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 a while back 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 an 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 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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Off center

The Copernican principle is an idea from cosmology that can be summed up as "we're nothing special."

I'm sure you all know that there was a widespread belief prior to Nicolaus Copernicus's proposal of the heliocentric model that the Earth was at the center of the universe, with everything up to and including the stars traveling in perfect circles around us.  Part of this came from observation, given that the Sun and stars and all appear to be circling us; but a large part of this misapprehension was motivated by religion.  Not only was there at least some passing mentions in the Bible that suggested geocentrism was correct (such as "Sun, stand thou still over Gibeon" from Joshua chapter 10), it seemed that as the site of the Garden of Eden and the Incarnation and Crucifixion, of course God would put us at the center of the universe.

Then, along came Copernicus, followed by Galileo (who, upon discovering four of the moons of Jupiter, demonstrated that at least some celestial bodies didn't revolve around us), Kepler, and Tycho Brahe, the latter two of whom showed that astronomical objects don't even demonstrate heavenly perfection by traveling in circles, but move in "imperfect" ellipses.

Since then, we've been pushed farther and farther from the center of things.  In 1924 astronomer Edwin Hubble proved that not only was the Milky Way not the only galaxy, but many of the "nebulae" (the Latin word for "cloud," since prior to that there were no telescopes powerful enough to resolve individual stars in them) were "island universes" themselves, with the nearest -- Andromeda -- at an astonishing 2.5 million light years away.

Hubble also used the strange red shift of light from these distant objects to conjecture that the universe was expanding, the first step toward establishing the Big Bang model of the origin of the universe.  Oddly, though, almost everything Hubble looked at was red-shifted; it appeared that the whole universe was rushing away from us, as if we -- once again -- were at the center of things.  But a bit of three-dimensional geometry showed that this is exactly what we'd expect if space itself were expanding, carrying objects along with it.  No matter where you are, whether here on Earth or on a planet in the Whirlpool Galaxy over thirty million light years away, it looks like everything is moving away from you.

The Whirlpool Galaxy (Messier 51) [Image is in the Public Domain courtesy of NASA and the ESA]

Most of the data we have suggests that the universe is largely homogeneous (any given volume of space is likely to have on average the same amount of matter in it) and isotropic (every direction you aim your telescope looks approximately the same).  Not even the region of space we sit in is remarkable in any way.

The Copernican principle is sometimes called the principle of mediocrity; we don't occupy a privileged place in the cosmos.  And this same principle has cropped up elsewhere.  Genetics and evolution have shown us humans to be part of the Great Continuum of Life, just one branch of the extensive tree that includes all living things.  (And our nearest relatives, the great apes, share something like 98-99% of our genetic makeup.)  We may be the smartest animals -- although events of the last year have made me question that -- but animals we most certainly are.

And a lot of people really don't like this.  I'm not just talking about the creationists, who have a doctrine-based reason for disbelieving all of the above; but there's a certain brand of woo-woo that rebels against the Copernican principle just as hard, only in a different way.  And even if they come to different conclusions than the biblical literalists, I find myself wondering if they're not, at their cores, motivated by the same drive.

"We are too special, really we are!"

This attitude is best exemplified by one Alex Collier, who "claims to have worked in military service as a helicopter pilot in the United States" (the equivocal language was the article writer's, not mine).  I first ran into Collier fifteen years ago, when he said the Earth was being "bombarded by demonic hyperdimensional entities who have engineered our current space-time continuum," that an "extraterrestrial war" in the 1930s propelled us into the wrong timeline, and that NASA is covering up evidence that we're about to be attacked by the Borg Cube.  So Collier wasn't exactly a reliable witness even back then, but if anything, his grasp on reality has gone downhill in the intervening fifteen years.

Because he's back at it, even bigger and better.  Now, he's telling us that the human species was created in a lab by superpowerful aliens from the Andromeda Galaxy, who pulled together and melded the DNA from twenty-two diverse alien species to produce us.  (I guess the fact of our having a near-perfect genetic overlap with other primates here on Earth is just a strange coincidence.)  He also has some insights about what to expect now that this astonishing information has been revealed:

[A] “dimensional collapse” [has] already begun, marked by changes in sound and color.  [Collier] mentioned that people would soon start hearing about “rods” — streaks of light captured on video.  According to him, these were etheric, fourth- and fifth-dimensional craft moving through space, unaware that they were passing right through our dimension.  He explained this as a sign of an ongoing implosion between dimensions...

[M]ore ghosts and apparitions would become visible because souls trapped between the third and fourth densities would appear more frequently as Earth’s frequency rose.  Many of these souls, unless healed, would eventually transition out of this plane.

