The cracked mirror

Why is there something rather than nothing?

It's the Mother of All Existential Questions, and has been batted around for as long as there've been philosophers there to ask it.  Some attribute the universe's something-ness to God, or some other uncreated Creator; predictably, this doesn't satisfy everyone, and others have looked for a more scientific explanation of why a universe filled with stuff somehow took precedence over one that was completely empty.

Probably the most thought-provoking scientific answer to the "something versus nothing" debate I came across in Jim Holt's intriguing book Why Does the World Exist?, in which he interviews dozens of scientists, philosophers, and deep thinkers about how they explain the plenitude of our own universe.  You've probably run across the Heisenberg Uncertainty Principle -- the bizarre, but extensively tested, rule that in the quantum realm there are pairs of measurable quantities called canonically conjugate variables that cannot be measured to a high degree of precision at the same time.  The best-known pair of canonically conjugate variables is position and momentum; the more accurately you know a particle's position, the less you can even theoretically know about its momentum, and vice-versa.  And this is not just a problem with our measuring devices -- that balance between exactitude and fuzziness is built into the fabric of the universe.

A less widely-known pair that exists in the same relationship is energy and time duration.  If you know the energy content of a region of space to an extremely high degree of accuracy, the time during which that energy measurement can apply is correspondingly extremely short.

The question Holt asks is: what would happen if you had a universe with nothing in it -- no matter, no energy, no fields, nothing?

Well, that would mean that you know its energy content exactly (zero), and the time duration over which that zero-energy state applies (infinitely long).  And according to Heisenberg, those two things can't be true at the same time.

The upshot: nothingness is unstable.  It's like a ball balanced at the top of a steep hill; a tiny nudge is all it takes to change its state.  If there had been a moment when the universe was completely Without Form And Void (to borrow a phrase), the Uncertainty Principle predicts that the emptiness would very quickly decay into a more stable state -- i.e., one filled with stuff.

There's another layer to this question, however, which has to do not with why there's something rather than nothing, but why the "something" includes matter at all.  I'm sure you know that for every subatomic particle, there is an antimatter version; one whose properties such as charge and spin are equal and opposite.  And every Star Trek fan knows that if matter and antimatter come into contact with each other, they mutually annihilate, with all of that mass turned into energy according to Einstein's famous mass/energy equation.

[Image licensed under the Creative Commons Dirk Hünniger, Joel Holdsworth, ElectronPositronAnnihilation, CC BY-SA 3.0]

[Nota bene: don't be thrown off by the fact that the arrows on the electrons and positrons appear to indicate one is moving toward, and the other away from, their collision point.  On a Feynman diagram -- of which the above is an example -- the horizontal axis is time, not position.  Matter and antimatter have all of their properties reversed, including motion through time; an electron moving forward through time is equivalent to a positron moving backward through time.  Thus the seemingly odd orientation of the arrows.]

More relevant to our discussion, note in the above diagram, the photon produced by the electron/positron pair annihilation (the wavy line labeled γ) is also capable of producing another electron/positron pair; the reaction works both ways.  Matter and antimatter can collide and produce energy; the photons' energy can be converted back to matter and antimatter.

But here's where it gets interesting.  Because of charge and spin conservation, the matter and antimatter should always be produced in exactly equal amounts.  So if the universe did begin with an unstable state of nothingness decaying into a rapidly-expanding cloud of matter, antimatter, and energy, why hasn't all of the matter and antimatter mutually annihilated by now?

Why isn't the universe -- if not nothing, simply space filled only with photons?

One possible answer was that perhaps some of what we see when we look out into space is antimatter; that there are antimatter worlds and galaxies.  Since antimatter's chemical properties are identical to matter's, we wouldn't be able to tell if a star was made of antimatter by its spectroscopic signature.  The only way to tell would be to go there, at which point you and your spaceship (and a corresponding chunk of the antimatter planet) would explode in a burst of gamma rays, which would be a hell of a way to confirm a discovery.

