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segfault
2003-Jan-13, 10:41 PM
I was just kind of mulling this over in my brain a while back, and I thought it might (I suppose I could be let down) make for an interesting topic of discussion.

Seems that most of the Sci-Fi I read always talks about things in terms of a single (usually our) galaxy as far as the limits of human expension, an empire, etc.

I was curious what additional challenges might be faced by explorers who travel BETWEEN galaxies. Aside from the obvious "They'd have to be incredibly patient people".

If we were to travel outside our solar system, we would encounter the Heliopause, is there a similar phenomena that defines the outer limits of the Milky Way's influence?

If we were to travel to say... the Galaxy of Andromeda, do we know enough about the layout of the stars within that galaxy to pick an interesting candidate for exploration, or would such information need to be gathered en route? (Again, assuming you've got a group of very patient, nearly immortal explorers)

JS Princeton
2003-Jan-14, 12:01 AM
It's not clear that they would have to be incredibly patient people if we were able to find away to constantly accelerate our space craft. Then trips wouldn't be so bad as time would dilate for the rest of the universe and it would take you a considerably shorter period of time to go than if you went at a constant velocity even just under the speed of light. Of course, there aren't any ideas for such a spacecraft yet, but as soon as there is one, you can bet we'll be galavanting all around the cosmos. (Only problem might be avoiding disasterous collisions.)

Dickenmeyer
2003-Jan-14, 01:20 AM
You might be able to gather some target information with some kind of giant interferometer array, say a couple of dozen big dishes orbiting out past Neptune, or maybe a really big space telescope with maybe a kilometer wide aluminized mylar mirror held in shape by some kind of superhightech framework with little nanomotors constantly adjusting the tension and microbots scurrying around fixing all the holes from impacting debris. You would have the problem of your info being about 4 million years out of date by the time you got to Andromeda though, even at relativistic speeds.

David Hall
2003-Jan-14, 09:32 AM
You'd probably not even have an exact destination when you set out. The best you'd probably be able to do is decide the general area you want to search in. Detailed observation would only begin en route, when you got close enough to the galaxy to observe stellar systems directly. But you would have to make your final decision far enough in advance to be able to easily alter your course to get to it.

Argos
2003-Jan-14, 12:02 PM
On 2003-01-13 19:01, JS Princeton wrote:
Then trips wouldn't be so bad as time would dilate for the rest of the universe

Well…

Even if they could take advantage of the time dilation, I see problems regarding the real meaning of such a trip. In a round-trip to Andromeda, for instance [at the speed of light], a human would feel the passage of some 80 years, while here on Earth four million years would have passed. Am I right?

Now consider traveling to galaxies farther away. It seems there would have to be some kind of multi-millennial mission control back on Earth to keep the plans going on. If you were to visit the Cartwheel galaxy (http://antwrp.gsfc.nasa.gov/apod/ap950702.html), for example, a couple of thousand years would have passed on your ship whilst a whole geological era would have passed on Earth when you [or your descendants] got back. What would be the historical meaning of such missions? A civilization would have to be very stable to sustain long-term projects of this kind. Don’t you think so?

It would only make sense if the journey was designed to open new settlements for the mankind, cutting the ties that bind the galactic travellers to the mother planet forever.

<font size=-1>[ This Message was edited by: Argos on 2003-01-15 12:36 ]</font>

kucharek
2003-Jan-14, 12:24 PM
I remember Poul Anderson's "World without Stars" about a journey to a planet orbiting a star outside the galaxy. Makes some assumptions about the environment, like old star, low radiation, no heavy elements available.

Harald

informant
2003-Jan-14, 06:29 PM
IF wormholes can be used for transportation, then I imagine that they would be a possibility...
There is some science fiction that involves traveling to other galaxies. Off the top of my head, I remember E. E. Smith's Lensman series, with a few trips to the Magellanic Clouds. [Comment about propulsion system in Lensman series edited out. On second thought, things may not be quite as simple as I had previously written.] There is also a space opera by Van Vogt that I read called Mission to the Stars...