He also apparently said that we should "be cautious about anyone claiming to be an angel," which is good advice, but not for the reason he thinks.

What struck me about all this is not that some wingnut has a crazy idea -- after all, that's what wingnuts do -- but that this is really nothing more than a modern iteration of the "We are too special!" mental set that has been plaguing us pretty much forever.  A lot of pseudoscience works this way, doesn't it?  Astrology posits that the (apparent) arrangements and movements of astronomical bodies somehow shapes the courses of human lives.  Numerology suggests that the chance occurrence of patterns of numbers is because the universe is set up to send us information.  Even practices like Tarot divination presuppose that your own life's path is important enough to influence magically what comes up from shuffling and dealing a deck of cards.

I mean, I get that life (way) off-center is a little scary and disorienting sometimes.  Bill Watterson's brilliant Calvin & Hobbes captured it perfectly:

But I think it's better to relax into the awe of living in a vast, grand, only-partly-comprehensible cosmos than either succumbing to fear of our own insignificance or else resorting to making shit up to try, futilely, to shove us back toward the center of things.

It's enough that we have, against all odds, begun to take our first tentative steps into understanding how everything works.  That's all the self-aggrandizement I need as a human.  I'll end with the short but mind-blowing quote from Carl Sagan: "The cosmos is within us.  We are made of star-stuff.  We are a way for the universe to know itself."

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Notes on a supercluster

Today I'm going to focus on outer space, because if I don't I'll be forced to deal with events down here on Earth, and it's a little early to start drinking.

The James Webb Space Telescope just posted information on a structure called the Saraswati Supercluster,  which at a diameter of 650 million light years and a mass of twenty quadrillion times the mass of the Sun, is one of the largest gravitationally-bound structures known.  If you look toward the constellation Pisces, visible in the Northern Hemisphere from August to early January, you're staring right at the Saraswati Supercluster.

Not that you can see it with the naked eye.  Its center is about four billion light years away, meaning not only that it's extremely faint, the light from it has taken about a third of the age of the universe to get here, so it's really red-shifted.  Here's the rather mind-blowing image the JWST team just posted on their site:

[Image licensed under the Creative Commons Pablo Carlos Budassi, Extended universe logarithmic illustration (English annotated), CC BY-SA 4.0]

On this diagram, the Sun and Solar System are at the center, and as you move outward the scale increases exponentially, allowing us to visualize -- or at least imagine -- the astonishing vastness of the universe.  (Saraswati is just slightly to the left of top center on the diagram.)

The name of the supercluster is from a Sanskrit word meaning "ever-flowing stream with many pools," which is appropriate.  It's made of forty-three galaxy clusters -- not galaxies, mind you, but galaxy clusters -- of which the largest, Abell 2631, is thought to be made up of over a thousand galaxies (and something on the order of a hundred trillion stars).

If your mind is not boggling yet, you're made of sterner stuff than I am.

Because of its distance and faintness, we haven't known about Saraswati for all that long.  It was discovered in 2017 by a team of Indian astronomers led by Joydeep Bagchi from the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune, India, and since has been the object of intense study by astrophysicists for two main reasons.  First -- although it's phenomenally massive, its vast diameter makes it remarkable that it hangs together gravitationally.  (Remember that gravitational attraction falls off as the square of the distance; it never goes to zero, but it does get really weak.)  The fact that it does seem to be acting as a single structure could give us valuable information about the role of the elusive dark matter in making large objects stick together over time.

Second, it might provide some insight into solving another mystery, the question of how (or if) dark energy, the strange force that seems to be making the expansion of the universe speed up, is changing over time.  You may recall that just this past August, a pair of papers came out suggesting that the strength of this peculiar phenomenon might be decreasing; that instead of heading toward the rather ghastly prospect of a "Big Rip," where dark energy overpowers every other known force and tears matter apart into a soup of subatomic particles, the expansion might eventually stop or even reverse.  The old "oscillating universe" idea, that the universe goes through an endless series of expansions and collapses -- popularized by such brilliant luminaries of physics as Paul Steinhardt and Roger Penrose -- might have legs after all.  Studying Saraswati might give us more information about how the strength of dark energy has changed in the four-billion-odd years it's taken the light from the supercluster to arrive here.

So next time you look up into a clear night sky, think of what lies beyond the bit you can actually see.  Every individual star visible to the naked eye lives in a (relatively) tiny sphere in the Orion Arm of the Milky Way.  The few bits that visible but are farther away -- the smear of light that is all we can discern of the rest of our own galaxy, as well as the few other galaxies we can see without a telescope (like Andromeda and the two Magellanic Clouds) are so distant that individual stars can't be resolved without magnification.  What we think of as the impressive grandeur of the night sky is, basically, like thinking you're a world traveler because you drove around your own neighborhood once or twice.

