Steven Weinberg is a remarkable man. A particle physicist and cosmologist, and Noble prize winner (due to his work on the electroweak theory), he is also passionately interested in the history of science and a popularizer of the work he's involved in.
In The First Three Minutes (1977) Weinberg tried to explain to the popular audience the current scientific insights about the origin of our universe. This was (to my knowledge) the first accessibe and complete account of this topic.
Ever since the 70's particle physics and cosmology have developed and seen the rise (and fall) of new theories and experiments. In Dreams of a Final Theory (1992), Weinberg explains the progress in physics from the ancient pre-Socratics throuh Newton and Einstein to modern conceptions.
Weinberg's main motive for writing this book is explicitly stated, and spans the final chapter and a postscript. He wants to explain the current status in particle physics as an argument to build the Super Conducting Supercollider (SCS). This device will let physicists experiment with bigger and better tools to cross the frontiers in particle physics (for example, the detection of certain predicted particles which require high energies to be detected).
The building of this SCS was cancelled a year after Weinberg published his book; CERN in Europe built the Large Hadron Collider and detected (among other things) the long-predicted Higgs particle.
So, Weinberg's plea went unheard. I still think his book is successful, though. The current status of pure science requires the expenditure of billions of dollars - money that could have been used in many other ways. In a democratic society (such as the US or European countries) there has to be a mechanism that allocates money in a democratic way. This means that if scientists want to spend public money, they have to explain why this money is so crucial. And besides, the allocation of these sums of money (but really any amount of money, in general) creates an obligation for the scientists involved in spending the money in explaining their results to the public.
(In this sense, we need more people like Steven Weinberg. Scientists are generally reluctant to publish books, while continuously publishing abstract articles in obscure and barely read journals. Most publish the general progress of their carreers in book-form when they retire, but this is just too little, too late. I would claim that the public has a right to know what the current status in important scientific domains looks like.)
But back to Weinberg's book. He has a gift for explaining difficult theories like general relativity and quantum mechanics in accessible terms. Of course this means a lot of generalizing and simplifying, but Weinberg manages to get his main theses across (whereas other popular writers like Krauss are more problematic in that respect).
In a sense, Dreams of a Final Theory explains how physicists have been homing in on ever simpler, singular and more beautiful theories. This means (in layman's terms) mathematical theories that cannot be changed without leading to absurdities. This leads Weinberg to the conclusion that the ultimate theory, a theory of everything, is near (at least in distance, it still can take a lot of time for us to get there).
A theory of everything would mean a mathematical theory that incorporates the standard model of particle physics and general relativity. The standard model is itself a major breakthrough of twentieth century physics: it incorporates the electroweak theory (the theory that incorporates the electromagneticity and the weak nuclear force that is responsible for nuclear reactions) and the strong nuclear force (which is responsible for keeping the quarks inside protons and neutrons).
The standard model incorporates three forces of nature - electromagneticity, the weak force and the strong force - and will have be combined, one way or another, with general relativity, which describes the fourth force of nature: gravity.
Thus far, attempts to combine Einstein's relativity and the Copenhagen interpretation of quantum mechanics into one single consistent equation have failed. Weinberg argues that structures like the earlier mentioned SCS as well as the European Large Hadron Collider could help with our search for the final theory. In other words: physics is at a relative standstill and we need better equipment to progress beyond the current frontier.
Since this book was published in 1992, it naturally is outdated. Since then, a lot has changed. As mentioned, CERN has build the LHC in Geneva and one its major discoveries is the Higgs particle. The experiment confirmation of the existence of Higgs particles shows the correctness of the Higgs field theory. This is a theory that explains the symmetry break in the theories of the standard model of particle physics. Basically, all the elementary particles (photons, electron, quarks, etc.) are bundles of energy, quanta, in various fields.
