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94 votes
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Why would space fleets be aligned?

The crews have evolved on worlds with orientation, so their psychology and conventions reflect the reality that they are planetary creatures. Orson Scott Card captured the importance of orientation ...
pojo-guy's user avatar
  • 9,722
66 votes

Killing a star safely

Problem: even if you could just stick a blanket over the sun, it is probably already too late. The solar system formed more than 4 billion years ago, and for all that time anyone who was watching and ...
Starfish Prime's user avatar
64 votes
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Is stealing the moon actually possible?

Plans for stealing the moon. Shrink it Well, this seems like the obvious solution. Just invent a shrink ray, zap the moon so it becomes the size of a basketball, then carry it home with you and ...
IndigoFenix's user avatar
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45 votes

Alternate universe where life is more common; is it feasible?

Feasible Can I have a universe with X? Yes you can! If anyone tells you otherwise, tell them their argument fails because they are using the logic of this universe. Your other universe has different ...
Daron's user avatar
  • 66.2k
43 votes

Could gravitational lensing be used to protect a spaceship from a laser?

There are several problems with this. First of all, when someone fires a laser at you, you aren't going to know it until it hits you, so this would only work if Ship A were CONTINUOUSLY creating a ...
Morris The Cat's user avatar
38 votes
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How much damage would a cupful of neutron star matter do to the Earth?

This is more or less my best guess. We're talking about a mass of about one hundred billion tons, composed of neutrons, previously held together by a terrifying gravitational field - and now ...
LSerni's user avatar
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37 votes
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A planet illuminated by a black hole?

This scenario is quite problematic for two main reasons: evaporation and peak wavelength. The black hole's lifetime is too short We can make a rough estimate of the properties of the Hawking radiation ...
HDE 226868's user avatar
  • 101k
35 votes

Is stealing the moon actually possible?

It's perfectly easy to steal the moon. Just register a claim on it in every country and start issuing legal notices. It's been done before: Spanish woman claims ownership of the sun
nzaman's user avatar
  • 12k
35 votes

A 1 kilometre wide sphere of U-235 appears in an orbit around our planet. What happens?

Normally, only the innermost kilogram of uranium in an implosion-type bomb actually undergoes fission (and only 0.6 to about 5g of mass are ultimately converted to energy - the sources don't agree on ...
LSerni's user avatar
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34 votes
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Black hole at the center of the planet

Your planet needs to be about 722500 times more massive than Earth for its core to undergo collapse into a black hole. Leaving aside the small detail that at this point your "planet" would ...
Darth Biomech's user avatar
33 votes

How can solar sailed ships be protected from space debris?

Generously spread the sail surface with self repair nanobots. Any impact with dust or sub-dust size object (which is more likely to happen) will pierce a hole through the sail (and leave a cloud of ...
L.Dutch's user avatar
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32 votes
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What elements are useful for humans, but rare in our galaxy?

People need boron, because plants need boron. https://en.wikipedia.org/wiki/Boron Boron is a chemical element with the symbol B and atomic number 5. Produced entirely by cosmic ray spallation and ...
Willk's user avatar
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32 votes
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Making A Geosynchronous Orbit Impossible

Easy: Put a moon right above geostationary orbit. If you have a 24h day, and a moon that takes 25h to circle the planet, any satellite orbit at geostationary height would be totally unstable. The ...
cmaster - reinstate monica's user avatar
32 votes

What are the repercussions of two asteroids in the asteroid belt colliding?

Probably nothing Robert Rapplean's answer is correct (upvoted) that without further information it is not possible to guess at an answer without more information, but there are some additional factors ...
KerrAvon2055's user avatar
  • 27.8k
31 votes

Why would space fleets be aligned?

In our world When you watch a movie, the ships are usually aligned. This is because of reasons that are most likely not based on our experience in space battle. I'm pretty sure I read about this and I ...
Legisey's user avatar
  • 4,554
31 votes
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The rotation of the sun's core doubles in speed every 10 years. How many years before the situation turns apocalyptical?

