Phase coherence is a property of quantum sources that classical sources do not seem to have, but in fact phase coherence affects all observers and sources in the universe, just in different ways. Instead of the single knowable state of a classical source, say a red color, two quantum sources with coherent phase can exist in a coherent superposition of states, say both red and blue. This entanglement can occur even though those the quantum sources might be located across the universe from each other.
The exact object color of one source is unknowable until an observer sees that source as red or blue. The observation of one of two coherent source superposition states as red then immediately determines the other source state as blue even across the universe. Before the measurement, though, the two sources existed as a superposition of both red and blue and so the exact state of both sources in the past is unknowable.
There is a knowable phase coherence that two classical objects also exhibit, but for classical objects in general relativity, all reality is determinate and therefore classical coherent states are knowable. A classical observer might not know which of two a classical sources is red or blue, but that classical knowledge is always knowable. That is, once an observer sees one classical source as red, they also immediately know that the other classical source is blue even if the other classical source lies across the universe. However, the colors for each of the two classical sources were always classically knowable and once an observer sees a classical source as red, they know that it was always red. There are no superposition states for classical sources nor is there any decay of the phase coherence between two classical sources except due to perturbations from other sources.
Classical determinate sources in general relativity do not appear to show quantum phase coherence, but really it is the decoherence of quantum phase that makes quantum sources different from classical sources, not really phase coherence per se. After all, two classical sources with coherent colors also remain perfectly coherent in a determinate classical universe in the absence of perturbations. Those two coherent colors represent determinate geodesic paths for general relativity as well.
On the one hand, correlated colors for two classical sources represent something that an observer can know about each source. Even though the observer might not know the color of either source to begin with, once seeing that a classical object is red, the classical observer also then immediately knows that classical sources was always red. The observer also then immediately knows that the source's coherent twin's color was blue even across the universe and that twin had its classical correlation for the same period of time.
Unlike two classical sources, two coherent quantum sources somehow oscillate between those coherent color states as a superposition of amplitudes and do not exist as either one or the other colors until an observation or some other action dephases them. In the quantum universe, dephasing is an inextricable part of seeing or measuring the color of a quantum source and immediately tells the observer the state of its coherent twin even across the universe. Since decoherence is an inextricable part of all sources in the universe, observers can never be absolutely certain about the natures of objects that they sense. That is because neither quantum twin existed as red nor blue prior to the measurement or action that dephased one of the sources into a red or blue state.
The mystery of quantum entanglement has to do not really with why a quantum source can be either of two colors or how two quantum sources can remain coherent with each other across time and space. The mystery of quantum entanglement has to do with even when an observer sees that an source is red, they still simply cannot know that that same source was always red before they observed it. As soon as the nearby quantum object is red for certain, the distant source decoheres to blue and stops its oscillation between red and blue. The distant quantum source can now only be blue even though before that time, it's state was not knowable.
Although quantum charge is a local force with very fast decoherence, quantum gravity is a long range force that has a much slower decoherence. In aethertime, every quantum charge state like red and blue with very fast decoherence has a complementary quantum gravity state with much slower decoherence. In fact, quantum gravity states exist with the decoherence times of the universe. While quantum charge is a very local force, quantum phase is also part of the glue that holds the universe together.
The color of a red source is due to a large number of photons of light across a wide spectrum of light around that red color. When we see a classical source as red, we sense only a very small fraction of a very large number of photons emanating from that red source. For such large and macroscopic classical sources as red apples, a red color is a property of a very large number of particles at the surface of that source.
In contrast to the color of a classical source, the color of a quantum source may be due to just one photon of light interacting with a single particle. Since observer eyes are not sensitive to just one photon, observers must use spectrometers to know whether a single particle is red or blue. That single photon still represents a whole spectrum of frequencies superimposed as a single time pulse that bonds the observer to the particle for some period of decoherence. During that superposition between the observer and the particle, the observer oscillates along with the particle between the possible futures of red or blue. When the observer becomes decoherent from the particle, that leaves the observer in the red or blue state as well as the quantum gravity state that goes along with the color.
The phase coherence of a quantum source decays as a result of not only measurement, but also due to perturbations with other objects just like perturbations affect the classical spins of objects. The decay of phase coherence is due to the classical noise of chaos as well as quantum phase noise and there is simply no classical meaning for quantum phase noise.
The meandering decay of earth's spin period means that a day has varied from +1.4 to -1.5 ms every year over the last 43 years (see figure below) and there are many different factors that perturb Earth's spin by as much as 4 ms per day. In a determinate classical universe, all of these perturbations are knowable and even in a quantum universe, most of these perturbations are likewise knowable. However the quantum dephasing of the universe at 0.255 ppb/yr has no cause other than being simply a property of the universe. Quantum decoherence is an assumption Earth's spin decay that is an unconditioned axiom of the universe.
According to reports, the Earth day has lost from 1.7 ms [0.20 ppb/yr, McCarthy and Seidelmann, 2009] to 2.4 ms [0.28 ppb/yr, Stephenson and Morrison, 1984] over the last 100 years, both decays are consistent with the classical 0.26 ppb/yr decoherence of aethertime within the uncertainty of the measurements. The dephasing of the universe represents phase information that is lost to observers of that same universe since observers dephase along with all other sources in the universe. However, the local decoherence rate does show up in various decays of matter and force and those measurements do provide an absolute velocity relative to the aethertime universe boundary. The shrinking of the universe in this epoch is what defines the speed of light, c, in aethertime.
Therefore, quantum entanglement and decoherence both represent a loss of information as quantum phase noise and so observers cannot know all quantum phase perturbations. While classical entanglement represents knowable perturbations with a determinate universe of local cause and effect, quantum entanglement also involves decoherence of quantum phase commensurate with the universe decay.