The Physical Worldornament
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The Restless universe
Introduction to The restless Universe

1 The lawful Universe

2 The clockwork Universe

3 The irreversible Universe

4 The intangible Universe

5 The uncertain Universe

6 Closing items


Other titles in the Physical World series

Describing motion

Predicting motion

Classical physics of matter

Static fields and potentials

Dynamic fields and waves

Quantum physics: an introduction

Quantum physics of matter

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Question 1.9
List the major revolutions in physics that have occurred since 1650. Describe each in one or two sentences, giving only enough detail to distinguish it from the others.

(i) Newtonian mechanics explained the motion of particles in terms of the forces acting on them. The law of gravitation illustrated how forces could be calculated, while Newton's laws of motion showed how forces influence the motion of particles.

(ii) Thermodynamics deals with processes involving energy transfers, including heat, and clarifies ideas about equilibrium and irreversibility.

(iii) Statistical mechanics interprets thermodynamics in terms of the statistical behaviour of a large number of particles.

(iv) Electromagnetism deals with electricity and magnetism. It replaced the concept of action at a distance by that of a field, and showed that electric and magnetic fields have their own dynamics, leading to the interpretation of light and radio waves as electromagnetic waves.

(v) Special relativity is based on the idea that all observers in uniform motion should agree about the laws of physics. When the laws of electromagnetism were included, this led to a revolution in our ideas of space and time, which were merged together into space-time. Different observers, in different states of uniform motion, disagree about which events are simultaneous in space-time.

(vi) General relativity grew from the desire to express physical laws in the same way for all observers, even those who were not moving uniformly. It became a theory of gravity in which the motion of bodies was determined by the curvature of space-time, caused by sources of gravitation.

(vii) Quantum mechanics describes systems of particles in the atomic domain. It asserts that the fundamental laws of physics involve probability in an intrinsic and unavoidable way, and so casts doubt on simple realism.

(viii) Quantum field theory extends the ideas of quantum mechanics and special relativity to fields. Particles are interpreted as quanta of excitation of the field and may be created or annihilated as the field becomes more or less excited.

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