Bounce

Today's post is about a pair of new scientific papers that have the potential to shake up the world of cosmology in a big way, but first, some background.

I'm sure you've all heard of dark energy, the mysterious energy that permeates the entire universe and acts as a repulsive force, propelling everything (including space itself) outward.  The most astonishing thing is that it appears to account for 68% of the matter/energy content of the universe.  (The equally mysterious, but entirely different, dark matter makes up another 27%, and all of the ordinary matter and energy -- the stuff we see and interact with on a daily basis -- only comprises 5%.)

Dark energy was proposed as an explanation for why the expansion of the universe appears to be speeding up.  Back when I took astronomy in college, I remember the professor explaining that the ultimate fate of the universe depended only on one thing -- the total amount of mass it contains.  Over a certain threshold, and its combined gravitational pull would be enough to compress it back into a "Big Crunch;" under that threshold, and it would continue to expand forever, albeit at a continuously slowing rate.  So it was a huge surprise when it was found out that (1) the universe's total mass seemed to be right around the balance point between those two scenarios, and yet (2) the expansion was dramatically speeding up.

So the cosmological constant -- the "fudge factor" Einstein threw in to his equations to generate a static universe, and which he later discarded -- seemed to be real, and positive.  In order to explain this, the cosmologists fell back on what amounts to a placeholder; "dark energy" ("dark" because it doesn't interact with ordinary matter at all, it just makes the space containing it expand).  So dark energy, they said, generates what appears to be a repulsive force.  Further, since the model seems to indicate that the quantity of dark energy is invariant -- however big space gets, there's the same amount of dark energy per cubic meter -- its relative effects (as compared to gravity and electromagnetism, for example) increase over time as the rest of matter and energy thins.  This resulted in the rather nightmarish scenario of our universe eventually ending when the repulsion from dark energy overwhelms every other force, ripping first chunks of matter apart, then molecules, then the atoms themselves.

The "Big Rip."

[Image is in the Public Domain courtesy of NASA]

I've always thought this sounded like a horrible fate, not that I'll be around to witness it.  This is not even a choice between T. S. Eliot's "bang" or "whimper;" it's like some third option that's the cosmological version of being run through a wood chipper.  But as I've observed before, the universe is under no compulsion to be so arranged as to make me happy, so I reluctantly accepted it.

Earlier this year, though, there was a bit of a shocker that may have given us some glimmer of hope that we're not headed to a "Big Rip."  DESI (the Dark Energy Spectroscopic Instrument) found evidence, which was later confirmed by two other observatories, that dark energy appears to be decreasing over time.  And now a pair of papers has come out showing that the decreasing strength of dark energy is consistent with a negative cosmological constant, and that value is exactly what's needed to make it jibe with a seemingly unrelated (and controversial) model from physics -- string theory.

(If you, like me, get lost in the first paragraph of an academic paper on physics, you'll get at least the gist of what's going on here from Sabine Hossenfelder's YouTube video on the topic.  If from there you want to jump to the papers themselves, have fun with that.)

The upshot is that dark energy might not be a cosmological constant at all; if it's changing, it's actually a field, and therefore associated with a particle.  And the particle that seems to align best with the data as we currently understand them is the axion, an ultra-light particle that is also a leading candidate for explaining dark matter!

So if these new papers are right -- and that's yet to be proven -- we may have a threefer going on here.  Weakening dark energy means that the cosmological constant isn't constant, and is actually negative, which bolsters string theory; and it suggests that axions are real, which may account for dark matter.

In science, the best ideas are always like this -- they bring together and explain lots of disparate pieces of evidence at the same time, often linking concepts no one even thought were related.  When Hess, Matthews, and Vine dreamed up plate tectonics in the 1960s, it explained not only why the continents seemed to fit together like puzzle pieces, but the presence and age of the Mid-Atlantic Ridge, the magnetometry readings on either side of it, the weird correspondences in the fossil record, and the configuration of the "Pacific Ring of Fire" (just to name a few).  Here, we have something that might simultaneously account for some of the biggest mysteries in cosmology and astrophysics.

A powerful claim, and like I said, yet to be conclusively supported.  But it does have that "wow, that explains a lot" characteristic that some of the boldest strokes of scientific genius have had.

