Accelerated reference frame

In theoretical physics, an accelerated reference frame is usually a coordinate system or frame of reference, that undergoes a constant and continual change in velocity over time as judged from an inertial frame.

An object in an accelerated frame will usually be compelled to move with the frame by some sort of Fictitious forces. If this force is applied mechanically to one part of the object, the transmission of this "holding force" through the object will make it seem to the object (feeling accelerational "gee-forces") as if it is suspended in a gravitational field.

Frames and flat spacetime

If a region of spacetime is declared to be Euclidean, and effectively free from obvious gravitational fields, then if an accelerated coordinate system is overlaid onto the same region, it can be said that a uniform gravitational field exists in the accelerated frame. An object accelerated to be stationary in the accelerated frame will "feel" the presence of the field, and thay will also be able to see environmental matter with inertial states of motion (stars, galaxies, etc.) to be apparently falling "downwards" in the field along "curved spacetime" trajectories as if the field is real.

In frame-based descriptions, this supposed field can be made to appear or disappear by switching between "accelerated" and "inertial" coordinate systems.

More advanced descriptions

As the situation is modelled in finer detail, using the general principle of relativity, the concept of a frame-dependent gravitational field becomes less realistic. In these Machian models, the accelerated body can agree that the apparent gravitational field is associated with the motion of the background matter, but can also claim that the motion of the material as if there is a gravitaitonal field, causes the gravitational field - the accelerating background matter "drags light". Similarly, a background observer can argue that the forced acceleration of the mass causes an apparent gravitational field in the region between it and the environmental material (the accelerated mass also "drags light"). This "mutual" effect, and the ability of an accelerated mass to warp lightbeam geometry and lightbeam-based coordinate systems, is referred to as frame-dragging.

Frame-dragging removes the usual distinction between accelerated frames (which show gravitaitonal effects) and inertial frames (where the geometry is supposedly free from gravitational fields). When a forcibly-accelerated body physically "drags" a coordinate system, the problem becomes an exercise in warped spacetime for all observers.