Time is a fundamental dimension of the physical universe that we use to order events, measure durations, and describe the sequence of cause and effect. It is commonly considered as the fourth dimension, along with the three spatial dimensions (length, width, and height).
In physics, time is treated as a coordinate within the framework of spacetime, which combines the three dimensions of space with the dimension of time into a four-dimensional continuum. This concept was developed as part of Albert Einstein's theory of relativity, which revolutionized our understanding of space, time, and gravity.
Regarding your question about the existence of time without an observer, it is important to note that the nature of time is a topic of philosophical and scientific debate. In physics, time is treated as an objective quantity that exists independently of observers. According to the theory of relativity, events and the passage of time are described by spacetime coordinates, and the laws of physics apply regardless of whether there are observers present.
However, the perception and experience of time can be influenced by the frame of reference of an observer. The theory of relativity states that time can appear to flow differently for different observers, depending on their relative motion or the strength of the gravitational field they are in. These effects, known as time dilation, arise from the fundamental properties of spacetime and have been experimentally confirmed.
In summary, while time is considered a fundamental dimension in the physical universe, its perception and measurement can be influenced by the frame of reference of an observer. The existence of time is not contingent on the presence of an observer, but our subjective experience and measurement of time can vary depending on the circumstances and conditions in which we find ourselves.