Experimentalists : trust what you see.

Experimentalists are in many ways different from theorists. Those behind their lab benches and those behind the black board. Earlier in History, those were only one, the polymaths. Then came the infatuation of the super specialists. Now is the intertwining of expertise in multi and trans-disciplinary teams.

It is therefore not unusual that experimentalists work along side theorists. But it is noticeable that they are usually forming two and not only one individual and that communication is a challenge.

Indeed, it is not the same community. It is not the same language, vocabulary, way of thinking.

Theorist vs Experimentalist

Typically, the theorist will take a problem (e.g. effect of vibration on anisotropic particles), shrink it down to its main components (application of forces on a fixed number of particles), polish it to make it perfect (100 particles of the same hexagonal shape placed in a homogeneous fluid in a closed box), then apply the fundamental laws as expected from this system (Newton’s law). After the first result obtained, she will have to assess and judge if it makes sense. If not, she will turn the knobs to refine the model and approach the real system’s behaviour. In short, she will start with a simplified reality and complexify it.

On the other hand, the experimentalist will face a complex system and carry out experiments to understand the key parameters that influence its fate. Once the system and its reactions are understood, she can use those parameters to influence it to control its behaviour as desired for an application. The scientific approach is thus the opposite: from a complex real system (e.g. polydispersed anisotropic particles dispersed in an inhomogeneous fluid) to a simplified version (acting on force 1 will drive the system into state 1).

Influencing the outcome?

In both cases, the person carrying the theoretical modelling or the experiment can influence the result. The theorist chooses how to simplify the system and judges the validation of the result. The experimentalist, on the other, chooses the experiment and how to measure. But the result should be independent of its will. Only the system itself decides of its own fate after the perturbation.

This to stress out that if the experimental result obtained is expected or not, in both cases there are concrete reasons that can explain it. It could be the method chosen, the analysis and the intrinsic properties of the complex system… All these can be varied to discard effects exterior to the system.

Matching the theory with the experiment?

Now the theorist will make the theory, the model, fit the experiment. But provided the complexity, it is not possible to force the experiment to fit the theory. If it cannot be modelled in simple terms, then another equation has to be taken into account.

Therefore, it is not because theory says it will not work, that it will not work. Models make assumptions, are based on simplified systems and might not cover all possibilities.

Experiment first

This sets the attitude of the experimentalist: if there is a doubt, a chance, a feeling, an intuition, that the experiment will provide this result, despite the modelling does not predict it: do the experiment. If there is a question about the response of the system to a perturbation, it is much faster and more reliable to do the experiment first, then look and analyze the result. The system’s response is always right.

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