How much do you know
🎛️ How well do you know the constants?
Eight questions on the numbers that decide whether a universe can hold anyone to notice it.
Question 1 of 8
Roughly what fraction of a hydrogen nucleus's mass is released when it fuses into helium?
Every question, and every answer
The whole quiz, written out — so you can read it without playing, and so a search engine can too.
Roughly what fraction of a hydrogen nucleus's mass is released when it fuses into helium?
Answer: About 0.7% — seven parts in a thousand
0.007 is the whole of stellar fuel economy. Below about 0.006 the deuterium step fails and the universe stays hydrogen forever; above about 0.008 hydrogen burns so readily it is gone early, leaving helium and no water. The Sun converts four million tonnes of mass to energy every second on that margin.
Read the essay →Fred Hoyle predicted an unknown energy level in carbon-12. What was his evidence?
Answer: That carbon exists, and he was made of it
This is the cleanest anthropic prediction ever made. The triple-alpha reaction is far too slow to produce the carbon we observe unless carbon-12 has an excited state near 7.7 MeV. Hoyle reasoned backwards from his own existence, told Fowler's group at Caltech where to look, and they found it.
Read the essay →By how many orders of magnitude does quantum field theory overestimate the cosmological constant?
Answer: About 120
Roughly 120 orders of magnitude — arguably the worst quantitative failure in the history of physics. Weinberg sidestepped the question in 1987 by asking instead how large it could be while still allowing galaxies to form, and got a bound that the supernova surveys vindicated eleven years later.
Read the essay →How lumpy was the early universe — the amplitude of primordial density ripples?
Answer: About one part in 100,000
Q is about 10⁻⁵, and both directions are lethal. Smoother and nothing ever collapses into a galaxy; lumpier and structure collapses straight into black holes without pausing to make stars. Planck measured it in the microwave background to several decimal places.
Read the essay →Why does the anthropic principle need three spatial dimensions specifically?
Answer: Stable orbits and stable atoms both require exactly three
In four or more spatial dimensions, inverse-cube and steeper force laws leave no stable bound orbits — planets spiral in or fly away, and atoms have the same problem. In two, there is not enough room for a complex nervous system or for waves to propagate cleanly. Three is the only one that works.
Read the essay →Who named the anthropic principle, and where?
Answer: Brandon Carter, at a Copernicus conference in Kraków in 1973
The venue was the joke. The Copernican principle says our position is not special; Carter's point was that it cannot be entirely typical either, because typical places in the universe are lethal. He argued for a correction to Copernicus at Copernicus's five-hundredth birthday party.
Read the essay →What is a Boltzmann brain, and why do cosmologists care?
Answer: An observer assembled by chance fluctuation — a test that rules theories out
If a universe lasts long enough, random fluctuations assemble conscious observers with false memories. In many models these vastly outnumber ordinary observers — so anthropic reasoning, applied consistently, would say you are almost certainly one. Nobody believes that, so a theory predicting mostly Boltzmann brains is generally taken to be ruled out.
Read the essay →Which ending do current measurements of dark energy most favour?
Answer: Heat death — indefinite expansion and cooling
The measured equation of state sits very close to a constant dark energy, which gives indefinite expansion: galaxies recede, stars burn out, black holes evaporate over unimaginable spans. A Rip needs dark energy to strengthen over time, and a Crunch needs it to reverse. Neither is what the data currently shows.
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