Record-breaking neutrino is most energetic ever detected | Hacker News Reader

Record-breaking neutrino is most energetic ever detected

nature.com

229 pointslnauta128 comments

It took a few tries, but I got Wolfram Alpha to compute its velocity compared to the speed of light[1].

I started with:

    sqrt(1-((1/(1+120 PeV / (neutrino mass * c^2)))^2))

but it simply said "data not available". So I changed:

    120 PeV to 120e15 * 1.602176634e-19 kg m^2 s^-2
    neutrino mass to 1.25e-37kg
    speed of light to 299792458 m/s

and finally it gave a numeric result:

    0.999999999999999999999999999999999999829277971

(that's 36 nines in a row). Pasting it in Google says the value is "1", which is… not far off.

If you want details about the way this is calculated, I dug up the formula from an article I'd written about particle velocities in the LHC, back in 2008[2]. For comparison, their 7 TeV protons were going at 0.999999991 × c.

[1] https://www.wolframalpha.com/input?i=sqrt%281-%28%281%2F%281...

[2] https://log.kv.io/post/2008/09/12/lhc-how-fast-do-these-prot...

We don't know the neutrino's masses, so this is a lower limit for v (since the mass you used is an upper limit)

I can see it came from your source but why is the neutrino mass specified in kg instead of g? why not 1.25e-34g?

The kilogram is the base unit of mass in the International System of Units (SI): https://en.wikipedia.org/wiki/SI_base_unit

Time is in seconds, length in meters, temperature in kelvin, etc. A unit of energy like a joule is then defined using these base units, so 1 joule is 1⋅kg⋅m^2⋅s^-2.

> The kilogram is the base unit of mass in the International System of Units (SI)

Arguably, an ugly wart, but one we are stuck with for historical reasons. The base units of the original metric system (metre and gram) were poorly proportioned for practical use, resulting in the two main scientific/engineering systems of metric units both choosing to prefix one base unit - the centimetre-gram-second (cgs) system chose to prefix the metre, the metre-kilogram-second (mks) system chose to prefix the gram, and eventually mks won out over cgs and evolved into SI.

Whatever warts SI has, they are nothing compared to the chaos of the Imperial/customary system

> The base units of the original metric system (metre and gram) were poorly proportioned for practical use

What is the dealbreaker here though? Because we have plenty of "poorly proportioned" SI units anyway; e.g. it would be much more practical to have megapascal, microfarad and megajoule as base units from an engineering pov (particle physicists might disagree;).

Pascal, farad, joule aren't base units, they are derived units.

Ideally, the base units should be prefixless. Except for kilogram, they all are.

Imagine a system exactly the same as SI, except instead of the kilogram, it had the kram, where 1 kram = 1 kilogram... then the gram would be the millikram, the milligram would become microkram, the microgram would become the nanokram, etc... if you were starting from scratch, without any historical baggage, wouldn't such a system be superior? But of course, we aren't starting without historical baggage – almost everybody knows what a kilogram is, kram is a word I just now made up.

I think some derived units being "poorly proportioned" is inevitable given the physics we have.

I understand what you mean-- I was just curious about why we could not just stick with gram-meter-second (since we have a bunch of "poorly proportioned" derived units anyway)...

Using the gram would not have removed the prefixes from all commonly used units.

In the beginning, the liter was a much more frequently used unit of volume than the cubic meter.

A liter was defined as the volume of a kilogram of water. In a system were the gram was the unit of mass, the corresponding unit of volume was the milliliter.

Which of the gram and the kilogram or which of the centimeter and meter were chosen as the units of mass and length did not matter much for mechanical units, in the way they were used in practice in the 19th century.

A definite choice of the base units has become important only after a bunch of new physical quantities have been defined for use in the theories of electricity, magnetism, heat and light, in the second half of the 19th century. When dealing with so many different physical quantities, not using unique base units would have caused too much confusion. While this necessity has been recognized, for many years 2 different choices for the base units were widespread, that based on meter-kilogram (used mostly by engineers) and that based on centimeter-gram (used mostly by theoreticians). Meter and kilogram were more typical for the sizes of practical machines, while centimeter and gram were more typical for the sizes of laboratory experiments.