And, as an added benefit, it seems to point to the effects of dark energy eventually going away entirely, meaning that the universe might well reverse course at some point and then collapse -- and, perhaps, bounce back in another Big Bang.  The cyclic universe idea, first described by the brilliant physicist Roger Penrose.  Which I find to be a much more congenial way for things to end.

So keep your eyes out for more on this topic.  Cosmologists will be working hard to find evidence to support this new contention -- and, of course, evidence that might discredit it.  It may be that it'll come to nothing.  But me?  I'm cheering for the bounce.

A fresh start might be just what this universe needs.

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Miracles and incredulity

I have a problem with how people use the word miracle.

The dictionary definition is "a surprising and welcome event that is not explicable by natural or scientific laws and is therefore considered to be the work of a divine agency."  So this would undoubtedly qualify:

The Miracle of St. Mark, by Jacopo Tintoretto (ca. 1548) [Image is in the Public Domain]

But other than claims of honest-to-goodness angels appearing and stopping someone from getting murdered, the occurrences people usually call miracles seem to fall into two categories:

1. Events that have a positive outcome where one can imagine all sorts of ways they could have gone very wrong.  An example is when I was driving down my road in the middle of winter, hit a patch of black ice, and spun out -- coming to rest in a five-meter-by-five-meter gravel patch without hitting anything, where other trajectories would have taken me into a creek, an embankment, or oncoming traffic.
2. Events that are big and impressive, and about which we don't understand the exact cause.

It's the second category that attracted the attention of one Michael Grosso, who writes over at the site Consciousness Unbound, in a post this week called "A Trio of Obvious Miracles."  I was intrigued to find out what Grosso thought qualified not only as miracles but as obvious ones, and I was a little let down to find out that they were (1) the Big Bang, (2) the appearance of life, and (3) the evolution of consciousness.

The problem with all three of these is a lack of information.  In the first case, we have a pretty good idea what happened shortly after the Big Bang -- and by "shortly after" I mean "more than 10^-35 seconds after" -- but no real idea what triggered the expansion itself, or what came before it.  (If "before the Big Bang" even has any meaning.  Stephen Hawking said the question was like asking "what is north of the North Pole?"  Roger Penrose, on the other hand, thinks that a cyclic universe is a real possibility, and there may be a way to detect the traces of iterations of previous universes left behind in our current one.  The question is, at present, still being hotly debated by cosmologists.)

As far as Grosso's second example -- the origins of life -- that's more in my wheelhouse.  The difficulty here is that even the biologists can't agree about what makes something "alive."  Freshman biology texts usually have a list of characteristics of life, which include:

• made of one or more cells
• shows high levels of organization
• capable of reproduction
• capable of growth
• has a limited life span
• responds to stimuli
• adapts through natural selection
• has some form of a genetic code
• has a metabolism/use of energy

Not only are there organisms that are clearly alive but break one or more rules (sterile hybrids are incapable of reproducing, bristlecone pines appear to have no upper bound on their life spans), there are others, such as viruses, that have a few of the characteristics (organization, reproduction, limited life span, adaptation, and genetic code) while lacking others (cells, growth, response, and independent metabolism).  We talk about something "killing viruses," but the jury's still out as to whether they were alive in the first place.  (Perhaps "inactivating" them would be more accurate.)  In any case, the search for some ineffable something that differentiates life from non-life, like Henri Bergson's élan vital, have been unsuccessful.

With the final example, consciousness, we're on even shakier ground.  Once again starting with the dictionary definition -- "an awareness of one's internal and/or external environment, allowing for introspection, imagination, and volition" -- it remains to be seen whether we're unique in having consciousness, or if it (like intelligence) exists on a spectrum.  I'd argue that my dogs are conscious, but are insects?  How about earthworms?  How about amoebas?  All of them have some awareness of their external world, as evidenced by their moving toward pleasant stimuli and away from unpleasant ones; but I doubt very much if amoebas think about it.  So is our much more complex experience of consciousness simply due to our large and highly-interconnected brains, which would suggest that consciousness arises from a purely physical substratum?  If so, would it be possible to emulate it in a machine?  Some people are arguing, from a Turing-esque "if you can't tell the difference, there is no difference" stance, that large language models such as ChatGPT are already showing signs of consciousness.  While I find that a little doubtful -- although admittedly, I'm no expert on the topic -- it seems like we're in the same boat with consciousness as we are with life; it's hard to argue about something when we can't even agree on what the definition is, especially when the characteristic in question seems not to exist on a binary, you've-got-it-or-you-don't basis.

