Botanist lobbies to save humanity
... from miniature black holes that will devour the earth
Black Holes 101
A black hole is a point of infinite density where mass has been compressed to almost zero volume. This causes the fabric of spacetime to warp so severely that it essentially forms a hole in spacetime (there's lots of speculation about what's on the "other side" of the hole, but nobody knows). These holes are black, because they don't emit radiation*, which is why we can't see one directly. Your garden-variety black hole forms when the core of a massive star collapses. Physicists also think that much larger black holes were formed as a product of the big bang, and grew by colliding with each other and feeding on gas and stars to become supermassive black holes at the centers of galaxies. It takes an extreme event to form a black hole.
The event horizon of a black hole (also referred to as the Schwarzschild radius) is the gravitational point of no return. It's the distance from the black hole at which the escape velocity equals the speed of light. The escape velocity is precisely what it sounds like: how fast you have to go in order to escape the gravity of something. The escape velocity of the earth, for instance, is 11 km/s. The escape velocity at the event horizon of a black hole is 300,000 km/s. Once something crosses the event horizon, even light, it's toast. Forever lost from view. Flushed down the cosmic toilet, never to be seen again. The event horizon is effectively the size of the black hole.
Time for a thought experiment. Imagine that super-intelligent beings have come to the solar system and decided to experiment with the Sun by compressing it down to form a black hole. The laws of physics say that the size of the black hole scales directly with mass. A black hole with the mass of the Sun would be 3 km in radius (a little under 2 miles), which means you'd have to come within 3 km of the solar black hole to be "sucked in." This is something I emphasize with my astronomy students. If the Sun were suddenly replaced with a black hole of the same mass, the earth and all the other planets of the solar system would continue to orbit exactly as they always have. Except for the lack of sunlight, there would be no noticeable difference. The Sun is 300,000 times more massive than the earth. If these same intelligent beings decided to squash the earth into a black hole, its size would be 1 cm.
So, at the CERN laboratory, where careless scientists are on the verge of creating tiny black holes that will consume the earth, let's think about the possible consequences. We know that it takes extreme physics to create black holes, but let's assume CERN scientists are capable of this and imagine that they create a black hole with the mass of, say, an M1 Abrams tank (60 tons). The size of such a black hole would be 2 x 10-20 cm. That's 0.00000000000000000002 cm. Something would have to get that close to the M1 Abrams black hole to be "sucked in" by it. But let's be realistic. These scientists are experimenting with much smaller masses -- sub-atomic particles, to be precise. A proton, for example, has a much smaller mass than the tank, 1.7 x 10-24 g. A trillion-trillionth of a gram. The size of a proton-mass black hole is so miniscule, it's not even worth contemplating. It's much smaller than the Planck length, the smallest size anything can be, so essentially a proton-mass black hole can't exist.
But there's another wrinkle to this. Black holes gradually evaporate through a process called "Hawking radiation," which has to do with quantum effects near the event horizon of the black hole. According to physics, the lifetime of a black hole is proportional to its mass to the third power. The M1 Abrams black hole would last about 0.6 seconds before it evaporated away. The lifetime of the proton-mass black hole (which theoretically can't exist) is much shorter than the Planck time (5 x 10-44 seconds), the smallest measurable increment of time. In other words, it would evaporate before we even knew it existed.
Conclusion: Miniature black holes are not a threat to humanity.
[* In theory, black holes can emit a small amount of radiation, the aforementioned Hawking radiation. So far this has not been directly observed.]
[Lightly edited to clarify sizes of micro black holes.]
A colourful American botanist, teacher, former biologist and sometime physicist says (in outline) that the LHC may rip a hole in the fabric of the space-time continuum and so destroy the Earth. He wants the US government to act now and delay the LHC's startup while a new safety review is carried out.The article is hilarious, but it's evident this "sometime physicist" doesn't understand physics very well. In fact, this touches on a subject a lot of laypeople misunderstand: Do we need to worry about miniature black holes? Read on and find out!
