SpaceWire is a spacecraft communication network based in part on the IEEE 1355 standard of communications. It is coordinated by the European Space Agency (ESA) in collaboration with international space agencies including NASA , JAXA , and RKA .
98-558: Within a SpaceWire network the nodes are connected through low-cost, low- latency , full-duplex , point-to-point serial links, and packet switching wormhole routing routers. SpaceWire's modulation and data formats generally follow the data strobe encoding - differential ended signaling (DS-DE) part of the IEEE Std 1355-1995. SpaceWire utilizes asynchronous communication and allows speeds between 2 Mbit/s and 200 Mbit/s, with initial signalling rate of 10 Mbit/s. DS-DE
196-442: A n c e r | s m o k i n g ) {\displaystyle P(cancer|smoking)} , and interventional probabilities , as in P ( c a n c e r | d o ( s m o k i n g ) ) {\displaystyle P(cancer|do(smoking))} . The former reads: "the probability of finding cancer in a person known to smoke, having started, unforced by
294-506: A progression of events following one after the other as cause and effect. Incompatibilism holds that determinism is incompatible with free will, so if determinism is true, " free will " does not exist. Compatibilism , on the other hand, holds that determinism is compatible with, or even necessary for, free will. Causes may sometimes be distinguished into two types: necessary and sufficient. A third type of causation, which requires neither necessity nor sufficiency, but which contributes to
392-424: A real-time operating system . Note that in software systems , benchmarking against "average" and "median" latency can be misleading because few outlier numbers can distort them. Instead, software architects and software developers should use "99th percentile". In simulation applications, latency refers to the time delay, often measured in milliseconds , between initial input and output clearly discernible to
490-512: A 'why' question". Aristotle categorized the four types of answers as material, formal, efficient, and final "causes". In this case, the "cause" is the explanans for the explanandum , and failure to recognize that different kinds of "cause" are being considered can lead to futile debate. Of Aristotle's four explanatory modes, the one nearest to the concerns of the present article is the "efficient" one. David Hume , as part of his opposition to rationalism , argued that pure reason alone cannot prove
588-511: A causal ordering. The system of equations must have certain properties, most importantly, if some values are chosen arbitrarily, the remaining values will be determined uniquely through a path of serial discovery that is perfectly causal. They postulate the inherent serialization of such a system of equations may correctly capture causation in all empirical fields, including physics and economics. Some theorists have equated causality with manipulability. Under these theories, x causes y only in
686-506: A cause and its effect can be of different kinds of entity. For example, in Aristotle's efficient causal explanation, an action can be a cause while an enduring object is its effect. For example, the generative actions of his parents can be regarded as the efficient cause, with Socrates being the effect, Socrates being regarded as an enduring object, in philosophical tradition called a 'substance', as distinct from an action. Since causality
784-429: A cause is incorrectly identified. Counterfactual theories define causation in terms of a counterfactual relation, and can often be seen as "floating" their account of causality on top of an account of the logic of counterfactual conditionals . Counterfactual theories reduce facts about causation to facts about what would have been true under counterfactual circumstances. The idea is that causal relations can be framed in
882-435: A cause of, or causal factor for, many other effects, which all lie in its future . Some writers have held that causality is metaphysically prior to notions of time and space . Causality is an abstraction that indicates how the world progresses. As such it is a basic concept; it is more apt to be an explanation of other concepts of progression than something to be explained by other more fundamental concepts. The concept
980-456: A complex and variable network latency profile. Latency limits total throughput in reliable two-way communication systems as described by the bandwidth-delay product . Latency in optical fiber is largely a function of the speed of light . This would equate to a latency of 3.33 μs for every kilometer of path length. The index of refraction of most fiber optic cables is about 1.5, meaning that light travels about 1.5 times as fast in
1078-480: A day making the trip or 10000, the latency of the trip would remain the same. From the point of view of flight operations personnel, latency can be entirely different. Consider the staff at the London and New York airports. Only a limited number of planes are able to make the transatlantic journey, so when one lands they must prepare it for the return trip as quickly as possible. It might take, for example: Assuming
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#17327907220721176-586: A definite time. Such a process can be regarded as a cause. Causality is not inherently implied in equations of motion , but postulated as an additional constraint that needs to be satisfied (i.e. a cause always precedes its effect). This constraint has mathematical implications such as the Kramers-Kronig relations . Causality is one of the most fundamental and essential notions of physics. Causal efficacy cannot 'propagate' faster than light. Otherwise, reference coordinate systems could be constructed (using