In any case, the whole thing seems to boil down to an argument from incredulity -- "I can't explain this, so it must be a miracle."  Grosso writes:

I grant the astonishing character of the miraculous, and the rarity.  But in the parapsychological definition, the term refers to phenomena that are extraphysical; cannot be physically explained. But what is causing these deviations from physical reality?...  Of course, we generally don’t kneel in awe at the miraculous sunrise or shudder with wonder as we wolf a burger down our gullet.  We are in fact swamped by what in fact are obvious miracles, the whole of nature and life in its wild multiplicity.  But thanks to habit and routine our imagination of the marvelous is deadened.

Honestly, I'm not even all that convinced about the rarity of miracles.  He's picked three things that -- so far as we know -- only happened once, and from that deduced that they're miraculous.  I did a post here a couple of years ago about Littlewood's Law of Miracles (named after British mathematician John Edensor Littlewood), which uses some admittedly rather silly mathematical logic to demonstrate that we should, on average, expect a miracle to occur every other month or so.  So I'm not sure that our perception of something as unlikely (and therefore miraculous) means much. 

The thing is, we can't really deduce anything from a lack of information.  Myself, I'm more comfortable relying on science to elucidate what's going on; like the astronomer Pierre-Simon Laplace famously said to Napoleon when the latter asked why Laplace's book on celestial mechanics made no mention of God, "Je n'avais pas besoin de cette hypothèse-là" ("I have no need of that hypothesis.").  If you're claiming something is a miracle, you're saying it's outside the capacity of science to explain, and that seems to me to be very premature.

My stance is that in all three cases he cited, science hasn't explained them yet.  And that little word at the end is doing a lot of heavy lifting.

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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 man who listened to the sky

Arno Allan Penzias was born on the 26th of April, 1933, in Munich, Germany.  It was a fractious time for Germany, and downright dangerous for anyone of Jewish descent, which Penzias was; his grandparents had come from Poland and were prominent members of the Reichenbachstrasse Synagogue.  Fortunately for the family, his parents saw which way the wind was blowing and evacuated Arno and his brother Gunther to Britain as part of the Kindertransport Rescue Operation.  Their father and mother, Karl and Justine (Eisenreich) Penzias, were also able to get out before the borders closed, eventually making their way (as so many Jewish refugees did) to New York City, where they settled in the Garment District.

The younger Penzias had shown a fascination and aptitude for science at a young age, so his choice of a major was never really in doubt.  He went to City College of New York, graduating with a degree in physics in 1954 and ranking near the top of his class.  For a time after graduating he worked as a radar officer in the U. S. Army Signal Corps, but the pull of research drew him back into academia.  In 1962, he earned a Ph.D. in microwave physics from Columbia University, studying with the inventor of the maser, Charles Townes.

Penzias then got a job with Bell Labs in Holmdel, New Jersey, where he worked on developing receivers for the (then) brand-new field of microwave astronomy.  He teamed up with Robert Wilson, an American astronomer, to develop a six-meter-diameter horn reflector antenna with a seven-centimeter ultra-noise receiver, at that point by far the most sensitive microwave detector in the world.

And while using that antenna in 1964, he and Wilson discovered something extremely odd.

At a wavelength of 7.35 centimeters, corresponding to a temperature of around three degrees Kelvin, there was a strong microwave signal -- coming from everywhere.  It seemed to be absolutely uniform in intensity, and was present in the input no matter which direction they aimed the antenna.  It was so perplexing that Penzias and Wilson thought it was an artifact of some purely terrestrial cause -- at first, they thought it might be from pigeon poo on the antenna.  Even after ruling out whatever they could think of (and cleaning up after the pigeons), the signal was still there, a monotonous hiss coming from every spot in the sky.