But I guess I need to come back down to Earth.  Unfortunately.  On the whole, I'm much happier looking up.  It makes the current horror show we're living through at least seem a little less overwhelming, and puts our own place in the universe into perspective.

Maybe if our so-called leaders spent more time stargazing, it might provide them with some much-needed humility.

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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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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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Bang or whimper

I've always loved Robert Frost's razor-sharp poem, written in 1920, called "Fire and Ice":

Some say the world will end in fire,
Some say in ice.
From what I’ve tasted of desire
I hold with those who favor fire.
But if it had to perish twice,
I think I know enough of hate
To say that for destruction ice
Is also great
And would suffice.

How the world will end has fascinated people for as long as we've been able to think about the question.  Various mythologies created their own pictures of the universe's swan song -- the best-known of which is the Norse tale of Ragnarök, when the forces of good (the Æsir, Vanir, and their allies) teamed up against the forces of evil (the Jötnar, trolls, and various Bad Guys like Surtr, the trolls, Midgard's Serpent, Níðhöggr, and, of course, Loki).  Interestingly, in the Norse conception of things, good and evil were pretty evenly matched, and they more or less destroyed each other; only a few on either side survived, along with enough humans to repopulate the devastated world.

Once we started to take a more rational view of things, scientists naturally brought their knowledge to bear on the same question.  After figuring out about stellar mechanics, we've become fairly certain that the Earth will meet its end when the Sun runs out of hydrogen fuel, swells up into a red giant -- at which point it's likely the Earth's orbit will be inside the radius of the Sun -- then ultimately jettisons its outer atmosphere to become a white dwarf.  

But what about the universe as a whole?

When I was in school, just about everyone (well, just about everyone who understood science, anyhow) accepted that the universe had begun at the Big Bang.  The mechanism for what caused it, and what (if anything) had come before it, was unknown then and is still unknown now; but once it occurred, space expanded dramatically, carrying matter and energy with it, an outward motion that is still discernible in the red shift of distant galaxies.  But would that expansion go on forever?  I think the first time I ran into a considered answer to the question was in Carl Sagan's Cosmos, where he explained that the ultimate fate of the universe depended on its mass.  If the overall mass of the universe was above a particular quantity, its gravity would be sufficient to halt the expansion, ultimately sending everything hurtling backward into a "Big Crunch."  Below that critical quantity -- the expansion would slow continuously but would nevertheless keep going, spreading everything out until it was a uniform, thin, cold gas, a fate that goes by the cheery name "the Heat Death of the Universe."

But it turned out the picture wasn't even that simple.  In 1998, Adam Riess and others discovered the baffling fact that the universe wasn't slowing at all, so neither of the above scenarios seemed to be right.  Data from distant galaxies showed -- and it has since been confirmed over and over -- that the universe's expansion is accelerating.  The existence of a repulsive force powering the expansion was proposed, and nicknamed dark energy, but how that could possibly work was (and is) unknown.

Then they found out that dark energy comprises just shy of three-quarters of the universe's total mass-energy.  Physicists had a huge conundrum to explain.

[Image licensed under the Creative Commons NASA/ESA, SN1994D, CC BY 3.0]

It also led to another possibility for the universe's fate, and one that's even more dire than the Heat Death.  If the amount of dark energy per unit volume of space is constant -- which it appeared to be -- then the relative proportion of dark energy will increase over time, because conventional matter and energy is thinning out as space expands (and dark energy is not).  As this happens, the relative strength of the dark energy repulsion will eventually increase to the point that it overwhelms all other forces, including electromagnetism and the nuclear forces -- tearing matter up into a soup of fundamental particles.

The "Big Rip."

Confused yet?  Because the reason all this comes up is that there's just been another discovery, this one by DESI (the Dark Energy Spectroscopic Instrument) indicating fairly strongly that the force of dark energy has been decreasing over time.  I say "fairly strongly" because at the moment the data sets this is based on range from 2.8 to 4.2 sigma (this is an indicator of how strongly the data supports the claim; for reference, 3 sigma represents a 0.3% possibility that the data is a statistical fluke, and 5 sigma is considered the threshold for breaking out the champagne).  So it appears that although the quantity of dark energy per unit volume of space is constant, the strength of the dark energy force is less now than it was in the early universe.

