The man who listened to the sky

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

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

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

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

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

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

That's just what Penzias and Wilson had observed.

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

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

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

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

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

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

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

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Paradoxes within paradoxes

Sometimes the simplest, most innocuous-seeming questions can lead toward mind-blowingly profound answers.

I remember distinctly running into one of these when I was in -- I think -- eighth grade science class.  It was certainly pre-high-school; whether it was from Mrs. Guerin at Paul Breaux Junior High School, or another of my teachers, is a memory that has been lost in the sands of time and middle-aged forgetfulness.

What I have never forgotten is the sudden, pulled-up-short response I had to what has been nicknamed Olbers's Paradox, named after 18th century German astronomer Heinrich Wilhelm Matthias Olbers, who first thought to ask the question -- if the universe is infinite, as it certainly seems to be, why isn't the night sky uniformly and dazzlingly bright?

I mean, think about it.  If the universe really is infinite, then no matter what direction you look, your line of sight is bound to intersect with a star eventually.  So there should be light coming from every direction at once, and the night sky shouldn't be dark.  Why isn't it?

The first thought was that there was something absorptive in the way -- cosmic dust, microscopic or submicroscopic debris left behind by stars and blown outward by stellar wind.  The problem is, there doesn't seem to be enough of it.  The average density of cosmic dust in interstellar space is less than a millionth of a gram per cubic meter.

When the answer was discovered, it was nothing short of mind-boggling.  It turns out Olbers's paradox isn't a paradox at all, because there is light coming at us from all directions, and the night sky is uniformly bright -- it's just that it's shining in a region of the spectrum our eyes can't detect.  It's called the three-degree cosmic microwave background radiation, and it appears to be pretty well isotropic (at equal intensities no matter where you look). It's one of the most persuasive arguments for the Big Bang model, and in fact what scientists have theorized about the conditions in the early universe added to what we know about the phenomenon of red-shifting (the stretching of wavelengths of light if the space in between the source and the detector is expanding) gives a number that is precisely what we see -- light peaking at a wavelength of around one millimeter (putting it in the microwave region of the spectrum) coming from all directions.

[Image licensed under the Creative Commons Original: Drbogdan Vector: Yinweichen, History of the Universe, CC BY-SA 3.0]

So, okay.  Olbers's paradox isn't a paradox, and its explanation led to powerful support for the Big Bang model.  But in science, one thing leads to another, and the resolution of Olbers's paradox led to another paradox -- the horizon problem.

The horizon problem hinges on Einstein's discovery that nothing, including information, can travel faster than the speed of light.  So if two objects are separated by a distance so great that there hasn't been time for light to travel from one to the other, then they are causally disconnected -- they can't have had any contact with each other, ever.

The problem is, we know lots of such pairs of objects.  There are quasars that are ten billion light years away -- and other quasars ten billion light years away in the opposite direction.  Therefore, those quasars are twenty billion light years from each other, so light hasn't had time to travel from one to the other in the 13.8 billion years since they were created.

Okay, so what?  They can't talk to each other.  But it runs deeper than that.  When the aforementioned cosmic microwave background radiation formed, on the order of 300,000 years after the Big Bang, those objects were already causally disconnected.  And the process that produced the radiation is thought to have been essentially random (it's called decoupling, and it occurred when the average temperature of the universe decreased enough to free photons from the plasma and send them streaming across space).

The key here is the word average.  Just as a microwaved cup of coffee could have an average temperature of 80 C but have spots that are cooler and spots that are hotter, the fact that the average temperature of the universe had cooled sufficiently to release photons doesn't mean it happened everywhere simultaneously, leaving everything at exactly the same temperature.  In fact, the great likelihood is that it wouldn't.  And since at that point there were already causally disconnected regions of space, there is no possible way they could interact in such a way as to smooth out the temperature distribution -- sort of like what happens when you stir a cup of coffee.

And yet one of the most striking things about the cosmic microwave background radiation is that it is very nearly isotropic.  The horizon problem points out how astronomically unlikely that is (pun intended) if our current understanding is correct.

One possible explanation is called cosmic inflation -- that a spectacularly huge expansion, in the first fraction of a second after the Big Bang, smoothed out any irregularities so much that everywhere did pretty much decouple at the same time.  The problem is, we still don't know if inflation happened, although work by Alan Guth (M.I.T.), Andrei Linde (Stanford), and Paul Steinhardt (Princeton) has certainly added a great deal to its credibility.

So as is so often the case with science, solving one question just led to several other, bigger questions.  But that's what's cool about it.  If you're interested in the way the universe works, you'll never run out of things to learn -- and ways to blow your mind.

