[HN Gopher] The Sun seen through the Earth in "neutrino light" (...
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The Sun seen through the Earth in "neutrino light" (2007)
Author : Anon84
Score : 199 points
Date : 2020-06-15 15:09 UTC (7 hours ago)
(HTM) web link (strangepaths.com)
(TXT) w3m dump (strangepaths.com)
| TallGuyShort wrote:
| So I understand how they can detect the presence of a neutrino,
| but how do they trace that back to form the image? Is the
| Cherenkov radiation directional?
| 0PingWithJesus wrote:
| The process behind this measurement is that the neutrino hits
| an electron in the detector. That electron will (with
| relatively high likelihood) travel in the same direction as the
| incident neutrino. The Cherenkov radiation produced by the
| electron is emitted in a cone shape along the direction of
| travel.
|
| The photo-detectors observe the Cherenkov light and through
| some well tuned algorithms the electrons direction is
| "reconstructed". Super-K has no doubt spent significant effort
| improving & evaluating their reconstruction algorithms.
|
| Once you have the reconstructed electron direction there's
| almost no hope that you can reconstruct the incident neutrino
| direction...but that's generally okay, b/c you can usually just
| assume the neutrino traveled exactly parallel to the electron
| (i.e. directly away from the sun). But that's sometimes wrong
| which is (partly) why you see a lot of "fuzz" around the solar
| core in the image.
| credit_guy wrote:
| Isn't this image a bit circular then (pardon the pun)? The
| "hot" pixels in the middle represent the electrons with a
| direction perfectly aligned with the direction to the Sun,
| while the cool-blueish outside pixels are a representation of
| the electrons traveling at an angle? Circular in the sense
| that you know where the Sun is, and are looking in that
| direction, and the electron trails are just confirming that.
|
| Is this image telling us anything new? Can this method be
| used for any type of observation? Or it simply serve as
| observation in the opposite direction: knowing where the
| neutrinos come from, you can infer in what cone the bounced
| electrons can move?
|
| A fun thought: if one day, a secret organization starts
| running an undisclosed nuclear fusion reactor, will it show
| up on this "photo"?
| 0PingWithJesus wrote:
| The detector does not "look" in any direction, it is in no
| way "pointed" at the sun. It records the direction of all
| events that occur within its volume. But once recorded they
| compare the direction of all events with the direction from
| the sun at the time of the event. The angle between the
| solar direction and the event direction is what makes up
| that image. If the neutrinos were not coming from the sun,
| the image would look like white-noise. Since there is a
| clear "peak" at the center you can make a good estimate
| about what fraction of events in your data set came from
| the sun. That amount is a direct measurement of nuclear
| processes going on with the sun over the course of the
| dataset...which is physically interesting. Here is the 1-D
| version of the neutrino "picture",
| https://i.imgur.com/7OmXXtn.png (cite:
| https://arxiv.org/pdf/1606.07538.pdf). You can tell quite
| clearly that there are many more events pointing away from
| the sun then are pointing back towards it. Exactly how much
| more is the interesting physics measurement done here.
|
| All that being said, the specific shape of the "sun" in the
| image is influenced by many factors many of which are
| related to the detection mechanism and the detector
| itself...and don't tell you that much about the sun.
| Eventually (one hopes), detectors will improve to the point
| where the "shape" information of the image is reliable
| enough to extract interesting solar physics measurements
| from it.
|
| P.S your fun thought on the detection of a fusion reactor
| is extremely on point. There exists a under-construction
| experiment in the UK called "Watchman" that hopes to detect
| a neutrino signature from a nuclear power plant being shut
| off and then being used to produce material for a nuclear
| weapon. The idea would be that you could observe activities
| of nuclear facilities in a "rouge nation". See here
| https://www.nytimes.com/2018/03/27/science/nuclear-bombs-
| ant... or here
| http://svoboda.ucdavis.edu/experiments/watchman/
| idlewords wrote:
| Yes.
| 1e-9 wrote:
| With an array of photomultipliers to detect the light, you can
| estimate direction by measuring the differences in arrival time
| between detectors.
| Ciantic wrote:
| I'm not very well versed on the physics, but every time neutrinos
| come up, I wonder when can we establish a data link that goes
| through the earth, instead of around it.
