Finding a definition for time has challenged thinkers and philosophers. The direction of the arrow of time is questioned because many physical laws seem to be symmetrical in the forward and backward direction of time.

We can show that the arrow of time must be in the forward direction by considering light. The speed of light is always positive and distance is always positive so the direction of time must always be positive. We could define one second as the time it takes for light to travel approximately 300,000 km. Note that we have shown the arrow of time to be in a positive direction without reference to entropy.

So we are defining time in terms of distance and velocity. Philosophers might argue that we then have to define distance and velocity but these perhaps are less challenging to define than time.

So let's try to define time. Objects that exist within the universe have a state of movement and the elapsed times that we observe result from the object being in a different position due to its velocity.

This definition works well considering a pendulum clock and an atomic clock. We can apply this definition to the rotation of the Earth and think of the elapsed time of one day as being the time for one complete rotation of the Earth.

The concept of time has been confused within physics by the ideas of quantum theory which imply the possibility of the backward direction of time and also by special relativity which implies that you cannot define a standard time throughout the universe. These problems are resolved when you consider light as a wave in the medium of space and this wave travels in the space rest frame.

Preprint Space Rest Frame (March 2022)

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