Strange places

In Kurt Vonnegut's novel Cat's Cradle, a scientist develops a polymorph of ice with a very strange property.

Unlike ordinary ice, that melts at temperatures above 0 C, the new form -- "ice-nine" -- melts at 45.8 C, above the temperature experienced anywhere but the hottest places on Earth's surface.  Even worse, a tiny bit of ice-nine acts as a seed crystal, converting any ordinary water it comes into contact with into more ice-nine.  Not only is it rapidly (nearly instantaneously) fatal if ingested, it is capable of wiping out all life on Earth if any is introduced into bodies of water.

While this is a science fiction scenario, there is some real science behind it.  Materials are stable when they are in a "potential well," a form that is the (locally) lowest energy state.  The situation changes, though, when something alters the energy required to overshoot the next highest "hill" in the thermodynamic landscape and allows whatever-it-is to achieve an even lower-energy, and thus more stable, state.

Something like this is what happens with prions, the misfolded bits of protein that are responsible for mad cow disease, Creutzfeldt-Jakob disorder, and other "spongiform encephalopathies."  The contagion occurs because the misfolded version of a protein called PrP is not only more stable than the one with the correct conformation, it triggers an ice-nine-like reaction when it comes into contact with normal PrP; a pair made up of one normal molecule of PrP and one misfolded one is intrinsically less stable than two abnormal ones, so it gradually converts the PrP in the brain into tangles of misfolded protein.

Not fatal as quickly as ice-nine, but still fatal.

This same idea crops up elsewhere.  You may have heard some talk about the possibility that the universe is in a "metastable state" -- a "false vacuum" that is, like ordinary water in Vonnegut's novel, only stable because it's in a local thermodynamic trough, but (given the right conditions) could be nudged up and over a hill into a much more stable state.  A "true vacuum."  If this happened, it would release so much energy that it would trigger neighboring regions into surmounting the hill and falling into the true vacuum state themselves, and on and on it would go, propagating outward at the speed of light and destroying everything in its wake.  The conversion would happen so quickly that if it swept past you and hit your feet first, the neural signal saying that your feet had been disintegrated wouldn't even have time to reach your brain before the rest of you disintegrated, too.  Which, honestly, wouldn't be a bad way to go.  No warning, not even the briefest moment of panic, just... poof.

There's one other example like this I know of, which comes from the realm of particle physics.  In 1950, a particle called the lambda baryon was discovered by a team at the University of Melbourne, and given its relatively high mass, it was unexpectedly stable -- decaying in one ten-trillionth of a second and not the predicted one hundred-sextillionth.  The team called this property strangeness, but it wasn't explained until 1968, when the quark model finally received experimental confirmation, and the lambda baryon was shown to be made of one up, one down, and one strange quark, an unusually stable configuration.

Its makeup exempts the lambda particle from the baryon version of the Pauli Exclusion Principle, which states that two or more particles with half-integer spins can't occupy the same quantum state.  And this is where things get interesting.

Initially, it was thought that all strange particles eventually decay into particles composed only of up and down quarks (the lambda can do this two different ways -- either into a proton and a negative pion, or into a neutron and a neutral pion).  They lose their "strangeness."  But the brilliant physicists Arnold Bodmer and Edward Witten have shown that this isn't always so -- that in larger assemblages of quarks, the most stable state is one with equal numbers of up, down, and strange quarks, which (like the lambda) would be immune to the Pauli Exclusion Principle, and thus could release energy by collapsing into (much) smaller volumes.

They called these assemblages strangelets.

And much like my previous examples, this release of energy could trigger the conversion of normal matter nearby into more strangelets, and the whole thing would spread.  It's been suggested that this might be the ultimate fate of any neutron star that continued to gain more mass.  The gravitational force would eventually rise to the point that the core would no longer have the capacity to support its own weight, and would release that energy in the most convenient way -- by converting to strange matter.

Like ice-nine, prions, and the true vacuum catastrophe, once that conversion happened, it'd be pretty much stuck that way.  There's no easy way out of the lowest local potential well.  In this case, though, the conversion would be limited to the neutron star; there'd be no mechanism for it to spread through the near-vacuum of space to the rest of the cosmos, which is good news for us.  It also bears mention that the hallmark of such "strange stars" suggested by Bodmer and Witten -- extremely high rotation rate, because of conservation of angular momentum as the strange matter at the core collapsed into a smaller volume -- has not been observed.

So it may well be that the Bodmer/Witten model for strange matter is flawed, and like the lambda baryon, anything containing strange quarks ultimately decays into ordinary matter.  Or conversely, perhaps some of the weird and unexplained behavior of astronomical objects is because they're strange, both in the technical and the vernacular sense of the word.

Either way, it's probably best if we stay right here in our nice, comfortable local well of stability.  None of the other options I've read about sound like all that much fun.

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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!]

Strange places

I remember when I took Quantum Physics as an undergraduate, many, many (many) years ago, my professor, Dr. John Matese, was fairly disparaging about the naming of the (then newly-discovered) quarks.  Up, down, top, bottom, strange, and charm, he said, were (1) misleading, because the names sound like they tell you something about the particle but don't, and (2) were cutesie, giving laypeople an impression of scientists as being "whimsical."

