What is quantum theory? Science and Religion in Schools Project Unit 3c[ii] 20 th century The New Physics. The early days Revolutionary new theory of matter Developed in the first 30 years of the 20th century Collective work of a group of highly talented physicists Development forced by experimental results - something funny was going on! Without quantum theory There would be no laser beams to read DVDs No integrated circuits (chips) No MRI scans for medicine Many other modern technologies depend on understanding quantum theory Mass Position Speed m = 9.11 kg x = 0.03 m v = 1 10 8 m/s New values of physical quantities Objective world The real electron Classical science and the world m = 9.11 kg x = 0.03 m 20% 0.04 m 30% 0.05 m 10% 0.06 m 20% 0.07 m 5% 0.08 m 5% 0.09 m 7% 0.10 m 3% v = 1 10 8 m/s 50% 1.5 10 8 m/s 40% 2.0 10 8 m/s 10% Objective world New range of probabilities ? Quantum theory and the world Uncertainty Discovered by Werner Heisenberg in 1927 Places a theoretical limit on our ability to measure position and momentum in the same experiment Heisenberg was encouraged to take a further step if in physics a quantity is defined by the way in which it is measured then the uncertainty principle tells us that position and momentum do not always mean anything Electrons are screwy too! Richard Feynman - brilliant theoretical physicist and teacher Said that all the mystery of quantum theory is wrapped up in one experiment Double slit experiment for electrons Double slit using light A classic experiment that shows how light is a wave Easy to do now with a laser The pattern of light and dark bands results from the light coming through two slits and combining on the far side How the double slit works Overlapping water waves from a pair of holes in a dam Projected onto a screen from a flat surface The choppy pattern at the bottom is very similar to the pattern of light and dark bands for light Imagine the pattern projected on a screen a right angles to the slide This is exactly the manner in which light waves from the two slits combine Send electrons at a pair of slits one by one Each electrons registers as a dot on a detector or photographic film As more and more electrons arrive, so a pattern of dots builds up The pattern looks very similar to the light and dark bands from the light experiment The same experiment with electrons So what is it? Is the electron a wave or a particle? Our categories of thought do not apply here The electron is not a wave nor is it a particle - it is a quantum object Moral?