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If you put your hand in the Large Hadron Collider... (kottke.org)
101 points by jlangenauer on Sept 24, 2010 | hide | past | favorite | 39 comments

By training I am a radiation physicist and actually do know about particle beams hitting people. The LHC beam would certainly give someone an appreciable radiation dose, although the secondary synchrotron X-rays would probably be worse than the proton beam itself. In fact a much lower energy proton beam would have a worse effect on your hand/body, since that beam would actually stop inside you (protons deposit most of their dose at the very end of their range).

Of course the injury you received would largely be determined by the length of time your hand was in the beam. Really not fun results can be radiation ulcers or radiogenic cancer. If the dose were high enough you could get a radiation syndrome, where some/all of the fast growing cells in your body die off and you die in a few days or months.

The only data I could find after a quick search indicated that the dose present in the beam line would be on the order of 10^4 Gy per year. That means if you managed to put your hand in the beam for 1 minute, you're only looking at about 0.01 Gy, which isn't that much.

There's actually a reported case of someone getting hit by a proton beam on the head in 1978:

     Bugorski was leaning over the piece of equipment when 
     he stuck his head in the part through which the proton 
     beam was running. Reportedly, he saw a flash "brighter 
     than a thousand suns", but did not feel any pain.

He is still alive.

In case people take what the first person in the video says combined with your quote from wikipedia but don't read the entire wikipedia page I'll quote this:

    The left half of Bugorski's face swelled up beyond
    recognition, and over the next several days started 
    peeling off, showing the path that the proton beam 
    (moving near the speed of light) had burned through 
    parts of his face, his bone, and the brain tissue

My work is indirectly related to proton beams. Your comment about energy deposition in human tissue reminded me they can be used for cancer treatment that's localised to a certain depth. In fact http://en.wikipedia.org/wiki/Proton_Beam_Therapy would go some way to answering the original question about the interaction between the LHC beam and a human hand. Presumably we can take it as given that there is some sort of exit window (not sure what material would be best?) from the beam guide into the air.

Aside from the bremstrahlung, proton beam interactions with matter include spallation from heavy nuclei (giving neutrons) and the formation of muons. Both of these would deviate from the original proton beam direction and irradiate other parts of the body.

In 1978, Anatoli Bugorski accidentally stuck his head through the 70GeV U-70 Synchrotron. http://en.wikipedia.org/wiki/Anatoli_Bugorski

He is alive, but suffered serious injuries. As I understand, the LHC is of a similar design, at 100 times the energy.

The beam path on the LHC is kept under high vacuum. At no point does it intersect air at atmospheric pressure. There's no way for anything to accidentally intersect the beams, which is good, since one of them is made of antimatter.

EDIT: Nope! Wrong! Mistook the LHC for the LEP. The LHC does not accelerate antimatter at any point.

Additionally, while the individual protons in the LHC may only be a hundred times more energetic, there are quite a few more total particles in the beams. I can't find any technical details of the U-70 synchrotron, but it came online in 1957, so there's that.

Sorry about the nitpick, but no, the LHC does not use antimatter. Both beams consist of protons (or heavy ions sometimes). Some of the accelerators at CERN, like the LEP (Large Electron Positron) Collider, do use antimatter, but the LHC does not.

Thanks for the correction. Upvoted.

Well we are talking hand vs head here. I think you would probably lose your hand, but why would anyone say that you'd die?

The LHC has beam dumps, where they re-direct the beam if they need to shut it down quickly. http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach... "Each beam dump absorber consists of a 7m long segmented carbon cylinder of 700mm diameter, contained in a steel cylinder" They seem to expect that there'd be a lot of force there.

http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach... also has some comparisons regarding beam energy and aircraft carriers, cars, etc.

I know hardly anything about proton beams. However, here's a thought experiment that's on my mind:

Instead of a beam of protons, lets think about something simpler: a reasonably high powered bullet. Instead of a 7m segmented carbon cylinder, lets have some slats of wood. So, in the same way as at the LHC, the bullet strikes the wooden slats, it deposits all of it's energy in the wooden slats, breaking them up and stopping the bullet.

I think that fits the use case of the beam dumps, where all the force of the beam gets dumped at once, and the important number is the total energy of the beam, since you want to totally stop it.

Now, the thought experiment: replace the wooden slats with single piece of paper. Now when the bullet strikes, it goes straight through - the mass of energy in the bullet mostly stays in the bullet, only enough energy to rip through a small circle in the paper gets dumped. The bullet will carry on it's merry way.