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Supernothing

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The signature of the creator

The Star Trek: The Next Generation episode "The Chase" is justly revered by Trekkies, and also by people who simply like a good story.  The gist -- giving as little in the way of spoilers as I can manage, if you've not seen it -- is that there's a message implanted in our DNA and the DNA of alien species across the galaxy.  No one species has the entire thing, so to find out what it means requires getting tissue samples from all over the place, extracting the piece of the message, then somehow putting the entire thing together to decipher what it says.

A secret code dispersed through time and space, so to speak.

While the quasi-scientific explanation behind the whole thing was a little dubious for those of us who know something about genetics and evolution, it was a hell of a good idea for a story.  A mysterious, super-powerful someone left its thumbprint on life everywhere in the universe, and there the message has sat, waiting for us to become smart enough and technologically advanced enough to find it.

"The Chase" brings up a theological question I've debated before with religious-minded friends; how, starting from outside of the framework of belief, you could tell there was a God by what you see around you.  I often hear "natural beauty" and "love and selflessness" brought up, but (unfortunately) there seems to be enough ugliness, hatred, and selfishness to more than compensate for the good stuff.  Put simply, how would a universe with a divine presence look different from one without?  I've never been able to come up with a good answer to that.  To me, the God/no God versions of the universe look pretty much alike.

Which is a large part of why I'm an atheist.  I'm perfectly okay with revising that if evidence comes my way, but at the moment, I'm not seeing any particular cause for belief in any of the various deities humans have worshipped along the way.

What brings all this up is a paper released last week in arXiv called, "Searching for a Message in the Angular Power Spectrum of the Cosmic Microwave Background."  The CMB is a relatively uniformly-spread (or isotropic, as the scientists put it) radiation that is the remnant of the Big Bang.  In the 13.8-odd billion years since the universe started, the searing radiation of creation has become stretched along with the space that carries it until it has an average wavelength of two millimeters, putting it in the microwave region of the spectrum, and that radiation comes at us from everywhere in the sky.

What the author, Michael Hippke of the Sonnenberg Observatory in Germany, proposed was something that is reminiscent of the central idea of "The Chase."  If there was a creator -- be it a god, or a super-intelligent alien race, or whatever -- the obvious place to put a message is in the CMB.  The minor fluctuations ("anisotropies") in the CMB would be detectable by a technological society pretty much from any vantage point in the visible universe, and so hiding a pattern in the apparent chaos would be as much as having a signature from the creator.

So Hippke digitized the most detailed map we have of the CMB, and then estimated what part of the signal would have been lost or degraded in 13.8 billion years due to quantum noise and interference with the much closer and more powerful radiation sources in our own galaxy.  After some intense statistical analysis, Hippke determined that there should be at least a one-thousand-bit remnant of sense somewhere in there, so he set about to find it.

Nothing.

"I find no meaningful message in the actual bit-stream," Hippke wrote.  "We may conclude that there is no obvious message on the CMB sky.  Yet it remains unclear whether there is (was) a Creator, whether we live in a simulation, or whether the message is printed correctly in the previous section, but we fail to understand it."

Despite how I started this post, I have to admit to being a little disappointed.  It was a clever approach, and no one would be more excited than me if he'd actually found something.  I don't honestly like the idea that we live in a chaotic, meaningless universe -- or, more accurately (and optimistically) that the only meaning is the one we create within it.  But if there's one thing I've learned in my sixty years on Earth, it's that reality is under no particular obligation to order itself in such a way that it makes me comfortable.  

But still, if there had been a message there, how cool would that be?  Even if, as the Cardassian commander Gul Ocett said in "The Chase," "it might just be a recipe for biscuits."

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I've always had a fascination with how our brains work, part of which comes from the fact that we've only begun to understand it.  My dear friend and mentor, Dr. Rita Calvo, professor emeritus of human genetics at Cornell University, put it this way.  "If I were going into biology now, I'd study neuroscience.  We're at the point in neuroscience now that we were in genetics in 1900 -- we know it works, we can see some of how it works, but we know very little in detail and almost nothing about the underlying mechanisms involved.  The twentieth century was the century of the gene; the twenty-first will be the century of the brain."

We've made some progress in recent years toward comprehending the inner workings of the organ that allows us to comprehend anything at all.  And if, like me, you are captivated by the idea, you have to read this week's Skeptophilia book recommendation: neuroscientist Lisa Feldman Barrett's brilliant Seven and a Half Lessons About the Brain.

In laypersons' terms, Barrett explains what we currently know about how we think, feel, remember, learn, and experience the world.  It's a wonderful, surprising, and sometimes funny exploration of our own inner workings, and is sure to interest anyone who would like to know more about the mysterious, wonderful blob between our ears.

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