# Tag Info

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Here's a first-order approximation based on a fundamental limit: diffraction and angular resolution. How far someone can see of course depends on the size of the object they're looking at, because the main limitation we have is one of angular size. The issue comes down to something called the Rayleigh criterion, which is a limitation telescopes have to deal ...

8

There are no equations in this answer, just arithmetic, because that's all that's necessary for a basic estimate using conservation of mass. How much oxygen do we need? A resting adult human breathes in and out 7-8 litres of air per minute, which is about 2000 litres in four hours. About 5% of that volume is oxygen that is taken into the bloodstream, ...

7

There is practical problem: microwaves is also what radar uses A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object(s). To ...

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Size is Totally Realistic An average length of 25 feet is easily achievable in snakes, as Anacondas regularly reach 18 feet in length, Burmese Pythons reach 23 feet, and the extinct Titanoboa reached over 42 feet. As for weight, anacondas can weigh up to 400 pounds, so that’s about what you should get for your snake dragons. Gliding is Possible If your ...

6

Yes, and some groups show particular potential in that direction There are a group of lemurs called the Archaeolemuridae, the last members of which which died out approximately 1280 C.E. Compared to other lemurs, the two genera of archaeolemurs (Archaeolemur and Hadropithecus) were adapted for life on the ground, highly omnivorous, and had a very monkey-...

5

The technology is known as "star lifting", and works through the "simple" expedient of removing enough mass from the star to slow down the rate of fusion reactions. If the people who do this are clever enough, they can store the excess hydrogen from their star lifting operations in artificial gas giant planets (probably the size of Uranus) and feed the ...

4

Our liver and kidneys make already a pretty good job at allowing us drinking non pure water. Coffee, tea, sodas, liquors, are basically water based solutions with "pollutants" in them: caffeine, alcohol and other substances. They are all processed by our liver and kidneys and expelled from our body. The twist is simply to improve kidneys and liver to be ...

4

Waste heat (on planetary scale) is not an issue today, and likely not going to be an issue for the next 100 years and even more. But as the civilization approaches a full Kardashev I level, it inevitably should deal with waste heat. Either through decreasing planetary albedo (for effective energy capture), or by building space collectors, beaming energy to ...

3

Stowed and Deployed Characteristics Approximating the fog body as solid aluminum (3,000 $kg \over m^3$ ), 1 kilogram of stowed utility fog takes up a space of about 7 centimeters (~ 2.8 inches) on a side. Deployed, the fog increases it's diameter by 10x from 10 micrometers to 100 micrometers. The deployed volume of 1 kilogram of utility fog is 70 ...

2

I took this panorama photo in the Oklahoma panhandle, one of the flattest places on Earth. It is 180 degrees (that's the same highway stretching in both directions). It was shot with an iPhone SE, whose aperture pupil is 1.86mm, smaller than what HDE226868 lists as a bound for the human pupil (therefore the human eye would do better on his limit calculations)...

2

There are a whole bunch of different ways to determine the thickness of a planet's ice sheets; over the decade, dozens have been tried on Europa and other icy bodies. Broadly speaking, as we're working from a purely theoretical perspective, our method will have to be thermodynamic in nature - we can't look at cratering patterns or rifts in the ice. I'm going ...

2

Poisons vary greatly. Ambroise Pare famously tested the efficacy of bezoar against poison. Bezoar was thought to be a universal antidote but Pare was skeptical. A condemned man agreed to do the test, on the condition that he would be pardoned if it worked. He ate bezoar (a big hairball) and then poison. The poison chosen for this experiment was lye ...

2

Even before getting to the consequences of easily created negative mass, remember that FTL by itself, even without considering how it is implemented, implies time travel. Note that it does not require time travel, and the existence of privileged reference frames or some form of chronology protection mechanism would prevent everything just disintegrating into ...

2

Defensive Dyson sphere. https://en.wikipedia.org/wiki/Dyson_sphere A Dyson sphere is a hypothetical megastructure that completely encompasses a star and captures a large percentage of its power output. The concept is a thought experiment that attempts to explain how a spacefaring civilization would meet its energy requirements once those ...

2

To drink seawater you can: Give them salt glands like various seabirds and marine reptiles have got. We already produce salty tears, so the human tear duct could be adapted for this. The downside is your people will look as if they are crying (or have an eye infection oozing salty liquid) even when they are not. Make their kidneys more efficient at ...

2

This is going to take some serious ground-up modifications to terrestrial animal biology. In order to have a reaction time fast enough to dodge a bullet, we're going to have to increase the conduction velocity of the nerves from some velocity measured in mere metres per second to something closer to lightspeed. Metal cored and sheathed nerves would ...

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TL;DR: flight is very energy intensive, and you'll have to build a lot of power stations and then build a vast and expensive network of directed energy weapons and persuade travellers that having you shoot at them is a good thing. It is a little bit hard to pin down exactly how much power is required to keep an airliner in the air, but this KLM blog post ...

1

The simple way to avoid problems with waste heat on Earth is to gradually move the most energy intensive aspects of human civilization off world. As more and more energy using and waste heat producing activities go off world, a larger and larger percentage of the human population will live in space close to energy using activities, and a smaller and smaller ...

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Volcanic ash can do this naturally. see https://en.wikipedia.org/wiki/Volcanic_winter So you aren't decreasing the luminosity of the sun but you would decrease the light penetrating the atmosphere.

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Yes. By the same pressures we did. That might sound trite, but evolution is a powerful force, and the only set of circumstances leading to our level of intelligence is our set of circumstances So take your lemurs. Force them into grasslands for a while. Expose them to coastlines and oily fish. Give tool users chances to shine. Eventually smart gets ...

1

Firstly, Rayleigh scattering, which effectively redirects a small portion of light as it travels through a perfectly clean atmosphere. In a pure nitrogen atmosphere at STP, the light you get out of a regular green laser (wavelength 532nm) will have a Rayleigh scattering cross section $\sigma$ of about 5.1x10-31m2. You might expect to find about 2x1025 ...

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