By Steven Weinberg
The New York Review of Books, September 25, 2008

Edited by Andy Ross

A tension between science and religion has been gradually weakening serious religious belief, especially in the West, where science has been most advanced. There are at least four sources of tension:

1   Religion originally gained much of its strength from the observation of mysterious phenomena that seemed to require the intervention of some divine being. But as time passed more and more of these mysteries have been explained in purely natural ways. We have not observed anything that seems to require supernatural intervention for its explanation. There are some today who cling to a God of the gaps. But as the gaps are filled in, their position gives an impression of desperation.

2   These explanations have cast increasing doubt on the special role of man as created by God to play a starring part in a great cosmic drama. The discovery that humans arose from earlier animals through natural selection acting on random heritable variations is the one that continues most to disturb religious conservatives. Both brain activity and behavior are in the same world of objective phenomena, and I know of no obstacle to their being integrated in a scientific theory.

3   Around 1100 CE, the Sufi philosopher Abu Hamid al-Ghazzali argued against the very idea of laws of nature, on the grounds that any such law would put God's hands in chains. I wish I knew enough to judge how great was the impact on Islam of his rejection of science. At any rate, science in Muslim countries went into a decline in the century or two later. A recent survey found just three areas in which the Islamic world produced excellent science: desalination, falconry, and camel breeding.

4   Traditional religions generally rely on authority, such as a prophet or a pope or an imam, or a body of sacred writings. Scientists rely on authorities of a very different sort. If I want to understand some fine point about the general theory of relativity, I probably would not look up the original papers of Einstein, because today any good graduate student understands general relativity better than Einstein did. Heroes in science are not infallible prophets.

Religious belief is only one aspect of the religious life. For many people, the important thing about their religion is not a set of beliefs but a host of other things. But I wonder how long religion can last without its metaphysical beliefs.

For a physicist, it is a joy to learn how we can use mathematics to understand the world. But we need not worry that giving up religion will lead to a moral decline. Belief in an omnipotent omniscient creator has no moral implications.


By Steven Weinberg
The New York Review of Books, November 7, 2013

Edited by Andy Ross

Cosmology first became a science when it was found that galaxies are all rushing away from us and from each other. So once they were all crunched together. The early universe must have been very hot and would have radiated light that survived to the present as radiation cooled by expansion.

The cosmic microwave background radiation has a present temperature of 2.725 K. Calculations of the formation of the nuclei of atoms in the first three minutes after the big bang predict a present abundance of light elements in agreement with observation. Heavier elements are produced in stars.

There are small ripples in the temperature of the microwave radiation. These ripples are due to chaotic sound waves in the early universe. When the universe cooled to 3 kK it became transparent. The radiation bears the imprint of the sound waves that filled the universe before it became transparent.

The universe became transparent some 12 Ts after the creation of atomic nuclei. The particles known to us are not enough to account for the mass of the hot matter in which the sound waves must have propagated. Five sixths of the matter of the universe seems to be dark matter.

The dark matter had already been inferred from the fact that clusters of galaxies hold together gravitationally. But the expansion of the universe is speeding up. In the general theory of relativity, this is explained by a dark energy that now makes up about three quarters of the total energy of the universe.

The universe has been expanding for 13.8 billion years since it became transparent. In the standard cosmological model, our expanding universe is mostly dark energy and dark matter. A few percent of it consists of the ordinary matter that makes up the stars and planets and us.

Elementary particle physics emerged from a deluge of data. Quantum electrodynamics is a quantum field theory. The quantities appearing in the fundamental equations are fields. Elementary particles are the quanta of the fields. Photons are the quanta of the electromagnetic field.

The quantum field theory of the weak nuclear force worked well for previous data but gave nonsense at first when used to calculate the rates of exotic processes. The electroweak theory says the weak nuclear force is transmitted by the exchange of W and Z particles.

In the electroweak theory there is an exact symmetry between weak and electromagnetic forces, but the symmetry is broken by four proposed scalar fields that permeate the universe, from which particles get masses. The recently discovered Higgs particle is the quantum of one of these fields.

The strong nuclear force that holds protons and neutrons together inside atomic nuclei suggests that three quarks combine to make up each proton and neutron in an atomic nucleus. In quantum chromodynamics, the strong forces between quarks are produced by the exchange of eight kinds of gluons.

The standard model of elementary particles includes quantum fields and the various elementary particles that are the quanta of those fields: the photon, three W and Z particles, eight gluons, six types of quarks, the electron and two types of similar particles, and three kinds of neutrinos.

The standard model is not the final theory. Its equations involve a score of numbers that have to be taken from experiment without our understanding why they are what they are. It does not include gravitation. We commonly describe gravitation using the general theory of relativity, but this is not a quantum theory.

In the 13.8 billion years since the universe became transparent there has not been time for radiation to have connected and homogenized all the parts we see. So we think the universe inflated exponentially at first. Tiny uniform regions would have inflated to become larger than our present observed universe.

Inflation is naturally chaotic. Quantum fluctuations during inflation would trigger just the sort of chaotic sound waves we find in the cosmic radiation background. Bubbles form in the expanding universe, each developing into a big or small bang. The ocean of all these bubbles is the multiverse.

String theory incorporates gravitation, it contains no infinities, and its structure is tightly constrained by mathematics. But the equations of string theory have a vast number of solutions. Different bubbles may realize all the different solutions. We live in a bubble allowing the evolution of life and intelligence.

AR This is a masterful summary, as one would expect.