Walter L Wagner and his fellow Hawaiian Luis Sancho, according to a report on MSNBC, filed suit in the Hawaii federal court last Friday. The men are worried about one of several planet-busting physicists' nightmares being unleashed in the LHC's bowels deep beneath the Franco-Swiss countryside. (According to Wagner's website, as of publication, the LHC is located "near Generva, Switzerland".)
Firstly Wagner is concerned that careless atom boffins might slip up and create a miniature black hole. This would then suck in surrounding mass, gaining unstoppably in size and power in a runaway process until it had engulfed the entire Earth and packed it down inside its swelling, unescapable event horizon.
Black Holes 101
A black hole is a point of infinite density where mass has been compressed to almost zero volume. This causes the fabric of spacetime to warp so severely that it essentially forms a hole in spacetime (there's lots of speculation about what's on the "other side" of the hole, but nobody knows). These holes are black, because they don't emit radiation*, which is why we can't see one directly. Your garden-variety black hole forms when the core of a massive star collapses. Physicists also think that much larger black holes were formed as a product of the big bang, and grew by colliding with each other and feeding on gas and stars to become supermassive black holes at the centers of galaxies. It takes an extreme event to form a black hole.
The event horizon of a black hole (also referred to as the Schwarzschild radius) is the gravitational point of no return. It's the distance from the black hole at which the escape velocity equals the speed of light. The escape velocity is precisely what it sounds like: how fast you have to go in order to escape the gravity of something. The escape velocity of the earth, for instance, is 11 km/s. The escape velocity at the event horizon of a black hole is 300,000 km/s. Once something crosses the event horizon, even light, it's toast. Forever lost from view. Flushed down the cosmic toilet, never to be seen again. The event horizon is effectively the size of the black hole.
Time for a thought experiment. Imagine that super-intelligent beings have come to the solar system and decided to experiment with the Sun by compressing it down to form a black hole. The laws of physics say that the size of the black hole scales directly with mass. A black hole with the mass of the Sun would be 3 km in radius (a little under 2 miles), which means you'd have to come within 3 km of the solar black hole to be "sucked in." This is something I emphasize with my astronomy students. If the Sun were suddenly replaced with a black hole of the same mass, the earth and all the other planets of the solar system would continue to orbit exactly as they always have. Except for the lack of sunlight, there would be no noticeable difference. The Sun is 300,000 times more massive than the earth. If these same intelligent beings decided to squash the earth into a black hole, its size would be 1 cm.
So, at the CERN laboratory, where careless scientists are on the verge of creating tiny black holes that will consume the earth, let's think about the possible consequences. We know that it takes extreme physics to create black holes, but let's assume CERN scientists are capable of this and imagine that they create a black hole with the mass of, say, an M1 Abrams tank (60 tons). The size of such a black hole would be 2 x 10-20 cm. That's 0.00000000000000000002 cm. Something would have to get that close to the M1 Abrams black hole to be "sucked in" by it. But let's be realistic. These scientists are experimenting with much smaller masses -- sub-atomic particles, to be precise. A proton, for example, has a much smaller mass than the tank, 1.7 x 10-24 g. A trillion-trillionth of a gram. The size of a proton-mass black hole is so miniscule, it's not even worth contemplating. It's much smaller than the Planck length, the smallest size anything can be, so essentially a proton-mass black hole can't exist.
But there's another wrinkle to this. Black holes gradually evaporate through a process called "Hawking radiation," which has to do with quantum effects near the event horizon of the black hole. According to physics, the lifetime of a black hole is proportional to its mass to the third power. The M1 Abrams black hole would last about 0.6 seconds before it evaporated away. The lifetime of the proton-mass black hole (which theoretically can't exist) is much shorter than the Planck time (5 x 10-44 seconds), the smallest measurable increment of time. In other words, it would evaporate before we even knew it existed.
