<text><span class="style10">uantum Theory and Relativity (1 of 4)</span><span class="style7">Three of the most important theories of the 20th century are the quantum theory and the theories of special and general relativity. When special relativity is combined with the full quantum theory and with electromagnetism, almost all of the physical world is described by it. The most important application is in the theory of subatomic particles. General relativity is as yet not fully combined with quantum theory and is a theory of gravity and cosmology.The physical world is not as simple as the theories of Newton supposed, although such views are appropriate simplifications for large objects moving relatively slowly with respect to the observer. Quantum mechanics is the only correct description of effects on an atomic scale, and special relativity must be used when speeds approaching the speed of light, with respect to the observer, are involved.</span><span class="style10">The development of quantum theory</span><span class="style7">At the very beginning of the 20th century scientists such as the German physicist Max Planck (1858-1947) discovered that the theories of classical physics were not sufficient to explain certain phenomena on the subatomic scale, particularly in the field of electromagnetic radiation and the study of light waves. Their work resulted in the development of the quantum theory, which states that nothing can be measured or observed without disturbing it: the observer can affect the outcome of the effect being measured.The Scottish physicist James Clerk Maxwell (1831-79) had developed a theory about the electromagnetic wave nature of light, and this was crucial to the development of quantum theory. Maxwell showed that at any point on a beam of light there is a magnetic field and an electric field that are perpendicular to each other and to the direction of the light beam. The fields oscillate millions of times every second, forming a wave pattern (as shown in diagram 1).</span></text>
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<text><span class="style10">. An electromagnectic wave</span><span class="style7"> traveling along O</span><span class="style26">x</span><span class="style7">, made of up of electrical and magnetic fields that point along O</span><span class="style26">y</span><span class="style7"> and O</span><span class="style26">z</span><span class="style7"> respectively and oscillate rapidly.</span></text>
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<text>ΓÇó TIMEΓÇó MOTION AND FORCEΓÇó WAVE THEORYΓÇó ELECTROMAGNETISMΓÇó ATOMS AND SUBATOMIC PARTICLESΓÇó ELEMENTS AND THE PERIODIC TABLE</text>