We have a problem here: we don't understand the solar core rotation really well. As you said, relatively recently (around 2017) it was discovered that the core rotates at about four times the speed ...
The Square-Cube Law's user avatar
30 votes

How much damage would a cupful of neutron star matter do to the Earth?

The answer isn't entirely clear what the final state of the Neutron Star matter would be, but it would most definitely completely destroy the "Totally Normal Office Building", and most of the country.....
abestrange's user avatar
  • 5,974
29 votes

How can solar sailed ships be protected from space debris?

A tiny piece of space debris is dangerous to the ship, as it may hit people, mechanisms, or fuel. But the damage to the hull itself would be negligible. It could simply be patched. The hull is the ...
Brythan's user avatar
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29 votes
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Practicality of building a space station in the tail of a comet

The station is anchored to the comet A comet's tail orients away from the star, and its size and properties change based on how close it is to the star. Because of a comet's elliptical orbit, there ...
Nosajimiki's user avatar
  • 95.1k
29 votes

What would happen if I fire a gun in an environment with hyper-gravity?

Gravity doesn't affect the velocity at which the bullet leaves the gun, that is a function of the energy released by the gunpowder. Gravity affects only how fast the bullet will reach the ground while ...
L.Dutch's user avatar
  • 289k
28 votes

If Earth had a smaller radius, but was rotating at the same speed, would its day be shorter?

The length of the day is strictly a function of the time earth takes to rotate. If your planet takes 24 hours to rotate then regardless of its radius, it will have a 24 hour day. You can develop an ...
sphennings's user avatar
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28 votes
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What is the largest fraction of Earth's sky that an astronomical object could take up (visually) before ripping Earth or itself apart?

The calculation turns out to be pretty straightforward and relies on two equations. Say the two objects have masses $M_p$ and $M_s$, with radii $R_p$ and $R_s$, with the $p$ denoting the more massive ...
HDE 226868's user avatar
  • 101k
27 votes
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Could the moon crash into the earth if we colonised it and increased its mass?

As mentioned in comments, I don't have the full stability answer to hand (although see edit below). But I do have a practical answer. The practical answer is that no feasible human effort could ...
Mark_Anderson's user avatar
27 votes
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How massive would a planet need to be to sustain negligible damage from impact with the Earth?

That really depends on what you consider 'negligible'. Is it 'Sterilization of all life, but planet is still there in one piece in the same orbit'? Or is it 'Everyone in the direct impact zone gets ...
subrunner's user avatar
  • 4,572
27 votes

Black hole at the center of the planet

No A natural occurring black hole that comes into existence due to mass collapsing onto itself must have more mass than the Tolman–Oppenheimer–Volkoff limit, which has been estimated to be around 2.17 ...
The Square-Cube Law's user avatar
27 votes

Earth is accelerated out of the solar system - do we keep the Moon?

You're going to lose the Moon. At the Moon's current distance, the Earth's gravity can only change its velocity by $0.002m/s^2$ The mentioned acceleration of about $0.25m/s^2$ dwarfs that, and if at ...
notovny's user avatar
  • 2,873
25 votes
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What is the minimum size for the Sun?

Black body radiation The Sun is, approximately, a black body. That means that the light it emits follows a particular spectrum according to Planck's law, with the shape of the spectrum determined ...
HDE 226868's user avatar
  • 101k
24 votes
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Moons that can't see each other

In theory if the two moons were in the exact same orbit on opposite sides of the planet then yes. Having the moons closer to the planet and smaller also makes that easier. For example geostationary ...
Tim B's user avatar
  • 77.1k
23 votes

Killing a star safely

A star shines because it has mass... You put enough mass together, it gets a dense core, heats up, and voila, solar fusion. Yes, that's an oversimplification, but, fundamentally, making a star not ...
SRM's user avatar
  • 25.5k
23 votes

Is stealing the moon actually possible?

You can't move the Moon, it just requires too much energy. But maybe we can deny everyone else the Moon... and ALL OF SPACE!!! Energy Required To Move the Moon out of the Earth's Orbit Let's say "...
Schwern's user avatar
  • 30.1k

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