“HERE’S THE PART that everyone forgets: when Schrödinger made up the cat thing, he meant it as a complaint.”
“I may as well go in order — in publication order, but also (coincidentally, and in my own opinion) from most crazed to most rational. The possibility that this puts them in descending order of reading fun hints, if nothing else, at the pitfalls of science writing. I also think it might tell us about the human need for prophets, and about why it’s so easy to trip when you search for truth… but let’s not get ahead of ourselves.”
“Tegmark approaches this conclusion with ever more unsubstantiated assertions. The External Reality Hypothesis (“there is an external physical reality completely independent of us humans”) sounds plausible. This hypothesis paired with general relativity allows us to picture the universe as a four-dimensional geometric structure, which leads to the Mathematical Universe Hypothesis (“a mathematical structure is our external reality, rather than being merely a description thereof”). To sharpen these claims, Tegmark then introduces the Computable Universe Hypothesis (“our external physical reality is defined by computable functions”) and the Finite Universe Hypothesis (“our external physical reality is a finite mathematical structure”).”
“When the ERH, MUH, CUH, and FUH are all simultaneously in play, the flurry of acronyms distracts from the basic argument. But the part that should arouse suspicion is the Mathematical Universe Hypothesis — the assertion that all mathematical descriptions are physical things.”
“To his credit, Tegmark doesn’t hide that this seems wrong. In high school geometry, we are taught that perfect circles don’t physically exist, because circles, like points, planes, angles, and all the rest, are abstractions, not directly linked to experience. Tegmark argues otherwise. Tegmark quotes the standard definition (penned by David Hilbert) of mathematical existence — “Mathematical existence is merely freedom from contradiction” — and asserts that mathematical existence implies physical existence. Every mathematical structure, from simple circle to quantum cosmos, is physically real within the Level IV multiverse. Tegmark welcomes them all. The experimentalist’s job, in his view, is just to figure out which one we inhabit.”
“Investigating the dark corners of well-known results allows Gleiser, at his best, to challenge science’s possible shortsightedness. In Chapter 11, “Cosmic Blindness,” he remarks that if our current view of the universe, with its increasing outward acceleration, is correct, then in the far future, some two trillion years from now (current age: 13.8 billion years), any observers will see only darkness outside their own galaxies. Their best observations will force them to adopt conclusions quite different from those of today’s science. “Ironically,” Gleiser writes, “their cosmology will return to that of a static cosmos, an island universe comprising the galaxies within the Local Supercluster, surrounded by a vast expanse of dark, empty space.””
“Gleiser respects evidence far more than Tegmark, but for readers, delusion is often preferable to boredom, and an insane doctrine is often preferable to no doctrine at all.”
“Albert writes like a philosopher and thinks like a physicist, parsing the logic of each argument while allowing physics to guide his insights.”