# 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:** 3
**Author:** ![Whack-a-Mole](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/whack-a-mole/32/141_2.png) [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)\ **Post date:** [September 14, 2023, 10:08am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/41 "2023-09-14T10:08:19Z")
I just saw this which some here may find interesting: > **[Wild New Technique Could Finally Measure The Elusive Neutrino](https://www.sciencealert.com/wild-new-technique-could-finally-measure-the-elusive-neutrino)** > > Neutrinos are abundant subatomic particles that have a crucial role in the composition of the Universe. From that article: > The answer, as put forward in a new study, could lie in tracking beta decay, specifically in the rare radioactive type of hydrogen called tritium. This natural radioactive decay process can be observed, and – potentially – will reveal the weight of the neutrinos involved. > > \< snip \> > > When tritium decays, it creates three subatomic particles: a helium ion, an electron, and a neutrino. By knowing the total mass and the mass of the other particles, scientists are hopeful that the missing mass will be that of the 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:** [September 15, 2023, 12:10am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/42 "2023-09-15T00:10:24Z")
Not really a “wild new technique”… It’s a very old technique, that they’re just hoping to do more precisely than before. I wish them luck. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 15, 2023, 2:52am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/43 "2023-09-15T02:52:41Z")
> [@Pasta](#): > > For certainly viable neutrino mass scenarios, it may be that _monatomic_ tritium gas is needed I wouldn’t want to stand close by. Does it help if it’s a pure H-T or D-T? Or T-F, or something else, for that matter? ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [September 15, 2023, 11:29am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/44 "2023-09-15T11:29:40Z")
> [@Buck\_Godot](#): > > 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. I’m not sure if that’s true. It may be that a blob of neutrinos might be much more likely to interact due to having just the right (small) amount of energy and being in proximity to other particles for longer. There might even be possible interactions between neutrinos (forming a particle with greater mass). I dunno, I’m just spitballing. I’m just saying, some of the common-sense rules of thumb that apply to our macro world don’t always work that way in QM. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [September 15, 2023, 11:32am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/45 "2023-09-15T11:32:27Z")
As an aside, AIUI, neutrinos having mass and not travelling at c is something inconsistent with the standard model. I mention this because a lot of pop sci articles get excited about potential breaks to the SM, while not mentioning that we already know of at least one. I guess it is just that neutrinos being such a PITA, it’s difficult to get more information about this observation that could lead us towards a better model. ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [September 15, 2023, 11:47am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/46 "2023-09-15T11:47:16Z")
> [@Mijin](#): > > I’m not sure if that’s true. It may be that a blob of neutrinos might be much more likely to interact […] Never mind, it seems the answer is no, they don’t do much. And indeed, there may be stationary neutrinos basically everywhere, left over from [the big bang](https://phys.org/news/2007-10-probing-neutrino.html#:~:text=These%20stationary%20neutrinos%20are%20almost,add%20up%20to%20much%20mass.). ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [September 15, 2023, 7:31pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/47 "2023-09-15T19:31:09Z")
> [@Chronos](#): > > Not really a “wild new technique”… It’s a very old technique, that they’re just hoping to do more precisely than before. I wish them luck. I can’t fault anyone that read that subpar article, but this experiment does center around a very new and very challenging technique. The article makes it sound like the new part is measuring the tritium beta decay endpoint, and indeed that is not new. The new part is _how_ they are measuring the spectrum. Older methods for measuring the high-energy tail of the spectrum are reaching the end of their experimental practicability. This new effort is carrying out R&D on a new technique that involves measuring individual beta-decay-electron’s energies through the cyclotron radiation they emit in a uniform magnetic field. The new result is groundbreaking in that has shown that this works for measuring the tritium spectrum at least in principle. The resulting upper limit on neutrino mass is not even close to competitive yet, but it’s an exciting step on the R&D road. > [@Dr.Strangelove](#): > > Does it help if it’s a pure H-T or D-T? Or T-F, or something else, for that matter? For the first two, there’s no huge difference in chemistry, so the energy smearing is similarly an issue for both. There are other compounds that could offer favorably narrower spectral smearing, but they are typically disfavored for practical reasons (for instance, a large volume of gaseous HF or HCl exposed directly to experimental apparatus materials – and possibly to humans under accident conditions – introduces understandable practical challenges). > [@Mijin](#): > > As an aside, AIUI, neutrinos having mass and not travelling at c is something inconsistent with the standard model. > I mention this because a lot of pop sci articles get excited about potential breaks to the SM, while not mentioning that we already know of at least one This is [correct](https://www.youtube.com/watch?v=0ZEuWJ4muYc), but to be fair the addition of neutrino mass is a fairly straightforward extension of the Standard Model as extensions go. I personally avoid using the “we broke the SM” angle (and I discourage it where I can) as it’s sort of beside the point. Naturally, the goal of particle physics isn’t to break some decade’s old snapshot of _the_ Standard Model; it’s to keep learning about how the universe works. Discovering neutrino mass did the latter – exciting – but the SM implications of the potential for non-zero neutrino mass have been known for a very long time. We just now know that we need to use that more complex picture in the (in my view, new) Standard Model. > [@Mijin](#): > > Never mind, it seems the answer is no, they don’t do much. And indeed, there may be stationary neutrinos basically everywhere, left over from [the big bang](https://phys.org/news/2007-10-probing-neutrino.html#:~:text=These%20stationary%20neutrinos%20are%20almost,add%20up%20to%20much%20mass.) Post #25 above might be of interest. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [September 15, 2023, 8:01pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/48 "2023-09-15T20:01:33Z")
