An intriguing experiment  in the use of reenactment to contacting presences from the past produced some anomalous results but these results and the theory behind the experiment do not clearly show that they were produced by non physical entities.
Ghost Armies, Battles and Morphogenetic fields
Ghost Armies and battles are encountered from the British Civil War and other conflicts. Some seem to be virtual replays of the conflict ( but may be imaginative recreations triggered in the minds while the individual is in an altered State of Consciousness) and are seen by a people who are not “psychic”. Others are restricted to sounds. In some ways sounds are easier to investigate scientifically than full replays: Anomalous sounds have been recorded in a number of contexts and may be harder to fake than photographs.
Remembrance of wars and battles often takes the form of annual or occasional rituals, from Remembrance Day in the UK to reenactments and individual offerings. These rituals may have created a cognitive signature, what Sheldrake calls a morphogenetic field, which can be imagined as a rut in reality formed by a wheel (ritual) repeatedly running over the same space, forming an “attractor” that drags perception into that rut and makes it harder to avoid the rut.
If this theory is correct in even a few cases it would mean that a morphogenetic field created by semi-repetitive activity focussed on an event could be perceived as a haunting or a visit from a deity or demon. Or the activity involved could actually be produced by some entity that was “allowed” to manifest by the ritual. In plainer terms the activity could have produced a piece of theatre based on collective imagination of how the past event proceeded, could be a replay on the “akashic record” of the event, could be one or more spirits created by the ritual activity, could be the spirits of people involved in the event, or could be some other entity play acting, as seems to happen in the case of UFOS  and Phantom Clowns  and Poltergeists .
In brief the hypothesis is that past memory and presence can be reconstructed, or “unearthed” via morphic resonance (itself a controversial theory) and that this is framed by soundmarks and production of these allows tuning in to the past event.
Reenactment and Recreation
The experiment involved carefully directed reenactment of events that produced sounds associated with the Civil War battle of Antietam, the sounds reenacted being those related to different parts of the battle field. The rationale of the experiment was to get away from the standard technology related forms of investigation that demand a sign from a ghost and instead attempt to manifest what the author calls contextual memories of the event, a contextual memory being something that could be triggered by one of the reenacted sounds, just as a trivial event such as the smell of bread can bring back total and indeed immersive recall of an associated event. Typical soundmarks included Bugle Calls, Drums, A role call, and period music. Actions involved also included female volunteers playing the role of women searching for the bodies of relatives. Care was taken to avoid using technology that would have appeared totally alien to any ghosts in the area and the experiments were performed at times tourists were unlikely to be in the area, for example at night.
Various anomalous sounds were recorded words, sentences and singing for example. More intriguingly during the roll call in response to the call 'Private Lewis Dayton,’ someone answered ‘Dayton Present.’ Some of the investigators felt as if they were being gently touched. At least one response was repeated in a later repeat of the reenactment lending support to the video-replay and morphic resonance theories, though not inconsistent with the notion of a real presence.
Can Morphic Resonance and Ritual create spirits?
If temporarily we accept the idea of morphic resonance we can theorise that the original event in this case the battle, created a “scar” in the universe that subsequent activity reinforced and that reenactment both tuned into and reinforced the resonance.
Extending beyond this investigation leads to the possibility that ritual works at least partly by morphic resonance. Reenacting a battle causes the manifestation of phenomena associated with the battle, a prayer meeting creates a field that tends to bring about the desired effect ( though competing prayers may nullify this), visualising a parking space may create it and half formed negative thoughts (much easier to generate than positive ones after being burned a few times) may tend to bring about bad luck, as may dwelling on possible negative futures. On a larger scale ceremonies such as Remembrance Day may make wars more likely, even though no one consciously wants them to happen, except those who profit from them so conscious reframing of the ritual as not just remembering the dead but preventing future wars may be a good idea, even if this is only something in the minds of those attending – for any effort to change the form of the ceremony will meet with resistance.
The repetition involved in the Toronto Group's creation of Philip of Diddington may have initially created a morphic resonance which then became something like an entity. This type of process may be repeated daily in spiritualist churches. Mainstream religions may create such resonances through their rituals and in the more intolerant religions and cults these resonances may act like malevolent entities.
The experiment described here shows that ritual and reenactment may allow tuning into a past event and that anomalous sounds related to that event may be captured. Ritual may create and tune into such resonances but can also conceivably allow communication from the dead and the creation of conscious non-physical entities. However much of this is speculation and must be tested experimentally.
 Creating Spirits
 Soundscape and the Culture of War on an American Civil War Battlefield: An Ethnography of Communication with Past Presences John G. Sabol Paranthropology Volume 3 Number 2 April 2012
 Colin Wilson cites historian Arnold Toynbee as experiencing spontaneous visions of battles that occurred while he was visiting the sites where the battles occurred. He also notes that while Toynbee had studied these battles there were some details that puzzled him and took some research to resolve.
 The Phenomenon
 Phantom Clowns