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This ancient thought exercise will have you questioning your identity
How much can something change and still be the same thing?
It’s a myth that you get a new body every 7-10 years. The reason is, different cells last different lengths of time. Colon cells last only about four days, skin cells two to three weeks, and neurons a lifetime. In that, the body you are in now is not the same as it was last week, last month, or last year, although it feels the same. So are you truly the same person?
It may predate him, but the ancient Greek historian Plutarch was the first to write this intriguing thought exercise down. It’s called the Theseus Paradox or the ship of Theseus. A hero of Greek mythology and the supposed founder of Athens, Theseus is said to have won a number of naval battles and defeated several monsters, including the Minotaur. Plutarch’s recording of the memorial set up to honor this epic founder has had great thinkers scratching their heads for millennia since.
The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same.
-Plutarch (Vita Thesei, 22-23)
Model of a Greek trireme. Credit: Deutsches Museum, Munich, Germany.
The memorial remained floating in Athens harbor for centuries, according to Plutarch. It’s said to have been erected during the lifetime of Demetrius Phalereus, a famous statesman and writer, who was thought to have walked the earth around 350-280 BCE. Over time, the ship’s boards began to rot. Like with the upkeep of any important monument, these were replaced.
At some point, all the boards in the ship must’ve been switched out. So the vital question is, is it still the same ship? If not, at what point does it cease to be the ship of Theseus? Replacing one board may not be such a big a deal. But what about when half of them are no longer original, most of them, or all of them? In a way, human life is like this.
Some philosophers say we are our body. But as we grow older, we get wrinkles and gray hair. We develop health problems and modify our diet. We change our look, our clothes, our hairstyle, and more. And then there’s the death and replacement of most of our cells. So our body isn’t a permanent fixture. Others say our mind is what gives us our identity. Yet, our outlook on life changes over time. We may become an addict or get sober, find religion or lose it, just as we maybe become jaded... or embrace an unbridled optimism.
There are those who say our title, occupation, position, and responsibilities lend us identity. And even so, we may have different friends in years to come or a different spouse. Our children will grow up and move away. And our career likely will not stay the same, either. On average, a person changes careers 5-7 times in their lifetime and has 11.7 jobs. That’s impressive, considering how much of our identity is derived from our work and career. We may move to another city or even the other side of the world. So with all of these changes, are we really the same person throughout? If not, which version is the real you? Is there one? There are many ways to answer.
Unlike a statue which is frozen in time, one of the only real constants in human life is change. But if that’s so, then what is our true identity and how may we get to know it? Credit: Getty Images.
Some philosophers say changing one plank alters the ship irrevocably. Others say if at least one original plank is still in the ship, it’s the real deal. Then there are those who posit that the monument remains Theseus’s ship throughout. Try as they might, it’s hard to pin down exactly why a gradual change is okay, while a sudden one feels unacceptable. Consider how shocking it is when someone has an accident, say a head trauma, and they wake up a completely different person. Yet, if they made the same changes gradually over time, we wouldn’t find it particularly jarring. One common answer is known as Spatio-temporal continuity.
This says that all objects change continuously as they travel through space-time. As such, they’ll have parts replaced from time to time, may even change form or composition. Yet, their identity remains. The famous Greek philosopher Heraclitus posited that we don’t step in the same river twice. Everything is constantly changing, though we’re not likely to notice. The equivalent in our species can be summed up very well in a statement by Harvard psychologist Daniel Gilbert. He said, “Human beings are works in progress that mistakenly think they’re finished.”
Many philosophers have put their own spin on the Theseus paradox over the years. 17th century English philosopher, scientist, and historian Thomas Hobbes, for instance, wrote a version where a collector took all the original boards that were replaced and one-by-one, built a second ship of Theseus. So which ship is the actual one, the immaculate memorial in the harbor or the rotting one in the dry dock? There is no right answer. What this paradox reminds us is, although we see identity as a fixed and solid structure, it’s actually thin, malleable, and ever-changing.