<font size=-1>[ This Message was edited by: informant on 2003-01-14 14:47 ]</font>

Thumper
2003-Jan-14, 07:37 PM
On 2003-01-14 07:02, Argos wrote:
Well…

I would say that even if they could take advantage of the time dilation, I see problems regarding the real meaning of such a trip. In a round-trip to Andromeda, for instance [at the speed of light], a human would feel the passage of some 80 years, while here on Earth four million years would have passed. Am I right?



I've always had a question about this and am now, apparently willing to display my ignorance. Take the example above:
A trip to the Andromeda Galaxy takes 40 years one way to the passengers on the ship. But 2 Million years have passed on Earth. Alot of things can happen in 2 million years. What if a much better propulsion system were worked out? The passengers on the first ship might find Andromeda completely explored and colonized by the time they got there.

Another thing: Speed or velocity is distance over time. To those on the ship they are traveling at (or near) the speed of light. But to observers on Earth, they are going ridiculously slower. Instead of dividing by 40 years, they would be dividing by 2 Million years. The ship would appear to be crawling to Earthbound visitors. Why wouldn't a ship much slower, be able to catch it?

(Applies generous amounts of flame retardant and waits patiently)

daver
2003-Jan-14, 08:10 PM
On 2003-01-14 14:37, Thumper wrote:


On 2003-01-14 07:02, Argos wrote:
Well?

I would say that even if they could take advantage of the time dilation, I see problems regarding the real meaning of such a trip. In a round-trip to Andromeda, for instance [at the speed of light], a human would feel the passage of some 80 years, while here on Earth four million years would have passed. Am I right?



I've always had a question about this and am now, apparently willing to display my ignorance. Take the example above:
A trip to the Andromeda Galaxy takes 40 years one way to the passengers on the ship. But 2 Million years have passed on Earth. Alot of things can happen in 2 million years. What if a much better propulsion system were worked out? The passengers on the first ship might find Andromeda completely explored and colonized by the time they got there.



Hmm, depends on what you mean by much better. Possibly FTL travel would have been discovered in the meantime, in which case, yes, the entire galaxy could have been colonized. Some effort might be made to contact the original colony ship, depending on the nature of the STL drive.

Possibly instead of FTL travel, someone invents an antigrav that allows the second ship to use much higher acceleration. So instead of 80 ship years to travel to Andromeda, it gets there in merely 5 ship years. It's still going to take marginally over 2 million earth years to get there--they might beat the first ship by decades (i'm eyeballing this; someone might want to plug the difference between 1 g and 100 g's into the relativistic rocket equations and see what falls out). Not enough time to matter.




Another thing: Speed or velocity is distance over time. To those on the ship they are traveling at (or near) the speed of light. But to observers on Earth, they are going ridiculously slower. Instead of dividing by 40 years, they would be dividing by 2 Million years. The ship would appear to be crawling to Earthbound visitors. Why wouldn't a ship much slower, be able to catch it?

(Applies generous amounts of flame retardant and waits patiently)

Was "much slower" a typo?

The ship would be crawling in the same sense that light is crawling. Instead of taking 2 million years to travel to Andromeda, the ship might take 2.0001 million years to travel to Andromeda. So an improved ship that would only take 2.00001 million years to travel to Andromeda would catch it if launched soon enough after the first ship.

darkhunter
2003-Jan-14, 08:14 PM
On 2003-01-14 07:02, Argos wrote:
Now consider traveling to galaxies farther away. It seems there would have to be some kind of multi-millennial mission control back on Earth to keep the plans going on. If you were to visit the Cartwheel galaxy (http://antwrp.gsfc.nasa.gov/apod/ap950702.html), for example, a couple of thousand years would have passed on your ship whilst a whole geological era would have passed on Earth when you [or your descendants] got back. What would be the historical meaning of such missions? A civilization would have to be very stable to sustain long-term projects of this kind. Don’t you think so?


<font size=-1>[ This Message was edited by: Argos on 2003-01-14 07:06 ]</font>


Stefphen Baxter deals with this in "Manifold Space" concerning individuals. They used a matter transmitter so they didn't age during transport. For the ones who kept making trips they were essentially returning to an alien civilization after each trip. Had to relearn even the simplest of things (flushing the toilet and turning on the lights) for example....