So what does this mean about the fate of the universe?  Will it be, in Frost's terms, fire or ice?  A bang or a whimper?  We don't know.  The first thing is to figure out what the hell dark energy actually is, and how it works, and -- if the DESI results hold up -- why it seems to be diminishing.

All I can say is the cosmologists have a lot of explaining to do.

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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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Order out of chaos

When I was an undergraduate, I sang in the University of Louisiana Choir in a production of Franz Josef Haydn's spectacular choral work The Creation.

The opening is a quiet, eerie orchestral passage called "The Representation of Chaos" -- meant to evoke the unformed "void" that made up the universe prior to the moment of creation.  Then the Archangel Raphael sings, "In the beginning, God made Heaven and Earth; and the Earth was without form and void, and darkness was upon the face of the deep."  The chorus joins in -- everything still in a ghostly pianissimo -- "In the spirit, God moved upon the face of the waters; and God said, "Let there be light.  And... there... was...

...LIGHT!"

The last word is sung in a resounding, major-chord fortissimo, with the entire orchestra joining in -- trumpets blaring, tympanis booming, the works.  

Even if you don't buy the theology, it's a moment that sends chills up the spine.  (You can hear it yourself here.)

Of course, the conventional wisdom amongst the cosmologists has been that the universe didn't begin in some kind of chaotic, dark void; quite the opposite.  The Big Bang -- or at least, the moment after it -- is usually visualized as a searingly hot, dense fireball, which expanded and cooled, leading to a steady entropy increase.  So by our current models, we're heading toward chaos, not away from it.

Well, maybe.

A recent paper by the pioneering Portuguese physicist and cosmologist João Magueijo has proposed a new model for the origins of the universe that overturns that entire scenario -- and far from being ridiculed off the stage, he's captured the attention even of hard-nosed skeptics like Sabine Hossenfelder, who did a video on her YouTube channel about his paper a few days ago that is well worth watching in its entirety.  But the gist, as far as a layperson like myself can understand it, goes like this.

It's long been a mystery why the fundamental constants of physics have the values they do, and why they actually are constant.  A handful of numbers -- the speed of light, the strength of the electromagnetic interaction, the strength of the gravitational force, the fine-structure constant, and a few others -- govern the behavior of, well, pretty much everything.  None seem to be derivable from more fundamental principles; i.e., they appear to be arbitrary.  None have ever been observed to shift, regardless how far out in space (and therefore how far back in time) you look.  And what's curious is that most of them have values that are tightly constrained, at least from our perspective.  Even a percent or two change in either direction, and you'd have situations like stars burning out way too fast to host stable planetary systems, atoms themselves falling apart, or matter not generating sufficient gravity to clump together.

So to many, the universe has appeared "fine-tuned," as if some omnipotent deity had set the dials just right at the moment of creation of the universe to favor everything we see around us (including life).  This is called the anthropic principle -- the strong version implying a master fine-tuner, the weak version being the more-or-less tautological statement that if those numbers had been any different, we wouldn't be here to ask the question.

But that doesn't get us any closer to figuring out why the fundamental constants are what they are.  Never one to shy away from the Big Questions, that's exactly what Magueijo has undertaken -- and what he's come up with is, to put it mildly, intriguing.

What he did was to start from the assumption that the fundamental constants aren't... constant.  That In The Beginning (to stick with our original Book of Genesis metaphor), the universe was indeed chaos -- the constants could have had more or less any values.  The thing is, the constants aren't all independent of each other.  Just as numbers in our mundane life can push and pull on each other -- to give a simple example, if you alter housing prices in a town, other numbers such as average salaries, rates of people moving in and moving out, tax rates, and funding for schools will shift in response -- the fundamental constants of physics affect each other.  What Magueijo did was to set some constraints on how those constants can evolve, then let the model run to see what kind of universe eventually came out.

And what he found was that after jittering around for a bit, the constants eventually found stable values and settled into an equilibrium.  In Hossenfelder's video, she uses the analogy of sand grains on a vibration plate being jostled into spots that have the highest stability (the most resistance to motion).  At that point, the pattern that emerges doesn't change again no matter how long you vibrate the plate.  What Magueijo suggests is that the current configuration of fundamental constants may not be the only stable one, but the range of what the constants could be might be far narrower than we'd thought -- and it also explains why we don't see the constants changing any more.

Why they are, in fact, constant.

Stable pattern of grains on a vibrating pentagonal Chladni plate [Image licensed under the Creative Commons Matemateca (IME USP), Chladni plate 16, CC BY-SA 4.0]

Magueijo's work might be the first step toward solving one of the most vexing questions of physics -- why the universe exists with these particular laws and constants, despite there not seeming to be any underlying reason for it.  Perhaps we've been looking at the whole thing the wrong way.  The early universe really may have been without substance and void -- but instead of a voice crying "let there be light!", things simply evolved until they reached a stable configuration that then generated everything around us.

