Tense situation

In my Critical Thinking classes, I did a unit on statistics and data, and how you tell if a measurement is worth paying attention to.  One of the first things to consider, I told them, is whether a particular piece of data is accurate or merely precise -- two words that in common parlance are used interchangeably.

In science, they don't mean the same thing.  A piece of equipment is said to be precise if it gives you close to the same value every time.  Accuracy, though, is a higher standard; data are accurate if the values are not only close to each other when measured with the same equipment, but agree with data taken independently, using a different device or a different method.

A simple example is that if my bathroom scale tells me every day for a month that my mass is (to within one kilogram either way) 239 kilograms, it's highly precise, but very inaccurate.

This is why scientists always look for independent corroboration of their data.  It's not enough to keep getting the same numbers over and over; you've got to be certain those numbers actually reflect reality.

This all comes up because of a new look at one of the biggest scientific questions known -- the rate of expansion of the entire universe.

[Image is in the Public Domain, courtesy of NASA]

A while back, I wrote about some experiments that were allowing physicists to home in on the Hubble constant, a quantity that is a measure of how fast everything in the universe is flying apart.  And the news appeared to be good; from a range of between 50 and 500 kilometers per second per megaparsec, physicists had been able to narrow down the value of the Hubble constant to between 65.3 and 75.6.

The problem is, nobody's been able to get closer than that -- and in fact, recent measurements have widened, not narrowed, the gap.

There are two main ways to measure the Hubble constant.  The first is to use information like red shift, Cepheid variables (stars whose period of brightness oscillation varies predictably with their intrinsic brightness, making them a good "standard candle" to determine the distance to other galaxies), and type 1a supernovae to figure out how fast the galaxies we see are receding from each other.  The other is to use the cosmic microwave background radiation -- the leftovers from the radiation produced by the Big Bang -- to determine the age of the universe, and therefore, how fast it's expanding.

So this is a little like checking my bathroom scale by weighing myself on it, then comparing my weight as measured by the scale at the gym and seeing if I get the same answer.

And the problem is, the measurement of the Hubble constant by these two methods is increasingly looking like it's resulting in two irreconcilably different values.  

The genesis of the problem is that as our measurement ability has become more and more precise, the error bars associated with data collection have shrunk considerably.  And if the two measurements were not only precise, but also accurate, you would expect that our increasing precision would result in the two values getting closer and closer together.

Exactly the opposite has happened.

"Five years ago, no one in cosmology was really worried about the question of how fast the universe was expanding," said astrophysicist Daniel Mortlock of Imperial College London.  "We took it for granted.  Now we are having to do a great deal of head scratching – and a lot of research...  Everyone’s best bet was that the difference between the two estimates was just down to chance, and that the two values would converge as more and more measurements were taken. In fact, the opposite has occurred.  The discrepancy has become stronger.  The estimate of the Hubble constant that had the lower value has got a bit lower over the years and the one that was a bit higher has got even greater."

This discrepancy -- called the Hubble tension -- is one of the most vexing problems in astrophysics today.  Especially given that repeated analysis of both the methods used to determine the expansion rate have resulted in no apparent problem with either one.

The two possible solutions to this boil down to (1) our data are off, or (2) there's new physics we don't know about.  A new solution that falls into the first category was proposed last week at the annual meeting of the Royal Astronomical Society by Indranil Banik of the University of Portsmouth, who has been deeply involved in researching this puzzle.  It's possible, he said, that the problem is with one of our fundamental assumptions -- that the universe is both homogeneous and isotropic.

These two are like the ultimate extension of the Copernican principle, that the Earth (and the Solar System and the Milky Way) do not occupy a privileged position in space.  Homogeneity means that any randomly-chosen blob of space is equally likely to have stuff in it as any other; in other words, matter and energy are locally clumpy but universally spread out.  Isotropy means there's no difference dependent on direction; the universe looks pretty much the same no matter which direction you look.

What, Banik asks, if our mistake is in putting together the homogeneity principle with measurements of what the best-studied region of space is like -- the parts near us?

What if we live in a cosmic void -- a region of space with far less matter and energy than average?

We've known those regions exist for a while; in fact, regular readers might recall that a couple of years ago, I wrote a post about one of the biggest, the Boötes Void, which is so large and empty that if we lived right at the center of it, we wouldn't even have been able to see the nearest stars to us until the development of powerful telescopes in the 1960s.  Banik suggests that the void we're in isn't as dramatic as that, but that a twenty percent lower-than-average mass density in our vicinity could account for the discrepancy in the Hubble constant.

"A potential solution to [the Hubble tension] is that our galaxy is close to the center of a large, local void," Banik said.  "It would cause matter to be pulled by gravity towards the higher density exterior of the void, leading to the void becoming emptier with time.  As the void is emptying out, the velocity of objects away from us would be larger than if the void were not there.  This therefore gives the appearance of a faster local expansion rate...  The Hubble tension is largely a local phenomenon, with little evidence that the expansion rate disagrees with expectations in the standard cosmology further back in time.  So a local solution like a local void is a promising way to go about solving the problem."

