I am a mile under a mountain. IAmA grad student researching dark matter. AMAA

Ever see a balrog?

So there's this section of the caves where we don't go. The official reason is because there's a vibration-sensitive geology experiment back there. We all know the real reason has to be more ominous...

What if an earthquake hit?

A very serious and deadly earthquake hit this area in 2009. Many people were killed and the nearest city was mostly ruined, and is just starting to rebuild.

The lab, though, was fine. I don't know why--I suspect being underground helps, but I'm not sure.

How do you go about trying to detect dark matter? How tedious is your job? How did you get your job?

Thanks for doing this AMA.

Detecting dark matter, at least with our approach, begins with setting up a very generic particle detector. In our case, it's a tank of liquid with light sensors trained on it. Any energetic particle that comes in can hit the liquid, which will produce a small flash of light, which the sensor detect. Now we know that something just happened. Is it dark matter?

The main way we tell if an event was dark matter is by eliminating the chance it was anything else. This is why reducing backgrounds is so important. We reduce the number of light flashes from everything that isn't dark matter by: * building everything out of ultra-pure non radioactive materials * putting the experiment underground * keeping everything very clean, so no radioactive dirt gets inside.

We still have some backgrounds left. So, we analyze the timing of the light flashes, and look for simultaneous light flashes in background detectors placed around the dark matter detector. With these methods, we can catch and ignore all of the remaining background signals. The only thing that should be left is dark matter.

So, if we see anything that doesn't look like a background, we have to conclude that it's dark matter. We've spend years (most of my PhD time, in fact) convincing ourselves that we will be able to eliminate or catch every background so nothing but dark matter will be left.

How tedious is my job? Better than most, I think. There's definitely times where I'll spend a few 12 hour days in a row just operating a simple piece of machinery or putting screws in a million light sensors, but there are also days when everything comes together and I get to see some exciting results. Most of my job is coding, and is probably like many coding jobs.

How'd I get my job? I applied to graduate school right after college. My grades were ok, my test scores were fine, and I had a pretty full resume of undergraduate research experience. That last part is definitely the most important part to getting into PhD programs.

why does dark matter produce flashes of light?

When any particle hits our liquid, it transfers a small amount of energy into the liquid. That energy goes into exciting the electrons in the atoms of the liquid at the point of impact. Those electrons will eventually release that energy, and go back to their usual orbits. They release the energy by emitting light.

This goes for any energetic particle, and in most liquids (and most solids). Ordinary water does this, and we use water for the biggest background detecting layer (because using more exotic liquids with better light emission would be too expensive to have many tons).

thanks for the explanation. if dark matter makes up a large part of our universe, why is it so hard to detect?

Dark matter is 100% invisible and 99.many 9's % intangible. There's a lot of it, but it can (and does, all the time) pass through ordinary matter without anything happening.

Detecting it by looking at the gravity it exerts is doable, and that's how we know it's out there to begin with.

To elaborate: Every particle can interact with other particles via the four fundamental forces: electromagnetic, strong, weak, and gravity. Many particles don't experience some of the forces, though. Neutrons, for example, don't interact with the electromagnetic force at all, because they have no electric charge.

Dark matter, we think, only interacts via the weak force and gravity. The weak force is (unsurprisingly) very, very weak. That means the chance the weak force actually creates an interaction between dark matter and other matter is very, very low.

Neutrinos, which are much better understood, are actually like dark matter in that they also interact only via the weak force (and maybe gravity? we don't know). The weak force has a much stronger connection to neutrinos than dark matter, though, so it's easier (but still hard) to make a neutrino detector. Many of the other experiments here at LNGS are neutrino experiments, because neutrinos and dark matter are enough alike that they both benefit from putting the detectors underground.

You do an incredible job at explaining this all in clear and simple way for everyone to understand.

Thank you! Lots of practice on my relatives. I beg forgiveness from the real scientists in the thread who may groan at some of my simplifications.

