Delia Perlov

An Expanding Universe

Shortly after completing the general theory of relativity, Einstein went on to apply his new theory to the universe as a whole.

The Fate of the Universe

Will the universe continue to expand forever, or will it eventually halt and start to collapse?

Testing Inflation: Predictions and Observations

We have seen how cosmic inflation can create an enormous universe from a tiny seed, while solving many problems that plagued pre-inflation models.

The Theory of Cosmic Inflation

The horizon and flatness problems had been recognized since the 1960s, but were rarely discussed—simply because no one had any idea as to what to do about them.

Dark Matter and Dark Energy

The composition of the heavens was a great mystery until the spectroscopic discoveries of the mid 1800s showed that the chemical elements in stars are the same as those on Earth (as we discussed in Chap. 6).

String Theory and the Multiverse

Much of the research in particle physics has been inspired by the quest for a unified, fundamental theory of Nature. The hope is that beneath the plurality of particles and forces, there is a single mathematical law that governs all natural phenomena. A major step towards the unification of forces was the development of the electroweak theory.

The Quantum World

Modern physics began with two revolutions at the turn of the 20th century. The first revolution, which radically changed our concepts of space and time, was single handedly accomplished by Einstein with his special and general theories of relativity.

Hubble’s Law and the Expanding Universe

In the early 1900s, Vesto M. Slipher of the Lowell observatory in Arizona analyzed the spectra of many spiral nebulae.

Newton’s Universe

In his monumental Principia, Newton formulated the general laws of motion and the law of universal gravitation. He then applied these laws to explain the motion of planets and comets, projectile trajectories, and the marine tides, among other things.

The Fabric of Space and Time

Einstein’s special theory of relativity was a great breakthrough in our understanding of the physical world, but it presented a problem: it was incompatible with Newton’s law of gravitation. Newton himself, and some ten generations of physicists and astronomers that followed, used this law to describe the motion of planets with remarkable accuracy. Granted, there was a tiny discrepancy in the calculated precession rate of the orbit of Mercury, but it did not seem to be a cause for concern. After all, theories seldom agree with all the data at any given time. Some of the data may simply be wrong and some discrepancies are later explained away with more careful theoretical analysis. Thus, Newton’s theory appeared rock solid. However, it did not fit into the framework of special relativity.