Questions tagged [reality-check]

Asks if a given concept is realistic in a given context. Answers should say yes or no, with supporting info. Compare this with the science-based and hard-science tags. This tag should never be the only tag on a question, because this tag frames how a question should be answered, not the topic.

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580 votes
19 answers
86k views

How can Santa keep his lists when the GDPR is around?

For my non-European readers, here is an excerpt of what the GDPR means: (emphasis mine) The General Data Protection Regulation (GDPR) is a regulation in EU law on data protection and privacy for all ...
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314 votes
25 answers
29k views

Tomorrow is Groundhog Day... For everyone. How does society respond? [closed]

You wake up tomorrow, and it's Wednesday again. Everybody remembers it, but whatever was physically done today is undone. Your favorite mug, which the dog knocked over, is un-broken. The kid down ...
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266 votes
22 answers
52k views

What's the smallest change to physics required to allow magic?

Yesterday my 7-year-old daughter asked me: Why can't I do magic for real? I answered: because of the law of conservation of energy! And I briefly explained this law. Thus she grumbled, "a ...
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243 votes
24 answers
68k views

How to safely check if you are immortal?

My hero lived his ordinary life until recently, when he realized that Magic actually exists. So far, he has been granted levitation for a short period, and invisibility for several hours. Both worked ...
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222 votes
13 answers
34k views

Is there a single historic event which could be changed to cause the USA to use SI units?

I am time traveller with aim to make world better. Last time I went to the past, all I heard was: "Kill Hitler!" So I went to the past and I must tell you, April 1945 was pretty loud in Berlin! ...
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213 votes
19 answers
19k views

What's the most reasonable way to fit Monsters in your Pocket?

Say you have a hollow sphere, about the size of a (small) grapefruit, comprised of a (let's say red) top half and a (let's say white) bottom half. There's an articulated lid, and an LED on the front. ...
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180 votes
19 answers
32k views

Russian Dolls - How do they reproduce?

Warning picture showing dissected Russian Doll My theory I believe that Russian Dolls reproduce asexually. They are born pregnant. At the time of birth, the outer doll dies. What is now the outer ...
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156 votes
17 answers
36k views

Would a bear cavalry be feasible?

Over the course of history humanity rode several kinds of animals to war: horses, camels and elephants being the most common. However, bears are not amongst them. So I was wondering, if they could be ...
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155 votes
41 answers
52k views

If time travel is possible in the future, no matter how distant, why haven't they come back to tell us?

In a world where time travel is possible, but has not been invented yet, would travelers from the future come back to prove it exists? Surely, they would bring that technology back in time to let the ...
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149 votes
34 answers
74k views

You can control a Demon by knowing its True Name, but why?

The power of True Names over demons is unbelievable: A Lamashtu demon can drain you of your blood in under 5 seconds, blend into shadows, and travel at the speed of darkness. Yet it will crumple like ...
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125 votes
9 answers
37k views

Releasing a T-Rex into a modern ecosystem wouldn't be that bad, right?

T-Rex Forever LLC has a mating pair of Tyrannosaurus rex. They're a bit shady on how they got them, time travel, cloning...they won't say. Third-party biologists and paleontologists have examined ...
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  • 52.1k
125 votes
19 answers
40k views

Could a planet made completely of water exist?

In the Star Trek: Voyager episode "Thirty Days", there was a planet made completely out of water, which is the inspiration for this question. However, that planet was held together by an artificial ...
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118 votes
17 answers
14k views

Which major solar system body could most realistically be artificial?

Which body in the Solar System is the best candidate for being an artificial construct, placed there by a Kardashev Type II Civilization? Some notes: The purpose of this body is to monitor earth, ...
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116 votes
11 answers
23k views

Could a Dwarven Civilization Exist?

Could a Dwarven society as described by Tolkien mythology actually work? Dwarves for the purposes of this question are short, stout, bearded men and women who live primarily underground. They have a ...
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114 votes
8 answers
50k views

How far back in time would English be understandable to a modern speaker?

As we all know, language in England has changed massively over the centuries. How far back would someone be able to travel in time and still have a basic understanding of what most people are saying?...
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  • 3,611
105 votes
31 answers
28k views

If 120 experts in 12 different fields were sent back 10,000 years, could they recreate the 21st century in 100 years?

Ten experts (CEOs, professors) of each of the fields of math, physics, chemistry, economics, engineering, electrical engineering, CS, sociology, psychology, art, politics and education (120 total) are ...
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104 votes
26 answers
19k views

Would relatively primitive people really confuse technology with magic?