You should join /r/askscience ;p

The problem is, I don't actually know that much about anything other than dark matter experiments. PhD study makes you know everything about nothing.

When you mean 100% invisible, are you talking across all spectrums?

Yup, any frequency photon will not interact with dark matter (except in certain exotic theories, and then only very rarely).

That's pretty neat. So is it assumed that dark matter has been around just as long as all the matter we can see?

I think most theories think it formed very early in the uninverse's life, when things were so hot and dense that the lower-temperature physics we know hadn't kicked in yet. But, I'm definitely not an expert on this.

just a short correction: neutrinos interact through the gravitational force as it is related to energy, not mass (photons do interact while they have no mass).

Yeah, fair point. Gravitational interactions don't work much like the other forces, so I get mixed up sometimes.

Photons have no mass? Is that correct? I'm totally a laymen but wikipedia doesn't have a simple "0" for it... I feel like I read something about photons containing such a minuscule amount of mass that you technically receive a ridiculously small amount of pressure at all times from being bombarded by them.

Photons do totally provide a small amount of pressure, because they have momentum... but no mass. I would say this is one of the weirder consequences of special relativity, but it doesn't even rank that high on the list of weirdness.

If it passes through most matter without interacting, then why will it interact with the water?

It usually won't. Many, many dark matter particles will pass through our detector and do absolutely nothing. But, there's a tiiiiiny chance each one will. There's so much dark matter around, so if we wait long enough, maybe we'll catch one.

We don't know for sure, though. We know that dark matter is 99.many 9's% intangible, but only have a vague idea how many 9's that is. It could be that we'll see one dark matter event per year, or one per 100 years. We're already planning a series of bigger detectors, because a detector 10x the size will see 10x the dark matter, so we won't have to wait forever if the chance is small.

[deleted]

The dark matter actual transfers energy to the atomic nucleus via the weak force. The nucleus then passes energy to the electrons via the EM force.

Most radiation WILL hit the electrons directly instead of hitting the nucleus first. This is actually critical to the experiment--it's a way to tell the difference between dark matter and some other radiation.

Say we eventually find that dark matter exists. What can we do with it/can it be useful?

http://www.reddit.com/r/IAmA/comments/1cgeh1/i_am_a_mile_under_a_mountain_iama_grad_student/c9g8h4p is my best answer so far

Can you define "ok grades" and "fine test scores" for me?

I think I ended up right around an A- GPA in college, at a school with more grade inflation than my current institution.

My physics GRE score, which I had to look up, was better than I remembered: 860 out of 990.

How do you get Wi-fi?!

There's a rather kickass wired connection to the surface. Speeds here are great, because they've invested a lot into a serious net connection make transferring large amounts of data not too painful.

Edit: Wow, this is like the #1 most frequently asked question in this thread.

It is dark. You are likely to be eaten by a grue.

LIGHT TORCH

Actually, the lights never go out down here. In fact, most of my time is spent in a stainless-steel-walled cleanroom, so everything is super bright. I feel a little bad about all the electricity we're burning 24/7, but the lights are a pretty minor drain compared to the air supply, which uses a lot of power purifying the radon out of the air in the cleanroom. Radon is another source of backgrounds, and it's particularly bad underground.

Actually, one time there was a blackout while I was in the cleanroom. That was a bit spooky.

What is dark matter (someone has to enlighten the un-scientific-educated)??

If you look at the galaxy (or other galaxies), you'll see the effects of lots of gravity coming from no visible source. Things like the gravity that keeps our spinning galaxy from spinning itself apart, or that bends light around far-off galaxies. We think this extra gravity comes from some "stuff" out there that is invisible and nearly intangible. That's not as crazy as it sounds, since we've found particles in the past that are invisible and pretty intangible. We call this extra stuff "dark matter".

We've detected dark matter already through its gravitation effects, but that's seeing its effects in bulk. We'd like to detect an individual dark matter particle, which is our project's goal.

