# If neutrinos have mass... **URL:** \ **Category:** Factual Questions\ **Created:** [May 24, 2019, 10:14pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480 "2019-05-24T22:14:06Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [May 24, 2019, 10:14pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/1 "2019-05-24T22:14:06Z")
which I am assured they do according to the Sci Am articles I’ve been reading, how can they be traveling at _c_? I get they have very little mass but wouldn’t they still need infinite energy to get them there if they have any mass at all? I’ve got a low baseline understanding of quantum theory and QCD (and barely enough math in any case to understand them) in particular, but this seems to violate General Relativity in a big way; what am I missing? ---
**Author:** ![Chingon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chingon/32/17645_2.png) [@Chingon](https://boards.straightdope.com/u/Chingon)\ **Post date:** [May 24, 2019, 10:18pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/2 "2019-05-24T22:18:01Z")
They’re not moving at the speed of light, but just a teensy bit slower. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 24, 2019, 10:19pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/3 "2019-05-24T22:19:35Z")
If neutrinos have mass, they don’t travel at c. Their speed is just slightly under c, because while they have mass, it’s just very, very little bit of mass. ---
**Author:** ![markn\_1](https://avatars.discourse-cdn.com/v4/letter/m/f9ae1b/32.png) [@markn\_1](https://boards.straightdope.com/u/markn_1)\ **Post date:** [May 24, 2019, 11:24pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/4 "2019-05-24T23:24:15Z")
[Here is the wikipedia article](https://en.wikipedia.org/wiki/Measurements_of_neutrino_speed) about measuring the velocity of neutrinos. Apparently there hasn’t yet been a result that clearly shows that neutrinos DON’T travel at c, although it is of course impossible for them to do so if they have mass. Experiments so far have determined that the difference between neutrino speed and c is at most a few parts per billion. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [May 24, 2019, 11:27pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/5 "2019-05-24T23:27:54Z")
> [@dtilque](#): > > Their speed is just slightly under c, because while they have mass, it’s just very, very little bit of mass. Nit: If they have mass, they can go any speed less than c. In principle you could encounter a neutrino at rest. You just usually don’t because the processes that make neutrinos tend to give them a bunch of energy when they do it, and there isn’t much to slow them down. ---
**Author:** ![Hari\_Seldon](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hari_seldon/32/5173_2.png) [@Hari\_Seldon](https://boards.straightdope.com/u/Hari_Seldon)\ **Post date:** [May 25, 2019, 12:19am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/6 "2019-05-25T00:19:32Z")
The way they know that neutrinos have mass is that do travel slower than c. If you are traveling at speed c, then you don’t experience time at all. Not at all. But neutrinos do experience time. Enough to change flavors. This was the solution to the solar neutrino problem. There were only about 1/3 the expected number of solar neutrinos. After they built detectors for all the flavors it turned out that in the time it takes for a neutrino to travel from the sun to the earth, starting out with only one flavor, they turn out to be 1/3 of each of the three flavors. At least that’s my understanding of the situation. IANAP. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [May 25, 2019, 1:37am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/7 "2019-05-25T01:37:41Z")
> [@leahcim](#): > > Nit: If they have mass, they can go any speed less than c. In principle you could encounter a neutrino at rest. You just usually don’t because the processes that make neutrinos tend to give them a bunch of energy when they do it, and there isn’t much to slow them down. Good point. We don’t know exactly how much mass neutrinos have, but we’ve been able to put an upper limit on it. One of the ways was from the neutrinos detected from SN1987A, a supernova in the Large Magellanic Cloud. About 20 neutrinos from it were detected by two different neutrino observatories. [Here’s](https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.58.1906) a paper on it. That gives a bound of 12 eV, although I understand the current upper bound is more like 2 eV. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [May 25, 2019, 3:03am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/8 "2019-05-25T03:03:23Z")
> [@leahcim](#): > > Nit: If they have mass, they can go any speed less than c. In principle you could encounter a neutrino at rest. You just usually don’t because the processes that make neutrinos tend to give them a bunch of energy when they do it, and there isn’t much to slow them down. Also, even if there were a bunch of neutrinos just hanging out having a siesta how would we detect them? They don’t interact with anything unless something runs into them and even then they would have so little energy that the effect would be negligible. So even if there were more slow moving neutrinos than there are fast moving ones we would never know. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 25, 2019, 12:11pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/9 "2019-05-25T12:11:11Z")
Interestingly, there are about a half a dozen completely independent experiments that put an upper bound on the neutrino mass, and they’re all in the vicinity of a few eV. I suspect that the actual mass is very close to that bound (i.e., of the same order of magnitude), and that the experiments finding the upper bounds give a best fit around there, but that they’re not confident enough to say anything because there’s no strong lower bound greater than zero. ---
