On “Penumbra” and Gregory Benford

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I’ll be posting about sci-fi and fantasy writers at this blog from time to time. This is the first:
Famed science fiction writer, Gregory Benford, has the alter ego: famed physicist, Gregory Benford. Your average genius would be pleased to reach the pinnacle of success in either the literary world or in science. Mr. Benford has done both. To understand, it’s best you go to his website [http://www.gregorybenford.com] and read his biography yourself. Two paragraphs in and I had a headache trying to comprehend how one person could cover so much ground in one lifetime. That story would make an interesting read.
Speaking of reading, while you’re at his website click on his bookstore tab and you’ll find a wealth of prize-winning science fiction that he has written. The fact that he collaborated with Larry Niven on Bowl of Heaven, a New York Times Best Seller, should convince you that this is top shelf sci-fi waiting to tickle your fancy.
I enjoy sci-fi that is written by a scientist, because the writing is usually laced with science fact and theory, therefore I get an education while enjoying the read.
As an example, let’s look at “Penumbra” by Benford. It’s a very short story that can generate a lot of fun discussion.
Penumbra, umbra and antumbra, are all different, but for now I’m going to say that all of those terms refer to the shadow that one astronomic body casts onto another when it passes between the shaded body and a source of radiation. An example is an eclipse, either of the sun or the moon. In a solar eclipse, the moon shades Earth from the sun; and in a lunar eclipse, Earth shades the moon from the sun.

Penumbra, gamma-ray burster, Benford, hard sci-fi

This is a drawing of a solar eclipse that I converted into a gamma-ray burster event, using the sun as the burster. A true burster would be far enough away that all radiation would be parallel rays. The point is that the hemisphere away from the burster would survive, as would to tiny spot shaded by the moon.


In “Penumbra,” the moon shades a small portion of Earth’s western hemisphere from a gamma-ray burster.
A gamma-ray burster is probably the most powerful activity in the universe based on a strict definition of power, i.e. massive amounts of energy are released in a short period of time. They are so powerful that we first saw them in other galaxies, which is good because we would never see one in our galaxy: It would kill us before our brains could process that we had seen it. A gamma ray burster is equivalent to the sun burning out all of its energy in a blink of the eye. More terrifying, some believe that this energy is directed in a beam. You can never be too far from such a beam. Some theorize that a single gamma-ray burster event could exterminate all life in its host galaxy. We believe this is theoretical overkill, because it is also calculated that a burster event has occurred every 100,000 year or so in our Milky Way. That is suspiciously close to the intervals between mass extinctions on Earth, but we know even during these mass extinctions some life survives. A burster might not kill all life because, while intense, it is short lived. Therefore life on the hemisphere shaded from the burst should survive the initial blast. However, we suspect that life on the sheltered side will have substantial challenges with weather, radiation, and other issues in the aftermath.
In the story, Penumbra, the moon passed between the burster and Earth, putting a small portion of the Western Hemisphere in its penumbra and saving that population from the initial blast. Or course, those in the protected hemisphere were also saved.
In Where Is Everybody? by Webb, he suggests that gamma blaster events could have disrupted advanced alien civilizations before they were established galactic travelers, i.e. bursters might explain the absence of extraterrestrial visitors.
It’s clear that we never want to experience a burster close up, say within 10,000 light-years distance. If the burster is a beam-like emission, then anywhere in our galaxy may be too close. Since it travels at the speed of light, those on the shielded side of the planet will figure out what happened to the exposed side after it’s over. The exposed side will never know; they’ll just be gone.
Overall, with one every 100,000 years, your chances are roughly .1% that one will happen in your life time, and .05% that you will be scorched in the initial blast. It’s a small number but enough to scare you into enjoying every minute that you’re alive—a good idea in any case.

4 thoughts on “On “Penumbra” and Gregory Benford

    • Wow. I’m honored that you came here, and I’m embarrassed at the misspelling, etc. in the article. I wrote it awhile back, and as usual in these things, moved on without doing a thorough edit. Anyway, as I said, I’m hugely honored that you posted a comment here.

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