Already discussed here: http://news.ycombinator.com/item?id=998734

This is an amazing topic for getting scientific misconceptions out in the open. Unfortunately, it does nothing for allaying them. People keep on insisting on ridiculous things like dropping the Earth into the Sun, even though there are far more efficient ways to reduce the whole planet to a featureless, lifeless molten glob. Most of the people who have the capacity to learn from such a thread have already learned and the people left haven't the inclination.

This particular article can't hold a candle to rec.arts.sf.science discussions of the same topic from the early 90's.

One point of note is that is that a small-enough black hole would be essentially harmless.

See http://www.aip.org/pnu/2008/split/871-1.html

Obviously, there is a tipping point where a black hole becomes dangerous - but it's worth remembering that gravity is the weakest of the major forces. Any physics geeks care to calculate how long it would take an Everest-sized black hole to eat the earth?

The calculations are impossible without lots more details, but do you mean Everest volume, or Everest mass?

Given this is entirely for entertainment purposes, any back-of-envelope speculation will do.

The article does mention Everest mass.

Everest volume would, of course, not be a "small" black hole at all.

Oh. I read this article years ago, so I didn't re-read it.

Everest mass would be a very tiny black hole.

As it oscillated back and forth it's picking up momentum from the earth, which slows down the oscillation. It would end up right in the center, but not moving.

After that it will wait for the pressure of the earth to feed it mass.

The inner core of the earth is solid. It's conceivable that the black hole, after it has settled down, will simply carve out a little cave and sit there in the center without accreting any more mass. In fact, I don't think you can completely rule out the possibility that this has already happened.

Wouldn't that be an unstable position? Even if the earth was a perfect ball and the cave was a perfect ball exactly in the middle then the gravity everywhere inside the cave is zero, so if you gave the black hole a little push it would crash into the earth again.

The center of the earth is the position that is "lowest" if you moved away from it gravity would cause it to "fall down" back into the center.

That is completely false. Modelling the inside of the earth as a hollow spherical shell, the force inside at all points due to the gravity of the surrounding shell is 0.

But it's not actually a shell.

In a solid sphere there is always force, and it always points to, and is lowest, at the center.

I assumed the black hole carved out a spherical hole in the center of the Earth. If it was inside it, then it would be inside a spherical shell (a very thick one at that).

But, you said it would be unstable, while actually if it crashed into the wall the resultant forces would put it back somewhere in the middle.

Or more accurately oscillating back and forth in the middle, but not touching the wall.

If there was any vapor in the middle (which seems likely to me, considering it would be a perfect vacuum at pretty extreme temperatures), then the gas would eventually slow down the oscillations and it would end up exactly in the middle.

Well, it would be sucking up the matter on the walls as well..

BTW, Sci fans of yesteryear were disappointed when it was discovered that Dyson Spheres and Ring Worlds gravitationally unstable...

> it would be sucking up the matter on the walls as well

It won't. The first time it touches (or comes near) the wall it will take what it can get, but it will never go farther than that. There is nothing that will "push" it closer to the walls.

You are missing the crucial point. The force in a cave in the middle of the earth is ZERO, there is NO force directed to the center of the cave. This is not an intuitively correct statement, but if you carry out the calculation you will see that it is true. If you take a solid sphere and carve out a spherical cave in the center, then everywhere (not just in the center) inside this cave all the little forces from all the atoms of the big solid sphere cancel out.

So this means that inside the cave the black hole will just move in one direction, until it hits the wall. Then it will suck up some mass and be pulled back to the center. Then it will suck up some mass on the other side, etc.

The only way the black hole will remain in the cave is if you put it in the cave with exactly zero velocity to begin with. As soon as one atom falls into it it will start to eat up the earth.

No, I am not missing that point.

You are missing a point.

Yes, inside the cave there is no force. But the black hole can hit the wall just once. After that it can not go any farther.

If passes thought/inside the wall it will be pulled back to the center, and the momentum exchange with the earth will slow it down (so next time it won't go as far). If it was just touching the wall, then that is as far as it can possibly go.

