The movie The Matrix popularized philosopher George Berkeley's idea that the world is simply a projection of our minds. The universe is fundamentally mental, according to people like Berkeley, it's not material at all. All that we experience when we observe an object are our ideas and ideas are in minds, they're not objectively real, so there actually is no world of solid matter.
Surprisingly, perhaps, a lot of physicists agree with the notion that the world is in large part the creation of our minds. Now, however, evidence is starting to point to the possibility that the world is really a hologram projected by some two-dimensional surface somewhere far away. A hologram, of course, is an image that gives the illusion of being substantial but which is really formed by light waves interacting with each other as they pass through, or reflect off, an image on a film. One of the bizarre properties of holograms is that every piece of the image contains the entire image. It's like a mosaic that's made of pieces every one of which contains the image of the entire mosaic.
If the universe is a hologram then it must be a reflection off a surface outside the universe which means that we must exist not only here, but also there. Moreover, our existence here is just an image, an illusion. Our real existence is there.
That the world is not really as it appears to us is something I'm quite convinced of. For me to accept that it's a hologram, however, is going to require a little more evidence, or maybe another good movie like the first Matrix.
RLC