Activity for HDE 226868
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
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A: Genetically engineered de-evolution Climate change Let's say that a species lives in a world that used to be temperature. Over time, though, greenhouse gases were released from deposits in the soil, thus increasing the temperature of the planet slowly. Over millions of years, the species evolved to better survive in these warmer condi... (more) |
— | almost 9 years ago |
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A: How much warning would a civilization have that a nearby star was about to go supernova? A few days, at best If you want to detect a supernova as quickly as possible, you need a neutrino detector. Supernovae produce substantial amounts of neutrinos - which actually carry away much of the explosion's energy. Even though these particles are hard to detect, they are detectable, and can giv... (more) |
— | almost 9 years ago |
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How could an underwater civilization develop fire? This is the follow-up question to How could an underwater civilization develop electricity?, as mentioned there. In that question, I never addressed how my civilization could have discovered/used fire. In our world, this would be a huge issue, because fire was the precursor to most of the entirety o... (more) |
— | almost 9 years ago |
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A: Are four lungs possible and what would their effects be? It's quite possible, and some animals already have them. Some arachnids have what are known as book lungs - small respiratory cavities that actually are not lungs, but different respiratory organs. They formed separately (in terms of evolution), but have taken the place of lungs in these arachnids. ... (more) |
— | almost 9 years ago |
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How could an underwater civilization develop electricity? Electricity pervades our daily lives, and makes possible a lot of technological achievements. Harnessing it helps the development of any civilization. The thing is, water - especially sea water - is a great conductor of electricity. I'd like to add electricity to an underwater civilization I'm worki... (more) |
— | almost 9 years ago |
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A: Could a universe with something like special relativity based on position instead of velocity be logically consistent? Both time dilation and length contraction depend on something called the Lorentz factor, commonly denoted by $\gamma$. It is defined in terms of the velocity, $v$, and speed of light, $c$, as $$\gamma=\frac{1}{\sqrt{1-v^2/c^2}}$$ Some like to simplify this a bit by writing $\beta=v/c$, and substituti... (more) |
— | almost 9 years ago |
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A: What could cause a planet to be highly electrified? Our universe is large enough that lots of weird things can happen. Believe it or not, we've found quite a few of them on exoplanets. This article about a paper on lightning on exoplanets (Bailey et al. (2014)) talks a bit about lightning in brown dwarfs and planetary atmospheres. The point of the pa... (more) |
— | about 9 years ago |
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How would the absence of tides influence the geography of a tidally-locked moon? On Earth, the presence of tides due to the Sun and Moon influence certain currents and other movements of water. This in turn leads to different forms of erosion, which can transform a landscape. I'm working on a moon that's tidally locked to a planet - pretty much identical to the Earth-Moon system... (more) |
— | about 9 years ago |
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A: Where would water come from in an underground colony? Given that they're 2.2 kilometers underground, it looks like they can take advantage of the water table, the place where rocks are saturated with stored groundwater. The water table often holds aquifers, which can be accessed with only a bit of drilling. Is groundwater accessible 2.2 kilometers down... (more) |
— | about 9 years ago |
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A: Apparent Color of the Sun and Sky Rayleigh scattering is the primary reason that the sky is blue. Particles in the atmosphere "scatter" light in random directions. Blue light (along with violet light) has a shorter wavelength, and is therefore scattered more. For this reason, the sky appears blue, because there is scattered blue ligh... (more) |
— | about 9 years ago |
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A: What would be the effects of galaxies colliding? For anyone who wants to see a cool simulation of a galaxy, merger, I can recommend a neat little applet): Galaxy Crash JavaLab.1 Two more good sites with a bunch of different simulations are the GALMER website and this one (which turns out to have Samuel's simulation). Cool, huh? Anyway, let's look... (more) |
— | about 9 years ago |
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A: In three spatial dimensions, would it be possible to have a force that decreases with the inverse of the distance? In our universe, electric and gravitational force decrease with $r^{-2}$ because of the inverse-square law. Imagine a spherical shell around some point source. The area of a shell at some radius $R$ is $4\pi R^2$; thus, the flux through that shell is reduced by a factor of $r^{-2}$. This is true in ... (more) |
— | about 9 years ago |
