After reading Is it possible to build a bridge between planets?, I wonder: what situation would provide technology support that enables them to make the trip, but limits them to walking speed?

The voyagers will need some way to make use of provided energy in order to produce food. They need to take and carry everything they need for a permanent settlement that will survive in isolation for years. So why don’t they have motors or whatnot?

Why don’t they use the initial segment just as an ordinary beanstalk and then make the crossing in a space capsule, which continues moving without a continued expenditure of energy?

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    $\begingroup$ Do you have any idea how long it would take to walk from Earth to Mars? A long trek on earth is ~1000 kilometers, like the Appalachian trail, and it takes months. Planets are 3-6 orders of magnitude farther apart. Walking speed would take a lifetime or more. $\endgroup$ – John Feltz Dec 23 '16 at 1:01
  • $\begingroup$ That's discussed on the parent thread, @JohnFeltz $\endgroup$ – JDługosz Dec 23 '16 at 1:02
  • $\begingroup$ @JDługosz It is discussed there, but it's entirely relevant. It's extremely unlikely that walking speed would be used - if you can't go reasonably fast, you probably won't go at all. $\endgroup$ – Zxyrra Dec 23 '16 at 1:25
  • $\begingroup$ Zxyrra: that's what makes it an interesting challenge and, therefore, an interesting story! :-) $\endgroup$ – SRM Dec 23 '16 at 2:15
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    $\begingroup$ Jack Williamson did something similar in "Nonstop to Mars" (Argosy, 25 February 1939; reprinted in his collection "The People Machines" [1971]), but not by walking, using an aircraft to fly an air bridge connecting Earth and Mars. A quick back-of-the-envelope calculation suggests it might take a 1930s aircraft about twenty years to fly this interplanetary distance! Beats walking. $\endgroup$ – a4android Dec 23 '16 at 12:39

I've been playing a lot with that question. My answer for the walk is religious pilgrimage.

The bridge was noticed by Homeworld when it was already a quarter built--- a telescope noticed a "stick" jutting off of a neighboring planet. As one citizen recalls, "Over a few decades, we watched it grow longer, reaching out toward us. Eventually it extended down to touch our North Pole. Thousands of people trekked up to see it. It were kinda anticlimax, know what I mean? Just a door. And a sign. 'Tell us your story. The worthy may pass.' So people would knock and talk into the little hole that opened. Sob stories, tales of bravery, comedy. For most, the door stayed shut. But for a few, it opened. And those people would wave and leave. They ain't never returned."

Those who are invited onto the bridge are the best, kindest, most worthy individuals. The walk is meant to purify the person, spiritually and bodily, to live in their new world. All along the route there are challenges, some intellectual, some ethical, some physical. What is at the other end? No one has walked the other way.

  • $\begingroup$ So it was built to support walkers? Your story doesn’t say that the people who go in need to walk or spend a lifetime on a slow transporter; I would guess after reading that that they are whisked across rapidly. $\endgroup$ – JDługosz Dec 23 '16 at 1:05
  • $\begingroup$ I'm still playing with variations. It is meant to be a true walk. Have you read "Kingdoms of the Wall"? Something like that. But longer. $\endgroup$ – SRM Dec 23 '16 at 1:11
  • $\begingroup$ No, I’ve never heard of it. $\endgroup$ – JDługosz Dec 23 '16 at 4:26
  • $\begingroup$ @JDługosz smile.amazon.com/gp/aw/d/B00J90F3BS/… $\endgroup$ – SRM Dec 23 '16 at 16:25

Let's jump into the list:

  • The original system broke down. It is too complicated and expensive to render the original tracks and cars useful again - severe meteor impacts, solar wind, space debris close to the planet etc. have caused widespread, irreparable damage. It's more economically viable to "shoot" a new track out in a new area than it is to clean up the current mess and remove the problems present, so people are confined to crawling through the inside of the original track in slower vehicles.
  • One company controls the bridge. They decide to limit its use - perhaps in protest to a planetary law; or they increase the price of use because all other space travel is not economically viable. People are unable to board their bridge crawlers / cars, and cars they attach will be seen, but they sneak up undetected if they use slower methods.
  • The apocalypse has happened. Whether it was aliens, robots, a virus, or war, large technological setbacks have occurred. We no longer have the infrastructure to build or fuel the cars that run on the bridge, meaning less efficient technology has to be used.
  • We don't understand the bridge. Humans did not create the bridge, but rather some other spacefaring species did. We have no clue how it's supposed to be run, so only our weak, makeshift devices can crawl up it - and they're slow.
  • High speeds are dangerous. They involve releasing high-energy waste into space, directly toward the planet; alternatively, since the bridge is always changing shape / size / location, speeds must be slow in order to accurately ride the bridge and not fly off or get jammed into the tracks.
  • There's traffic. Whether caused by high demand / usage or by construction, the bridge is accessible - cars are just moving very slowly.

No hard-science tag, so let's explore alternate universes with their very different physics:

Outer Space is a Cave

One of Vasily Golovachev's books explores the concept of alternate universe's space being a solid rock with planets being caves in it, and the stars being a time-space burning.

FTL drive expands the universe

Another concept of alternate universe is, that initially all objects (galaxies, star systems) are packed very closely, but invention of FTL drives causes them to literally fly away from each other, making what was a walking distance to become light years away.


The bridge is a spatial anomaly, the actual connection is just a wormhole connecting different parts of the bridge, so actual distance walked is much less than the observable length.



Economics. Why aren't all bridges today just a simple 'park your car on a latch and get speeded to the other side'? Surely it would be quicker and waste less of your fuel right? But that doesn't happen, because the cost of building, running and fueling such a bridge would be astronomical.

The same prinipal applies to space, if anything it becomes more accurate. The cost of building a space building period is going to be rediculously high, never mind building a millions of miles long elevator. No matter how you look at it, it is too expensive.

There are two reasons they would not bring their own vehicle on the ride;

  1. Cultural, perhaps this culture sees vehicles as a sign of weakness and laziness. Perhaps crossing the bridge is a rite of passage. People do all kinds of dumb or pointless things for their cultural norms.
  2. They haven't invented the wheel, despite how this sounds, it is not as ridiculous as you may think. The Aztecs never had wheeled vehicles or transports, not even carts.
  • $\begingroup$ The question assumes it HAS been built. The question is why. $\endgroup$ – SRM Dec 23 '16 at 1:05
  • $\begingroup$ @SRM well if a bridge was built with a shuttle then a walk is impossible, the question assumes a shuttle was not made and asks why this is $\endgroup$ – TrEs-2b Dec 23 '16 at 1:07
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    $\begingroup$ You are missing the question. Sure, the bridge doesn't include a useable vehicle. But why can't the people bring their own? They need a level of technology to make the trip possible at all. $\endgroup$ – JDługosz Dec 23 '16 at 1:08
  • $\begingroup$ @JDługosz edited to bring up the other choices $\endgroup$ – TrEs-2b Dec 23 '16 at 1:12
  • $\begingroup$ @JDługosz exactly. $\endgroup$ – SRM Dec 23 '16 at 1:13

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