It's common for people to say that if a time traveler or an alien displayed advanced technology to ancient or medieval people, that they'd assume it was magic, and either worship him as a god or burn ...
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  • 13.5k
102 votes
24 answers
18k views

A believable place for your secret lair

In a modern, "western" country, where can I set my secret facility so that authorities won't find me for about 30 years? The needed amount of area is relatively large, a bit less than 200 m2. The ...
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102 votes
28 answers
14k views

How to monetize uploaded consciousness?

In 2039, our company was the first to bring a safe and reliable solution to upload someone's mind to the cloud. Although it was 10 years ago, you probably remember the news, don't you? We guaranteed ...
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97 votes
15 answers
30k views

If the Romans found one working steam engine would they have been able to copy and use it?

I Previously asked if the Romans could have built a steam engine to power a ship, which received a number of answers perhaps best summarised as “probably not but…”. Assuming the Romans couldn’t have ...
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93 votes
14 answers
25k views

Lembas bread (2000 Calories per bite)

In the lord of rings the elves invented an incredibly nutritious bread/biscuit, as Legolas clearly says only a small bite is just enough to satisfy the needs of an adult man for 1 day. An adult ...
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  • 3,772
90 votes
12 answers
25k views

Would a submarine make a great spaceship?

I know a submarine would NOT make the greatest spaceship in the universe, but could it allow people inside to live in space? A submarine can resist pressure, can hold oxygen inside, and there is a ...
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  • 2,936
89 votes
17 answers
16k views

Would a robot really need to use a heads up display (HUD)?

It's a common staple of science-fiction films (e.g The Terminator or Robocop) to have a POV shot from a robot or cyborg's perspective with a HUD being used to observe its surroundings. This can be ...
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88 votes
20 answers
146k views

Possible distance travelled by horse over 6 weeks?

I always get very annoyed if a writer is sloppy with maps and travel-distances. E.g. "They left city Y and arrived in city X 5 days later." When you look at the supplied map Y and X are a 1600 ...
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85 votes
19 answers
25k views

Humans can now run 40 mph. How do I keep the stupid people alive?

Let's assume that humans can now run 40 mph and the human body can handle it. I know and understand that this is not feasible, but let's just play pretend. Naturally people would have all kinds of fun,...
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  • 55.1k
83 votes
19 answers
23k views

Would a 'World Tree' be feasible in real life?

A livescience.com article claims that trees can reach a theoretical height of 400 to 426 feet (122 to 130m). This is due to the tree being unable to carry water up to the top at that certain point due ...
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  • 9,958
82 votes
15 answers
16k views

How Long Could an "Eternal" Fire Last?

How Long could an "Eternal" Fire last? At some point there is a fire very spiritually important to a certain people - so important that they build a city around it, and begin developing an empire ...
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  • 1,029
80 votes
28 answers
23k views

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

In The Walking Dead, the survivors have seen plenty a wall. From Woodsbury, to Wellington, to Alexandrea, they are all different and they all have their advantages. One issue that none of them have ...
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  • 55.1k
79 votes
18 answers
19k views

Is there any real reason for Dwarves not to have cavalry?

It's a fairly common trope in fantasy worlds/stories that dwarves don't use cavalry. But is there any real reason why? Off the top of my head the two most likely ones seem to be: Their size. Except ...
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  • 12.4k
78 votes
36 answers
15k views

How can a pacifist country protect itself?

Think of a more or less traditional medieval fantasy world: multiple races, magic, some alchemy/magitech that is of comparable power and reliability to ordinary magic. And in this world there exists ...
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  • 1,690
77 votes
12 answers
19k views

Can Average Joe reboot the nuclear power plant?

Setup: The year is 2018. Malicious virus escaped secret lab and managed to kill 99% of all humans between January and April 2016. Not-so-average Joe spent his last two years of basic survival with the ...
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76 votes
12 answers
11k views

How does the government cover up alien crash landings?

One night a spacecraft of extraterrestrial origin crash-landed in the densely populated city of Philadelphia, Pennsylvania. The force of the impact leveled the entire city within a radius of 1 ...
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  • 45.9k
76 votes
11 answers
14k views

Anatomically correct "XKCDius lethalissimus"

Inspired by today's XKCD comic How could a creature, momentarily called XKCDius lethalissimus, evolve to have the following features: Be radioactive (intended as more radioactive than the ...
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  • 236k
75 votes
23 answers
24k views

Can Communism become a stable economic strategy? How?