I reckon that an intergalactic round trip would be much the same--need some top notch historians and language experts to peice together how to communicate and function is the new societies....

Colt
2003-Jan-14, 08:34 PM
On 2003-01-14 07:02, Argos wrote:


On 2003-01-13 19:01, JS Princeton wrote:
Then trips wouldn't be so bad as time would dilate for the rest of the universe

Well…

I would say that even if they could take advantage of the time dilation, I see problems regarding the real meaning of such a trip. In a round-trip to Andromeda, for instance [at the speed of light], a human would feel the passage of some 80 years, while here on Earth four million years would have passed. Am I right?

Now consider traveling to galaxies farther away. It seems there would have to be some kind of multi-millennial mission control back on Earth to keep the plans going on. If you were to visit the Cartwheel galaxy (http://antwrp.gsfc.nasa.gov/apod/ap950702.html), for example, a couple of thousand years would have passed on your ship whilst a whole geological era would have passed on Earth when you [or your descendants] got back. What would be the historical meaning of such missions? A civilization would have to be very stable to sustain long-term projects of this kind. Don’t you think so?

It would only make sense if the journey was designed to open new settlements for the mankind, cutting the ties that bind the galactic travellers to the mother planet forever.

<font size=-1>[ This Message was edited by: Argos on 2003-01-14 07:06 ]</font>


It reminds me of what happend to the City Builders in Niven's Ringworld series. Some of them left on the interstellar ram-ships and when they returned there was nothing of their society left and they spend the last of their days wondering the ruins. -Colt

xriso
2003-Jan-15, 06:05 AM
On 2003-01-14 14:37, Thumper wrote:
Another thing: Speed or velocity is distance over time. To those on the ship they are traveling at (or near) the speed of light. But to observers on Earth, they are going ridiculously slower. Instead of dividing by 40 years, they would be dividing by 2 Million years. The ship would appear to be crawling to Earthbound visitors. Why wouldn't a ship much slower, be able to catch it?

(Applies generous amounts of flame retardant and waits patiently)


According to the people in the ship, the distance between the milky way and andromeda is much shorter. /phpBB/images/smiles/icon_smile.gif

Thumper
2003-Jan-15, 12:35 PM
On 2003-01-14 15:10, daver wrote:

Was "much slower" a typo?



I know I'm missing something and I also didn't phrase my question well. So I'll try again. Using Argos' example above:
There are people on a ship traveling to the Andromeda galaxy. It is 40 light years distant and the trip takes 40 years to get there. The average speed of the ship is the speed of light (or 0.99999999c) if we don't want to break the "speed limit".

Now a kid on Earth wants to calculate the speed of the ship from his point of view. He knows that the distance to Andromeda is 40 light years. He asks an historian how long it took the ship to get there. The historian looks it up and says 2 million years give or take. So the kid divides the distance (40 LY) by the time (2 mill yrs.) and gets an average speed of 0.00002xc. If I'm not mistaken that's roughly 6 km/sec or 21600 km/hour. Isn't that slower than the space shuttle or ISS in low Earth orbit?

SeanF
2003-Jan-15, 02:43 PM
Thumper . . .

In the given example, the distance to the destination galaxy is about two million light-years, not 40. The people on the ship see it as being 40 light-years away and taking 40 years to get there. The people on Earth see it as being 2,000,000 light-years away and taking 2,000,000 years to get there. So, they would both calculate the velocity of the ship (distance / time) the same.

Relativity predicts that the people on the ship would see both time and space as being equally "compressed."

Thumper
2003-Jan-15, 03:14 PM
Thanks SeanF,

I think I'm understanding it better. I misinterpreted the numbers in Argos' example. To observers on Earth or any location not on the ship, the distance to a destination and the time it takes to get there will jive with the speed of the ship. To those on the ship, the time it takes to get there is much shorter but as you say, their perceived distance is also shorter. I didn't understand that the 40 LY figure (actually 80 LY round trip) was a perceived distance only to those on the ship.