Before publishing their findings, they started looking for possible explanations, and they found a profound one.  Almost twenty years earlier, physicists Ralph Alpher, Robert Herman, and Robert Dicke had predicted the presence of cosmic microwave background radiation, the relic left behind by the Big Bang.  If the Big Bang model was correct, the unimaginably intense electromagnetic radiation generated by the beginning of the universe would have, in the 13.8-odd billion years since, been "stretched out" by the expansion of the fabric of spacetime, increasing its wavelength and dropping into the microwave region of the spectrum.  Alpher, Herman, and Dicke had predicted that the relic radiation should be under twenty centimeters in wavelength, and should be isotropic -- coming from everywhere in space at a uniform intensity.

That's just what Penzias and Wilson had observed.

In July of 1965, they published their results in the Astrophysical Journal, and suddenly Penzias and Wilson found themselves famous.

Penzias and Wilson at the Holmdel Horn Antenna in June of 1962 [Image is in the Public Domain courtesy of NASA]

At the time, there were two competing theories in cosmology -- the Big Bang model and the Steady-State model.  The latter theorized that the universe was expanding (that much had been undeniable since the discovery of red shift and Hubble's Law) but that as space expanded, matter was continuously being created, so the universe had no fixed start point.  Steady-State was championed by some big names in cosmological research -- Hermann Bondi, Thomas Gold, and Fred Hoyle amongst them -- and trying to figure out a way to discern which was correct had become something of a battle royale in astronomical circles.

But now Penzias and Wilson had made an accidental discovery, coupled it with a pair of (at the time) obscure papers making predictions about the temperature and wavelength of background radiation, and in one fell swoop blew the Steady-State model out of the water.

In 1978 Penzias and Wilson were awarded the Nobel Prize for research that changed the way we see the universe.

Since then, the cosmic microwave background radiation has been studied in phenomenal detail, and we've learned a great deal more about it -- starting with the fact that it isn't perfectly isotropic.  There are tiny but significant irregularities in the temperature of the radiation, something that has yet to be fully explained.  But the majority of the implications of the discovery have stood firm for nearly seventy years; 13.8 billion years ago, spacetime started to expand, and everything we see around us -- all the matter and energy in the universe -- condensed out of that colossally powerful event.  And coming from everywhere in the sky, like a ghostly afterimage of an explosion, is the radiation left behind, stretched out so much that it is outside of the range of human vision, and can only be detected by a telescope tuned to the microwave region of the spectrum.

On Monday, the 22nd of January, 2024, Arno Penzias died at the venerable age of ninety.  The world has lost a brilliant and innovative thinker whose contributions to science are so profound they're hard even to estimate.  The boy who escaped Nazi Germany with his family in the nick of time grew up to be a man who listened to the sky, and in doing so forever altered our understanding of how the universe began.

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The greatest wall

Sometimes simple words can be the hardest to define accurately.

For example, in physics, what do we mean by the word structure?  The easiest way to conceptualize it is that it's a material object for which whatever force is holding it together outcompetes any other forces that might be involved.  For example, a brick could be considered a structure, because the chemical bonds in the fired clay are stronger than the forces trying to pull it apart.  The sand on a beach, however, doesn't form a single structure, because the forces between the sand grains aren't strong enough to hold them together against the power of the wind and water.

Simple enough, it'd seem, but once you get out into space, it gets a little more difficult.

In astronomy, a structure is something that is bound together by gravity so that on some scale, it acts as a single unit.  The Solar System is a cosmic structure; within it, the gravitational pull of the Sun overwhelms all other forces.  The Milky Way is a cosmic structure by the same definition.  But how big can you get and still call it a single structure?  The question gives astronomers fits, because (to abide by the definition) you have to show that the pieces of the structure are bound together in such a way that the mutual gravitational attraction is higher than the other forces they experience -- and given that a lot of these things are very far away, any such determination is bound to rest on some fairly thin ice.

The largest generally accepted cosmic structure is the Hercules-Corona Borealis Great Wall, a galactic filament that (from our perspective) is in the night sky in the Northern Hemisphere in spring and early summer.  It's ten billion light years in length -- making it a little over a tenth as long as the entire observable universe!

