Why the LHC Won't Destroy the World 508
An anonymous reader writes "Most people are aware of the recent articles contending that the Large Hadron Collider at CERN might destroy the world. While most scientists have no such concerns, a recent preprint released to arxiv systematically dismantles the notion. The gist of the argument is this: Everything that will be created at the LHC is already being created by cosmic rays. If a black hole created by the LHC is interactive enough to destroy the world within the lifetime of the sun, similar black holes are already being created by cosmic rays. Such black holes would be stopped by dense cosmic objects (neutron stars and white dwarfs). A black hole stopped in one of these objects would eventually absorb it. We see sufficiently old neutron stars in the sky, thus any black hole that could be created at the LHC, even if it is stable, would have no effect on the earth on any meaningful timescale."
Re:"cosmic rays" argument is bogus (Score:4, Informative)
Hence the argument concerning neutron stars which would stop such a particle.
Re:Fools! (Score:2, Informative)
neutron stars emit radio waves at regular intervals.
black holes emit nothing.
Re:This discussion has already been held (Score:3, Informative)
Review of the Safety of LHC Collisions (Score:5, Informative)
Re:Stopped black hole? (Score:3, Informative)
astrophysics buffs, please correct this if I'm wrong, I'm only an amateur.
Re:Logic (Score:3, Informative)
Naturally occurring high energy particles (Score:3, Informative)
Way lower, here, can be as much as a factor of ten million.
Here's a nerdy but popular account of an extreme high energy cosmic ray detected at the Fly's Eye II [fourmilab.ch]. And that's just what we've detected in a few decades of running small detectors. What the planet has intercepted in the last few billion years must be even more staggering.
Re:Fools! (Score:2, Informative)
Why would you be worried about that? What are the odds of getting hit by a golfball (or a billion) compared to the size of the universe? As far as I know the earth is still here so they can't be that dangerous. Or one of them might hit us tomorrow and we'd all be dead. Nothing we can do about it, no need to worry.
Keep in mind that to create a golf-ball sized black hole you need to compress a LOT of matter. According to wikipedia, the article about black holes, a black hole with the mass of the moon would have a 0.1 mm diameter. Thus it is safe to assume these black holes, if they exist, were not, in fact, created by cosmic rays hitting something (the wikipedia article suggests that tiny black holes might have been created during the big-bang).
Re:Fools! (Score:3, Informative)
Re:Fools! (Score:5, Informative)
black holes emit nothing.
Ha!
http://en.wikipedia.org/wiki/Hawking_radiation [wikipedia.org]
Re:Fools! (Score:1, Informative)
black holes emit nothing.
Oh, I'm sorry, the correct answer was "Black holes emit X-rays [wikipedia.org] of varying intensity in a repeating pattern over regular intervals [eurekalert.org]." Thanks for playing, though.
Re:Hang on a minute (Score:5, Informative)
Whatever small compass we shove the matter into, it'll have exactly the same amount of gravity before and after. If we happen to shove it into a tight enough space that it becomes a black hole, it will be spectacularly tiny. It'll only start to accrete matter as it interacts with it. And, it'll have to get close enough to do it.
Gravity being what it is, it seems far more likely that a black hole formed in the lab would get drawn to the Earth's center of gravity (just like everything else on Earth is) rather than causing the Earth's center of gravity to shift. Shifting the Earth's center of gravity dramatically toward the LHC would take way more energy than what we're putting into the particles at the LHC.
Bottom line (Score:4, Informative)
- Energy of maximum LHC collision: 14 TeV
- Energy of "Oh My God Particle" cosmic ray that hit the sky over Utah in 1991: 300,000,000 TeV
Sources:Re:Fools! (Score:5, Informative)
Re:Group collision mergers (Score:2, Informative)
When a high energy lone particle collides with something, a veritable shower of particles is released which are then free to smash into other stuff. Also, cosmic rays can be waaaaaaaaay more powerful than anything we can make on earth. One of those slamming into our atmosphere or the Moon would have done something catastrophic already if it was going to.
Re:Huh? (Score:4, Informative)
Re:Hang on a minute (Score:1, Informative)
Oops. Black holes are densely packed matter--in fact, black holes are the most densely packed matter. Thus, they are neither infinitesimal in size, nor that infinitely dense, they are just very, very dense--and relatively small (depending on their mass).
This I agree. Little size (even for a black hole) and little mass (compared to other black holes as well as humans, ants, and molecules) doesn't make it for heavy gravity.
