Time is the most fundamental aspect of our experience, and yet it remains mysterious in many ways. A longstanding problem is time's arrow – the directionality displayed by most physical processes, for example, clocks run down, organisms age, stars burn out. Ultimately that leads to cosmology (is study of the Universe in its totality). Most physicists are convinced that the origin of time’s arrow can be traced to the initial conditions of the universe, but the details depend on the specific cosmological model, and there is no agreed solution.
Another problem is the psychological perception of time, the feeling we all have that time is flowing or passing. Yet no such phenomenon is apparent in physics. So how does this impression of a moving present arise? Is it linked in some way to memory, or is there a deeper link – for example, between quantum mechanics (the study of matter and radiation at atomic level) and the observer – that plays a role?
Origin of physical laws
Science works because the universe is ordered in an intelligible way. The most refined manifestation of this order is to be found in the laws of physics, the fundamental mathematical rules that govern all natural phenomena. One of the biggest of the big questions of existence concerns the origin of those laws. Where do they come from, and why do they have the form that that they do?
Until recently, this problem was considered off-limits to science. The job of the scientist, it was maintained, is to discover the laws and apply them, not inquire into their form or origin. Now things had change one reason for this is the thrust toward a final unified theory of physics, sometimes called a “theory of everything,” that would encapsulate a complete description of nature in a single mathematical scheme.
A distinctive feature of the laws of physics is that (with one minor exception) they are symmetric in time, that is, they make no distinction between past and future. Yet the world about us has a definite temporal directionality, manifested for example in the way that the sun and stars are slowly and irreversibly burning up their fuel. The one-way slide towards degeneration, decay and entropy (degradation of matter) is often expressed by the so-called second law of thermodynamics. Just how a temporally asymmetric world has emerged from time–symmetric laws is a very old and still unsolved problem.
Origin of the universe
Most of the Cosmologists agree that the universe began with a big bang 13.72 billion years ago, but they disagree about some pretty basic questions, like:
- What happened before the big bang?
- Did time begin with the big bang?
- Are there other big bangs and other universes, and if so, will they be like ours or fundamentally different?
- Is it a lucky fluke that our universe is so well suited to life?