[Image licensed under the Creative Commons Pablo Carlos Budassi, Hercules-CoronaBorealisGreatWall, CC BY-SA 4.0]

In the above image, each one of the tiny dots of light is an entire galaxy containing billions of stars; the brighter blobs are galaxy clusters, each made up of millions of galaxies.

And the whole thing is bound together by gravity.

What's kind of overwhelming about this is that because there are these enormous cosmic structures, there are also gaps between them, called supervoids.  One of the largest is the Boötes Void.  This thing is 330 million light years across, and contains almost no matter at all; any given cubic meter of space inside the void might have a couple of hydrogen atoms, and that's about it.  To put it in perspective; if the Earth was sitting in the center of the Boötes Void, there wouldn't be a single star visible.  It wouldn't have been until the 1960s that we'd have had telescopes powerful enough to detect the nearest stars.

That, my friend, is a whole lot of nothing.

What's coolest about all this is where these structures (and the spaces between them) came from.  On the order of 10^-32 seconds (that's 0.00000000000000000000000000000001 seconds) after the Big Bang, the bizarre phenomenon of cosmic inflation had not only blown the universe up by an amount that beggars belief (estimates are that in that first fraction of a second, it expanded from the size of a proton to about the size of a galaxy), it also smoothed out any lumpy bits (what the cosmologists call anisotropies).  This is why the universe today is pretty smooth and homogeneous -- if you look out into space, you see on average the same number of galaxies no matter which way you look.

But there are some pretty damn big anisotropies, like the Hercules-Corona Borealis Great Wall and the Boötes Void.  So where did those come from?

The current model is that as inflation ended, an interaction between regular matter and dark matter triggered a shock wave through the plasma blob that at that point was the entire universe.  This shock wave -- a ripple, a pressure wave much like a sound wave propagating through the air -- pushed some bits of the regular matter closer together and pulled some bits apart, turning what had been a homogeneous plasma into a web of filaments, sheets... and voids.

These baryon acoustic oscillations, that occurred so soon after the Big Bang it's hard to even wrap my brain around a number that small, are why we now have cosmic structures millions, or billions, of light years across.

So that's our mindblowing science for today.  Gravitationally-linked structures that span one-tenth of the size of the observable universe, and spaces in between containing damn near nothing at all, all because of a ripple that passed through the universe when it was way under one second old.

If that doesn't make you realize that all of our trials and tribulations here on Earth are insignificant, nothing will.

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Here are the answers to the puzzles from yesterday's post.  If you haven't finished thinking about them on your own, scroll no further!

1.  The census taker puzzle

The first clue is that the product of the daughters' ages is equal to 36.  There are eight possible trios of numbers that multiply to 36: (1, 1, 36), (1, 2, 18), (1, 3, 12), (1, 4, 9), (1, 6, 6), (2, 2, 9), (2, 3, 6), and (3, 3, 4).  Clue #2 is that the ages sum to equal the house number across the street, so the next step is to figure out what the house number could be.  Respectively: 38, 21, 16, 14, 13, 13, 11, and 10.

The key here is that when the census taker looks at the house number across the street, he still can't figure it out.  So it can't be (1, 4, 9), for example -- because if it was, as soon as he saw that the house number was 14, he'd know that was the only possible answer.  The fact that even after seeing the house number, he still doesn't know the answer, means it has to be one of the two trios of numbers that sums to the same thing -- 13.  So it either has to be (1, 6, 6) or (2, 2, 9).

Then, clue #3 is that the man's oldest daughter has red hair.  In the first possibility, there is no oldest daughter -- the oldest children are twins.  So his daughters have to be a nine-year-old and a pair of two-year-old twins.

2.  The St. Ives riddle

The answer is one.  "As I was going to St. Ives..." -- it doesn't say a thing about where the other people he met were going, if anywhere.

3.  The bear

It's a white bear.  The only place on Earth you could walk a mile south, a mile east, and a mile north and end up back where you started is if your starting place was the North Pole.

4.  A curious sequence

The pattern is that it's the names of the single digit numbers in English, in alphabetical order.  So the next one in the sequence is 3.

