# 2.6 Closing items

## 2.6.1 course summary

1. Laws summarise regularities observed in Nature. They can summarise large numbers of similar phenomena and make it possible to predict the course of particular phenomena.

2. In physics, many of the laws are expressed mathematically and concern measurable quantities. This aids precision and clarity, and it supports rational argument.

3. Newtonian mechanics is based on equations (Newton's laws of motion, Newton's law of universal gravitation) that are deterministic: they have the property that the present is entirely determined by the past. Complete knowledge of the state of the Universe at any one time would make possible, in principle, the determination of its state at all other times.

4. Thermodynamics, with its emphasis on energy conservation (the first law) and entropy growth (the second law) indicates an effectively unavoidable irreversibility in the laws of Nature.

5. Electromagnetism was ultimately responsible for the introduction of the field as a new fundamental ingredient in physical world-views. Although attempts were made to formulate mechanical models of the electromagnetic field, such efforts are no longer a serious topic of scientific investigation. Fields are introduced to avoid the use of action at a distance.

6. Special relativity is based on the idea that observers in uniform motion should agree about the laws of physics. It has the effect of unifying space and time into a space-time that different observers slice into space and time in ways that depend on their relative motion.

7. General relativity represents gravity as a manifestation of space-time curvature: 'matter tells space how to curve, space tells matter how to move'.

8. Quantum physics is characterised by the intrinsic and unavoidable use of probability (implying indeterminacy in the behaviour of individual systems). Quantum mechanics is a major subdivision of quantum physics that deals with particles and calls into question the simplest kind of realism. Quantum field theory is another major subdivision of quantum physics. It deals with fields and represents a natural fusion of quantum physics and special relativity. Quantum fields can be interpreted in terms of particles and provide a good way of describing at least three of the four fundamental forces of Nature.

OpenLearn - The restless Universe
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