If the base unit were gram, megapascals would be gigapascals, microfarads would be nanofarads, and megajoules gigajoules. Similarly a watt would be what's now a milliwatt and most "everyday" powers (except in electronics) would be kilowatts or megawatts.

In particle physics you just use GeV (with varying powers) for most parameters :)

That’s fast! But for how much energy? For comparison, the total energy from this one particle (0.0192 joules) is equivalent to keeping a 50 mW LED lit for a third of a second.

Ars Technica has an article, as well, with some additional context/explanation.

https://arstechnica.com/science/2025/02/most-energetic-neutr...

And an interesting, somewhat related, video from PBS Space Time exploring how supernovas act as particle accelerators (but don't quite explain particles like this one or the 'Oh My God' particle):

https://www.youtube.com/watch?v=2sSNWIJbV3Q

Neutrinos “interact with regular matter so rarely that it's estimated you'd need about a light-year of lead to completely block a bright source of them. Every one of us has tens of trillions of neutrinos passing through us every second, but fewer than five of them actually interact with the matter in our bodies in our entire lifetimes.”

They have 1/500,000 the mass of electrons. They interact only through the super short range weak force (and gravity). Nearly 5% of fission energy is expressed in neutrinos.

And, they may be their own antiparticles, meaning they can potentially annihilate each other.

Wild that these things can carry so much energy!

>Every one of us has tens of trillions of neutrinos passing through us every second, but fewer than five of them actually interact with the matter in our bodies in our entire lifetimes.”

Oh, but those five...

Next time I trip over nothing I am blaming those "darn neutrinos messing up my knee!"

The funny thing is a km^3 scale detector like km3net or icecube has roughly the same mass as all humans combined

Equally hilarious, the Kalgoorlie Super Pit has a volume of 3.15 cubic kilometers.

That's a single, albeit large, gold mining pit and a fraction of the even greater volume excavated by humans looking for shiny stuff.

We mine about a cubic mile of oil every year (https://en.wikipedia.org/wiki/A_Cubic_Mile_of_Oil). That’s 4 km³.

These rare interactions with matter are also a cause of concern in voting machines, right? Or at least it was a concern at one point. A random bit being flipped or something.

Other types of particles interact much more frequently. But yes: bits do get flipped (even with ECC memory).

It is mostly a problem of DRAM memory cells, though theoretically with enough energy it could flip SRAM cells to or override the driver of a given wire. It is not specific to voting machines.

But the main source is from cosmic rays and local radiation sources in the ceramic packaging and/or decaying elements in the metal frame/leads/solder.

Interesting "fact" - The total amount of lead in the universe is a somewhat less than a cubic light year.

How could we possibly estimate that if we don't even know the size of the universe?

The article references the "Oh-My-God particle, the most energetic particle yet encountered. Here's the late John Walker's excellent piece on that:

https://fourmilab.ch/documents/OhMyGodParticle/

> These calculations involve some elementary but easy to mess up algebra and some very demanding numerical calculations for which regular IEEE double precision is insufficient. If you'd like to double-check these results, be sure to use a multiple precision calculator with at least 30 significant digits of accuracy.

So you're saying my iPhone built-in calculator app is going to have problems....?

Time to whip out dc on the terminal.

https://www.wolframalpha.com/

Or ChatGPT to output Julia code

> So you're saying my iPhone built-in calculator app is going to have problems....?

Your Android phone's built-in calculator app, however, will not. :^)

https://dl.acm.org/doi/pdf/10.1145/3385412.3386037

That was indeed excellent reading, thank you.

The Nature paper itself can be found here [0], for those curious. Was just published today.

0: https://www.nature.com/articles/s41586-024-08543-1

For context, 120 PeV is about 10% the kinetic energy of a ping pong ball during typical play.

One of the lead researchers in KM3NeT mentioned that the particle was emitting 2 horse power in light during detector transit. A typical body builder expends about 1 horse power while performing, so its 2 body builders in a single particle.

