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111

But in most stories, FTL doesn't actually follow Newton's 1st law; everybody knows that once your hyperdrive fails, you're dead in the water. Otherwise, the Enterprise could hit warp 9.9 and easily coast across the galaxy. And that actually makes sense in the warp-style of FTL: FTL travel is only possible within the field generated by a functioning FTL ...

106

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, Plougshares Fund, 2018 Federation of American Scientists, 2018 Assuming an average yield of 200 kilotons, which is what most US nukes have, we could assemble ...

85

an antagonist desires to cripple humankind down to simple-living status [without killing people] This is impossible. Modern society is a highly integrated web of sophisticated transport and production systems, most notably in terms of agriculture, water, sewage and waste, and materials distribution (roads, rail, air, sea). One you remove these people will ...

80

Countering the gravitational binding energy of a (earth-sized) planet takes roughly 2.4E32 joules. That's enough to make it come apart, but it would be a slow process; if you want it to blow apart you'll need to add more than that. It doesn't matter too much how you deliver that energy, just that it gets to that total somehow. So what does that mean in ...

72

1. Space is mostly empty If you pull the trigger on this, you're ruining someone's day, somewhere and sometime Well, not necessarily. There's so much empty space between anything interesting in the universe, that it's very likely that those "shots from a cosmic shotgun" will just keep traveling through the cosmic void, never even approaching ...

71

If you're a billionaire and already under the focus of the TLA Agencies, best how to disappear for a year is... not to disappear. If you'd suddenly disappear from today to tomorrow a dozen of alerts will go of with every single agency, not only from the government. Even more if you're already known as a mad man. So you need a perfectly instructed body ...

67

A Jupiter-sized mass of antimatter Based on some quick Googling: If 1 kg of antimatter came into contact with 1 kg of ordinary matter, they would annihilate with 1.8 × 1017 joules of energy. Jupiter has a mass of around 1.9 × 1027 kg A supernova can release as much as 1044 joules of energy. Based on these numbers, if you sent a lump of antimatter with the ...

66

Rock and clay don't burn well, leaving you with a lot of dressed stone lying around to say there was once a city here. Fire from above implies volcanoes, as we learned from Pompeii, that's actually a great way to preserve a city so that 4000 years later we know exactly what happened, down to what specific individuals were doing when it hit, so that's out. ...

63

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 continental crust and 2 km beneath oceanic crust. Recent estimates are that up to 70% of the microbial life on the planet is, in fact, in the deep biosphere. ...

59

Turn on the news. This may seem obvious when what you want is to get informed about the world, but it should work fine for this. Most of the biggest news channels-- CNN, Fox, MSNBC-- have 24-hr news cycles, meaning somebody is always on the air discussing something. Allowing for commercial breaks, you should see someone doing a live broadcast within a few ...

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Well, at best you're depositing in the planet (or the powdered remnants thereof) energy equal to its gravitational binding energy. According to Wikipedia, the one true source of truth, the gravitational binding energy of Earth is about 1032 J which is about as much energy as the Sun emits (in all directions) in a week. This is converted into kinetic energy ...

55

Having had a quick read of the source material, it seems clear that the devices do not explode as such, but vigourously emit heat and radiation sufficient to burn and melt their surroundings. We already know of a way to release the energy stored in a fissile material over a period of time, of course: a nuclear reactor. Regular reactors are limited by their ...

52

How about a catastrophic flood? Have the city built on a large river. A landslide further up blocks the river and causes an enormous lake to form (also cutting off water supply to the city causing hardship for the inhabitants). When the dam fails...it really fails and a wall of water rushes down the valley wiping out the city and thoroughly destroying it, ...

48

would it triggers extinction level event? Since they'd evaporate more or less instantaneously (known as Hawking radiation), releasing energy according to the famous equation beginning E=, the spaceship would last a few microseconds at best, Earth would be fine. Yes, the aliens in the ship would become extinct.

47

You need an Alcubierre Warp Missile. Let's take the theoretical route for this. Theoretically, as the missile goes into warp, the Alcubierre drive creates a bubble around the missile. The missile warps the fabric of spacetime as it travels to its destination (which should be set right in front of the target). The space behind the ship expands, the space in ...