So, relative to the LHC beam, which is your hand more alike: the sheet of paper, or the slats of wood?

It's a simplistic model which ignores radiation from the beam, and lots of other things, but I think it's informative. My guess is that the beam would behave like a laser cutter: cutting a smallish hole, possibly with secondary damage, but largely powerful enough to carry on it's way once it has punched through.

A bullet going at relativistic velocity hitting a piece of paper might not punch such a nice hole - it would bust up molecules and atoms, and some subatomic particles, there would be tons of secondary radiation from that, and the rest of the paper would be destroyed along the way by some type of explosion.

It would be pretty spectacular.

Each proton would, at the full power of 7 TeV, have 1.12 microjoules of energy. 1.15x10^11 protons per pulse, 2808 pulses per beam and two beams, one of antiprotons, and one of protons; for a total energy of 352,235,520 joules. 87 kilograms of TNT.[1][2]

Your hand would evaporate fairly quickly, then turn into a plasma, then get hot enough to start radiating x-rays. There would be quite a lot of bremsstrahlung from the hyperenergetic protons punching through the cloud of plasma, and producing showers of secondary radiation,[3] which means you would be quite well irradiated by the time the shockwave from the explosion killed you.

1: All this is straight from the wikipedia page, but I double checked the math.

2: I'm not including energy liberated from antimatter annihilation energy, since the total mass of the antiprotons is quite small.

Typing that out, it sounds like a pretty lame excuse. Let's do the math.

3.2292x10^14 protons per beam. Atomic weight of 1, of course, so:

(3.2292x10^14)/(6.0221415x10^23)[4] = 5.362212x10^-10 grams. .536 nanograms of antimatter.

Since annihilating antimatter gets you 9x10^13 joules per gram, you get... 48,259.9089 joules. That's actually larger than I expected, but .01% of the kinetic energy of the beam.

3: Just how much secondary radiation, I don't know, since that depends on the density of the cloud of plasma, which would change over time, be pretty anisotropic, and be a general pain in the ass to model.

4: Avogadro's constant

Buncha edits: forgot HN uses the asterisk to style text.

Can't edit this now, of course, but as fjh pointed out elsewhere, I confused the details of the LHC for the LEP, partially. The LHC collides protons and sometimes lead nuclei; but at no point collides antiprotons.

Posting after midnight: Not always a good idea.

Don't worry, you had me at "bremsstrahlung".

Braking radiation ? What they don't teach that in school anymore ?

Just kidding.

I'm a big fan of the whole Sixty Symbols series. For those of you not familiar: http://www.sixtysymbols.com/

There's also a "sister" site for chemistry: http://www.periodicvideos.com/

It's good stuff. I've enjoyed pretty much every video I've seen from both of them.

Why don't we drop a pig into the LHC. If nothing happens, problem solved. If something happens, dinner solved.

Obviously you're joking, but I cringe at the thought of a pig carcass anywhere near a 6 billion dollar (USD)[1] machine.

[1] http://askanexpert.web.cern.ch/AskAnExpert/en/Accelerators/L...

Peta would be all over that.

"You can do the same thing to a tofu pig without harming innocent animals"

I'm sure someone would take offense to it being shaped like a pig, or even referred to as a pig, as the implications are still remotely offensive.

Heck, to use the technique of some parents: some starving kid in Africa would love to eat that tofu. We, therefore, should clearly be offended at its waste.

Gas pipelines have little machines crawling inside them for inspection and maintenance purposes. These machines are called pigs.

The LHC is basically a big pipe, so maybe it does have pigs inside it already.

Sorry to be a buzzkill, but the LHC beam circulates in an extremely high vacuum. There's no way a hand could even get in the beam without breaking the vacuum, thereby causing the accelerator to shut down automatically. Also, it's cryogenically cooled. Radiation dose aside, the hand would freeze and probably fall off.


Incidentally, when I was working at CERN in the mid 1990's, the Large Electron-Positron Collider (the predecessor to the LHC) was shut down by an act of sabotage involving 2 Heineken bottles placed in the beam pipe. The electrons and positrons (and many physicists) were not happy bunnies. http://blogs.nature.com/news/thegreatbeyond/Beer%20bottles.p...

Update: Now I see that the vacuum point has already been made. There are no heavy ions in the LHC main collider, they're produced by bashing protons into a target in one of the secondary beamlines. Also, antimatter is frequently the byproduct of extremely high center of mass proton-proton collisions.