It would also, he said, line up with data on baryon acoustic oscillations, the fossilized remnants of shock waves from the Big Bang, which account for some of the fine structure of the universe.

"These sound waves travelled for only a short while before becoming frozen in place once the universe cooled enough for neutral atoms to form," Banik said.  "They act as a standard ruler, whose angular size we can use to chart the cosmic expansion history.  A local void slightly distorts the relation between the BAO angular scale and the redshift, because the velocities induced by a local void and its gravitational effect slightly increase the redshift on top of that due to cosmic expansion.  By considering all available BAO measurements over the last twenty years, we showed that a void model is about one hundred million times more likely than a void-free model with parameters designed to fit the CMB observations taken by the Planck satellite, the so-called homogeneous Planck cosmology."

Which sounds pretty good.  I'm only a layperson, but this is the most optimistic I've heard an astrophysicist get on the topic.  Now, it falls back on the data -- showing that the mass/energy density in our local region of space really is significantly lower than average.  In other words, that the universe isn't homogeneous, at least not on those scales.

I'm sure the astrophysics world will be abuzz with this new proposal, so keep your eyes open for developments.  Me, I think it sounds reasonable.  Given recent events here on Earth, it's unsurprising the rest of the universe is rushing away from us.  I bet the aliens lock the doors on their spaceships as they fly by.

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A new field

I was fortunate enough that the day-job of my bandmate of many years, Kathy Selby, was working as a physicist at Cornell University.

As you might suspect, our conversations while traveling to gigs were pretty interesting.

One time we were on our way to play for a dance in Rochester, and I asked her what she thought about dark matter and dark energy -- which according to current models make up, respectively, 27% and 68% of the mass-energy content of the universe.  [Nota bene: the use of the word "dark" in both names does not mean that they are in any sense the same thing.  Dark matter is a name for the observation that the gravitational attraction of conventional matter is insufficient to account for the measured velocities of galaxies and galaxy clusters; there must be some other, unseen matter there that does not interact with ordinary matter electromagnetically, or else our model for gravity is incorrect.  Dark energy, on the other hand, is a theoretical energy inherent in space itself that might explain the accelerating expansion of the universe.]

So yes, only five percent of the universe is the regular stuff we see around us on a daily basis.  The other 95% is largely unexplained, and is yet to be detected directly.

In any case, I asked Kathy what her opinion was about the rather uncomfortable situation of having the vast majority of the universe thus far inaccessible to scientific study.

"In my opinion," she said, "we're in a situation a bit like physicists were in the late nineteenth century.  They knew light had strange properties.  It acted like a wave much of the time, so they'd postulated a medium -- the luminiferous aether -- through which the wave was propagating.  The problem was, every attempt to detect the aether failed.  Then Michelson and Morley came along and showed that the prediction of an 'aether drag' caused by the motion of the Earth through space didn't exist, suggesting very much that the aether didn't either.  The speed of light in a vacuum seemed to be the same in all reference frames, which was unlike any other wave ever studied.  Then Einstein said, 'Well, let's start by assuming that the speed of light in a vacuum is the same regardless of your reference frame, and see what happens,' and the aether became unnecessary.  Of course, what came out of that shift in perspective was the Theories of Relativity.

"What I think," she concluded, "is that we're waiting for this century's Einstein to tell us that we've been looking at everything the wrong way -- and suddenly the problems of dark matter and dark energy will evaporate, just like the aether did."

Well, we may have just gotten a glimpse at one possibility for that shift in perspective, courtesy of physicist Lucas Lombriser of the Université de Genève.

A paper published two weeks ago in the journal Classical and Quantum Gravity started by looking at what has been called "the worst prediction in physics" -- the value of the cosmological constant, which sets the expansion rate of the universe.  The prediction by theoretical physicists of what the cosmological constant should be given what we know about matter, and what we actually measure it to be, differ by 120 orders of magnitude -- that's 1 followed by 120 zeroes.

Oops.  Major oops.  This is what gave rise to the mysterious dark energy, some peculiar property of space itself that solves the mismatch.  But as far as what exactly this dark energy might be, physicists have come up empty-handed, so more and more it's seemed like a placeholder to cover up for the fact that we don't really understand what's going on.

This, Lombriser says, is because -- like with Einstein's solution to the aether -- we're starting out with the wrong assumption.

Maybe the universe is flat and static, as Einstein himself believed (after the discovery of red shift and the expansion of the universe, Einstein was forced unwillingly to accept an expanding universe and a cosmological constant -- which he later called "the greatest blunder of my career").  Perhaps space isn't expanding; it's the masses of particles that have changed over time.  The altered masses change the gravitational field that permeates space, and that's what generates red shift and the appearance of expansion.  So there is a cosmological constant, but it comes from the particles themselves, and the field in which they reside, evolving.