1274-409: A delay in transmission of game events, a player with a high latency internet connection may show slow responses in spite of appropriate reaction time . This gives players with low-latency connections a technical advantage. Joel Hasbrouck and Gideon Saar (2011) measure latency to execute financial transactions based on three components: the time it takes for information to reach the trader, execution of
1372-589: A draft specification in place for the Protocol ID. The following Protocol ID's have been assigned in ECSS-E-ST-50-11: SpaceWire IP Cores: Articles: Latency (engineering) Latency , from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag , as it is known in gaming circles , refers to the latency between
1470-514: A gateway receives multiple packets from different sources heading toward the same destination. Since typically only one packet can be transmitted at a time, some of the packets must queue for transmission, incurring additional delay. Processing delays are incurred while a gateway determines what to do with a newly received packet. Bufferbloat can also cause increased latency that is an order of magnitude or more. The combination of propagation, serialization, queuing, and processing delays often produces
1568-408: A known causal effect or to test a causal model than to generate causal hypotheses. For nonexperimental data, causal direction can often be inferred if information about time is available. This is because (according to many, though not all, theories) causes must precede their effects temporally. This can be determined by statistical time series models, for instance, or with a statistical test based on
1666-403: A mathematical definition of "confounding" and helps researchers identify accessible sets of variables worthy of measurement. While derivations in causal calculus rely on the structure of the causal graph, parts of the causal structure can, under certain assumptions, be learned from statistical data. The basic idea goes back to Sewall Wright 's 1921 work on path analysis . A "recovery" algorithm
1764-443: A metaphysical account of what it is for there to be a causal relation between some pair of events. If correct, the analysis has the power to explain certain features of causation. Knowing that causation is a matter of counterfactual dependence, we may reflect on the nature of counterfactual dependence to account for the nature of causation. For example, in his paper "Counterfactual Dependence and Time's Arrow," Lewis sought to account for
1862-419: A non-trivial network, a typical packet will be forwarded over multiple links and gateways, each of which will not begin to forward the packet until it has been completely received. In such a network, the minimal latency is the sum of the transmission delay of each link, plus the forwarding latency of each gateway. In practice, minimal latency also includes queuing and processing delays. Queuing delay occurs when
1960-411: A process and a pseudo-process . As an example, a ball moving through the air (a process) is contrasted with the motion of a shadow (a pseudo-process). The former is causal in nature while the latter is not. Salmon (1984) claims that causal processes can be identified by their ability to transmit an alteration over space and time. An alteration of the ball (a mark by a pen, perhaps) is carried with it as
2058-418: A real number. One has to be careful in the use of the word cause in physics. Properly speaking, the hypothesized cause and the hypothesized effect are each temporally transient processes. For example, force is a useful concept for the explanation of acceleration, but force is not by itself a cause. More is needed. For example, a temporally transient process might be characterized by a definite change of force at
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#17327907220722156-489: A rough way of measuring round-trip delay time. Ping cannot perform accurate measurements, principally because ICMP is intended only for diagnostic or control purposes, and differs from real communication protocols such as TCP . Furthermore, routers and internet service providers might apply different traffic shaping policies to different protocols. For more accurate measurements it is better to use specific software, for example: hping , Netperf or Iperf . However, in
2254-402: A triangle. Nonetheless, even when interpreted counterfactually, the first statement is true. An early version of Aristotle's "four cause" theory is described as recognizing "essential cause". In this version of the theory, that the closed polygon has three sides is said to be the "essential cause" of its being a triangle. This use of the word 'cause' is of course now far obsolete. Nevertheless, it
2352-504: A vacuum as it does in the cable. This works out to about 5.0 μs of latency for every kilometer. In shorter metro networks, higher latency can be experienced due to extra distance in building risers and cross-connects. To calculate the latency of a connection, one has to know the distance traveled by the fiber, which is rarely a straight line, since it has to traverse geographic contours and obstacles, such as roads and railway tracks, as well as other rights-of-way. Due to imperfections in
