# Book Review: “Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos”

“The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos” – by Brian Greene

Since I was young, I’ve always enjoyed reading about cosmology and the physics of the Universe. This book was a tour and explanation of how the latest theoretical equations coming from the experts in the field of cosmology can be explained (as much as reasonable) to the layman. Without resorting to intimidating math, the author takes the reader on a mental roller coaster ride. Ultimately approaching the question “What is space?” from every angle.

Space has some very interesting properties, and even more interesting consequences depending on how you define space 3-dimensions, (3+1) space-time, (9+1) string theory, (10+1) m-theory. The consequences of how you define space, also affect the nature of the whole universe. This book covers different ways that the quantum mechanics formulas can potentially manifest into our understanding of a “multi-verse”.

So we’ve heard of the big-bang. The start of our universe. The start of everything from a singularity about 13.7 billion years ago. And since then our universe has been expanding. Space has been expanding. Edwin Hubble observed that every galaxy is moving away from us, with the farther ones moving faster, which has been connected to the theory that space is expanding due to some cosmological constant.

#### Interesting facts:

- Our Universe is 13.7 billion years old, so our “cosmic horizon” – how much we can observe (due to the speed of light) is 13.7 billion light years.
- The speed of light is fixed in all frames of reference to “c”, but the speed of expansion of space itself has no limit.
- Things that maybe be in our universe/cosmic horizon now, might not be later due to spatial inflation.
- Planck length – the smallest distance at which the concept of distance loses all meaning. 1.616×10^-35meters
- The most information that can be stored in a given space (using bits 1-0) in this universe is defined by the surface area of an object measured in “squared planck lengths”.
- Cosmological constant (why space expands) on the order of 10^-122

Another book that I recently read, that I’ll lump into this post due to the subject matter overlap “Grand Design” by Stephen Hawking & Leonard Mlodinow. If you’ve ever read any other best seller by Stephen Hawking, it’s probably already on your reading list.