[Image licensed under the Creative Commons Original image by User:Vlad2i, slightly modified by User:mapos., Gravitational red-shifting2, CC BY-SA 3.0]

This new take solves three problems at once.  It does away with the cosmological constant mismatch; dark energy pretty much disappears completely; and the field itself that's responsible for the mass change could account for dark matter, as it shares many properties with an axion field, and axions are one of the leading candidates for the constituents of dark matter.  

This simultaneous solution of three vexing problems is certainly intriguing.  But the question is, is Lombriser right?  "The paper is pretty interesting, and it provides an unusual outcome for multiple problems in cosmology," said physicist Luz Ángela García, of the Universidad ECCI Bogotá, who was not involved in the research.  "The theory provides an outlet for the current tensions in cosmology.  However, we must be cautious.  Lombriser's solution contains elements in its theoretical model that likely can't be tested observationally, at least in the near future."

Which, of course, is the issue, and is all too common in this branch of science.  Even though Einstein's Theories of Relativity did a good job of accounting for various anomalies in the properties of light, the first precise confirmation of his predictions didn't occur until 39 years after he wrote his seminal paper in 1915.  How to detect the fluctuating field Lombriser postulates -- and, more importantly, how to distinguish its effects from the current model of expanding space -- is currently beyond us.

So maybe Lombriser is what my bandmate Kathy called "this century's Einstein."  Or maybe his ideas will prove to be just another unverified or (worse) unverifiable hypothesis.  But I have to say, when I read about what he's proposing, my ears did perk up.  It has the feel of a paradigm shift -- just what we've been waiting for.

And you can bet that the physicists are going to be all over this, looking for ways either to confirm or refute what he's saying.

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Behind the mirror

I know I've snarked before about the how unbearably goofy the old 1960s television show Lost in Space was, but I have to admit that every once in a (long) while, they nailed it.  And one of the best examples is the first-season episode "The Magic Mirror."

Well, mostly nailed it.  The subplot about how real girls care about makeup and hair and being pretty is more than a little cringe-inducing.  But the overarching story -- about mirrors being portals to a parallel world, and a boy who is trapped behind them because he has no reflection -- is brilliant.  And the other-side-of-the-mirror world he lives in is hauntingly surreal.

I was thinking about this episode because of a paper that appeared in Physical Review Letters last week entitled, "Symmetry of Cosmological Observables, a Mirror World Dark Sector, and the Hubble Constant," by Francis-Yan Cyr-Ravine, Fei Ge, and Lloyd Knox, of the University of New Mexico.  What this paper does is offer a possible solution to the Hubble constant problem -- that the rate of expansion of the universe as predicted by current mathematical models is significantly smaller than the actual measured expansion rate.

What Cyr-Racine, Ge, and Knox propose is that there is an unseen "mirror world" of particles that coexists alongside our own, interacting only through gravity but otherwise invisible to detection.  At first, I thought they might be talking about something like dark matter -- a form of matter that only (very) weakly interacts with ordinary matter -- but it turns out that what they're saying is even weirder.

"This discrepancy is one that many cosmologists have been trying to solve by changing our current cosmological model," Cyr-Racine told Science Daily.  "The challenge is to do so without ruining the agreement between standard model predictions and many other cosmological phenomena, such as the cosmic microwave background...  Basically, we point out that a lot of the observations we do in cosmology have an inherent symmetry under rescaling the universe as a whole.  This might provide a way to understand why there appears to be a discrepancy between different measurements of the universe's expansion rate.  In practice, this scaling symmetry could only be realized by including a mirror world in the model -- a parallel universe with new particles that are all copies of known particles.  The mirror world idea first arose in the 1990s but has not previously been recognized as a potential solution to the Hubble constant problem.  This might seem crazy at face value, but such mirror worlds have a large physics literature in a completely different context since they can help solve important problem in particle physics.  Our work allows us to link, for the first time, this large literature to an important problem in cosmology."

The word "important" is a bit of an understatement.  The Hubble constant problem is one of the biggest puzzles in physics; why theory and observation are so different on this one critical point, and how to fix the theory without blowing to smithereens everything that the theory does predict correctly.  "It went from two and a half Sigma, to three, and three and a half to four Sigma. By now, we are pretty much at the five-Sigma level," said Cyr-Racine.  "That's the key number which makes this a real problem because you have two measurements of the same thing, which if you have a consistent picture of the universe should just be completely consistent with each other, but they differ by a very statistically significant amount.  That's the premise here, and we've been thinking about what could be causing that and why are these measurements discrepant?  So that's a big problem for cosmology.  We just don't seem to understand what the universe is doing today."

I know that despite my background in science, I can have a pretty wild imagination.  It's an occupational hazard of being a speculative fiction writer.  I hear some new scientific finding, and immediately start putting some weird spin on it that, though it might be interesting, is completely unwarranted by the actual research.  But look at Cyr-Racine's own words: a parallel universe with new particles that are all copies of known particles.  I think I'm to be excused for thinking of "The Magic Mirror" and other science fiction stories about ghostly worlds coexisting, unseen, with our own.

