Sagnac Effect (FM Perspective)

What is observed

The Sagnac effect occurs when light is sent in opposite directions around a rotating loop.

Two beams:

travel the same closed path
but in opposite directions

When they return and interfere:

a phase difference is observed

This difference increases with the rotation rate of the system.

Standard description

In conventional physics, the Sagnac effect is explained by:

rotation of the reference frame
differences in path length or travel time
relativistic treatment of non-inertial frames

The result is that:

the two beams take different times to complete the loop

The FM perspective

In the Field Medium Model, light propagation is local reorganization.

Propagation always proceeds step by step:

each region reorganizes
and induces the next

The propagation speed is determined locally and is the same in all directions.

Rotation of the system

In the Sagnac setup, the loop itself is rotating.

This means:

the physical path is moving while the wave is propagating
each segment of the path changes position over time

The wave does not travel through a fixed path.
It propagates through a sequence of local regions that are themselves in motion.

Co-propagating beam

For the beam traveling in the same direction as the rotation:

each next region has moved slightly forward
the wave must “catch up” to a continuously advancing path

This effectively increases the total distance the wave must propagate.

Counter-propagating beam

For the beam traveling opposite to the rotation:

each next region moves toward the wave
the wave meets the path segments sooner

This effectively reduces the total distance required.

Origin of the phase difference

Both beams propagate locally at the same speed.

However:

the path is not static
the endpoints shift during propagation

As a result:

one beam completes the loop later than the other

This produces a difference in the number of completed cycles.

When recombined:

a phase shift is observed

No change in propagation speed

At no point does the propagation speed of light change.

At every location:

local reorganization proceeds with the same intrinsic behavior

The difference arises entirely from:

the motion of the system during propagation

Closed-loop geometry

The Sagnac effect depends on:

a closed path
rotation of that path

It does not require:

a preferred rest frame
a background medium with flow

The effect arises from how propagation unfolds in a moving geometry.

Relation to other effects

The Sagnac effect is closely related to:

propagation in non-uniform motion
path-dependent accumulation of cycles
differences between wave propagation and structural motion

It illustrates that:

propagation is always local
but measurement depends on the full path taken

Comparison of interpretations

Both descriptions agree:

a phase shift appears under rotation

They differ in explanation:

Standard interpretation:

differences arise from time and frame-dependent effects

FM interpretation:

differences arise because the path moves during propagation
the wave follows a changing sequence of local regions

Summary

In the Field Medium Model:

Light propagates through local reorganization
The propagation speed is the same everywhere
The loop rotates during propagation
One beam follows a receding path, the other an approaching path
This creates a difference in total propagation distance
The resulting difference in accumulated cycles produces a phase shift

Final statement

The Sagnac effect does not require changes in time or propagation speed.

It arises because wave propagation occurs step by step
in a system whose geometry is changing during the process.