> typical body builder expends about 1 horse power while performing

Close, but ackshually...

Bodybuilders just oil up and pose in beauty pageants.

1 horsepower is basically one 250-pound bench press in one second. (550 foot pounds of work; the aforementioned bench press assumes a 2.2-foot stroke length.)

Most bodybuilders and serious weight lifters can do that, but they can't keep it up for long.

Neither could this neutrino.

Ha, that made me laugh, thanks for the correction!

So the neutrino is just doing a PB 1RM?

It must have been a very short amount of time. 2 HP is 1,500 watts, probably more light than all lightbulbs in my house combined.

1500 watts is about what an electric kettle uses.

American kettles. Kettles in hard core countries push 2300 to 2400 watts ;-)

Slow-boiled water gives superior flavor!

Keeps the midichlorians from jumping out.

I always cook my water sous-vide

Meh, Lidl sells 3200w kettles.

Where are the three phase models??

Seriously though, a 15A kettle sounds great.

Photonicinduction's 10-second kettle[1] managed about 10kW max (took around 5s to boil water) for a short time, 440V 23A. Then the resistance dropped, it went up to 16kW (426V 33A) and popped. 7-8kW (375V 19A to 400V 20A) seemed more sustainable.

[1] https://www.youtube.com/watch?v=dDLw1Rx_cAI

2500W on 240V, single phase AC, 16A, German 'Schuko'-plug is normal. Or was. Some EU-regulation limits that to 2000, or even 1500W only now, for new devices, or something.

Don't care. Still have the old ones, and whatever the electrician wired as '120V 3-phase AC' for the full US-style range in the US.

UK 240V with 13A sockets, 3120W. Sounds like Lidl are rounding up.

American stove startups can do it in 40 seconds with ??? watts by precharging a battery.

https://www.youtube.com/watch?v=YdawGen0QPc

The muon traverses a few hundred meters of detection volume very close to the speed of light, so in the order of one microsecond.

Particle on steroids.

Fun fact, a typical horse exerts about 1 horse power of usable work while performing. That's so weird, I'm sure almost no one would've been able to guess that - but it's true.

(To be clear, that's sustained effort over time, not just momentary. Athletically trained humans can do about 1 HP of peak momentary effort, and around 0.3 HP if sustained over time.)

And a horse can do quite a bit more in peak as well— 1 HP is definitely meant to be the long term continuous output of a typical horse under load, especially a consistent load such as turning a millstone.

That's an all-day number. Peak HP/horse is somewhere in the 6-15 range.

Track cyclists (sprinters, world class) do 2KW+ peak for a few seconds at a time. That's potentially ~3HP. (and while doing so, average more than 70kph over a 200m distance)

The funny thing is that a typical horse probably has closer to 2 or 3 horsepower and a big chonkin draft horse up to 4 or 5 times.

James Watt just picked the smallest possible value of horse when defining the unit so he could sell more steam engines.

https://www.youtube.com/watch?v=7qxTKtlvaVE (donut, How Much Horsepower is a Horse?)

Can we harvest that energy?

This particle spread this energy through a volume of seawater a few km deep in the Mediterranean. It's going to raise the temperature of that volume a few billionths of a degree, if that. So, no, we can't.

What if our existing solar panels are optimized to detect these? Then will it improve the quality of solar panels to capture more energy from sunlight as well? Sorry, I'm no expert in this - asking more of a curiosity.

It's an enormous amount of energy packed into a single tiny particle.

But it's still just a single tiny particle, so it's not a lot of total energy.

It's like how you can lift a heavy weight for a second, but that's all you can do. You would need to be able to lift it for hours to be useful as a replacement for a crane. Same idea: Intensity vs total work.

If we had the ability to detect neutrinos in such a small volume as a solar panel they’d be immensely valuable for communication - we’d be able to beam signals directly through the Earth, or through deep water.