But there's a pretty good argument that everything we see is matter, not antimatter.  Suppose some galaxy was made entirely of antimatter.  Well, between that galaxy and the next (matter) galaxy would be a region where the antimatter and matter blown away from their respective sources would come into contact.  We'd see what amounts to a glowing wall between the two, where the mutual annihilation of the material would release gamma rays and x rays.  This has never been observed; the inference is that all of the astronomical objects we're seeing are made of ordinary matter.

I'm pretty sure the two would not connected by a weird, foggy celestial bridge, either.

So at the creation of the universe, there must have been a slight excess of matter particles produced, so when all the mutual annihilation was done, some matter was left over.  That leftover matter is everything we see around us.  But why?  None of the current models suggest a reason why there should have been an imbalance, even a small one.

Well -- just possibly -- until now.  A press release from CERN a couple of weeks ago found that there is an asymmetry between matter and antimatter, something called a charge-parity violation, that indicates our previous understanding that matter and antimatter are perfect reversals might have to be revised.  And it's possible this slight crack in the mirror might explain why just after the Big Bang, matter prevailed over antimatter.

“The more systems in which we observe CP violations and the more precise the measurements are, the more opportunities we have to test the Standard Model and to look for physics beyond it,” said Vincenzo Vagnoni, spokesperson for the Large Hadron Collider.  “The first ever observation of CP violation in a baryon decay paves the way for further theoretical and experimental investigations of the nature of CP violation, potentially offering new constraints for physics beyond the Standard Model.”

So that's our mind-blowing excursion into the quantum realm for today. A slight asymmetry in the world of the extremely small that may have far-reaching consequences for everything there is.  And -- perhaps -- explain the deepest question of them all; why the universe as we see it exists.

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The conservation conundrum

A major underpinning of our understanding of physics has to do with symmetry and conservation laws.

Both have to do with order, balance, and the concept that you can't get something for nothing.  A lot of the most basic research in theoretical physics is driven by the assumption that despite the seeming complexity and chaos in the universe, at its heart is a deep simplicity, harmony, and beauty. 

The mathematical expression of this concept reaches its pinnacle in the laws of conservation.

You undoubtedly ran into conservation laws in your high school science classes.  The law of the conservation of matter and energy (you can move matter and energy around and change its form, but the total amount stays the same).  Conservation of charge (the total charge present at the beginning of a reaction is equal to the total charge present at the end; this one is one of the fundamental rules governing chemistry).  Conservation of momentum, conservation of spin, conservation of parity.

All of these are fairly well understood, and physicists use them constantly to make predictions about how interactions in the real world will occur.  Add to them the mathematical models of quantum physics, and you have what might well be the single most precise system ever devised by human minds.  The predictions of this system match the actual experimental measurements to a staggering accuracy of ten decimal places.  (This is analogous to your taking a tape measure to figure out the length of a two-by-four, and your answer being correct to the nearest billionth of a meter.)

So far, so good.  But there's only one problem with this.

Symmetry and conservation laws provide no explanation of how there's something instead of nothing.

We know that photons (zero charge, zero mass) can produce pairs of particles -- one matter, one antimatter, which (by definition) have opposite charges.  These particles usually crash back together and mutually annihilate within a fraction of a second, resulting in a photon with the same energy as the original one had, as per the relevant conservation laws.  Immediately after the Big Bang, the universe (such as it was) was filled with extremely high energy photons, so this pair production was going at a furious rate, with such a roiling sea of particles flying about that some of them survived being annihilated.  This, it's thought, is the origin of the matter we see around us, the matter we and everything else are made of.

But what we know about symmetry and conservation suggests that there should have been exactly equal amounts of matter and antimatter created, so very quickly, there shouldn't have been anything left but photons.  Instead, we see an imbalance -- an asymmetry -- favoring matter.  Fortunately for us, of course.

So there was some matter left over after everything calmed down.  But why?

One possibility is that when we look out at the distant stars and galaxies, some of them are actually antimatter.  On the surface, it seems like there'd be no way to tell; except for the fact that every particle that makes it up would have the opposite properties (i.e. protons would have a negative charge, electrons a positive charge, and so on), antimatter would have identical properties to matter.  (In fact, experimentally-produced antihydrogen was shown in 2016 to have the same energy levels, and therefore exactly the same spectrum, as ordinary hydrogen.)  From a distance, therefore, it should look exactly like matter does.

