# Space time and the universe

## The Universe in Your Hand: A Journey Through Space, Time, and Beyond by Christophe Galfard

If Ms. Frizzle were a physics student of Stephen Hawking, she might have written THE UNIVERSE IN YOUR HAND, a wild tour through the reaches of time and space, from the interior of a proton to the Big Bang to the rough suburbs of a black hole. Its friendly, excitable, erudite, and cosmic.—Jordan Ellenberg,

*New York Times*besteselling author of

*How Not To Be Wrong*

Quantum physics, black holes, string theory, the Big Bang, dark matter, dark energy, parallel universes: even if we are interested in these fundamental concepts of our world, their language is the language of math. Which means that despite our best intentions of finally grasping, say, Einsteins Theory of General Relativity, most of us are quickly brought up short by a snarl of nasty equations or an incomprehensible graph.

Christophe Galfards mission in life is to spread modern scientific ideas to the general public in entertaining ways. Using his considerable skills as a brilliant theoretical physicist and successful young adult author,

*The Universe in Your Hand*employs the immediacy of simple, direct language to show us, not explain to us, the theories that underpin everything we know about our universe. To understand what happens to a dying star, we are asked to picture ourselves floating in space in front of it. To get acquainted with the quantum world, we are shrunk to the size of an atom and then taken on a journey. Employing everyday similes and metaphors, addressing the reader directly, and writing stories rather than equations renders these astoundingly complex ideas in an immediate and visceral way.

Utterly captivating and entirely unique,

*The Universe in Your Hand*will find its place among other classics in the field.

## Space-Time

In physics , spacetime is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams can be used to visualize relativistic effects such as why different observers perceive where and when events occur differently. Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe its spatial expression in terms of coordinates, distances, and directions was independent of one-dimensional time. However, in , Albert Einstein based his seminal work on special relativity on two postulates: 1 The laws of physics are invariant i. The logical consequence of taking these postulates together is the inseparable joining together of the four dimensions, hitherto assumed as independent, of space and time. Many counterintuitive consequences emerge: in addition to being independent of the motion of the light source, the speed of light has the same speed regardless of the frame of reference in which it is measured ; the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference this is the relativity of simultaneity ; and the linear additivity of velocities no longer holds true.

In physics, spacetime is any mathematical model that fuses the three dimensions of space and Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its spatial expression in terms of .

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## A Simple Ultimate Theory?

A hundred years ago today Albert Einstein published his General Theory of Relativity—a brilliant, elegant theory that has survived a century, and provides the only successful way we have of describing spacetime. But about 35 years ago, partly inspired by my experiences in creating technology, I began to think more deeply about fundamental issues in theoretical science—and started on my long journey to go beyond traditional mathematical equations and instead use computation and programs as basic models in science. Quite soon I made the basic discovery that even very simple programs can show immensely complex behavior—and over the years I discovered that all sorts of systems could finally be understood in terms of these kinds of programs. But sometime in —around the time the first version of Mathematica was released—I began to realize that if I changed my basic way of thinking about space and time then I might actually be able to get somewhere. Indeed, the history of physics so far might make us doubtful—because it seems as if whenever we learn more, things just get more complicated, at least in terms of the mathematical structures they involve. But—as noted, for example, by early theologians—one very obvious feature of our universe is that there is order in it. But just how simple might the ultimate theory for the universe be?

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The Data Structure of the Universe