Alexandra Jan said:
TL;DR Summary: Beyond astrophysics, what real-world applications stem from solving the neutron-star EoS?
I’m writing an article on how cracking the neutron-star equation of state could unlock breakthroughs far beyond astrophysics—into materials science, energy systems, computing, and more.
If physicists nail down the neutron-star EoS, what concrete advances should we expect—and how might those advances flow into everyday technologies or industries?
• Could new high-pressure materials or alloys emerge?
• How might this reshape AI or quantum computing architectures?
• Could it inform next-generation nuclear technology or fusion research?
Beyond pure theory, why should the every day person care about the practical applications of neutron star EoS?
tl;dr The practical applications of determining the neutron star EoS are most likely to involve the nuclear matter models, mathematical methods, and technologies developed in the pursuit of this goal, rather than the end result neutron star EoS which would have few practical engineering applications itself.
Understanding the neutron star Equation of State would achieve a few things:
1. It is a fairly high precision test of very strong gravitational fields in general relativity and some EoS results could deviate from the GR prediction hinting, for example, at quantum gravity effects. But, this is likely to have only very subtle engineering relevance indeed. These kinds of discoveries are exceedingly unlikely, however, to identify tweaks to GR that could make faster than light travel or communications viable, for example.
2. The very strong gravitational forces near and inside a neutron star suggest that some percentage of dark matter particles (if they exist) should be captured within neutron stars, and that this should alter the neutron star EoS is predictable and quantifiable ways. So, precise knowledge of the neutron star EoS could either confirm the existence of dark matter particles and put some bounds on its properties, or alternatively, could strongly rule out a huge swath of dark matter particle parameter space. Progress in identifying the properties and nature of dark matter particles if they exist, could open up discovery of a whole hidden sector of beyond the Standard Model particles not found in our existing understanding of the basic laws of physics. Ruling out dark matter particles that significantly contribute to the neutron star EoS, in contrast, would encourage more research into modified gravity theories and fifth forces to explain dark matter phenomena. But while this would be very helpful in pointing astrophysicists in the right direction, it wouldn't itself produce useful engineering applications, because existing constraints on dark matter particles already basically rule out the use of this kind of matter in any useful machine or material.
3. The neutron star EoS is a test of how strong force physics (i.e. QCD) and nuclear physics work at extremely high pressures in condensed matter.
If the model of a neutron star as something truly made up of tightly packed neutrons fits a precisely determined neutron star EoS then this rules out exotic materials made of something other than nucleons at essentially all physically possible energies and make searches for them in Earth-based labs look much less promising.
But if the neutron star EoS is consistent with some sort of hadron other than a proton or a neutron being stable at neutron star pressures, this would imply that some exotic materials with unknown properties are possible at pressures above the highest ones measured at Earth-bound laboratories, which could possibly be possible at pressures far below those found in a neutron star. The race would be on to determine just what pressures and circumstances are necessary to make such exotic materials stable. Of course, however, even if we could make, for example, stable strange quark matter, it would probably be insanely expensive to make and have only very niche engineering applications (much like anti-matter atoms, which we can make now, but which is so expensive to make that they have very limited practical applications).
4. Precise calculations of the neutron star EoS require precise values of the relevant physics constants including the strong force coupling constant and its beta function (which shows how its strength changes at different energy scales), Newton's constant of gravity, the light quark masses, and a variety of properties of nucleons that are derived from them. It would also corroborate the validity of the models of how nucleons behave at extremely high energies and how the nuclei of heavy chemical elements behave that worked to calculate a neutron star EoS consistent with what is observed.
The physical constant measurements and nuclear physics models used to match what we know from nuclear physics on Earth to the neutron star EoS could provide tools of wide applicability in high pressure condensed matter systems and nuclear physics (although probably only incrementally).
This could also allow condensed matter physicists and nuclear physicists to make estimates of how high pressure materials behave not just from a lower bound extrapolated up to higher pressures, as we do now, but from the ultrahigh upper bound of neutron stars extrapolated down to lower pressures, greatly reducing the uncertainty involved in predicting how condensed matter would behave at energies beyond those currently observed, but that could be reached in the future. This could have applications in materials science for engineering things to operate in ultrahigh pressure environments, in precisely predicting the properties of heavy radioactive elements without doing very costly experiments to produce and observe these elements (potentially relevant, for example, in nuclear power and nuclear weapons), and could also have applications for geology and the improved understanding of the behavior of materials in the most dense parts of Earth's core.
Admittedly, however, all of these things are likely to be modest refinements of current knowledge. We are talking about cutting uncertainties in half or less in areas where our existing crude models are "good enough for government work" already, even if they are less rigorous and precise.
Progress on these things from from the neutron star EoS might influence which of multiple proposed new high energy physics experiment investments hold the most promise for generating useful new high energy physics discoveries.
For example, it might point to an energy scale that would be a sweet spot at which to look for new physics that is a hundred rather than ten times as high at that reached by existing particle accelerators and favor "skipping" a generation of new accelerators in favor of a more expensive program that takes longer to build but is more likely to see something interesting.
The understanding achieved in determining the neutron star EoS could also be relevant in refining some of the more messy experimental measures designed to detect neutrino flux, dark matter, and neutrinoless double beta decay that all rely on moderately crude models of the behavior of protons and neutrons bound together in large atomic nuclei. At a practical level, this could have usefulness in medical radiology and border control and/or military devise designed to detect nuclear fuel or nuclear missile materials, and in locating radioactive waste hot spots that crude methods might miss.
5. The tools used to observe neutron stars in astronomy to determine their EoS could produce improved remote sensors and better image processing software, better big data management tools, and other statistical and IT tools with a wide-range of applicability.
By analogy, the Chi-square test and a surprising number of other statistical tests related to hypothesis testing and quality control in manufacturing were original devised by the lead manufacturing engineers for Guinness Breweries in Ireland to get better quality and more consistent beer production, but has much more wide usefulness in every area of science and engineering and medicine and manufacturing today.
The technology used to locate and observe neutron stars in order to confirm if a predicted EoS is correct, or to calibrate EoS models, involves bleeding edge developments in image analysis, in addressing the data science issues of finding neutron star signatures in huge astronomy data sets, and improvements in figuring out how systemic uncertainty in an isolated few neutron system scales to an entire neutron star.
These developments could have applications very far afield of astrophysics in areas like AI image recognition (which is valuable for applications like self-driving cars and AI in drone guidance systems), effectively identifying uncommon profiles in large data sets (which could be used in areas from credit scoring to epidemiology), manufacturing quality control for high precision computer chips and other products, and figuring out what margins of safety are necessary in large complex systems like dams, bridges, and skyscrapers, potentially allowing us to confidently get closer to the line to make more extreme structures.
The neutron star EoS would also be a good problem as a proof of concept test of quantum computing and a good trial run for computer engineers to figure out how to effectively use quantum computing to solve wickedly difficult physics problems, which is currently in its infancy, in an area where there is already a well-developed literature of the non-quantum computing methods used to address the same problems in a very different manner.
Less dramatically, the efforts used to build space telescopes of various types to make the observations of neutron stars needed could led to practical insights into how to put fragile things into space without damaging them, how to power satellites for sustained periods of time, how to shield electronics from cosmic radiation and debris from space junk in space, and how to launch satellites in a cost effective manner that minimizes the risk of mishaps in the launching process.
6. Efforts to determine the neutron star EoS are global scientific projects that involve multiple cooperating scientific collaborations, but have few obvious or direct partisan political implications. So, it provides a good forum for developing high quality international scientific cooperation, in a manner that doesn't stir up too much political concern about sharing state secrets about scientific findings.