To learn more about the Theseus paradox, click here:
Scientists discovered footprints made by some of the largest creatures ever to walk the Earth.
- Paleontologists published a paper on the discovery of dinosaur footprints on the roof of a French cave.
- The prints are deep underground and were made during the Middle Jurassic period.
- The footprints belonged to titanosaurs, the largest land animals ever.
French scientists found gigantic dinosaur footprints on the roof of the Castelbouc cave the Lozère region of southern France. A new paper outlines the discovery approximately 1640 feet under ground by the paleontologist Jean-David Moreau from the University of Burgundy–Franche-Comté and his colleagues.
The footprints likely belonged to an unknown species of titanosaur and were made 166 to 168 million years ago, in the Middle Jurassic Period. Titanosaurs, a group of long-necked, lizard-like sauropods, could be found all over the world in present day Africa, the Americas, Europe, and Australia. Among titanosaurs were the largest land animals to have ever existed, like the Patagotitan, which stretched 121 feet long and weighed 138,000 pounds.
The titanosaur Alamosaurus.
Credit: Bogdanov, 2006. Creative Commons.
Some of the 38 tracks found in France were as large as 4 feet long. They were likely made by three dinosaurs at the time when the area was on the surface, making up a muddy shoreline along which the giant creatures traveled. Over time, the site was buried by geological processes, with the tracks becoming moldings in the roof of a cave that's half a kilometer underground.
They were spotted as part of a caving expedition in December 2015 by the paper's authors. To find them, the scientists had to go down a narrow labyrinth of crawl spaces that often get flooded. The tracks were in a space about 260 feet long, 66 feet wide and 33 feet high.
Dinosaur tracks in the ceiling of Castelbouc Cave in France.
Credit: Jean-David Moreau et al./J. Vertebr. Paleontol.
Speaking to the French science magazine Sciences et Avenir, Jean-David Moreau explained that a caver "who was ahead of me turned to me and with the lamp of his helmet projected a grazing lighting on the ceiling which allowed to bring out the marks."
You can read the paper "Middle Jurassic tracks of sauropod dinosaurs in a deep karst cave in France," published in the Journal of Vertebrate Paleontology.
Humans may have evolved to be tribalistic. Is that a bad thing?
- From politics to every day life, humans have a tendency to form social groups that are defined in part by how they differ from other groups.
- Neuroendocrinologist Robert Sapolsky, author Dan Shapiro, and others explore the ways that tribalism functions in society, and discuss how—as social creatures—humans have evolved for bias.
- But bias is not inherently bad. The key to seeing things differently, according to Beau Lotto, is to "embody the fact" that everything is grounded in assumptions, to identify those assumptions, and then to question them.
Ancient corridors below the French capital have served as its ossuary, playground, brewery, and perhaps soon, air conditioning.
- People have been digging up limestone and gypsum from below Paris since Roman times.
- They left behind a vast network of corridors and galleries, since reused for many purposes — most famously, the Catacombs.
- Soon, the ancient labyrinth may find a new lease of life, providing a sustainable form of air conditioning.
Ancient mining areas below Paris for limestone (red) and gypsum (green).Credit: Émile Gérards (1859–1920) / Public domain
"If you're brave enough to try, you might be able to catch a train from UnLondon to Parisn't, or No York, or Helsunki, or Lost Angeles, or Sans Francisco, or Hong Gone, or Romeless."
China Miéville's fantasy novel Un Lun Dun is set in an eerie mirror version of London. In it, he hints that other cities have similar doubles. On the list that he offhandedly rattles off, Paris stands out. Because the City of Light really does have a twisted sister. Below Paris Overground is Paris Underground, the City of Darkness.
Most people will have heard of the Catacombs of Paris: subterranean charnel houses for the bones of around six million dead Parisians. They are one of the French capital's most famous tourist attractions – and undoubtedly its grisliest.