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Are ghosts made entirely of gas possible? I'd like to create a temple haunted by beings who are ostensibly ancestral spirits - basically, ghosts. How could ghosts be explained without an afterlife? gives me some intriguing ideas, but I'd like to go in a slightly more tangible direction: Creatures made of gas. I mentioned this idea in chat, ... (more) |
— | about 9 years ago |
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A: Creatures that intentionally blow themselves up How could a creature explode itself? Use Hexamethylene triperoxide diamine (or another organic peroxide)! Hexamethylene triperoxide diamine is an organic peroxide, which can be formed when hydrogen peroxide and hexamine (obtainable via the combination of formaldehyde and ammonia). Certain... (more) |
— | about 9 years ago |
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A: Thicker cerebrospinal fluid: Results? How can I achieve this[?] Make them cavemen. Cerebrospinal fluid (CSF) keeps the brain in neutral buoyancy, effectively lessening its weight against itself. This means that the brain can be heavier than it would be otherwise, meaning that it can be denser. Increasing the amount of CSF would mea... (more) |
— | about 9 years ago |
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A: Can non-intelligent life naturally evolve the ability to space travel and to live in interplanetary space? Yes, via panspermia. Panspermia is the idea that extremophiles "hitch a lift", as it were, on ejecta from collisions between celestial bodies. There are a few obstacles, because the microbes would have to survive all three phases of travel: Launch (as well as the impact event) Travel in the harsh ... (more) |
— | about 9 years ago |
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A: Every now and again God puts us on pause. Can we detect this? No, because of Hamilton's equations and conservation laws. At some time $t$, the configuration of the universe is represented (classically) by a point in phase space. Phase space describes the position and momentum of the components of a system. We can define these locations using canonical coordina... (more) |
— | about 9 years ago |
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A: How can I get my DeLorean to 88 miles per hour without a train? Hill Valley is, apparently, somewhere in the Sierra Nevada range in Northern California. That fact, as well as its name, should make it clear that the region has an abundance of hills, which are handy little devices capable of converting potential energy into kinetic energy. All you have to do is bri... (more) |
— | about 9 years ago |
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A: Could a force with these properties exist in a parallel universe? Yes. We can write out the force as $$\mathbf{F}=-k\frac{\sqrt{e1e2}}{r^2}\mathbf{u}r$$ where $\mathbf{u}r$ is the unit vector in the direction of $\mathbf{r}$, defined as $$\mathbf{u}r=\frac{\mathbf{r}}{r}$$ Is this possible? Well, it's an inverse-square law (i.e. $\mathbf{F}\propto r^{-2}\mathbf{u}... (more) |
— | about 9 years ago |
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Is a moon inside a hollow Earth possible? The Hollow Earth theory is/was a pseudoscientific idea that our world is actually on the inside of a large sphere. The "sky" points inward towards the center, where the "Sun" (a light source) is, while the "ground" points outward. Let's assume that we have a planet the size of Earth, except that it ... (more) |
— | about 9 years ago |
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A: That's no moon! It's a space station! How big can a space ship be before it collapses on itself? The defining equation of hydrostatic equilibrium - the state a celestial body must be in to maintain some semblance of a spherical shape - is $$\frac{dP}{dr}=-\frac{GM(r)\rho(r)}{r^2}$$ where $P$ is pressure, $r$ is radius, $M$ is mass, $\rho$ is density, and $G$ is the universal gravitational consta... (more) |
— | about 9 years ago |
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A: Making doomsayers right - a moon(s), planet alignment that matters I'm 99% certain that the effects of a second celestial body on seismic activity on an Earth-like planet has been covered before (in that case, by a second Earth-like planet); if anyone can point me to it, that would be great. The conclusion - if I remember correctly, and I think I do - was that there... (more) |
— | about 9 years ago |
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A: How can I safely brighten my secondary star? What if the other star was not all by itself, but had its light magnified? One way to do that is to put it in a reflection nebula. Reflection nebulae are clouds of dust that reflect light from a star embedded with the nebula. They're often found around young, hot stars, but it's not implausible to ha... (more) |
— | about 9 years ago |
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A: Orbiting one star in a binary system: what are the effects of the second star on the planet? Is the light from the distant star significant? Does it illuminate the planet as much as, say, the earth's moon does at night when full, or is this basically just another bright star in the night sky? (Could it be brighter than the moon, even, making a sort of "second day" during part of the night... (more) |
— | about 9 years ago |
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A: What is the most effective way to brake from interstellar speeds? Use a solar sail. Advantages: Solar sails are lightweight(-ish) They can be used for propulsion According to Dandouros et al., solar sails built with technology in the near future could easily travel to a nearby star system in 60 years, reaching a top speed of $0.16 c$. You might want to use a s... (more) |