It's a too little sample to be statistically significant in any way, but I find interesting that no two men have the same favorite symbol, while both the women coincidentally chose infinity and what its symbol represents.

If the universe were to be remade, perhaps physical constants would change, like gravity could be 7.1 instead of 6.67.

But mathematical constants like pi would remain the same, wouldn't it? A circle is a circle no matter what kind of universe it's in, so the ratio of the radius to the arc length would remain the same.

As I look at it, math is the universal truth of the universe, because everything is derived using the first principles.

1) Perhaps yes. 2) Mathemtical contstans are purely abstact - pi only exists in a perfectly euclidian plane. It's an abstraction that works for us in a scertain scale because it matches close enough. In real life, there aren't circles.. they're just close enough. So no - a universe could have completely different maths required to describe it. 3) Math is purely abstract and detached from the universe. It operates on theoretical models that try to model reality. Math has it's own universal truths, but reality does not. The universe came before math - math is a tool invented by man to analyze the universe.

> So no - a universe could have completely different maths required to describe it.

That wasn't the question, though. Pi is the ratio between circumference and diameter of a perfect circle, whether or not you can create a perfect circle in your universe. We can't even create one in ours, and yet pi still "exists" here. Undoubtedly, wiggly-space mathematicians would also have a conception of pi, though it might be as esoteric to them as toroidial universes are to us.

To put that another way: Math has very simple axioms (e.g. set theory), and everything else derives from them. What theories can be proven from those axioms in this universe, can be proven from those axioms in any universe (and a universe that doesn't obey those axioms likely wouldn't "function" as a universe—it wouldn't have any reason to be causal, for example.) The maths describing a particular universe is its physics, which do change from universe to universe—however, those physics are all just different subsets of the set of mathematical physical models—which are, themselves, a subset of the mathematical theories provable from the axioms.

No, it isn't universal, even in our universe. If you go and draw a circle on the surface of the Earth, with a 1km diameter, the ratio of the diameter to the circumference will not be pi, due to the curvature of the Earth's surface. I suppose that you could say that I wasn't measuring the right diameter in this case, and that the true diameter passes underneath the surface of the Earth. But there is an similar deformation introduced by the curvature of spacetime caused by the Earth's mass, so you still won't get pi as a result when measuring the ratio between the circumference and the diameter.

That said, I would very much like to understand why c = 2 x pi x r actually works. pi itself can be derived from pure mathematics, knowing the relationship e^(i x pi) = -1. So why a circle should have such a relationship with this constant is to me a fascinating question.

> Why [should] a circle should have such a relationship with this constant?

Because the "circles" we talk about in mathematics are found in Euclidean space—which is defined to have simple metric properties. Our own space is non-Euclidean.


Umm, yes, I understand that c = 2 x pi x r only holds in Euclidean space (indeed, my original post gave two examples of circles in non-Euclidean spaces, to illustrate my point), but my question was more about why it holds at all. That is, if you consider pi as being a constant that you can derive from e (which is itself just a power series), and i (again, just a mathematical construct), it seems quite stunning to me that this constant (pi) should have such strong ties of Euclidean space. It implies a deeper connection between Euclidean Space, e, and i. Why should that be so?

1. Taking e to a complex power (using θi) walks you through the complex plane at a given angle θ. (That is, f(x) "draws" a continuous curve, where the "pen" has a constant rotational torque of θi.)

2. When θ = pi, f(x) is periodic (the angle is such that f(x) intersects itself or "loops.")

3. The set of complex numbers is isomorphic to a 2D Euclidean plane. Therefore, a walk at angle i*pi through the set of complex numbers is isomorphic to a circle.

The real question should be: what super powers would you get?

You are not allowed to joke in HN.

If you put a hot dog in the collider, will you get little smokies from the spallation process?

I think I just solved world hunger guys...

So, these are not the same people who are in charge of determining whether or not a black hole might form and persist, correct?

Except they have done research on the black hole possibility, there work centres on the beams colliding not what happens if it hits a certain combination of atoms that make up a human hand.

I guess it's kind of like someone saying to a programmer, hey can you fix my computer, you work in computer right?

I guess it struck me as more like someone saying to a C programmer, "Hey, can you help me find the bug in this Java routine?" The C programmer might not know Java intimately but at least he's not going to stroke his beard and act like it's something he's never considered before.

I certainly wouldn't expect two or three competent C programmers to offer wildly divergent opinions if asked a question that fell slightly outside their everyday practice.

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