So could there be antimatter planets, stars, and galaxies out there?  Maybe even with Evil Major Don West With A Beard?

The answer is almost certainly no.  The reason is that if there was a galaxy out there made of antimatter, then between it and the nearest ordinary matter galaxy, there'd be a boundary where the antimatter thrown off by the antimatter galaxy would be constantly running into the matter thrown off by the ordinary galaxy.  So we'd see a sheet dividing the two, radiating x-rays and gamma rays, where the matter and antimatter were colliding and mutually annihilating.  Nothing of the sort has ever been observed, so the conclusion is that what we see out in space, out to the farthest quasars, is all made of matter.

This, though, leaves us with the conundrum of how this happened.  What generated the asymmetry between matter and antimatter during the Big Bang?

One possibility, physicists thought, could be that the particles of matter themselves are asymmetrical.  If the shape or charge distribution of (say) an electron has a slight asymmetry, this would point to there being a hitherto-unknown asymmetry in the laws of physics that might favor matter over antimatter.  This conjecture is, in fact, why the topic comes up today; a paper last week in Science described an experiment at the University of Colorado - Boulder to measure an electron's dipole moment, the offset of charges within an electron.  Lots of molecules have a nonzero dipole moment; it's water's high dipole moment that results in water molecules having a positive end and a negative end, so they stick together like little magnets.  A lot of water's odd properties come from the fact that it's highly polar, including why it hurts like a sonofabitch when you do a belly flop off a diving board -- you're using your body to break simultaneously all of those linked molecules.

What the team did was to create a strong magnetic field around an extremely pure collection of hafnium fluoride molecules.  If electrons did have a nonzero dipole moment -- i.e., they were slightly egg-shaped -- the magnetic field would cause them to pivot so they were aligned with the field, and the resulting torque on the molecules would be measurable.

They found that to the limit of their considerable measuring ability, electrons are perfectly spherical and have an exactly zero dipole moment.

"I don’t think Guinness tracks this, but if they did, we’d have a new world record," said Tanya Roussy, who led the study.  "The new measurement is so precise that, if an electron were the size of Earth, any asymmetry in its shape would have to be on a scale smaller than an atom."

That's what I call accuracy.

On the other hand, it means we're back to the drawing board with respect to why there's something instead of nothing, which as a scientific question, is kind of a big deal.  At the moment, there don't seem to be any other particularly good candidates out there for an explanation, which is an uncomfortable position to be in.  Either there's something major we're missing in the laws of physics -- which, as I said, otherwise give stunningly accurate predictions of real-world experimental results -- or we're left with the even less satisfying answer of "it just happened that way."

But that's the wonderful thing about science, isn't it?  Scientists never write the last word on a subject and assume nothing will ever change thereafter.  There will always be new information, new perspectives, and new models, refining what we know and gradually aligning better and better with this weird, chaotic universe we live in.

So I'm not writing off the physicists yet.  They have a damn good track record of solving what appear to be intractable problems -- my guess is that sooner or later, they'll figure out the answer to this one.

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Figure and ground

One of the most fundamental unanswered questions in physics is why there is something instead of nothing.

I don't mean this in an existential sense, although now that I come to think of it, it's about the most existential question there is.  But this isn't asking if there is some sort of final cause for the universe, be it a Creator or whatever other spin you could put on it.  No, this is a purely scientific question, and one which has defied all attempts to answer it.

The basic problem stems from the issue of antimatter.  You probably know that for every particle, there is a corresponding antiparticle that has the same mass-energy but opposite properties -- protons and antiprotons, electrons and positrons (anti-electrons), neutrons and antineutrons, and so forth.  Brought into contact, matter and antimatter undergo mutual annihilation, and all of that mass is converted to gamma rays with an energy release as determined by Einstein's famous equation E = mc^2.

So far, nothing particularly surprising, especially if you've watched any of the various iterations of Star Trek, with their starships powered by an "antimatter core" brought into contact with matter in a controlled way and using the energy released to propel the ship.  (And, just about every other week, having a "warp core breach" leading to an uncontrolled matter-antimatter explosion, a catastrophe averted each time only minutes before the credits roll.)