I'm not going to pretend to understand the math behind the Cyr-Racine et al. paper; despite having a B.S. in physics, academic papers in the discipline usually lose me in the first paragraph (if not the abstract).  But it's a fascinating and spooky idea.  I doubt if what's going on has anything to do with surreal worlds behind mirrors and boys who are trapped because they have no reflection, but the reality -- if it bears up under analysis -- isn't a whole lot less weird.

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Weighty matter

Springboarding off yesterday's post, about a discovery of fossils that seem to have come from animals killed the day the Chicxulub Meteorite struck 66 million years ago, today we have a paper in arXiv that looks at why the meteorite hit in the first place.

When you're talking about an event that colossal, I suppose it's natural enough to cast about for a reason other than just shrugging and saying, "Shit happens."  But even allowing for that tendency, the solution landed upon by Leandros Perivolaropoulos, physicist at the University of Ioannina (Greece), seems pretty out there.

Perivolaropoulos attributes the meteorite strike to a sudden increase in Newton's gravitational constant, G -- the number that relates the ratio of the product of two masses and the square of the distance between them to the magnitude of the gravitational force:

The generally accepted value for G is 6.67430 x 10^-11 m^3 kg^-1 s^-2.  Being a constant, the assumption is that it's... constant.  And always has been.

Perivolaropoulos's hypothesis is that millions of years ago, there was a sudden jump in the value of G by about ten percent.  As you can tell from the above equation, if you keep the masses and the distance between them constant, F is directly proportional to G; if G increased by ten percent, so would the magnitude of the gravitational force.  His thought is that this spike in the attractive force caused the orbits of asteroids and comets to destabilize, and sent them hurtling in toward the inner Solar System.  The result: collisions that marked the violent, sudden end of the Mesozoic Era and the hegemony of the dinosaurs.

To be fair to Perivolaropoulos, his surmise is not just based on a single meteorite collision.  He claims that this increase in G could also resolve the "Hubble crisis" -- the fact that two different measures of the rate of the expansion of the universe generate different answers.  The first, using the cosmic microwave background radiation, comes up with a value of 67.8 kilometers/second/megaparsec; the second, from using "standard candles" like Cepheid variables and type 1A supernovas, comes up with 73.2.  (You can read an excellent summary of the dispute, and the current state of the research, here.)

[Image is in the Public Domain courtesy of NASA]

Perivolaropoulos says that his hypothesis takes care of both the Hubble crisis and the reason behind the end-Cretaceous meteorite collision in one fell swoop.

Okay, where to start?

There are a number of problems with this conjecture.  First -- what on earth (or off it) could cause a universe-wide alteration in one of the most fundamental physical constants?  Perivolaropoulos writes, "Physical mechanisms that could induce an ultra-late gravitational transition include a first order scalar tensor theory phase transition from an early false vacuum corresponding to the measured value of the cosmological constant to a new vacuum with lower or zero vacuum energy."  Put more simply, we're looking at a sudden phase shift in space/time, analogous to what happens when the temperature of water falls below 0 C and it suddenly begins to crystallize into ice.  But why?  What triggered it?

Second, if G did suddenly increase by ten percent, it would create some serious havoc in everything undergoing any sort of gravitational interaction.  I.e., everything.  Just to mention one example, the relationship between the mass of the Sun, the velocity of a planet, and the distance between the two is governed by the equation

 

So if the Earth (for example) experienced a sudden increase in the value of G, the radius of its orbit would (equally suddenly) decrease by ten percent.  Moving the Earth ten percent closer to the Sun would, of course, lead to an increase in temperature.  Oh, he says, but that actually happened; ten million years after the extinction of the dinosaurs we have the Paleocene-Eocene Thermal Maximum, when the temperatures went up by something like 7 C.  However, the PETM is sufficiently explained by a fast injection of five thousand gigatons of carbon dioxide into the atmosphere and oceans, likely triggered by massive volcanism in the North Atlantic Igneous Province -- and there's significant evidence of a carbon dioxide spike from stratigraphic evidence.  No need for the Earth to suddenly lurch closer to the Sun.

It wouldn't just affect orbits, of course.  Everything would suddenly weigh ten percent more.  It would take more energy to run, jump, even stand up.  Mountain building would slow down.  Anything in freefall -- from boulders in an avalanche to raindrops -- would accelerate faster.  Tidal fluctuations would decrease (although with the Moon now closer to the Earth, maybe that one would balance out).  

Also, if G did increase everywhere -- it's called the "universal gravitational constant," after all -- then the same thing would have happened simultaneously across the entire universe.  Then, for some reason, there was a commensurate decrease sometime between then and now, leveling G out at the value we now measure.  So we really need not one, but two, mysterious unexplained universal phase transitions, as if one weren't bad enough.

