en.wikipedia.org/wiki/Galaxy_cluster) and the [Great Attractor](https://en.wikipedia.org/wiki/Great_Attractor), they may be of interest to you.  
> **username_2**: Only if you want to use something besides our galaxy's origin as your frame of reference. You could structure any maths to accurately describe our galaxy as the ONLY stationary one. It just isn't very modest to do so.  
> **username_3**: "Through space" is not a thing. Space doesn't have locations. Motion is always relative to something else, like another galaxy, or the Cosmic Microwave Background, or whatever. You've already received some answers for the relative motion, see below.  
> **username_0**: It's hard to think about something that has locations. Very interesting to think about. Thanks!  
> **username_4**: I have a term that you might be interested in to Google: laniakea  
> **username_5**: In Soviet Union, space moves through Milky Way!  
> **username_6**: @username_5  and in several other reference frames :-)  
> **username_0**: @username_4 - I looked up laniakea and came across an amazing Youtube video. Very very interesting, thank you mentioning it. You know, deep thinking about the universe, Milky Way, and other universes I wonder if we will be able to see the end or edge of space. I understand space most likely has no end, but crazy to think what things would look like if you could have an outside view of the over-all peak of what all this is.  
> **username_7**: I think it's worth mentioning that not only does it "move", but it'll also [collide with the Andromeda galaxy](https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_collision) (our neighbor).  
> **username_8**: I would advise a tall glass of skepticism when watching videos on YouTube. A good portion (though certainly not all) of them will be... inaccurate.  
> **username_9**: It sounds like you have just embarked on your journey to understanding the cosmos. There is a lot of high quality, easily accessible material to help you learn, no matter how little you know. Three good things that jump to mind are Stephen Hawking's book "A Brief History of Time", Brian Greene's book/videos "The Fabric of the Cosmos" and Neil deGrasse Tyson's reboot of the "Cosmos" series (available on Netflix!).  Really, that's just the tip. Plenty of videos have been made by Nova/PBS, BBC, National Geographic, Discovery, Science Channel, etc. Numerous books, suitable for laymen, also exist.  
> **username_10**: the answer is "Very much so ...."  
> **username_11**: Motion is relative, so the question "Does the Milky Way move through space?" is technically not a valid question because it does not specify relative to what. Like any object, in the frame of itself it does not move.  In any other frame, it does move.  However, in the specific case of galaxy motions there is a special frame which is used by cosmologists to study and understand galaxy motions, and that is the frame of the Microwave Background. The mean of galaxy motions over very large scales is insignificant in this frame of reference.  

---

## 4 answers

### Answer by username_23 on 2017-09-12. Score: 85 | Accepted answer

> Does the Milky Way move through space?

Yes it does.

> I'm very fascinated with space, although I don't have a degree or any formal education, I'm still very in love with everything about it and want to learn constantly.

Good man username_0.

> One thing I ask myself is if our galaxy moves through space?

It does. When we look at the Cosmic Microwave Background Radiation we see a "dipole anisotropy" due to the motion of the Earth relative to it:

![enter image description here](https://i.sstatic.net/MsvXR.jpg)

Image courtesy of William H. Kinney's [Cosmology, inflation, and the physics of nothing](https://ned.ipac.caltech.edu/level5/Sept02/Kinney/Kinney_contents.html/%22title%22)

See [Wikipedia](https://en.wikipedia.org/wiki/Cosmic_microwave_background#CMBR_dipole_anisotropy) for more:

*"From the CMB data it is seen that the Local Group (the galaxy group that includes the Milky Way galaxy) appears to be moving at 627±22 km/s relative to the reference frame of the CMB (also called the CMB rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 276°±3°, b = 30°±3°.[82][83] This motion results in an anisotropy of the data (CMB appearing slightly warmer in the direction of movement than in the opposite direction).[84]"*

627 km/s is quite fast. See [this article](https://astrosociety.org/edu/publications/tnl/71/howfast.html#6), which says it's 1.3 million miles an hour. The speed of light is just under 300,000 km/s or 670 million miles per hour, so the Milky Way is moving through the Universe at circa 0.2% of the speed of light. Also see [the CMBR](https://physics.stackexchange.com/a/25929/76162) physics answer by ghoppe which talks about the CMBR reference frame, which is in effect the reference frame of the universe.

> Or does it stay in a single location? If it does move, what causes it to move?

I'm afraid I don't know why it's moving. Perhaps it's because the Universe is full of things moving in fairly random directions. Like a gas.

> Hopefully the question makes sense, if not I can elaborate.

