Neutrinos' maximum possible mass shrinks further
32 comments
·April 10, 2025mdturnerphys
PaulHoule
Not that difficult by water. Remember there was global trade in commodities like bananas and maple sugar when we were still on the solar economy.
pavel_lishin
I suppose it's not a spoiler to comment on this, but this was recently on an episode of Tom Scott's "Lateral" podcast.
ReptileMan
We really need some form of uber blimps for such projects.
pantalaimon
This has been tried, but the company folded before delivering anything tangible and the hangar is now Germany's largest indoor pool.
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bsder
Why this huge roundabout route? The route looks like autobahn almost all the way. Fixed comment about weight: 200 tons is 400,000 lbs--it's heavy but not absurdly so.
We'd put this on the road in the US without much fanfare. You'd need some civil engineers to check the road ratings and clearances.
I mean, this is what we consider heavy for roads in the US: https://www.youtube.com/watch?v=Y4pn4a4a2lA
Edit: I can't read. It's 200 tons not 100 tons. That's getting heavy, but I would still expect things like the autobahn to be able to handle that with an appropriate carrier.
bayindirh
For these kinds of cargo, you can't decide the route yourself. You ask to the government bureau which handles the roads with your specs, and they give you the route after checking it with the road specs and clearances. Insurance also needs these documents.
After you insure your cargo, you take the exact route the bureau provided, and if something happens due to road conditions, government pays your damages.
Dad was working in insurance. This is the standard procedure.
bsder
> After you insure your cargo, you take the exact route the bureau provided, and if something happens due to road conditions, government pays your damages.
That is not how it works in Texas.
Yes, the state gives you a route. However, it is always the responsibility of the carrier to make sure that everything on the way has appropriate ratings and heights. If the state runs your 15' load under a 14' 6" bridge or runs your 80,000lb load over a 40,000lb rated bridge, it is incumbent upon the driver/carrier to not hit the bridge or collapse it.
I knew several of the people who used to work out these permits. If they missed something, sometimes a driver would have to back a load up (yes, in reverse as the load would be too big to turn around) for 20 or 30 miles to change routes. If you were on an unusual route, for some reason, the maps they used didn't always have the correct heights marked for every interchange.
plorg
If I had to guess the biggest problem for most roads is the height, followed by the width. Weight might still come into play for some potential routes that otherwise had enough clearance. It's not clear from that video but it's quite possible the load fits in the 14' height limit for interstates in the state of Texas. That would make this at least twice as tall.
bsder
Yeah, I hadn't thought about it, but you're probably correct that height is the issue.
The Jochenstein lock that was mentioned is 7.8m and they barely cleared under it. That would be quite a tall load and then you have to add the height of the carrier. You can easily run out of options for something that tall and the German routes look like they use cloverleaf interchanges which could easily be obstacles.
> load fits in the 14' height limit for interstates in the state of Texas
There are special routes up and out from the Houston ship channel that use mostly diamond interchanges that could accommodate even something like this. However, the roads that this would have traversed in Germany are laughably small by Texas freeway standards so I can certainly see there being no way to get between the two points.
roomey
I would imagine the size meant it wouldn't get far by road. Bridges and houses would have made the route too narrow.
It looks like they only just squeezed under a bridge on the Danube in the bottoms pictures
Hikikomori
Our roads are made for Fiat 500, not Ford f750.
drdeca
Hm, one thing I’m unclear on is…
Well, from what I understand, the mass eigenstates and the flavor eigenstates for neutrinos aren’t the same, so a mass eigenstate is a linear combination of the different flavor eigenstates, and a flavor eigenstate is a linear combination of the different mass eigenstates,
But, in these experiments with the electron neutrino, which is a flavor eigenstate, well, it isn’t in a mass eigenstate, so, what does that say about the momentum and such?
And like, when they use this to get a bound on the mass, is this like, a bound on the mass of the largest of the 3 mass eigenstates, or of the expected value of mass when in the electron neutrino flavor eigenstate, or what?
tlogan
I believe they are measuring weighted average of the mass eigenstates.
juliuswaldmann
I love to see KATRIN represented here. I am a student at the university this is at. The area (nothern campus) this is at is a bit secluded and normally not accessible to students but I managed to take part in a tour of the northern campus. I even got some points (ects) for it which is nice.
