<p>It depends greatly on the nature of your "hypothetical spacecraft".</p>

<p>Any spacecraft travelling through interstellar space will have to deal with interstellar gas and dust. At sufficiently high relativistic velocities, running into a hydrogen atom is like being hit by a high-energy cosmic ray, and running into a dust particle could seriously ruin your afternoon.</p>

<p>The intergalactic medium has substantially less matter than the interstellar medium within the galaxy. A route that exits the body of the galaxy by going "galactic north", then travels parallel to the disk, then re-enters the galaxy at another point will obviously be longer than a straight-line route, but it will encounter significantly less matter along the way. If the maximum safe velocity of the USS Hypothetical depends strongly on the density of the medium through which it's travelling, then the indirect route could be faster.</p>

<p>Whichever route you choose, this will take a long time. You should bring a book and plenty of snacks.</p>

CC BY-SA 3.0
2015-04-01T21:51:57.637Z
2015-04-01T21:51:57.637Z
Keith Thompson
<p>Not really, for the same reason that you cannot travel west by jumping up in the air and let Earth rotate underneath you, such that you land a little farther to the west.</p>

<p>The reason is that standing on Earth's surface, you already have a velocity toward the east which matches exactly the speed of the surface. Thus, in the reference frame of Earth, you simply jump up and down.</p>

<p>In the same manner, if you use your mad hypothetical spacecraft to fly "up", i.e. away from the Galactic plane, you already have a velocity of $\sim$250 km s$^{-1}$ in the direction of the rotation of the plane, so that in the reference frame of the plane, you simply fly straight up.</p>

<p>Apart from this, in order to leave the Galactic plane, you need to fly roughly 500 lightyears. This will take a long time. You should stay home.</p>

CC BY-SA 3.0
2015-04-01T19:16:44.633Z
Good point! Negligible for most purposes, but nevertheless true :)
pela
CC BY-SA 3.0
2015-03-31T21:58:19.920Z
2015-04-01T08:00:57.847Z
2015-04-01T08:00:57.847Z
pela
<p>If we had a hypothetical spacecraft, would it be possible to exit our galaxy, wait for some time and enter back into another section? Will this method be more efficient that a more traditional flight path? </p>

CC BY-SA 3.0
2015-03-31T21:53:15.280Z
Yes. Hypothetically you can go anywhere with Hypothetical spacecraft. But the speed of that hypothetical spacecraft cannot be greater than speed of light. So if we consider the spacecraft having the speed equivalent(not exact equal) to speed of light then you will require 500 Light year to go away from the disk of our galaxy as thickness of our Milkyway is 1000 light year or so and we are in the middle of the disk.
AmitG
CC BY-SA 3.0
2015-04-01T21:44:52.230Z
@barrycarter: That's 28 years ship time; it's still about 2.5 million years for the folks back home.
Keith Thompson
CC BY-SA 3.0
2015-04-02T10:31:51.437Z
Theoretically if you plan to cross a fair distance through the milky way, a gravity assist around a fast moving orbit could be beneficial.   Using stars rather than trying to fly outside the Milky way would probobly be the best approach.    It would still be a crazy-long journey though.
userLTK
CC BY-SA 3.0
2015-07-28T13:45:17.827Z
@userLTK I wonder how large the acceleration would be during such a gravity assist...
gerrit
CC BY-SA 3.0
2015-07-29T03:45:06.383Z
Might be better as a new question but briefly, the maximum added velocity in a stellar gravity assist is twice the relative velocity between the launch star (our sun) and the gravity assist star. (so, you have to get there before you gain any velocity).   All local stars are orbiting in the Milky way, but the "milling" velocity in our region is around 43,000 MPH, find a fast one, maybe 60,000-70,000 MPH and if it's perfectly positioned, you could add double that (120-140,000 MPH).   http://astrosociety.org/edu/publications/tnl/71/howfast.html  a tight binary star system, you could add more.
userLTK
<milky-way><galactic-dynamics>
Leaving the Milky Way
theVerma
# Leaving the Milky Way

(Asked by: username_0 on 2015-03-31)

If we had a hypothetical spacecraft, would it be possible to exit our galaxy, wait for some time and enter back into another section? Will this method be more efficient that a more traditional flight path?

**Tags:** milky-way, galactic-dynamics

> **Comments:**
> **username_1**: Yes. Hypothetically you can go anywhere with Hypothetical spacecraft. But the speed of that hypothetical spacecraft cannot be greater than speed of light. So if we consider the spacecraft having the speed equivalent(not exact equal) to speed of light then you will require 500 Light year to go away from the disk of our galaxy as thickness of our Milkyway is 1000 light year or so and we are in the middle of the disk.  
> **username_2**: @barrycarter: That's 28 years ship time; it's still about 2.5 million years for the folks back home.  
> **username_3**: Theoretically if you plan to cross a fair distance through the milky way, a gravity assist around a fast moving orbit could be beneficial.   Using stars rather than trying to fly outside the Milky way would probobly be the best approach.    It would still be a crazy-long journey though.  
> **username_4**: @username_3 I wonder how large the acceleration would be during such a gravity assist...  
> **username_3**: Might be better as a new question but briefly, the maximum added velocity in a stellar gravity assist is twice the relative velocity between the launch star (our sun) and the gravity assist star. (so, you have to get there before you gain any velocity).   All local stars are orbiting in the Milky way, but the "milling" velocity in our region is around 43,000 MPH, find a fast one, maybe 60,000-70,000 MPH and if it's perfectly positioned, you could add double that (120-140,000 MPH).   http://astrosociety.org/edu/publications/tnl/71/howfast.html  a tight binary star system, you could add more.  

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## 2 answers

### Answer by username_5 on 2015-03-31. Score: 14 | Accepted answer

Not really, for the same reason that you cannot travel west by jumping up in the air and let Earth rotate underneath you, such that you land a little farther to the west.

The reason is that standing on Earth's surface, you already have a velocity toward the east which matches exactly the speed of the surface. Thus, in the reference frame of Earth, you simply jump up and down.

In the same manner, if you use your mad hypothetical spacecraft to fly "up", i.e. away from the Galactic plane, you already have a velocity of $\sim$250 km s$^{-1}$ in the direction of the rotation of the plane, so that in the reference frame of the plane, you simply fly straight up.

Apart from this, in order to leave the Galactic plane, you need to fly roughly 500 lightyears. This will take a long time. You should stay home.

> **Comments:**
> **username_5**: Good point! Negligible for most purposes, but nevertheless true :)  

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### Answer by username_2 on 2015-04-01. Score: 1

It depends greatly on the nature of your "hypothetical spacecraft".

Any spacecraft travelling through interstellar space will have to deal with interstellar gas and dust. At sufficiently high relativistic velocities, running into a hydrogen atom is like being hit by a high-energy cosmic ray, and running into a dust particle could seriously ruin your afternoon.

The intergalactic medium has substantially less matter than the interstellar medium within the galaxy. A route that exits the body of the galaxy by going "galactic north", then travels parallel to the disk, then re-enters the galaxy at another point will obviously be longer than a straight-line route, but it will encounter significantly less matter along the way. If the maximum safe velocity of the USS Hypothetical depends strongly on the density of the medium through which it's travelling, then the indirect route could be faster.

Whichever route you choose, this will take a long time. You should bring a book and plenty of snacks.


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