365DaysDate: February 28, 2009


Title: Edgar Allan Poe and the Riddle of Darkness at Night

Podcaster: Paul Halpern

Links: Paul Halpern’s website:

Description: The night sky is a dark canopy speckled with stars. Yet, as German astronomer Wilhelm Olbers pointed out in the 1820s, if the universe were spatially infinite and you looked in any direction you should see the light from some star. Then why is darkness at night the rule—not a brilliant blaze? Remarkably, Edgar Allan Poe, whose 200th birthday is being celebrated this year, deduced at least part of the solution in his 1848 work Eureka. He speculated that light takes much longer from astronomical objects that previously thought. Assume a finite-aged, expanding universe and the answer is clear.

Bio: Paul Halpern is a physics professor and the author of eleven widely-acclaimed popular science books exploring space, time, extrasolar planets, cosmology and higher dimensions. His books include “What’s Science Ever Done for Us? What the Simpsons Can Teach Us About Physics, Robots, Life and the Universe,” “Brave New Universe,” “Faraway Worlds,” “The Great Beyond,” “The Quest for Alien Planets” and “Cosmic Wormholes.” Halpern has appeared on the History Channel, the PBS series “FutureQuest,” and a number of other televisions and radio programs. He is the recipient of a Guggenheim Fellowship, a Fulbright Scholarship and an Athenaeum Literary Award.

Today’s Sponsor: The sponsor for today’s episode is anonymous. He is just happy to support something that will, hopefully, spread the joy of astronomy.


Greetings and welcome to the February 28th podcast of the International Year of Astronomy. My name is Paul Halpern, and I am a professor of physics at the University of the Sciences in Philadelphia.  I’ve written a number of books about space, time, higher dimensions, scientific prediction, exoplanets and the structure of the universe.  My most recent book “What’s Science Ever Done for Us?” explores science on the Simpsons.   I’ve also published numerous articles about astrophysics and other subjects.  For more information about my work please see my website:

In our imagination, let us leave the bright lights of cities and suburbs behind and venture deep into the countryside.  In some of the remote places on earth, where astronomers appreciate the lack of luminous interference, the night is as black as ravens’ wings.  The darkness hangs low like a stealthy, shadowy bird, tap, tap, tapping on an observatory door.

“Deep into that darkness peering, long I stood there wondering, fearing,

Doubting, dreaming dreams no mortal ever dared to dream before

But the silence was unbroken, and the darkness gave no token,

And the only word there spoken was…”

Poe?   What does Edgar Allan Poe, the author of numerous tales of mystery, horror and suspense, as well as eerie poems such as “The Raven,” an excerpt of which I’ve just read, have to do with astronomy?  Coincidentally the International Year of Astronomy corresponds to Poe’s bicentennial, being celebrated by fans around the world.  Born on January 19, 1809, Poe arrived in this world halfway between the first astronomical use of the telescope and the present day.

Interesting coincidence.  Still, there must be more of a connection that justifies the words in this podcast.  How did Poe contribute to our understanding of the universe?  If you know the answer, shout “Eureka.”

Poe was not just a fiction writer, as it turns out. He also dabbled in scientific speculation.  In Eureka – A Prose Poem, published in 1848, one year before he died, Poe outlined some of his theories of the cosmos.  His goals were by no means modest. “I design to speak of the Physical, Metaphysical and Mathematical – of the Material and Spiritual Universe – of its Essence, its Origin, its Creation, its Present Condition and its Destiny,” he wrote.  Most ambitious indeed!

One of the questions Poe pondered has to do with the riddle of darkness at night, known as Olbers’ Paradox.  The conundrum is named for German astronomer Wilhelm Olbers who proposed it in the 1820s.  Olbers supposed that the universe is infinitely large, has lasted indefinitely, and is evenly distributed with stars.  He calculated that if you look in any direction in the nighttime sky you should see the light from some star at a particular distance away.  Some points in the sky would represent light from nearer stars; others, farther stars.  Therefore, the nocturnal sky should be ablaze with light!  Midnight, the time when Poe’s raven poetically appeared, should be as bright as noon, thanks to the collected power of an infinite number of suns.

Poe phrased the riddle in the following way:

“Were the succession of stars endless, then the background of the sky would present us a uniform luminosity, like that displayed by the Galaxy-since there could be absolutely no point, in all that background, at which would not exist a star.”

Nighttime without darkness would certainly not do for horror writers.  There would be no murky mansions for gruesome ghouls to haunt.  Therefore Poe’s livelihood demanded a solution to the dilemma.  And Poe was clever enough to come up with at least part of the answer.

Poe knew that light moves extremely quickly.  However, if the stars are far enough away then it would take many, many years-even thousands or millions of years-for their rays to travel to Earth.  Could it be that many stars are young enough and sufficiently remote that their light hasn’t had a chance to reach us yet?  As Poe expressed this idea in Eureka:

“The only mode, therefore, in which, under such a state of affairs, we could comprehend the voids which our telescopes find in innumerable directions, would be by supposing the distance of the invisible background so immense that no ray from it has yet been able to reach us at all.”

Thus, as Poe suggested, only a smidgen of the sky represents directions where stars are old enough and relatively close, enabling us to see their light.  In most other directions, no starlight was emitted long enough ago to have arrived here by now.  The bold implication of Poe’s hypothesis is that the universe has a finite age, and that far enough back in time no stars existed.

In the time of Poe, a finite-aged universe was mere speculation.  There was no direct indication that the cosmos had a beginning.  However, in the 1920s American astronomer Edwin Hubble demonstrated that space contains numerous galaxies-“island universes” in their own right-and that these galaxies (except for our nearest-neighbors) are moving away from ours.  The farther out one observes, the faster galaxies appear to be fleeing-as measured by the shifting of galactic light toward the red end of the spectrum.  This effect became known as the Hubble expansion.

Throughout the late 1940s and 1950s several teams of astronomers offered competing interpretations of the Hubble expansion.  One group, led by George Gamow and Ralph Alpher, proposed that the universe was born in a single creation-a simple substance produced from nothingness-that built up in that fiery era into the natural elements.  Thus the Hubble expansion is the result of the universe growing from a hot, highly compact state.  Another team, led by Fred Hoyle, Hermann Bondi and Thomas Gold, argued that although the universe is expanding, new galaxies are slowly but continuously being created.  The universe, they argued, has always existed, albeit with a different mix of galaxies.  They dubbed the single creation theory, the Big Bang, and their own theory the Steady State.

As Edward Harrison later proved, the Big Bang theory elegantly explained Olbers’ Paradox by showing that before a certain time no stars could exist.  To allow for an infinitely-old, Steady State universe, Bondi developed an alternative explanation that the red-shifting of galactic light reduced its energy and thus its visibility.  This effect would hold true for both theories.

Observations of the Cosmic Microwave Background-radiation left over from the hot, early state of the universe first detected in the 1960s by Arno Penzias and Robert Wilson-have conclusively verified the Big Bang theory.  The universe is believed to be 13.7 billion years old, and no star could be older than that.  Moreover, current observations show that the bulk of material in space is non-luminous dark matter. Therefore, Poe is right that for most parts of the sky, no visible light from a radiating object has had the opportunity to reach us.

In Poe’s bicentennial, corresponding to the International Year of Astronomy, we are able to cast the mystery of darkness at night aside, not to have to think about it again.  Or as Poe would say “Nevermore!”

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.