The asymmetrical universe

I'm currently reading the 2006 book Warped Passages: Unraveling the Mysteries of the Universe's Hidden Dimensions, by the brilliant theoretical physicist Lisa Randall.  As you might imagine from the title, it's a provocative and mind-blowing read.  And although it's written for laypeople, with most of the abstruse mathematics removed -- theoretical physics is, honestly, 99% math -- I must admit that a good chunk of it is going so far over my head that it doesn't even ruffle my hair.

The rest, though, is way cool.

The heart of the book is the consideration of superstring theory as a model for the way the universe is built.  The idea -- at least at the level I understand it -- is that the fundamental building block of matter and energy is the string, a one-dimensional structure that can either be open-ended or a closed loop, and the various manifestations we see (particles, for instance) are the different vibrational modes of those strings.  But deeply embedded in this model is the idea that the universe has fundamental symmetries, which unify seemingly disparate forces and allow you to make predictions about what exists but is as yet undiscovered based upon what might be necessary to complete the symmetry of the theory.

This search for underlying patterns in what we see around us drives a lot of theoretical physics.  And certainly there are times the approach pays off.  It was that mode of inquiry that allowed Sheldon Glashow, Abdus Salam, and Steven Weinberg to come up with electroweak theory, which showed that at high enough energy the electromagnetic and weak nuclear forces act as a single force.  (It was later experimentally confirmed, and the three won the Nobel Prize in Physics in 1979 for the discovery.)  Carrying this approach to its extreme are people like Garrett Lisi, whose eight-dimensional model of particle physics (based upon a mathematical structure called a Lie group) tries to unify everything we know from experimental results into a symmetrical whole based upon it seeming to fit into a pattern that is "too beautiful not to be true."

The superstring model, too, makes predictions of particles and forces, largely based upon arguments of symmetry and symmetry breaking.  Each of the particles in the Standard Model should, the math tells us, have a "supersymmetric partner" -- each known fermion paired with a boson with the same charge and similar interactions, but a higher mass, and vice versa.

Experimental confirmation, of course, is the hill on which scientific theories live or die, and what the theorists need is hard evidence that these predicted particles exist.  Randall's book is peppered with optimistic statements such as the following:

In a few years, CERN will be the nexus of some of the most exciting physics results.  The Large Hadron Collider, which will be able to reach seven times the present energy of the Tevatron, will be located there, and any discoveries made at the LHC will almost inevitably be something qualitatively new.  Experiments at the LHC will seek -- and very likely find -- the as yet unknown physics that underlies the Standard Model.

Randall's book was published in 2006; the LHC came online in 2008.

And in the sixteen years since then, not a single particle has been found confirming superstring theory -- no superpartners, no Kaluza-Klein particles, nothing.  It did find the Higgs boson, which was a coup, but that was already predicted by the Standard Model, and didn't explain anything about the fundamental messiness of particle physics; why particles have the masses they do, forces have the strength they do, and (most vexing) why the extremely weak gravitational force seems to be irreconcilable with the other three.

This understandably bothers the absolute hell out of a lot of particle physicists.  It just seems like the most fundamental theory of everything should be a lot more elegant than it is, and that there should be some underlying beautiful mathematical logic to it all.  Instead, we have a model that works, but has a lot of what seem like arbitrary parameters.

But the fact is, every one of the efforts to get the Standard Model to fit into a more beautiful and elegant theoretical framework has failed.  Physicist Sabine Hossenfelder, in a brilliant but stinging takedown of the current approach that you really should watch in its entirety, puts it this way: "If you follow news about particle physics, then you know that it comes in three types.  It's either that they haven't found that thing they were looking for, or they've come up with something new to look for which they'll later report not having found, or it's something so boring you don't even finish reading the headline."  Her opinion is that the entire driving force behind it -- research to try to find a theory based on beautiful mathematics -- is misguided.  Maybe the actual universe simply is messy.  Maybe a lot of the parameters of physics, such as particle masses and the values of constants, truly are arbitrary (i.e., they don't arise from any deeper theoretical reason; they simply are what they're measured to be, and that's that).  In her wonderful book Lost in Math: How Beauty Leads Physics Astray, she describes how this century-long quest to unify physics with some ultra-elegant model has generated very close to nothing in the way of results, and maybe we should accept that the untidy Standard Model is just the way things are.

Because there's one thing that's undeniable: the Standard Model works.  Just to give one recent example, a paper last year in Physical Review Letters described a set of experiments showing that a test of the Standard Model passed with a precision that beggars belief -- in this case, a measurement of the electron's magnetic moment that agreed with the predicted value to within 0.1 billionths of a percent.

