Assuming neutrinos have mass and so therefor can exist as speeds slower than C, are there likely large numbers of low energy neutrinos around that we just can’t detect?
Suppose I had a neutrino solar cell that could absorb and redirect with 100% efficiency the energy of all neutrinos as they passed through it. About how much power could is produce per square meter. of material?
All the Great Debates about neutrinos always end in tears.
I am moving this to General Questions before that happens.
I believe that the main issue is they’re electrically neutral and teeny tiny, so unless they just happen to get a direct hit with another subatomic particle at a scale where lead, to such a measly lepton, is as empty as the vacuum of interplanetary space (just a WAG), a lower speed would carry less energy.
You correctly imply that the probability for a neutrino to interact decreases with energy. However, it is rather difficult to detect any neutrino. So, your neutrino solar cell, with it’s 100% efficiency, would be overwhelmingly dominated by neutrinos moving at highly relativistic speeds (i.e., essentially c). The sub-relativistic neutrinos you are after are a negligible fraction of the total flux through your cell.
The sun is the brightest neutrino source nearby. A neutrino power of about 3 kW passes through each square meter on Earth. These are essentially all relativistic, with fewer than one-in-a-trillion being sub-c enough to think of as non-relativistic.
If you really only wanted to count non-relativistic neutrinos, you need to count the ones from the Big Bang. In analogy to the more familiar cosmic microwave background, there is a cosmic neutrino background. When the early soupy universe cooled enough to become transparent to neutrinos, the ones left zipping around were more or less here to stay. As the universe expanded, their energies became red-shifted. (They’re red-shifted a bit more than the photons since electromagnetic transparency came a bit later.) Today there should be a few hundred relic neutrinos per cubic centimeter of space. These are non-relativistic, with speeds around 2% of c (depends on the actual masses of the neutrinos, which are unknown). Detecting (or demonstrating the absence of) this relic neutrino background would a tremendous development. It’s one of the things I’d like to try before I die, but boy is it tough. (It’s some 8 to 10 orders of magnitude away from feasible with current techniques.)
How are the odds looking for neutralinos existing now that the noose is tightening around SUSY?
Since this thread has “neutrino” in the title, I’ll head off any potential confusion by noting that neutralinos don’t have anything to do with neutrinos. The similarity in the names stems from the fact that they’re both neutral. The SUSY superpartner of the neutrino is dubbed the “sneutrino”. Meanwhile, neutralinos are the superpartners of the gauge bosons (W, Z, photon) and the Higgs boson. (More correctly, they are related to the superpartners of the W, Z, photon, and Higgs. In general, there needn’t be a one-to-one correspondence due to quantum mechanical mixing of the superpartners.)
In certain SUSY models, the lightest of these neutralinos is stable and would present itself as “missing energy” in particle collisions. (The energy is dubbed “missing” since the not-very-interactive neutralino would leave the detector invisibly, leaving a hole in the energy/momentum accounting). In other models, neutralinos, as well as the superpartners of the quarks and leptons, could appear as deviations in the observed rates of “mundane” decays with respect to the Standard Model predictions. No such evidence for SUSY particles has been found, so the space of models is indeed shrinking, as you note. However, SUSY, like most theoretical models these days, has a lot of variants and wiggle room. The question will become not “is SUSY (and, for your specific question, are neutralinos) dead?” but rather “is SUSY not really going to simplify things anymore if it’s discovered?” In particular, SUSY is meant to relieve the extreme fine-tuning required in the Standard Model. However, if it only accomplishes that by introducing as many questions as it solves (for instance, by putting all the squarks and sleptons at extremely high masses for no particular reason), then it could still be true while just not being satisfyingly so. Even in such ugly versions, SUSY or something like it still has motivation as a dark matter solution, but those not wed to SUSY will start to lose interest in it in a few years if nothing appears. Indeed, the main surprise for SUSY advocates has just been that SUSY hasn’t manifested itself as low masses, which would have been the cleanest way for it to do so.
Actually I brought it up due to the proposed relationship between neutrinos and beta decay. That doesn’t seem to be panning out and the most recent speculation seems to involve neutrilinos.
I’m not sure what you are referring to here. Neutrinos and beta decay are indeed related, as one of the products of beta decay is a neutrino (actually an antineutrino). In fact, observations of beta decay led to the proposal of the neutrino in 1930 and its eventual detection in 1953. Neutralinos aren’t related to beta decay at all.
Ooops! I meant to ask this in GQ. After I posted it I wondered where it had gone.
Thanks this was very informative. Alas I was hoping the power output would be orders of magnitude greater so I could fantasize about my neutrino powered science fiction world. I guess I’ll have to power it with unbalanced dark energy instead.
Pasta: Sorry, I was being unnecessarily vague as usual – I was referring to the apparent seasonality of beta decay. I’ll try to find the article but it’s in New Scientist so the link won’t do you much good unless you subscribe.
Ah, that. Yes, this was a result from a few years back, where a group from Purdue observed time dependence in the rates of beta decay. It was only that single lab that ever saw this, and there have been multiple attempts by others to reproduce the results, to no avail. The most popular explanation at present is that they are actually observing unexplained seasonal changes in their experimental apparatus as opposed to unexplained seasonal changes in the rate of beta decay.
no, it’s actually progressed beyond that point and it seems that they’re actually on to something. That’s what the article was about. I just don’t remember enough to give a fair accounting. I’ll see if I can find it and post a link later.
