I managed to understand (mostly) approximately the first half of the book, but couldn't keep up when Penrose dipped into conformal space-time diagrams. I really liked the opening discussion on entropy and the explanation that early entropy was very special. In a sense the entropy was very low, which is why it can keep increasing, but also that as the universe was very hot at first that the entropy was as high as it could be. Only recommended for students of general relativity and cosmology! ( )

I am very intrigued by physicist attempts to explain the fundamental structures of time and space, but unfortunately in this case, I feel compelled to give up. I think I need someone to explain Roger’s thinking for me to gain much from it. There is a reliance on formulas and jargon that become increasingly confusing as I proceed, and I simply feel that it could be mind blowing if only I could make sense of it. Oh well! There are many other physics writers to try. ( )

Picked this off the 'in' shelf at the library. I can see from the date stamps that loads of people have been reading this.... Technically it lost me very soon. While I have previously encountered null cones and think I get the drift - I have also previously encountered strict conformal diagrams - and they are still complete mysteries. Maybe next time. Because that is what I love - I might not understand very much but each time I read a book like this I do understand a little more. And I just love to know that so many people are borrowing this book! ( )

En Ciclos del tiempo, su libro más ambicioso, Penrose desarrolla una visión inédita de la cosmología y propone una respuesta inesperada a la pregunta «¿Qué pasó antes del Big Bang?». Las dos ideas clave que hay detrás de esta nueva visión son un penetrante análisis de la Segunda Ley de la termodinámica (que establece el principio de la entropía) y el estudio de la geometría de conos de luz del espacio-tiempo. Penrose logra combinar estos dos temas para demostrar que el destino último de nuestro universo en expansión y aceleración puede ser visto como el «big bang» de uno nuevo. Por el camino, comenta también varios modelos cosmológicos (tanto ortodoxos como heterodoxos), el papel fundamental y ubicuo de la radiación cósmica de microondas o la eventual desaparición de los agujeros negros a través del misterioso proceso de evaporación de Hawking. Una obra fundamental para los amantes de la ciencia. «Aquellos interesados en los secretos del universo y su inquietante pasado, presente y futuro no pueden perderse este fascinante relato del gran divulgador de la astrofísica contemporánea.» La Razón

I like to refresh myself on my intuitive understanding of physics every once in a while since I won't ever admit to understanding more than 30%-40% of the math.

Even so, what I do understand is still more than enough to endlessly fascinate and make me sit around fantasizing and ruminating and dreaming up new ways to describe what I know and how to apply it in interesting ways.

It's the curse of reading a ton of SF, too, and I'm pretty sure I'm not alone in this weird little habit of mind games and flights of attempted non-entropic fancy.

That being said, I did understand everything in this book, at least in the broad strokes, because Mr. Penrose almost never deviated from common ground.

You know, background radiation proving the Big Bang, gravitational lensing effects to prove or disprove dark matter and/or dark energy, and a few other common steps along the way to build a standard case for our current understanding of the cosmology.

No problem. He's a good writer and his analogies are interesting even if they're ones I've heard a hundred times. You know, like the one about Einstein on a Train. Raindrops on a tarmac for mass distributions of black holes and the eventual release of their captured radiation over a grand long time until entropy has its final way.

Where the good stuff is, (in my opinion,) lies in the idea of time and its reversibility in the grand 10 to the 124 schema, or if we eventually throw this whole universe down a gravitational funnel, the 10 to the 125 manifold. Is this the reversal, the homogenous transformation of matter back into straight energy that preceded the original big bang? Is this an ongoing cycle that repeats?

Well, that was what *I* wanted to know, anyway. Let me let you in on a big spoiler: We still don't know.

Honestly, this is good, even with all the talk about the lambda, Einstein's cosmological constant, and how it still maintains a strong presence in the grand discussion, but really? I truly have a much better time trying to wrap my puny little brain around the string theories more. Holographic universes also float my boat. Still, for all that this text tried to convince me of an old theory that may or may not be quite up to date, it's still a fun read.

Maybe one of these days I'll do more than just nod my head at some of the more complex equations. :) Truly, enough exposure to these, book after book, IS doing me a lot of good. Maybe if I collect enough great analogies and get a spinal shunt with a couple hundred external parallel processors to hang my brain on, I'll be just about ready to transform a few tensors. :) ( )