**Author:** ![leahcim](https://avatars.discourse-cdn.com/v4/letter/l/b4bc9f/32.png) [@leahcim](https://boards.straightdope.com/u/leahcim)\ **Post date:** [May 25, 2019, 5:05pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/10 "2019-05-25T17:05:37Z")
> [@Buck\_Godot](#): > > Also, even if there were a bunch of neutrinos just hanging out having a siesta how would we detect them? Easy. Just swing your detector around at 99.99999% of the speed of light until one of the stationary neutrinos interacts with it. 🙂 ---
**Author:** ![Chimera](https://avatars.discourse-cdn.com/v4/letter/c/8e8cbc/32.png) [@Chimera](https://boards.straightdope.com/u/Chimera)\ **Post date:** [May 25, 2019, 5:07pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/11 "2019-05-25T17:07:44Z")
If they do, are they Catholic? ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [May 27, 2019, 1:59pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/12 "2019-05-27T13:59:27Z")
Thank you for the responses thus far. Upon review the article does mention that they travel very near\* c\*, so once again my reading comprehension skills amaze… Now as a follow up question I’m reading about Fermilabs next experiment where they plan to shoot neutrinos generated from their particle accelerator at a tank filled with 17000 tons of liquid argon. Since that strikes me as an item that you can’t order from your local scientific supply warehouse where do they get that much inert gas (inert liquid??) from? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 27, 2019, 4:07pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/13 "2019-05-27T16:07:14Z")
Argon is cheap: It’s about 1% of the atmosphere. And while 17,000 tons is a lot of it, it’s a fairly standard commodity: The same companies that produce bottled oxygen and bottled nitrogen will also produce it, and it’s used for a wide variety of commercial purposes. ---
**Author:** ![PastTense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pasttense/32/14550_2.png) [@PastTense](https://boards.straightdope.com/u/PastTense)\ **Post date:** [August 29, 2023, 11:24pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/14 "2023-08-29T23:24:02Z")
> [@Buck\_Godot](#): > > Also, even if there were a bunch of neutrinos just hanging out having a siesta how would we detect them? > **[The first observation of neutrinos at CERN's Large Hadron Collider](https://phys.org/news/2023-08-neutrinos-cern-large-hadron-collider.html)** > > Neutrinos are tiny and neutrally charged particles accounted for by the Standard Model of particle physics. While they are estimated to be some of the most abundant particles in the universe, observing them has so far proved to be highly challenging,... ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [August 29, 2023, 11:29pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/15 "2023-08-29T23:29:58Z")
Nice username post combo given the age of my post 😁, but what I was referring to was the possibility of detecting low energy neutrinos. All of the ones from Cern (and any other neutrino detectors) have been high energy. Given their lack of charge an low mass, I don’t think it would be possible with current instrumentation to detect such things in the (unlikey/) event that they exist. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 29, 2023, 11:43pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/16 "2023-08-29T23:43:52Z")
And neutrinos detected from the LHC isn’t really all that big a deal: There have been plenty of other particle accelerators that have produced neutrinos that have been detected. The LHC is, in some specific ways, the best particle accelerator we have, but it’s not the best in every way, and neutrinos are just something that really isn’t their specialty. More specifically, what’s impressive about the LHC is its extremely high energies, which allows it to produce high-mass particles that no other accelerator is capable of. But you don’t need extreme energies to produce tiny things like neutrinos. What’s more useful for neutrinos is luminosity, meaning that what matters isn’t how hard you’re throwing the particles, but just how many of them. Neutrinos are so hard to detect that you want to produce lots and lots of them. ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [August 29, 2023, 11:59pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/17 "2023-08-29T23:59:49Z")
> [@Buck\_Godot](#): > > Also, even if there were a bunch of neutrinos just hanging out having a siesta how would we detect them? This brings up an interesting point. Suppose there was a very slow or even stopped neutrino sitting on a lab table. As it only interacts via the weak force and gravity, I assume it wouldn’t sit on the lab table, but the Earth’s gravity would cause it to accelerate towards the center of the Earth. Would the weak force stop this? Or did we just lose our stopped neutrino? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 30, 2023, 12:04am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/18 "2023-08-30T00:04:05Z")
Presumably, if you have some way of producing low-energy neutrinos, you also have some way of preventing that. How to do either, we have no idea. Or you could just put your lab in orbit. Cold neutrinos should orbit just like anything else. ---
**Author:** ![Buck\_Godot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/buck_godot/32/6573_2.png) [@Buck\_Godot](https://boards.straightdope.com/u/Buck_Godot)\ **Post date:** [August 30, 2023, 12:07am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/19 "2023-08-30T00:07:08Z")
Well, yes, but it would pass through the center come out the other side and then fall back up so maybe we could catch it on the rebound, except that the surface of the earth (and neutrino as well I guess\*) are also rotating so I’m not sure we would be in the same spot when it found its way back. \*I don’t know how the orbit paths work when the orbiting object moves through the object its orbiting. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 30, 2023, 10:04pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/20 "2023-08-30T22:04:07Z")
Well, the orbits are no longer Keplerian, so it’d be a pain to calculate where it’d resurface (almost certainly not in the same lab), but conservation of energy is enough to see that it would resurface somewhere. [Next page](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480.md?page=2)