|
| When neutrinos can be captured and emitted with good ability, and
| they can go through the earth, then how feasible it is to build a
| data link with them from between let's say Japan and US?
|
| It's not possible today of course, because it would have been
| done already.
| arethuza wrote:
| Yottawatt level fusion power generation levels has been
| demonstrated at about 1% of solar output. Maybe those could be
| used in a pattern to send messages? ;-)
| csunbird wrote:
| What about using neutrinos for interplanetary communication
| between ground bases on different planets? Since they are hard
| to be stopped by any kind of matter, it should be a good way of
| ensuring the link stays stable with only one base, instead of
| having 3 or 4 depending on Earth's location and day cycles.
| whatshisface wrote:
| It's possible today but not economically practical. You could
| get low-latency messages, but you would miss most of the bits
| coming through.
| Ciantic wrote:
| Interesting, care to elaborate more? I haven't found that
| it's even possible with long distances like that.
|
| If corporates are literally blowing holes to mountains to get
| faster and more direct data links between trading places.
| Then it sounds like just a question of time when the
| technology matures enough (if it's possible already).
| ClumsyPilot wrote:
| Blowing holes in miuntains is junior league for nuclear
| physics. The exact same factor that allows neutrinos to
| pass through a planet make them impossible to work with.
|
| The detector here weighs 50,000,000kg, and still like
| 99.9..% of neutrinos pass though it without being detected
| - imagine that kind of signal loss in a data link.
|
| This detector does not notice tiny amount of neutrinos
| produced at particle accelerators. It would have to placed
| right next to a 4GW nuclear powerplant to detect neurinos
| at any kind of reasonable rate.
|
| The only man made source of neutrinos you could detect from
| another continent is a massive thermonuclear blast.
|
| https://www.sciencedirect.com/science/article/pii/S24056014
| 1...
| Evidlo wrote:
| Here's an article about communicating with neutrino beams:
|
| https://blogs.scientificamerican.com/observations/message-
| en....
|
| In short, they were able to achieve about 0.1 bps with
| hardware that costs hundreds of millions of dollars.
| ClumsyPilot wrote:
| Also note that the distance transmitted is a mere
| kilometer. Carrier pigeons are more practical
| est31 wrote:
| That's only two orders of magnitude away from a 100bps
| line, which would incur 10 ms latency due to the
| transmission method (in addition to the latency of the
| neutrinos actually having to get there), and that's for
| reliable communication.
|
| Unreliable communication that gives you an advantage over
| mere chance 1% of the time can already be advantageous,
| you'll be right 51% of the time.
| macintux wrote:
| Three orders.
| afthonos wrote:
| That image was captured over 503 days of exposure, with a
| detector the size of a swimming pool. I won't claim it's
| _impossible_ , but I'll give you fantastic odds against it
| in the next, say, twenty years.
| drdrey wrote:
| And that's with a pretty decent source of neutrinos
| cryptonector wrote:
| All you need is one bit: silence -> neutral!, 0 -> buy!, 1 ->
| sell! Or two: 00 -> neutral!, 01 -> sell!, 02 -> buy!, 11 ->
| wait!
|
| Plus error correction... When you add error correction and
| consider the number of missed bits and the need to retransmit
| / keep transmitting, it's probably not possible to realize a
| latency win here.
| mhh__ wrote:
| > latency win
|
| Perhaps, but if you consider the probability of missing an
| individual neutrino your error correcting scheme will have
| to be either very long or very clever because your odds of
| collecting the right neutrino at the right time will go
| down very quickly as the packet gets longer.
|
| On top of that, if you used some kind of pulse scheme (i.e.
| morse code with neutrinos) it has to be slow enough to be
| detectable, but fast enough to beat the latency of a cable
| (let's say 100ms - speed of light + processing and errors)
| and also fast enough not to use enough power as to be
| unprofitable.
| cryptonector wrote:
| > Perhaps, but ...
|
| Isn't that what I wrote:
|
| > > it's probably not possible to realize a latency win
| here
|
| ?
