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posted by martyb on Wednesday April 17 2019, @02:36AM   Printer-friendly
from the or-they-are-being-eaten-by-a-grue dept.

At the April 13th and 14th meeting of the American Physical Society in Denver, Co. Physicists debated new ways to determine how long neutrons actually live. While neutrons are typically bound up with protons in the nucleus of atoms, and are perfectly stable there, they don't last long on their own.

Depending on the approach taken to measure it, the average lifetime of a neutron returns different values.

Using the bottle method (put a bunch of Neutrons in a 'bottle' and count how many are left after a period of time), the average lifetime is 14 minutes, 39 seconds.
Using the 'beam' method (count the protons given off in a detector as neutrons decay), the average lifetime is 14 minutes, 47 seconds.

These two methods are so precise that they do not overlap even taking the worst possible margins of error of both. It is a puzzler.

"The discrepancy has bedevilled researchers for nearly 15 years."

One possibility is that one of the two methods is doing something wrong. In that case, researchers might want to combine beam and bottle in a single device. At the meeting, physicist Zhaowen Tang of the Los Alamos lab described how researchers could put a particle detector inside a bottle neutron trap and count neutrons using both methods. His team has acquired funding to start building the device.

Another possibility is that the beam and bottle approaches have been measuring the neutron lifetime correctly, but that some unseen factor accounts for the discrepancy between the two. A leading idea is that neutrons might occasionally decay into not just protons but also dark matter, the mysterious unseen material that makes up much of the Universe's matter.

Interesting that plain old neutrons might be the key to opening the door on dark matter.

Pinpointing the lifetime of a neutron is important for understanding how much hydrogen, helium and other light elements formed in the first few minutes after the Universe was born in the Big Bang, 13.8 billion years ago. Scientists also think they can hunt for new types of physics if they can better pin down the neutron's lifetime, because that would help to constrain measurements of other subatomic particles.

A few seconds goes a long way in physics.


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  • (Score: 2) by crafoo on Wednesday April 17 2019, @03:30AM (8 children)

    by crafoo (6639) on Wednesday April 17 2019, @03:30AM (#830808)

    Neutrons may be the key to dark matter. Very interesting. Cool post. Thanks for another rabbit hole to dive down...

    • (Score: 2) by Demena on Wednesday April 17 2019, @07:18AM (7 children)

      by Demena (5637) on Wednesday April 17 2019, @07:18AM (#830900)

      I have not yet seen a sufficient reason for the invention of dark matter. It does not even answer the questions/problems it was invented for. I do not think you will find one dark matter proponent that can tell you what inertia is in the first place. They will all tell you some equivalent of "God did it".

      • (Score: 2) by Gaaark on Wednesday April 17 2019, @10:12AM (5 children)

        by Gaaark (41) on Wednesday April 17 2019, @10:12AM (#830944) Journal

        "I have not yet seen a sufficient reason for the invention of dark matter. "

        To save General Relativity: without dark matter, GR fails, and we can't have THAT!, Harumph harumph!

        Yeah, dark matter is pretty scammy.

        --
        --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
        • (Score: 0) by Anonymous Coward on Wednesday April 17 2019, @09:36PM (4 children)

          by Anonymous Coward on Wednesday April 17 2019, @09:36PM (#831325)

          Scientists are looking into other ideas as well, including adjusting GR, the problem is that no solution works in all cases.

          An idea that does work in all cases is imagining unseeable matter existing in different proportions in different locations.

          Most will agree it is a poor answer, but better than all the other answers they have tried.

          • (Score: 2) by Gaaark on Wednesday April 17 2019, @10:03PM (3 children)

            by Gaaark (41) on Wednesday April 17 2019, @10:03PM (#831345) Journal

            "but better than all the other answers they have tried."

            Beg to differ: THIS is better...

            http://physicsfromtheedge.blogspot.com/ [blogspot.com]

            --
            --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
            • (Score: 0) by Anonymous Coward on Thursday April 18 2019, @05:00PM (2 children)

              by Anonymous Coward on Thursday April 18 2019, @05:00PM (#831713)

              I'm sure EVERYONE doing research in GR is trying to suppress this guy and prevent him revealing the DIRTY truth and take away their GRANT MONEY ($65k/year salary). Physicists just love hiding the truth, including (fake) climate science which they are exploiting for all that lovely free grant money.

              • (Score: 2) by Gaaark on Thursday April 18 2019, @11:16PM

                by Gaaark (41) on Thursday April 18 2019, @11:16PM (#831947) Journal

                Did you READ the web-site (you CAN read, can't you?)?