Then there's the issue that the discrepancy in the measurement in the Hubble constant isn't as big as all that -- it's only 3.4 sigma, not yet reaching the 5 sigma threshold that is the touchstone for results to be considered significant in (for example) particle physics.  Admittedly, 3.4 sigma isn't something we can simply ignore; it definitely deserves further research, and (hopefully) an explanation.  But explaining the Hubble constant measurement issue by appeal to an entirely different set of discrepant measurements that have way less experimental support seems like it's not solving anything, it's just moving the mystery onto even shakier ground.

Last, though, I come back to two of the fundamental rules of thumb in science; Ockham's razor (the explanation that adequately accounts for all the facts, and requires the fewest ad hoc assumptions, is most likely to be correct) and the ECREE principle (extraordinary claims require extraordinary evidence).  Perivolaropoulos's hypothesis not only blasts both of those to smithereens, it postulates a phenomenon that occurred once, millions of years ago, then mysteriously reversed itself, and along the way left behind no other significant evidence.

I hate to break out Wolfgang Pauli's acerbic quote again, but "This isn't even wrong."

Now, to be up front, I'm not a physicist.  I have a distantly-remembered B.S. in physics, which hardly qualifies me to evaluate an academic paper on the subject with anything like real rigor.  So if there are any physicists in the studio audience who disagree with my conclusions and want to weigh in, I'm happy to listen.  Maybe there's something going on here that favors Perivolaropoulos's hypothesis that I'm not seeing, and if so, I'll revise my understanding accordingly.

But until then, I think we have to mark the Hubble crisis as "unresolved" and the extinction of the dinosaurs as "really bad luck."

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In the dark

You've all heard of dark matter, the strange stuff that comprises 85% of the total matter in the universe and about a quarter of its overall mass-energy, and the nature of which -- although its presence has been shown in a variety of ways -- we're no nearer to understanding than we were when investigations of galactic rotation rates demonstrated its existence to astronomer Vera Rubin in 1978 (as I mentioned in yesterday's post).

Less well-known, and even more mysterious, is dark energy.  It's a little unfortunate the monikers of these two strange phenomena sound so similar, because dark energy is entirely different from dark matter (both obtained the sobriquet "dark" mainly because they've resisted all methods for direct detection, so we still have not a damn clue what they are).  Dark energy is a peculiar (hypothesized) form of energy that permeates all of space, and is responsible for the observation that the rate of expansion of the universe is accelerating.  Dark energy, whatever it is, acts on matter as if something were pushing it, working opposite to the pull of gravity that otherwise would cause the expansion to reverse eventually, ending the universe in a "Big Crunch."

Oh, and whatever it is, looks like it's common.  Measurements based on the expansion rate of the universe put estimates in the range of 68% of the total mass-energy of the universe.  So that places ordinary matter and energy -- the kind we are made of and interact with on a daily basis -- at a mere 7% of the stuff in the universe.

Kind of humbling, isn't it?  If the data are correct, 93% of the mass-energy of the universe is made up of stuff we can't detect and don't understand.

[Image licensed under the Creative Commons Design Alex Mittelmann, Coldcreation, Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation, CC BY-SA 3.0]

Well, maybe.  According to a press release two days ago from Yonsei University (Seoul, South Korea), scientists at the Center for Galaxy Evolution and Research are suggesting that the foundational assumption that led to the "discovery" of dark energy may simply be wrong.

I'm no astrophysicist, so I won't try to summarize the press release, but simply quote the salient paragraphs:

The most direct and strongest evidence for the accelerating universe with dark energy is provided by the distance measurements using type Ia supernovae (SN Ia) for the galaxies at high redshift.  This result is based on the assumption that the corrected luminosity of SN Ia through the empirical standardization would not evolve with redshift.

New observations and analysis made by a team of astronomers at Yonsei University (Seoul, South Korea), together with their collaborators at Lyon University and KASI, show, however, that this key assumption is most likely in error.  The team has performed very high-quality (signal-to-noise ratio ~175) spectroscopic observations to cover most of the reported nearby early-type host galaxies of SN Ia, from which they obtained the most direct and reliable measurements of population ages for these host galaxies.  They find a significant correlation between SN luminosity and stellar population age at a 99.5% confidence level.  As such, this is the most direct and stringent test ever made for the luminosity evolution of SN Ia.  Since SN progenitors in host galaxies are getting younger with redshift (look-back time), this result inevitably indicates a serious systematic bias with redshift in SN cosmology.  Taken at face values, the luminosity evolution of SN is significant enough to question the very existence of dark energy.  When the luminosity evolution of SN is properly taken into account, the team found that the evidence for the existence of dark energy simply goes away.

I don't know about you, but I read this with my mouth hanging open.  The idea that 68% of the mass-energy density of the universe could disappear if you alter the assumptions came as a bit of a shock.