|
| > On top of that, if you used some kind of pulse scheme
| (i.e. morse code with neutrinos) it has to be slow
|
| "slow pulse" == long pulse. It will be "fast" in that it
| will go faster than the speed of light in fiberoptics and
| the path will be shorter, but it will be slower because
| error correction will demand a great deal of redundancy
| which, among other things, means long pulses.
|
| I think we're in agreement.
| mhh__ wrote:
| I have the attention span of a hyperactive toddler so
| when I write HN comments I can end up responding to
| everything I've read in the comment tree, sorry.
| cryptonector wrote:
| Lol. Me too sometimes :)
| whatshisface wrote:
| You don't need error correction, you can win on the stock
| market with something that's very poorly correlated.
| close04 wrote:
| Think about it like this: the absolute vast majority of
| neutrinos pass through the whole planet without interacting
| with a single particle. One descriptive saying is that a
| neutrino can pass through 100 light-years of steel without
| interacting. This puts in context how hard it is to detect
| them (have them interact with your detector).
|
| So your communication turns into some random string of
| detections where you never know if the absence of a
| detection means there was no neutrino, or it was just
| missed.
| qubex wrote:
| You can easily send them through the earth _because_ they are
| hard to detect: it's two sides of how low their interaction is.
| What's the point sending data that you cannot pick up? Femilab
| could probably modulate their bean to Oklahoma (or wherever the
| detector is located) but you can't work up enough bandwidth for
| it to be worthwhile. Ever, for anything.
| jfengel wrote:
| It was kicked around a few years ago as a way to get a jump on
| competitors in high-frequency trading:
|
| https://www.math.columbia.edu/~woit/wordpress/?p=4646
|
| It's not impossible, but it's kind of absurd. Neutrinos are
| insanely hard to detect. You need immense detectors, and even
| you get only a ludicrously tiny fraction of the neutrinos
| passing through. You'd have to modulate it by turning on and
| off an immense nuclear power plant, so despite shaving off
| milliseconds of latency you still wouldn't be able to
| communicate fast.
|
| There's no reason to expect any of that to become more
| practical any time soon. Neutrinos are too small, too fast, and
| too devoid of interaction to manipulate easily.
| winter_blue wrote:
| Would _a concentrated high-energy beam of neutrinos_ be
| easier to detect?
|
| There was a new HN thread about such a beam just an hour ago:
| https://news.ycombinator.com/item?id=23528970
|
| We'd modulate this high-energy beam. Data bandwidth would
| likely be quite low, but _in terms of latency, it should be
| the fastest_.
|
| A beam directly going through Earth (e.g. from North America
| to Asia) is definitely going to be faster than optical fibre
| (or satellite) links that have wrap around the Earth.
|
| I'm assuming neutrinos are sparse in nature, which is 50,000
| metric ton pool of water was needed to detect the neutrinos
| emanating from the sun. But if we artificially create a
| highly concentrated beam of many many neutrinos, even a
| 99.99% loss / non-detection rate shouldn't be problem.
| (Again, bandwidth would be low, but we are aiming to minimize
| latency.)
| jerf wrote:
| "in terms of latency, it should be the fastest."
|
| Unfortunately, not even then. Nowadays you generally
| neglect the latency of the physical act of receiving a bit
| and being sure whether it is a one or a zero because it is
| such a small amount of time compared to the other
| characteristics of the journey, but in this case you can't
| do that. The amount of time it will take to be sure whether
| it's a 1 or a 0 being sent will be dwarfed by the amount of
| time it would take to send a conventional TCP packet
| containing significantly more than one bit.
|
| Note that while we neglect it, it still exists. If you zoom
| down to a small enough scale, you don't get a pristine
| series of ones and zeros, but a noisy voltage or light
| signal, and there can be plenty of attoseconds where the
| current voltage/light could correspond to either a 0 or a 1
| coming in next.
| anfractuosity wrote:
| Heh, they talk about neutrinos for HFT in 'The Hummingbird
| Project' briefly - https://www.imdb.com/title/tt6866224/
| marcosdumay wrote:
| > You'd have to modulate it by turning on and off an immense
| nuclear power plant
|
| A particle accelerator would be much more responsive.
