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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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!]

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.