He said the last word in tones that left us in no doubt about his opinion of whimsy.

At least one of those names is apt, though, and that's "strange."  There's a hypothesis going around -- among serious physicists, I hasten to state, not among the whimsical -- that under sufficient pressure, matter can form which contains strange quarks.  (Ordinary matter is formed entirely of the two lightest-mass quarks, up and down.)  This "strange matter" has the property of being able to convert surrounding matter to strange matter, a little like "Ice-Nine" in Kurt Vonnegut's Cat's Cradle.  And if that's not weird enough, if a hypothesis pieced together from papers by A. R. Bodmer in 1971 and Edward Witten in 1984 is correct, it might be that the ordinary matter you see around us is the fluke; it's "metastable," meaning given the right conditions it could convert to the more stable strange matter, and our regular old atoms and molecules would condense into droplets...

... called "strangelets."

Speaking of cutesie names.

[Image licensed under the Creative Commons Brianzero, Quark wiki, CC BY-SA 3.0]

A paper published in the Journal of Astrophysics last week pushes the "strange matter hypothesis" a step further by suggesting that some of the astronomical objects we see may be strange, rather than ordinary, matter.  One possible place this stuff could live is the interior of neutron stars -- up till now thought to be extremely dense stuff, but the usual sort.  A team made up of physicists Abudushataer Kuerban, Jin-Jun Geng, Yong-Feng Huang, Hong-Shi Zong, and Hang Gong, of Nanjing University, has suggested that such bizarre matter may not just be confined to the cores of neutron stars -- it may be that there are whole planets of the stuff orbiting pulsars and even white dwarfs.

The authors write:

Since the true ground state of the hadrons may be strange quark matter (SQM), pulsars may actually be strange stars rather than neutron stars.  According to this SQM hypothesis, strange planets can also stably exist.  The density of normal matter planets can hardly be higher than 30 g cm−3. As a result, they will be tidally disrupted when its orbital radius is less than ∼5.6×10^10 cm, or when the orbital period (Porb) is less than ∼6100s.  On the contrary, a strange planet can safely survive even when it is very close to the host, due to its high density.  The feature can help us identify SQM objects.  In this study, we have tried to search for SQM objects among close-in exoplanets orbiting around pulsars. Encouragingly, it is found that four pulsar planets completely meet the criteria... and are thus good candidates for SQM planets.  The orbital periods of two other planets are only slightly higher than the criteria.  They could be regarded as potential candidates.  Additionally, we find that the periods of five white dwarf planets are less than 0.1 days.  We argue that they might also be SQM planets.  It is further found that the persistent gravitational wave emissions from at least three of these close-in planetary systems are detectable to LISA [the Laser Interferometer Space Antenna].  More encouragingly, the advanced LIGO [the Laser Interferometer Gravitational-Wave Observatory] and Einstein Telescope are able to detect the gravitational wave bursts produced by the merger events of such SQM planetary systems, which will provide a unique test for the SQM hypothesis.

 These planets would be, in a word, strange.  Their densities aren't just "high," as the authors state; they're "really fucking high."  (I realize that descriptor might not pass the editors for the Journal of Astrophysics, but I maintain that it's more accurate.)  For purposes of comparison, gold -- one of the densest familiar substances -- has a density of 19.3 grams per cubic centimeter.  The material making up a strange planet is predicted to be on the order of 400 trillion grams per cubic centimeter.

A planet with this density would have a gravitational pull so intense that taking one step up onto a hill a centimeter high would require more energy than leaping from sea level to the top of Mount Everest in one bound.

Suffice it to say that walking about on a strange planet would be pretty much out of the question.

Of course, the idea that the planets analyzed by Kuerban et al. are made of strange matter may not turn out to bear up under further scrutiny.  But the fact that it's even possible we've located some large chunks of such an exotic material is pretty fantastic.  Whether it pans out or no, I think we can all agree on one thing:

The universe is a very strange place.

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I am not someone who generally buys things impulsively after seeing online ads, so the targeted ad software that seems sometimes to be listening to our conversations is mostly lost on me.  But when I saw an ad for the new book by physicist James Trefil and astronomer Michael Summers, Imagined Life, it took me about five seconds to hit "purchase."

The book is about exobiology -- the possibility of life outside of Earth.  Trefil and Summers look at the conditions and events that led to life here on the home planet (after all, the only test case we have), then extrapolate to consider what life elsewhere might be like.  They look not only at "Goldilocks" worlds like our own -- so-called because they're "juuuuust right" in terms of temperature -- but ice worlds, gas giants, water worlds, and even "rogue planets" that are roaming around in the darkness of space without orbiting a star.  As far as the possible life forms, they imagine "life like us," "life not like us," and "life that's really not like us," always being careful to stay within the known laws of physics and chemistry to keep our imaginations in check and retain a touchstone for what's possible.

It's brilliant reading, designed for anyone with an interest in science, science fiction, or simply looking up at the night sky with astonishment.  It doesn't require any particular background in science, so don't worry about getting lost in the technical details.  Their lucid and entertaining prose will keep you reading -- and puzzling over what strange creatures might be out there looking at us from their own home worlds and wondering if there's any life down there on that little green-and-blue planet orbiting the Sun.

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