                He's been given a grant from DARPA to further his research ($1.3 million)
                https://motherboard.vice.com/en_us/article/7x3ed9/darpa-is-researching-quantized-inertia-a-theory-of-physics-many-think-is-pseudoscience [vice.com]
                https://en.wikipedia.org/wiki/Quantized_inertia [wikipedia.org]

                So SOMEONE is taking him QUITE seriously.

                --
                --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
              • (Score: 2) by Gaaark on Thursday April 18 2019, @11:35PM

                by Gaaark (41) on Thursday April 18 2019, @11:35PM (#831957) Journal

                https://en.wikipedia.org/wiki/Quantized_inertia [wikipedia.org]

                As of 2018, two kinds of observations have been shown to be incompatible with dark matter but can be explained by quantized inertia:

                Globular clusters: in 2006, ESO researchers confirmed Mordehai Milgrom's main point, i.e. that the dynamics of stars becomes non-Newtonian when their gravitational acceleration drops below a critical threshold of about {\textstyle 2\times 10^{-10}{\text{m}}/{\text{s}}^{2}} {\textstyle 2\times 10^{-10}{\text{m}}/{\text{s}}^{2}}, however they also showed that such peculiar behavior does not only occur at the periphery of large galaxies but also in much smaller structures such as globular clusters, a phenomenon impossible to explain by dark matter (which has a large and smooth distribution over the whole galaxy).[20]

                Wide binaries: in 2012 and 2014, UNAM researchers published results of the study of a particular type of wide binary star system. When such a pair of stars is separated by more than 7000 AU, so that their gravitational acceleration drops below the threshold of {\textstyle 2\times 10^{-10}{\text{m}}/{\text{s}}^{2}} {\textstyle 2\times 10^{-10}{\text{m}}/{\text{s}}^{2}}, their behavior also becomes non-Newtonian, i.e. their observed orbital speed becomes so large that the centripetal acceleration should produce centrifugal forces overcoming their gravitational attraction, so that they should separate, but they do not do so. The behavior of such a small system remains unexplainable by dark matter.[21][22]

                --
                --- Please remind me if I haven't been civil to you: I'm channeling MDC. ---Gaaark 2.0 ---
      • (Score: 3, Informative) by Anonymous Coward on Wednesday April 17 2019, @01:52PM

        by Anonymous Coward on Wednesday April 17 2019, @01:52PM (#831013)

        I have not yet seen a sufficient reason for the invention of dark matter.

        Well, then you either have not looked, or wilfully decided to ignore them.

        It does not even answer the questions/problems it was invented for.

        It does.

        I do not think you will find one dark matter proponent that can tell you what inertia is in the first place.

        If you think that is what dark matter was invented for, you only proved that you have not the slightest clue.

  • (Score: 3, Insightful) by DrkShadow on Wednesday April 17 2019, @04:06AM (8 children)

    by DrkShadow (1404) on Wednesday April 17 2019, @04:06AM (#830817)

    Why not take a super computer or two and _calculate_ the statistical half-life of a neutron?

    Seriously. Don't we know the attributes of the fundamental forces and particles sufficiently well that, given some subatomic particles in a particular starting configuration, given a particular noise input (or none), we can determine the life of that particle (neutron)? Repeat with a great many different starting conditions (charges in different place, particles in different places, momentums slightly different) and take the average. This seems like it would be an easy, solved problem. Verify with tests.

    Though the summary. Neutrons are stable when combine with protons. (Curious on its own.) Then, "We'll shove a lot of unstable neutrons in a jar and count 'em" vs "We'll leave a neutron bound to a proton until they react in a particular way and a neutron shifts off" -- these seem like fundamentally different measurements. One, the neutron is stable, by itself. The other, the neutron is fresh out of a reaction that stripped it from a proton -- what energy has that reaction imparted unto the neutron?. That strikes me as different.

    • (Score: 5, Informative) by PiMuNu on Wednesday April 17 2019, @05:38AM (5 children)

      by PiMuNu (3823) on Wednesday April 17 2019, @05:38AM (#830849)

      > Why not take a super computer or two and _calculate_ the statistical half-life of a neutron?

      It is quite hard because you have to calculate the sum of a series that doesn't converge very well. The quarks are bound by gluon interactions, but the gluons themselves are also bound by gluon interactions (and so on). Each step in the calculation is already quite lengthy, and it turns out it is rather a difficult problem to solve computationally. There is a summary on wikipedia which probably makes a better explanation.

      https://en.wikipedia.org/wiki/Quantum_chromodynamics [wikipedia.org]

      > Though the summary

      You misunderstood the beam method. A beam of neutrons is created using neutron spallation. Many of the neutrons decay to a proton, electron and electron anitneutrino. The resultant decay protons are counted and, by comparing the initial number of neutrons to the number that decayed one can infer a half life.