Re:Do I have this Right? (Score:5, Informative)
Right? I'm not a physicist.
In short, you are correct. If you were to magically replace our Sun with a black hole of 1 solar mass, the gravitational pull would not change. There would be a whole lot of other stuff going on, but black holes don't magically increase the gravitational pull of a mass.
If I made a blackhole out of the amount of mass that the LHC is accelerating, and put it suspended in a sealed jar on my desk, I would only feel the gravitational pull of the mass that actually is the black hole. So, unless people are having difficulty with the gravitational pull of things on their desk, I wouldn't be too worried about it.
Re:Hang on a minute (Score:5, Informative)
Doubt away...
The Black Hole would be a very tiny mass at creation, so small that the difference between where the earth's center of mass was before and is after is insignificant.
(In effect the before state is equal to finding the gravitational center of the earth, minus the gravitational center of a bunch of electrons that are about to power the LHC, then finding the separate center of those electrons poured into the LHC, and comparing that to the after state - where we have to find the gravitational center of the rest of the earth, and the gravitational center of the mini black hole) The center of the rest of the earth doesn't change significantly in the before and after pictures, and the power put into the LHC wasn't enough to cause any noticible wobble before it was used, was it? So it's not going to cause a wobble afterwards.
Now, assuming a stable black hole, it is drawn towards the center of the earth by gravity. Repulsion by solid matter isn't enough to stop it. (Repulsion is an electromagnetic effect - the cloud of electrons around normal nuclei push and so keep matter from passing through other matter. The hole doesn't have a cloud of electrons, so it falls. It 'wants' to go into a narrow elliptical orbit around the earth's core. (It's not falling straight towards the core, because the spot where it formed on the earth's surface has sideways velocity from the earth's rotation). As the hole falls it eats stuff, but that means it also emits electromagnetic radiation as stuff falls in. This works out in the end as a kind of friction, so the hole slows in its orbit and spirals inward. By the time it is up to a few milligrams weight, it is in a tight little orbit around the earth's core, and we are all alive, waiting for it to gradually gain weight. (If the boffins have told us). This takes a year or so, with us not really noticing anything until the hole weighs kilotonnes, at which point the last twelve hours or thereabouts get very impressive and the earth goes bye-bye.
So yes, you end up with the moon peacefully orbiting the black hole as the hole orbits the sun, in orbits that are so close to the existing ones it would be a real challenge to find the differences.
Now, the side of the moon towards us got some interesting radiation exposures during the final few minutes, perhaps enough to melt crater walls and such. The effect of all that light from the final flash might conceivably be measurable, out in the 20th decimal place or so when someone measures the Moon's rotational velocity.
Fortunately, this is all based on the idea that a black hole barely bigger than a proton is somehow stable, which we doubt very much.
Re:Hang on a minute (Score:3, Informative)
Yes. It would orbit the the center of mass of the Earth, inside the Earth. Every once in a while it would collide with a particle, absorbing it and acquiring the mass, momentum, and charge of the particle. As a result its orbit would shrink over time. In a few billion years it would settle to the center of the Earth.
Re:Cost vs Benefit? (Score:2, Informative)
A2: The experiments planned for the LHC and any high energy collider are supposed to simulate the very early universe. The only comparable high energy events are a few cosmic rays. The problem with cosmic rays is they interact somewhere in the atmosphere not in the middle of a giant array of detectors like they ought. Cosmic rays also don't happen all that often. So while the reaction is similar the collider gives better rate and controlled location.
A1: This is research. Foreseeable applications are only used to part venture capitalists with their money. There are many ways that people justify research for the sake of research, just like art for the sake of art, but you are being lied to if they tell you there is an application.
For my money this probably has about the same chance of developing cost-efficient solar as the average bay area start-up; 0.
CERN Coffee (Score:5, Informative)
You obviously haven't tasted CERN coffee - they have expresso machines and its generally very good. Much more likely is "This food is offal". I remember several times going to to the coop and the three dishes of the day were things like calf's head, tripe sausage and tongue...yummmm!
Re:Fools! (Score:5, Informative)
Cosmic rays travel through the Universe with enough energies to boil a cup of water (in one single proton). That's up to 100 000 000 times more energy than the LHC. Those particles collide with everything, at a rate of a few per square kilometer per millenium. It might seem small, but consider the size and lifetime of the Earth, the Moon, the Sun, etc; combined. Particles whose interactions with the atmosphere would have the same energy as the LHC's collisions hit us more than 100 times per day per square kilometer. Over the lifetime of the Earth, every event that can happen in 10 years of LHC operation would already have happened hundreds of thousands of times [arxiv.org] on the Earth alone. Since we're here, there's clearly no need to worry.