|
| The immense detectors on the other side would stay, and
| you'll need entire minutes just to get a single neutrino
| anyway (and then, how many do you need to be sure? at least
| 2, I imagine.)
| piyh wrote:
| Really you'd need a duplex connection, so double the
| accelerators and detectors.
| lgats wrote:
| From 2012:
| https://blogs.scientificamerican.com/observations/message-
| en... We report on the performance of a low-
| rate communications link established using the NuMI beam line
| and the MINERvA detector at Fermilab. The link
| achieved a decoded data rate of 0.1 bits/sec with a bit error
| rate of 1% over a distance of 1.035 km, including 240 m of
| earth.
| moftz wrote:
| Just for some comparison, a bit error rate of 0.001% is a
| typical benchmark for digital satellite communications.
| ufmace wrote:
| I'm gonna say not at all.
|
| First, you have to modulate the source in such a way as to
| encode a message. I think we can rule out things that involve
| blocking the beam, so you'll have to adjust the generation
| power. You're gonna need a massively powerful nuclear reactor
| or particle accelerator or something to be at all possible to
| notice the message, so it will probably be pretty tough to
| modulate that much power at a frequency high enough to get any
| kind of decent data rate.
|
| Then we need a detector. Since the article is about a massive
| and massively expensive detector being able to create sort of
| an image of the Sun after multiple years of observation, I'm
| not optimistic about that side. We can build a detector that
| can tell if a manmade beam is on or off, eventually. I'm not
| very optimistic about building a detector sensitive enough to
| detect subtle variations in the power of the beam. We're gonna
| have a real tough time getting a decent data rate.
|
| Doesn't make much difference if 1 bit can be transmitted
| through the earth faster than an electric signal can make it
| around if the electronic one can send billions of bits in the
| time the neutrino detector takes to send two.
| heavenlyblue wrote:
| You could just steer the beam away
| lopmotr wrote:
| You can't make a directed neutrino beam because the
| direction they're emitted in a reaction is random. That
| includes particle accelerators which make neutrinos by
| colliding other particles. A single reaction product comes
| out in a random direction even though the momentum and
| energy of them all together are conserved.
| gus_massa wrote:
| The beam is directional. From
| https://home.cern/science/accelerators/cern-neutrinos-
| gran-s...
|
| > _To create the neutrino beam, a beam of protons from
| the Super Proton Synchrotron at CERN was directed onto a
| graphite target. The collisions created particles called
| pions and kaons, which were fed into a system of two
| magnetic lenses that focused the particles into a
| parallel beam in the direction of Gran Sasso. The pions
| and kaons then decayed into muons and muon neutrinos in a
| 1-kilometre tunnel. At the end of the tunnel, a block of
| graphite and metal 18 metres thick absorbed protons as
| well as pions and kaons that did not decay. Muons were
| stopped by the rock beyond, but the muon neutrinos
| remained to streak through the rock on their journey to
| Italy._
| k2xl wrote:
| Question from someone who has no physics background - they
| mention the neutrino can go "faster than speed of light" - how is
| that possible?
| jameskilton wrote:
| I think you're talking about "the electron is accelerated at a
| speed greater than the speed of light in water"? The "in water"
| is the important bit. Light travels [as measured in a straight
| line] slower in water due to bouncing off of the water
| molecules. It's not that light itself is slow it just takes
| light longer to make it through the water because it takes a
| longer path.
| lopmotr wrote:
| It's not taking a zig-zag path like you imply. That would be
| scattering and it would end up in a random direction.
| w1 wrote:
| It goes faster than the speed of light _in water_. While the
| speed of light in a vacuum is fixed, light will pass slower
| through different mediums (i.e. it goes slower in water than
| air, which is how you get refraction).
| [deleted]
| lekanwang wrote:
| You can't go faster than the speed of light in a vacuum. But,
| you can definitely go faster than light in a medium. Speed of
| light in water, for example, is around 0.75c.
| [deleted]
| mhh__ wrote:
| https://en.wikipedia.org/wiki/Cherenkov_radiation
|
| ("The Cherenkov Effect, completely normal phenomenon" if you've
| seen Chernobyl - if you haven't, it's very good)
| perl4ever wrote:
| I got sidetracked reading about Oliver Heaviside, and noticed
| that it is claimed his theories allowed a 10x increase in
| transatlantic telegraph bandwidth...from 0.1 characters per
| minute to 1 character per minute.