It probably shouldn't have, of course, because this sort of thing has happened before.  There was phlogiston (the mysterious substance inherent in combustible matter) and the luminiferous aether (the mysterious substance through which light propagates in the vacuum of space), both of which turned out to be not so much mysterious as nonexistent.  Both of these vanished when the baseline assumptions changed -- in the first case, when a good theory of chemical energy was developed, and in the second when Einstein showed that light didn't act like an ordinary wave.

And honestly, even if I'm shocked by the way the dark energy scenario is playing out, I've been half expecting something like this to happen.  A physicist friend of mine was chatting with me one day about dark matter and dark energy (as one does), and she said that just like the aether stuck around until Einstein came and blew away the need for it by changing the perspective, the same would happen with the strange and undetectable dark matter and dark energy.

"We're just waiting for this century's Einstein," she said.

But it seems like it might not even require something as groundbreaking as a Theory of Relativity, here, at least in the case of dark energy.  All it might take is reevaluating the data on supernova luminosity to remove the need for the hypothesis.

Also would explain why we haven't detected it.

But this, like any scientific claim, is bound to be challenged, especially consider that it's nixing 68% of the universe in one fell swoop.  So keep your eyes on the physics journals -- I'm sure you haven't heard the last of this.

And you can count on the new research casting some light on the darkness -- whatever the ultimate outcome.

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This week's Skeptophilia book of the week is simultaneously one of the most dismal books I've ever read, and one of the funniest; Tom Phillips's wonderful Humans: A Brief History of How We Fucked It All Up.

I picked up a copy of it at the wonderful book store The Strand when I was in Manhattan last week, and finished it in three days flat (and I'm not a fast reader).  To illustrate why, here's a quick passage that'll give you a flavor of it:

Humans see patterns in the world, we can communicate this to other humans and we have the capacity to imagine futures that don't yet exist: how if we just changed this thing, then that thing would happen, and the world would be a slightly better place. 

The only trouble is... well, we're not terribly good at any of those things.  Any honest assessment of humanity's previous performance on those fronts reads like a particularly brutal annual review from a boss who hates you.  We imagine patterns where they don't exist.  Our communication skills are, uh, sometimes lacking.  And we have an extraordinarily poor track record of failing to realize that changing this thing will also lead to the other thing, and that even worse thing, and oh God no now this thing is happening how do we stop it.

Phillips's clear-eyed look at our own unfortunate history is kept from sinking under its own weight by a sparkling wit, calling our foibles into humorous focus but simultaneously sounding the call that "Okay, guys, it's time to pay attention."  Stupidity, they say, consists of doing the same thing over and over and expecting different results; Phillips's wonderful book points out how crucial that realization is -- and how we need to get up off our asses and, for god's sake, do something.

And you -- and everyone else -- should start by reading this book.

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

Rushing toward a paradigm shift

I have a sneaking suspicion that the physicists are on the threshold of a paradigm-breaking discovery.

The weird data have been building up for some time now, observations and measurements that are at odds with our current models of how the universe works.  I say "models (plural)" because one of the most persistent roadblocks in physics is the seeming incompatibility of quantum mechanics and general relativity -- in other words, coming up with a Grand Unified Theory that pulls a consistent explanation of gravity into our conceptual framework for the other three fundamental forces (electromagnetism and the weak and strong nuclear forces).  All attempts to come up with an amalgam have either "led to infinities" (had places in the relevant equations that generate infinite answers, usually an indicator that something is seriously wrong with your model) or have become so impossibly convoluted that even the experts can't agree on the details (such as string theory with its eleven spatial dimensions, something that's always reminded me of Ptolemy's flailing about to save the geocentric model by adding more loops and twists and epicycles so the data would fit).

And still the anomalous data keep rolling in.  Three weeks ago I wrote about a troubling discrepancy that's been discovered in the value of the Hubble Constant, which describes the rate of expansion of the universe -- there are two ways to measure it, which presumably should give the same answer, but don't.

Then last week, physicists at a lab in Hungary announced that they'd found new evidence of "X17," a mysterious particle that could be a carrier for a fifth fundamental force.  The argument is a bit like the observation that led to the discovery of the neutrino back in 1959 -- during beta radioactive decay, the particles emitted seemed to break the laws of conservation of energy and momentum, until that time strictly enforced in all jurisdictions.  Wolfgang Pauli said, basically, "Well, that can't be right," and postulated that an undetected particle was carrying off the "lost" momentum and energy.  It took twenty-eight years to prove, but he was right.

Here, it's the behavior another radioactive substance, beryllium-8, which emits light at the "wrong" angle to account for all of the energy involved (again, breaking the law of conservation of energy).  Conservation could be re-established if there was an undetected particle being emitted with a mass of 17 MeV (about 33 times the rest mass of an electron).  Even considering the neutrino, this seemed a little bit ad hoc -- "we need a particle, so we'll invent one to make our data fit" -- until measurements from an excited helium nucleus generated anomalous results that could be explained by a fifth force carried by a particle with exactly the same mass.

Hmm.  Curiouser and curiouser.

