Hence, all the effects that the thought of separation engendered have already occurred, as well as the correction of the Holy Spirit for every misthought.  As the Course states: "This world was over long ago" (T-28.I.1:6) And we are simply "reviewing mentally what has gone by," for "the script is written" (W-pI.158.4:5,3).  These two "scripts" can be likened to two holograms -- the holograms of hatred and correction -- which are shown in the diagram below.  The part of the mind that chooses between these two is the decision maker.

The following important passage from the text explains these two holograms:

God gave His Teacher* [the Holy Spirit] to replace the one you made, not to conflict with it. And what He would replace has been replaced. Time lasted but an instant in your mind, with no effect upon eternity. And so is all time past, and everything exactly as it was before the way to nothingness was made. The tiny tick of time in which the first mistake was made, and all of them within that one mistake, held also the Correction for that one, and all of them that came within the first. And in that tiny instant time was gone, for that was all it ever was. What God gave answer to is answered and is gone (T-26.V.3; italics ours).

The Course's understanding of time and space is summarized in the following passage from the text:

For time and space are one illusion, which takes different forms. If it has been projected beyond your mind you think of it as time. The nearer it is brought to where it is, the more you think of it in terms of space (T-26.VIII.1:3-5).

The "one illusion" is the belief in the separation from God, and it is this thought that underlies the entire physical universe that appears to span billions of years, and an almost infinite number of miles. Yet since ideas leave not their source (W-pI.167.3:6-7), the seemingly vast universe is still the manifestation of this simple, single thought, always remaining within the split mind that conceived it in madness.

It is an integral part of the ego's strategy to keep this thought of separation protected -- "the tiny, mad idea" that never truly happened -- by projecting it from the mind so that the Son could never undo it by turning to the presence of the Holy Spirit Who is also in his mind. If the Son forgets he has a mind, and therefore is no longer in contact with his mind's decision to be separate, then there is no way he can ever change his mind. This is the ultimate goal in the ego's plot to sustain its own existence.

Therefore, when the thought of separation is projected "far away" from the mind of the Son, it is expressed in the dimension of time: The past, the seeming present, and the future do appear to reflect the huge gap of billions of years the ego wishes to introduce between the mind's decision to be separate from God and the Holy Spirit, and the Son's experience of himself as a body. When the thought of separation is experienced between an individual and another person -- i.e., closer to his experience of himself -- then it is known as space, the physical gap we experience between ourselves and others in our special relationships. To state this another way, time (and therefore space as well) was specifically made by the ego to keep cause (the mind and its thoughts) and effect (our pain and suffering) separated. Thus, there is now a huge gap in our experience between the mind's decision to be separate, and the multiple scripts of different dreams where we experience pain and suffering as figures in these dreams. Only when cause and effect are brought together and therefore undone, can there be true healing; i.e., when the figure I call myself awakens from the dream of separation and accepts the Atonement.

In conclusion, therefore, we can understand that the world of time (and also of space) is nothing more than the projection and expression of form -- outside the Son's mind -- of the thought of separation that remains concealed within the Son's mind, cleverly hidden behind the defense of time and space.