That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."

Would that pose problems for scanning and tracking while you were traveling at that velocity? With time and space both distorted from your perspective, how would that effect accurate measurements from targets or between targets?

gethen
2003-Jan-15, 03:48 PM
Another old sf book, I think by Poul Anderson, titled Tau Zero deals with ever-accelerating space travel and winds up with the ship and crew actually observing the collapse of the universe and the next "Big Bang,", then settling in a star system in that future universe. Very strange.

Argos
2003-Jan-15, 04:53 PM
Thumper, I thought your figures were a joke. Sorry. Thanks Sean for the answer I should have given.

Anyway, I think that intergalactic travel would only be reasonably feasible if we discovered a means of using the geometric properties of space-time to dislocate matter [wormholes come to my mind]. Even an ever-accelerating ship wouldn´t have a practical use, since time dilation would work only for the ship´s crew. Back on Earth the years would go on passing by the millions. Would you buy a one-way ticket to Andromeda? /phpBB/images/smiles/icon_smile.gif

(*) Btw, even within the boundaries of our galaxy a speed of light cruise won´t be of much use. A journey at the speed of light to a star located at the other side of the galaxy, in a position analog to that of our Sun, would take some few months in the crew´s point of view, but something like 60,000 years for the Earthlings; the problem related to the historical meaning of the mission still lingers.


<font size=-1>[ This Message was edited by: Argos on 2003-01-15 12:35 ]</font>

traztx
2003-Jan-15, 05:03 PM
On 2003-01-15 11:53, Argos wrote:
the problem related to the historical meaning of the mission still lingers.


Sort of like a dandelion releasing her seeds into the wind and never knowing what becomes of them. Yet this behavior is necessary for the species to survive.

GrapesOfWrath
2003-Jan-15, 05:23 PM
On 2003-01-15 10:14, Thumper wrote:
I didn't understand that the 40 LY figure (actually 80 LY round trip) was a perceived distance only to those on the ship.

40 years, not 40 lightyears.


That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."
Careful. They don't accelerate to c--if they somehow were, the elapsed time would be zero, instead of 40 years. No time to even consider it. /phpBB/images/smiles/icon_smile.gif

Argos
2003-Jan-15, 05:23 PM
On 2003-01-14 07:24, kucharek wrote:
I remember Poul Anderson's "World without Stars" about a journey to a planet orbiting a star outside the galaxy.


I wouldn´t mind living in a “world without stars” since I could behold the milky way rising periodically in all its glory across a 90 degrees arc. /phpBB/images/smiles/icon_smile.gif

Argos
2003-Jan-15, 05:27 PM
On 2003-01-15 12:03, traztx wrote:
Sort of like a dandelion releasing her seeds into the wind and never knowing what becomes of them. Yet this behavior is necessary for the species to survive.


Very poetic. Congratulations. /phpBB/images/smiles/icon_wink.gif

I agree with you. As I said somewhere above, this is the only sense I can see in intergalactic travel.

Colt
2003-Jan-16, 12:04 AM
Still, why would you go to another galaxy? There is already an insane amount of space in this one. -Colt

segfault
2003-Jan-16, 01:40 AM
On 2003-01-15 19:04, Colt wrote:
Still, why would you go to another galaxy? There is already an insane amount of space in this one. -Colt



True, it was mainly a philosophical question. I just like the 'neat-o' value of it. I've seen some interesting discussion, so that's all I was really after /phpBB/images/smiles/icon_smile.gif

But, if you go to andromeda, you could hang out with the blamanges from the planet skyron in the galaxy of andromeda (assuming they don't eat you or conscript you to make kilts for them).

Colt
2003-Jan-16, 04:53 AM
Kilts. /phpBB/images/smiles/icon_biggrin.gif -Colt

Kaptain K
2003-Jan-17, 06:20 PM
That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."
No! It would still be 2 mly away. It's just that their subjective speed would be 50,000c.

