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Could a time dialtion effect at near FTL speeds used to space apart in time the arrival of multiple ships to a distant destination?

Let's say there's a terraformable planet somewhere in the Milky Way Galaxy many light years away from the Solar System. Instant FTL travel is not possible ie you can't reach destination within reasonable amount of time for a generation of humans(couple weeks/years/decades). The journey takes many hundreds if not thousands of standard Earth years for the observer.

Multiple Terraforming and Colonizing ships are launched either at the same time or within reasonable interval for our civilization(months/years/decades). The idea is that those ships arrive to the destination multiple millions of years apart each preparing the planet for another.

  1. The Atmospheric Processing Unit ship arrives first and starts shifting local atmosphere to that close to Earth's which would enable simple life. The process takes however long it needs, be it several thousand years or millions.
  2. Then comes the Life Genesis Ship whose job is to create microcosmos life on that planet out of raw minerals(guided abiogenesis) that will in turn accumulate enough "biomass" to sustain more complex ecosystem. I would assume this process would be the longest taking dozens or hundreds of millions of years.
  3. Multiple waves of Seeding ships with complex life arrive next spaced apart millions of years to enable the continious growth and development of ecosystem on that planet until becomes near identical to our own.
  4. Final ship brings the template for Humans and tools to enable newly cloned populations to form an advanced civilization. The plausibility of this scenario would be explored in another question.

All sips are AI guided and carry digital DNA, all critters are built on site from either raw materials or microcosmos biomatter. Redundancy and durablity are ensured by careful planning and calculation ie each step will perform its' job before the next ship arrives(no sheep on a grassless methane filled death world).

Could such an endeavour be accomplished using Time Dilation effect? Total amount of time on the destination planet from the APU arrival unitl Human creation should be within several dozen millions of years. Yet ships themselves can't travel from their point of view for said duration.

Could the ships be launched in reverse order?

EDIT: ships themselves can't be traveling for millions of years from their perspective. The travel time should be reasonable for each of them to maintain integrity and still be operable once it arrives to a destination. Say within hundreds or thousands of years on the active journey.

The plausibility of continious ecosystem development and human civilization creation aren't a factor in this particular question.

Fluff: Nobody cares what happens to humans on Earth by the time the new civilization is created. Plotwise some of the planets have developed a bizzare yet human compatible ecosystmes or even sentient life forms of their own. There's an instance where one of the APU's arrived after human colony was already established but regressed to feudalism and started converting atmosphere into a toxic one due to an error.

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    $\begingroup$ Unless I'm overseeing something, what you are describing has nothing to do at all with time dilation. If you travel from a to b by foot for 20h, someone who startet at the same time but with a car might be waiting for you for 19h already. If you want ships to take longer, make them travel longer $\endgroup$
    – Raditz_35
    Sep 29, 2019 at 9:29
  • $\begingroup$ Seems like I forgot one of the key parameters. I will edit the question. $\endgroup$
    – Nick Dzink
    Sep 29, 2019 at 15:06
  • $\begingroup$ If the life-seeding and human-seeding ships are only carrying information, why do they need to arrive separately? Surely the physical storage for that data is smaller and easier to manipulate than multiple whole spaceframes. Your AI can simply wait until conditions are ripe before introducing the next wave of critters - and that way, it's not twiddling its thumbs when a step takes less time than expected. $\endgroup$
    – Cadence
    Sep 30, 2019 at 15:48

2 Answers 2

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So, it sounds like you want a spaceship journey with a proper time of under a thousand years, and you want two flights to leave within (say) a thousand years of each other in coordinate time but to arrive a million years apart. And you want to use relativistic time dilation to do this.

This presents something of a problem. At a high Lorentz factor, your ship is flying fairly close to the speed of light. From the point of view of an external observer (say, the terraforming AI at the target world) your second-wave ship needs to fly a million lightyears in order for a million years to pass before it arrives. This means that your second ship must fly much, much further than your first ship. You're basically flying around in intergalactic space to kill time.

In order for the second ship to experience only a thousand years during that million lightyear journey, its needs to have a Lorentz factor of 1000 and hence a velocity of approximately 0.9999995c. This will cause a relativistic blueshift of the cosmic microwave background from a wavelength of 2mm to about 1μm, so visible with a night-vision camera. The friendly 500nm emission peak photons of a G2 star like our own become rather more punishing 250pm hard x-rays. Every microgram of dust you hit has a kinetic energy of about 100GJ (or about 24 tonnes of TNT). I'm not sure how much if that you'll run into on a million lightyear extragalactic journey, but I hope you have some good energy shielding.