If that's not enough, just this week a paper appeared in Nature Astronomy about that elusive and mysterious substance "dark matter" that, despite defying every effort to detect it, outweighs the ordinary matter you and I are made of by a factor of five.  Its gravitational signature is everywhere, and appears to be most of what's responsible for holding galaxies together -- without it, the Milky Way and other rotating galaxies would fly apart.

But what is it?  No one knows.  There are guesses, but once again, those guesses have come up empty-handed with respect to any kind of experimental verification.  (And that's not even considering the even-weirder dark energy, which outweighs dark matter by a factor of two, and is thus the most common stuff in the universe, comprising 68% of what's out there -- even though we have not the slightest clue what it might be.)

The paper, by a team led by astrophysicist Qi Guo of the Chinese Academy of Sciences, is called, "Further Evidence for a Population of Dark-Matter-Deficient Dwarf Galaxies," and describes no less than nineteen different galaxies that have significantly less dark matter than conventional explanations (such as they are) would need to explain (1) how they formed, and (2) what's holding them together.  Lead author Guo, for her part, is baffled, and although the data seem solid, she admits to being at a bit of a loss.  "We are not sure why and how these galaxies form," she said, in a press release in Science News.

Elliptical galaxy Abell S740 [Image is in the Public Domain, courtesy of NASA]

So the anomalous observations keep piling up, and thus far, no one has been able to explain them, much less reconcile them with all the others.  I'm reminded of what Thomas Kuhn wrote, in his seminal book The Structure of Scientific Revolutions: "Scientific revolutions are inaugurated by a growing sense... that an existing paradigm has ceased to function adequately in the exploration of an aspect of nature to which that paradigm itself had previously led the way."

It must be both nerve-wracking and exhilarating to be a physicist right now.  Nerve-wracking because suddenly finding out that your previous model, the one you were taught to understand and cherish during your training, is inadequate -- well, the response is frequently to do what Irish science historian, writer, and filmmaker James Burke calls "scrambling about to stop the rug from being pulled out from under years of happy status-quo."  On the one hand, you can understand that, apart from any emotional attachment one might have to an accepted model; it is an accepted model because it worked perfectly well for a while, accounting for all the evidence we had.  And there are countless examples when a model was challenged by what appeared to be contradictory data, and it turned out the data were mismeasurements, misinterpretations, or outright fabrications.

Which is why Pauli was so sure that the neutrino existed -- the law of conservation of energy, he reasoned, was so well-supported that it just couldn't be wrong.

But now -- well, as I said, that data keep piling up.  Whatever's going on here, they aren't all mismeasurements.  It remains to be seen what revision of our understanding will sweep away all the oddities and internal contradictions and make sense of what the physicists are seeing, but I have no doubt we'll find it at some point.

And there's the exhilarating part of it.  What a time to be in research physics -- when the race is on to pull together and explain an increasingly huge body of anomalous stuff, and revise our understanding of the universe in a fundamental way.  It's the kind of climate in which Nobel Prizes are won.

Being an observer is exciting enough; I can't imagine what it might be like to be inside it all.

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Long-time readers of Skeptophilia have probably read enough of my rants about creationism and the other flavors of evolution-denial that they're sick unto death of the subject, but if you're up for one more excursion into this, I have a book that is a must-read.

British evolutionary biologist Richard Dawkins has made a name for himself both as an outspoken atheist and as a champion for the evolutionary model, and it is in this latter capacity that he wrote the brilliant The Greatest Show on Earth.  Here, he presents the evidence for evolution in lucid prose easily accessible to the layperson, and one by one demolishes the "arguments" (if you can dignify them by that name) that you find in places like the infamous Answers in Genesis.

If you're someone who wants more ammunition for your own defense of the topic, or you want to find out why the scientists believe all that stuff about natural selection, or you're a creationist yourself and (to your credit) want to find out what the other side is saying, this book is about the best introduction to the logic of the evolutionary model I've ever read.  My focus in biology was evolution and population genetics, so you'd think all this stuff would be old hat to me, but I found something new to savor on virtually every page.  I cannot recommend this book highly enough!

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

The problem with Hubble

In my Critical Thinking classes, I did a unit on statistics and data, and how you tell if a measurement is worth paying attention to.  One of the first things to consider, I told them, is whether a particular piece of data is accurate or merely precise -- two words that in common parlance are used interchangeably.

In science, they don't mean the same thing.  A piece of equipment is said to be precise if it gives you close to the same value every time.  Accuracy, though, is a higher standard; data are accurate if the values are not only close to each other when measured with the same equipment, but agree with data taken independently, using a different device or a different method.

A simple example is that if my bathroom scale tells me every day for a month that my mass is (to within one kilogram either way) 239 kilograms, it's highly precise, but very inaccurate.

This is why scientists always look for independent corroboration of their data.  It's not enough to keep getting the same numbers over and over; you've got to be certain those numbers actually reflect reality.

This all comes up because of some new information about one of the biggest scientific questions known -- the rate of expansion of the entire universe.