It might not be as audibly dramatic as Haydn's vision of The Creation, but it's just as much of an eye-opener.

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Bubbles, dimensions, and black holes

One of the weirder claims of modern physics, which I first ran into when I was reading about string theory a few years ago, is that the universe could have more than three spatial dimensions -- but the extra ones are "curled up" and are (extremely) sub-microscopic.

I've heard it explained by an analogy of an ant walking on a string.  There are two ways the ant can go -- back and forth on the string, or around the string.  The "around the string" dimension is curled into a loop, whereas the back-and-forth one has a much greater spatial extent.

Scale that up, if your brain can handle it, to three dimensions of the back-and-forth variety, and as many as nine or ten of the around-the-string variety, and you've got an idea of what the claim is.

The problem is, those extra dimensions have proven to be pretty thoroughly undetectable, which has led critics to quote Wolfgang Pauli's quip, that it's a theory that "is not even wrong," it's unverifiable -- which is synonymous to saying "it isn't science."  But the theorists are still trying like mad to find an indirect method to show the existence of these extra dimensions.

To no avail at the present, although we did have an interesting piece added to the puzzle a while back that I somehow missed the first time 'round.  Astronomers Katie Mack of North Carolina State University and Robert McNees of Loyola University published a paper in arXiv that puts a strict limit on the number of macroscopic dimensions -- and that limit is three.

So sorry, fans of A Wrinkle in Time, there's no such thing as the tesseract.  The number of dimensions is three, and three is the number of dimensions.  Not four.  Nor two, unless thou proceedest on to three. 

Five is right out.

The argument by Mack and McNees -- which, although I have a B.S. in physics, I can't begin to comprehend fully -- boils down to the fact that the universe is still here.  If there were extra macroscopic spatial dimensions (whether or not we were aware of them) it would be possible that two cosmic particles of sufficient energy could collide and generate a miniature black hole, which would then give rise to a universe with different physical laws.  This new universe would expand like a bubble rising in a lake, its boundaries moving at the speed of light, ripping apart everything down to and including atoms as it went.

"If you’re standing nearby when the bubble starts to expand, you don’t see it coming," Mack said.  "If it’s coming at you from below, your feet stop existing before your mind realizes that."

This has been one of the concerns about the Large Hadron Collider, since the LHC's entire purpose is to slam together particles at enormous velocities.  Ruth Gregory of Durham University showed eight years ago that there was a non-zero possibility of generating a black hole that way, which triggered the usual suspects to conjecture that the scientists were trying to destroy the universe.  Why they would do that, when they inhabit said universe, is beyond me.  In fact, since they'd be standing right next to the Collider when it happened, they'd go first, before they even had a chance to cackle maniacally and rub their hands together about the fate of the rest of us.

"The black holes are quite naughty," Gregory said, which is a sentence that is impossible to hear in anything but a British accent.  "They really want to seed vacuum decay.  It’s a very strong process, if it can proceed."

"No structures can exist," Mack added.  "We’d just blink out of existence."

Of course, it hasn't happened, so that's good news.  Although I suppose this wouldn't be a bad way to go, all things considered.  At least it would be over quickly, not to mention being spectacular.  "Here lies Gordon, killed during the formation of a new universe," my epitaph could read, although there wouldn't be anyone around to write it, nor anything to write it on.

Which is kind of disappointing.

Anyhow, what Mack and McNees have shown is that this scenario could only happen if there was a fourth macroscopic dimension, and since it hasn't happened in the universe's 13.8 billion year history, it probably isn't going to.

So don't cancel your meetings this week.  Mack and McNees have shown that any additional spatial dimensions over the usual three must be smaller than 1.6 nanometers, which is about three times the diameter of your average atom; bigger than that, and we would already have become victims of "vacuum decay," as the expanding-bubble idea is called.

A cheering notion, that.  Although I have to say, it's an indication of how bad everything else has gotten that "We're not dead yet" is the best I can do for good news.

That's our news from the world of scientific research -- particle collisions, expanding black holes, and vacuum decay.  Myself, I'm not going to worry about it.  I figure if it happens, I'll be gone so fast I won't have time to be upset at my imminent demise, and afterwards none of my loved ones will be around to care.  Another happy thought is that I'll take Nick Fuentes, Tucker Carlson, Elon Musk, Stephen Miller, and Andrew Tate along with me, which might almost make destroying the entire universe worth it.

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