Feynman Probability Quotes & Sayings

The strange feature of partial reflection by two surfaces has forced physicists away form making absolute predictions to merely calculating the probability of an event. Quantum electrodynamics provides a method for doing this-drawing little arrows on a piece of paper. The probability of an event is represented by the area of the square of an arrow. For example, an arrow representing a probability of 0.04 (4%) has a length of 0.2. — Richard Feynman

If a guy tells me the probability of failure is 1 in 100,000, I know he's full of crap. — Richard P. Feynman

If we have an atom that is in an excited state and so is going to emit a photon, we cannot say when it will emit the photon. It has a certain amplitude to emit the photon at any time, and we can predict only a probability for emission; we cannot predict the future exactly. — Richard P. Feynman

The only thing that can be predicted is the probability of different events. — Richard Feynman

Figure 18. As the thickness of a layer increases, the two surfaces produce a partial reflection of monochromatic light whose probability fluctuates in a cycle from 0% to 16%. Since the speed of the imaginary stopwatch hand is different for different colors of light, the cycle repeats itself at different rates. Thus when two colors such as pure red and pure blue are aimed at the layer, a given thickness will reflect only red, only blue, both red and blue in different proportions (which produce various hues of violet), or neither color (black). If the layer is of varying thicknesses, such as a drop of oil spreading out on a mud puddle, all of the combinations will occur. In sunlight, which consists of all colors, all sorts of combinations occur, which produce lots of colors. — Richard Feynman

Thus we can get the correct answer for the probability of partial reflection by imagining (falsely) that all reflection comes from only the front and back surfaces. In this intuitively easy analysis, the 'front surface' and 'back surface' arrows are mathematical constructions that give us the right answer, whereas ... a more accurate representation of what is really going on: partial reflection is the scattering of light by electrons inside the glass. — Richard P. Feynman

It is probably better to realize that the probability concept is in a sense subjective, that it is always based on uncertain knowledge, and that its quantitative evaluation is subject to change as we obtain more information. — Richard Feynman

The situation today is, we haven't got a good model to explain partial reflection by two surfaces; we just calculate the probability that a particular photomultiplier will be hit by a photon reflected from a sheet of glass. I have chosen this calculation as our first example of the method provided by theory of quantum electrodynamics. I am going to show you "how we count the beans"-what the physicists do to get the right answer. I am not going to explain how the photons actually "decide" whether to bounce back or go through; that is not known. (Probably the question has no meaning.) I will only show you how to calculate the correct probability that light will be reflected from glass of a given thickness, because that's the only thing physicists know how to do! What we do to get the answer to this problem is analogous to the things we have to do to get the answer to every other problem explained by quantum electrodynamics. — Richard Feynman

It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management. — Richard P. Feynman

Figure 36. A "trick" can be played on Nature by slowing down the light that takes shorter paths: glass of just the right thickness is inserted so that all the paths will take exactly the same time. This causes all of the arrows to point in the same direction, and to produce a whopping final arrow-lots of light! Such a piece of glass made to greatly increase the probability of light getting from a source to a single point is called a focusing lens. — Richard Feynman

The probability of an event is always represented by a single final arrow-no matter how many arrows were drawn, multiplied, and added to achieve it. — Richard Feynman