So once it's inside it's little cave, it's done. It can't eat anymore. (Unless of course there is no cave and the earth feeds it, but we are assuming a cave.)

You are missing three points: one is that if there is no cave, and it's oscillating through the earth, it will be pulled to the center. Two is that it looses momentum each time through the earth. And three is that once it's inside it's hollow cave it can no longer reach the wall.

I don't know what to say. On one hand you seem to agree that there is no force to slow the black hole down inside the cave, but on the other hand you claim that the black hole will remain inside the cave.

> You are missing three points: one is that if there is no cave, and it's oscillating through the earth, it will be pulled to the center.

Agreed.

> Two is that it looses momentum each time through the earth.

I'm not so sure about that. Mass is added to the black hole, and perhaps this causes the total momentum to increase.

> And three is that once it's inside it's hollow cave it can no longer reach the wall.

If it is stopped inside the cave. But there is no force to stop it.

Well we agree on the basics, that's good.

Imagine a tiny black hole arriving on earth. It grabs some mass. The black hole is moving, but the mass it ate is not. So rather than free falling, it looses momentum. As it falls through the earth it keeps doing that.

So it will not rebound back up to the top at the same height it fell. It will be lower. The second time through the same thing will happen.

Each time it oscillates it will get lower and lower.

Next. Say the black hole is a bit bigger. And it eats some mass on one side of the earth - now there is an imbalance. There is more mass on the other side. So the forces will cause it to slow down more than it otherwise would.

When it finally settles down enough to make a cave, it will "swing" as much as it can. But each swing can not be any higher than the one before. Over time, with random atoms falling into the cave it, it will come to rest at the exact center.

Assuming the cave is spherical, each swing will reach the other side, because inside the cave the black hole will not be slowed down, do you agree? So in this perfect situation, it is impossible that the black hole will come to stop exactly in the center. Even if it was stopped exactly in the center, if one atom hits it from one side, the black hole will crash into the other side (but slowly of course).

I see your point (I didn't before).

There is no force on the black hole, so if it moved at all it would crash into the wall. Only when it actually ate some of the wall would it turn around. So each swing would eat more and more.

Not if the black hole carved a spherical cave there. The forces in all directions cancel each other out inside the spherical cave.

In the perfectly spherical earth hypothesis, being the center of mass in the black hole, wouldn't there be a resulting force towards the center, although very small?

[EDIT] Hmm I think I see the point. The resulting force would be proportional to the ratio (black hole mass / earth's mass). Very small indeed.

No, that's irrelevant: http://hyperphysics.phy-astr.gsu.edu/hbase/mechanics/sphshel...

That's for a hollow shell.

For a solid sphere, there is always force toward the center. (And the closer to the center the lower the force, reaching 0 in the middle.)

No, the force is EXACTLY zero, not just very small.

Inside the cave yes, but not when it's inside the solid mass of the earth. Inside a solid sphere the force is toward the center.

Yes, but we're talking about the situation where there is a cave?

The cave is an interesting idea.

But with a bit of thought, it occurs to me that the iron at the center of the earth is only 'sold' dues to the intense pressure it is under (360 gigapascals). Relieve the pressure and you've got molten iron (at 5,700 degrees K).

http://en.wikipedia.org/wiki/Inner_core#Temperature

A Sunday wikipedia-ing...

The physics is different down deep, as we've found to our chagrin in other circumstance...

It's solid because of the pressure. If you had a void the pressure would be high enough to cause even solid rock to flow like water.

> One point of note is that is that a small-enough black hole would be essentially harmless.

I never realized that.

... Can I have one as a pet?

That article is a good demonstration of scientific entertainment. I liked that method: --- "What you need to do is to point our most powerful radio-telescope transmitters at likely solar systems and taunt them. 'The girly-beings in your miserable solar system could never destroy a planet as cool as this one...'" ---

Many think that all we have to do is show:

1) we are here

2) that we're savages who have nuclear weapons and who are perfectly willing to use them on each other.

3) we're going to develop interstellar spacecraft

I think many civilizations worthy of the name would want to bomb us before we get out of Earth's gravity well en masse.