Here's the rub, though.  All of the current models of the Big Bang suggest that at the beginning of the universe, matter and antimatter should have been created in equal amounts, like the energy equivalent of figure and ground.  They then should have collided, releasing the energy as photons, ultimately resulting in a universe that has zero matter of either kind except for the transient "virtual" particle pairs that are created from photons and more or less instantaneously come back together again, mutually annihilating and producing more photons.

Why, then, is there an imbalance?  Why do we see all this left-over matter -- the planets and stars around us -- instead of a universe filled with nothing but photons?  (Yes, I know, if that were the case we wouldn't be there to "see" it.  Just play along, okay?)

Some have suggested that distant galaxies might be antimatter; after all, at a distance you wouldn't be able to tell the difference.  But the problem with that is if this were true, there would be an interface somewhere between the supposed antimatter galaxy and the nearest matter galaxy, and at that interface there would be constant collisions of matter and antimatter -- so you'd see a sort of curtain of gamma-ray production representing the boundary.  We see no such thing anywhere we look.  From the observational data we have, it appears that all of the visible objects in the universe are made of ordinary matter.

Nota bene: Observational data also do not support that a planet made of antimatter would have identical people with opposite personalities, such as Evil Spock With A Beard.

So physicists surmised that if the processes during the Big Bang did produce equal amounts of matter and antimatter, perhaps the asymmetry came from the particles themselves -- i.e., the antimatter particles don't have exactly identical-but-opposite properties from their matter equivalents, but some small difference that made the matter particles either more numerous or more likely to survive.

Well, a paper last week in Nature appears to have ruled that out as well.

Researchers at CERN working on the Baryon-Antibaryon Symmetry Experiment (BASE) looked at the oscillations of a single antiproton trapped in a magnetic field, and compared those oscillations with the equivalent from an ordinary proton.  After taking data from over 24,000 of these pairs, they found that the measured properties of the two are absolutely identical -- to an accuracy of 1.6 billionths of a percent.

That pretty much settles it, I'd think.

However, this means the original question still stands.  What caused the imbalance?  Is there still a possibility that some of the most distant galaxies -- possibly ones on opposite side of the 330-million-light-year-wide Boötes Void -- might be made of antimatter?  It's possible, but we've seen nothing to support that as an explanation.  Or that there's a "multiverse" with equal numbers of matter and antimatter galaxies all "separated causally" (i.e., so far apart they can't even potentially interact), so the entire thing is balanced, but only on the biggest scales?  The problem with that is if they are causally separated, then they've never been in contact in such a way as to be able to interact or influence each other, so it's hard to imagine how they'd have been created by a single event at one space-time location.  Also, in such a model, it's not even theoretically possible to obtain any information about these supposed antimatter regions, because they're beyond the distance limit from which we could observe them.  This puts the issue outside of what is even potentially verifiable by observational data, so as a hypothesis -- to use Wolfgang Pauli's acerbic quote -- "it's not even wrong."

Which leaves one of the biggest puzzles in physics still unanswered.

But it's this kind of conundrum that drives science, and had pushed us toward understanding some of the deepest mysteries of the universe.  It might be frustrating, but that's the way research works.  As Richard Feynman put it, "I'd rather have questions that cannot be answered than answers that cannot be questioned."

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Like many people, I've always been interested in Roman history, and read such classics as Tacitus's Annals of Imperial Rome and Suetonius's The Twelve Caesars with a combination of fascination and horror.  (And an awareness that both authors were hardly unbiased observers.)  Fictionalized accounts such as Robert Graves's I, Claudius and Claudius the God further brought to life these figures from ancient history.

One thing that is striking about the accounts of the Roman Empire is how dangerous it was to be in power.  Very few of the emperors of Rome died peaceful deaths; a good many of them were murdered, often by their own family members.  Claudius, in fact, seems to have been poisoned by his fourth wife, Agrippina, mother of the infamous Nero.