|
| I wonder how much more feasible it is to send information via
| neutrinos if 0.000000013 Mbps were considered reasonable
| speed.
| [deleted]
| [deleted]
| hinkley wrote:
| There was a detector that had a catastrophic failure during
| construction, and I am thinking it was this one. Anyone recall
| that story?
|
| Effectively, a bad unit cracked, and because they were submerged
| in a fluid, it created a shock wave that caused other units to
| crack, which caused more units to crack. They had to replace some
| large percent of the sensors and it set them back something like
| a year.
| 0PingWithJesus wrote:
| You are correct, that happened to the Super-K detector in the
| early 2000s. It's briefly mentioned here
| https://en.wikipedia.org/wiki/Super-Kamiokande#History
| [deleted]
| idlewords wrote:
| There's a fun paper on how you could use a particle accelerator
| to blow up nuclear weapons in their silos from the other side of
| the planet with a neutrino beam. There would be no defense
| against this (highly fanciful) countermeasure.
| https://arxiv.org/pdf/hep-ph/0305062.pdf
| ISL wrote:
| Wow. I've never seen a paper like it. At the surface level --
| if you kick a core hard enough with enough neutrinos, sure,
| it'll probably initiate -- the argument seems plausible. My
| expertise doesn't let me go deeper than that.
|
| The moral implications of such a device are fraught. To use it
| is to detonate the very weapons that one should not detonate.
| mhh__ wrote:
| There is probably a lot more scientific research like this
| buried away in the vaults of the superpowers. Even more if
| you include the "scientific" research done by programs like
| MK-ULTRA (most files where successfully destroyed AFAIK).
|
| For example, when Project Orion was being seriously
| considered the scientists had to find ways of making large
| quantities of fairly powerful nuclear weapons cheaply and
| quickly. Based on something Freeman Dyson said, I think they
| succeeded to some extent, but that secret now has died with
| the scientists who worked on it.
|
| There has to be a lot of writing squirrelled away somewhere,
| because there are restrictions like "You agree to obtain a
| validated export license when exporting if this product is
| incorporated into the design, development, production, or
| other activities related to chemical weapons, biological
| weapons, _nuclear weapons_ , or ballistic missiles." but no
| available literature on how these packages may actually be
| used in this context. (https://welsim.com/download)
|
| One of the reasons Nuclear Testing is now very uncommon is
| because computers and software are now advanced enough to
| simulate them accurately. And yet, despite that, there is no
| "Nuclear Weapons design: A modern approach" available for
| public consumption. These are worked on by physicists so
| someone must be wasting time by writing books somewhere.
| andbot wrote:
| Good luck generating a 1000 TeV neutrino beam with that flux.
| Currently, humanity is at 6.5 TeV for protons, which are easily
| acceleratable because they're charged. Neutrinos have to be
| produced through a fixed target collision setup which
| translates only a small fraction of the original energy into
| neutrinos. So I dare to predict that by the time we can have
| such a beam we have wiped ourselves out with nuclear bombs.
| spacemark wrote:
| Not to mention you'd have to know where to aim your neutrino
| beam...
| wcoenen wrote:
| The abstract of this paper is one of the funnier descriptions I
| have come across about how hard it is to stop a neutrino:
|
| https://journals.le.ac.uk/ojs1/index.php/pst/article/view/85...
| hinkley wrote:
| On the other hand, someone is trying to harness neutrinos for
| power:
|
| https://www.power-technology.com/features/neutrino-energy-ha...
|
| One of my far-future-tech fantasies is that we someday learn to
| make photovoltaics that are powered by cosmic rays and/or
| neutrinos.
| misnome wrote:
| This thing is bizarre. It reads and looks like the standard
| "use trappings of actual science to sell bullshit", except
| they don't seem to be selling anything?
|
| To be "charitable", maybe someone multiplied the solar
| neutrino flux/sqcm by their "maximum" energy (wikipedia
| numbers: 17e10 x 8e6 ~= 0.2w) and thought "that could power
| things!!!"