2450-404: A window and it breaks. If Alice hadn't thrown the brick, then it still would have broken, suggesting that Alice wasn't a cause; however, intuitively, Alice did cause the window to break. The Halpern-Pearl definitions of causality take account of examples like these. The first and third Halpern-Pearl conditions are easiest to understand: AC1 requires that Alice threw the brick and the window broke in
2548-439: Is a process that is varied from occasion to occasion. The occurrence or non-occurrence of subsequent bubonic plague is recorded. To establish causality, the experiment must fulfill certain criteria, only one example of which is mentioned here. For example, instances of the hypothesized cause must be set up to occur at a time when the hypothesized effect is relatively unlikely in the absence of the hypothesized cause; such unlikelihood
2646-462: Is a smoker") probabilistically causes B ("The person has now or will have cancer at some time in the future"), if the information that A occurred increases the likelihood of B s occurrence. Formally, P{ B | A }≥ P{ B } where P{ B | A } is the conditional probability that B will occur given the information that A occurred, and P{ B } is the probability that B will occur having no knowledge whether A did or did not occur. This intuitive condition
2744-505: Is a subtle metaphysical notion, considerable intellectual effort, along with exhibition of evidence, is needed to establish knowledge of it in particular empirical circumstances. According to David Hume , the human mind is unable to perceive causal relations directly. On this ground, the scholar distinguished between the regularity view of causality and the counterfactual notion. According to the counterfactual view , X causes Y if and only if, without X, Y would not exist. Hume interpreted
2842-536: Is an influence by which one event , process , state, or object ( a cause ) contributes to the production of another event, process, state, or object (an effect ) where the cause is at least partly responsible for the effect, and the effect is at least partly dependent on the cause. The cause of something may also be described as the reason for the event or process. In general, a process can have multiple causes, which are also said to be causal factors for it, and all lie in its past . An effect can in turn be
2940-618: Is best illustrated by the following two examples involving air travel . From the point of view of a passenger, latency can be described as follows. Suppose John Doe flies from London to New York . The latency of his trip is the time it takes him to go from his house in England to the hotel he is staying at in New York. This is independent of the throughput of the London-New York air link – whether there were 100 passengers
3038-852: Is currently used by NASA , JAXA , RKA , and many other organizations and companies. Some NASA projects using it include the James Webb Space Telescope , Swift's Burst Alert Telescope , the Lunar Reconnaissance Orbiter , LCROSS , the Geostationary Operational Environmental Satellite (GOES-R), and the SCaN Testbed, previously known as the Communications, Navigation, and Networking Reconfigurable Testbed (CoNNeCT). It has also been selected by
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3136-424: Is essentially one of change of perspective or displacement of objects such as the horizon, which takes some time to build up to discernible amounts after the initial acceleration which caused the displacement. A simulator should, therefore, reflect the real-world situation by ensuring that the motion latency is equal to or less than that of the visual system and not the other way round. Causality Causality
3234-456: Is handled by the software. A SpaceWire router is usually a crossbar switch -type device, operating in wormhole switching mode. This also may limit the speed of the communication to the lowest common speed. The routing decisions are based on the programmed routing table and the initial incoming frame contents. SpaceWire is used all around the globe. Its use began primarily in ESA projects, but it
3332-460: Is like those of agency and efficacy . For this reason, a leap of intuition may be needed to grasp it. Accordingly, causality is implicit in the structure of ordinary language, as well as explicit in the language of scientific causal notation . In English studies of Aristotelian philosophy , the word "cause" is used as a specialized technical term, the translation of Aristotle 's term αἰτία, by which Aristotle meant "explanation" or "answer to
3430-459: Is more basic than causal interaction. But describing manipulations in non-causal terms has provided a substantial difficulty. The second criticism centers around concerns of anthropocentrism . It seems to many people that causality is some existing relationship in the world that we can harness for our desires. If causality is identified with our manipulation, then this intuition is lost. In this sense, it makes humans overly central to interactions in
3528-409: Is not adequate as a definition for probabilistic causation because of its being too general and thus not meeting our intuitive notion of cause and effect. For example, if A denotes the event "The person is a smoker," B denotes the event "The person now has or will have cancer at some time in the future" and C denotes the event "The person now has or will have emphysema some time in the future," then
3626-416: Is often a limit on the amount of information that is in-flight at any given moment. Perceptible latency has a strong effect on user satisfaction and usability in the field of human–machine interaction . Online games are sensitive to latency ( lag ), since fast response times to new events occurring during a game session are rewarded while slow response times may carry penalties. Due to
