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Plot Details/Summary

The premise of this tale is that a scientist, or small group of scientists, have created a device that will allow them to open a viewing portal to the past. With it, the operator can watch events unfold from a given time/place through the created portal. The portal is one way, so the observed cannot see the observers. The one quirk in the design is that when it is activated, it creates a glowing outline of the where the portal has manifested in the past. Both as it forms, and for a time afterwards, IIRC.

The bulk of the story details with the scientists (possibly also historians of a sort?) observing the construction of Stonehenge. There are passages about the stone being hauled up, etc. I don't recall if the viewing was time-lapse or real time. As the viewing ends, the scientists in the present consider the entire experiment to be a resounding success and an historical breakthrough.

It is then we get the story's twist. One of the other scientists suddenly raises a concern with the lead scientists. Since the glowing effect of the portal would have been visible well-before they began viewing the construction of Stonehenge, and probably would have been seen as magical or unearthly, what if their own experiment was the inspiration for Stonehenge? (There is a term for this sort of effect, I believe, but I cannot recall what it is).

Publication Details

I read this one in the 1980s, as usual. I'm almost positive that it was part of an anthology in my dad's collection. I'd guess 1970's or earlier for the story's publication date.

Helbent IV
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    "There is a term for this sort of effect, I believe, but I cannot recall what it is" Closed time loop, stable time loop, causal loop, predestination paradox. – Acccumulation May 15 '18 at 15:20
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    Time Parodox. As the reason for the trip back was because they made a trip back already which caused the Henge to be built. – Ochuko Sagua May 15 '18 at 15:38
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    That's not really a time paradox, just reverse causality. Now, if their observations had caused stonehenge to not be built, that would be a time paradox. – Pete Becker May 15 '18 at 16:14
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    This literally sounds like something Futurama's Professor Farnsworth would do. – White Prime May 15 '18 at 16:17
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    @PeteBecker Yes. I am not sure what a specified-end thing like what Ochuko Sagua is called, but a paradox is something that results in something else that resulted in the first result not happening, therefore causing the second result to not happen, causing the first result and then the second result to happen, and etc. – Darth Vader May 15 '18 at 16:41
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    https://en.wikipedia.org/wiki/Causal_loop, https://en.wikipedia.org/wiki/Novikov_self-consistency_principle, https://en.wikipedia.org/wiki/Closed_timelike_curve – Mooing Duck May 15 '18 at 20:12
  • "it creates a glowing outline of the ? where the portal has manifested in the past." Missing word? – Faheem Mitha May 15 '18 at 21:28
  • @MooingDuck Not quite a closed loop. In the story, they send the device to 1680 BC based on Lockyer's estimate for time of construction, which assumed that the midsummer sun rose directly over the heel stone and then worked out the date at which that would be the case. So if the real reason they built it was because the the builders saw the time machine, and had nothing to do with the sun, why was that estimate correct? (In reality, it wasn't correct, but that's immaterial.) – Ray May 15 '18 at 22:04
  • @Ray: At least for a casual reading of the wiki page, Closed Timelike Curve is an unrelated concept relying on curvature of spacetime itself. Neither causal loops or Novikov's self-consistency principle, rely on "how the loop got started". It is merely sufficient that the loop be self-consistent. Ergo, the estimate was correct because that's when the afterglow appeared in the past. – Mooing Duck May 15 '18 at 22:16
  • @MooingDuck Sorry, I was unclear. Since Stonehenge was built when it was because that's when the time machine showed up, some date it got sent back to would be correct. And the last date they tried would be correct, since that's when they stopped. That's consistent. But Lockyer selected 1680 as the estimate because that's when the sun would rise directly over the heel stone. And yet the reason Stonehenge was built then had nothing to do with the sun. The event without a cause is "Lockyer being correct". Not a paradox, since he could have just gotten very lucky, but an unlikely coincidence. – Ray May 15 '18 at 23:24
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    @Ray: According to Novikov's self-consistency principle, it's not an unlikely coincidence, but literally the only possibility. Stonehenge was built at that time because that's the time he guessed. His reasoning for that guess is irrelevant. It would be impossible for him to guess wrong, by definition. – Mooing Duck May 15 '18 at 23:45
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    Isn't the effect just an aspect of fatalism? This is more usually related by the time-travelling scientist who devises a plan to stop something bad happening (birth of Hitler is common) but his plan actually instigates the event that kicks off the bad thing, or stops it happening via one avenue, but creates circumstances for it to happen another way. The only difference here is the intent to change something is missing. – mcalex May 16 '18 at 09:30
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    Sounds similar to a story I read in Analog, about archaeologist scientists using a time travel technology to find out why the people in prehistoric England stopped burying their dead in graves and switched to tree-burial. – Aaron Gullison May 16 '18 at 21:18

1 Answers1

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This is "The Secret of Stonehenge" by Harry Harrison as per this Goodreads discussion, and is available at the Internet Archive as user14111 pointed out.

Unfortunately, I've yet to find a description to quote, but it's just as you recall, that the afterimage of the time machine was why they built Stonehenge. The closest I've found is the summary here:

In "The Secret of Stonehenge," a chronostasis temporal-recorder allows two men to take pictures of events in the past-as far back as 10,000 B.C

Here's the ending of the story:

"Correct. The golden glow of the machine caused by all those stops must have been visible on and off for years. It gave me a jolt when I first saw it, and it must have been much more impressive to the people then."

"It fits," Lanning said, smiling happily and beginning to repack the machine. "They built Stonehenge around the image of the device sent back to see why they built Stonehenge. So that's solved."

"Solved! The problem has just begun. It's a paradox. Which of them, the machine or the monument, came first?"

Slowly, the smile faded from Dr. Lanning's face.

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FuzzyBoots
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    Wow, that was quick! Definitely the story I am looking for here. Will accept answer as soon as site lets me. – Helbent IV May 15 '18 at 14:35
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    @HelbentIV: I was recently rereading Stainless Steel Visions, which has this and a story I recently got the answer to (as well as another from a few years back that I asked). – FuzzyBoots May 15 '18 at 14:36
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    As I remember, they send the machine to the center of Stonehenge. But however they turn it, the people always seem to be looking straight at it. Also, the machine leaves an afterglow in the present. The scientists realise that it must leave an afterglow in the past too, which is what the people were worshipping. – SQB May 15 '18 at 17:38
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    Of course the story is available at the Internet Archive. – user14111 May 15 '18 at 18:55
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    That was an enjoyable short read. – Willtech May 16 '18 at 10:11
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    As I recall they send a camera on a tripod back to stone henge and the image shows a worshipping crowd bowing towards the camera, they decide that the object of worship is behind the camera, so they turn the camera around and send it back, the new image also shows a worshipping crowd and they realise they are worshipping the camera – Bob May 20 '18 at 19:49