|
| But more likely this is some sort of deliberate scam.
| JumpCrisscross wrote:
| Why not communications? Neutrino-based communication is
| borderline ideal. A properly-aimed low-energy beam _will_
| make it to its target, obstructed or not.
| skykooler wrote:
| Serious answer: because bandwidth is terrible. A
| transmitter the size of the LHC can only produce enough
| neutrinos (a few quadrillion per second) for a detector to
| receive a hundred per second or so. Accounting for noise,
| that means you can only achieve a few bytes per second at
| best, and again, that's with using the LHC to produce the
| neutrinos in the first place. With far less power you could
| instead use ultra-low frequency radio waves and still get
| better bandwidth.
| iso947 wrote:
| You'd think the HFT lot would jump at the chance to knock
| 100ms off Singapore to New York.
| saberdancer wrote:
| Next step in HFT.
| carlob wrote:
| ...and through its target...
| jerf wrote:
| That's not someone harnessing neutrinos for their power,
| that's someone harnessing technobabble for it's ability to
| separate rubes from their money.
|
| If I'm reading that paper above correctly, which despite its
| silly premise appears to have been seriously written (by
| undergrads, but the numbers pass the smell test), neutrinos
| have ~1/70th the power flux of solar anyhow, assuming you
| could catch all of them, which you can't.
| hinkley wrote:
| Yeah I wondered about that. And their initial target
| application sounds pretty sketchy too. You have a brand new
| power source, you sell it to NASA first, not to Motorola,
| right?
|
| From a little poking around it sounds like cosmic rays have
| a more useful power flux.
| es7 wrote:
| The science doesn't add up here. There are dozens of fluffy
| "this-will-save-the-world" articles without any substance
| which eventually led me to a single website that claims to
| represent a team working on that technology. That site seems
| to be seeking investors.
|
| Without a miraculous scientific breakthrough the math doesn't
| add up. We don't know of any way to capture neutrons in a way
| that would provide meaningful power. For those reasons, I'll
| suggest this is more likely a scam than a sincere or
| realistic effort.
| andrewflnr wrote:
| I'm surprised it's still so thick with neutron star matter. I
| would have thought that was at least a scifi route to efficient
| neutrino capture.
| dfee wrote:
| > We find that a thickness of 34000 light years would be
| necessary if a sheet of osmium were used, whereas neutron star
| matter could achieve this at 189 km thickness. We conclude that
| a neutrino sail is not a practical method of propulsion.
|
| Not practical, hmm?
| short_sells_poo wrote:
| I think that even if we ignore the practicality of building
| it, at that thickness the neutron star material would
| immediately collapse into a black hole :)
| jbay808 wrote:
| The osmium, too!
| ur-whale wrote:
| New theory: maybe black holes are scrapped alien neutrino
| detectors?
| typon wrote:
| Thanks for sharing that, hilarious. Neutrinos really are shy
| aren't they?
| googlryas wrote:
| I always thought neutrinos would be a much better medium for
| other civilizations sending out messages to the rest of the
| universe because of this fact. Radio waves like SETI is
| looking for attenuate at a significant rate and seem very
| primitive compared to harnessing neutrinos.
| SmooL wrote:
| Might be great for sending your message through space, but
| how to capture and read it back again?
| devin wrote:
| Should the article's title on HN reflect its publication date?
| (2007)
| rydre wrote:
| Can we use this principle to decrease the latency between
| continents over the internet? Like transmitting data via
| artificially generating neutrinos and sending them directly from
| say Asia to Latin America? There has to be a way, no?
|
| I'm not a physics guy so it would bee be better if someone with
| domain knowledge could chime in.
| The5thElephant wrote:
| I don't think we can detect enough neutrinos to make this work.
| The reason it works with the Sun is the massive number of
| neutrinos it generates and exposing over 500 days since even
| then so few are detected.
| bognition wrote:
| The challenge is detecting neutrinos is very hard. The image in
| the article required a 500d exposure.
| _jal wrote:
| Sure. Your 'NICs' would be rather expensive[1] and you'd need
| to minimax bandwidth vs. error correction for the number of
| detection misses.