Conclusion: Miniature black holes are not a threat to humanity.
[* In theory, black holes can emit a small amount of radiation, the aforementioned Hawking radiation. So far this has not been directly observed.]
[Lightly edited to clarify sizes of micro black holes.]
19 Comments:
Well, tickle my inner geek! I love black holes and love to find out everything I can (although my grasp of the mathematics required for balancing a check book are sorely lacking, which makes some of the concepts a little hard to grasp).
I'd be more worried about some sort of chain reaction we're not familiar with happening. Great scientific discoveries are usually precluded with "Hmm. That's odd" rather than "Eureka!".
Now, onto a pedantic question. Why do they always illustrate black holes like some sort of vortex tornado shaped thing. It makes it look like you could skim the surface and go straight across. Isn't the pull fairly spherical (yeah, I know they can rotate and bulge a little at the sides. I'm bulging at the sides and not rotating so I can't blame the black hole).
Robb,
The problem with black holes is that it's difficult to come up with an accurate yet illustrative schematic of what they are. Most of the time we use awkward 2-D/3-D combinations to represent something that is in four dimensions. If you could show me a typical picture of what you mean, I can better answer your question. But I'm assuming it's something like the second picture in my post. The first photo is actually a better representation. Spacetime is like a flexible fabric. Some people use a rubber sheet as an analogy, which is flawed because spacetime isn't 2-D, but let's use it anyway. If you place a mass on the rubber sheet, something like a baseball or a bowling ball, the sheet will stretch and become warped. The more massive the object, the more it warps space. Also, the more dense the object (the more you compress the same mass), the more extreme the warp becomes.
This image might help in the visualization. Or this.
Let's imagine that we have a bowling ball on this sheet that represents a planet, and let's imagine placing you in a rocket ship, which we'll represent with a marble. Now imagine rolling the marble along the sheet. Far enough away from the bowling ball the fabric is still smooth and flat. But once the marble gets close to the bowling ball, its path is deflected by the warp in the sheet. If it gets too close to the ball and isn't moving very fast, then it'll roll down and smack into the bowling ball, i.e. your rocketship will crash/land on the planet.
Keep in mind that your marble rocketship can't just leap over the bowling ball and continue on the other side. It's confined to the sheet (spacetime) and any space beyond the rubber sheet is "hyperspace." You can't go there. (Or at least we don't yet know the physics of hyperspace, but conceivably this would be a great way to travel enormous distances in no time.)
Let's take this a step further. Black holes are so dense that, instead of creating just a dent in the fabric of spacetime, they create an infinite warp. This is essentially a hole in spacetime. If you get too close to a black hole, you will be forced, like the marble, by the extreme curvature of space to follow the warp all the way in to the black hole.
The difficult part is transferring all of this in your mind to the actual four dimensions of spacetime. I have a hard time doing this, myself. Even though in illustrations of black holes it looks like something you could just jump over, you have to remember that the warping occurs in all dimensions (including time!)
If you're interested, I recommend two excellent books on this topic. The first, Cosmic Catastrophes by J. Craig Wheeler, is an excellent starting point for the non-scientific reader. I bought this for my dad, and he loved it. The second is Black Holes and Time Warps by Kip Thorne. The latter is a bit more advanced, but still accessible to the intelligent layman.
Here are some interesting videos about black holes. The first is a quick fun little musical montage of compact objects (black holes, neutron stars, white dwarfs). The second is a link to several videos of NASA simulations.
Black holes, neutron stars, etc.
NASA simulations
By the way, the last part of the first video (supermassive black holes) is the subject of my research.
It's the "constrained to the piece of fabric" that gets me, I guess. That and the illustrations (even like the second link you gave) still makes it seem like you could possibly move off the grid and be safe.
I think about it almost like a fuzzy sphere - the further away you are, the less pull (at a specific speed).
