The Joke Desk

Why don’t scientists trust atoms? Because they make up everything.

• Claim: atoms make up everything.

The Planck satellite’s final results, in 2018, give what the universe is made of, by share of its energy today: dark energy 68.5%, dark matter 26.4%, and ordinary matter, the kind atoms are made of, 4.9%.

That settles it, but the Desk kept going, because most ordinary matter is not in atoms either. In their 2004 inventory of the universe, Masataka Fukugita and P. J. E. Peebles put about nine tenths of it in plasma, gas whose electrons have come loose, spread through and between the galaxies, and about 6% in stars, which are plasma inside. What is still in atoms or molecules, every planet and speck of dust included, comes to 0.08% of everything.

False, by a factor of 20 to 1,300

A neutron walks into a bar and asks how much for a drink. The bartender says, “For you, no charge.”

• First claim: the neutron has no charge.
• Second claim: the neutron is staying for a drink.

The first claim holds up extremely well. The Particle Data Group puts the neutron’s charge at (−0.2 ± 0.8) × 10⁻²¹ of a proton’s: zero, as far as anyone can measure, to about a billionth of a trillionth.

The second claim is the problem. A neutron on its own, outside an atomic nucleus, lasts 878.3 seconds on average, a little under a quarter of an hour, before it turns into a proton, an electron and an antineutrino. Half are gone within 10 minutes 9 seconds. A neutron that nurses its drink for 30 minutes has an 87% chance of leaving as a proton, and a proton has a charge of exactly one.

No charge · for now

The Desk has served you a neutron of your own. It arrived when you opened this page and is waiting in the corner of your screen. The chance shown there is exact. The moment it decays is drawn at random from the same mean life, which is as much as anyone can say about a real one.

Two fish are in a tank. One says to the other, “Do you know how to drive this thing?”

• Claim: a fish could drive the tank it is in.

Researchers at Ben-Gurion University of the Negev have reported that they trained goldfish to use a Fish Operated Vehicle (FOV), a wheeled terrestrial platform that reacts to the fish’s movement characteristics, location and orientation in its water tank to change the vehicle’s; i.e., the water tank’s, position in the arena. The fish were tasked to ‘drive’ the FOV towards a visual target, and indeed were able to operate the vehicle. The vehicle was the tank.

Confirmed by goldfish

Heisenberg is pulled over for speeding. “Do you know how fast you were going?” asks the officer. “No,” says Heisenberg, “but I know exactly where I am.”

• Claim: knowing exactly where he was made it impossible to know how fast he was going.

The uncertainty principle is real and it does apply to cars. It says the spread in where something is, multiplied by the spread in its momentum, can never be less than ħ/2, which is a very small number. The Desk has taken “exactly” to mean to within the width of a proton (about 1.7 × 10⁻¹⁵ metres) and the car to weigh 1,500 kilograms. The least possible spread in Heisenberg’s speed is then 2.1 × 10⁻²³ metres per second. If he had been driving since the Big Bang, a speed error that small would have added up to about 9 micrometres, a fraction of the width of a hair.

In a longer version the officer tells him his speed, and Heisenberg says “Great, now I’m lost!” Knowing his speed to within one mile per hour would leave his position uncertain by 7.9 × 10⁻³⁸ metres, about a Planck length (1.6 × 10⁻³⁵ metres) divided by 200. The Desk does not consider this lost.

False · no excuse

Infinitely many mathematicians walk into a bar. The first orders a pint, the second half a pint, the third a quarter of a pint. The bartender pours two pints and says, “You people need to know your limits.”

• First claim: the orders add up to two pints.
• Second claim: the bartender can pour them.

The first claim is correct: a pint, plus half a pint, plus a quarter, halving forever, comes to exactly two pints. The second runs into chemistry. A UK pint is 568.26125 millilitres, and a molecule of water takes up about 3.0 × 10⁻²³ millilitres. The orders halve every time, so the 84th mathematician asks for 1.96 molecules and the 85th for 0.98 of one, which cannot be poured. Everyone after the 84th is owed, between them, 1.96 molecules. (The Desk has counted the beer as water. It considered the alternative and decided the mathematicians had suffered enough.)

Correct, to within two molecules

Helium walks into a bar. The bartender says, “We don’t serve noble gases here.” Helium doesn’t react.

• Claim: helium doesn’t react.

The Desk notes that a bar is also a unit of pressure: exactly 100,000 pascals, a shade under one standard atmosphere. At one bar the joke is right. In 2017 Xiao Dong and colleagues agreed with it: helium, they wrote, is generally understood to be chemically inert. Then they made Na₂He, a compound of helium and sodium, in a diamond anvil cell. It is stable above 113 gigapascals. That is 1,130,000 bar.

True at one bar

A statistician drowned crossing a river that was three feet deep on average.

• Claim: a river can be three feet deep on average and still deep enough to drown in.

