La fisica semplice per non fisici
Theory in Simple Terms (Fonte)
Chaos theory is the theory of the unpredictable behaviour that can arise in systems obeying deterministic laws as a result of their sensitivity to variations in the initial conditions or to an excessive number of variables. Although deterministic laws enable the condition of a system to be predicted at any time in the future, to do so often depends on an ability to specify with great precision a set of parameters at an exactly specified moment. An example of chaos theory occurs in long-term weather forecasting. T'he meteorological laws may be well understood, but obtaining exact parameters to use with them may not be possible. In the butterfly effect, for example, it is postulated that the flap of a butterfly's wings can so upset the sensitive meteorological dynamics that an unforecast tornado may be set off by it.
Relativity in Simple Terms (Fonte)
The theory of relativity is in fact two theories. The special theory of relativity (1905) and the general theory of relativity (1915). The special theory gives a unified account of the laws of mechanics and of electromagnetism. Einstein rejected the concepts of absolute space and time and made two postulates (a) the laws of nature are the same for all observers in uniform relative motion and (b) the speed of light is the same for all such observers.
The transformation of time implies that two events that are simultaneous according to one observer will not necessarily be so according to another in uniform relative motion. It will appear to two observers in uniform relative motion that each other's clock runs slowly. This is the phenomenon of time dilation.
A mathematical formulation of the special theory of relativity is based on the idea that an event is specified by four co-ordinates: three spatial co-ordinates and one time co-ordinate. These co-ordinates define a four-dimensional space and the motion of a particle can be described by a curve in this space.
The special theory of relativity is concerned with relative motion between non-accelerated frames of reference. The general theory deals with general relative motion between accelerated frames of reference. In accelerated systems of reference, certain fictitious forces are observed, such as the centrifugal and Coriolis forces found in rotating systems. These are known as fictitious forces because they disappear when the observer transforms to an non-accelerated system.
The predictions of general relativity only differ from Newton's theory by small amounts and most tests of the theory have been carried out through observations in astronomy. For example, it explains the shift in the perihelion of Mercury, the bending of light or other electromagnetic radiation in the presence of large bodies, and the Einstein shift.
Super-String Theory in Simple Terms (Fonte)
In the considerable amount of (welcome!) e-mail we recieve from this site, we have been continuously getting requests for a simple explanation of super-string theory. We have therefore decided that it would be more appropriate to create a new section of the time travel web site dedicated to answering this very important question for our visitors. As always, your comments are welcome.
The super-string theory of elementary particles is based on the idea that the fundamental entities are not point-like particles, but finite lines (strings) or closed loops formed by strings. The original idea was that an elementary particle was the result of a standing wave in a string.
A considerable amount of theoretical effort has been put into developing string theories. In particular, combining the idea of strings with that of supersymmetry leads to the idea of superstrings. This theory may be a more useful route to a unified theory of fundamental interactions than quantum field theory because it probably avoids the infinities that arise when gravitational interactions are introduced into field theories. Thus, superstring theory inevitably leads to particles of spin 2, identified as gravitons.
Superstring theories involve the idea of higher dimensional spaces: 10 dimensions for fermions and 26 dimensions for bosons. It has been suggested that there are the normal 4 space-time dimensions, with the extra dimensions being tightly 'curled' up.
There is no direct experimental evidence for superstrings. An extension
of the theory postulates that the fundamental entities are not one dimensional