Re:Group collision mergers (Score:2, Informative)
Yeah, but those particles resulting from cosmic-ray collisions are travelling near c, and consequently won't linger near other particles. The probability of collisions seems much greater in a manmade particle accelerator with a fixed target.
I asked in an earlier thread, only half-joking, if the cosmic gamma-ray bursts we observe about once a day might not be instances of other civilizations building something like the LHC and turning it on. The question was promptly modded down to -1, Troll.
Seeing as how our last words as a species are either going to be "Hmm, that's weird..." or "Die, capitalist scum!", death by LHC mishap actually wouldn't be a bad end to things, IMHO. I would rather we all died trying to learn something, than trying to wipe each other out.
But apparently all further discourse on the subject is just so much trolling. Yay, Slashdot.
Re:Hawking radiation? (Score:3, Informative)
---I'm a physicist (working on my PhD), but I've had one nagging question about hawking radiation noone's been able to answer (satisfactorially)
I'm a lowly EE student :) I think I understand though.
---So, the process of hawking radiation can be thought of as a particle/anti-particle pair being created near the event horizon. Suppose that one of them is juusssttt close enough to the event horizon that it falls in and the other one remains outside. We assume that (to conserve total energy) the antiparticle falls in, annihilates a regular particle trapped within the black hole and the regular particle that was just far enough away escapes. From the outside, it appears the black hole is radiating mass.
Not quite. The particle/anti-particle is actually created from the vacuum. Quantum physics allows for virtual particles to exist as a form of catalyst, however that energy debt must be paid no matter what.
Lets say one has a controlled black hole. If one was to watch the event horizon, you would see virtual particles swarming in and around the black hole. If the pair falls in, the net energy is 0. This is the case we dont care about because energy/mass is conserved. The other case is where 1 falls in and the other is ejected into space. In that case, the black hole did "eject" mass, but the energy debt must be paid. Because of that, the black hole must pay to create the pair via its own energy.
We call this effect where the black hole pays energy to create "real" virtual particles Hawking Radiation.
---A) I would think that there would be an equal probability distribution of which particle is closer to the event horizon. However, if that were the case then there would be an equal probability that normal/anti particles would fall in, and that would cause the black holes to not evaporate. We know they do, so I don't know how to rectify that. What makes the antiparticle more likely to be closer to the event horizon?
That's where you are mistaken. Overall energy is lowered when 1/2 of the pair is absorbed by the black hole. Once the black holes lose enough energy (some critical value), they explode violently. What we dont know is what exactly happens in a black hole, nor do we know what form of matter/energy is in there, but we do know that the energy debt must be paid.
---B) Suppose you were able to accrete enough antimatter that you could produce a black hole with it. Virtual particles are created on the outside. In this instance, the normal particles must fall in and the anti-particles must escape to conserve total energy. How does that happen? How can the particles see beyond the event horizon to know that's what's within?
I think you're getting hung up on matter and antimatter. They're all quarks. They all combine somehow with U, D, U-bar and D-bar, and even if they did annihilate and release energy, the energy is still trapped. And since the event horizon seems to be a sort of heisenberg shield, I dont think they need ever "collide".
That's why we're studying them cause traveling 100+ Ly is impossible for us now.
A few corrections (Score:3, Informative)
The LHC collides protons, not electrons.
This depends on whether or not it is a charged black hole. In all likelihood it will be since it would have been produced by colliding two protons. Since EM interactions are many, many orders of magnitude above gravitational ones (calculate the difference in the gravitational vs. electric forces in an atom for an excellent illustration) I would expect a charged black hole to interact via EM far more strongly than by gravity.
Re:Hang on a minute (Score:3, Informative)
The formula for the lifetime of a black hole is t = 8.4 x 10^-17 * M^3, where M is in kilograms and t is in seconds; as the mass decreases, the lifetime decreases very rapidly. A 1000kg black hole will have a lifetime about equal to the mass of the universe. A 1kg black hole has a lifetime of 10 attoseconds.
Of course, during that 10 attoseconds, the entire mass of the black hole evaporates away as energy --- and there is a lot of it in a 1kg mass; roughly the equivalent of 23 megatonnes, assuming I haven't dropped a decimal place or three...