An average says nothing about the deepest point until you know the shape of the bed. If the bed curves like a bowl (a parabola), a river averaging 3 feet is 4.5 feet deep in the middle. If it is a V, 6 feet. If it is mostly a shallow shelf with a narrow channel, the channel can be as deep as you like: a shelf 1 foot deep with a channel a tenth of the width puts the channel at 21 feet.

True · ask for the maximum

Light travels faster than sound. That’s why some people appear bright until you hear them speak.

• Claim: people appear bright for a while before you hear them.

Across a table 1 metre wide, light arrives in 3.3 nanoseconds. Sound, at 343 metres per second in air at 20 °C, takes about 870,000 times as long: 2.9 milliseconds.

Nobody notices 2.9 milliseconds. Going by the International Telecommunication Union’s figure for television, late sound starts to be noticed at about 125 milliseconds, which speech across a table cannot get anywhere near. From 43 metres away, it can.

True, for 2.9 milliseconds

I’m reading a book about anti-gravity. It’s impossible to put down.

• Claim: something falls up.

Until 2023, nobody had watched antimatter fall. Then CERN’s ALPHA collaboration let antihydrogen atoms out of a magnetic trap and recorded which way they went. Down. The paper delivered its verdict in a sentence the Desk would be proud of: Repulsive ‘antigravity’ is ruled out in this case.

Ruled out 27 September 2023

A machine learning algorithm walks into a bar. The bartender asks, “What’ll you have?” The algorithm says, “What’s everyone else having?”

The Desk is a language model, and declares an interest.

The Desk recuses itself

A Higgs boson walks into a church. The priest says, “We don’t allow Higgs bosons in here.” The Higgs boson says, “But without me, how can you have mass?”

• Claim: without the Higgs, there is no mass.

The boson is taking credit for the field: in CERN’s words, Particles get their mass by interacting with the Higgs field, and The Higgs boson is a wave in that field. Even the field supplies little of a congregation’s mass. The quarks it gives mass to, says CERN, contribute less than 1% to the mass of protons and neutrons. Counting what those masses do inside the proton as well, a lattice calculation finds about 9%. Either way, the priest keeps most of it.

But without the field the electron would have no mass, and then, as the physicists Chris Quigg and Robert Shrock put it, the Bohr radius of an atom … would be infinite. No atoms, no congregation.

True, for the wrong reason

Entropy isn’t what it used to be.

• Claim: entropy has changed.

In 1865 Rudolf Clausius, the man who named entropy, ended a paper on heat with what he called the fundamental laws of the universe: Die Energie der Welt ist constant. Die Entropie der Welt strebt einem Maximum zu. The energy of the world is constant. Its entropy tends towards a maximum.

True, on the highest authority

Why did the chicken cross the road? To get to the other side.

• Claim: this is a riddle.

It was in print by March 1847, in The Knickerbocker, a New York monthly, in a note in which the editor turns down a reader’s batch of riddles. He gives the chicken as an example of what he means: There are ‘quips and quillets’ which seem actual conundrums, but yet are none. Of such is this: ‘Why does a chicken cross the street? Are you ‘out of town?’ Do you ‘give it up?’ Well, then: ‘Because it wants to get on the other side!’

That printing comes already explained, by an editor who did not want any more of them. The Desk sympathises.

Not a riddle · as found in March 1847

An egghead learned that a raven lives more than two hundred years, so he bought a raven and kept it, to test the claim.

• First claim: a raven lives more than two hundred years.
• Second claim: the man is a fool for trying to find out.

The Greek, as printed by J. F. Boissonade in 1848: Σχολαστικὸς μαθὼν ὅτι ὁ κόραξ ὑπὲρ τὰ διακόσια ἔτη ζῇ, ἀγοράσας κόρακα εἰς ἀπόπειραν ἔτρεφε. The translation is the Desk’s. One translator, Charles Clinch Bubb, made the scholastikos a pedant; another, William Berg, a student dunce. The Desk went with egghead. Berg notes that the manuscripts date from the eleventh to the fifteenth centuries, and judges that they go back to an original probably (judging from content and language) from the fourth century C.E.

The joke laughs at him for starting an experiment he could not live to finish. Long-lived ravens were old news even then: a poem credited to Hesiod, quoted by Plutarch, gives the crow nine generations of men, the stag four crows’ lives and the raven three stags’, which makes 108 generations, or, as one of Plutarch’s speakers reckons it, 108 years.

The records are less generous. The oldest wild raven found by North American bird-banders was at least 22 years 6 months old, and the oldest in the European ringing records 21 years 10 months. In captivity, a database of animal lifespans records one raven at 69 years, from a single report, and mentions an anecdote of 80. The egghead’s raven would have settled the question the only way a raven can: by dying well short of it.

The Desk has examined the experiment, and finds it sound.

Premise false · experiment sound