Scientific experiment - SpeedyLook encyclopedia

Principle

Generally a Hypothèse tries to identify a connection cause-consequence. For example, my assumption perhaps “ the light allows the growth of a plant ”.

The experiment consists in reproducing the phenomenon “ growth of a plant ”, in 2 manners:

On the one hand without the factor to be tested ( without light ); it is the pilot negative.
in addition, a pilot positive, with the factor to be tested ( with light ). This last device makes it possible to check that all the other elements not tested are operational ( the plant functions well)

Before even the implementation, the results of the experiment must be envisaged:

If the growth does not occur in the 2 devices, I can nothing deduce, if it is not that my handling is not adapted to my research.
If the growth does not occur without light, but with the light, then the assumption is validated: " the light makes push the plants ".
If the phenomenon occurs in the 2 devices, then the assumption is not validated, but it is not rejected for as much.

It should be noted that:

Apart from the factor to be tested that it is necessary to vary, all the devices must be rigorously identical. Without that of other factors could be at the origin of the difference in results with the witness. For example, if the weather is colder in the first dispostif one without light, the absence of growth perhaps as well charged to this factor temperature.
the results of the experiments must be envisaged before their implementation.

Scientific experiment using Model

When certain natural phenomena are too complex, too vast, too dangerous, too expensive, or too length to be reproduced in an experiment, one has recourse to a simplified device: the Model.

It can be a question:

of a small-scale model (Model). One speaks about analogical Modélisation, to which the geologists studying the Tectonique had recourse.
of a digital model (program of simulation by Computer)
of an alive model, as the Mouse which makes it possible to avoid experiments on Humain S.

Theoretical structure of an experiment

From a very general point of view, the isolated experiment comprises three phases summarily: preparation; the experimentation; the evaluation; two last being the simple result by what preceded them.

A total experiment made up of experiments partially individualisables comprises the three same poles. However so in the isolated experiment the three phases constitute as many regulated stages Chronologiquement, in the total experiment, it acts of three registers which Interagissent permanently. As follows:

*L' evaluation is more or less associated with the parameters taken into account in the preparation, for example, the results question the sampling procedure;

*L' experimentation can be repeated, according to the two other phases;

The preparation is carried out around a double intention: the success of the experiment, i.e. control until its term; the relevance or success of the experiment, i.e. the access to a positive test, with regard to the initial objective.

Each intention justifying and organizing the experiment finds its limits in at least a form of uncertainty: basic uncertainty relating to the realization of the experiment is joined per as many uncertainties as there are possible choices for the initial conditions.

The preparation is thus based on prospects and operations of Anticipation; calculations of the experiment which can reduce uncertainty on such or such parameter.

The preparation leads thus to the meeting of Facteur S of effectiveness.

In the total experiment, each phase not resulting simply from the preceding one, the bonds between the initial conditions and the results are affected by a complexity which brings a new load of uncertainty.

The evaluation refers to criteria which will have been clarified in partnership with the determination of the factors of effectiveness.

The preliminary qualitative experiment

Wolfgang Köhler notes that " the physicists spent centuries to gradually replace observations direct and especially qualitative by others, indirect, but very precise ". It quotes some examples where such scientist makes a singular observation but only of a qualitative nature before this fact - once discovered - serf of base to a method evaluation quantitative of the phenomenon; these methods often concretizing itself out of measuring instruments increasingly more sophisticated.

It generalizes this historical report while posing that any news Science develops naturally by the progressive passage of the " direct experiments and qualitatives" with the " indirect experiments and quantitatives" ; those being a major characteristic of the " sciences exactes". He insists on the necessary preliminary accumulation of the primarily qualitative experiments; essential conditions of the later quantitative investigations.

It is the challenge which he proposes with the Psychologie that he regards as a " young science . He thus invites to resist the imitation of physics; not to plate the methods of a ripe science on the gropings of that which is sought and thus to support before all the growth of the essential experiments preliminary to the future rigorous quantitative experiments.

Recognizing the complexity of the object of the Psychology compared with simplifications that the Physique authorizes, it ensures after having mentioned the question of the Test S qu" one could not stress enough the importance of the qualitative Information like complement necessary of quantitative work ".

W. Köhler, Gestalt Psychology , 1929. French translation the psychology of the form , Gallimard, Paris, 1964. Translated by Serge Bricianer.

The typical example is that of Galileo, which discovers the movement of planets by the observation with a Telescope.

Experiments in blocks

In the experiments in field, in the broad sense (field, orchard, forest, etc), which is carried out in agronomic research, one calls blocks whole of close pieces which are used to compare various treatments (various manures for example).

The blocks are known as complete when all the elements which play a part in the experiment (all studied manures for example) there are present. They are on the contrary known as incomplete when only some of these elements are present there.

The distribution of the various elements is carried out randomly inside the various blocks, and independently of one block to the other, reason for which the blocks are often described as random .

The most frequent case is that of the experiments in complete random blocks .

The use of blocks (in English: ) intervenes also, sometimes under other denominations, in other fields that the experimentation in field and the agronomic research (research industrial or technological, medical research or pharmaceutical, etc). In the medical field for example, the blocks can be made up of groups of patients who show similar characteristics.

The '' square Latin '' and the graeco-latin '' square '' are other experimental devices, much less used than the blocks.

Pierre Dagnelie. Principles of experimentation: planning of the experiments and analyzes their results. Agronomic presses, Gembloux, 2003,397 p. and electronic edition (pdf).

See too

Simple: Experiment

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