It certainly makes sense to me!

**Edit 13/09/2017** : as Dave points out in the comments, there are other motions, including the motion of the solar system around the galaxy, which is circa 514,000 mph. (See the Wikipedia [Galactic Year](https://en.wikipedia.org/wiki/Galactic_year) article). And the motion of galaxies isn't neat and tidy either.

> **Comments:**
> **username_0**: Awesome response! There's a ton for me to look-up and read about. I really appreciate your time/explanation.  
> **username_23**: My pleasure username_0. I try!  
> **username_16**: "Why is it moving?" It would be an incredible coincidence if it were perfectly still. There are uncountable numbers of objects in the universe exerting gravitational attractions in different directions. They would have to exactly balance out the for the galaxy not to move.  
> **username_23**: @username_16 : good point. Why didn't I think to say that? Duh!  
> **username_24**: Well, at least everything *continues* to move (how it all started to is still up for debate I suppose ;) because stuff is still hot. When everything gets cold, absolutely nothing will move anymore.... supposedly: [heat death of the universe](https://en.wikipedia.org/wiki/Heat_death_of_the_universe). To put it simply as I understand it, eventually once all the atoms in the universe equalize in temperature, no work can be done anymore because there will be no potential energy left anywhere to do any work. Or something like that.  
> **username_24**: "there exists the view that the mechanical movement of the universe will run down, as work is converted to heat, in time because of the second law [of thermodynamics]."  
> **username_18**: @username_16: From "A brief history of time" : `Newton realized that, according to his theory of gravity, the stars should attract each other, so it seemed they could not remain essentially motionless. Would they not all fall together at some point?` and `We now know it is impossible to have an infinite static model of the universe in which gravity is always attractive.`  
> **username_25**: I think this answer is confusing, because the graphic shows motion of the solar system, rather than motion of the galaxy, and the solar system moves relative to the center of mass of the galaxy.  Then the answer discusses the motion of the local group, but the Milky Way moves relative to the center of mass of the local group.  See the article http://iopscience.iop.org/article/10.1086/527428/meta especially the caption of Fig. 3, for more information.  
> **username_23**: @DavePfD : noted Dave. I've edited my answer to include something on that.  
> **username_26**: _"627 km/s is quite fast. See this article, which says it's 1.3 million miles an hour."_ One might think that in Physics.SE, it would be sort of assumed that the reader knows how to convert km/s to miles/hour. Especially when 627 m/s is 1.4 mi/h, not 1.3, so the article probably uses other data.  
> **username_27**: @username_16 Given the amount of advanced mathematics used in the study of physics, and the fact that the word "uncountable" has a specific mathematical meaning that almost certainly doesn't apply in this case, it might make sense to clarify whether you are asserting that the set of objects (planets, stars, motes of dust etc.) acting on the influence of gravity in the universe has equal cardinality with the set of real numbers or not.  

---

### Answer by username_12 on 2017-09-12. Score: 41

Galaxies move *through* space with velocities of the order of a several 100 km per second; small velocities for small groups (~100 km/s; e.g [Carlberg et al. 2000](https://arxiv.org/abs/astro-ph/0008201)) and large velocities for rich clusters (~1000 km/s; e.g [Girardi et al. 1993](http://adsabs.harvard.edu/abs/1993ApJ...404...38G)).

In addition to this so-called "peculiar velocity", galaxies also also carried away from each other due to the expansion of the Universe, at a velocity proportional to the distance from each other (the "[Hubble flow](https://en.wikipedia.org/wiki/Hubble%27s_law)"). But this is not a motion *through* space; rather it is space itself that is expanding (and hence the velocity may exceed the speed of light for sufficiently large distances).

One may define a "global reference frame" with respect to which velocities are measured. Any reference is valid, but it makes sense to use the frame in which all galaxies are, on average, in rest (when the Hubble flow is subtracted)$^\dagger$. In this frame, the Local Group that the Milky Way is a part of moves with some $620\, \mathrm{km \, s}^{-1}$ (as noted in username_23 username_23's answer above), whereas the center of **the Milky Way has a velocity$^\ddagger$ of** $\mathbf{565 \pm 5 \, km \, s^{-1}}$ ([Planck Collaboration et al. 2020](https://ui.adsabs.harvard.edu/abs/2020A%26A...641A...1P)).

What causes this movement of galaxies? Galaxies that are not too far from each (i.e. closer), "feel" each others mutual gravitational forces. A galaxy in a group or cluster moves around in the common gravitational field, but for galaxies that are farther away, the Hubble flow carries them away from each other too fast for them to attract each other.

