I really enjoyed the first parts of this book, mainstream Astrophysics and how we know the stuff we do. Tegmark told us how the ancients deduced values like the diameter of the Earth, merely by observing the position of the sun at two different points at the same time (work out the difference in the angle of the sun at noon, then scale this up using the distance they are apart). The ancients deduced that the Earth is spheroid, given that ships on the horizon disappear bottom first, and you see their tops last (Yes, flat-earthers are stupider than people from millennia ago).
I was a staunch skeptic of the multiverse but Tegmark argues well and has convinced me that some form of multiverse likely exists. If space is infinite, then there must be planets very similar to Earth in the unobservable universe (Level 1). I didn’t fully understand Level 2 (pockets of inflation with different values for constants) but I was willing to give the author the benefit of the doubt. The so called many world’s interpretation (Level 3), I do find ridiculous and remain unconvinced (partly because I don’t fully understand it), the theory that the universe splits every time a decision is made. Tegmark does say that the Quantum Mechanics math is simplest in this interpretation and is the reason for apparent randomness in the universe. The Level 3 Universe lives in the infinite dimensional magical land of Hilbert Space, which we cannot reach, to test this. How convenient. He also unifies Level 1 and 3. I am rather ambivalent to the inclusion of his personal forays into academia and I’m not sure they add much. Though his tale about re-discovering decoherence was rather amusing. I always wondered that if the world was quantum mechanical, then why do we not observe quantum mechanical behaviour in our macroscopic world? The answer is decoherence or the breaking of “quantum secrecy” and is built on the idea of the Heisenberg uncertainty principle. The way I understand it is, once an object has interacted with something e.g. air, then decoherence occurs, the wavefunction appears to collapse as does the various superpositions, and we don’t get any quantum weirdness only classical physics.
The magic bullet for defeating the multiverse argument was that these hypotheses do not make any testable predictions and are therefore unscientific. Tegmark counters saying that the multiverse is a prediction of a testable theory, that of inflation. However, he later admits the theory of eternal inflation is flawed because the data doesn’t back it up (The measure problem). Later he backtracks on this, are you as confused as I am? To pacify your doubts of the multiverse he uses a bizarre theological argument borrowed from Alan Guth:”Cars are created by car factories, rabbits are created by rabbit parents and solar systems are created from gravitational collapse in giant molecular clouds. So it’s quite reasonable to assume that our Universe was created by some sort of universe-creation mechanism.” …And what created the universe-creation mechanism? Turtles all the way down!
Unfortunately, when the chapter on the Mathematical Universe Hypothesis progressed, it did devolve into philosophical gobbledegook and I struggled to follow his arguments. Helpfully, at the end of each chapter there is a summary containing the main points. A central question to the universe is why can mathematical equations describe reality and I think the author says, it is because it is a mathematical structure (Level 4, different equations of Physics). He says everything that can be expressed mathematically exists as a mathematical structure in life. Though the evidence he provides for Level 4 in a figure is rather tenuous, that of “Unreasonable effectiveness of math in physics”. His later argument is fine tuning, it is highly unlikely that numerous constants would all be finely tuned to ensure life.
The last chapter I really enjoyed where he talks about the future of physics and existential threats. Though I think the AI Singularity should be treated with skepticism. However, his idea that if an AI were to achieve sentience would effectively become a god (through omniscience), I agree with. Literally deus ex machina. He didn’t really explain what the death bubble hypothesis was in much detail. Self-referentially, he also deals with anti-intellectualism, something which is highly pertinent today. He argues we should use similar marketing techniques that opponents use without lowering ourselves to their levels of lies.
If we’re lucky congress may solve a 20 year old problem today. When in fact they should be solving problems arising in the future.
My guess is that we’ll one day, understand consciousness as yet another phase of matter.