Up, down, round and round

I recall seeing a comic strip a while back making fun of one of the features of Star Trek that doesn't seem ridiculous until you think about it a little.  Have you noticed that whenever two starships are near each other -- whether it's the Enterprise and other Federation ships, or they're being threatened by the Romulans or Klingons or whatnot -- the ships are almost always oriented the same way?  The only time this is not the case is when the showrunner wanted to make it clear that the other ship was disabled and drifting.  Then it was shown at some odd angle relative to the Enterprise.  In the comic strip, it showed what it would look like if all the ships were at random orientations -- how ridiculous it appeared -- but really, isn't that what you'd expect?  In the Star Trek universe, each ship is supposed to come with its own artificial gravity, so within any ship, up is "toward the ceiling" and down is "toward the floor."  It wouldn't need to line up with any other ship's artificial gravity, so except for an occasional coincidence, they should all be at various angles.

In space, there's no preferred direction, no "up" or "down."  You always have to describe position relative to something else -- to the axis of the Earth's rotation, or the plane of the Solar System, or the plane of revolution of the Milky Way.  But even those aren't some kind of universal orientation; as I described in a recent post, the universe is largely isotropic (the same in every direction).  Just like the starships in Star Trek, there shouldn't be any preferred directionality.

Well, that's what we thought.

A new paper this week in the journal Monthly Notices of the Royal Astronomical Society describes a set of data from the James Webb Space Telescope that is absolutely astonishing.  Here's how the authors describe it:

JWST provides a view of the Universe never seen before, and specifically fine details of galaxies in deep space.  JWST Advanced Deep Extragalactic Survey (JADES) is a deep field survey, providing unprecedentedly detailed view of galaxies in the early Universe.  The field is also in relatively close proximity to the Galactic pole.  Analysis of spiral galaxies by their direction of rotation in JADES shows that the number of galaxies in that field that rotate in the opposite direction relative to the Milky Way galaxy is ∼50 per cent higher than the number of galaxies that rotate in the same direction relative to the Milky Way.  The analysis is done using a computer-aided quantitative method, but the difference is so extreme that it can be noticed and inspected even by the unaided human eye.  These observations are in excellent agreement with deep fields taken at around the same footprint by Hubble Space Telescope and JWST.

This adds a whole new twist (*rimshot*) to the horizon problem and the isotropy of the universe as a whole.  Not only do we have the issue that causally-disconnected regions of the cosmic microwave background radiation, that are too far apart to have ever influenced each other (something I describe more fully in the above-linked post), are way more similar in temperature than you'd expect -- now we have to figure out how causally-disconnected galaxies on opposite sides of the universe could possibly have ended up with correlated rotational axes.

The authors admit it's possible that this measurement is due to something about the Milky Way's own rotation that we're not compensating for in the data, but there's a more out-there explanation that the paper's authors are seriously considering.

"It is not clear what causes this to happen," said study co-author Lior Shamir, of Kansas State University, in an interview with Independent.  "[But] one explanation is that the universe was born rotating.  That explanation agrees with theories such as black hole cosmology, which postulates that the entire universe is the interior of a black hole."

Black holes are defined by three properties -- mass, electric charge, and... angular momentum.  That we're inside a rotating black hole would explain the anomaly JWST just observed.  Since -- at least as far as our current understanding goes -- anything inside a black hole's event horizon is forever inaccessible, perhaps this means that event horizons are boundaries between universes.  As bizarre as that sounds, there is nothing about what we know of the laws of physics and cosmology that rules that out.  Which would mean that...

... black holes are bigger on the inside.

The Doctor tried to tell us.

Of course, the more prosaic explanation -- that the data were somehow influenced by our own motion through space -- has yet to be decisively ruled out.  I can't help but feel, though, that if the authors thought that was likely, they (or their reviewers) would have suggested waiting and re-analyzing before publishing in a prestigious journal like MNRAS.  The greater likelihood is that this is a real signal, and if so, it's mighty odd.

As far as what it would mean if we found out we are inside a black hole, well -- I'm hardly qualified to weigh in.  It probably wouldn't affect our day-to-day life any.  After all, it's not like we were going to find a way out of the universe anyhow, much as recent events here on Earth have made many of us wish we could.  All I can say is stay alert for further developments, and keep looking up.

Whatever direction that actually is.

