122 votes
Accepted

Is it possible to kill all life on Earth?

Not with the time constraint given. Let's start with the most destructive thing we've got: nukes. There are about 15,000 nukes worldwide, of varying yields. Sources: World Nuclear Weapon Stockpile, ...
The Square-Cube Law's user avatar
108 votes
Accepted

Car headlights in a world without electricity

Back in the day before portable electric lights, carbide lamps were used: A mechanism dripped water onto carbide, which then gave off acetylene gas, which burned in a controlled fashion. This was used ...
Klaus Æ. Mogensen's user avatar
92 votes

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

Water Basins If every 300ft or so the tree grew water basins to catch rain, (or maybe as a place to deposit water that it had already pulled up from below?) the higher parts could draw from these ...
Madcow's user avatar
  • 1,793
91 votes

Create "gold" from lead (or other substances)

What I need is a substance which could have been mixed by an alchemist and is as gold-like as possible. How about gold itself? Bear with me, here: While there are a lot of things that look kinda ...
type_outcast's user avatar
  • 7,245
84 votes

How would people conceivably escape a planet too large for chemical rockets?

A pulsed fission engine like project Orion would have been able to move a 10 million ton ship into earth orbit. The downside is that they were achieving the propulsion with nuclear detonations. They ...
TCAT117's user avatar
  • 21.1k
82 votes

Can I use a trebuchet to launch satellites into space from a lunar colony?

No. No matter how much velocity you can give your satellite, its trajectory will either contain the point it was launched from or not be a closed curve. an object is in orbit if it returns to its ...
SilverCookies's user avatar
78 votes
Accepted

What elements would be created in a star composed entirely of gold?

Unfortunately, no matter how much pure gold you add to your mass, you will never end up with a star. The reason for this is that fusing gold is an endothermic process, meaning that it requires energy,...
Gryphon's user avatar
  • 10.9k
74 votes

Is it now possible to undetectably cross the Arctic Ocean on ski/kayak?

I am going to claim expertise on this issue for a major reason: I live in the Arctic. I've also participated in search and rescues in the Arctic. The basic answer to this is that small groups of ...
Keith Morrison's user avatar
70 votes

Of strange atmospheres - the survivable but unbreathable

an atmosphere that is lethal if you get a breath or two but won't burn your skin off or poison you anyway when you walk out the door without your moon suit? take our atmosphere and remove all the ...
L.Dutch's user avatar
  • 283k
67 votes

Is it possible to kill all life on Earth?

No. Most of the preceding responses have overlooked one relatively-recently identified home for life on the planet; within the crust itself. Researchers have found bacteria up to 4 kilometers down in ...
Keith Morrison's user avatar
66 votes

Would planets be cubic in my "cuboverse"?

TMM;DR (Too Much Math, Didn't Read): For anyone who doesn't want to go through the derivations and calculations below, here are the important points from my answer: We're not working with the same ...
HDE 226868's user avatar
  • 101k
63 votes

Need a way for Earth not to detect an extrasolar civilization that has radio

Radio Waves Are Hard To See, And We Didn't Think To Look At Them There are about 134,000 stars within 200 light years of Earth. That's a lot of stars. We can't look at even a significant fraction of ...
Schwern's user avatar
  • 30.1k
62 votes

Would EMP From a Nuke Stall a car?

Depends on the car It also depends on luck, sometimes an EMP will do permanent damage, sometimes it won't. The chances are you'll blow a bunch of fuses at the very least. If you're running a diesel ...
Separatrix's user avatar
  • 118k
57 votes

Can a gunsafe survive a nuclear blast level attack?

As specified, this question is trivial - you're saying that a thermonuclear weapon is going off within nine yards of the safe. Though there's variation, a relatively typical thermonuclear weapon in ...
jdunlop's user avatar
  • 31.3k
56 votes

What elements would be created in a star composed entirely of gold?

This star would not fuse gold. Fusion reactions producing elements beyond zinc-60 are not energetically favorable; they are endothermic, and so consume energy. Several elements heavier than iron are ...
HDE 226868's user avatar
  • 101k
54 votes

Can I use a trebuchet to launch satellites into space from a lunar colony?