— | over 9 years ago |
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A: Is it practical to build dirt scrapers instead of skyscrapers? Yes, and it's being worked on right now. The Above Below project aims to take a disused mine in Arizona and convert it into a underground building. The terraces of the mine will be covered by a large domed roof, with some skylights and artificial lighting providing natural light. The building will b... (more) |
— | over 9 years ago |
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A: How much play is there in building bigger-than-Earth planets that support humans? Not much. I assume that by "14% less gravity" you mean that at the surface, the force of gravity is only 0.86 times its strength on Earth's surface, i.e $g=0.86g{\oplus}$. You also say that the size is 46.7 times the size of Earth, or $V=46.7V{\oplus}$. Putting these requirements together tells us t... (more) |
— | over 9 years ago |
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A: Blind spot in the Solar System The Oort Cloud The far edge of the Oort Cloud is believed to be 100,000 AU from the Sun. In fact, Duncan et al. (1987) created simulations that showed the inner edge of the Cloud to be at 3,000 AU. Given that 1 AU $\approx$ 8 light-minutes, $$3,000\text{ AU}\times\frac{8\text{ light-minutes}}{\text... (more) |
— | over 9 years ago |
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A: Design me a Mars drone I'm incredibly embarrassed to be chasing the bounty here, but I can't resist the challenge. Besides, drones are cool. Okay, to start with this, we need to know just what developments have been made in this area. The major project in the rotor-powered-drones-on-Mars field is the ESA's Dropter project... (more) |
— | over 9 years ago |
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A: With current technology, what would be the best way to store energy for future generations? Flywheels The method[3]: Generate electricity normally. Use the electricity to accelerate a flywheel to very high speeds. Capture the kinetic energy of the flywheel when needed. The benefits Essentially no maintenance is required.[1] The flywheel cannot decay as chemicals in batteries can. Whi... (more) |
— | over 9 years ago |
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Creating a realistic world(s) map - Stars This question is a sort of follow-up to Samuel's previous world map question, Creating a realistic world(s) map - planetary systems. Lots of science fiction stories involve journeying to nearby stars. Many involve the first human explorers setting out for a new star system. It's easy to pick from th... (more) |
— | over 9 years ago |
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A: How to render a large percentage of humans infertile? Chemical castration Cyproterone acetate Cyproterone acetate is one choice for chemical castration. Hormonal Therapy for Male Sexual Dysfunction describes it as a "potent, dose-dependent antiandrogenic and progestational agent" which can block "T and estrogen synthesis in the gonads" - meaning that ... (more) |
— | over 9 years ago |
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Could life exist in a circumstellar disk? I could have sworn that there was a question that covered this, but I suppose I'm misremembering. If anyone finds one, let me know. Back in the early days of the Solar System, things were pretty bad. There were many collisions, which made it hard for any particular object to stay the way it was for ... (more) |
— | over 9 years ago |
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A: What is the best planetary orbit around a black hole in order to support life? 1.Could any planetary orbit sustain life long-term without an imported energy source? I believe that black holes emit Hawking energy. Could that be of use to living creatures? The power emitted by Hawking radiation (see Hawking (1974)) is $$P=\frac{\hbar c^6}{15360\pi G^2M^2}\tag{1}$$ For a blac... (more) |
— | over 9 years ago |
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Can stars that are not powered by nuclear fusion exist? Stars generate their energy by fusing lighter elements into heavier elements. The most common reaction in Sun-like stars is the conversion of hydrogen to helium via the proton-proton chain, but heavier elements can also be synthesized, typically in more massive stars. Before nuclear fusion was propo... (more) |
— | over 9 years ago |
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A: How realistic is the power generation depicted in The Legend of Korra? Not very realistic. HowStuffWorks has an interesting article about generating electricity from lightning. There are several problems with harnessing natural lightning: The logistical problems involved in making it work are significant. First of all, there's the basic fact that thunder storms are... (more) |
— | over 9 years ago |
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A: What pressures could drive evolution of a floating creature? The need for surprise attacks. Most humans (and, in many cases, animals) don't think in three dimensions. All of the people we interact with are, in general, at the same elevation we're at, moving at the level as us. When you walk down the street, you don't often look straight up. Something that fl... (more) |
— | over 9 years ago |