But they constitute only a small fragment of what the locals themselves call les carrières de Paris ("the mines of Paris"), a collection of tunnels and galleries up to 300 km (185 miles) long, most of which are off-limits to the public, yet eagerly explored by so-called cataphiles.
The Grand Réseau Sud ("Great Southern Network") takes up around 200 km beneath the 5th, 6th, 14th, and 15th arrondissements (administrative districts), all south of the river Seine. Smaller networks run beneath the 12th, 13th, and 16th arrondissements. How did they get there?
Paris stone and plaster of Paris
It all starts with geology. Sediments left behind by ancient seas created large deposits of limestone in the south of the city, mostly south of the Seine; and gypsum in the north, particularly in the hills of Montmartre and Ménilmontant. Highly sought after as building materials, both have been mined since Roman times.
The limestone is also known as Lutetian limestone (Lutetia is the Latin name for ancient Paris) or simply "Paris stone." It has been used for many famous Paris landmarks, including the Louvre and the grand buildings erected during Georges-Eugène Haussmann's large-scale remodelling of the city in the mid-19th century. The stone's warm, yellowish color provides visual unity and a bright elegance to the city.
The fine-powdered gypsum of northern Paris, used for making quick-setting plaster, was so famed for its quality that "plaster of Paris" is still used as a term of distinction. However, as gypsum is very soluble in water, the underground cavities left by its extraction were extremely vulnerable to collapse.
Like living on top of a rotting tooth: subsidence starts far below the surface, but it can destroy your house.Credit : Delavanne Avocats
In previous centuries, a road would occasionally open up to swallow a chariot, or even a whole house would disappear down a sinkhole. In 1778, a catastrophic subsidence in Ménilmontant killed seven. That's why the Montmartre gypsum quarries were dynamited rather than just left as they were. The remaining gypsum caves were to be filled up with concrete.
The official body governing Paris down below is the Inspection Générale des Carrières (IGC), founded in the late 1770s by King Louis XVI. The IGC was tasked with mapping and, where needed, propping up the current and ancient (and sometimes forgotten) mining corridors and galleries hiding beneath Paris.
A delightful hiding place
Also around that time, the dead of Paris were getting in the way of the living. At the end of the 18th century, their final destination consisted of about 200 small cemeteries, scattered throughout the city — all bursting at the seams, so to speak. There was no room to bury the newly dead, and the previously departed were fouling up both the water and air around their respective churchyards.
Something radical had to happen. And it did. From 1785 until 1814, the smaller cemeteries were emptied of their bones, which were transported with full funerary pomp to their final resting place in the ancient limestone quarries at Tombe-Issoire. Three large and modern cemeteries were opened to receive the remains of subsequent generations of Parisians: Montparnasse, Père-Lachaise, and Passy.
The six million dead Parisians in the Catacombs, from all corners of the capital and across many centuries, together form the world's largest necropolis — their now anonymized skulls and bones methodically stacked, occasionally into whimsical patterns. The Catacombs are fashioned into a memorial to the brevity of life. The message above the entrance reads: Arrête! C'est ici l'empire de la Mort. ("Halt! This is the empire of Death.")
That has not stopped the Catacombs, accessible via a side door to a classicist building on the Avenue du Colonel Henri Rol-Tanguy, making just about every Top 20 list of things to see in Paris.
An underground economy
However, while the Catacombs certainly are the most famous part of the centuries-old network beneath Paris, and in non-pandemic times draw thousands of tourists each day, they constitute just 1.7 km (1 mile) of the 300-km (185-mile) tunneling total.
Subterranean Paris wasn't just used for mining and storing dead people. In the 17th century, Carthusian monks converted the ancient quarries under their monastery into distilleries for the green or yellow liqueur that still carries their name, chartreuse.