|
| [1] Here's a picture of one:
| https://amp.businessinsider.com/images/5b23cd9d1ae66220008b5...
| [deleted]
| pphysch wrote:
| Article says the image is from a 503 day exposure--it doesn't say
| how, if at all, the nighttime data is decoupled from the daytime
| data. Perhaps it is something like "technically 0.0001% of this
| image might be from nighttime readings".
| rwmj wrote:
| The detector is deep underground (1000m) so it always goes
| through a bit of the earth. But they can easily select only the
| parts of the raw data which correspond to neutrinos going
| through the whole earth by only using detections which happened
| at night, local time. I guess they didn't mention this because
| it's obvious?
| ClumsyPilot wrote:
| There is no nighttime, nutrinos go straight through stars and
| planets.
| [deleted]
| JuettnerDistrib wrote:
| For neutrinos there is no nighttime. The neutrinos are captured
| when they need to travel the maximum distance through the
| earth. That way, there are fewer other particles that need to
| be distinguished from neutrinos.
| 0PingWithJesus wrote:
| This article is quite old but a more recent measurement from
| the same experiment (Super-K) used a 1600 day dataset. Of that
| 1600 days of exposure 860 "days" were nights. So it's pretty
| close to half and half. (Cite: Section V-B, bottom left of page
| 22, of https://arxiv.org/pdf/1606.07538.pdf )
|
| The daytime data and night time data are decoupled quite
| easily. Whenever an event is recorded by the detector you just
| make sure a timestamp is associated with the event. Then you
| use that timestamp to determine the location of the sun at the
| time of the event. If the sun is below the horizon it's "night"
| and if it's above the horizon it's day.
| ISL wrote:
| Looks like Figure 17 is the updated analog of the original HN
| article-figure.
| linuxhansl wrote:
| Do we know how many neutrinos were registered during the 503
| days? I'd be curious about the resolution of this image.
|
| Also, in order to cause the Cherenkov radiation, the neutrino has
| interact at least with an electron, I wonder about the percentage
| of the number of neutrinos interacting with the water in this vs.
| the number of neutrinos that interacted with Earth on the way.
|
| Not anything practical... I'd just be curious.
| 0PingWithJesus wrote:
| For their more recent data they reported seeing ~32000 solar
| neutrino events over a 1600 day dataset (cite: top-right of
| page 13 https://arxiv.org/pdf/1606.07538.pdf). Their detector
| nowadays is more sensitive than it was when the OP was
| published so I would estimate the image comes from probably
| around 5000 neutrino events.
|
| And I don't know any specific numbers but you can be sure a
| large amount more of neutrinos interacted with the air/rock
| between the Sun and Super-K than interacted in the detector
| volume. But that number (whatever it is) is still tiny compared
| to the total flux (which is ~5 million per square centimeter
| per second).
|
| And that's of just the "high energy" type neutrinos that
| Super-K is sensitive to. The lower energy varieties are more
| like 10 billion per square centimeter per second.
| kmm wrote:
| Since fusion is only happening in the center of the Sun, and the
| outer layers are almost entirely transparent to neutrinos, this
| is actually a direct image of the solar core. Which makes it even
| cooler imo.
| ahazred8ta wrote:
| The core is about 20% of the width of the sun, so about 0.1
| degree wide as seen from Earth.
| yummybear wrote:
| So they can use this image to directly measure the width of the
| core?
| 0PingWithJesus wrote:
| In principle yes....although the specifics of the physics
| involved kinda make the question itself not well posed.
|
| There is no hard boundary to the core of the sun. The "core"
| is by definition where nuclear fusion reactions occur.
| However, those reactions don't just stop at a certain
| radius...but instead just occur at a lower and lower rate. So
| even if you could determine with 100% precision where a
| neutrino came from within the sun, you would still measure
| some exponential-like decay as a function of radius.
