
The Sun seen through the Earth in “neutrino light” (2007) - Anon84
http://strangepaths.com/the-sun-seen-through-the-earth-in-neutrino-light/2007/01/06/en/
======
kmm
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.

~~~
yummybear
So they can use this image to directly measure the width of the core?

~~~
0PingWithJesus
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](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](https://arxiv.org/pdf/1606.02558.pdf)

~~~
sudhirj
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.

------
wcoenen
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...](https://journals.le.ac.uk/ojs1/index.php/pst/article/view/859)

~~~
hinkley
On the other hand, someone is trying to harness neutrinos for power:

[https://www.power-technology.com/features/neutrino-energy-
ha...](https://www.power-technology.com/features/neutrino-energy-harnessing-
the-power-of-cosmic-radiation/)

One of my far-future-tech fantasies is that we someday learn to make
photovoltaics that are powered by cosmic rays and/or neutrinos.

~~~
JumpCrisscross
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
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
You’d think the HFT lot would jump at the chance to knock 100ms off Singapore
to New York.

~~~
nikanj
That's assuming the LHC has less latency than 100ms.

------
Ciantic
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.

~~~
jfengel
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](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
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](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
"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.

------
TallGuyShort
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
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
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
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](https://i.imgur.com/7OmXXtn.png) (cite:
[https://arxiv.org/pdf/1606.07538.pdf](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...](https://www.nytimes.com/2018/03/27/science/nuclear-bombs-
antineutrinos.html) or here
[http://svoboda.ucdavis.edu/experiments/watchman/](http://svoboda.ucdavis.edu/experiments/watchman/)

------
idlewords
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](https://arxiv.org/pdf/hep-ph/0305062.pdf)

~~~
andbot
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
Not to mention you'd have to know where to aim your neutrino beam...

------
linuxhansl
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
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](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.

------
k2xl
Question from someone who has no physics background - they mention the
neutrino can go "faster than speed of light" \- how is that possible?

~~~
jameskilton
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
It's not taking a zig-zag path like you imply. That would be scattering and it
would end up in a random direction.

------
pphysch
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".

~~~
ClumsyPilot
There is no nighttime, nutrinos go straight through stars and planets.

~~~
frumiousirc
There is in principle a day-night effect which may be measured. The electron
flavor component of the neutrino can be enhanced or diminished by the presence
of matter.

------
fallingfrog
How do you image neutrinos? I mean if you’re imaging the sun with light you’d
use a pinhole camera, for normal images lenses or mirrors, but if neutrinos go
straight through the whole planet how do you make a lens for that? Or a
pinhole camera?

Edit: I see that someone else asked a similar question, the answer being that
you image electrons that have been knocked loose by neutrinos, which is much
easier.

~~~
saagarjha
> much easier

Well, that's relative ;) It still takes hundreds of highly-sensitive detectors
and many tons of hyperpure water to detect neutrino reactions.

------
hinkley
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
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](https://en.wikipedia.org/wiki/Super-Kamiokande#History)

------
rydre
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.

~~~
_jal
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...](https://amp.businessinsider.com/images/5b23cd9d1ae66220008b5296-2732-1366.jpg)

~~~
phinnaeus
Also note this is only the receiver, you'd need another device of similarly
massive scale to transmit.

------
gabrielfv
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
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).

------
praveen9920
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
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](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](https://icecube.wisc.edu/news/view/449)

------
c-smile
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 (7.25° from those) ?

~~~
0PingWithJesus
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...](http://www-
sk.icrr.u-tokyo.ac.jp/sk/physics/image/image_solarnu/solpic_1500d_2_1.jpg)

------
devin
Should the article’s title on HN reflect its publication date? (2007)

