We may have very good reason for saying that we are ourselves beings of four dimensions and are turned towards the third dimension with only one of our sides, i.e. with only a small part of our being. Only this part of us lives in three dimensions, and we are conscious only of this part as our body. The greater part of our being lives in the fourth dimension, but we are unconscious of this greater part of ourselves. Or it would be still more true to say that we live in a four-dimensional world, but are conscious of ourselves only in a three-dimensional world. This means that we live in one kind of conditions, but imagine ourselves to be in another.

We live in a three-dimensional world, and our brains are organized in three dimensions, so we might as well compute in three dimensions. ...Right now, chips, even though they're very dense, are flat.

There are really four dimensions, three which we call the three planes of Space, and a fourth, Time.

We live between two worlds; we soar in the atmosphere; we creep upon the soil; we have the aspirations of creators and the propensities of quadrupeds. There can be but one explanation of this fact. We are passing from the animal into a higher form, and the drama of this planet is in its second act.

It is a sad hardship and slavery to people who live in towns, that in their movements they know of one dimension only; they walk along the line as if they were led on a string. The transition from the line to the plane into the two dimensions, when you wander across a field or through a wood, is a splendid liberation to the slaves, like the French Revolution. But in the air you are taken into the full freedom of the three dimensions; after long ages of exile and dreams the homesick heart throws itself into the arms of space.

Our scientists assert that human life does not exist on such planets as Mars, Venus, Jupiter, etc. This assumption arises out of their ignorance of the etheric levels of matter. Their technology is still inadequate to measure the full range of the material planes. Had they etheric vision, they would know that all the planets of our system are inhabited and that many are far more advanced in evolution than we are on Earth. The time is fast approaching when a more open-minded view of life with its mysteries will supersede the arrogance of the ignorant, to the benefit of us all. (Preface)

We exist on several different planes, and when we said nothing had any reason we were referring to the psychological and social plane.

Life, as it exists on Earth in the form of men, animals and plants, is to be found, let us suppose in a high form in the solar and stellar regions. Rather than think that so many stars and parts of the heavens are uninhabited and that this earth of ours alone is peopled – and that with beings perhaps of an inferior type – we will suppose that in every region there are inhabitants, differing in nature by rank and all owing their origin to God, who is the center and circumference of all stellar regions

Life can exist on other planets, in other solar systems, in other galaxies and universes.

Do you ever wonder if — well, if there are people living on the third planet?'
'The third planet is incapable of supporting life,' stated the husband patiently. 'Our scientists have said there's far too much oxygen in their atmosphere.

Poincaré analyses how the reality of three dimensional Euclidean (or non-Euclidean) space, has been constructed from our daily experiences as a human being with the objects that are most important for us (rigid bodies), and closely around. This does not mean that this three dimensional space is an ‘invention’ of humanity. It exists, but the way we have ordered, and later on formalized it, by means of specific mathematical models, does make part of it. In other words, what we call the three dimensional reality of space partly exists in its own and partly exists by the structures that we have constructed, relying on our specific human experience with it.

It's the 21st century and still we have no universally agreed upon definition of life. It seems the universe does not care about our desire for tidy categories and tight descriptions. Our intellectual comfort is irrelevant to reality. When it comes to life, gray zones and blurry boundaries abound. This is bizarre considering life has been on our planet for more than 3.5 billion years and it's all around us now. Life saturates Earth's surface zone, from more than a mile deep in the crust to the stratosphere miles above. Its diversity and overall success are staggering, difficult to comprehend. For example, some scientists estimate that there are more than one trillion species alive right now. In total, Earth may have hosted more than 100 trillion species so far. Life is no stranger to us. And yet, what is it?

It seems to me that we do live in two worlds... there is this physical one, which is coherant, and there is the spiritual one, which to the average man with his flashes of religious experience, is very often incoherant. This experience of having two worlds to live in all the time, or not all the time, is a vital one, and is what living is like.

All my life, I've wondered about life beyond the earth. On those countless other planets that we think circle other suns, is there also life? Might the beings of other worlds resemble us, or would they be astonishingly different? What would they be made of? In the vast Milky Way galaxy, how common is what we call life? The nature of life on earth and the quest for life elsewhere are the two sides of the same question: the search for who we are.