For a layperson, this last statement might seem arcane and/or trivial, but it really is a radical break with the past. Gone is the mechanism of Newton and Laplace: everything in the universe is the result of fluctuations in various fields. The radicality of the new science (relativity, quantum mechanics) is legitimate, since they yield the exact same theories as the old ones (like Newton's gravity being incoroporated, as a special condition, in Einstein's general relativity), as well yielding very narrow predictions, which have been validated by the most accurate and precise experiments ever conducted.
There is a whole collection of elementary particles - Weinberg even admits (with a smile) that physicists, at all times, have to carry a list in their pocket which sums up all the different particles - and the quest is to unite them all into one consistent theory.
Weinberg's approach to science is reductionist, albeit in a reasonable sense. Reductionism claims that a science has to be explained, ultimately, in terms of the science which describes its building blocks. So for example, sociology - the study of human social groups and human interaction - has to be explained in terms of the behaviour of individual human beings. Hence, since the building blocks of sociology are human minds, psychology and neuroscience is the foundation at which sociology rests. Likewise, chemistry is the interaction of molecules and atoms; hence, chemists have to explain, ultimately the building blocks in their theories (i.e. atoms) in terms of physics.
According to people like Weinberg, physics is the ultimate resting ground for all the sciences. But this has to be interpreted in a very precise way: the chemist studies chemical processes and the sociologists studies human group interactions; they both don't need physics to study the emergent processes in their domains. Reductionism just means that any scientific field has to have its foundation in a more basic science. Reductionism has been a very fruitful way to approach science, while anti-reductionists have never been able to mount a serious alternative.
What does this mean for physics? Physics has to rests on some foundation as well, right? Well, according to Weinberg - and he uses two chapters in getting this point across - physicists are looking for a mathematical equation that is simple and beautiful, in the sense that (1) it contains all the current theories in physics (quantum mechanics, general relativity), (2) it is consistent and coherent, and (3) it cannot be changed in any way without leading to obvious absurd results. This means that physics, ultimately, rests in a mathematical equation that could legitimatelly called a theory of everything. In practice, we are still far from this, though we can never be sure when - and if - this equation will ever be found.
I found this book to be a revelation. Weinberg is able to explain the most important theories and discoveries in physics in a very easy-to-grasp style and he is able to paint the general picture. He also manages to emphasize the dualistic and mudy approach of science: observation and theory development are in continuous interaction, without the one being dominant over the other. Lastly, Weinberg clearly makes explicit when he gives his own opinion and when he tells the generally accepted view - something that not many authors manage to do.
I much liked Weinberg's description of the Super Conducting Supercollider as being just the last piece of equipment in a long line of inventions. Those inventions are the crutches that we use to overcome the fallibity of our own senses. Galileo's telescope started it all; the particle accelerators are the latest crutch.
As a last remark, I'd like to mention Weinberg's view on religion and science. Weinberg explains that scientific developments have pushed God out of the world of science and that conservatists as well as scientists realize the importance of this, as opposed to the liberal masses. Hence, the continuous struggle of movements like Creationism and Intelligent Design. For Weinberg, there is no place for God in this universe; the scientific laws discovered explain anything from the big bang onwards.
What I find remarkable in Weinberg is his honest reluctance to admit the success of science in explaining the world. Weinberg longs for the mystery of the past and even admits that the scientific outlook is barren; it lacks emotion and spiritual fulfilment. Yet, he is a seeker of truth and hence has to apply his own methods to his own outlook, leaving him an atheist.
I sympathize with this view, it is something I fully subscribe to as an atheist and reductionist. But in the end, we have to strive to rationally approach all the important matters of life. As Weinberg himself explains, the irrationality of the past (i.e. religion or other forms of superstition) has led to immense human suffering. Science has given us better weapons, true, but it has also given us the tools to lead better (and safer) lifes. There has never been a war about a scientific idea (those are fought in journals) or a war between scientists. Irrationality is dangerous; rationality is, though no sinecure, the best we've got.