It is possible...eventually To be clear @SilverCookie's answer is correct. In simple Kepler mechanics, when you give a single delta-v to an object there are two 'orbital' possibilities: the orbit ...
kingledion's user avatar
  • 85.4k
54 votes

A non-technological, repeating, phenomenon in the sky, holding its position in the sky for hours

It's physically possible. Put a spherical object in a geostationary orbit, make it rotate about its own axis at a rate suited to your own visibility/non-visibility requirements, and make a portion of ...
Samuel's user avatar
  • 48.5k
53 votes
Accepted

Can two moons have intersecting orbits yet be guaranteed not to collide?

Ok, so you say 'Harmonic Orbits', but actual Space-Talking-Dudes call that 'orbital resonance', and it's the solution to your problem. We've got an example of something ALMOST exactly like what you'...
Morris The Cat's user avatar
52 votes

Of strange atmospheres - the survivable but unbreathable

My suggestion: 60% Xenon 20% Oxygen 15% Nitrogen 5% Carbon dioxide Why Xenon? Xenon is a noble gas. It has very few common chemical reactions, and is frequently used in situations where air is too ...
Adrian Hall's user avatar
  • 3,858
51 votes

How can a person Insulate copper wire in a medieval world?

The practice in the first half of the 20th century was to wrap wire in cotton cloth, resulting in something like a shoelace from https://www.vycombe-arts.co.uk/onlineshop/prod_3699705-Double-Cotton-...
nzaman's user avatar
  • 12k
50 votes
Accepted

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

Assuming you can fix the water problem using some of the other answers given, like having pools along the height of the tree, extracting water directly from passing clouds, etc., you will still have ...
BarbalatsDilemma's user avatar
49 votes

In theory, could all mammals be wiped out by a single pathogen?

Yes, but not in the way you are thinking. One way this could happen is if some killer fungus starts growing unchecked throughout the planet, on land and sea. By killing all plant life it would destroy ...
The Square-Cube Law's user avatar
48 votes

Would one atom of antimatter be lethal if annihilated inside the brain?

No. The mass of a proton is about $1.67\times10^{-27}$ kg. Therefore the total maximum energy released by its annihilation with an antiproton is $2mc^2= 2\times1.67\times10^{-27}\times9\times10^{16} = ...
b.Lorenz's user avatar
  • 6,381
48 votes
Accepted

How useful would a hydroelectric power plant be in the post-apocalypse world?

On September 28 2003, Italy experienced a nation wide black out. After three hours, energy was restored in northern regions. Electricity was restored gradually in most places, and in most cities ...
L.Dutch's user avatar
  • 283k
43 votes
Accepted

Could a large bird be used as transportation?

I decided to try to extrapolate from some known data. I used various sources to find that: The Harpy Eagle at 6 to 9 kg can lift a Three-Toed Sloth of 3.5 to 4.5 kg A Peregrine Falcon of 0.3 to 1.0 ...
cobaltduck's user avatar
  • 8,615
43 votes
Accepted

How fast does an antimatter bullet need to move to pierce rather than explode?

There's a very simple bit of math that tells you how far an antimatter projectile can penetrate something, assuming that the massive amounts of energy released aren't involved in that penetration. As ...
Salda007's user avatar
  • 8,320
43 votes

Is there anything about photons and/or space-time that would allow the detection of an energy-based attack from a distance of ten light seconds?

Since it is hard-scince question - the answer is NO, defending ship can do nothing to detect incoming laser attack from enemy ship it does not see. Argumentation is obvious: speed of light is the ...
ksbes's user avatar
  • 9,913
42 votes

If Earth's Core had ALL Of the Heavy Metals

How would this difference affect Earth's overall chemistry? Not much (but see below). Here's why: Let's start with some background The core–mantle differentiation event was the melting event which ...
Gimelist's user avatar
  • 3,858
42 votes

Would an antimatter bullet fired from a sniper rifle even reach its target?

The bullet will not go far It depends somewhat on the cross-section of the antimatter bullet. Let's assume that the bullet is slightly under 10mm in diameter, giving it a cross-section of 0.0000762 ...
KerrAvon2055's user avatar
  • 26.6k
41 votes

How to build a tank equipped with a 1 GJ railgun

SCIENCE The value with which you must be concerned when designing against recoil is not energy but momentum. The Kinetic Energy of a projectile is formulated with the equation: where E is the ...
MozerShmozer's user avatar
  • 4,967

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