I love the concept of black holes. There was an audio book I listened to a while back about the Tunguska blast actually being a micro black hole and instead of passing through the earth, it got caught up and was actually orbiting inside, gradually heading towards the center where it would eventually start eating the planet up. The guy who wrote it is / was a physicist so the science was pretty plausible.
Gotta remember what that was called...
Ah, "Singularity" by Bill DeSmedt.
Robb,
"That and the illustrations (even like the second link you gave) still makes it seem like you could possibly move off the grid and be safe.
I think about it almost like a fuzzy sphere - the further away you are, the less pull (at a specific speed)."
You're close to the mark. The 2D pictures aren't very good because space is 4D.
Think of the Earth's gravitational pull, it works in a spherical zone around the Earth, right? Black holes work in the same manner, so there is no 'off' for the grid.
The difference is that with the Earth, you can escape the gravitational pull with enough thrust, even if you are on the surface of the Earth. We do that with rockets, they have enough thrust to push their payload out of the gravitational pull.
While with a black hole, once you have passed the event horizon, you can't get out. No amount of thrust can push you past that edge again. Of course, you'll be squished to a small point and won't care much about that sort of thing.
The only thing we suspect can 'escape' a black hole is radiation, the Hawking radiation that Sarah mentioned at the end of her post.
"In other words, it would evaporate before we even knew it existed."
Heck, it could be happening now, and we'd never know!
The fuzzy sphere concept is good. Even though black holes look disky in some illustrations, their boundaries (event horizons) are three-dimensional. The gravitational force of attraction diminishes with distance squared, so that's where the fuzziness would come from.
That and the illustrations (even like the second link you gave) still makes it seem like you could possibly move off the grid and be safe.
In terms of our current understanding of physics, the inhabitants of the 2-D world in the illustrations could no more move off the grid than you could move off the 3-D (spacial) grid you inhabit.
Have you ever read Flatland? If not, that's a good primer for the concept of dimensions and space. This segment from Carl Sagan's Cosmos pretty much sums up the ideas. Keep in mind, however, towards then end when he's talking about tesseracts and a fourth dimension, he's talking about a fourth spacial dimension (as we tend to take time as the fourth dimension).
Here's a video about spacetime that's got some neat animation. One thing to keep in mind: they are showing spacetime as a 2-D fabric, and representing masses as 3-D spheres. It's confusing, but remember that in this analogy you cannot leave the fabric of spacetime. Anything above or below it is hyperspace. Towards the end they show the warping of spacetime in 3-D -- just imagine a black hole is in place of the Sun.
Will you pardon a couple of really dumb questions, Doc? I mean, I'm just some bozo who once got a B.S.E.E. but got sidetracked into software early in the course of his checkered career. So black holes don't figure much in my daily routine.
You've calculated the gravitational point of no return for an object moving at the speed of light. I can't move my tired old butt much faster than 15 m/s, and I can't sustain that for very long. Wouldn't my gravitational point of no return be a whole lot farther from the center of the black hole? So if I were somehow able to create a black hole in my garage, might it not suck me in?
When a black hole sucks stuff in, does its mass increase? If it does, wouldn't its gravitational attraction to other nearby stuff increase? If a black hole formed in a place where it had lots of stuff to suck in, why wouldn't it continue to suck stuff in until it ran out of stuff to suck?
You ask good questions, Gringo. Let's think about this.
The formula for the radius of the event horizon is R = GM/c^2. But we can substitute any velocity for c, e.g. to calculate the Gringo horizon, we'll use a velocity of 15 m/s instead of the speed of light. For the M1 Abrams black hole, the Gringo horizon would be 7.8 x 10^-6 cm. Some part of you would have to get within about a millionth of a cm to get "sucked in." Any part of you that's further away from that would not be sucked in.
