The Universe Within by Neil Turok Page A

advanced form of life capable of comprehending and picturing the functioning of the universe in ways we cannot. Our quantum future is awesome, and we are fortunate to be living at the time of its inception.
    Â· · ·
    OVER THE COURSE OF the twentieth century, in spite of Einstein’s qualms, quantum theory went from one triumph to the next. Curie’s radioactivity was understood to be due to quantum tunnelling: a particle trapped inside an atomic nucleus is occasionally allowed to jump out of it, thanks to the spreading out in space of its probability wave. As the field of nuclear physics was developed, it was understood how nuclear fusion powers the sun, and nuclear energy became accessible on Earth. Particle physics and the physics of solids, liquids, and gases were all built on the back of quantum theory. Quantum physics forms the foundation of chemistry, explaining how molecules are held together. It describes how real solids and materials behave and how electricity is conducted through them. It explains superconductivity, the condensation of new states of matter, and a host of other extraordinary phenomena. It enabled the development of transistors, integrated circuits, lasers, LED s, digital cameras, and all the modern gadgetry that surrounds us.
    Quantum theory also led to rapid progress in fundamental physics. Paul Dirac combined Einstein’s theory of relativity with quantum mechanics into a relativistic equation for the electron, in the process predicting the electron’s antiparticle, the positron. Then he and others worked out how to describe electrons interacting with Maxwell’s electromagnetic fields — a framework known as quantum electrodynamics, or QED . The U.S. physicists Richard Feynman and Julian Schwinger and the Japanese physicist Sin-Itiro Tomonaga used QED to calculate the basic properties and interactions of elementary particles, making predictions whose accuracy eventually exceeded one part in a trillion.
    Following a suggestion from Paul Dirac, Feynman also developed a way of describing quantum theory that connected it directly to Hamilton’s action formalism. What Feynman showed was that the evolution in time of Schrödinger’s wavefunction could be written using only Euler’s e , the imaginary number i, Planck’s constant h , and Hamilton’s action principle. According to Feynman’s formulation of quantum theory, the world follows all possible histories at once, but some are more likely than others. Feynman’s description gives a particularly nice account of the “double-slit” experiment: it says that the particle or photon follows both paths to the screen. You add up the effect of the two paths to get the Schrödinger wavefunction, and it is the interference between the two paths that creates the pattern of probability for the arrival of particles or photons at various points on the screen. Feynman’s wonderful formulation of quantum theory is the language I shall use in Chapter Four to describe the unification of all known physics.
    As strange as it is, quantum theory has become the most successful, powerful, and accurately tested scientific theory of all time. Although its rules would never have been discovered without many clues from experiment, quantum theory represents a triumph of abstract, mathematical reasoning. In this chapter, we have seen the magical power of such thinking to extend our intuition well beyond anything we can picture. I emphasized the role of the imaginary number i, the square root of minus one, which revolutionized algebra, connected it to geometry, and then enabled people to construct quantum theory. To a large extent, the entry of i is emblematic of the way in which quantum theory works. Before we observe it, the world is in an abstract, nebulous, undecided state. It follows beautiful mathematical laws but cannot be described in everyday language. According to quantum theory, the very act of our