You'll probably also need a warp drive to reach that kind of speed in the first place. It'd take a ridiculous amount of energy to do it via a rocket or beamed-propulsion system.

Here's the big problem though... at that time dilation factor, you could fly about 80000 lightyears with 80 years of ship time. That basically means that you can reach almost any point in our galaxy in under the lifetime of a present-day human. For your plan to make sense, there must be no habitable planets (or planets that can be terraformed in under a few million years) around any of the hundreds of billions of stars in our galaxy.

(there are also additional problems of the form "you can make a warp-drive to fly you to within a hair's breadth of lightspeed but you can't X? really?" where X includes stuff like "terraform a world in under a million years", "build a wormhole", "upload a human mind", "just build some really nice space habitats right now and not muck about with this weird 'terraform the distant future' nonsense" and so on, but those are your story issues which you'll have to handwave away yourself)

Could the ships be launched in reverse order?

Sure, if you're happy for the ship that needs to arrive second to just spin its wheels in extragalactic space for however long the ship that needs to arrive first takes to get to its destination. Given that you'll need warp drives to make your flights at all plausible, it can be entirely up to you how long they can be sustained for.

Final ship brings the template for Humans and tools to enable newly cloned populations to form

You're going to need AI that can realistically mimic a human personality and have a theory of mind at least a strong as a human if you're going to clone and raise humans on site rather than bringing them with you as popsicles or uploads. Said AI is going to need to be stable and patient and nurturing and dedicated to grand plans over vast timescales. Quite frankly, that sort of AI sounds like a much better successor to humanity than a load of carbon-copy meat that will do the same old dumb primate things and die after short, confusing lives. It will definitely be better suited to life in a universe which seems quite hostile. I'd much rather invest in something I could talk to and plan the future with than a load of digitised spaff that may or may not ever be incarnated. Why would the population of earth invest in your "maybe terraform a world in the distant future" gamble, an investment that can't ever give them any tangible rewards, when there are more practical and more rewarding shorter-term alternatives?

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    $\begingroup$ Also, if you can engineer a generation ship that will support colonists (and their descendants) for millions of years, what do you need terraformed planets for in the first place? $\endgroup$
    – Cadence
    Sep 29, 2019 at 11:13
  • $\begingroup$ @Cadence the question seems a little fuzzy on that, but talks about "human templates", so maybe new humans are made by the AI on arrival, and no old humans are shipped out at all. I've never seen the point of that sort of colonisation, myself. If you can make AI, they're as good a set of descendants as any, and much better suited to survival in a hostile universe. Forget the meat. $\endgroup$
    – Starfish Prime
    Sep 29, 2019 at 11:15
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    $\begingroup$ @StarfishPrime, I don't know about you, but us humans are quite emotionally attached to our meat, thank you very much. ;) $\endgroup$
    – user66450
    Sep 29, 2019 at 11:48
  • $\begingroup$ @JosephSnarley are you attached to the possibility of meat maybe one day perhaps existing somewhere, millions of lightyears away, if everything goes to plan? How much time and effort and money are you prepared to contribute to a gamble that will never have any payback for you, ever? Would you rather spend that time and money on other plans, inlucing interstellar colonisation plans, that might actually have a payback, and might actually bear fruit in your lifetime, and might even involve you or your family? $\endgroup$
    – Starfish Prime
    Sep 29, 2019 at 11:51
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    $\begingroup$ Ironically time dilation. It's like putting the ingredients of your ship into a freezer, it's kept fresh for some time. If we go into details, no, but I don't agree that it's safer on earth $\endgroup$
    – Raditz_35
    Sep 29, 2019 at 12:57
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If I am understanding the question correctly, it does not even matter if the ships are moving at a relativistic velocity. All that is required is the lead ships are either launched first, or are accelerated harder to reach a higher velocity than the next ships in line. You could launch everyone at the same time, much like starting a race with one person driving a car, one riding a horse, one riding a bicycle and the last person walking to the destination.

From the point of view of the ships, everything is going to be measured in ship time anyway. The external observers on Earth are the ones who will see the startling differences in transit time, but simply by adjusting the velocity of each ship in transit, they can be timed to arrive with the required spacing (even arriving within seconds of each other if desired). While the math is fairly complex, there are on line relativistic calculators available:

https://keisan.casio.com/exec/system/1224059993

http://convertalot.com/relativistic_star_ship_calculator.html

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