6 ms·

Edit: A big brain fart, ignore the retracted part below. Colonizing the universe is of course impossible in 100My, barring FTL. What the paper I referred to [1]

Edit: A big brain fart, ignore the retracted part below. Colonizing the universe is of course impossible in 100My, barring FTL. What the paper I referred to [1] says is that colonizing the Milky Way may take less than that, and if you can do that, spreading to the rest of the observable universe is fairly easy, very relatively speaking. <retracted> According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years. It's much too fast for the expansion to affect except marginally.</retracted> The relative jump in difficulty from interstellar to intergalactic is much smaller than from interplanetary to interstellar. Anyway, as others said, mere intragalactic (and intra-Local Group) travel is not affected by expansion in any way whatsoever. [1] https://www.sciencedirect.com/science/article/abs/pii/S0094576513001148 https://www.sciencedirect.com/science/article/abs/pii/S00945..., PDF at https://www.aleph.se/papers/Spamming%20the%20universe.pdf https://www.aleph.se/papers/Spamming%20the%20universe.pdf

hn_acc1 1y ago
I found someone saying colonize the Milky Way Galaxy in ~90m years? Is that what you meant? The observable universe is ~93B LY - unless you're assuming FTL (and MUCH faster than light), I don't see how that's possible?
- Sharlin 1y ago
  Yes, my brain totally froze. Added a correction.
- omnicognate 1y ago
  Time dilation means that you can get anywhere while experiencing an arbitrarily small amount of time. You can cross the galaxy in a second as far as special relativity is concerned. (With the expenditure of insanely vast amounts of energy, ofc.) To an observer back home you'd look like you're travelling at merely extremely close to the speed of light, but to you the journey would take a second.
  - mr_toad 1y ago
    > You can cross the galaxy in a second as far as special relativity is concerned. Sure, but the rest of the universe will keep on changing. In 90 billion years it’s going to be a very old universe. Galaxies will become consolidated and isolated, fewer young stars will be born. Only the dim light of red dwarf stars will shine among a graveyard of dead stars.
    - omnicognate 1y ago
      Hey, I didn't say it would be fun :-D Tau-Zero by Poul Anderson explores this, BTW. It's a great little sci fi novel about a spaceship doomed to accelerate at 1G indefinitely. It is significant from a colonisation PoV. With sufficient acceleration capability and the ability to survive travelling through the interstellar medium at extreme velocity (rather than getting vaporised by a mote of dust), a single generation of humans could in theory colonise the whole galaxy within their own lifespans. Indeed, some of them could even come back together and meet again after visiting those distant worlds, on an Earth many millions of years older, if their worldlines end up with similar proper times.
xoa 1y ago
>According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years ...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0]. Even if the universe wasn't expanding nobody could get to everything any faster than that number of years right? Maybe you saw something that was talking about the local (Virgo) supercluster, which I think has a radius of around 55 million light years, so that sounds more like something that could be done on that timescale "in theory". But there are millions and millions of superclusters in the observable universe overall. ---- 0: https://en.wikipedia.org/wiki/Observable_universe https://en.wikipedia.org/wiki/Observable_universe
- palmotea 1y ago
  >> According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years > ...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0]. I guess it depends on whose hundred million years you're talking about: the colonists' or those who stay home's. I don't know how to do the calculations, but it seems plausible that you could traverse the entire observable universe at near light-speed in 100 million years ship time.
  - grvbck 1y ago
    You need ridiculous speeds for time dilation to really kick in though. Mathematically, it starts as soon as an object moves. But if a spaceship travels at 90 % of light speed (0.9 c), their local time moves just approximately at half speed compared to local time on earth. A year for the astronauts is just over 2 years on earth. At 0.995 c, the ship clock runs 10 x slower. At 0.999 c, 22 x slower. Then if you push the turbo button to 0.9999 c, 71 x slower. The fastest man-made object to date is the Parker Solar Probe, at 0.059 c.
- Sharlin 1y ago
  Oops, yes, I don't know what I was thinking. A total brain fart. The paper I referred to is Sandberg and Armstrong's 2012 "Eternity in Six Hours", and of course they don't claim such a thing. Only that it's possible to start a colonization wave that has plenty of time to spread to everything visible now before they slip outside of our future light cone. The ~100M years refers to the colonization of the Milky Way. Sorry! [1] https://www.sciencedirect.com/science/article/abs/pii/S0094576513001148 https://www.sciencedirect.com/science/article/abs/pii/S00945...
delta_p_delta_x 1y ago
> The relative jump in difficulty from interstellar to intergalactic is much smaller than from interplanetary to interstellar. Interesting way to put it... This doesn't seem that accurate. With sufficiently advanced technology, many of which we already possess, we could expect to propel a minute spacecraft to a considerable fraction of the speed of light, and reach nearby stars possibly within the end of the century. Reaching the other end of the galaxy is a massive undertaking. It's a logarithmic scale at every step of the way. Pluto is about 38 AU from Earth. Proxima Centauri is about 6.3 × 10^4 AU away (or about 4.24 ly), and that's roughly a 2 × 10^3 multiplication. The Milky Way is about 50000 ly in radius, and the Andromeda Galaxy is about 3 × 10^6 ly away. Going from interplanetary distances to interstellar, and thence to intergalactic, involves at least a 10^5 factor (give or take) at each step.
- mkl 1y ago
  If you can get to a star 100 light years away, you can get to Andromeda. It doesn't require going faster, just waiting longer.
  - michaelmrose 1y ago
    I feel like waiting longer in some sense may itself represent a substantial increase in difficulty in terms of creating something which remains stable for tens of thousands of years. On the other hand who knows with zero samples how stable societies are thousands of years beyond our present level of development.
    - mkl 1y ago
      Yes, that's why I said 100 light years rather than 4.3. Maybe it's still too low, but I think there are targets within the Milky Way that would require solving pretty much all the problems of getting to Andromeda.
  - ASalazarMX 1y ago
    Imagine doing that, and being greeted with ALL THESE WORLDS ARE YOURS EXCEPT ANDROMEDA
deleted 1y ago
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hn_acc1 1y ago

I found someone saying colonize the Milky Way Galaxy in ~90m years? Is that what you meant? The observable universe is ~93B LY - unless you're assuming FTL (and MUCH faster than light), I don't see how that's possible?