SeanF
2003-Jan-17, 07:21 PM
On 2003-01-17 13:20, Kaptain K wrote:

That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."
No! It would still be 2 mly away. It's just that their subjective speed would be 50,000c.



No, yourself! Subjective velocity remains constant at relativistic speeds. Both subjective time and subjective distance change equally, so that distance/time remains the same.

John Kierein
2003-Jan-18, 02:35 PM
My website shows a link to a picture of life actually travelling intergalactially! Really! There is some reasonable speculation involved.
http://www.geocities.com/CapeCanaveral/Galaxy/7827/

Lexx_Luthor
2003-Jan-19, 12:54 PM
...someone invents an antigrav that allows the second ship to use much higher acceleration. ~~Daver

Yeah, to span galaxies in a human lifetime what kind of accelaration do you have to come up with--and whose reference frame? Would it be a bone crusher?

Kaptain K
2003-Jan-19, 10:35 PM
On 2003-01-17 14:21, SeanF wrote:


On 2003-01-17 13:20, Kaptain K wrote:

That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."
No! It would still be 2 mly away. It's just that their subjective speed would be 50,000c.



No, yourself! Subjective velocity remains constant at relativistic speeds. Both subjective time and subjective distance change equally, so that distance/time remains the same.

If you travel 2 mly in 40 subjective years, your subjective speed is by definition 50k c.

_________________
"There's a whole lotta things I've never done, but I ain't never had too much fun."
Commander Cody and the Lost Planet Airmen

<font size=-1>[ This Message was edited by: Kaptain K on 2003-01-19 17:37 ]</font>

SeanF
2003-Jan-20, 03:21 PM
On 2003-01-19 17:35, Kaptain K wrote:


On 2003-01-17 14:21, SeanF wrote:


On 2003-01-17 13:20, Kaptain K wrote:

That would be weird to passengers on the ship. Just before stepping on, they look up and see their destination 2 million LY distance. They fire up and accelerate to c and look out again. "Holy cow! we're only 40 LY away."
No! It would still be 2 mly away. It's just that their subjective speed would be 50,000c.



No, yourself! Subjective velocity remains constant at relativistic speeds. Both subjective time and subjective distance change equally, so that distance/time remains the same.

If you travel 2 mly in 40 subjective years, your subjective speed is by definition 50k c.

_________________
"There's a whole lotta things I've never done, but I ain't never had too much fun."
Commander Cody and the Lost Planet Airmen

<font size=-1>[ This Message was edited by: Kaptain K on 2003-01-19 17:37 ]</font>


Okay, fine, if you want to argue after the fact like that. But the OP was in specific reference to subjective distance to the destination while in transit - so your "No" response is still in error. /phpBB/images/smiles/icon_razz.gif

/phpBB/images/smiles/icon_wink.gif

JS Princeton
2003-Jan-20, 05:31 PM
On 2003-01-19 07:54, Lexx_Luthor wrote:

...someone invents an antigrav that allows the second ship to use much higher acceleration. ~~Daver

Yeah, to span galaxies in a human lifetime what kind of accelaration do you have to come up with--and whose reference frame? Would it be a bone crusher?




Actually, if I remember correctly, you can do it quite nicely with a constant 1G acceleration.

Jetmech0417
2003-Jan-21, 11:10 AM
Posts like these always make me wanna read some hard sci-fi........

darkarmy
2010-Feb-20, 10:40 AM
Not only time stretch occurs when traveling near light speed, but also distance compression, and mass increase.
Velocity= distance over time, where velocity would be the only constant (0.99c), therefore, mathematically, 40 years would be relative to the space contraction generated by the speed.
Actually a bigger challenge would be to accelerate a ship with an increasing mass relative to light speed. Some prototypes have been made by Nasa with a hydrogen bomb attached to a metal dish, which could supply enough energy to push such a heavy ship after reaching speeds near light.
But then the risk of encountering debris in space that could destroy the ship would increase exponentially, making such travel impossible, unless a force shield would be invented some how.

