Arrow of time

The arrow of time is the idea of ​​a unique and directional connection between past and future. Each different meanings combine with this idea in the sciences, but also in everyday life. The term " arrow of time " ("time 's arrow " ) was first described by Sir. Arthur Eddington in 1927 coined ( Gifford Lectures ).

Arrows of time

Psychologically

The psychological arrow of time describes our subjective distinction between past and future events. We can remember the past but not the future. The common view of the time arrow considered the future it (ie in the viewing direction ). See also: Philosophy of time.

Language

Conversely, linguistically, however, often the local adverb "front" used for the past, for example, "before", "anticipate ", " before" (English), " avant " (French), while the word for local " then " is used for the future, eg "after" (English), " après " (French).

Also in Andean cultures (eg, Quechua, Aymara ), the future than at rear ( ie contrary to the view direction, since unknown future ) looks at what according to the languages ​​of the Andes ( Quechua, Aymara ) puts it, in which the local adverb for "front" ( Quechua: " ñawpa ") in the temporal sense " earlier passed " means, while the adverb for " back" ( Quechua: " qhipa " ) " future " in the temporal sense.

Causal

After that causes their effects go ahead always. The causal arrow of time is a postulate reflects the everyday experience. However, it is not clear whether causality is mandatory or is not generated by perception.

Historically

The story is reconstructed on the basis of documents. Documents is generally found only of operations of the past, not the future of operations. When an archaeologist digs up remains of a city, he may conclude that once stood on the said location a city. From a city that will be at this point in the future, he can dig up any leftovers.

Thermodynamic

The thermodynamic arrow of time is based on the second law of thermodynamics: The future is the time direction in which entropy increases. An interesting point is that this arrow of time does not exist in thermodynamic equilibrium: For an equilibrium state, there is no thermodynamically defined past and future; the equilibrium state is a way timeless.

Cosmologically

The universe began with the Big Bang and expands from since. Whether it will extend to all eternity, is not known for sure. According to the calculations and theories prevailing it looks. Thus, one can read off the elapsed time on the size of the universe: the future is the direction of the larger universe.

But even if the universe contracts again, the old, collapsing cosmos looks different than the early, expanding: it contains burnt out stars, which are collapsed partly into black holes, and heavy elements are created in supernova explosions. Thus, one can also to the composition of the universe, its age, and thus read the time direction.

The CP violation

While the difference between past and future is omnipresent at the macroscopic level, applied to the microscopic laws of matter hitherto always been that these were time-reversal invariant: If a task can run forward, then he can just as well run backwards, provided only that the conditions are met. For example, the fact that an excited atom can fall into the ground state by emitting a photon, that the reverse process, the excitation of an atom in the ground state by an absorbed photon, the same mechanism is possible.

Now measurements of certain elementary particles, the so-called kaons, a violation of the so-called CP- invariance have shown. This says that for each process in matter and the ( spatial) mirror-image process exists in anti-matter, and runs in the same way.

The violation of the CP invariance is interesting because of the CPT theorem, which states that for any process with matter, the mirrored and time-reversed process runs with antimatter in the same way at this point. This theorem is quite basic and therefore not normally be called into question. But if the CPT theorem holds, so is a violation of CP invariance also a violation of time-reversal invariance.

This does not mean that the fundamental laws of physics to know the difference between past and future, but only that the exact time-reversed analogue of a process also requires a space reflection and charge inversion.