Here is the link to the article and a snippet
However my memory was screwing with me - that and my ignorance. The particles they are talking about are neutrellos and not neutrelinos.
Thanks for the lead. Some thoughts after reading through the relevant journal articles…
This is all coming from the same research group still. They’ve sifted through other decay rate data to collect a handful of examples with similar (though not the same) behavior. Of note, I couldn’t find anything in the literature where they describe how many null data sets they had to go through to find a few that are supportive.
I was rather unimpressed with the quantitative aspects of the relevant articles. They are written in a rather unconvincing way, and at most of the points where you’d like to see a particular figure or number to convince yourself of a claim that is given in words, such a figure or number isn’t given. Some of the supporting data they are using was not collected with any particular need to precision rate measurements (e.g., calibration data collected for a completely separate purpose at a research reactor.) However, to be fair, they often conclude with something like, “We don’t know what this is, but better-designed experiments with appropriate controls and environmental measurements should be conducted.” I agree.
The thing is, there are seasonal variations in just about everything. Temperature, pressure, a building’s heating/cooling system cycling, other electrical systems having varying duty cycles, ambient radon rates, cosmic ray rates, sunlight… Also, some of the collated data show annual cycles, some show more frequenct cycles, and some are not quite in phase with one another.
This is all a long-winded way of saying that the claim is far from convincing at present. They’re doing good science, in that they’re reporting what they’re finding and trying to tease out what the heck is going on, and I hope they continue to push on it in an increasingly controlled way. But for now, I’m not surprised that this isn’t getting a lot of air time.
As for “neutrellos”: it’s little more than a word made up by the researchers. There is no production or interaction model proposed. There is no suggestion for how such a beast would fit into a broader particle physics context. It’s just, “If these rate variations are going to be caused by something happening in the sun, then we need something to be travelling from the sun to here. We should give it a name.” So, they did.
So your opinion is that the rate fluctuations are simply phantasms? Because even their harshest critic seems to have moved past that point. Here’s another quote.
No, my opinion is just that the data don’t point to any clear and convincing picture. I am convinced that they are seeing rate fluctuations, but those fluctuations are not convincingly explained.
I’m not harping on any of this as bad science. The popular science media tend to over dramatize this stuff and make it sound like good guys vs. bad guys. However, what you’ve got here is simply one of many forefront research results that don’t have a good explanation at present, which is what keeps things moving. Whether it turns out to be due to overlooked systematic biases in the experiment or whether new physics will explain it all, only future study will say. In other words, my opinion is that one cannot really say it is this or it is that, and that the proper next step scientifically is to continue with improved tests that isolate potential outside causes or that more clearly demonstrate a solar origin of the phenomena. And that’s exactly what these folks are trying to do, so all is good.
Based on seeing many past cases of very similar sorts of controversies, I would lay decent odds that this effect goes away in the fullness of time. But I still think it needs to be followed up on in a serious way.
First, I take exception to lumping New Scientist in with the rest of the lay press. It is infinitely better than that. Ask any of your colleagues who read it and they will agree.
Second, they are not overdramatizing this. “The Structure of Scientific Revolutions” was written over 30 years ago and yet the lessons that SHOULD have been learned from that seminal work are ignored with monotonous regularity in every journal every month.
It would be nice if things were in fact as you paint them - a world of dispassionate inquiry. But I know from very good friends involved in basic research that it is anything but.
Perhaps everyone should just remain neutral on this matter.
No need to defend the periodical. I agree, it is better than most. But it is still miles more fluffy than the underlying scientific articles. I read the New Scientist article you linked to first, and then I read the journal articles it was drawing from. All I’m saying is that if you need to fill pages in a magazine, this is a ripe story.
I’m not painting science as anything. I’m saying that this controversy is fairly run-of-the-mill and there are dozens of similar controversies contemporary with this one. I lump New Scientist in with the rags here only in the sense that its having run a piece on this subject doesn’t take away from any underlying truth about how unclear things are. The fact that the article is very person-oriented (“He said… She said…”) is exactly what I’m dismissing as noise. That’s why I always jump to the journal articles on these things. In this case, including the personalities in the story makes for better TV, which is why the magazine did so.
That’s fine, but the reason why scientists have conferences is just so that they can talk to one another - right? So that sort of dialog is useful. And my point here is that such dialog, whether from an in person dialog or an in person interview will give you insights that a journal article simply can’t. It’s not designed to. Do you see my point?
And what you get from the NS article is this sense of tension and frustration over the fact that one side says there are anomalies and the other side says they are crying wolf - that’s basically what it boils down to. So is one side trying to force the evidence to fit the existing paradigm and the other being the iconoclasts?
But as you get deeper into the article you begin to understand that from certain perspectives, both sides may be right and even grudging admit the possibility - until you get to the conclusion that clearly a lot of things simply don’t add up and the standard model isn’t cutting it in terms of an explanation - at least none that matches any aspect of the model known to date.
So yes, this is “fluffy” as you so denigratingly put it, but I think I got a lot of important unquantifiable information you probably didn’t find in your journal articles.