I'm looking for a word that describes how simply measuring something changes it

An engineer friend of mine said something once like “when you measure something, you need to take into account that sometimes the measuring of the thing affects the thing’s performance…” Sort of like putting a wind speed monitor on a plane might affect its trajectory or power…

Is there an engineering term for this? Measurement impact? Measurement affect?

• The Heisengberg Uncertainty Principle is sometimes referenced for such a thing. – jxh Jul 17 '18 at 18:28
• Note that it's "effect", not "affect". – Acccumulation Jul 17 '18 at 18:40
• When you talking about measuring, do you mean looking (and not touching), or do you mean adding instrumentation to something? As previously commented, it makes a difference. Just looking (or knowing a particular something) is the uncertainty principle, while adding instrumentation to something is the observer effect (as per the answers). The latter seems more like what you want (because you talk about adding a wind speed monitor) but it's not completely clear due to the ambiguity of the word measure. – Jason Bassford Jul 17 '18 at 18:47
• Completely off-topic, but yours is the 99,000th question on the site. Congrats. – Mari-Lou A Jul 17 '18 at 18:57

In physics we call them observer effects, the classic ones are:

1. In order to measure a current you need to couple either directly or inductively to the circuit, which inherently changes the current running through the circuit. For example if you are using a multimeter to measure resistance, there is an observer effect that gets stronger if the resistance you're measuring is larger than the resistance of your multimeter: more current is going through your multimeter than is going through the object you're investigating.

2. In order to measure a quantum system, for example the "which way" information of a double-slit experiment, you generally need to entangle another system with that system so that measuring the other system reveals information about the quantum system under study. It turns out that entanglement and quantum coherence are twin sisters that are never seen in the same room at the same time -- the better you are at measuring this information, the less waviness is seen in the results of that system.

• Some engineering textbooks use the same term or the related term "measurement interferences", both mean basically the same thing "you have to poke it to know stuff about it; poking it makes a difference". – Ash Jul 17 '18 at 18:46

In physics, the observer effect is the theory that simply observing a situation or phenomenon necessarily changes that phenomenon. wikipedia