3724-423: Is particularly important that the latency of the motion system not be greater than of the visual system, or symptoms of simulator sickness may result. This is because, in the real world, motion cues are those of acceleration and are quickly transmitted to the brain, typically in less than 50 milliseconds; this is followed some milliseconds later by a perception of change in the visual scene. The visual scene change
3822-467: Is possible to reduce the latency to the length of the longest task. If some steps have prerequisites, it becomes more difficult to perform all steps in parallel. In the example above, the requirement to clean the plane before loading passengers results in a minimum latency longer than any single task. Any mechanical process encounters limitations modeled by Newtonian physics . The behavior of disk drives provides an example of mechanical latency. Here, it
3920-744: Is specifically characteristic of quantal phenomena that observations defined by incompatible variables always involve important intervention by the experimenter, as described quantitatively by the observer effect . In classical thermodynamics , processes are initiated by interventions called thermodynamic operations . In other branches of science, for example astronomy , the experimenter can often observe with negligible intervention. The theory of "causal calculus" (also known as do-calculus, Judea Pearl 's Causal Calculus, Calculus of Actions) permits one to infer interventional probabilities from conditional probabilities in causal Bayesian networks with unmeasured variables. One very practical result of this theory
4018-406: Is that cause and effect are of one and the same kind of entity, causality being an asymmetric relation between them. That is to say, it would make good sense grammatically to say either " A is the cause and B the effect" or " B is the cause and A the effect", though only one of those two can be actually true. In this view, one opinion, proposed as a metaphysical principle in process philosophy ,
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4116-426: Is that every cause and every effect is respectively some process, event, becoming, or happening. An example is 'his tripping over the step was the cause, and his breaking his ankle the effect'. Another view is that causes and effects are 'states of affairs', with the exact natures of those entities being more loosely defined than in process philosophy. Another viewpoint on this question is the more classical one, that
4214-425: Is that the physical addresses are deleted from the frame header during routing - which is used for hop-based routing (based on path specified in the frame itself). Logical addresses may be deleted as well, depending on the router configuration. The hardware devices may be connected either directly, or via a SpaceWire router. In the former case, usually pairs of devices are used to guarantee a fail-safe operation, which
4312-718: Is the characterization of confounding variables , namely, a sufficient set of variables that, if adjusted for, would yield the correct causal effect between variables of interest. It can be shown that a sufficient set for estimating the causal effect of X {\displaystyle X} on Y {\displaystyle Y} is any set of non-descendants of X {\displaystyle X} that d {\displaystyle d} -separate X {\displaystyle X} from Y {\displaystyle Y} after removing all arrows emanating from X {\displaystyle X} . This criterion, called "backdoor", provides
4410-404: Is the delay between the events generated by the hardware clock and the actual transitions of voltage from high to low or low to high. Many desktop operating systems have performance limitations that create additional latency. The problem may be mitigated with real-time extensions and patches such as PREEMPT RT . On embedded systems, the real-time execution of instructions is often supported by
4508-412: Is the delay between when an audio signal enters and when it emerges from a system. Potential contributors to latency in an audio system include analog-to-digital conversion , buffering , digital signal processing , transmission time , digital-to-analog conversion and the speed of sound in air. Video latency refers to the degree of delay between the time a transfer of a video stream is requested and
4606-446: Is the time seek time for the actuator arm to be positioned above the appropriate track and then rotational latency for the data encoded on a platter to rotate from its current position to a position under the disk read-and-write head . Computers run instructions in the context of a process . In the context of computer multitasking , the execution of the process can be postponed if other processes are also executing. In addition,
4704-500: Is to be established by empirical evidence. A mere observation of a correlation is not nearly adequate to establish causality. In nearly all cases, establishment of causality relies on repetition of experiments and probabilistic reasoning. Hardly ever is causality established more firmly than as more or less probable. It is most convenient for establishment of causality if the contrasting material states of affairs are precisely matched, except for only one variable factor, perhaps measured by
4802-431: Is well-favored because it describes modulation, bit formats, routing, flow control , and error detection in hardware, with little need for software. SpaceWire also has very low error rates, deterministic system behavior, and relatively simple digital electronics. SpaceWire replaced old PECL differential drivers in the physical layer of IEEE 1355 DS-DE by low-voltage differential signaling (LVDS). SpaceWire also proposes