It's always made me wonder what could possibly be so attractive about achieving power that comes with such an enormous risk.  This is the subject of Mary Beard's book Twelve Caesars: Images of Power from the Ancient World to the Modern, which considers the lives of autocrats past and present through the lens of the art they inspired -- whether flattering or deliberately unflattering.

It's a fascinating look at how the search for power has driven history, and the cost it exacted on both the powerful and their subjects.  If you're a history buff, put this interesting and provocative book on your to-read list.

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

Twinkle, twinkle, little antistar

It's a big mystery why anything exists.

I'm not just being philosophical, here.  According to the current most widely-accepted cosmological model, when the Big Bang occurred, matter and antimatter would have formed in equal quantities.  As anyone who has watched Star Trek knows, when matter and antimatter come into contact, they mutually annihilate and all of the mass therein is converted to a huge amount energy in the form of gamma rays, the exact quantity of which is determined by Einstein's law of E = mc^2.

So if we started out with equal amounts of matter and antimatter, why didn't it all eventually go kablooie, leaving a universe filled with nothing but gamma rays?  Why was there any matter left over?

The answer is: we don't know.  Some cosmologists and astrophysicists think that there may have been a slight asymmetry in favor of matter, driven by random quantum fluctuations early on, so while most of the matter and antimatter were destroyed by collisions, there was a little bit of matter left, and that's what's around today.  (And "a little bit" is honestly not an exaggeration; the vast majority of the universe is completely empty.  An average cubic meter of space is very unlikely to have much more than an atom or two in it.)

One question this sometimes brings up is whether the stars and galaxies we see in the night sky are matter; if, perhaps, some entire galaxies are made of antimatter, and there really are equal amounts of the two.  After all, antimatter is predicted to act exactly like matter except that its fundamental particles have the opposite charges -- its protons are negative, its electrons positive, and so forth.  So a planet entirely formed of antimatter would look (from a safe distance) exactly like an ordinary planet.

And just to throw this out there, an antiplanet wouldn't have copies of all of us except for having the opposite personalities, for example some people who are good guys being evil and/or having beards, as outlined in the highly scientific Lost in Space episode "The Antimatter Man:"

Nor would there be a creepy bridge between the two universes, covered with fog and backed by eerie music:

Which is a shame, because I always kinda liked that episode.

Considerations of evil Major Don West with a beard notwithstanding, here are two arguments why most physicists believe that the stars we see, even the most distant, are made of ordinary matter.  The first is that there is no known process that would have sorted out the matter from the antimatter early in the universe's life, leaving isolated clumps of each to form their respective stars and galaxies.  Secondly, if there were antistars and antigalaxies, then there'd be an interface between them and the nearest clump of ordinary stars and galaxies, and at that interface matter and antimatter would be constantly meeting and mutually annihilating.  This would produce a hell of a gamma ray source -- and we haven't seen anything out there that looks like a matter/antimatter interface (although I will return to this topic in a moment with an interesting caveat).

A paper last year found that the key to understanding why matter prevailed might lie in the mysterious "ghost particles" called neutrinos.  There are three kinds of neutrinos -- electron neutrinos, muon neutrinos and tau neutrinos -- and one curious property they have is that they oscillate, meaning they can convert from one type to another.  The rate at which they do this is predicted from current theories, and it's thought that antineutrinos do exactly the same thing at exactly the same rate.

The experiment described in the paper took place in Japan, and found that there is an unexpected asymmetry between neutrinos and antineutrinos.  Beams of muon neutrinos and muon antineutrinos were sent on a six-hundred-kilometer journey across Japan, and upon arriving at a detector, were analyzed to see how many had converted to one of the other two "flavors."  The surprising result was that the neutrinos had oscillated a lot more than predicted, and the antineutrinos a lot less -- something called a "CP (charge-parity) violation" that shows antimatter doesn't, in fact, behave exactly like matter.  This asymmetry could lie at the heart of why the balance tipped in favor of matter.

