119
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, ...
- 131k
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 ...
- 15.9k
93
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 ...
- 1,803
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 ...
- 7,226
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 ...
- 20.9k
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 ...
- 6,645
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,...
- 10.9k
74
votes
Accepted
Stealth in Space: How realistic is it?
Forget it, there ain't no stealth in space.
The linked site explains in excruciating detail why stealth in space either do not work or is, when it works, extremely unwieldy or practically useless.
I ...
- 14.6k
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 ...
- 21.1k
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 ...
- 262k
66
votes
Design a non-computerized biometric door
The dog is trained to recognize specific scents/people. It barks if it knows you, at which point the guard opens the door. New people can be introduced, at which point it knows your scent and you're ...
- 34.4k
66
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 ...
- 21.1k
64
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 ...
- 98.2k
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 ...
- 30k
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 ...
- 116k
59
votes
Accepted
What would it take to build a ship capable of crossing the Pacific?
They fail and suffer whatever evil fate awaits them.
...or this
I say this mainly due to this pre-condition:
The refugees are traders, not craftsmen or metal smiths. Iron is known
to them but ...
- 32.8k
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 ...
- 26.1k
56
votes
What would it take to build a ship capable of crossing the Pacific?
This has already been tried and proven, and is referred to as the Kon-Tiki expedition:
Heyerdahl believed that people from South America could have settled Polynesia in pre-Columbian times. ... His ...
- 3,074
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 ...
- 98.2k
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 ...
- 48.3k
53
votes
Accepted
With current technology, what would be the best way to store energy for future generations?
Use the extra power to convert atmospheric CO2 to hydrocarbons and store it underground. This offers the long term storage requirements and ease of handling specified in the question.
Various Energy ...
- 52.5k
53
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 ...
- 84.8k
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'...
- 16.8k
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 ...
- 3,868
51
votes
Accepted
Close Quarters Combat... In Space
As a general rule, it seems natural that you would want an opponent as absolutely far away as possible. The further away they are, the fewer tools they have to hurt you.
However, there are a class ...
- 130k
51
votes
Accepted
Moons of Moons of Moons
Let's make a bunch of assumptions:
The largest primary is about 3 times bigger than Jupiter.
To really be a parent, the barycenter of a parent-satellite system must be within the parent.
Everything ...
- 841
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-...
- 11.9k
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 ...
- 676
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 ...
- 131k
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} = ...
- 6,391
Only top scored, non community-wiki answers of a minimum length are eligible