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A: Magnetic Celestial Bodies in Orbit Interesting models have been made of T Tauri stars, pre-main sequence stars that can have strong magnetic fields (though clearly not as strong as those of magnetars). Data is given in Johns-Krull (2007). The effects of this magnetic field on interactions between the star and its surrounding disk were... (more) |
— | over 9 years ago |
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A: Hot rods into space! As a first approximation, we treat the rod as a one-dimensional rod of length $L$. On each end is a heat source (the mantles of each of the two "Earths". We can begin to model the system as following the one-dimensional heat equation: $$\frac{\partial T}{\partial t}=k\frac{\partial^2T}{\partial x^2}\... (more) |
— | over 9 years ago |
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A: What is the best practice for (alien) archaeology? Prevent contamination. Contamination is something that NASA and other space agencies are careful about when sending rovers to other planets (e.g. Mars). Rovers could accidentally release bacteria from Earth, thereby making it harder to tell if organic material is from Mars or from Earth. Returning s... (more) |
— | over 9 years ago |
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Can a (habitable) planet change its rotation speed? This is inspired by a comment by JDÅ‚ugosz. Planets change their angular velocity when they orbit stars because they follow Keplerian orbits with (typically) non-zero eccentricity. The bottom line is that they are not always revolving at the same speed. Note: The planet should be habitable. I'd li... (more) |
— | over 9 years ago |
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A: Equatorial icecaps and polar jungles a fantasy or reality? First, as JDÅ‚ugosz pointed out, the orbit you've drawn has a very high eccentricity - much higher than any of the planets in the Solar System, or many other planetary systems. To have something that is briefly out of the habitable zone, try something like Gliese 832c: It's orbit has an eccentrici... (more) |
— | over 9 years ago |
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A: A Completely Different Kind of Reef I don't think that any of them would have an advantage over corals when it comes to building reefs. Perhaps they could manage to build some, but it would be hard. Echinoderms Coral create coral reefs by secreting calcium carbonate[1]. Echinoderms have partial skeletons composed of calcite[2], which... (more) |
— | over 9 years ago |
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A: What changes would be needed for humans to live in an ocean? Water pressure gets very problematic very quickly: The deeper you go under the sea, the greater the pressure of the water pushing down on you. For every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi. 14.5 PSI $\approx$ 99.974 Pascals That said, if humans aren't going a... (more) |
— | over 9 years ago |
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Could humans split into two species living on two separate planets? This is inspired by The Time Machine, by H. G. Wells. In the book - in the far future - humans have split into two races, the Eloi, who live aboveground, and the Morlocks, who live underground. The two have become extremely different after living for a long time in different conditions. Humans can o... (more) |
— | over 9 years ago |
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A: Creating a realistic world(s) map - planetary systems Ordering of planets (mass and type) Can I start out by jokingly complaining that you picked a rather complex system? We've found a lot of exoplanets, but there are not many that reside in complex systems like this. This is going to be a tough question. As Green predicted, Kepler data is useful here ... (more) |
— | over 9 years ago |
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What types of musical instruments would develop underwater? Water is different from air, and sound waves propagate through water in a different way than they do in air (caused in part by interactions with the bottom of the body of water). For a society living underwater, this could lead to some interesting innovations in music, and musical instruments. For ex... (more) |
— | over 9 years ago |
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A: What society might survive the 3 generation rule There are two parts to the problem: short-term issues and long-term issues. Short-term issues Part of the problem of the Three Generation Rule is that people like procrastinating. Why do today what you can put off 'til tomorrow? Or, in this case, why do today what you can put off 'til the next gene... (more) |
— | over 9 years ago |
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Can people upload their consciousnesses to computers? The idea of uploading one's personality and consciousness to a computer is a semi-common science fiction trope. It has been suggested as a way to essential immortality. In a story I'm working on, an entire society has transferred itself from brains to computers. They're on a spaceship, heading to a ... (more) |
— | over 9 years ago |
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What stellar number density would two galaxies have to have for another star to collide with the Sun during a galactic merger? The Milky Way and Andromeda will collide a few billion years in the future. Stellar collisions will be rare because - as Douglas Adams put it - "Space is big. Really, really big." In the galactic disk, the number density of stars is quite low. Chances are good that the Solar System will not be ejecte... (more) |
— | over 9 years ago |