Because the mines generally keep a constant cool temperature of around 15° C (60° F), they were also ideal for brewing beer, as happened on a large scale from the end of the 17th century until well into the 20th century. Several caves were dug especially for establishing breweries, and not just because of the ambient temperature: going underground allowed brewers to remain close to their customers without having to pay a premium for real estate up top.
Overview of the Paris Catacombs.Credit: Inspection Générale des Carrières, 1857 / Public domain.
At the end of the 19th century, the underground breweries of the 14th arrondissement alone produced more than a million hectoliters (22 million gallons) per year. One of the most famous of Paris' underground breweries, Dumesnil, stayed in operation until the late 1960s.
In that decade, the network of corridors and galleries south of the Seine, long since abandoned by miners, became the unofficial playground for the young people of Paris. They explored the fantastical world beneath their feet, in some cases via entry points located in their very schools. Fascinated, these cataphiles ("catacomb lovers") read up on old books, explored the subterranean labyrinth, and drew up schematics that were passed around among fellow initiates as reverently as treasure maps.
As Robert Macfarlane writes in Underland, Paris-beneath-their-feet became "a place where people might slip into different identities, assume new ways of being and relating, become fluid and wild in ways that are constrained on the surface."
Some larger caves turned into notorious party zones: a 7-meter-tall gallery below the Val-de-Grâce hospital is widely known as "Salle Z." Over the last few decades, various other locations in subterranean Paris have hosted jazz and rock concerts and rave parties — like no other city, Paris really has an "underground music scene."
Hokusai's Great Wave as the backdrop to the "beach" under Paris.Credit: Reddit
Cataphiles vs. cataphobes
With popularity came increased reports of nuisance and crime — the tunnels provided easy access to telephone cables, which were stolen for the resale value of their copper.
The general public's "discovery" of the underground network led the city of Paris to officially interdict all access by non-authorized persons. That decree dates back to 1955, but the "underground police" have an understanding with seasoned cataphiles. Their main targets are so-called tourists, who by their lack of knowledge expose themselves to risk of injuries or worse, and degrade their surroundings, often leaving loads of litter in their wake.
The understanding does not extend to the IGC. Unlike in the 19th century, when weak cavities were shored up by purpose-built pillars, the policy now is to inject concrete to fill up endangered spaces — thus progressively blocking off parts of the network. That procedure has also been used to separate the Catacombs to prevent "infiltration" of the site by cataphiles.
Many subterranean streets have their own names, signs and all. This is the Rue des Bourguignons (Street of the Burgundians) below the Champs des Capucins (Capuchin Field), neither of which exists on the surface.Credit: Jean-François Gornet via Wikimedia and licensed under
The cataphiles, however, are fighting back. In a game of cat and mouse with the authorities, they are reopening blocked passages and creating chatières ("cat flaps") through which they can squeeze into chambers no longer accessible via other underground corridors.
Catacomb climate control
Alone against the unstoppable tide of concrete, the amateurs of Underground Paris would be helpless. But the fight against climate change may turn the subterranean labyrinths from a liability into an asset — and the City of Paris into an ally.
The UN's 2015 Climate Plan — concluded in Paris, by the way — requires the world to reduce greenhouse gas emissions by 75 percent by 2050. And Paris itself wants to be Europe's greenest city by 2030. More sustainable climate control of our living spaces would be a great help toward both targets. A lot of energy is spent heating houses in winter and cooling them in summer.
This is where the constant temperature of the Parisian tunnels comes in. It's not just good for brewing beer; it's a source of geothermal energy, says Fieldwork, an architectural firm based in Paris. It can be used to temper temperatures, helping to cool houses in summer and warming them in winter.
One catch for the cataphiles: it also works when the underground cavities are filled up with concrete. So perhaps one day, Paris Underground, fully filled up with concrete, will completely fall off the map, reducing the city's formerly real doppelgänger into an air conditioning unit.
Cool in summer, warm in winter: Paris Underground could become Paris A/C.Credit: Fieldwork
Strange Maps #1083
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