4900-497: Is within the scope of ordinary language to say that it is essential to a triangle that it has three sides. A full grasp of the concept of conditionals is important to understanding the literature on causality. In everyday language, loose conditional statements are often enough made, and need to be interpreted carefully. Fallacies of questionable cause, also known as causal fallacies, non-causa pro causa (Latin for "non-cause for cause"), or false cause, are informal fallacies where
4998-463: The Lorentz transform of special relativity ) in which an observer would see an effect precede its cause (i.e. the postulate of causality would be violated). Causal notions appear in the context of the flow of mass-energy. Any actual process has causal efficacy that can propagate no faster than light. In contrast, an abstraction has no causal efficacy. Its mathematical expression does not propagate in
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#17327907220725096-568: The United States Department of Defense for Operationally Responsive Space. SpaceWire initiatives are being coordinated between several space agencies in the frame of Consultative Committee for Space Data Systems (CCSDS) in order to extend its communication model to the network and transport layers of the OSI model . SpaceWire supports highly fault-tolerant networks and systems, which is one reason for its popularity. The ESA has
5194-449: The counterfactual conditional , has a stronger connection with causality, yet even counterfactual statements are not all examples of causality. Consider the following two statements: In the first case, it would be incorrect to say that A's being a triangle caused it to have three sides, since the relationship between triangularity and three-sidedness is that of definition. The property of having three sides actually determines A's state as
5292-415: The skeletons (the graphs stripped of arrows) of these three triplets are identical, the directionality of the arrows is partially identifiable. The same distinction applies when X {\displaystyle X} and Z {\displaystyle Z} have common ancestors, except that one must first condition on those ancestors. Algorithms have been developed to systematically determine
5390-512: The (mentioned above) regularity, probabilistic , counterfactual, mechanistic , and manipulationist views. The five approaches can be shown to be reductive, i.e., define causality in terms of relations of other types. According to this reading, they define causality in terms of, respectively, empirical regularities (constant conjunctions of events), changes in conditional probabilities , counterfactual conditions, mechanisms underlying causal relations, and invariance under intervention. Causality has
5488-412: The above are done consecutively, minimum plane turnaround time is: However, cleaning, refueling and loading the cargo can be done at the same time. Passengers can only be loaded after cleaning is complete. The reduced latency, then, is: The people involved in the turnaround are interested only in the time it takes for their individual tasks. When all of the tasks are done at the same time, however, it
5586-404: The absence of firefighters. Together these are unnecessary but sufficient to the house's burning down (since many other collections of events certainly could have led to the house burning down, for example shooting the house with a flamethrower in the presence of oxygen and so forth). Within this collection, the short circuit is an insufficient (since the short circuit by itself would not have caused
5684-448: The actual time that transfer begins. Networks that exhibit relatively small delays are known as low-latency networks, while their counterparts are known as high-latency networks. Any individual workflow within a system of workflows can be subject to some type of operational latency. It may even be the case that an individual system may have more than one type of latency, depending on the type of participant or goal-seeking behavior. This
5782-473: The actual work. AC3 requires that Alice throwing the brick is a minimal cause (cf. blowing a kiss and throwing a brick). Taking the "updated" version of AC2(a), the basic idea is that we have to find a set of variables and settings thereof such that preventing Alice from throwing a brick also stops the window from breaking. One way to do this is to stop Bob from throwing the brick. Finally, for AC2(b), we have to hold things as per AC2(a) and show that Alice throwing
5880-472: The antecedent to precede or coincide with the consequent in time, whereas conditional statements do not require this temporal order. Confusion commonly arises since many different statements in English may be presented using "If ..., then ..." form (and, arguably, because this form is far more commonly used to make a statement of causality). The two types of statements are distinct, however. For example, all of
5978-478: The asymmetry of the causal relation is unrelated to the asymmetry of any mode of implication that contraposes. Rather, a causal relation is not a relation between values of variables, but a function of one variable (the cause) on to another (the effect). So, given a system of equations, and a set of variables appearing in these equations, we can introduce an asymmetric relation among individual equations and variables that corresponds perfectly to our commonsense notion of