> [@Pasta](#): > > For the first two, there’s no huge difference in chemistry, so the energy smearing is similarly an issue for both. Okay; I guess I was thinking that at least some of the vibrational modes would be affected by nuclear mass, so having one of the atoms be a different mass might shift the energy spectrum to somewhere more favorable. HF is nasty, but monatomic tritium scares me more, I think… ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [September 15, 2023, 8:32pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/49 "2023-09-15T20:32:46Z")
> [@Pasta](#): > > Naturally, the goal of particle physics isn’t to break some decade’s old snapshot of _the_ Standard Model; it’s to keep learning about how the universe works. Discovering neutrino mass did the latter – exciting – but the SM implications of the potential for non-zero neutrino mass have been known for a very long time. We just now know that we need to use that more complex picture in the (in my view, new) Standard Model. Yep agreed. I was using “breaks” the standard model in some colloquial sense, but I am aware that it is a misleading framing. As much as popular culture seems to want to believe that science is about revolutions that overturn everything we thought we knew, the reality is more incremental. And given that the standard model is arguably our most successful theory ever – making incredibly accurate predictions in countless experiments and indeed enabling various technologies – it’s _just not_ going to be outright wrong. It’s going to be superceded by a model that incorporates it in some sense. ---
**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:** [September 15, 2023, 9:34pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/50 "2023-09-15T21:34:48Z")
The Standard Model also doesn’t specify everything. For instance, we don’t know for sure (or at least, didn’t, when I was last active in the field) whether neutrinos are Dirac or Majorana particles (personally, I favor Dirac, if only because it’d be remarkable for lepton number to be conserved so well if it doesn’t even exist). The distinction is moot for massless neutrinos, but relevant for massive ones. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [September 15, 2023, 10:52pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/51 "2023-09-15T22:52:20Z")
We still don’t know. Note, though, that lepton number is likely not actually conserved in the Standard Model anyway; it is only approximately conserved since the non-perturbative [sphaleron](https://en.wikipedia.org/wiki/Sphaleron) process is frozen out at low energies. Most people in the field would bet on Majorana neutrinos, based on the guiding principle that “If the math allows it, it happens, unless there’s a reason for it not to happen.” You’d need a reason to arbitrarily disallow Majorana mass terms, and there isn’t a compelling one at hand. And any additional lepton number non-conservation that is introduced is no easier or harder to explain away than the extreme lightness of the neutrinos (which, in turn, you definitely _would_ want to explain in the Dirac case. In the Majorana picture, there is a [reasonably elegant way](https://en.wikipedia.org/wiki/Seesaw_mechanism) to induce very light neutrinos.) Of course, the universe can do whatever it pleases. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [September 15, 2023, 10:59pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/52 "2023-09-15T22:59:04Z")
> [@Mijin](#): > > it’s _just not_ going to be outright wrong. > It’s going to be superceded by a model that incorporates it in some sense. True. Another way to say that the addition of neutrino mass isn’t changing the SM in a big way is that the addition of neutrino mass doesn’t necessarily solve any problem other than neutrino mass. “Oh no, my neutrinos are massless!” was never a concern, just an observation. Now that they are known to be massive, lots of new cool stuff can happen, but it’s a self-contained path. In contrast, explaining the origin of dark matter, or the cosmological constant, or the hierarchy problem, or even gravity (from a quantum field perspective) will likely require actually “breaking” the SM rather than just adding some DLC. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [September 15, 2023, 11:16pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/53 "2023-09-15T23:16:16Z")
This is one of the problems with the Standard Model - it can accommodate things like massless or massive neutrinos, without disrupting much else. It’d be nice to have a theory that _predicted_ (or now, _retrodicted_) the observed masses of the neutrinos (etc.) ---
**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:** [September 16, 2023, 1:09pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/54 "2023-09-16T13:09:34Z")
Sure, but it’s one thing to have a quantity that’s conserved by most interactions, but with a few interactions that are much rarer for some reason that don’t conserve it, so it’s mostly-conserved. That’s not too different from conservation of strangeness, say. But it’s another thing entirely when all of the interactions that change particle identity at all fail to conserve that quantity… but it still nonetheless acts like it’s conserved, even through those interactions. As an aside, I love the concept of neutrino mass as a DLC to the Standard Model. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [September 16, 2023, 11:08pm UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/55 "2023-09-16T23:08:22Z")
> [@Pasta](#): > > DLC What’s DLC? ---
**Author:** ![Mijin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mijin/32/9369_2.png) [@Mijin](https://boards.straightdope.com/u/Mijin)\ **Post date:** [September 17, 2023, 12:47am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/56 "2023-09-17T00:47:19Z")
Downloadable content. IOW, Chronos is saying that neutrino mass is a small addition to the standard model (DLC) and not a significant update (e.g. a sequel to a game) ---
**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:** [September 17, 2023, 1:03am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/57 "2023-09-17T01:03:34Z")
In the modern game marketplace, you can pay, say, $50 for a game, but then can also add a few bucks here or there to make your character be wearing a cowboy hat, or have a couple of extra missions available, or whatever. Those optional extras that don’t fundamentally change the game are DLC. ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [September 17, 2023, 1:12am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/58 "2023-09-17T01:12:40Z")
Thanks. ---
**Author:** ![smithsb](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/smithsb/32/12107_2.png) [@smithsb](https://boards.straightdope.com/u/smithsb)\ **Post date:** [September 17, 2023, 2:57am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/59 "2023-09-17T02:57:03Z")
It appears I’ll need a bigger power source for my neutrino death ray. How do you package a supernova? ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [September 17, 2023, 4:13am UTC](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480/60 "2023-09-17T04:13:56Z")
> [@smithsb](#): > > t appears I’ll need a bigger power source for my neutrino death ray. How do you package a supernova? Very carefully [Previous page](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480.md?page=2) [Next page](https://boards.straightdope.com/t/if-neutrinos-have-mass/834480.md?page=4)