What is the one thing that has happened that made you go "shit, thats cool"

The first moment was when I entered the outer shell of our experiment for the first time. Our experiment has three layers--the inner detector is for detecting dark matter, and the two layers outside of it detect backgrounds so we can disregard signals from the inner detector when a background is passing through.

The outermost layer is a four story high water tank, and inside sits a metal sphere containing the middle layer. That sphere bristles with light sensors and various ports.

So, I'm inside a giant echo chamber, looking at a mini death star, and imagining the whole thing full of many tons of water--and this is just the ancilliary, background-detecting stuff. We're not even to the actual core of the experiment yet.

I was pretty impressed.

Pic: Imgur

We also just finished building the core of the detector. Pictures just went out to the rest of the collaboration, so I shouldn't share them here until the insiders have gotten to look them over, but it's pretty beautiful. It's all pure white light reflectors, bright copper electron drift rings, and intricate light sensors. I helped build it, so instead of having one "shit, that's cool" moment, I saw it go from pieces to this beautiful thing.

So what happens if you discover darkmatter? any use for humans?

Dark matter is 99.many 9's % intangible, so it'd be pretty hard to build anything useful out of it. However, it's also one of the clearest examples of a particle outside our existing Standard Model, which classifies all the particles that have already been detected. The point of finding this stuff is to hopefully start unlocking a whole new sector of physics understanding--and who knows what will come out of that?

I'm a big sci-fi fan, and it's a pretty big disappointment to me that physics as we know it forbids a lot of the exciting stuff in sci-fi. That's why I'm excited to be working on something that may help us unlock physics-as-we-don't-know-it.

So... You're saying we can definitely teleport? That's what I heard.

Teleportation was my childhood dream project. I'll always be a little sad I'm not working on that. Maybe I will someday!

I wish governments gave more money to projects like these.

LNGS was built as an extension of a highway tunnel through this mountain. So, it was probably a small extra cost on top of an already very expensive civil works project. Still, it must have cost a ton to dig out so much rock. I think it's paid off, in terms of jobs created locally for Italian scientists and local support staff.

The US has recently cut funding for a facility that would have served a similar purpose, called DUSEL. It's a shame.

The US has recently cut funding for a facility that would have served a similar purpose, called DUSEL. It's a shame.

That is so saddening. I really hate the direction my country is heading with scientific research. We seem to be investing less and less into it as time goes on.

To be fair, DUSEL was a very expensive project, and lots of the money saved by cutting it went to other experiments, not just to other parts of the government. I'm not in a position to judge whether DUSEL was worth more than the other places that money went.

That said, yeah, I'd love it if science got the funding necessary for all the worthwhile projects to be funded.

Do you ever feel claustrophobic realising you're under a mountain?

Also, how large is the complex? Is it mainly researchers or is there a whole underground apparatus/office down there?

I don't, which is a good thing. The caves aren't that claustrophobia-inducing, but some of the buildings we built inside have some tightly enclosed spaces, because there's not room to build lovely open rooms down here.

The whole complex has three large halls, each 4-5 stories tall. It's actually pretty huge down here. Most of the space is full of experiments, though, so there's not that much room for office space. We have a small office of a few rooms, and more space in a separate office complex above ground.

A volcano base would give you more room

Unfortunately, all the volcano bases we looked at had problems with secret agent infestations.

Ok, going to take my 15 minutes of internet fame to soapbox for a bit about a pet cause.

Are you raising children or planning on raising kids some day? Please, if you care about science, learn enough basic, school-level science and math to help them on those subjects as much as you'll help them with the rest of school.

In our society, it's far more acceptable to say "I couldn't figure out my kids' math/science homework" than to say "I don't understand their reading or history homework." Don't be one of those people. Even if science and math doesn't come naturally to you, if you're planning on helping to raise kids through school, you owe it to them to be able to given them a hand in science and math. (People who are struggling to get by and have no time off work to help their kids with any homework are excused.)

