Topic: time

topics > Group: philosophy

communicating sequential processes
communication protocols
event time
general relativity
managing shared memory
Newtonian physics
real time systems
spatial vs. temporal representation
special relativity
temporal relationships


Time is normally thought of as an irreversible continuum marked by events. A regular sequence of events, such as clock ticks, serves to indicate time, but this is not necessary.

Traditional ways of viewing computers, ignore the transitions between states, i.e., a computer is always in a state. This view serves for writing single processor programs, but problems occur when systems consist of many concurrent, interacting sequences.

Perhaps time should not only be concurrent sequences of events, but also bidirectional. But this goes against experience. I would rather say that the attribute of time is its irreversibility. The question is similar to the existence of cyclical activities, because if such truly exist then they could cycle either forward or backward. (cbb 7/83)

Subtopic: what is time? up

Quote: what is time? I know as long as no one asks me to explain it [»theoCI3_1991]
Quote: time does not exist in its own right; it is part of things at motion and at rest; what happens to things in the past, present, and future [»lucr_55]

Subtopic: time as language up

Quote: time is nothing but the form of our internal intuition; it has empirical reality but not absolute reality [»kantI_1781, OK]
Quote: there is no absolute space, no absolute time, no simultaneity across distance, not even geometry; these concepts are no more than a language [»poinH_1902, OK]

Subtopic: measuring time up

Quote: we probably can not define time; we measure it by the repetition of some apparently periodic event [»feynRP_1963]
Quote: confirmation of Galileo's experiment of rolling balls down an inclined plane with time measured by water [»settTB1_1961]

Subtopic: time as light up

Quote: the propagation of light assigns equal tracts to equal time intervals [»einsA_1923]

Subtopic: simultaneous event up

Quote: all judgments of time concern simultaneous events [»einsA9_1905]
Quote: if time is a continuous real variable, then simultaneous events have measure zero [»peteJL_1981]
Quote: everyday experience fails to differentiate between "simultaneously seen" and "simultaneously happening"; i.e., the difference between local time and time
Quote: choice uncertainty principle -- can not chose between near-simultaneous events within a deadline [»dennPJ11_2007]

Subtopic: space time up

Quote: the time of an event depends on the event's reference-body or co-ordinate system [»einsA_1916b]
Quote: Newton--time and space are immutable and absolute [»newtI_1685, OK]
Quote: time and space are really statistical concepts, like temperature; meaningless for a single particle [»creaRP_1986]
Quote: events outside of the light cone from event P have a time-like relation to P; those inside have a space-like relation [»einsA_1956, OK]

Subtopic: time as change up

Quote: time and change have always been [»aris_322a]
Quote: time is either the same as change or is in some way bound up with it
Quote: since an object's state changes with time, an object exists 'in time'; unlike a value [»maclBJ12_1982]
Quote: the dimension of change is best represented through time, not through past versions [»laurB_1991]
Quote: since objects exist in time, they can be created and destroyed [»maclBJ12_1982]
Quote: memory is a wire turned sideways in time

Subtopic: physical time up

Quote: time-of-day can be seen as shared memory; maintained locally with periodic corrections from a network time server [»cherDR5_1986]
Quote: without physical time, there is no way to distinguish a failed process from one that is just pausing between events [»lampL7_1978]
Quote: leap year calculations are a generalization of Bresenham's algorithm for drawing lines [»harrMA3_2004]

Subtopic: clocks up

Quote: if ideal clocks go at the same rate, they always go at the same rate; e.g., sharp spectral lines from atoms of the same chemical element; a foundation of 4-d space-time
Quote: objective time requires a local time (clock) that is extended to events in the whole space [»einsA3_1936]
Quote: can model time as a sequence of states, as date stamps in a database, as temporal relations
Quote: a clock is an unbounded number of ticks, i.e., CLOCK = (tick -> CLOCK) [»hoarCA_1985]
Quote: a clock is a body or system that counts a series of events which can be regarded as equal
Quote: time is activity; the ticking of a clock is the simplest activity; or is time a single tick [»cbb_1980, OK]
Quote: synchronize clocks by mutual influence, occasional corrections, or accuracy [»leibGW11_1696]

Subtopic: clock synchronization up

Quote: globally synchronize clocks to 1/10'th second by exchanging messages with 3 other nodes every 4 minutes; for protocols, authentication, capabilities [»liskB9_1989]
Quote: an interval-based algorithm for fault-tolerant external clock synchronization [»schmU3_1997]

Subtopic: timer, time-out up

Quote: use hashed and hierarchical timing wheels for constant time maintenance of timers; practical for thousands of active timers [»vargG12_1997]

Subtopic: time as state transition up

Quote: a hiker going between valleys is like a clock whose ticks are the hiker's transitions from valley to ridge [»holtAW11_1980]
Quote: a digital device is always in some state; so states partition its existential time and transitions are instantaneous [»holtAW11_1980]
Quote: atomic state can not have duration separate from the duration of the processes that hold the state [»holtAW11_1980]

Subtopic: points vs. intervals up

Quote: though we can refer to times as points or intervals, most temporal references are implicitly stated by tense and event relationships [»alleJF11_1983]
Quote: most philosophical work on time are point-based theories instead of intervals [»alleJF11_1983]
Quote: events occur over an interval, so time associated with events can be decomposed; point times not useful [»alleJF11_1983]
Quote: can model time with discrete (integers) or dense (reals) elements; discrete time points is more widespread [»theoCI3_1991]
Quote: efficient algorithm to convert timestamps into event clocks; reduces state space for model checker of distributed protocols [»dereF3_2001]

Subtopic: time as sequence up

Quote: time in the infological model was an index of recorded facts by time [»theoCI3_1991]
Quote: extrinsic time--every statement is embedded in the temporal context that it occurred [»theoCI3_1991]
Quote: the order of acoustical experiences in time can differ from the order of corresponding visual experiences [»einsA_1916b]
Quote: the time sequence of events is not the same as the time sequence of experiences

Subtopic: reversible system up

Quote: the abstract description of a physical system is independent of temporal direction [»petrCA1_1966]
Quote: by exchanging 0s and 1s a switching element becomes its dual; if the element also exchanges 0s for 1s, the dual equals reversing temporal direction [»petrCA1_1966]

Subtopic: model time vs. system time up

Quote: every CML object includes time intervals for model time (system's knowledge) and system time (system's belief about its knowledge)

Related Topics up

Topic: change (28 items)
Topic: communicating sequential processes (33 items)
Topic: communication protocols (62 items)
Topic: concurrency (33 items)
Topic: event time (45 items)
Topic: events (44 items)
Topic: general relativity (47 items)
Topic: managing shared memory (74 items)
Topic: light (46 items)
Topic: Newtonian physics (79 items)
Topic: physics (51 items)
Topic: real time systems (14 items)
Topic: spatial vs. temporal representation (21 items)
Topic: special relativity (73 items)
Topic: temporal relationships (40 items)
Topic: timestamps
(19 items)

Updated barberCB 3/06
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