But now a new analysis of data from the Fermi Gamma-ray Space Telescope has thrown another monkey wrench into the works.  The study was undertaken because of a recent puzzling detection by an instrument on the International Space Station of nuclei of antihelium, which (if current models are correct) should be so rare in the vicinity of ordinary matter that they'd be entirely undetectable.  But what if the arguments against antistars and antigalaxies I described earlier aren't true, and there are such odd things out there?  Antistars would be undergoing fusion just like the Sun does, and producing antihelium (and other heavier antielements), which then would be shed from the surface just like our Sun sheds helium.  And some of it might arrive here, only to fall into one of our detectors.

But what about the whole gamma-rays-at-the-interface thing?  Turns out, the study in question, the subject of a paper last week in the journal Physical Review D, found that there are some suspicious gamma-ray sources out there.

Fourteen of them, in fact.

These gamma-ray sources are producing photons with an energy that's hard to explain from known sources of gamma rays -- pulsars and black holes, for example.  In fact, the energy of these gamma rays is perfectly consistent with the source being ordinary matter coming into contact with an antistar.

Curiouser and curiouser.

It doesn't eliminate the problem of why the universe is biased toward matter; even if these are antistars, their frequency in the universe suggests that only one in every 400,000 stars is an antistar.  So we still have the imbalance to explain.

But it's a strange and fascinating finding.  Astrophysicists are currently re-analyzing the data from every angle they can think of to try and account for the odd gamma-ray sources in any way other than it being evidence of antistars, so it may be that the whole thing will fizzle.  But for now, it's a tantalizing discovery.  It brings to mind the famous quote from J. B. S. Haldane -- "The universe is not only queerer than we imagine, it's queerer than we can imagine."

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When people think of mass extinctions, the one that usually comes to mind first is the Cretaceous-Tertiary Extinction of 66 million years ago, the one that wiped out all the non-avian dinosaurs and a good many species of other types.  It certainly was massive -- current estimates are that it killed between fifty and sixty percent of the species alive at the time -- but it was far from the biggest.

The largest mass extinction ever took place 251 million years ago, and it destroyed over ninety percent of life on Earth, taking out whole taxa and changing the direction of evolution permanently.  But what could cause a disaster on this scale?

In When Life Nearly Died: The Greatest Mass Extinction of All Time, University of Bristol paleontologist Michael Benton describes an event so catastrophic that it beggars the imagination.  Following researchers to outcrops of rock from the time of the extinction, he looks at what was lost -- trilobites, horn corals, sea scorpions, and blastoids (a starfish relative) vanished completely, but no group was without losses.  Even terrestrial vertebrates, who made it through the bottleneck and proceeded to kind of take over, had losses on the order of seventy percent.

He goes through the possible causes for the extinction, along with the evidence for each, along the way painting a terrifying picture of a world that very nearly became uninhabited.  It's a grim but fascinating story, and Benton's expertise and clarity of writing makes it a brilliant read.

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

The symmetrical universe

I try to avoid writing about topics I don't fully understand, because that's just too great an opportunity for my sticking my foot in my mouth (and having to write a retraction afterwards).  Because of this reluctance, and because I'm pretty up-front about it when I don't know something, I don't get caught out very often, and I'd like to keep it that way.

So I'm gonna put a disclaimer right here at the beginning of this post: today's topic is one I have only a shallow understanding of.  If you ask me for more information, I'm likely to give you a puzzled head tilt, the same look my dog gives me when I ask him questions he doesn't have a good answer to, like why he chewed up my magazine before I had a chance to read it.  And if you are an expert in this field, and I get some of the facts wrong, let me know so I can fix 'em.

Okay, that being said: have you heard of CPT symmetry?

The initials stand for "charge," "parity," and "time," and the idea goes something like this: if you take any physical process, and reverse the charges (replace particles with their antiparticles), reverse the parity (reverse everything left-to-right), and run time backwards, the two would be indistinguishable.  Such a mirror universe would proceed according to exactly the same physical laws as ours does.

(As far as I know, it would not generate the scientific result elucidated in the Lost in Space episode "The Antimatter Man," wherein the mirror universe had an evil Don West with a beard.)

