My understanding is that as we approach a nexus point, many timelines will be merging in complex ways, and this has already been happening. There are timelines happening where things did not go so well for humanity, but they are unreal and their power is limited. Parts of ourselves may merge with us in a more real, abundant, timeline as we move along. We ourselves are merging back towards the divine timeline.
How do we know when this happens? I don't think we do. You can guess, that's probably as close as your going to get...
If we have interesting experiences like the 2012 movie one described, I suggest it is to help us see there is More to Life and keep connecting to that More. We shouldn't write off any spiritual experiences, they are guidepost along the Way.
The key is to keep climbing higher. Now is the critical time. Make progress in consciousness, let nothing stand in the Way. Follow your heart, hear, listen, heed the still small voice and Be.
What's coming is a rebirth of planet earth on the divine timeline. All of us must do the inner work in order to make the jump. The old timelines where things don't work out or darkness prevails will be no more. So clean your cup, time for More
