**Jennifer Ouellette Correspondent**

“Einstein’s Dice and Schrödinger’s Cat”, by Paul Halpern. On a cold January day in 1947, Erwin Schrödinger took the podium at the Royal Irish Academy in Dublin and triumphantly announced that he had succeeded where Albert Einstein had failed for the past 30 years. Schrödinger said he’d devised a unified theory of everything that reconciled the general theory of relativity with quantum mechanics.

His announcement caused a sensation in the international Press, which shamelessly played up the David and Goliath angle, much to Schrödinger’s discomfort and Einstein’s irritation.

It nearly destroyed their longstanding friendship. Matters became so acrimonious at one point, with rumours of potential lawsuits, that another colleague, Wolfgang Pauli, stepped in to mediate.

A full three years would pass before the estranged friends gingerly began exchanging letters again.

This tale of two physicists, their shared quest for unification and the media frenzy that tore them apart is the focus of Paul Halpern’s latest book, “Einstein’s Dice and Schrödinger’s Cat”.

The men were natural allies. Both were Nobel laureates, recognised for foundational work in the earliest days of quantum mechanics.

Each had a strong philosophical bent, which shaped his worldview. Einstein favoured the work of Spinoza, while Schrödinger had an affinity for Schopenhauer and dabbled in Eastern mysticism. Those philosophical influences contributed to their mutual dislike of the probabilistic nature of quantum mechanics, despite its stunning experimental success.

Einstein wasn’t shy about voicing his objections, famously declaring that God “does not play dice”, which prompted Niels Bohr to retort, “Stop telling God what to do!” Schrödinger vacillated a bit more in his stance — maintaining, Halpern says, “a quantum superposition of contrasting views” — but did ruefully confess, “I don’t like it, and I’m sorry I ever had anything to do with it.” To highlight the absurdity of the Copenhagen interpretation of quantum mechanics, he proposed his famous cat paradox.

At its heart, this is also the tale of two equations: Einstein’s equation of general relativity and Schrödinger’s wave equation, governing the realms of the very large and the very small.

The physicist Paul Dirac reconciled the wave equation with special relativity in 1928, sharing the Nobel Prize with Schrödinger for his efforts.

But general relativity thus far has resisted all efforts at being similarly assimilated into a complete theory of quantum gravity. To fully understand why requires delving into some very heady, mathematically dense material.

Halpern, a physicist at the University of the Sciences in Philadelphia, does his best to ground the casual reader with creative analogies and prose peppered with flashes of wit. Negatively curved (hyperbolic) space-time — usually described as a saddle shape — becomes “a curvy potato chip” for those whose “tastes are more epicurean than equestrian.” Max Planck’s notion of quanta is envisioned as “filling a piggy bank with a pile of coins of various denominations”, while Schrödinger’s wave equation is akin to “a scanner that processes wave functions and in some cases reads out their energy value and keeps them, while in other cases it discards them”.

Many a physics graduate student has gnashed her teeth in frustration over the mathematics of general relativity. Perhaps he/she should try envisioning a flat, boundless desert, with rocks of various sizes scattered across its surface, whose mass creates dips of various depths in the sand.

A sturdy canopy looms over that desert, stretched tightly over a skeleton of tent poles linked by bars, matching the rises and dips in the sand beneath it.

The desert is all the matter and energy in the universe, while the canopy is the geometry of space-time.

The poles and bars are the equations of general relativity, connecting the stuff of the universe with the shape of the universe. As Halpern writes: “Mass and energy warp space-time, telling it where and how to curve. The shape of space-time, in turn, governs how things move within it.”

Despite this knack for clear explication, such moments are all too often preceded by large chunks of technical, jargon-filled prose and dry rehashings of well-travelled historical ground.

The first half of the book in particular suffers in this respect; there is little that is new to surprise and delight the reader. The one fresh twist is the media angle, and Halpern’s writing shines when he returns to this theme, most notably in a lively chapter devoted to the dangers of conducting physics by Press release in the eagerness to unseat Einstein.

It remains a relevant issue, evidenced by the so-called faster-than-light-neutrinos fiasco a few years ago when a European experiment called OPERA stunned the world with a premature public announcement that it had clocked neutrinos travelling fractions of a second faster than the speed of light — an apparent violation of Einstein’s cosmic speed limit. (That result was later shown to be a calibration error, not a violation of relativity.)

For all the media excitement over Einstein’s attempts at unification, Halpern rightly notes that his peers were largely indifferent.

Mainstream physics left him behind as the Standard Model of particle physics took shape, and the mathematical approaches once explored by Einstein and Schrödinger have long since given way to string theory and loop quantum gravity, two of the most promising candidates for quantum gravity.

Should physicists ultimately succeed where they failed, will that be sufficient to wholly describe our universe? Halpern suspects not, because there are still many open questions in physics; he cites the mysterious nature of dark matter and dark energy as examples. Yet they will persevere, just like Einstein, who asked for a pencil and his notes the day before he died so he could continue to work on his calculations — tilting at windmills to the bitter end in his quixotic quest for unification. – NY Times.