It was really impressive. The whole northern campus is full of giant science experiments like this one, old nuclear test reactors and so much more. I'm glad I got the opportunity to see it. They even got an entire water treatment plant, direct heating and direct cooling networks and produces more electricity than it uses on average.
I was really fascinated by the scale of everything. The direct heating plant for example uses a few giant room sized gas-burning generators and uses their excess heat. But just for backup, in case gas drops out there are also 2-3 absolutely massive tanks next to the building that hold something like 2 million or so liters diesel fuel each, just as a backup. One of the technicians joked "yeah, we fill up a few thousand liters now and then when its cheap"
All in all absolutely amazing experience and really cool campus.
D-Coder
I clicked on the link and saw the article was by Dr. Emily Conover, a name that I recognized as an excellent science writer. Then I looked at the top of the article... _Science News_, which I consider an excellent source for keeping up with science. Strongly recommend both.
mytailorisrich
> [Neutrinos] have a mass of less than 0.45 electron volts, physicists report in the April 11 Science.
For reference, a proton has a mass of 938.272 MeV and an electron has a mass of 0.5110 MeV, so this is extremely 'light' in comparison, less than a millionth of an electron.
tlogan
I read somewhere that this experiment has sensitivity of 0.2 eV (I could be wrong here so please correct me).
What is this 0.45 eV then? Are they still running the measurements and trying get to 0.2 eV or this is maximum they can achieve?
[ I misread the original article explaining their equipment and project - their goal is to go all the way down to 0.2ev ]
thatnerd
I think it's an upper limit of around 0.2 eV^2, so √(0.2 eV^2) = 0.45 eV.
I'd like to see an experiment that's sensitive enough to eliminate the m=0 hypothesis. Their prediction of m^2 = -0.14eV^2 is a bit disconcerting.
tlogan
How can we prove that one of neutrinos is massless? That would be impossible - but I do not understand these things so I can be wrong.
colanderman
I believe GP is proposing the opposite -- a test capable of proving it is not massless. (Presumably this has never been done.)
PaulHoule
The nature of the neutrino mass is one of the few outstanding mysteries of physics which can certainly be cleared up by an experiment, I can't think of any higher priority area for fundamental physics.
moi2388
TIL you can express mass in volts, and that electrons do not have a mass of 1 electron volt.
filmor
Others have explained it already, but just to make this clear: The mass is not expressed in volts but in "electron volts" that is a different unit in the same sense as "watt hours" is a measure of energy and not time.
bezmiran
Because an eV is a unit of energy (1 eV = 1.602e-19 Joules). It's defined as the kinetic energy of an electron that is accelerated by a potential difference of 1 Volt, nothing to do with its rest mass.
When rest mass is stated in energy units such as eV, they're calculating it using E=mc^2.
maxnoe
You can express rest energy in electron volt, a unit of energy. The energy an electron gains by being accelerated in an electric field of 1 Volt.
But since E=mc², you can say the mass is X eV/c² and then people become lazy and forget the c² or even define a new system of units in which c=1.
perihelions
- "or even define a new system of units in which c=1"
thatnerd
You can't express mass in volts. A volt is energy per unit of charge. To get energy, you need to multiply by a charge.
One Joule of energy is what you get when you move one Coulomb of charge across a 1V potential.
One electronVolt (eV) is the energy you get from moving one electron's worth of charge across 1 volt of potential.
It's an accident of what we chose to be a Joule of energy and what we chose to be a Coulomb of charge, so there should be no expectation that this would turn out to be the mass of an electron (when divided by the square of the speed of light, which is unstated because everyone knows E = mc^2).
_kulang
More specifically it’s that you can express mass as energy, and that voltage is the energy per unit charge
drdeca
Volts are energy per charge, right? So the cost of moving X charge from one place to another where the electric potential between them differs by voltage V, is X V?
Kind of like how lifting a mass involves increasing the g h , so costs energy m g h ?
This measurement was performed in a lab in Germany. The main spectrometer of the apparatus used for the measurement was fabricated in Germany. The delivery route was almost 9000 km. https://www.symmetrymagazine.org/article/march-2007/deconstr...