3243: Crystal Gazing

Crystal Gazing

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Title text: 'Beyond that lies a vale of fire through which my vision cannot penetrate' is the kind of fun thing geologists, heliophysicists, and early universe cosmologists have a lot of opportunities to say.

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Explanation

A geochronologist (someone who estimates the ages of rocks, fossils, etc.) dressed up as a wizard (assuming that isn't how they normally dress) announces — in archaic language befitting his costume — that he has determined the age of the Earth by analyzing zircon. Zircon is a crystal with the formula ZrSiO₄. During its formation it can incorporate uranium instead of zirconium in its crystal lattice, but cannot incorporate lead. The uranium then decays (via several intermediates) into lead. Thus a sufficiently old zircon crystal will contain some lead, allowing geologists to calculate its age. This method is especially reliable, since uranium-238 decays into lead-206 with a half-life of 4.5 billion years, while uranium-235 decays into lead-207 with a half-life of 0.7 billion years, allowing geologists to determine the age even where some lead was lost from the crystal. The geochronologist says he predicted the age of the Earth by gazing into the crystal, similar to the traditional fortune tellers' method of making predictions by gazing into crystal balls.

A prophet of doom is someone who predicts impending disasters, particularly the end of the world (and there are lots of ridiculous ways that could happen). These prophets and predictions are especially common in fantasy media. The joke in the caption is that someone who can determine when the world began is just doing this in reverse, and that's what geochronologists are doing when they calculate the age of the Earth. His last line, "the beginning was nigh", is a reversal of the phrase stereotypically used by prophets of doom: "the end is nigh". This is in keeping with the idea represented in the comic.

The title text points out, in similar flowery language (in keeping with the character being a wizard from a Tolkienesque or Dungeons & Dragons-type world, where vales are often part of the geographical language), that many areas of physical sciences have a limiting horizon to their ability to study their subject. Geologists are limited by the early molten history of the Earth, in that most of the crust has been recycled back into the molten mantle at some point, and the mantle acts as a physical 'vale of fire' for the core — each limiting what can be studied. Similarly, heliophysicists have difficulty knowing what happens within the Sun due to the physical 'vale of fire' that is the Sun's surface. Finally, cosmologists have difficulty studying beyond the 'recombination' era, beyond which the universe is shielded by a 'vale of fire' (cosmic microwave background) from electromagnetic observation — both in time (investigating the early universe) or in space (investigating beyond the event horizon of the visible universe).

D&D is a recurring topic on xkcd.

Transcript

[A character in wizard garb with long beard and hair talks to Cueball. To the left of the wizard is a poster with illegible text over a graph with two lines intersecting.]

Wizard: By gazing into my crystals of zircon, I have divined the date of the hour of fire marking the limit of this world's existence.

Wizard: 4.54 billion years ago, the beginning was nigh!

[Caption below comic:]

Geochronologists are just reverse prophets of doom.

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Discussion

F1RST P0ST!!--158.123.138.25 17:52, 8 May 2026 (UTC)

Not counting any posts made before the vale and/or veil of fire. 150.221.155.241 22:10, 8 May 2026 (UTC)

Why is it "vale of fire" instead of "veil of fire"? 174.20.245.60 18:06, 8 May 2026 (UTC)

"vale" is a poetic term for a valley. Barmar (talk) 19:06, 8 May 2026 (UTC)

That is indeed the definition, but seems less appropriate than "veil" which has the connotation of blocking/obscuring.174.20.245.60 20:59, 8 May 2026 (UTC)

Not just a poetic term, but used in placenames (e.g. the "Vale of Evesham"), a vale generally more being a wide valley/flood-plain, framed by hills, rather than a 'mere' river-cut. But one of the more figurative/poetic terms I hear used is "vale of tears", a particularly sorrowful episode of life.

(PPE: a 'veil' and a 'vale' of obscuration would each be rather different concepts. Veil is a thin barrier, vale a 'territory' of (iin this case) inpenetrability. I think the chosen wor is as good a term, if not better, than the other... But, I don't know if it's an intentional choice or merely a slipup that fortunately landed on a somewhat-synonymic term.) 81.179.199.253 21:09, 8 May 2026 (UTC)

I think there's definitely a "veil" pun going on there. "Beyond the veil" is something you can't see. Dogman15 (talk) 02:46, 9 May 2026 (UTC)

Alternative the vale of fire for the heliophysists could just be the photosphere, a barrier in space rather than time.76.180.39.133 01:44, 9 May 2026 (UTC)

I'm not sure if "before the big bang" is a meaningful concept, at least from the inside of the universe. BunsenH (talk) 03:48, 9 May 2026 (UTC)

Pretty darn sure that would be >18bya, 4.5bya would be the beginning of our start and planetary systemSeebert (talk) 18:09, 11 May 2026 (UTC)

Um, what's the complaint about, exactly? 81.179.199.253 20:14, 11 May 2026 (UTC)

I think Seebert has assumed that BunsenH's comment was in reference to the aging of the Earth in the first paragraph, whereas it was actually related to a now removed reference to the Big Bang in the last paragraph. 82.13.184.33 13:42, 12 May 2026 (UTC)

Surely the vale of fire for early universe cosmologists is the surface of last scattering? 137.25.230.78 07:13, 9 May 2026 (UTC)

I'm fairly certain the 'vale of fire' is not always time-related, but also physical. Edited it to better reflect that.174.89.130.8 15:04, 9 May 2026 (UTC)

Is “vale” supposed to mean veil? 68.187.4.2 (talk) 15:59, 11 May 2026 (please sign your comments with ~~~~)

See above... 81.179.199.253 20:27, 11 May 2026 (UTC)

In the forward prophet of non-doom category, will the next comic be another Tuesday comic? 2603:8081:9700:1224:0:0:0:2 05:29, 12 May 2026 (UTC)
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