One day, your kids will have a bad science or math teacher (hopefully only one day). On that day, you'll be the resource they turn to first. A year or two of a bad teacher with no help at home can be enough to turn a kid off from science and math, and that's a pity for the kid and a pity for society.

If you're reading this, you like science enough to care, even if you think you can't do it yourself. Please, take out a prep book for the local standardized tests and learn what's in it. If a kid has to do it to be able to graduate, I bet you can too. Be ready to help your kids through the stupid academic requirements they're going to hate. That's as important as telling them to love science or getting them excited about cool stuff like dark matter, because it's going to be hard to hold onto that love during troubles at school.

How would your life change if your laboratory discovered dark matter?

To be honest, I don't really know! We've been so focused on getting the detector ready, I don't know much about the process of publishing and defending results.

At a minimum, it'd help when I'm looking for postdoctoral jobs after I graduate. Not so much because it proves I'd be a good hire, but it'd mean everyone I'd be applying to would have heard of this experiment I've worked on.

Aren't you depressed by working underground ? I've spent the last 4 months in the basement of my company's building, and i know how hard it can be sometimes, not being able to see the sunlight. And I'm only in the basement, not under a whole mountain...

Well, neither of us gets much natural light, that's for sure. I don't get sunlight-related depression (good thing). The feel of being under a mountain isn't really that different from being in a stone-walled basement, though--you can't really tell the difference from being in this office to being in any basement office. In the caves is a little different, but it's cool enough that I'm not depressed.

We go up for lunch, and the surrounding countryside is very beautiful, so that improves my mood.

It may help to take some vitamin D supplements since you're not getting much naturally from the sun. Just thought I'd throw that out there.

I try to get my vitamin D from supplements anyway, and keep sunscreen on if I'm getting much sun exposure.

As a PhD theory student here working on dark matter.. http://i.imgur.com/PYs86.gif

Hello fellow member of the "working on something we're only pretty sure exists" club.

Have you gotten any hints of a positive result yet?

How much of the experiment's time is spent in maintenance as opposed to observation?

Some experiments have gotten hints. Some even go so far as to claim they've seen dark matter, but those results are contentious.

We're still building our detector, so we won't actually start taking data that "counts" for some time yet--but it shouldn't be too long now that the thing is mostly built.

Once everything is up and running, we should spend almost all the time in observation. We're trying to rack up years of watching the detector to have the best chance of seeing these rare dark matter events. Some small fraction of the time (maybe minutes a day? I'm not sure yet) is spent checking the calibration of the light sensors. We also have some "deadtime" after the background detecting layers detect a background, to make sure that background particle doesn't then go, hit the central detector, and get counted as a dark matter event. Each deadtime section is a tiny fraction of a second, but they add up if our background rate is high.

How long from now is 'some time'?

And how much do you get paid, of curiosity?

To borrow from every MMO I've played: "Soon"

We're working hard, but knowing when everything will be ready is rough to guess. If we're not taking real data within a year, I'll be very disappointed, but it could happen if something goes really wrong (like dropping one key part). If we're taking real data within two months, I'll probably be dead of overwork.

I get paid about $26k a year. Once I have my PhD, I'll get about double that.

not to sound like an asshole, but that seems much lower than I thought your salary would be. First, is that U.S dollars? And also, is that to say that a good majority of the people you work with get ~$52k?

Yeah, USD.

I'm a student, so in addition to paying me, my project pays a lot more to the university for my tuition. I get typical student amenities, including classes, gym access, subsidized housing, etc. for the trouble.

Italian scientists earn waaaaaaay less. I make more than plenty of Italians with more experience.

My immediate supervisor, a postdoc, makes around $50k. My thesis advisor, a tenured professor, gets somewhere between $100k-$200k, I think.

That is a very cool topic to be working on. What was your path to get to the point you are at? Not specific schools, but majors, PhD, all that good stuff.

I've wanted to be a scientist pretty much all my life. I did a lot of summer programs as a kid involving science--summer courses, a sort of camp that let us work in a lab for a few weeks, and eventually a summer job in a lab before my last two years of high school.