      Reference for "bottle method"
      https://arxiv.org/pdf/1707.01817.pdf [arxiv.org]

      Reference for "beam method"
      https://physics.aps.org/synopsis-for/10.1103/PhysRevLett.111.222501 [aps.org]
      (annoyingly the original article is paywalled, I thought PRL was open access journal but maybe not)

      • (Score: -1, Troll) by Anonymous Coward on Wednesday April 17 2019, @08:43AM

        by Anonymous Coward on Wednesday April 17 2019, @08:43AM (#830928)

        ah! the electron "anti" neutrino.
        most curious: the universe is flooded
        with neutrinos and hydrogen is most abundant but
        but "somehow" the universe doesnt cogel into a neutron
        soup that turns everything unstable and radioactif.
        srsly, those neutrons are a biiiig secriit ^_^

      • (Score: 2) by OrugTor on Wednesday April 17 2019, @04:08PM (1 child)

        by OrugTor (5147) Subscriber Badge on Wednesday April 17 2019, @04:08PM (#831110)

        In the beam method are the particles travelling at relativistic speeds, requiring time dilation adjustment?

        • (Score: 2) by PiMuNu on Wednesday April 17 2019, @09:19PM

          by PiMuNu (3823) on Wednesday April 17 2019, @09:19PM (#831315)

          > In the beam method are the particles travelling at relativistic speeds, requiring time dilation adjustment?

          I assume they thought of that. Other sources of bias - what is the efficiency with which the incident neutrons are counted? what is the efficiency with which incident protons are counted? Again, I am sure they thought of this stuff e.g. calibrated with a known source.

      • (Score: 2) by Osamabobama on Wednesday April 17 2019, @11:03PM

        by Osamabobama (5842) on Wednesday April 17 2019, @11:03PM (#831374)

        ...one can infer a half life.

        This is the first reference to half life I have seen on this page. The other references are to 'average lifetime". Is this article dumbing it down for us? Is the measurement method using a half life of something else to determine the lifetime of a neutron?

        The article says the two measurements don't overlap, but we are talking about the calculation of the average. Does the distribution of lifetimes overlap? What sort of distribution is it?

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        Appended to the end of comments you post. Max: 120 chars.
      • (Score: 0) by Anonymous Coward on Thursday April 18 2019, @05:03PM

        by Anonymous Coward on Thursday April 18 2019, @05:03PM (#831715)

        STOP being sensible.

        You're implying that a guy on the internet who gave it 3 minutes thought can't blow through what hundreds of people specializing in physics have been pondering for decades.

    • (Score: 5, Informative) by stormwyrm on Wednesday April 17 2019, @09:00AM (1 child)

      by stormwyrm (717) on Wednesday April 17 2019, @09:00AM (#830933) Journal

      Why not take a super computer or two and _calculate_ the statistical half-life of a neutron?

      The strong interaction is notoriously difficult to computationally simulate, given that the interaction is highly non-linear and has a large coupling constant at low energies. The perturbation theory that was so successful with quantum electrodynamics does not work for quantum chromodynamics (the quantum field theory of the strong interaction) as a result. The most successful approach so far to computationally modelling the strong interaction is Lattice QCD [wikipedia.org], and it is so computationally intensive that it's been used as a benchmark for high-performance supercomputers [arxiv.org]. The main problem is that even today's supercomputing systems still don't have enough memory bandwidth to do these kinds of calculations efficiently. Lattice QCD can't even be applied for some classes of problems involving the strong interaction, such as those for which there is a numerical sign problem [wikipedia.org]. A general-purpose quantum computer would probably be able to help greatly in simulating these kinds of things, if we can build one.

      --
      Numquam ponenda est pluralitas sine necessitate.
      • (Score: 0) by Anonymous Coward on Wednesday April 17 2019, @08:24PM

        by Anonymous Coward on Wednesday April 17 2019, @08:24PM (#831291)

        As a physicist with a different focus area than this, I wanted to thank you for your informative post.

  • (Score: 2) by inertnet on Wednesday April 17 2019, @11:44AM (1 child)

    by inertnet (4071) on Wednesday April 17 2019, @11:44AM (#830966) Journal

    I assume this has already been taken into account, but could it be due to a difference in speed of the particles in the two methods?

    Also, in "count the protons given off in a detector", is the whole bottle a detector here, while in the beam method a 'directional' detector is used? In other words, are the detectors the same?

    • (Score: 0) by Anonymous Coward on Thursday April 18 2019, @05:06PM

      by Anonymous Coward on Thursday April 18 2019, @05:06PM (#831718)

      THanks for that. Where can we send your nobel prize genius?

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