Sharlin 1y ago
Yes, my brain totally froze. Added a correction.
omnicognate 1y ago
Time dilation means that you can get anywhere while experiencing an arbitrarily small amount of time. You can cross the galaxy in a second as far as special relativity is concerned. (With the expenditure of insanely vast amounts of energy, ofc.) To an observer back home you'd look like you're travelling at merely extremely close to the speed of light, but to you the journey would take a second.
- mr_toad 1y ago
  > You can cross the galaxy in a second as far as special relativity is concerned. Sure, but the rest of the universe will keep on changing. In 90 billion years it’s going to be a very old universe. Galaxies will become consolidated and isolated, fewer young stars will be born. Only the dim light of red dwarf stars will shine among a graveyard of dead stars.
  - omnicognate 1y ago
    Hey, I didn't say it would be fun :-D Tau-Zero by Poul Anderson explores this, BTW. It's a great little sci fi novel about a spaceship doomed to accelerate at 1G indefinitely. It is significant from a colonisation PoV. With sufficient acceleration capability and the ability to survive travelling through the interstellar medium at extreme velocity (rather than getting vaporised by a mote of dust), a single generation of humans could in theory colonise the whole galaxy within their own lifespans. Indeed, some of them could even come back together and meet again after visiting those distant worlds, on an Earth many millions of years older, if their worldlines end up with similar proper times.

xoa 1y ago

>According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years ...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0]. Even if the universe wasn't expanding nobody could get to everything any faster than that number of years right? Maybe you saw something that was talking about the local (Virgo) supercluster, which I think has a radius of around 55 million light years, so that sounds more like something that could be done on that timescale "in theory". But there are millions and millions of superclusters in the observable universe overall. ---- 0: https://en.wikipedia.org/wiki/Observable_universe https://en.wikipedia.org/wiki/Observable_universe

palmotea 1y ago
>> According to some calculations, it should in principle be possible to colonize the entire observable universe in less than a hundred million years > ...what? That doesn't seem right, just from a really quick gut check it looks like the observable universe has a radius of 45.7 billion light years [0]. I guess it depends on whose hundred million years you're talking about: the colonists' or those who stay home's. I don't know how to do the calculations, but it seems plausible that you could traverse the entire observable universe at near light-speed in 100 million years ship time.
- grvbck 1y ago
  You need ridiculous speeds for time dilation to really kick in though. Mathematically, it starts as soon as an object moves. But if a spaceship travels at 90 % of light speed (0.9 c), their local time moves just approximately at half speed compared to local time on earth. A year for the astronauts is just over 2 years on earth. At 0.995 c, the ship clock runs 10 x slower. At 0.999 c, 22 x slower. Then if you push the turbo button to 0.9999 c, 71 x slower. The fastest man-made object to date is the Parker Solar Probe, at 0.059 c.
Sharlin 1y ago
Oops, yes, I don't know what I was thinking. A total brain fart. The paper I referred to is Sandberg and Armstrong's 2012 "Eternity in Six Hours", and of course they don't claim such a thing. Only that it's possible to start a colonization wave that has plenty of time to spread to everything visible now before they slip outside of our future light cone. The ~100M years refers to the colonization of the Milky Way. Sorry! [1] https://www.sciencedirect.com/science/article/abs/pii/S0094576513001148 https://www.sciencedirect.com/science/article/abs/pii/S00945...

delta_p_delta_x 1y ago

> The relative jump in difficulty from interstellar to intergalactic is much smaller than from interplanetary to interstellar. Interesting way to put it... This doesn't seem that accurate. With sufficiently advanced technology, many of which we already possess, we could expect to propel a minute spacecraft to a considerable fraction of the speed of light, and reach nearby stars possibly within the end of the century. Reaching the other end of the galaxy is a massive undertaking. It's a logarithmic scale at every step of the way. Pluto is about 38 AU from Earth. Proxima Centauri is about 6.3 × 10^4 AU away (or about 4.24 ly), and that's roughly a 2 × 10^3 multiplication. The Milky Way is about 50000 ly in radius, and the Andromeda Galaxy is about 3 × 10^6 ly away. Going from interplanetary distances to interstellar, and thence to intergalactic, involves at least a 10^5 factor (give or take) at each step.

mkl 1y ago
If you can get to a star 100 light years away, you can get to Andromeda. It doesn't require going faster, just waiting longer.
- michaelmrose 1y ago
  I feel like waiting longer in some sense may itself represent a substantial increase in difficulty in terms of creating something which remains stable for tens of thousands of years. On the other hand who knows with zero samples how stable societies are thousands of years beyond our present level of development.
  - mkl 1y ago
    Yes, that's why I said 100 light years rather than 4.3. Maybe it's still too low, but I think there are targets within the Milky Way that would require solving pretty much all the problems of getting to Andromeda.
- ASalazarMX 1y ago
  Imagine doing that, and being greeted with ALL THESE WORLDS ARE YOURS EXCEPT ANDROMEDA

deleted 1y ago

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