5.  Classifying the letters

The letters are classified by their symmetry.  (The capital letters only, of course.)  Group 1 is symmetrical around a vertical line, Group 2 around a horizontal line, Group 3 is around either a horizontal or a vertical line, Group 4 has no line symmetry but is symmetrical through a 180-degree rotation around their central point, and Group 5 are asymmetrical.

6.  The light bulb puzzle

Turn on switch one, and leave it on.  Turn on switch two for ten minutes, then turn it off.  Leave switch three off.  Go up to the tenth floor.  The bulb operated by switch one will be on; the one operated by switch two will be dark, but hot; and the one operated by switch three will be dark and cold.

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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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The next phase

When I put on water for tea, something peculiar happens.

Of course, it happens for everyone, but a lot of people probably don't think about it.  For a while, the water quietly heats.  It undergoes convection -- the water in contact with the element at the bottom of the pot heats up, and since warmer water is less dense, it rises and displaces the cooler layers above.  So there's a bit of turbulence, but that's it.

Then, suddenly, a bit of the water at the bottom hits 100 C and vaporizes, forming bubbles.  Those bubbles rapidly rise, dispersing heat throughout the pot.  Very quickly afterward, the entire pot of water is at what cooks call "a rolling boil."

This quick shift from liquid to gas is called a phase transition.  The most interesting thing about phase transitions is that when they occur, what had been a smooth and gradual change in physical properties (like the density of the water in the teapot) undergoes an enormous, abrupt shift -- consider the difference in density between liquid water and water vapor.

The reason this comes up is that some physicists in Denmark and Sweden have proposed a phase transition mechanism to account for the evolution of the (very) early universe -- and that proposal may solve one of the most vexing questions in astrophysics today.

A little background.

As no doubt all of you know, the universe is expanding.  This fact, discovered through the work of astronomer Edwin Hubble and others, was based upon the observation that light from distant galaxies was significantly red-shifted, indicating that they were moving away from us.  More to the point, the farther away the galaxies were, the faster they are moving.  This suggested that some very long time in the past, all the matter and energy in the universe was compressed into a very small space.

Figuring out how long ago that was -- i.e., the age of the universe -- depends on knowing how fast that expansion is taking place.  This number is called the Hubble constant.

[Image licensed under the Creative Commons Munacas, Big-bang-universo-8--644x362, CC BY-SA 4.0]

This brings up an issue with any kind of scientific measurement, and that's the difference between precision and accuracy.  While we use those words pretty much interchangeably in common speech, to a scientist they aren't the same thing at all.  Precision in an instrument means that every time you use it to measure something, it gives you the same answer.  Accuracy, on the other hand, means that the value you get from one instrument agrees with the value you get from using some other method for measuring the same thing.  So if my car's odometer tells me, every time I drive to my nearby village for groceries, that the store is exactly eight hundred kilometers from my house, the odometer is highly precise -- but extremely inaccurate.

The problem with the Hubble constant is that there are two ways of measuring it.  One is using the aforementioned red shift; the other is using the cosmic microwave background radiation.  Those two methods, each taken independently, are extremely precise; they always give you the same answer.

But... the two answers don't agree.  (If you want a more detailed explanation of the problem, I wrote a piece on the disagreement over the value of the Hubble constant a couple of years ago.)

Hundreds of measurements and re-analyses have failed to reconcile the two, and the best minds of theoretical physics have been unable to figure out why. 

Perhaps... until now.

Martin Sloth and Florian Niedermann, of the University of Southern Denmark and the Nordic Institute for Theoretical Physics, respectively, just published a paper in Physics Letters B that proposes a new model for the early universe which makes the two different measurements agree perfectly -- a rate of 72 kilometers per second per megaparsec.  Their proposal, called New Dark Energy, suggests that very quickly after the Big Bang, the energy of the universe underwent an abrupt phase transition, a bit like the water in my teapot suddenly boiling.  At this point, these "bubbles" of rapidly dissipating energy drove apart the embryonic universe.