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#17327907220726076-419: The ball goes through the air. On the other hand, an alteration of the shadow (insofar as it is possible) will not be transmitted by the shadow as it moves along. These theorists claim that the important concept for understanding causality is not causal relationships or causal interactions, but rather identifying causal processes. The former notions can then be defined in terms of causal processes. A subgroup of
6174-434: The brick breaks the window. (The full definition is a little more involved, involving checking all subsets of variables.) Interpreting causation as a deterministic relation means that if A causes B , then A must always be followed by B . In this sense, war does not cause deaths, nor does smoking cause cancer or emphysema . As a result, many turn to a notion of probabilistic causation. Informally, A ("The person
6272-503: The case that one can change x in order to change y . This coincides with commonsense notions of causations, since often we ask causal questions in order to change some feature of the world. For instance, we are interested in knowing the causes of crime so that we might find ways of reducing it. These theories have been criticized on two primary grounds. First, theorists complain that these accounts are circular . Attempting to reduce causal claims to manipulation requires that manipulation
6370-442: The conceptual frame of the scientific method , an investigator sets up several distinct and contrasting temporally transient material processes that have the structure of experiments , and records candidate material responses, normally intending to determine causality in the physical world. For instance, one may want to know whether a high intake of carrots causes humans to develop the bubonic plague . The quantity of carrot intake
6468-428: The derivation of a cause-and-effect relationship from observational studies must rest on some qualitative theoretical assumptions, for example, that symptoms do not cause diseases, usually expressed in the form of missing arrows in causal graphs such as Bayesian networks or path diagrams . The theory underlying these derivations relies on the distinction between conditional probabilities , as in P ( c
6566-533: The destination plus the one-way latency from the destination back to the source). Round-trip latency is more often quoted, because it can be measured from a single point. Many software platforms provide a service called ping that can be used to measure round-trip latency. Ping uses the Internet Control Message Protocol (ICMP) echo request which causes the recipient to send the received packet as an immediate response, thus it provides
6664-434: The effect, is called a "contributory cause". J. L. Mackie argues that usual talk of "cause" in fact refers to INUS conditions ( i nsufficient but n on-redundant parts of a condition which is itself u nnecessary but s ufficient for the occurrence of the effect). An example is a short circuit as a cause for a house burning down. Consider the collection of events: the short circuit, the proximity of flammable material, and
6762-455: The experimenter, to do so at an unspecified time in the past", while the latter reads: "the probability of finding cancer in a person forced by the experimenter to smoke at a specified time in the past". The former is a statistical notion that can be estimated by observation with negligible intervention by the experimenter, while the latter is a causal notion which is estimated in an experiment with an important controlled randomized intervention. It
6860-415: The fiber, light degrades as it is transmitted through it. For distances of greater than 100 kilometers, amplifiers or regenerators are deployed. Latency introduced by these components needs to be taken into account. Satellites in geostationary orbits are far enough away from Earth that communication latency becomes significant – about a quarter of a second for a trip from one ground-based transmitter to
6958-423: The fire) but non-redundant (because the fire would not have happened without it, everything else being equal) part of a condition which is itself unnecessary but sufficient for the occurrence of the effect. So, the short circuit is an INUS condition for the occurrence of the house burning down. Conditional statements are not statements of causality. An important distinction is that statements of causality require
7056-509: The following definition of the notion of causal dependence : Causation is then analyzed in terms of counterfactual dependence. That is, C causes E if and only if there exists a sequence of events C, D 1 , D 2 , ... D k , E such that each event in the sequence counterfactually depends on the previous. This chain of causal dependence may be called a mechanism . Note that the analysis does not purport to explain how we make causal judgements or how we reason about causation, but rather to give
7154-417: The following statements are true when interpreting "If ..., then ..." as the material conditional: The first is true since both the antecedent and the consequent are true. The second is true in sentential logic and indeterminate in natural language, regardless of the consequent statement that follows, because the antecedent is false. The ordinary indicative conditional has somewhat more structure than
7252-410: The following three relationships hold: P{ B | A } ≥ P{ B }, P{ C | A } ≥ P{ C } and P{ B | C } ≥ P{ B }. The last relationship states that knowing that the person has emphysema increases the likelihood that he will have cancer. The reason for this is that having the information that the person has emphysema increases the likelihood that the person is a smoker, thus indirectly increasing the likelihood that