Now, to answer your other question, yes, when a black hole "sucks in" matter its mass increases thereby increasing its gravitational force of attraction. The gravitational force per unit mass of the black hole is expressed as F = GM/R^2. F increases linearly with mass, but decreases as a function of the square of the distance. Even as the black hole's mass increases, eventually stuff will be too far away to be "sucked in." This is the principle behind why quasars power on and off. Quasars are supermassive black holes in the centers of galaxies that are actively feeding on gas and stars, but they don't devour the whole galaxy. Eventually they run out of nearby stuff to feed on and just shut off and sit there quietly in the center of the galaxy until some process drives more gas and stars to the center. We have such a quasar fossil in our own Milky Way.
That's another myth that a lot of people have about black holes - that they have an infinite gravitational pull and suck everything in.
While I'm not a black hole scientist, it is in my understanding that they do have an infinite pull, but only at the infinitely small point in the middle. Any distance from the singularity and you have less than infinite pull.
If I was allowed the option to choose the method of my death (and this is NOT a joke) it would be to board a rocket and head into the biggest black hole in the universe. Backwards. So I could have a look around for a while and see the back of my head and the beginning of the universe before spaghettification.
And, if I may be so bold, I'd like to comment to Gringo that the event horizon is that limit where NOTHING can escape, even light. The Gringo Horizon is going to be well beyond that one!
If y'all will pardon another dumb question or three, what if a black hole somehow got loose in earth's atmosphere? Could a black hole of some critical mass sustain itself indefinitely by capturing air molecules? If so, what would that critical mass be, at say, STP?
Could a black hole of somewhat larger mass let loose in the atmosphere eventually absorb the whole atmosphere, not by gravitational attraction, but by differential presure? (I expect that pressure would decrease near the black hole as air molecules are captured.) Would we eventually notice an extremely strong wind blowing from all points of the compass toward the black hole? If I were observing these events, would the words, "Man! That black hole really does suck!" be my last?
Suppose I had a machine in my garage emitting black holes with a mass of one AMU each into the atmosphere without an EPA permit. Most of these black holes would have a very short life, but some would collide with one another, with air molecules, and with the walls of the garage to form more massive black holes. I guess that the probability that these one AMU black holes combine into a self-sustaining black hole increases with density. What would a plot of that probability versus density look like?
Upon reflection, a black hole wouldn't remain in the atmosphere long. It's collisions with air molecules would be entirely inelastic, so it would just fall. Being a point mass, it'd fall right though solid ground, picking up a bunch of electrons and any nucleons it strikes. It'd probably have a negative charge. If it increased its mass sufficiently, it'd fall all the way into the earth's core. Could that be a good thing?
There's no easy way to contain a black hole, is there? You can only hope that it has too short a life span to do any damage.
Gringo,
You're making my poor befuddled brain hurt!
The easiest way for me to answer this is to point out that any black hole capable of remaining in the atmosphere would evaporate so quickly that it wouldn't even matter. Remember, the 60-ton black hole would last only a fraction of a second.
You're making my head hurt, Stickwick. In addition to more mundane matters like auto and computer maintenance, now I've got to read up on Hawking radiation.
What is the loss via Hawking radiation for a black hole?
Russ,
I'm actually not sure what the expression is for Hawking radiation. But it must be related to the equation for the lifetime of a black hole
t = 10,240 pi^2 G^2 M^3 / h c^4
G = gravitational constant
h = Planck's constant
or
t = 8.36 x 10^-26 M^3
where M is in units of grams.
Gringo: Again, I recommend Thorne's Black Holes & Time Warps. It's very sparing on the math, but it explains the concepts well. If either of you are looking for something more mathy, I can dig up a reference.
So unless a blackhole is massive, or has a massive amount of material pouring into it, it'll be gone fast?
Yep. And the maximum rate at which a black hole can consume matter depends on its mass, so the small ones wouldn't be able to accrete matter fast enough to live very long anyway.
So a little knowledge is a dangerous thing!
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