How measurements influence the result of any experiment

A simple thought experiment make us think how measurements we make respect to a particle (considering at quantum level) changes its physical quantities.

Consider an electron travelling in a free space (deep space) with a constant velocity, free of all froces , no matter(mass) or any energy gradient existing but only the electron alone.

Now how do we intend to measure the velocity of electron?

Well at first as an observer we need light to see the particle(electron) ,then we try to magnify the image of the electron and measure the distance coverred by it at various instants and finally calculate it's velocity. When we go subatomic level we have to make some considerations here mass of electron is very less , and also treating light as a particle entity,

A Collison occurs between the electron and photon leading to increasing the momentum of the electron , hence the velocity of electron is changed by a measurable amount, the velocity observed by the observer is different from its initial value leading to error in measurements.

In macro world these effects are negligible and we get accurate results.

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