Re:Hang on a minute (Score:3, Informative)
Depends on the model. One of the more popular theories holds that the heart of a black hole is a singularity--a hole in spacetime infinitely small and infinitely dense
Re:Fools! (Score:3, Informative)
Even still, they don't precisely emit Hawking Radiation either, but rather that its origin is just beyond the event horizon.
Re:Hang on a minute (Score:3, Informative)
The problem with black holes having non-infinite density is as follows: forces cause interaction between particles by having them exchange virtual gauge particles. These gauge particles move at most at the speed of light, just like everything else. However, the only possible direction inside the event horizon of a black hole is down; gauge particles are no exception, they fall down like everything else. Consequently, a particle can never learn that there's any other particles beneath it (closer to the center of the hole), since it never receives the gauge particles sent by them; and consequently, there's nothing to halt it's fall. This is true for any distance from the center, so nothing stops the particle from going ever closer.
When this happens for all the particles falling into the hole, they all pack into its center. A finite amount of particles packed into a single point (infinitesimal space) means infinite density.
See, the common perceptual mistake people do is to think the event horizon of a black hole as a wall of some kind. That implies that you could view the singularity if you went inside. It's not true; what the event horizon is is the cosmic equivalent of a sign saying: "the road is one way from this point on". You pass it, you still can't view the singularity, because light can't move outward from there. Neither can anything else, for that matter. Even light that's sent outward will simply fall a bit slower, that's all. The gauge particles sent by the atoms on the tip of your nose will still reach the ones on the base of it, so your flesh doesn't disintegrate; but only because your nose is falling even faster than them, so it falls past them. But there's no way to stop the fall.
Then again, general relativity and the curvature of space mean that the distance between the event horizon and the center of a black hole is infinite, because space is infinitely curved (or rather, it's curvature approaches infinite without bound near the center), so maybe that's the solution: mass doesn't pack into infinite density at the bottom of the black hole's gravity well, because there is no bottom, just eternal fall.
Now I managed to spook myself :)...
Re:Fools! (Score:3, Informative)
You're right within several orders of magnitude (sort of). The "ultra-high energy" cosmic rays have, perhaps, 50 - 200 J of energy. To raise a cup of water by _one_Kelvin_ takes nearly 1000 J. So we're off by a factor of 5 right there. To actually boil the water takes many, many times this amount of energy (raise its temperature by 100 K, and then pump enough energy in to actually effect the phase change, at least at STP). Even without taking into account the latent heat of the water, already we're off by 3 orders of magnitude. Water is curious stuff!
Re:Huh? (Score:3, Informative)
I agree, as far as "science doesn't deal with deduction, as opposed to induction."
This proof, however, lacking any experimental results or direct observation of the phenomena in question, is unquestionably a deductive proof. It's quite a simple one actually:
"If cosmic rays spawn world devouring strings/black holes, then we'd see a marked absence of quasars and neutron stars"
"We don't see a marked absence of quasars and neutron stars"
"Therefore cosmic rays don't spawn world devouring strings/black holes"
This is fricking modus tolens; it's one of the most basic deductive constructs. Saying therefore, that his proof is fallacious is perfectly legitimate.
Re:Group collision mergers (Score:4, Informative)
The OP isn't talking about the nano black-hole being miles above the surface of the Earth.
The nano black-hole is so small it will orbit the center of the Earth from within the Earth. It's so tiny that it will simply miss most of the matter in the Earth. Keep in mind that the vast majority of "solid" matter is empty space.
Re:Fools! (Score:3, Informative)
To calculate the mass, the calculation is just r*c^2/(2*G). Therefore, a black hole the size of a golf ball (21.33mm radius) would have to have a mass of 1.4E25 kg, or about 2.4 earths.
For those wondering, you calculate this by setting the escape velocity equal to the speed of light. Another interesting thing about black holes is that you don't technically need very dense matter to form a black hole. If you assumed all the mass of the black hole was evenly distributed, if you got a sphere of water (density 1kg/L) with a radius of 2.68AU, you would have a black hole. Of course, with all that mass (approximately 136 million solar masses), gravity would compress it.
Re:CERN Coffee (Score:2, Informative)
Ok, time to lose some karma and be modded down:
There is no such thing as expresso. Yes, i am a Nazi about this.
No, I wouldn't mind this being the last thing that is ever said before being sucked into a black hole. It's really that important (obviously).
Re:Fools! (Score:3, Informative)
Re:CERN Coffee (Score:3, Informative)