In the continental tradition, however, it seems more is said. Heidegger, of course, made the question famous, but throughout the continental figures I think we find a shared conception of being. I do not intend to argue that any particular individual held this view, but rather, here, I would like to focus on sketching it. If theoretical physics loses you, skim those paragraphs, the rest should only be as hard as usual.
First, some background. Kant held that there was only one unified experience, at least in any individual's case. That is, I have a single unified experience of a continuum of space and of time which are tied together, and likewise for everyone else. Thus, everything I find around me belongs to the same space-time. Every object is affected by what is before it in time, affects what is after it in time, and mutually affects what is at the same time as it (See the Critique of Pure Reason I. Division one, Bk.2, Sec.III.3 titled "Analogies of experience"). On Kant's view, these relations are how things get ordered in time to begin with.
This fits well with current understandings of spacetime and relativity on which an object which is unable to have an effect on another object does not stand in any particular relation of before, after, or simultaneous with the other object. On the other hand, it clashes with views of quantum mechanics which permit backwards-causality or hold that events are determined by the boundary conditions, i.e., the conditions at the start, end, and along the light-cone bounding an area. It also has the consequence that if God cannot be effected from without, then he is necessarily in the past. One could, however, strip the claim that the causal relations order events in time, and simply claim that for an object to exist, it must effect other objects, and that the collection of objects effected, mediately or immediately, constitute a reality.
Kant does not hold the view I am seeking to sketch, since he holds that noumena may exist, and that we have no way of knowing how they really are. However, from here, it seems Kant's followers, in seeking to do away with the noumena, wind up holding that for something to exist, not merely for us but at all, it must be related to other existent things in just this manner. Thus, a reality is given as a set of things which interact with each other, whether mediately or immediately. In order to be part of reality, then, an object must somehow have an effect on other parts of reality.
The difficulty with such a definition is that it seems to permit multiple realities, so that existence is relative to realities. Such realities would be incapable of interacting, otherwise they would form a single reality. One might say, then, that existence would be relative to the observer. An observer in one reality would find different existent things than would an observer in a different reality, and each reality would fail to exist from the point of view of the other.
Let us return to the possibility that God effects all of reality without, himself, being effected by it. In order for such a God to exist on this view, the view must hold that an object can exist even if it only effects other objects without being effected itself. However, one does not want realities to be able to branch. If we say that there is only one continuum of time, and that events are ordered in time by how they effect each other, we can avoid branching while maintaining the possibility of effecting without being effected, but at the cost of excluding some quantum mechanical views and likely relegating God to the past (although the later could be handled by holding that God's place in time would always be found just a moment ago, since he acts at all times, and thus he would be found to be at all times).
If we permit events in time to have separate orders, which Kant does not but relativity might, then we can get branching even if relations of what affects what determine temporal order. If objects only affect further objects, however, then some objects are affected. If we exclude for other reasons the possibility of two creators, we can limit unaffected things to God, and everything else will both affect and be affected. This still does not guarantee a unified reality, but it does make it vastly more plausible.