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 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!]