This puts the Standard Model in the category of being one of the most thoroughly-tested and stunningly accurate models not only in all of physics, but in all of science.  As mind-blowingly bizarre as quantum mechanics is, there's no doubt that it has passed enough tests that in just about any other field, the experimenters and the theoreticians would be high-fiving each other and heading off to the pub for a celebratory pint of beer.  Instead, they keep at it, because so many of them feel that despite the unqualified successes of the Standard Model, there's something deeply unsatisfactory about it.  Hossenfelder explains that this is a completely wrong-headed approach; that real discoveries in the field were made when there was some necessary modification of the model that needed to be made, not just because you think the model isn't pretty enough:

If you look at past predictions in the foundations of physics which turned out to be correct, and which did not simply confirm an existing theory, you find it was those that made a necessary change to the theory.  The Higgs boson, for example, is necessary to make the Standard Model work.  Antiparticles, predicted by Dirac, are necessary to make quantum mechanics compatible with special relativity.  Neutrinos were necessary to explain observation [of beta radioactive decay].  Three generations of quarks were necessary to explain C-P violation.  And so on...  A good strategy is to focus on those changes that resolve an inconsistency with data, or an internal inconsistency.

And the truth is, when the model you already have is predicting with an accuracy of 0.1 billionths of a percent, there just aren't a lot of inconsistencies there to resolve.

I have to admit that I get the particle physicists' yearning for something deeper.  John Keats's famous line, "Beauty is truth, and truth beauty; that is all ye know on Earth, and all ye need to know" has a real resonance for me.  But at the same time, it's hard to argue Hossenfelder's logic.

Maybe the cosmos really is kind of a mess, with lots of arbitrary parameters and empirically-determined constants.  We may not like it, but as I've observed before, the universe is under no obligation to be structured in such a way as to make us comfortable.  Or, as my grandma put it -- more simply, but no less accurately -- "I've found that wishin' don't make it so."

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A lens into the dark sector

I don't really regret the weird, meandering path I took through the educational system -- but I have to admit to a bit of envy when it comes to people who are true experts in their field.

My inveterate dilettantism means I'm reasonably conversant in a lot of areas, but don't really have a deep understanding of anything.  Being a dabbler is neither a bad background to have as a high school teacher nor as a blogger, but it does mean that I often run into topics and think, "Wow, I really wish I could wrap my brain around this."

This happened just yesterday when I happened upon a paper in The European Physical Journal C called, "A Warped Scalar Portal to Fermionic Dark Matter."  My Bachelor of Science diploma in physics should have come with a sticky note appended to it that says, "... yeah, but he pretty much sucked as a physics student."  I struggled in virtually all of my upper-level physics classes, due to a combination of lack of focus and troubles with mathematics that I never figured my way out of.  The result is that I have a degree in physics, but reading an academic paper on the topic loses me after the first couple of paragraphs.

But so much of physics is so incredibly cool that I wish I understood it better.  The paper I took a look at yesterday (it'd be a vast exaggeration to say I "read" it) is a real coup -- if its findings bear out, it stands a good chance of solving two of the most perplexing questions of subatomic physics.

The first is akin to the planetary spacing issue I dealt with here a couple of days ago.  It asks a curious question: why do the fundamental particles have the masses they do?  Photons are massless; neutrinos damn close, but have a very tiny amount of mass; electrons are next (along with their relatives, muons), then protons and neutrons, and on up the scale to very heavy (and short-lived) particles like the "double-charmed xi baryon" which has four times the rest mass of a proton and a half-life so short it hasn't been measured yet, but is probably less than 10 ^-14 seconds (that's a decimal point, followed by thirteen zeros and a one -- better known to us non-physicists as "really, really short").

The other question is one I've looked at here before; the nature of the mysterious "dark matter" that makes up something like a quarter of the known mass of the universe, but thus far has resisted all detection by anything but its mysterious gravitational signature.  We don't know what it's made of, nor how (or if) it interacts with itself or other forms of matter.

I've commented about it that just as the odd constancy of the speed of light in a vacuum regardless of the reference frame of the observer waited around for a genius -- in this case, Einstein -- to explain it, the baffling dark matter is waiting for this century's Einstein to have the requisite insight.