In the grand scheme of things, I have come to realize nuclear warheads are not that fearsome. Thus far they have caused less damage to the surface of the earth than a pimple causes to your face. And the earth is insignificantly small.

They are definitely scalable, but they are certainly no Dr. Device

Interstellar drives are the dangerous bit. The point is that we have a history of being willing to use weapons of mass destruction on our own species. This should make other species a bit nervous.

There are a couple of comments here about the phrase "destroy the world" normally referring to life on earth.

In that vein I'd like to say that killing all life currently within 6500 kilometers of the Earth's center of mass is, in some ways, harder than simply destroying the Earth.

Take for instance the humble Water Bear they range from microscopic to a millimeter in size and can survive being frozen to within a degree of 0k and have survived 10 days in hard vacuum, during which time eggs were laid and hatched. It seems likely that any of the various "disassemble Earth" methods would fail to kill them. Similarly any chunk of Earth with a sealed ecosystem, like some caves, might continue to keep going indefinitely.

Killing everything might require vaporizing the planet in the sun or eating it with a black hole.

Heating the biosphere and the crust to a depth of 5 miles to 500 degrees and keeping it there for at least a couple of hours would likely do it, even for the Water Bears and radiolarens. That could be accomplished with asteroid/comet bombardment. The energy budget for that is many orders of magnitude smaller than most of the proposals in the article.

Well you'd probably want to go deeper than 5 miles to be sure. But a massive comet strike doesn't guarantee the sterilization of ejected material which is really the difficult part. Because there is life that can handle vacuum you have to not only heat the world to 200C (we think) but you have do it in a way that nothing larger than individuals molecules escape due to heating. which is also tricky because at some altitude in the atmosphere evaporative cooling might allow for something to survive indefinite periods of superheated crust.

EDIT: really what it comes down to is how many 9s of biocide do you want. Ramming Luna into the Earth might accomplish 7 or 8 9s, but if you want to kill everything, 100% of life from LEO down not just practically everything it's going to take more finesse than that.

Heating the biosphere by using a large cloud of orbital mirrors and inducing runaway greenhouse might accomplish your goal of 100% containment and sterilization, but if a few mites and microorganisms escape, that's close enough for me.

slacker

It's called GTD. Getting Things Destroyed!

They left out one possible solution: create a time machine to traveled back to a minute before 4.54 billion years ago. Equipment needed: high-pressured suction vacuum machine preferably solar-powered with a dustbag hard enough to store around 1.08321 × 1012 km3 mass volume of solar's dust and gas left over. Contrary to popular believe, it is actually easy to shop for a decent time-traveled machine: imdb.com Feasibility: 1/10

"Give me the place to stand, and I shall move the earth." Archimedes. Said to be his assertion in demonstrating the principle of the lever.

Moving the Earth is dealt with in some (err, much) depth here: http://qntm.org/moving

In terms of Archimedes:

"Give me a place to stand, and I will move the Earth", proclaimed Archimedes upon discovering the principles of leverage. Unfortunately, that place needs to be immovable, which is impossible. Also, what he didn't specify is that he also needs an equally immovable fulcrum - equally impossible - and a lever of stunning length which is unbreakable. Hah! Nice try, Archimedes.

"Unfortunately, that place needs to be immovable"

No, it merely needs to be of sufficient mass. As a practical strategy for moving the earth, this would clearly be infeasible, but, strictly speaking, I don't think that it is impossible.

When Newton came along we realized that all we needed to do was jump. Granted, we don't move the earth very much, and it comes right back, but still...

Destroying the Earth is kind of overkill. Unless you're making way for a hyperspace bypass, most supervillains' needs could be served by destroying what makes it different from any other planet. Burn off the atmosphere, melt the crust, release a metagenic virus that kills the biosphere, dump 130 million gallons of oil into the Gulf of Mexico...

And?

Did you read the article?

And what?

I read it the last couple times it was posted here.

And so what if destroying the earth is overkill.

That isn't what the article is about.

This is fun and all, but my question is: what happens when all the honeybees die out?

Let them eat cake.

This is completely old, but so funny every time, I have to up it. :)

An Illudium Q-36 Explosive Space Modulator will not suffice?