Following that same line, if we had that ability, it would be useful for communicating to deep submarines like the U.S. used to do with Project Sanguine[0] and ELF waves :)

[0] https://en.wikipedia.org/wiki/Project_Sanguine

Neutrinos interact extremely weakly with ordinary matter, which is why the detectors are typically huge volumes of water. Even then, the neutrinos interact with the purpose-built detectors on the order of one in a trillion. A neutrino power generator is not a feasible thing to build.

Unless you're next to an exploding star, in which case you have other problems/opportunities.

There's nothing to optimize here, neutrinos just interact very very weakly with anything else because they don't carry charge (so no electrical interactions), don't carry color charge (so no nuclear interactions), don't carry weak charge (so no weak force interactions) and have tiny tiny masses, but they are still bosons (so don't act as field carriers like photons do, they're just regular matter). Their low chance of interacting with matter is a fundamental property of them, there's nothing you can do about it through technology, just like you can't create heavier electrons or weaker quarks.

> don't carry weak charge (so no weak force interactions)

Left neutrino have weak hypercharge, so they are produce by weak interactions and are detected using the weak interaction. And also gravity.

Right neutrinos (if they exist) have no weak hypercharge so they only interact by gravity.

Thanks for the correction!

It might improve the quality of neutrino astronomy to have the world's solar panels also be neutrino detectors.

Not for that particular neutrino, it's gone. But yes, my home (and yours) is being heated by neutrino power as we speak. It's not a significant enough amount of energy to make a dent in the utility bill however.

Most inefficient thermal power plant possible: utilize the difference in neutrino flux between the hemisphere that's open to space vs. the hemisphere where Earth is in the way.

But now I'm wondering what percentage of the useful thermal power in a nuclear power plant is produced by the neutrinos created in the reactions (the infinitesimally small fraction that happen to interact with the matter within the reactor, that is).

On the contrary, it would have to be efficient indeed to do anything useful underneath all of the shielding that we'd need to keep those baser forms of radiation at bay. Gamma rays: yuck.

So, 2,000 milliSchwarzeneggers if we use SI units?

Yes, but please observe SI rules [1]: it's millischwarzeneggers.

> This means that they should be typeset in the same character set as other common nouns (e.g. Latin alphabet in English, Cyrillic script in Russian, etc.), following the usual grammatical and orthographical rules of the context language. For example, in English and French, even when the unit is named after a person and its symbol begins with a capital letter, the unit name in running text should start with a lowercase letter (e.g., newton, hertz, pascal) and is capitalised only at the beginning of a sentence and in headings and publication titles.

[1] https://en.wikipedia.org/wiki/International_System_of_Units#...

Right, and it is this amount of energy in a single particle. A ping-pong ball is comprised of who-knows-how-many billions of particles, so the energy of any one particle is a fraction of the whole.

A ping pong ball would be roughly 2 trillion trillion atoms, for reference

Now, what will happen if you get hit by a ping-pong ball mass of 120 PeV neutrinos? 120 PeV is about 2e-16 grams, so a ping-pong ball will have about 1e16 of them.

From nothing, to detectable, to lethal, to big boom?

My intuition would be "detectable" but I don't know enough to do the maths.

And by the way, I am using the mass-energy, not proper mass, because the question is crazy enough not to even consider what would be the mass of a neutrino.

Sounds like a great topic for an xkcd video

There is a what if about it. https://what-if.xkcd.com/73/

The mean free path of neutrinos through lead is around one light-year. So, taking the thickness of the body to be 1/2 a meter, you would expect the probability of any individual neutrino to interact with the body to be ~5 x 10^-17. So you'd ballpark have around a 20--40% chance that a single neutrino interacts with your body. It would probably cause a localized radiation burn. Detectable, but probably not lethal unless you got really unlucky with where it hit you.

The mean free path of much lower energy neutrinos in lead is about a light year.

The MFP of a 120 PeV neutrino in lead would be something like 10 kilometers, I think.

More like 100 km I'd think but yeah, the neutrino nucleon cross section gets much bigger at high energies

Total energy of impact would be 120 PeV x 10^16 = 120 x 10^31 eV = ~60 kilotons TNT, or 4 Hiroshimas.

So BIG boom.