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Lost horizon

While our knowledge of the origin of the universe has grown tremendously in the past hundred years, there are still plenty of cosmological mysteries left to solve.

One of the most vexing is called the horizon problem.

It's one of those situations where at first, it seems like "where's the problem?"  Then you look into it a little more, and kind of go, "... oh."  The whole thing has to do with how fast a change can percolate through a system.  Amongst the (many) outcomes of the General Theory of Relativity, we are reasonably certain that the upper bound at which disturbances of any kind can propagate is the speed of light.

So if a change of some sort happens in region A, but it is so far away from region B that there hasn't been enough time for light to travel between the two, it is fundamentally impossible for that change to have any effect at all in region B.  Such regions are said to be causally disconnected.

So far, so good.  The thing is, though, there are plenty of sets of causally disconnected regions in the universe.  If at midnight in the middle of winter you were to aim a very powerful telescope straight up into the sky, the farthest objects you could see are on the order of ten billion light years away.  Do the same six months later, in midsummer, and you'd be looking at objects ten billion light years away in the other direction.  The distance between the two is therefore on the order of twenty billion light years (and this is ignoring the expansion of the universe, which makes the problem even worse).  Since the universe is only something like 13.8 billion years old, there hasn't been enough time for light to travel between the objects you saw in winter and those you saw in summer.

Therefore, they can't affect each other in any way.  Furthermore, they've always been causally disconnected, at least as far back as we have good information.  By our current models, they were already too far apart to communicate three hundred thousand years after the Big Bang, the point at which decoupling occurred and the 2.7 K cosmic microwave background radiation formed. 

Herein lies the problem.  The cosmic microwave background (CMB for short) is very nearly isotropic -- it's the same no matter which direction you look.  There are minor differences in the temperature, thought to be due to quantum fluctuations at the moment of decoupling, but those average out to something very close to uniformity.  It seems like some process homogenized it, a bit like stirring the cream into a cup of coffee.  But how could that happen, if opposite sides of the universe were already causally disconnected from each other at the point when it formed?

A map of the CMB from the Wilkinson Microwave Anisotrophy Probe [Image is in the Public Domain courtesy of NASA]

It's worse still, however, which I just found out about when I watched a video by the awesome physicist and science educator Sabine Hossenfelder a couple of days ago.  Because a 2003 paper found that the CMB isn't isotropic after all.

I'm not talking about the CMB dipole anisotropy -- the fact that one region of the sky has CMB a little warmer than average, and the opposite side of the sky a little cooler than average.  That much we understand pretty well.  The Milky Way Galaxy is itself moving through space, and that creates a blue shift on one side of the sky and a red shift on the other, accounting for the measurably warmer and cooler regions, respectively.

What Hossenfelder tells us about is that there's an anisotropy in the sizes of the warm and cool patches.  It's called the hemispherical power spectrum asymmetry, and simply put, if you sort out the sizes of the patches at different temperatures, you find that one side of the sky is "grainier" than the other.  Like I said, we've known about this since 2003, but there was nothing in any of the models that could account for this difference, so cosmologists kind of ignored the issue in the hopes that better data would make the problem go away.

It didn't.  A recent paper using newly-collected data from the Planck mission found that the hemispherical power spectrum asymmetry is real.

And we haven't the first idea what could have caused it.

In a way, of course, this is tremendously exciting.  A great many scientific discoveries have started with someone looking at something, frowning, and saying, "Okay, hang on a moment."  Here we have something we already didn't understand (CMB isotropy and the horizon problem) gaining an added layer of weirdness (it's not completely isotropic after all, but is anisotropic in a really strange way).  What this shows us is that our current models of the origins of the universe are still incomplete.

Looks like it's a good time to go into cosmology.  In what other field is there a universe-sized problem waiting to be solved?

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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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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!]

The unbalanced universe

In her brilliant 2011 TED Talk "On Being Wrong," journalist Kathryn Schulz said, "For good and for ill, we generate these incredible stories about the world around us, and then the world turns around and astonishes us."

That astonishment is at the root of scientific discovery.  Many laypeople have the sense that scientists do what they do by patiently adding data bit by bit, assembling a theory from the results of experiment -- less understood is the fact that much of the time, the experiments themselves happened because of something unexpected that the old model couldn't explain.  It's those moments of, "Hey, now, wait a moment..." that have generated some of the most fundamental theories we have -- universal gravitation, relativity (special and general), evolution, genetics, plate tectonics.