I did a physics major in college, but the most important thing I did in college was work in a lab every summer. I asked professors I had if I could work for them, or work for anyone they knew, and mostly worked for free. That gave me the biggest advantage on my application to my PhD program. I had worse grades and test scores than average for my PhD program, but my research resume was good enough to get me in.

I feel guilty that I had this big advantage that wouldn't have been available if my family didn't have the means to support me during those summers while I worked for free in labs. Finding paying lab work is very possible, but it takes a lot more digging to get jobs.

Working those summer lab jobs in college was what got me interested in dark matter, so when I applied to PhD programs I already knew that was one of the topics I was interested in. Of the schools I got into, one had a dark matter project on a good schedule for me (starting when I joined, reaching a major milestone by the time I graduate). It also had the biiiig advantage of having multiple professors working on it. Once you start working on your PhD, you really don't want to have to switch projects because you don't get along with your professor--you'll likely end up graduating years late. Having a choice of professors was good insurance, then--though it turns out I like all of them, so it wasn't needed.

If you don't mind sharing, what was your thesis for your PhD? I'd imagine it would be hard to do a thesis on a subject that is hard to test (financially and practically).

I haven't completed my PhD yet, so I'm still working on it. It'll be on the experiment, with as much data as exists when it's time for me to graduate.

Since neutrinos are detected via very similar means, how do you eliminate them from any of the positive hits you get?

Neutrino events with the energy we are looking at should be even more rare than dark matter, so we're covered there.

Edit: Asking a more experienced guy in here with me: We have a decent number of neutrino background that hit the electrons of the detector atoms, but those are easy to tell apart from dark matter which hits the nucleus of the atom. Solar neutrinos don't have enough energy to give a nucleus hit with as much energy as we think the dark matter particle would. Atmospheric neutrinos could be a major background, but not so much under a mile of rock. At some point, as we keep growing the detectors, neutrinos will become the single biggest background problem (and you're right in thinking they'll be very hard to deal with then).

So....have you tried any experiments to communicate with the Dark Matter? Like using the Chinese I Ching or an alethiometer? Have you read the Golden Compass by Phillip Pullman?

Really, what I'm getting at here, is...have you found Dust, and when do I get a daemon?

I'm rather fond of the Schlock Mercenary "dark matter is destructive aliens" idea, myself.

I've spent some time swearing at dark matter, but never heard back.

What's a regular day for you? Wake up, work, have fun, etc...?

I wake up at about 8 in our apartment in the tiny town near the lab's aboveground office complex. I walk up to that complex, which take about 20 minutes, in time to catch the 9am shuttle that drives into the underground portion.

After a short morning meeting, I head into the cleanroom where we are assembling the detector. It's a few minutes to get into the bunnysuit (cleanroom suit, hair cover, mask, gloves, boots) and then 5 minutes waiting in a sort of airlock that keeps the radon that came in the front door with me from reaching the detector.

Once inside, the job is mostly following instructions and putting the detector together. There are bags full of parts, not all of which fit together as well as they should, so there's quite a bit of problem solving to do.

Two weeks ago, I was mostly operating an evaporator, which coats our parts with a chemical needed to convert the light emitted by particle events into something our light sensors can see. That involved a lot of preparing samples, loading very delicate and expensive parts into the evaporator, and monitoring the equipment while it ran.

We leave for lunch on the shuttle around 12:40, eat in the cafeteria in the aboveground complex, get some excellent coffee from the coffee bar there, and return at 2.

I usually finish around 7, though during the peak of the assembly work I was leaving around 10:30.

When I'm back in the States, which is most of the time, I come into work at 11, code and do some hardware work, and leave at 8-10ish. The job in the States has a ton of variety, because we're always working on a different part of the detector and trying different tools (data analysis, simulation, prototyping) to figure out how well it can work.

any interesting discoveries or findings as of yet? good luck, and have fun!

Prototypes of our detector have exceeded our performance targets, so that's making us very excited for what we'll see when the real detector goes live soon.

