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Let's say that creating warp gates is possible, so long as both ends of the warp gate are stationary within some universal reference frame (no time travel please). The only problem with this universal reference frame is that the galaxy is traveling at about 0.05c in this reference frame. As a result, the ends of the warp gate would need to be traveling at 0.05c relative to the galaxy in a predetermined direction.

In order to set up a pair of warp gates, you need both gates to start co-located. They can then be separated by an arbitrary distance and accelerated to the universal reference frame. Once both gates of the pair are at-rest in the universal reference frame, they can be activated, at which point they create a stable, traversable wormholes between the two gates, allowing instantaneous transit between the two.

Warp gates are expensive to create. It takes ~0.1% of the annual GDP of the species trying to make them to produce one pair of gates (wormhole containment is hard to make). Gates can be deactivated and reused, as long as they can be sent to the right place. The species in question has torch-ships that can accelerate up to or down from 0.05c in about 20 days, but can't really get to speeds above 0.1 or 0.2c.

How would an interstellar species use such devices most effectively? For efficiency here, my primary concern is the average trip time that travelers would take to get between planets (while being reasonably conservative in terms of the number of gates needed to run the system).

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    $\begingroup$ A reduction in interstellar distance shipping time? $\endgroup$ Apr 26, 2023 at 20:34
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    $\begingroup$ This gate arrangement is the FTL basis of Iain Banks's book "The Algebraist." In that book, gates could be collapsed by strong gravitational fields. I believe it took 160 years to replace the one that collapsed, but most people in the story are functionally immortal, so it was mostly an inconvenience. $\endgroup$ Apr 26, 2023 at 21:58
  • $\begingroup$ Does "sent to the right place" include sending one or both terminals through another, working gate pair? $\endgroup$
    – notovny
    Apr 26, 2023 at 22:15
  • $\begingroup$ @notovny You could send a deactivated gate through a larger, active one. Sending it through in pieces would not work however (so can't go through one of the same size) $\endgroup$
    – Zags
    Apr 26, 2023 at 22:17
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    $\begingroup$ Any particular reason you are making it harder with the whole "stationary within some universal reference frame" when there is no universal reference frame(and is likely unknowable with expanding universe)? $\endgroup$ Apr 26, 2023 at 23:55

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Attach the gate to a ship

With a max speed of 0.2c, a ship can average 0.1c if it is speeding up and slowing down while moving at max acceleration. So, if you leave a gate open for 40 days and move it for the next 40 days, it can catch back up to its relative starting location. So, if each trade route has 2 gate ships, it can at all times have 1 open, and 1 closed in transit.

Is this cost and time effective?

This means that there will always be an open gate going to the same destination somewhere in the same relative 13,000 AU (0.022 ly) stretch of local space. While this could generally mean venturing well out into interstellar space to reach your jump gate, it's still hundreds of times faster than actually trying to fly between stars. Also, each solar system can cluster thier gates so that getting to a gate cluster might take you 20-80 days depending on the quality of your ship and launch window, but it would only take a mere few minutes to leap frog from one gate to another until you arrive anywhere you want in the gateway network. This means that any inner stellar trip to anywhere in the colonized universe will generally take between 40-160 days in total. This is about how long it takes for Ocean freighters to make thier trips; so, this inconvenience should not be enough to prevent trade between star systems.

As for the cost of making the gates, they are not that bad. The US spent an average of 0.8% of its GDP for 36 years building the interstate highway system; so, if your gate system is an equally valuable piece of infrastructure, your species could crank out 4 new gateways a year at this relative cost. Following the same thinking, you could connect about 150 star systems over the same period of time and equivalent spending.

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With space distances 0.05c doesn't make much difference. The civilization would use as it would use the ordinary gates, it just would be somewhat less useful.

Build them 0.5 light year away "upstream", use for 20 years, build a new one.

I don't see how this minor annoyance would benefit any story.

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    $\begingroup$ At 0.5 light years away from an inhabited star system, that's not very useful, as it would take 5 years to get to or from the warp gate at 0.1c. At some point, you'd just wait till the gate got to you, rather than actually trying to get to it. $\endgroup$
    – Zags
    Apr 26, 2023 at 20:43
  • $\begingroup$ @Zags. Build it closer then. You would have to rebuild them more often though. Considering you potentially jump hundreds of light years 5 years is just the price of doing business. $\endgroup$
    – D'Monlord
    Apr 26, 2023 at 20:55
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If we look at the real world examples - what you are effectively describing is a Shipping Port.

So, you have a bunch of gates near your home planet and these are all paired with gates that are close to resource rich planets.

Someone mentioned the US Freeway system - this is a very good analogue for how they would be used. Most likely a Tolled system (like the Panama Canal) - but the decrease in Time, Fuel, Resources, Crew Wages etc. etc. would be easily justified.

You would end up with a series of primary trade routes (for example how there was the Spice Trade, or the Trans-atlantic Slave Trade) and then you'd probably see a sort of Parrallel import system setup (Ship goes out with Mining Equipment/Supplies to the remote station, comes back with Ore and minerals etc.).

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  • $\begingroup$ But how do you deal with the gates needing to be "moving"? These would travel 1 AU relative to any planet every 3 hours. $\endgroup$
    – Zags
    Apr 26, 2023 at 22:06
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    $\begingroup$ The planets are also moving with the galaxy at 0.05c, you wouldn't have the gate right up close to the Planet, but close enough that once you've exited, it's a 'short' (in space flight terms) trip to the destination. $\endgroup$ Apr 26, 2023 at 22:11
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If you can pass one gate through another then the simplest solution would be to have a 'universal hub' set somewhere where it can keep moving at 0.05c for the forseeable future without hitting anything. Every star-system would have a warpgate from their planet to the hub, so any journey would consist

  • Leave system A planet on a torch ship
  • accelerate to meet the local worm-hole for system A,
  • pass through to the universal hub
  • enter the other end of the worm-hole to system B,
  • ac/de-celerate to system B

When a wormhole got to far away from system A to be practical, commision a new pair of holes a bit upstream and transport one end through the receeding wormhole to the hub, at which point the receeding wormhole can be decomissioned. Although if you initially aimed it in the correct direction, then in 50 or a hundred years it might become useful for another system to use (assuming it passes close enough). It could be interesting to see what civilizations B and C might be willing to pay civilization A in order to get them to aim their new wormhole in theirdirection for future use.

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