7350-494: The form of "Had C not occurred, E would not have occurred." This approach can be traced back to David Hume 's definition of the causal relation as that "where, if the first object had not been, the second never had existed." More full-fledged analysis of causation in terms of counterfactual conditionals only came in the 20th century after development of the possible world semantics for the evaluation of counterfactual conditionals. In his 1973 paper "Causation," David Lewis proposed
7448-498: The idea of Granger causality , or by direct experimental manipulation. The use of temporal data can permit statistical tests of a pre-existing theory of causal direction. For instance, our degree of confidence in the direction and nature of causality is much greater when supported by cross-correlations , ARIMA models, or cross-spectral analysis using vector time series data than by cross-sectional data . Nobel laureate Herbert A. Simon and philosopher Nicholas Rescher claim that
7546-471: The input to a simulation and the visual or auditory response, often occurring because of network delay in online games. Latency is physically a consequence of the limited velocity at which any physical interaction can propagate. The magnitude of this velocity is always less than or equal to the speed of light . Therefore, every physical system with any physical separation (distance) between cause and effect will experience some sort of latency, regardless of
7644-548: The latter as an ontological view, i.e., as a description of the nature of causality but, given the limitations of the human mind, advised using the former (stating, roughly, that X causes Y if and only if the two events are spatiotemporally conjoined, and X precedes Y ) as an epistemic definition of causality. We need an epistemic concept of causality in order to distinguish between causal and noncausal relations. The contemporary philosophical literature on causality can be divided into five big approaches to causality. These include
7742-410: The material conditional. For instance, although the first is the closest, neither of the preceding two statements seems true as an ordinary indicative reading. But the sentence: intuitively seems to be true, even though there is no straightforward causal relation in this hypothetical situation between Shakespeare's not writing Macbeth and someone else's actually writing it. Another sort of conditional,
7840-406: The nature of the stimulation to which it has been exposed. The precise definition of latency depends on the system being observed or the nature of the simulation. In communications , the lower limit of latency is determined by the medium being used to transfer information. In reliable two-way communication systems, latency limits the maximum rate at which information can be transmitted, as there
7938-424: The need for separate time discretes. Each transferred character starts with a parity bit and a data-control flag bit. If data-control flag is a 0-bit, an 8-bit LSB character follows. Otherwise one of the control codes, including end of packet (EOP). The network data frames look as follows: One or more address bytes are used for the routing. Addresses are either physical ones (0–31), or logical ones. The difference
8036-430: The notion of causality is metaphysically prior to the notions of time and space. In practical terms, this is because use of the relation of causality is necessary for the interpretation of empirical experiments. Interpretation of experiments is needed to establish the physical and geometrical notions of time and space. The deterministic world-view holds that the history of the universe can be exhaustively represented as
8134-482: The operating system can schedule when to perform the action that the process is commanding. For example, suppose a process commands that a computer card's voltage output be set high-low-high-low and so on at a rate of 1000 Hz. The operating system schedules the process for each transition (high-low or low-high) based on a hardware clock such as the High Precision Event Timer . The latency
8232-426: The ordinary sense of the word, though it may refer to virtual or nominal 'velocities' with magnitudes greater than that of light. For example, wave packets are mathematical objects that have group velocity and phase velocity . The energy of a wave packet travels at the group velocity (under normal circumstances); since energy has causal efficacy, the group velocity cannot be faster than the speed of light. The phase of
8330-415: The person will have cancer. However, we would not want to conclude that having emphysema causes cancer. Thus, we need additional conditions such as temporal relationship of A to B and a rational explanation as to the mechanism of action. It is hard to quantify this last requirement and thus different authors prefer somewhat different definitions. When experimental interventions are infeasible or illegal,
8428-441: The process theories is the mechanistic view on causality. It states that causal relations supervene on mechanisms. While the notion of mechanism is understood differently, the definition put forward by the group of philosophers referred to as the 'New Mechanists' dominate the literature. For the scientific investigation of efficient causality, the cause and effect are each best conceived of as temporally transient processes. Within
