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As discussed here, a sun technically can orbit a planet with a sufficiently small sun or large planet (at that point brown dwarf). By doing so, you can theoretically avoid the issues mentioned in t...
Option 1: Continuous spectrum Your first choice would be to recreate the black body spectrum of the star. For a black body at a temperature $T$, the intensity $J(\nu)$ is $$J(\nu)=\frac{2h\nu^3}{c...
Like Cort Ammon says, it would depend on how your VR functions. The brain has mechanisms that prevent what's going on in your brain to affect your body in any way: that's what happens when you're d...
If a planet is far enough from its star, it will be cold, water will be frozen etc. To have plants, you'd need liquid water for at least part of the year (something like the tundra, at least.), or ...
If all the fauna on earth has been killed (vertebrates and invertebrates), there are no pollinators left. Which would kill off many plants. (That is, make them unable to reproduce, so once they die...
There are some places on Earth that have an unusually high frequency of lightnings. For instance, Venezuela. The explanation, in this case, consists in moisty air locked by mountain ridges, and the...
Mining on the moon would remove some mass, but I don't think you'd notice. First mining on the moon probably won't involve strip mining and hauling all of the material away. Instead rock will be du...
It's deactivated Grey goo, Smartdust, Programmable matter, Computronium, or something like that. Basically trillions of nano machines that at some point in the past ate the planet and converted i...
Assuming there is a possibility that the inhabitants had full molecular nanotechnology, it could be an underwater version of a utility fog. Basically lots of little 12 sided nano machines, with ...
Your dragons are vegetarians and have a lot of different stomachs - just like cattle To cite from the Wikipedia article on cattle (emphasis mine): Gut flora in cattle include methanogens that ...
Spaceships are not supposed to withstand a lot of external pressure Have a look at our sister site Space.SE and the question Do spacecraft have similar structural integrity requirements as submari...
Aqua power is going to be the easiest to harness, especially with the (Personal opinion: Ridiculous) restriction of no mining. Without any organized industry (Opinion the same as the above), you c...
1. Orbit a high-mass planet In the Solar System, two moons are covered with ice and have subsurface oceans: Europa and Enceladus. Europa orbits Jupiter; Enceladus orbits Saturn. In the case of the...
So they essentially look the same, minus the ears, live the same length, have the same magical aptitude... Am I right in understanding that you just want it to be like different dog breeds? If so t...
You could make a different colour scheme for your elves: just as humans are all shades of brown (from pinky-beige "Caucasian" to dark), with pink or yellow undertones, your elves could be different...
So, to get a couple comments out of the way first, I'm not really sure why you would want to rob the train from another train (except for the rule of cool), especially since they are traveling so s...
Do it the way NASA did it in the 1960s -- with ropes and pulleys! No, really. I distinctly recall seeing a video clip, but can't recall exactly where, of how Apollo astronauts trained for walking ...
Try thermosynthesis. Thermosynthesis is a hypothetical mechanism, usually applied to the RNA world theory for the rise of life on Earth. In a nutshell, it states that an organism could function as...
Any light source is a propellant-less drive (often called a "photon drive"), it's just extremely energy inefficient. With perfect conversion efficiency, the impulse of the device is (energy suppli...
I'd suggest the simplest and cheapest of them all: gravity. Recall that gravity pull is zero only at infinite distances. For convenience of the story, the drone will always be under the gravity pu...
There will be little difference. The lower atmospheres are the same. Let's assume that the atmospheric pressure, $P$, follows a simple exponential scale height model: $$P=P_0\exp\left(-\frac{z}{H}...
The idea of an ocean planet isn't too far-fetched. There are several moons in the Solar System - Enceladus and Europa, for instance - that have subsurface oceans. If the ice covering their surfaces...
I have aphakia, so I can address the near-UV end from personal experience. For the near-IR, I can only reason from other sources. In daylight, subtle effects like the patterns on flowers mentione...
Use chicken manure. Other animals, besides livestock, also produce good manure, with different qualities. Now, not all manures are created equal; they differ in composition, volume, and production...
To create a complete new biochemistry, we are going to make carbon-carbon bonds obsolete. Carbon-carbon bonds are the backbone of our carbon-based life. To make them obsolete, we will force life to...