"If we trust the observations and calculations, we must accept that our current model of the universe cannot explain the data, and then we must improve the model," Sloth said.  "Not by discarding it and its success so far, but by elaborating on it and making it more detailed so that it can explain the new and better data.  It appears that a phase transition in the dark energy is the missing element in the current Standard Model to explain the differing measurements of the universe's expansion rate.  It could have lasted anything from an insanely short time -- perhaps just the time it takes two particles to collide -- to 300,000 years.  We don't know, but that is something we are working to find out...  If we assume that these methods are reliable -- and we think they are -- then maybe the methods are not the problem.  Maybe we need to look at the starting point, the basis, that we apply the methods to.  Maybe this basis is wrong."

It's this kind of paradigm shift in understanding -- itself a sort of phase transition -- that triggers great leaps forward in science.  To be fair, some of them fizzle.  Most of them, honestly.  But sometimes, there are visionary scientists who take previously unexplained knowledge and turn our view of the universe on its head, and those are the ones who revolutionize science.  Think of how Galileo and Copernicus (heliocentrism), Kepler (planetary motion), Darwin (biological evolution), Mendel (genetics), Einstein (relativity), de Broglie and Schrödinger (quantum physics), Watson, Crick, and Franklin (DNA), and Matthews and Vine (plate tectonics) changed our world.

Will Sloth and Niedermann join that list?  Way too early to know.  But just the fact that one shift in the fundamental assumptions about the early universe reconciled measurements that heretofore had stumped the best theoretical physicists is a hopeful sign.

Time will tell if this turns out to be the next phase in cosmology.

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Supernothing

The things that keeps astrophysicists up at night are the irritating little questions about the universe that are simple to ask, and wildly difficult to answer.

Of course, they probably like being kept up at night.  Part of the job, really.

In any case, one of the most curious is why the universe is almost isotropic, but not quite.  "Isotropic" means, basically, "the same everywhere you look."  You can pick out any point in the night sky, and the amount of matter and energy within that region should be the same as if you picked out somewhere else.  Now, there are local conglomerations of matter -- you're residing on one, and working your way up the size ladder, the Solar System and the Milky Way are both clumps with higher matter density than the surrounding regions -- but on the largest scales, you'd expect things to be evenly spread out.

When I first ran into the idea of the Big Bang as a teenager, this was one of the hardest things for me to grasp.  If there really was a giant explosion at the beginning of the universe, why can't we find out where that explosion occurred?  You'd expect high matter density in that direction, and low density at the antipodal spot in the sky.  In fact, you see no such thing.  But far from being an argument against the Big Bang, it's an argument in its favor.  I didn't understand why until I took an astronomy class in college, and the professor, Dr. Whitmire, explained it as follows:

Imagine you're on the surface of an enormous balloon, and the surface is covered with dots.  You're standing on one of the dots.  Then, someone inflates the balloon.  What do you see?  You see all the other dots moving away from you, and in every direction, there are just about equal numbers of dots.  It's isotropic -- similar densities and recession speeds no matter where you look.  It doesn't depend on your perspective; you didn't just happen to choose the one dot that was at the center of the expansion.  It would look the same if you were standing on any other dot.  The reason is that the dots aren't moving through space; the space itself -- the surface of the balloon -- is expanding, carrying the dots with it.

"So there is no center of the universe," Dr. Whitmire said.  "Or everywhere is the center.  It amounts to the same thing."

In the first milliseconds after the Big Bang, the expansion rate was so fast that it smoothed everything out, spreading matter and energy fairly uniformly (again, allowing for localized clumps to form, but even the clumps would be expected to have a uniform distribution, like chocolate chips in cookie dough).  When the cosmic microwave background radiation was discovered in 1965 by Arno Penzias and Robert Wilson, it was powerful evidence for the Big Bang Model, especially when they found that -- like matter -- the CMBR was isotropic: the same no matter where you looked.

Well, almost.  One of the annoying little questions I mentioned in the first paragraph is that the CMBR is nearly isotropic -- but there are "cold spots," which have a lower temperature than the surrounding regions.  I'm not talking about a big difference, here; the average temperature in interstellar space is 2.7 K (-270.5 C), and the largest of these cold spots -- the Eridanus Supervoid -- is 0.00007 K lower.  The difference was small enough that at first it was thought to  be a glitch in the equipment or some sort of error in the data, but repeated measurements by the Wilkinson Microwave Anisotropy Probe (WMAP) has found that it is, in fact, a real phenomenon.