46

By doing it every couple of years in some totally innocent way. Some years you spend sailing in the Southern Ocean, some years you spend 6 months skiing in the Alps or solo trekking across the Australian outback. Eventually they get used to your disappearing for months at a time and it taking them slightly longer than they'd like to work out where you are ...

43

I have much academic experience with some of this, especially the second part of your question. I'll address a few different sides of things. The most drastic way I can think of that could ostensibly be caused by some natural occurrence would be a low altitude meteoric air burst similar to the Tunguska event. Such an event would cause a lot of surface ...

42

Well, Mark Olson and Samuel provide some very respectable math that winds up with the world destroying shot being taken from about 1 AU or the distance from Earth to sun. Yes, yes; it seems very reasonable. But what fun is that? A little flash of light, a great disturbance in the force; bah. You want a ringside seat. I propose that your world ...

42

Thou shall now kill. (Inscribed in a stone tablet) In the original Hebrew, change לא ("thou shall not") to לו .לו by itself means "to him" or "for him" or something similar (hard to explain exactly). But together with other words it is sort-of possessive, sort-of permission. It would become something like "For him is to kill". There are actually places in ...

42

To make a statement. There is no real requirement for a laser to be red - in fact it is likely 'invisible' unless it shines through a gas or other medium that scatters the light. So perhaps the makers of the Death Star want to make a statement: they want everyone to know that they mean business. After all, the power of the Death Star is the threat of its ...

41

You simply would not be able to do it with raw energy alone. Using a table that I simply love, consider three lines: $3.9×10^{22}\text{ J }$ estimated energy contained in the world's fossil fuel reserves as of 2010 $2.2×10^{23}\text{ J }$ total global uranium-238 resources using fast reactor technology $3.8×10^{26}\text{ J }$ total energy output of the Sun ...

41

The conserved quantity causing the recoil is the product of mass and velocity. The projectile is a small fraction of the mass of the ship. The recoil will be the same fraction of the velocity. E.g. if the projectile is 100g and shot at a million miles per hour, and the ship was 100 tons then its recoil would be 1 mile per hour. The additional energy ...

36

You do not. Unless... This is not realistic. However... see addendum for some hand-waving. Ok, so Polonium-210 has a really high LD-50 value, that is all fine and well. But where are you going to get it? Your first problem is that Polonium is an extremely rare substance because it can only be created in nuclear reactors. The next problem that it has ...

36

Redundancy Go the other way. Rather than restricting access to, or use of, antimatter, let it be a thing that's known but not particularly useful in a weapons situation. With effectively free unlimited energy there's no reason why something as difficult and dangerous to handle as antimatter would be a weapon of choice. All you need is something as ...

35

Update: The original version of this answer was based on an arithmetic error which underestimated the required material by factor 1000. It was subsequently rewritten. How do you define "Death Star"? Depending on what your space station is going to be capable of, there is no upper bound to how complicated the engineering challenges can become. But to ...

35

Viruses are highly species-specific, i.e. a human virus will only kill humans. So a biological weapon will do the job. The best virus to use is beyond my knowledge, and I am a bit concerned a terrorist would read this. If we stick to sci-fi convention, then zombie virus is the most obvious choice. But realistically, even the deadliest viruses leave some ...

34

Moved from comment to answer because I've done more research. Try the biblical account of Sodom and Gomorrah, believed to be near the coast of the Dead Sea . The cities were destroyed by means of volcanism (fire and brimstone), and 4000 years later we still don't know where they are for sure. As an argument for the effectiveness of this approach, there is ...

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Diplomacy The body count is really going to depend on how long humanity has to prepare. Hi, glad to meet you, the reverse not so much. We're the galaxy's big bad and you just got on our radar. Pro tip, don't be on our radar. Listen, we consider your technology a threat. We're going to, how do you say, bomb you back to the stone age. However your society ...

31

Situation: Humanity is killing the planet Aim: Reduce load on the planet by reducing population Maintain current lifestyle for the survivors Options to achieve the aims Starting with a standard bad guy option, I gather all my wealthy friends to my volcanic fortress and kill everyone else. Outcome: Terrible. Wealth is mostly real estate and companies. ...

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