|
| But to add even more complexity there's ~10 different nuclear
| processes within the sun that produce neutrinos. Those
| processes all have different radial profiles. So even if you
| measure with 100% accuracy the radial profile of neutrinos
| associated with one or two nuclear processes...you still
| haven't really measure the core of the sun...you've just
| measured it for a few specific reactions. And for the
| neutrinos produced by many of the reactions this method
| cannot work, those neutrinos are too low in energy to provide
| direction information. And beyond that there are a handful of
| nuclear reactions that occur within the sun that don't
| produce neutrinos. So there doesn't really exist any way to
| measure the radial profile of those nuclear processes.
|
| And this all assume you can perfectly tell where the neutrino
| came from within the sun, which is also impossible. There
| will always be some relatively poor "resolution associated
| with your ability to place a neutrinos origin. Here is the
| "hard" physics limit to your angular resolution for a
| relatively high solar energy neutrino...it only gets worse as
| the energy goes down https://i.imgur.com/h3n8c4V.png. But
| getting to even that resolution is impossible b/c an
| interaction will only produce so many photons from Cherenkov
| radiation (think 100s of photons). Then it becomes a
| statistics problem...what's the best angular resolution you
| could possibly achieve given an average number of photons
| that's around (say) 500. It ends up the answer is "pretty
| good" but far from perfect. And all of that is assuming the
| electron scattered from the solar neutrino will travel in
| only one direction...that's extremely untrue, the electron
| will always bounce off of other electrons & atoms after
| scattering. This multiple-scattering leads to even worse
| angular resolution.
|
| Here's a paper on the subject if you'd like further detail
| https://arxiv.org/pdf/1606.02558.pdf
| sudhirj wrote:
| Most lines of this kind are drawn based on some value we
| agree on, not any intrinsic rule in physics. The boundary
| of the atmosphere, earth's crust, the extent of the solar
| system, etc.
| cp_mlreef wrote:
| Thank you for sharing! Extremly interesting and mind
| boggling - what a time to be alive!
| lopsidedBrain wrote:
| To an extent. I'm actually curious about its angular
| resolution.
| zyxzevn wrote:
| The circle in the centre of the image is much wider than the
| sun. Sadly, we can not see any meaningful imagery from it.
| praveen9920 wrote:
| I wonder if there were there any attempts to observe the rest of
| the universe with this kind of equipment considering there are n
| number of neutrino sources.
|
| It could reveal the general shape of the universe or center of
| universe.
| 0PingWithJesus wrote:
| The Ice Cube experiment has done that exact thing. Here's the
| most recent publication from them on that subject,
| https://arxiv.org/abs/1910.08488. Here's a slight older but
| perhaps more digestible result from them
| https://icecube.wisc.edu/news/view/449
| c-smile wrote:
| The most interesting fact on the image (IMO) is that the halo is
| clearly elliptical, why?
|
| Is the image aligned to the "main" ecliptic plane of Solar system
| or rather to Sun's rotation plane (7.25deg from those) ?
| 0PingWithJesus wrote:
| I think what you're seeing is either a random noise
| fluctuations, or perhaps a result of the coordinate system
| they're using for that image. If you take a look at a similar,
| more up to date, image from Super-K that uses more data you
| don't see any sort of elliptical nature. http://www-
| sk.icrr.u-tokyo.ac.jp/sk/physics/image/image_sola...
| gabrielfv wrote:
| That's impressive. But I'm also curious as to what other
| applications this setup can be useful for, because that looks to
| be one hell of an expensive operation. It's awesome to see such
| things actually happening.
| jjk166 wrote:
| While not done with neutrinos (at least not yet), a very
| similar setup is used for stufying geological structures.
| Usually either cosmic rays or muons produced by cosmic ray
| collisions are detected and depending on the number of
| detections over time, the density of the rock they pass through
| can be determined. By filtering the energy of the particles,
| you can look at radiation directionally (particles coming
| straight down have more energy than those that come at a
| shallower angle). You can have a detector next to a volcano and
| get an "x-ray" of that volcano.
|
| Neutrino detectors can also "see" active nuclear reactors. One
| could imagine using a detector located outside of a suspect
| nation to validate their claims with regards to nuclear
| nonproliferation (ie that they're not running their reactors
| overtime to produce more plutonium than they report).
| zuzun wrote:
| It was initially used to observe proton decay. By not detecting
| a decaying proton in the water tank, they could place the mean
| lifetime of a proton above 10^30 years.
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