[Image licensed under the Creative Commons Illustris Collaboration, Illustris Dark Matter and Gas, CC BY-SA 4.0]

Well, the waiting may be over.  A trio of physicists at Johannes Gutenberg University Mainz -- Adrian Carmona, Javier Castellano Ruiz, and Matthias Neubert -- have come up with a theoretical framework that, if it bears out, explains both the fundamental particle masses and the nature of dark matter in one fell swoop, by proposing an additional fundamental particle and force that act on matter through a tightly-coiled extra spatial dimension.

A press release at Science Daily describes their research this way:

In a recent paper published in the European Physical Journal C, the researchers found a spectacular resolution to this dilemma.  They discovered that their proposed particle would necessarily mediate a new force between the known elementary particles (our visible universe) and the mysterious dark matter (the dark sector).  Even the abundance of dark matter in the cosmos, as observed in astrophysical experiments, can be explained by their theory.  This offers exciting new ways to search for the constituents of the dark matter -- literally via a detour through the extra dimension -- and obtain clues about the physics at a very early stage in the history of our universe, when the dark matter was produced.

"After years of searching for possible confirmations of our theoretical predictions, we are now confident that the mechanism we have discovered would make the dark matter accessible to forthcoming experiments, because the properties of the new interaction between ordinary matter and dark matter -- which is mediated by our proposed particle -- can be calculated accurately within our theory," said study co-author Matthias Neubert.  "In the end -- so our hope -- the new particle may be discovered first through its interactions with the dark sector."

This, gentle readers, is what is known as "Nobel Prize material."

If, of course, it is confirmed by further research and investigation.  The thing that makes me hopeful is that the theories with the greatest likelihood of success are the ones that explain several problems at once; consider, for example, how the quantum mechanical model simultaneously accounted for the energy levels in hydrogen atoms, the bizarre double-slit experiment, Heisenberg's Uncertainty Principle, and the collapse of the wave function (most famous for being responsible for the Schrödinger's Cat phenomenon).  A really powerful model has enormous breadth, depth, and explanatory power, and this one -- at least from a preliminary look -- seems to have all three.

But, as I pointed out at the beginning, that's from the point of view of a dilettante.  I'm hardly qualified to assess whether the Carmona et al. paper will withstand scrutiny from the experts or will end up as another in the very long list of ideas that didn't pan out.  So keep your eyes on the news.

It might be that we are about to turn the lights on in the dark sector for the first time ever.

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Science fiction enthusiasts will undoubtedly know the classic 1973 novel by Arthur C. Clarke, Rendezvous with Rama.  In this book, Earth astronomers pick up a rapidly approaching object entering the Solar System, and quickly figure out that it's not a natural object but an alien spacecraft.  They put together a team to fly out to meet it as it zooms past -- and it turns out to be like nothing they've ever experienced.

Clarke was a master at creating alien, but completely consistent and believable, worlds, and here he also creates a mystery -- because just as if we really were to find an alien spacecraft, and had only a limited amount of time to study it as it crosses our path, we'd be left with as many questions as answers.  Rendezvous with Rama reads like a documentary -- in the middle of it, you could easily believe that Clarke was recounting a real rendezvous, not telling a story he'd made up.

In an interesting example of life imitating art, in 2017 astronomers at an observatory in Hawaii discovered an object heading our way fast enough that it has to have originated outside of our Solar System.  Called 'Oumuamua -- Hawaiian for "scout" -- it had an uncanny, if probably only superficial, resemblance to Clarke's Rama.  It is long and cylindrical, left no gas or dust plume (as a comet would), and appeared to be solid rather than a collection of rubble.  The weirdest thing to me was that backtracking its trajectory, it seems to have originated near the star Vega in the constellation Lyra -- the home of the superintelligent race that sent us a message in the fantastic movie Contact.

The strangeness of the object led some to speculate that it was the product of an extraterrestrial intelligence -- although in fairness, a team in 2019 gave their considered opinion that it wasn't, mostly because there was no sign of any kind of internal energy source or radio transmission coming from it.  A noted dissenter, though, is Harvard University Avi Loeb, who has laid out his case for 'Oumuamua's alien technological origin in his new book Extraterrestrial: The First Sign of Intelligent Life Beyond Earth.

His credentials are certainly unimpeachable, but his book is sure to create more controversy surrounding this odd visitor to the Solar System.  I won't say he convinced me -- I still tend to side with the 2019 team's conclusions, if for no other reason Carl Sagan's "Extraordinary Claims Require Extraordinary Evidence" rule-of-thumb -- but he makes a fascinating case for the defense.  If you are interested in astronomy, and especially in the question of whether we're alone in the universe, check out Loeb's book -- and let me know what you think.

[Note: if you purchase this book using the image/link below, part of the proceeds go to support Skeptophilia!]