Since the velocity is so close to the speed of light, you can think of this like the energy released by annihilating a ping pong ball made of antimatter.

Edit: Commenter asked what would happen if they "hit", so I'm assuming a hypothetical 100% collision. But yes to stop 1/e of a neutrino beam with normal matter, you'd need a light year of lead.

> big boom

The probability of interaction of neutrinos with matter increases with the energy. I've asked o1 to estimate the mean free path of a 120 PeV neutrino in water and it came up with 1000km. So let's say, conservatively, that 10^-7 of the total energy gets deposited in your body when the beam goes through. The mass equivalent of a ping pong ball is about 2.5x10^14 J, which gives us 2.5x10^7 J total, or about 6kg TNT equivalent. This is only an order-of-magnitude estimate, but it would definitely not be healthy.

So, according to basic Ant-Man theory, if I were hit by one of these, it should be like getting all that (10% of a) ping pong ball energy concentrated in a tiny spot, causing me to fly backwards across the room?

I would expect it to be more likely to punch through skin than to actually propel you.

But also neutrinos don't typically collide with things very easily, they're more likely to pass through you without you ever knowing.

Yeah there's no way it would be able to grip onto anything, probably more like the Bugorski case, where he stuck his head into a particle accelerator and a proton beam went right through his head.

I was thinking the same though. It doesn't interact often, but if it randomly does annihilate with another particle in your body, at such a small scale (subatomic) that force/pressure just destroys anything in its path no? Like a paint flake hitting a space ship. Or is it more like "light" (since they're iirc their own antiparticle), which is then absorbed by surrounding matter and turns into heat?

In the wrong spot, this sounds to me like it kills you?

Nothing to be afraid of, of course, for the reason you mentioned. Just wondering, xkcd "what if" style

Isn't Ant-Man logic that he still has the same mass when he shrinks and, as such, can generate the same force?

Unless you get thrown back by ping pong balls normally, I think you'd be fine.

And yet when he grows he still has enough strength to punch a leviathan out of the sky. I'm not sure there's such thing as ant man logic - It doesn't seem like it should result in strength both ways.

His weight also changes with size, or doesnt, depending on what would be more convenient for the current scene

Does this count as "Americans will measure with anything but the metric system"?

No, it is called giving context.

Are you implying that people who use the metric system have an intuitive sense of what 120 PeV means?

There's interesting "end of life" scenario. Nearby supernova exploding and sending so many high energetic neutrinos that even with their rare interactions they could mess up all chemistry that biology uses. And you wouldn't be able to shelter from it since the whole planet is basically transparent to them.

120 PeV is 0.020 of a Joule, or 20 milliwatt-seconds.

the way I play ping pong (holding the paddle like an ice cream stick)? or the way a professional ping pong player plays (which probably means they are serving aces on me all day)?

It's mentioned in the article that the highest energy ever recorded for a single particle was 320,000 PeV which is about 50 joules, i.e. the energy of a golf ball at 100 mph @_@

That was a cosmic ray proton, which has probably 10 billion times the mass of a neutrino and interacts much more strongly with normal matter. A nuclear juggernaut vs a ninja by comparison.

Most likely a heavier nucleus than a proton too

Would a nucleus composed of multiple nucleons stay stuck together with that much energy? If it's zipping along and not interacting with the anything then sure but how did it get that much energy in the first place?

Yes, while there is a large amount of uncertainty, it is believed they the majority of the highest energy cosmic rays are nuclei of elements like iron. For people like me, in the business of finding high energy neutrinos (I'm not involved in km3net, btw), that's a bad thing since that means the highest energy cosmic rays convert less efficiently into neutrinos when interacting with the cosmic microwave background.

How they got so much energy in the first place is kind of an open question. Generally it involves magnetic fields and shock fronts, getting a little kick each time (but yes, you also have to avoid disintegrating the nucleus in the acceleration environment!)

also reported in the NYT: https://www.nytimes.com/2025/02/12/science/astrophysics-univ...

It looks like they detected a muon and are inferring a neutrino from the fact it went through a lot of solid. Couldn't it be any other weakly-interacting particle though?