Initially, physicists thought that there was also CP symmetry -- that processes needed only charge and parity reversal to maintain symmetry, but that was found to be false when CP violations were found, most notably the decay of the particle called a neutral kaon.  The fact that symmetry is not preserved with reversal of charge and parity is thought to be the key to why there were unequal amounts of matter and antimatter produced in the Big Bang.  Fortunately for us.  If the matter/antimatter ratio had been exactly 1:1, ultimately it would all have mutually annihilated, and the universe would now be devoid of matter -- just space filled with photons zinging merrily about.

So CPT symmetry and CP violations are apparently fundamental to the nature of matter.  Which is why physicists have been pushing on the CPT symmetry idea, trying to find out if it holds -- or if there are circumstances, as there were with CP symmetry, where CPT symmetry is not preserved.

The latest test, described in a paper this week in Nature Physics, finds that even one of the oddest particles ever created in a laboratory preserves CPT symmetry.  In "Measurement of the Mass Difference and the Binding Energy of the Hypertriton and Antihypertriton," written by a team of particle researchers at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory in Upton, New York, we read about bizarre particles that instead of the "up" and "down" quarks (and antiquarks) found in ordinary matter (and antimatter, if there's such a thing as "ordinary antimatter"), additionally have "strange" quarks (and antiquarks), which have higher mass and only form under extremely high energy conditions.  These particles -- the hypertritons and antihypertritons in the title -- have never had their masses calculated accurately before, and the theory is that if the masses are different, it would break CPT symmetry and require a huge rethinking of how matter works on the smallest scales.

The result?  Hypertritons and antihypertritons have exactly the same mass.  CPT symmetry -- the fact that a charge reversed, mirror-image, time-running-backwards universe would look exactly the same as ours -- is preserved.  "It is conceivable that a violation of this symmetry would have been hiding in this little corner of the universe and it would never have been discovered up to now," said study co-author Declan Keane of Kent State University.  "But CPT symmetry was upheld even in these high-energy conditions."

This discovery gives physicists a clue about what might be happening in some of the most extreme and hostile spots in the universe -- the interiors of neutron stars.  The heat and crushing pressure in the core of a neutron star is thought to have enough energy to produce strange quarks and antiquarks, and therefore if those quarks (and the particles made from them) broke CPT symmetry, it would be a lens into a place where the known laws of physics do not hold.

But the symmetrical models won out.  Also, the measured energy of the hypertriton and antihypertriton were higher than expected, which squares with known neutron star masses.  "The presence of hyperons would soften the matter inside neutron stars," said Morgane Fortin, of the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences in Warsaw.  "Softer neutron stars would more easily collapse into black holes, so neutron stars couldn’t become as massive.  That feature makes hyperons’ potential presence difficult to reconcile with the largest neutron stars seen in the cosmos — which range up to about two solar masses.  But the newly measured, larger binding energy of the hyperon helps keep alive the idea of a hyperon-filled center to neutron stars.  The result suggests that hyperons’ interactions with neutrons and protons are stronger than previously thought. That enhanced interaction means neutron stars with hyperons are stiffer and could reach higher masses.  So neutron stars may still have strange hearts."

Strange indeed.  Mirror universes, neutron stars, and symmetry preserved to the smallest scales and highest energies.  Amazingly cool stuff, even if (1) I don't understand it all that well, and (2) it doesn't involve evil Don West with a beard.

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This week's Skeptophilia book-of-the-week is brand new: Brian Greene's wonderful Until the End of Time.

Greene is that wonderful combination, a brilliant scientist and a lucid, gifted writer for the scientifically-inclined layperson.  He'd already knocked my socks off with his awesome The Elegant Universe and The Fabric of the Cosmos (the latter was made into an equally good four-part miniseries).

Greene doesn't shy away from difficult topics, tackling such subjects as relativity, quantum mechanics, and the nature of time.  Here, Greene takes on the biggest questions of all -- where the universe came from, how it has evolved and is evolving, and how it's going to end.

He begins with an observation that as a species, we're obsessed with the ideas of mortality and eternity, and -- likely unique amongst known animals -- spend a good part of our mental energy outside of "the now," pondering the arrow of time and what its implications are.  Greene takes a lens to this obsession from the standpoint of physics, looking at what we know and what we've inferred about the universe from its beginnings in the Big Bang to its ultimate silent demise in the "Heat Death" some billions or trillions of years in the future.