Or, as another luminary of the philosophy of science put it -- James Burke, in his brilliant documentary series The Day the Universe Changed -- "The so-called voyage of discovery has, as often as not, made landfall for reasons little to do with the search for knowledge...  As far as one discovery following another along the way as part of some grand plan, what way?  Going where?"

Now, this is not to say that the lazy student's complaint, "why should we learn science, since it could all be proven wrong tomorrow?", has much merit.  The big ideas, like the ones I listed before, have been so extensively tested that it's unlikely they'll change much.  Any refinements will most probably be on the level of details.  Still... those head-scratching moments do occur, and sometimes they result in an overturning of what we thought we understood -- like the observation that was announced this week from NASA's Chandra X-ray Observatory.

[Image courtesy of NASA/Harvard University/Chandra X-ray Observatory]

One of the basic pieces of the Big Bang theory is that it resulted in a universe that is isotropic -- it basically looks the same no matter which direction you're looking.  The idea here is that when the universe began to expand, the fabric of space/time stretched out so much in the first tiny fraction of a second (something called cosmological inflation) that it resulted in a uniform, isotropic universe.

The analogy that's been around a long time to explain this -- I remember my college astronomy teacher using it, back in the early 1980s -- is to picture yourself as a tiny person, standing on one dot of a deflated polka-dotted balloon.  If the balloon is inflated, you see all the other dots moving away from you, regardless of which dot you're standing on; and in every direction, the dot-density is pretty much the same.  "There is no center of the universe," I recall our professor, Dr. Daniel Whitmire, saying.  "Or, perhaps, everywhere is the center.  It means essentially the same thing."

So the idea of isotropy is pretty deeply built into the Big Bang cosmology.  So the observation from Chandra announced this week that the universe seems to be anisotropic was a little startling, to say the least.

"Based on our cluster observations we may have found differences in how fast the universe is expanding depending on which way we looked," said study co-author Gerrit Schellenberger of the Center for Astrophysics of Harvard University.  "This would contradict one of the most basic underlying assumptions we use in cosmology today."

Or, as Konstantinos Migkas of the University of Bonn in Germany, who led the new study, put it, "One of the pillars of cosmology... is that the universe is 'isotropic....'   Our work shows there may be cracks in that pillar."

It's possible that the measurement doesn't mean what it seems to mean.  One possibility the researchers came up with that would be less-than-earthshattering is that some of the distant clusters might be moving together because of the gravitational pull of an unseen massive object or objects, throwing off the data enough to make it look like an anisotropy.  Another possibility -- which in my mind raises more questions than it solves -- is that the hypothesized "dark energy" that makes up three-quarters of the energy density of the universe is unevenly distributed, meaning its repulsive force is greater in some places than in others.  "This would be like if the yeast in the bread isn't evenly mixed, causing it to expand faster in some places than in others," said study co-author Thomas Reiprich, also of the University of Bonn, adding, "It would be remarkable if dark energy were found to have different strengths in different parts of the universe."

Remarkable especially since we still basically have no idea what dark energy is.  Going from there to any kind of cogent explanation of why there's more of it here than there seems to me to be a significant leap.

Or, perhaps, none of those is correct, and the anisotropy was built-in at the moment of the Big Bang by some process we haven't even dreamed of.

Whatever it turns out to be, this seems to me to be one of those "wait a moment..." discoveries that could potentially lead to a major revision of what we thought we knew.  What's certain is that it demonstrates how far we have to go in science -- and despite our progress, to paraphrase Kathryn Schulz, the universe will time after time turn around and astonish us.

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This week's Skeptophilia book recommendation of the week is brand new -- only published three weeks ago.  Neil Shubin, who became famous for his wonderful book on human evolution Your Inner Fish, has a fantastic new book out -- Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA.

Shubin's lucid prose makes for fascinating reading, as he takes you down the four-billion-year path from the first simple cells to the biodiversity of the modern Earth, wrapping in not only what we've discovered from the fossil record but the most recent innovations in DNA analysis that demonstrate our common ancestry with every other life form on the planet.  It's a wonderful survey of our current state of knowledge of evolutionary science, and will engage both scientist and layperson alike.  Get Shubin's latest -- and fasten your seatbelts for a wild ride through time.