How? Quarks can't change into leptons. Charged leptons can't change directly into other charged leptons. And neither charged leptons nor hadrons are going to pass through such a quantity of matter, as you say. I mean I assume other cases are technically possible but they don't seem very likely...

Nothing else that we know of would create a muon of that energy deep inside bedrock.

Nit: As I read the article, they aren't sure that it went through any solid. Went through a lot of seawater, though. And your argument still applies.

It could be beyond the standard model physics but no other standard model particle could work other than a neutrino.

If I understand correctly, the interaction length of such an energetic neutrino in rock is only in the tens of kilometers.

Anybody here able to tell me what it means? Where do neutrinos get their energy from? Is there a limit? Will this make my phone smaller? My microwave quicker?

I can answer last two questions with definite "no".

>Observation of an ultra-high-energy cosmic neutrino with KM3NeT

https://www.nature.com/articles/s41586-024-08543-1

What's faster than satellite communication? Neutrinos baby

Not even sure if that's worth doing, either create/emit or use encode data into them as they fly by to be received by someone else

Edit: that's cool people have tried though

Neutrinos can go straight through the Earth, yes, but since they have mass their velocity is less than c.

It’s very close to c though, close enough that it beats sending a signal around the Earth.

The drawback is the impractical size and cost of a receiver.

Come on, we gotta convince the finance bros to find building better neutrino beams and detectors.

HFT peeps are Comfortable spending millions on custom high speed undersea cables to save few ms o'er request.

How about saving few hundred ms across the earth?

That's covered in RFC 1217. https://www.rfc-editor.org/rfc/rfc1217.html

Its in section 4: Jam-Resistant Underwater Communication

Would have really been faster if this result was true

https://en.wikipedia.org/wiki/2011_OPERA_faster-than-light_n...

which was something that would have happened in

https://en.wikipedia.org/wiki/Steins;Gate

Funny the idea that the neutrino might be a tachyon never seems to go away. The best fit of OPERA results is within error bars of the speed of light but towards the superluminal side. Superluminal neutrinos of the energy they were generating with the kind of mass we expect wouldn't be going measurably faster than the speed of light.

I visited the site of this experiment

https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lar...

where the best fit for the squared mass was just a tiny bit negative but within bounds of zero. There is the classic 1985 Chodos paper

https://www.academia.edu/27606971/The_neutrino_as_a_tachyon?...

and people still keep writing papers about it

https://www.mdpi.com/2073-8994/14/6/1172

somebody is going to have to measure a positive mass squared to really put a stake in its heart.

It's worth noting that we received the neutrinos from Supernova 1987a before the photons. We think that's because the photons have a difficult time escaping the ejecta cloud, while neutrinos stream away freely, but who knows ...

Oddly another detector caught a burst of low energy neutrinos that came a few hours before the burst that everyone accepts was from 1987a

https://www.sciencedirect.com/science/article/pii/S092765051...

Low energy tachyons would go a little faster, but you've got the additional problem of explaining why neutrinos got emitted in a spectral line.

That is weird. Is the conventional explanation a flash from one of the last fusion stages right before core collapse?

The core collapse itself produces most of the neutrinos. All of these protons are squeezed together with electrons which produces neutrons and neutrinos.

I was referring to the earlier monoenergetic flash. Yes, most should be produced through electron capture in the collapse, but for earlier event to be monoenergetic suggests a specific nuclear process to me.

We already do, so the conspiracy theory goes. In Antarctica

Why do they place the receiver in a large body of water, like the Mediterranean?

Neutrino interactions with nuclei of water produce charged particles which move faster than the speed of light in water (but slower than through a vacuum tube) creating a cone of light known as Cherenkov radiation, which is the optical equivalent to a sonic boom. This is projected onto a ring around the detector.

Doesn't need to be submerged in a body of water as large as this. The Super-Kamiokande[0] detector for instance is located in a body of water inside a mountain.

0: https://en.m.wikipedia.org/wiki/Super-Kamiokande

bit of a redundant title

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