190 votes

How can I build a door to repel a horde of zombies?

Human engineering can, 100%, keep out a horde of zombies. In The Walking Dead things fail because if they didn't the show would be boring. In real life, there exist castle gates hundreds of years old ...
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  • 34.5k
184 votes

Reason for an exterior control panel on a space ship

A spaceship is a very expensive piece of hardware. So expensive that very few entities could afford to buy one outright. Most spacefarers would have to buy theirs on credit. And as we all know if you ...
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  • 1,580
151 votes
Accepted

What would cause a nuclear power plant to break down after 2000 years, but not sooner?

Software licencing. Software for your automated maintenance and refuelling robots was under a 999-years licence (similar to common law permanent lease) . After it ran out, the licence was ...
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  • 1,064
118 votes

An infinite train circling the planet that never stops

A similar concept has been mentioned in other answers, but one way to make a train like this viable would be to have pods at stations that "dock" with the main train rather than many trains running at ...
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  • 923
113 votes
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How can I build a door to repel a horde of zombies?

We humans are pretty good at building gates to keep people out. We've been doing it for a long time for military purposes and to stop thieves. Why Do We Have Gates? Because there has to be some way ...
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  • 29.7k
111 votes
Accepted

Spiders In Space: How to design a space suit for an arachnid?

Yeah. For the spiders, this is gunna suck, but it’s not undoable. I do suspect it will be more of an exo-exoskeleton than a suit though. There’s a couple of reasons why it won’t be particularly ...
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  • 65.6k
102 votes

How can I ensure my Evil Tower is always stormy?

Ash cloud. Your tower is hollow, and the interior is a conduit to the underworld - perhaps the column extends straight down through the underworlds of K'n-Yan, Yoth and N'Kai all the way to the ...
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  • 283k
95 votes

Making a sword in the stone, in a medieval world without magic

Requirements: One large hollow rock One dwarf One large pair of pliers One tunnel One loud voiced announcer of who is about to try to pull the sword out Tunnel under the rock for your dwarf to get ...
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  • 114k
87 votes

How can I hide my island in the 1600s?

Publish the highest-quality maps for your area (Google maps.) As more people see that your maps are the best, they will come to rely on them. Obviously, leave your island out. Mark safe waterways far ...
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84 votes
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An infinite train circling the planet that never stops

While hopping on one moving train seems reasonable for a healthy young adult, hopping two hundred seems a little excessive and dangerous... Also I would imagine that most people going on a long ...
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  • 10.6k
83 votes

What distinction could there be between space torpedoes and space missiles?

Send your torpedos through sub space. They go "underneath" so they're torpedos. Missiles travel through normal space. Different tactics and countermeasures apply to the distinct types of weapons.
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  • 5,130
82 votes
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Building a bridge to the stars

That is a surprisingly reasonable project! Let's dismantle the Earth, and use it as building material to Alpha Centauri. The Earth is $5.974 \times 10^{24}~\text{kg}$, and Alpha Centauri is roughly $...
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82 votes
Accepted

How can I hide my island?

Announce that you are building a resort. Put up a website. Make it look nice. Don't take reservations. Make people think its real Hire some (doltish but good looking) celebrities to come vacation ...
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  • 84.4k
81 votes

Reason for an exterior control panel on a space ship

The AI in the ship is not the very first one to go rogue, and probably will not be the last one either. Hence all ships have an outside panel where the AI cannot see and reach, as a safety measure for ...
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81 votes

An engineering enigma: the useless "wings" behind giant robots. What is their TRUE purpose?

The fins behind mecha are molten salt heat sinks. Firing directed-energy weapons repeatedly produces a lot of residual heat, unless a superconductor is being used to transfer energy. To dump this heat ...
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  • 10.2k
79 votes
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What can plausibly explain many of my very long and low-tech bridges?

These aren't long-span bridges, but causeways The current record for a single span is just under 2km long, and any single vehicular span over oh, 100 to 200m long is going to require modern truss or ...
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  • 11.1k
79 votes

What single change in history would make rear steering cars a standard?

Rear-steering wheels are dynamically unstable, that is, when the car is moving forward, any small misalignment of rear wheels position vs fixed front wheel axis will cause a force that would turn them ...
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  • 952
76 votes

What distinction could there be between space torpedoes and space missiles?

Hi and welcome on board the star cruiser Pedant's Dream! On board this state-of-the-art warship we carry plenty of weaponry- railguns, lasers, missiles, torpedoes- What's the difference between those ...
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  • 2,849
75 votes
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Why would space traders pick up and offload their goods from an orbiting platform rather than direct to the planet?

Other answers have already covered the fact that surface-to-orbit travel is energetically unfavorable (and therefore expensive and awkward) and that making a ship that can operate in an atmosphere as ...
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72 votes
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How long would it take to dig a 10 km canal with Bronze Age technology?

Fun trivia: the word canal, and related words like cane, are most likely the only words in modern English derived from the ancient Sumerian language (from 𒄀𒈾, "qi.na") - spoken by a culture that has ...
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  • 13.4k
71 votes
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A purely mechanical bell in a clock tower that automatically rings gradually faster on a specific night of the year

In clock-making such a feature is called a complication. Movements with complications are quite common, from simple-minded calendars (which need to be reset at the end of every month shorter than 31 ...
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  • 75.4k
69 votes

Spiders In Space: How to design a space suit for an arachnid?

They don't need a spacesuit just oxygen Warning - Video of a spider in a vacuum chamber (it walks around and lives to tell the tale). https://youtu.be/tA9jcIwvge0?t=243 Judging by the video, they ...
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66 votes

How can I ensure my Evil Tower is always stormy?

It needs to be hot, at least the top of it does. If you create a constant low pressure zone over your tower, by heating the air around the top of it so that said air rises, this will create a ...
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  • 44.4k
64 votes

How can I make the supporting pillars of an underground city less obstructive?

Mirrors, greenery, sculpture and waterfalls. You can’t hide these things. The best you can do is make them more easily ignored or more pleasant to look at. Mirrors provide the illusion of space and ...
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  • 65.6k
62 votes

Making a sword in the stone, in a medieval world without magic

'Lock' the blade in place Give the sword blade a fuller, the groove used to lighten some blades, and end it before the tip of the blade. It can then be inserted into a well crafted, close fitting, ...
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  • 721
61 votes

What would cause a nuclear power plant to break down after 2000 years, but not sooner?

Remember Y2K? Software is hard, programmers are human. If you want your readers to know exactly what went wrong, you can babble at length about data types or speculative branching or null references ...
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61 votes
Accepted

What kind of war would lead to Ultra-Heavy tanks being useful?

A lot of people are focusing on the viability of making giant land vehicles. I mean... we already have stupidly large land vehicles, don't we? That's the BelAz. It's a huge cargo truck, to move ...
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  • 7,434
60 votes

Advantages of "Spider Mechs" over Tanks?

Okay, so a did a bunch of research into legged robots for my thesis and they aren't going to replace armored vehicles any time soon. The most basic reason, they aren't as efficient in doing what ...
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  • 15.1k
58 votes
Accepted

How can sapient beings engineer transportation and building when they can only count 0, 1 and many?

As far as you want. Humans have trouble conceptualising large numbers. We can’t count them, so above a certain point we see the number ‘178654’ and our brains turn it into ‘many’. Doesn’t change the ...
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  • 65.6k
58 votes
Accepted

Why are UFOs disk shaped?

They have a ring-shaped fusion reactor, like a Tokamak, inside the ship The crew quarters is smaller than the reactor. It is necessary to make the ship circular, so that the donut-shaped reactor fits ...
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  • 3,585

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