8526-478: The properties of antecedence and contiguity. These are topological, and are ingredients for space-time geometry. As developed by Alfred Robb , these properties allow the derivation of the notions of time and space. Max Jammer writes "the Einstein postulate ... opens the way to a straightforward construction of the causal topology ... of Minkowski space." Causal efficacy propagates no faster than light. Thus,
8624-419: The reality of efficient causality; instead, he appealed to custom and mental habit, observing that all human knowledge derives solely from experience . The topic of causality remains a staple in contemporary philosophy . The nature of cause and effect is a concern of the subject known as metaphysics . Kant thought that time and space were notions prior to human understanding of the progress or evolution of
8722-403: The satellite and back to another ground-based transmitter; close to half a second for two-way communication from one Earth station to another and then back to the first. Low Earth orbit is sometimes used to cut this delay, at the expense of more complicated satellite tracking on the ground and requiring more satellites in the satellite constellation to ensure continuous coverage. Audio latency
8820-449: The simulator trainee or simulator subject. Latency is sometimes also called transport delay . Some authorities distinguish between latency and transport delay by using the term latency in the sense of the extra time delay of a system over and above the reaction time of the vehicle being simulated, but this requires detailed knowledge of the vehicle dynamics and can be controversial. In simulators with both visual and motion systems, it
8918-664: The skeleton of the underlying graph and, then, orient all arrows whose directionality is dictated by the conditional independencies observed. Alternative methods of structure learning search through the many possible causal structures among the variables, and remove ones which are strongly incompatible with the observed correlations . In general this leaves a set of possible causal relations, which should then be tested by analyzing time series data or, preferably, designing appropriately controlled experiments . In contrast with Bayesian Networks, path analysis (and its generalization, structural equation modeling ), serve better to estimate
9016-428: The time-directedness of counterfactual dependence in terms of the semantics of the counterfactual conditional. If correct, this theory can serve to explain a fundamental part of our experience, which is that we can causally affect the future but not the past. One challenge for the counterfactual account is overdetermination , whereby an effect has multiple causes. For instance, suppose Alice and Bob both throw bricks at
9114-429: The trader's algorithms to analyze the information and decide a course of action, and the generated action to reach the exchange and get implemented. Hasbrouck and Saar contrast this with the way in which latencies are measured by many trading venues that use much more narrow definitions, such as the processing delay measured from the entry of the order (at the vendor's computer) to the transmission of an acknowledgment (from
9212-402: The use of space-qualified 9-pin connectors. SpaceWire and IEEE 1355 DS-DE allows for a wider set of speeds for data transmission, and some new features for automatic failover . The fail-over features let data find alternate routes, so a spacecraft can have multiple data buses, and be made fault-tolerant . SpaceWire also allows the propagation of time interrupts over SpaceWire links, eliminating
9310-410: The vendor's computer). Trading using computers has developed to the point where millisecond improvements in network speeds offer a competitive advantage for financial institutions. Network latency in a packet-switched network is measured as either one-way (the time from the source sending a packet to the destination receiving it), or round-trip delay time (the one-way latency from the source to
9408-480: The world, and he also recognized the priority of causality. But he did not have the understanding that came with knowledge of Minkowski geometry and the special theory of relativity , that the notion of causality can be used as a prior foundation from which to construct notions of time and space. A general metaphysical question about cause and effect is: "what kind of entity can be a cause, and what kind of entity can be an effect?" One viewpoint on this question
9506-455: The world. Some attempts to defend manipulability theories are recent accounts that do not claim to reduce causality to manipulation. These accounts use manipulation as a sign or feature in causation without claiming that manipulation is more fundamental than causation. Some theorists are interested in distinguishing between causal processes and non-causal processes (Russell 1948; Salmon 1984). These theorists often want to distinguish between
9604-712: Was developed by Rebane and Pearl (1987) which rests on Wright's distinction between the three possible types of causal substructures allowed in a directed acyclic graph (DAG): Type 1 and type 2 represent the same statistical dependencies (i.e., X {\displaystyle X} and Z {\displaystyle Z} are independent given Y {\displaystyle Y} ) and are, therefore, indistinguishable within purely cross-sectional data . Type 3, however, can be uniquely identified, since X {\displaystyle X} and Z {\displaystyle Z} are marginally independent and all other pairs are dependent. Thus, while
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