What kind of internet speeds are you getting down there?

http://speedtest.net/

80 Mbps up and down.

Hi, do you like Italy, and more specifically Abruzzo? I live in L'Aquila (a city 15 minutes away from the mountain) and I visited the lab last year, it's one of the coolest thing I've ever seen! :)

I like Italy a lot, although I'd rather be vacationing here than working! There are certainly plenty of frustrations too, mostly just things I'm not used to as an American--like the small town grocery stores nearby having very limited opening hours.

The lab is far enough from L'Aquila that I don't get over there often (particular given the hours we work) and so I don't get much in the way of urban entertainment. The countryside is stunningly beautiful, and the skiing is great.

I'm ready to go home, though--I miss my girlfriend, and my apartment at home is nicer than the one the project rented for us here, where I sleep in an attic with a low ceiling where I can't even stand up fully. I'm also ready to eat something other than Italian food, although I'll miss Italian food as soon as I go home.

L'Aquila reminded me of one thing: earthquakes. Do you know how is the whole complex actually protected from earthquakes, which are frequent in Italy?

I don't, but apparently the devastating L'Aquila-region earthquake in 2009 didn't damage anything in the lab, so maybe just being underground helps?

Any comments on this paper that proposes dark matter is just plain old hydrogen, but with its electron squeezed to a lower-than-ground-state orbital?

The hypothesis is backed by empirical observations of solar/galactic spectral emissions that match the predicted calculations.

Nope, no comments. I'm just an experimentalist, and a student at that, so I focus on building what they tell me and trying to understand why they want it. Toml42's analysis looks relevant to me, though.

So is there a "Mile under" club like the mile high club? Are you a member?

It's pretty impossible to get unauthorized people down here. I haven't asked the people dating other scientists.

Why does it have to be dark matter huh?! Are you some kind of matter racist?!

It's not even a particularly accurate name--it's more invisible than it is dark. At one point, we thought it might be actually dark--that is, it didn't reflect much light to our telescopes--but now we think it never interacts with light at all.

is it hot down there??

It's actually pretty chilly in the caves, even in the summer. We're surrounded by so much rock, it doesn't matter what the temperature is outside. It's also a little damp, because there's lots of water in the surrounding rocks.

How long does it take to get that far underground? Do you go down in an elevator?

We actually drive in. Instead of going down, we drive into a tunnel at the base and the mountain goes up above us. To go in, we drive through the whole tunnel to the other side of the mountain, take a special U-turn for lab personnel, and drive halfway back. That takes about 20 minutes. It's only about 5 minutes to get out.

The tunnel is not just for us, ordinary drivers use it. The lab is just a detour off the side of this highway tunnel.

I first read it as "dive in". Imagined long steel tubes and scientists all around in their white coats sliding at high speeds.

Man, I want this now.

Do all the lights/other experiments in the caves cause background radiation for your experiment? If so, How do you cancel them out?

No, the lights emit only low-energy photons (including visible light and a bit of UV) that can't penetrate into even the outer layer of our detector.

The facility has pretty strict rules about how much radiation experiments can emit, so except for rare cases (like when another experiment wants to use a very radioactive source to calibrate their detector) we don't see any background from other experiments. In those rare cases, we'd just turn off our detector for the day.

Do you have plans to use your secret underground facility to survive major disasters (nuclear wars, zombies, ect)?

Zombies could literally walk in here, and we need a huge air supply from outside, so nuclear fallout would get right in. There's also no food down here besides kinda gross vending machine sandwiches :(

That said, there are very armed guards around, in what I've always assumed was an overreaction by the Italian government, but they could likely hold out against quite a lot of zombies.

What is dark matter?

http://www.reddit.com/r/IAmA/comments/1cgeh1/i_am_a_mile_under_a_mountain_iama_grad_student/c9g908n

Did you hear about the bombing at the Boston marathon?

Yes, it's horrifying. I feel kinda bad taking attention from the Boston AMA.