Styx
2010-Feb-25, 05:42 PM
Why are we being so foolish we are speculating a trip to Andromeda in HUMAN terms ? A civilization capable of that would not be human at all. By the time a civilization has enough energy and resources it would entirely be post biological. They can wait a long time if they desire because to them our mentality is same as an individual ant.

Craigboy
2010-Feb-25, 10:25 PM
Why are we being so foolish we are speculating a trip to Andromeda in HUMAN terms ? A civilization capable of that would not be human at all. By the time a civilization has enough energy and resources it would entirely be post biological. They can wait a long time if they desire because to them our mentality is same as an individual ant.
That's assuming that we'd still be using chemical rockets to get around.

Starfury
2010-Feb-27, 11:13 PM
If you're traveling to the Andromeda Galaxy and want some idea of where to go when you get there, you can draw on knowledge of our own galaxy to make some determinations:

1. The core of the Andromeda, with its 30 million solar mass supermassive black hole, is right out. If the core of the Milky Way is any indication, the radiation there would be just as bad, if not worse.

2. Avoid areas with lots of high-mass stars, like our own Orion Nebula and Eta Carinae, are probably not good if you're looking for something habitable. A few million to tens of millions of years, and they end their lives as supernovae. Not good for nearby lower-mass stars whose planets might otherwise be candidates for the development and evolution of life.

3. The spiral arms, especially the further out you go, are much better places to find planets that are inhabitable or even inhabited (or even planets, period). Try to find regions with plenty of low-mass yellow, orange, and red dwarf stars.

As has been pointed out, relativistic travel to Andromeda could be done within a human lifetime (from the point of view of the passengers on the ship) or we might find a way to use some theoretically possible but as yet infeasible means of traveling there, such as wormhole travel or the Alcubierre warp drive.

m74z00219
2010-Feb-28, 04:31 AM
If you travel 2 mly in 40 subjective years, your subjective speed is by definition 50k c.

Just for simplicity's sake, let's ignore the acceleration. Let's say they left at a particular speed and then they reached andromeda at the same particular speed. If the question being asked is, "If it takes andromeda 40 years to reach the astronauts from their perspective, how fast were they going relative to earth and etc" then check out the following:

Time traveled according to astronauts: 40 years
Time traveled according to earthlings: 2000000.000400 years (approx 2E6years)

Distance andromeda traveled according to astronauts: 40.0000016548 light-years
Distance astronauts traveled according to earthlings: 2000000.000000 (2E6 light-years)

This is with a velocity of 0.9999999998% of the speed of light.
And a gamma factor of 49999.997931


So, to clear things up. There is no such thing as subjective speed. Subjective speed is always by definition zero. Someone in an inertial frame would not think that they are moving, but rather that the rest of the universe is moving by them.


Hope this helps all,
M74

PS: I also wanted to point out that if these astronauts can travel arbitrarily close to 100% of the speed of light, that this implies that it can take an arbitrarily short time for Andromeda to reach the astronauts. However, the time it takes the astronauts to reach andromeda from the earthlings perspective would be arbitrarily close to 2E6 years.







_________________
"There's a whole lotta things I've never done, but I ain't never had too much fun."
Commander Cody and the Lost Planet Airmen

<font size=-1>[ This Message was edited by: Kaptain K on 2003-01-19 17:37 ]</font>[/QUOTE]

eburacum45
2010-Feb-28, 10:34 AM
IF wormholes can be used for transportation, then I imagine that they would be a possibility...

Well, that is a bit of a self-referential statement, but let's imagine if it were possible. You could make a wormhole with two spacially separated mouths here in the solar system, load one mouth into a fast ship and send it off to Andromeda. The trip would take forty years for the crew on the ship, and for the wormhole mouth itself. Now on arrival the crew could go back to Earth via the forty-year-old wormhole, and because the two wormhole mouths are causally connected they would arrive back there forty years after they set off.

But wait! From the frame of reference of Earth the ship will not arrive in Andromeda for another two million years! In four milllion years time we could confirm this fact using powerful telescopes to watch it arrive. So the Andromeda wormhole would be a time machine as well.

For more details see
http://en.wikipedia.org/wiki/Wormhole#Time_travel