[Image licensed under the Creative Commons Piquito veloz, Eridanus supervoid in celestial sphere, CC BY-SA 4.0]

The "Eridanus Supervoid" is a name for the universe's largest collection of nothing.  It's a region on the order of between 500 million and one billion light years in diameter, in which there is so little matter that if the Earth sat in the center of it, you wouldn't be able to see a single star in the night sky.  It wouldn't have been until the 1960s that we would have found out about the existence of stars and galaxies, at the point that there were telescopes powerful enough to see something that distant.

This empty spot is a bit of a bother to cosmologists.  During the "inflationary period" -- thought to be between 10 ^-36 and 10 ^-33 seconds after the Big Bang -- space was stretching so unimaginably fast that it smoothed out most of the local variability, rather like taking a crumpled-up bedsheet and having four people pull on the corners; most of the wrinkles and folds disappear.

So what caused the Eridanus Supervoid?  Are we left with, "Well, it just happened because it happened?"

A new study hasn't exactly answered the question, but has generated another piece of data -- and a partial explanation.  A paper in Monthly Notices of the Royal Astronomical Society describes research that uses information from WMAP and from the Dark Energy Survey to see what's different about that region of space, and they found something curious.  The mysterious and elusive "dark matter" -- a component of the universe that amounts to 27% of its detectable mass, and six times more than all the ordinary matter put together -- has as its sole observable characteristic its gravitational effects on the matter and space around it, and that's measurable even if you can't see it, because it bends the path of light passing through it.  (The "gravitational lensing effect.")  And the recent study found that the Eridanus Supervoid has way less dark matter than is normal for other regions in the universe.  As it expands, it becomes a sink for energy -- a photon crossing it is moving through successively more stretched-out space, and its energy drops, as does its frequency.  The photon, therefore, is red-shifted, not because its source is moving away from us, but because it's traveling through expanding space.

As study co-author Juan Garcia-Bellido, of the Institute for Theoretical Physics at the University of Madrid, explained:

Photons or particles of light enter into a void at a time before the void starts deepening, and leave after the void has become deeper.  This process means that there is a net energy loss in that journey; that’s called the Integrated Sachs-Wolfe effect.  When photons fall into a potential well, they gain energy, and when they come out of a potential well, they lose energy.  This is the gravitational redshift effect.

Then once the region became a little less dense than the surrounding areas, every photon that crossed through it dropped its temperature and energy density a little more.

This still doesn't explain where the original anisotropy came from; the current thought is that it was caused by random fluctuations on the quantum level when the universe was still smaller than a grain of sand.  At that scale and energy, quantum effects loom large, and any minor unevenness might get "locked in" to the pattern of the universe; after that the process described by Garcia-Bellido takes over and makes it bigger.

And 13.7 billion years later, we have a huge blob of space that is just about completely empty, and ridiculously cold.  The Eridanus Supernothing.

So that's our excursion into deep space for the day.  And some more data on one of those mysterious questions that have, thus far, defied all attempts to answer them.  I'm nowhere near an expert, but I'm still endlessly fascinated with these sorts of things -- even if all we've got at the moment are unsatisfying partial solutions.

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It's obvious to regular readers of Skeptophilia that I'm fascinated with geology and paleontology.  That's why this week's book-of-the-week is brand new: Thomas Halliday's Otherlands: A Journey Through Extinct Worlds.

Halliday takes us to sixteen different bygone worlds -- each one represented by a fossil site, from our ancestral australopithecenes in what is now Tanzania to the Precambrian Ediacaran seas, filled with animals that are nothing short of bizarre.  (One, in fact, is so weird-looking it was christened Hallucigenia.)  Halliday doesn't just tell us about the fossils, though; he recreates in words what the place would have looked like back when those animals and plants were alive, giving a rich perspective on just how much the Earth has changed over its history -- and how fragile the web of life is.

It's a beautiful and eye-opening book -- if you love thinking about prehistory, you need a copy of Otherlands.

[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!]