[Image is in the Public Domain, courtesy of NASA]

A few months ago, I wrote about some recent experiments that were allowing physicists to home in on the Hubble constant, a quantity that is a measure of how fast everything in the universe is flying apart.  And the news appeared to be good; from a range of between 50 and 500, physicists had been able to narrow down the value of the Hubble constant to between 65.3 and 75.6.

The problem is, nobody's been able to get closer than that -- and in fact, recent measurements have widened, not narrowed, the gap.

There are two main ways to measure the Hubble constant.  The first is to use information like red shift and Cepheid variables (stars whose period of brightness oscillation varies predictably with their intrinsic brightness, making them a good "standard candle" to determine the distance to other galaxies) to figure out how fast the galaxies we see are receding from each other.  The other is to use the cosmic microwave background radiation -- the leftovers from the radiation produced by the Big Bang -- to determine the age of the universe, and therefore, how fast it's expanding.

So this is a little like checking my bathroom scale by weighing myself on it, then comparing my weight as measured by the scale at the gym and seeing if I get the same answer.

And the problem is, the measurement of the Hubble constant by these two methods is increasingly looking like it's resulting in two irreconcilably different values.

The genesis of the problem is that our measurement ability has become more and more precise -- the error bars associated with data collection have shrunk considerably.  And if the two measurements were not only precise, but also accurate, you would expect that our increasing precision would result in the two values getting closer and closer together.

Exactly the opposite has happened.

"Five years ago, no one in cosmology was really worried about the question of how fast the universe was expanding.  We took it for granted," said astrophysicist Daniel Mortlock of Imperial College London.  "Now we are having to do a great deal of head scratching – and a lot of research...  Everyone’s best bet was that the difference between the two estimates was just down to chance, and that the two values would converge as more and more measurements were taken.  In fact, the opposite has occurred.  The discrepancy has become stronger.  The estimate of the Hubble constant that had the lower value has got a bit lower over the years and the one that was a bit higher has got even greater."

The discovery of dark matter and dark energy, the first by Vera Rubin, Kent Ford, and Ken Freeman in the 1970s, and the second by Adam Riess and Saul Perlmutter in the 1990s, accounted for the fact that the rate of expansion seemed wildly out of whack with the amount of observable matter in the universe.  The problem is, since the discovery of the effects of dark matter and dark energy, we haven't gotten any closer to finding out what they actually are.  Every attempt to directly detect either one has resulted in zero success.

Now, it appears that the problems run even deeper than that.

"Those two discoveries [dark matter and dark energy] were remarkable enough," said Riess.  "But now we are facing the fact there may be a third phenomenon that we had overlooked – though we haven’t really got a clue yet what it might be."

"The basic problem is that having two different figures for the Hubble constant measured from different perspectives would simply invalidate the cosmological model we made of the universe," Mortlock said.  "So we wouldn’t be able to say what the age of the universe was until we had put our physics right."

It sounds to me a lot like the situation in the late 1800s, when physicists were trying to determine the answer to a seemingly simple question -- in what medium do light waves propagate?  Every wave has to be moving through something; water waves come from regular motion of water molecules, sound waves from oscillation of air molecules, and so on.  With light waves, what was "waving?"

Because the answer most people accepted was, "something has to be waving even if we don't know what it is," scientists proposed a mysterious substance called the "aether" that permeated all of space, and was the medium through which light waves were propagating.  All attempts to directly detect the aether were failures, but this didn't discourage people from saying that it must be there, because otherwise, how would light move?

Then along came the brilliant (and quite simple -- in principle, anyhow) Michelson-Morley experiment, which proved beyond any doubt that the aether didn't exist.  Light traveling in a vacuum appeared to have a constant speed in all frames of reference, which is entirely unlike any other wave ever studied.  And it wasn't until Einstein came along and turned our entire understanding upside down with the Special Theory of Relativity that we saw the piece we'd been missing that made sense of all the weird data.

What we seem to be waiting for is this century's Einstein, who will explain the discrepancies in the measurements of the Hubble constant, and very likely account for the mysterious, undetectable dark matter and dark energy (which sound a lot like the aether, don't they?) at the same time.  But until then, we're left with a mystery that calls into question one of the most fundamental conclusions of modern physics -- the age of the universe.

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This week's Skeptophilia book recommendation is a fun book about math.

Bet that's a phrase you've hardly ever heard uttered.

Jordan Ellenberg's amazing How Not to Be Wrong: The Power of Mathematical Thinking looks at how critical it is for people to have a basic understanding and appreciation for math -- and how misunderstandings can lead to profound errors in decision-making.  Ellenberg takes us on a fantastic trip through dozens of disparate realms -- baseball, crime and punishment, politics, psychology, artificial languages, and social media, to name a few -- and how in each, a comprehension of math leads you to a deeper understanding of the world.

As he puts it: math is "an atomic-powered prosthesis that you attach to your common sense, vastly multiplying its reach and strength."  Which is certainly something that is drastically needed lately.

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