In a capitalist Society, you work, you earn money and you buy a shovel to dig a hole In a communist Society, you are given a shovel and told to work Alt History Hub Communism was a major rival ...
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74 votes
20 answers
16k views

How could an ancient race warn the future in a universally understandable way?

Let's say that an ancient race of beings locked away some sort of evil that could destroy the world if unleashed. Let's also say that unleashing it would be relatively easy to do if not warned of ...
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  • 1,025
74 votes
15 answers
12k views

How could we fake a moon landing now?

The moon landings actually happened, and there's plenty of contemporaneous evidence of it. But what if the United States government wanted to fake a moon landing now? We have the technology to ...
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  • 2,607
74 votes
6 answers
4k views

Are geographically typed planets realistic?

In many science fictions we see planets which are designated by a particular terrain type. For example, Dagobah is a swamp planet, Tatooine is a desert planet, and Kamino is an ocean world. However, ...
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  • 18k
73 votes
12 answers
17k views

Is it possible to create a practical sword that's naturally toxic?

While doing research, I stumbled across the alloy "arsenical bronze", in which copper is smelted with arsenic instead of (or in addition to) tin. This apparently gives you "a stronger final product ...
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  • 14k
73 votes
18 answers
12k views

How do I make an alien technology feel alien?

In a lot of science fiction series, such as Halo, Mass Effect and Gears of War, they show alien technology that is flatly human with a few added-on bells and whistles. It lacks the awe or feel of ...
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  • 55.1k
72 votes
32 answers
21k views

Why Would Aliens Enslave Humans?

Often in science fiction, we see aliens enslaving humans for one reason or another. This is a trope I'm attempting to repurpose, but before I go any farther, I'd like to ask: what possible motive or ...
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  • 1,569
71 votes
17 answers
14k views

Stealth in Space: How realistic is it?

This has been considered other places on the net, but I thought it would be good for the hard-science challenge, since it is often an example of the subtle difference between soft and hard science. ...
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  • 12k
70 votes
28 answers
18k views

How can I prevent the collapse of the Soviet Union?

During the era of the Soviet Union, Russia was a much scarier nation: The Cold War, the Cuban Missile Crisis, and the Space Race. No one can deny these were major events in Russia's history. Let's say ...
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  • 55.1k
70 votes
18 answers
14k views

Would a culture with magic consider it magic? [closed]

I was discussing with a buddy of mine about magic and how it could easily be explained using alternate laws of physics. She replied simply "Magic that relies on alternate physics is only magic to ...
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  • 55.1k
69 votes
30 answers
13k views

How to monetize magical mirrors in today's world?

This is kinda a followup question to my earlier question about magical mirrors: Magical internet - unique addressing system Two months ago, I discovered an ancient house in the middle of woods. As I ...
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69 votes
21 answers
15k views

How do we tell if we're living in a virtual reality world?

Since I haven't found anything like this yet. I was reading a novel and it talked about how some people created a 'Artificial Virtual Reality World' where the denizens were Human Artificial ...
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  • 9,958
69 votes
11 answers
16k views

How much steel armor can you wear and still be able to swim?

I know there are many historical accounts of soldiers trying to cross a body of water and drowning, but this got me thinking how much of this was due to panic, lack of swimming skills, water currents ...
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  • 1,566
69 votes
15 answers
13k views

What would be left of a civilization founded in dinosaur times?

65 million years ago, a mass extinction event (likely caused by the Chicxulub Meteor) wiped out the dinosaurs, and their remains were hidden from us for millions of years. Humanity was not around ...
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  • 3,882
67 votes
20 answers
15k views

Architecture of the perfect zombie apocalypse refuge

Your mission, whether or not you choose to accept it, is to design the perfect refuge from the zombie apocalypse. Starting assumptions and constraints: The zombies will be slow (walking) zombies (...
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  • 28.1k
67 votes
18 answers
14k views

How could a language that uses a single word extremely often sustain itself?

The most commonly used word in english is "the" accounting for about 6% of all the words being used. The second most common word is "be" account for less than 1% of all the words used (see ngram ...
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  • 863
67 votes
14 answers
11k views

How would people living in eternal day learn that stars exist?

In a world I am building, the day lasts longer than the year, 9 times longer in fact. The native people of this world have been forced to migrate around the world, both avoiding the scorching desert ...
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