# Observer In physics, particularly relativity, an observer is essentially equivalent to a [Reference Frames](Reference%20Frames.md). It represents an entity making measurements or observations from a particular reference frame. This entity is not necessarily a person, but rather a conceptual viewpoint for describing physical phenomena. ### Why are observers so important in physics? Given that physics attempts to describe reality at its most fundamental level, it is natural to ask: why do we need the concept of observers? It seems oddly human-centric. The prominence of observers in physics, even at the most fundamental levels, arises from the need to *measure* and *describe* physical phenomena. 1. **Measurement**: Physics aims to understand and describe the natural world through measurements of various quantities such as position, velocity, time, energy, etc. These measurements are inherently tied to an observer because an observer is required to perform the measurement. 2. **Relativity of Measurement**: Many physical quantities are [relative](Principle%20of%20Relativity.md), meaning their values can change depending on the observer’s frame of reference. This relativity necessitates the inclusion of the observer to accurately describe and compare measurements. As a simple example consider a ball flying through the air. It is natural for us to try and measure it's motion. We'd like to know "how fast is it moving through space"? To do so, we have no choice but to pick something to measure it's velocity *with respect to*. In other words, certain physical quantities simply cannot be described without the concept of an observer and the associated [Reference Frames](Reference%20Frames.md). --- Date: 20240630 Links to: Tags: References: * []()