Hand in the universe

At the other end of Caleb Scharf's book on gravity at it's most intense he sums up the relevance of some of the largest and most powerful structures in the universe to our own existence.  He recaps his descriptions of how black holes are not just the simple uncomplicated dents in space time you and I thought they were, but are the most efficient means the universe has of converting matter to energy, working like electrical batteries to power and shape galaxies and create the conditions for our own existence:

Take a look at your hand.  It contains atoms of carbon, oxygen, and nitrogen that were forged a million miles below the surface of another star billions of years ago.  Your hand also contains hydrogen that was present at the very beginning of the universe.  All these elements have felt the presence of black holes.  Right now, a tiny fraction of the vast electromagnetic sea of photons racing through the universe is reaching down through our own atmosphere, hitting the ancient atoms of your flesh.  Some of these photons originate in the fearsome spinning of matter around black homes, or from the jets of particles rushing at near light speed out into the cosmos.  We are awash in their radiation, but it is nothing new to the atoms in your hand.  As the cosmic dark ages lifted 13 billion years ago, some of the primordial hydrogen in your body was likely buffeted and tickled by the radiation of feeding black holes.  Billions of years later, the stars that built your heavy elements existed because of the history of gravity and energy in one zone of what was becoming the Milky Way galaxy.

Black Holes and Dams

For some stories of gravity at its most intense I have been checking out Caleb Scharf's Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos.  For such mind blowing subject matter it turns out to be a pretty good read, partially because he can find metaphors for the phenomena he describes that the reader reader can intuitively grasp.  The Hoover Dam is one such metaphor.  Scharf calls it a "temple of gravity":

The enormous forms of concrete and steel are poised in space and time, feeding off the energy of the Colorado River as it squeezes through the gorge.  The dam is much more than a great engineering feat; it feels profoundly connected to the hidden glue and threads binding the universe together.

He continues to use the dam as a way introduce the reader to the mind bending effects of gravity on scales impossible to image, bolstering his metaphor with the star map set in the floor beneath the winged sentinels representing the republic.  The positions of the stars depicted in the map point to the exact date the dam was dedicated by President Roosevelt.  These kind of connections root his descriptions and allow us to follow him to the edges of our perceptions and well beyond our everyday understanding of how things work.