It's definitely a book that takes a wide focus, very likely the widest focus an author could take.  And in Greene's deft hands, it's a voyage through time you don't want to miss.

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

Unexpected asymmetry

The question "why are we here?" has vexed scientists and philosophers alike.

The philosophical answers to this are beyond the purview of this blog, and, frankly, beyond my expertise.  I've got a decent background in a lot of areas -- one of the unforeseen benefits of changing one's major over and over -- but philosophy is a subject on which I am unqualified to weigh in.

The scientific twist on this question, however, is equally thorny.  Why is there something rather than nothing?  The current model of the Big Bang Theory predicts with considerable certainty that when the universe formed, there should have been equal amounts of matter and antimatter.  The two are (in a physics sense) symmetrical; every property that matter has, with the exception of mass, antimatter has the opposite.  Positrons (anti-electrons) are positively charges; anti-protons are negative.

The rub is that if you look around the universe, you don't see antimatter.  At all.  Which is, on one level, unsurprising; when matter and antimatter meet, the result is mutual annihilation (and the release of tremendous energy, as per E = mc^2), as any aficionado of Star Trek knows.

In another way, however, this is puzzling.  If matter and antimatter were created in equal amounts during the Big Bang, in the intervening years it should all have mutually annihilated, leaving behind nothing but gamma rays.  If the symmetrical production of matter and antimatter is correct, then our universe should be devoid of anything but energy -- and we wouldn't be here to consider the question.

[image courtesy of NASA/JPL]

So physicists have been refining their techniques to study antimatter, to see if there's something to account for the imbalance.  Just three days ago, a paper appeared in the journal Nature, by Mostafa Ahmadi of the University of Liverpool et al., called, "Characterization of the 1S-2S Transition in Antihydrogen," in which the team created molecules of antihydrogen -- made of an antiproton and a positron -- to see if it exhibited different properties than ordinary hydrogen.  They did this by creating 90,000 antiprotons, mixing them with five million positrons, and allowing them to form atoms -- then trapping a small number of these in a "magnetic bottle."  (Remember that antimatter violently explodes if it comes into contact with ordinary matter.)

The outcome: antihydrogen seems to behave exactly like ordinary hydrogen.  It emits the same spectral lines (the particular property Ahmadi et al. were studying).  As Aylin Woodward wrote in LiveScience:

As expected, hydrogen and antihydrogen ­— matter and antimatter — behave identically. Now, we just know that they're identical at a measurement of parts per trillion.  However, [coauthor Stefan] Ulmer said the 2-parts-per-trillion measurement does not rule out the possibility that something is deviating between the two types of matter at an even greater level of precision that has thus far defied measurement. 

As for [coauthor Jeffrey] Hangst, he's less concerned with answering the question of why our universe of matter exists as it does without antimatter — what he calls "the elephant in the room."  Instead, he and his group want to focus on making even more precise measurements, and exploring how antimatter reacts with gravity.

The results of this study don't rule out one possibility -- which is that some distant galaxies may actually be composed of antimatter.  As the Ahmadi et al. study shows, it's increasingly unlikely we'd be able to tell that from a distance.  The spectral lines of antihydrogen in an "antisun" would look the same as those of hydrogen from an ordinary star, so there'd be no way to tell unless you went there (which would be unfortunate for you, because you'd explode in a burst of gamma rays).

Whether such an antimatter galaxy would have all of the same people in it, only the good guys would be evil and would have beards, is a matter of conjecture.

But if, as many scientists believe, there really is an imbalance between the amount of matter and antimatter -- if unequal amounts were created during the Big Bang, so during the mutual annihilation that followed, some ordinary matter was left over -- it points to some physics that we haven't even begun to understand.

Which is pretty exciting.  As I pointed out in yesterday's post, unanswered questions are the bread-and-butter of scientific research.  The team is hoping to have even more precise measurements made by the end of 2018, at which point CERN is shutting down for two years for upgrades.  As Jeffrey Hangst put it, "We have other tricks up our sleeve.  Stay tuned."

Which even Evil Spock would have approved of, I think.