Wabbits. (Admittedly, not the best reference, since there was no FUD in that episode.)

Hilarious.

Talk about exactly the kind of article title I wouldn't want to be easy to find by bad guys.

If they have the kind of time, money and resources to pull these things off, I think their discovery of this article is the least of our problems.

I mean, if you've got 25,000,000,000,000 tonnes of antimatter just laying around in a warehouse somewhere, I don't care if you want to kill me and destroy the earth- I want to shake your hand.

if no one existed there would be no suffering.

This is somewhat entertaining, but it's a giant strawman. When someone talks about destroying earth, they don't mean literally making the planet cease to be a such, they don't even mean annihilating humanity. They mean permanently making earth a significantly less pleasant place to live for a significant portion of its population. Such as, cutting down the rain forest, disrupting the CO2 pump (or whatever) and lowering the air quality with more disease to follow (or some variation - either way, it's still a planet, and it's still very much populated by humans).

When a writer chooses a definition, as long as the definition is not insane ("When I say 'brutal murder', I actually mean the color purple"), you really have to go along with it. English is not a sufficiently precise language to be immediately suitable to the expression of all ideas.

I don't know what the original title was, but I do know the contents of the article, in which the author makes it abundantly (and if you read everything in that section, repeatedly) clear that he is aware of the usual use of the phrase "destroy the Earth". It is not a "strawman", it is the topic of the essay. If anyone is erecting a strawman, it is those who refuse to deal with the text on its own terms and insist on forcing their personal definitions of various terms onto the text, despite clear, repeated disclaimers, and the obvious fact that the entire idea of the essay is predicated on the author's definition.

Maybe you were just reacting to this title, but this has been linked in a few places and every time it seems this reminder needs to be given, so even if you are now satisfied by the new title, this still needs saying. An author is free to choose their topic and the precise meaning of some of the terms they are using; nothing else makes any sense.

Insane? How about nonsensical? The "blow up the earth real good" goal is of the mentality of someone who watches Star Wars and decides the movie portrays real physics. Vaporizing the oceans and turning the crust into molten lava is plenty of destruction. It's also many orders of magnitude less energy than a lot of the patently unphysical proposals in the article. Equivalent mass of antimatter? You'd need a lot less than that to exceed the gravitational binding energy of planet Earth, and even that is ridiculously inefficient.

That's like the proposal to achieve AI by simulating a whole human body down to the molecules. It sounds clever to college freshmen, but it really just shows people are ignorant of the orders of magnitude of what they're discussing.

> They mean permanently making earth a significantly less pleasant place to live for a significant portion of its population.

In the context of this article such people would be termed either "wannabes" or "lacking in vision".

Really? We're talking about those who can see a way to achieve basically the same thing, but whose methods are dozens of orders of magnitude more efficient. That strikes me as clever. To me, the ones who propose such a ridiculous goal are those "lacking in vision."

The number of times 'vision' has been correlated with 'efficiency' or frankly even 'cleverness' is very small. Vision isn't about building a better cow, but how you apply that cow.

RISC? Super-Scalar? Out of Order execution? JIT? Sorry, but vision often does result in orders of magnitude improvement.

You're offering up RISC as an example of vision in a discussion of destroying planets?

Moving Jupiter via fusion candle is vision, RISC is optimization.

The fusion candle idea is neat. It's entertaining because it resembles the thinking behind real engineering. Most of the items from the article are like, "Gee whiz, let's spend about 2 seconds applying knowledge from a 2 second skim of a bunch of Wikipedia entries. Golly, look at the big numbers!"

If you really want to do a thorough job, you'll need a Vogon and a bulletin board.

You mean "Vogon constructor fleet"? A single Vogon seems a non-optimal strategy (seeing as mass suicide via poetry is only a partial solution)

I don't know, bureaucrats operate in packs. A single Vogon might be all you need to set the wheels in motion, and indeed might be more effective than touching on several distributed Vogons.

Exactly. More than one Vogon might have a meeting.

I have updated the title. It represents the article better, and hopefully makes it clear that the article is tongue-in-cheek :)