Mapping the Heavens—The Radical Scientific Ideas that Reveal the Cosmos

Author: Priyamvada Natarajan
Publisher: Yale University Press 2016

Priyamvada takes the reader through four-thousand-years of cosmic history in 224 pages.  She begins the journey with the Nebra Sky disk, an artifact made in the bronze age (2000 BCE), and ends it with multiverses and exoplanets.  I am somewhat familiar with this tour—from my previous readings—but she takes us into side roads throughout the journey making me realize that I missed a lot of sightseeing in my previous trips.  It seems like a very ambitious project at the beginning, but in the end, she succeeded beautifully.  I would consider this as a masterpiece in scientific writing.  

It would be extremely difficult to condense the materials she covered into a short note, but I will give it a try to encourage you to read this book.  If you cannot follow this condense version, then get the book and read it.

The book is divided into seven chapters; 1. Early Cosmic maps, 2. The Growing Border: The Universe Expands, 3. The Dark Matter: Black Holes Becomes Real, 3. The Invisible Grid: Coping with Dark Matter, 5. The Changing Scale: The Accelerating Universe, 6. The Next Wrinkle: The discovery of Cosmic Background Radiation, 7. The New Reality and the Quest for Other Worlds, and an epilogue.  

In the first chapter, we find that the Babylonians studied the sky, made star charts, and used those charts to draw connections between celestial and terrestrial.  They assumed that the world rested on a back of a turtle, which was supported below by yet another turtle, with turtles all the way down.  Greek astronomer Anaximander (610 BCE) is the first to propose that the Earth was freely suspended.  In the second century CE, Claudius Ptolemy collected all the astronomical data known then and wrote the treatise, the Almagest.  The ability to predict positions of celestial objects lent the Almagest authority throughout the middle ages.  Copernicus in 1514 proposed a heliocentric model and Johann Kepler proposed elliptic orbits for planets.  Viewed from Earth, Mars appears to travel backward periodically in the sky only to resume its forward motion.  Kepler’s ellipses finally able to account for this movement.  In 1687 Newton outlined the universal law of gravity which provided explanations to almost all observations.  Stephan Weinberg covers the content of this first chapter in much more detail in his book “To Explain the World”.

The second chapter takes us to the big bang model.  One of the problems remained unsolved by Newton’s law of gravity is the peculiarities of the orbit of mercury. (See the “Hunt for Vulcan” by Thomas Levenson) Einstein’s general theory of relativity solved this mystery.  Einstein included a cosmological constant lambda in his field equations in 1917 to ensure stars and galaxies remained fixed in the sky.  However, Alexander Freidman in 1922 showed that there is another time-varying solution to field equations that predicted an expanding universe.  Edwin Hubble by studying nearby galaxies found evidence for an expanding universe.  Einstein reluctantly withdrew the cosmological constant.

In the third chapter priyamvada introduces us to Subramanian Chandrasekhar.  Chandrasekhar’s calculations indicated that stars that were initially 1.4 (Chandrasekhar limit) to 3 times more massive than the sun would end up as a neutron star while those that are ten or more massive than the sun would end up as a black hole.  Now we know that there are super massive black holes in the centers of galaxies.  A new project aims to map the black hole at the center of our galaxy with a new instrument—The Event Horizon Telescope.  

The dark matter is the subject of the fourth chapter.  Fritz Zwicky studying the motions of galaxies in the Coma Cluster of galaxies in 1933 found out that the mass in the Cluster is four hundred times denser than expected.  He proposed that there must be some unseen dark matter that accounts for the extra mass.  In 1970 Vera Rubin and Ken Ford discovered that the stars in spiral galaxies were experiencing a stronger pull of gravity than could be inferred from just the visible mass of stars.  Rubin and Ford’s discovery proved to be dark matter’s tipping point.  The existence of dark matter and the significant role it plays in the cosmos is widely accepted today.  

Remember Einstein’s cosmological constant? It turned out that a cosmological constant needed after all.  In the fifth chapter, we find out that there is a mysterious dark energy that is accelerating the expansion of the universe and the cosmological constant must be 0.7.  Of the total mass-energy of the universe, 70% is dark energy, 25% is dark matter, 4% is free hydrogen and helium, 0.5% are stars, 0.3% are neutrinos, and just 0.03% are heavy elements.  

The next wrinkle (chapter 6) is the cosmic background radiation (CMBR).  George Gamow (the author of One Two Three … infinity), Ralph Alpher and Robert Herman in 1944 conjectured that the early universe left behind a radiation known as cosmic background radiation.  Arno Penzias and Robert Wilson discovered the cosmic background radiation in 1964.  Scientific instruments on three satellites (COBE, WMAP and Plank) studied the CMBR since 1989.

It turns out that to fully specify all the relevant properties of the universe, all we need is six numbers known as cosmological parameters. Those parameters are \(N\) - ratio of electric force to gravitational force between atoms, \(\epsilon\) - binding strength of atomic nuclei, \(\Omega\) -Total mass-energy content of the universe, \(\lambda\) - the cosmological constant, \(Q\) - size of initial fluctuations, and \(D\) - number of special dimensions. The values of these parameters are known.  However, if the values of these parameters deviate even slightly then the universe that we know of would not exist. This leads to the idea that there may be other universes where these six numbers are different.

This is the fourth book of this kind that I have seen within a year.  What is the reason for so many books in such a short time? Primvada seems to provide an answer in the epilogue.

“… Given all this, why are we still witnessing the most vehement denial of science?  In my opinion, what fuels rampant denialism is not lack of knowledge of scientific facts but rather ignorance about how science and scientific reasoning work.”