This movement can be traced back to the tiny quantum mechanical fluctuations in the primordial soup of particles during [cosmic inflation](https://en.wikipedia.org/wiki/Inflation_(cosmology)), i.e. less than $\sim10^{-32}\,\mathrm{s}$ after the Big Bang. As time went by, ever-so-slight overdensities grew in amplitude, until they collapsed to form the structure we see in the Universe today. During this collapse, matter grew turbulent, whirling clumps around that eventually became the galaxies that orbit each other.

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$^\dagger$Formally, one uses the frame in which the [cosmic microwave background](https://en.wikipedia.org/wiki/Cosmic_microwave_background) is isotropic.

$^\ddagger$Taking into account our motion around the Galactic center, our Sun (currently) moves through space at $369.82\pm0.11\,\mathrm{km\, s^{-1}}$.

> **Comments:**
> **username_0**: I'm in awe by the intelligence of you guys. I had to read your response a few times to barely grasp what you are saying. But none nonetheless, I'm going to be researching/learning about everything you are talking about. (which I'm sure that will raise more questions, lol)  
> **username_13**: @username_0 It's less a question of intelligence and more one of experience and study. Most things in life are like that.  
> **username_12**: I second that, @username_13!  

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### Answer by username_14 on 2017-09-13. Score: 9

**NO**, if don't want to consider it to be doing so.

Everything in the universe only "moves" when considered from a different frame of reference. From the [observational frame of reference](https://en.wikipedia.org/wiki/Frame_of_reference) of the Milky Way galaxy, every *other* object in the universe is moving, and the Milky Way is stationary.

When I walk to work, what I am actually doing is dragging the surface of the Earth, and everything on it, towards me with my feet, until my office arrives.

> **Comments:**
> **username_15**: man, no wonder I need coffee when i get to the office..  
> **username_16**: What about someone else walking to work from the opposite direction? Don't the two of you cancel each other out?  
> **username_17**: That's certainly how it feels today. Maybe I need to reset my reference frame. Or find a better office!  
> **username_18**: If you walk to work, you're not just dragging Earth but the whole universe. You're also rotating it by a few millidegrees.  
> **username_18**: @username_16: Both people think that they're stationary, that the universe is moving towards them at 5km/h and the other person is walking towards them at 10km/h.  
> **username_18**: @username_14 : `"Does the Milky Way move through space?"` Since the frame of reference is defined, the answer must be **YES**. What you think you're doing when you walk to work is irrelevant.  
> **username_14**: @username_18 Yes, that's why I qualified it with "if you don't want it to" — and my answer was mostly a somewhat tongue-in-cheek counterpoint to the more technical answers already given.  
> **username_19**: Einstein is reputed to have asked a ticket inspector, "Does Crewe stop at this train?".  
> **username_20**: I'm stunned that an intelligent person could type that last paragraph, mate.  

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### Answer by username_21 on 2017-09-13. Score: 7

Monty Python does not seem very accurate in scientific issues, but this time it does it's job quite well in the Galaxy Song also mentioning the milky ways movement.

```
Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day
In an outer spiral arm, at forty thousand miles an hour,
Of the galaxy we call the 'Milky Way'.
Our galaxy itself contains a hundred billion stars.
It's a hundred thousand light years side to side.
It bulges in the middle, sixteen thousand light years thick,
But out by us, it's just three thousand light years wide.
We're thirty thousand light years from galactic central point.
We go 'round every two hundred million years,
And our galaxy is only one of millions of billions
In this amazing and expanding universe.

The universe itself keeps on expanding and expanding
In all of the directions it can whizz
As fast as it can go, at the speed of light, you know,
Twelve million miles a minute, and that's the fastest speed there is.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger all down here on Earth.

```

And yes, these figures are accurate: (at the time of publish)
<https://en.wikipedia.org/wiki/Galaxy_Song#Accuracy_of_astronomical_figures>

> **Comments:**
> **username_22**: But, just to be a killjoy, it doesn't answer the question.  
> **username_21**: "We're thirty thousand light years from galactic central point.We go 'round every two hundred million years," is a clear "YES" IMHO for the "Milky Way is moving" topic  
> **username_22**: Of course it isn't. It is a clear statement that the Milky Way is a rotating disc of which we are a part. Rotation and translation (moving thru space) are two entirely different things.  
> **username_16**: True. All the motions mentioned in the song are rotations, except for the expansion of the universe. And giving a single speed for the latter is wrong.  

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