The Astral Plane is not a country—is not a place at all—in the usual sense. Its dimensions are not those of space, but of vibration. In a way, it may be said that the dimensions of the Astral Plane are the dimensions of Time, for vibrations can be measured only by their rate of motion, and that rate is determined only in terms of Time. The same is true of all vibrations whether of Astral energy or the lower forms of energy. The vibrations of light are measured in terms of Time, that is to say so many vibrations to the second, and so on. The higher the rate of vibration, the greater the rate of speed manifested in the vibration.
The substance of the Astral Plane is, of course, very much finer than that of the material plane—its vibrations very much higher than the finest form of material substance. But there is the widest range between the vibrations of the lowest planes and those of the higher ones. In fact, the difference between the lowest plane of the Astral, and the highest of the material plane is less than the difference between the lowest and highest of the Astral itself. So that between these two extremes of Astral vibrations, we have the same great territory that we would have on the material plane, with this difference, however, that the material territory is measured by space dimensions, while that of the Astral is to be measured only in terms of vibration, or time, and not of space.
For instance, when one travels on the material plane, he must traverse space—feet, yards, or miles. But, on the Astral Plane, when one travels he traverses rates of vibrations—that is to say, he passes from a high rate of vibration to a lower, or vice versa. And these various planes or sub-planes of vibratory energy constitute the geographical features of the Astral Plane. There are countless planes and sub-planes, or regions of the Astral Plane, which may be travelled, but all Astral travel is performed simply by passing from one degree of vibration to another. Using a crude example, we may say that it is somewhat akin to passing from the state of ice to that of water, and then of steam. Or, again, it may be thought of as passing from ordinary atmospheric air to liquid air, and then to solid air (the latter is theoretically possible, although science has not yet been able to solidify air).
There are many states or conditions of existence on the Astral Plane, which are spoken of as planes and sub-planes. These planes and sub-planes are inhabited by souls fitted to dwell upon the particular series of planes or sub-planes upon which they awaken from the soul-slumber. Subtle principles of soul attraction draw each soul to the particular place for which it is fitted. The great law of attraction operates unerringly here. There is no chance or haphazard about the mechanism of the law of attraction. The law operates with absolute precision and uniformity—it makes no mistakes.
Each soul is restricted in its range by its own inherent limitations and degrees of development. There is no need of Astral policemen to keep the disembodied souls in their rightful places. It is impossible for the disembodied soul to travel into planes above its own immediate series. The law of vibration prevents this. But, on the contrary, each and every soul may, if it so chooses, freely visit the planes and sub-planes beneath its own series, and freely witness the scenery and phenomena of those lower planes and mingle with the inhabitants thereof. (This entirely apart from the high form of telepathic communication which prevails between disembodied souls on the Astral Plane). This is a very wise provision of the Law, for were it otherwise the higher planes would be open to the influence of those dwelling on the lower, and the soul-life and development would be interrupted, just as a classroom in a school of philosophy might be interrupted by a gang of hoodlums from the slums of a large city. (For, remember, the Astral Plane has its slums and hoodlums, as well as the material plane).
It is absolutely impossible for a soul to go beyond the plane to which it belongs, although those on the upper planes may freely revisit the lower planes, this being the rule of the Astral Plane—not an arbitrary law, but a law of nature. Imagine a large screen or series of screens, such as are used for sorting coal into sizes. The large coal is caught by the first screen, the next size by the second, and so on until the tiny coal is reached. Now, the large coal cannot get into the receptacle of the smaller sizes, but the small sizes may easily pass through the screen and join the large sizes if force be imparted to them. Just so on the Astral Plane, the soul with the greatest amount of materiality, and coarsest nature, is stopped by the screen of a certain grade or plane, and cannot pass on to the higher ones; while one which has passed on to the higher planes, having cast off more confining sheaths, can easily pass backwards and forwards among the lower planes, if it so desires. In fact, souls often do so, for the purpose of visiting friends on the lower planes, and giving them enjoyment and comfort, and, in case of a highly developed soul, much spiritual help may be given in this way, by means of advice and instruction, when the soul on the lower plane is ready to receive it.
The one exception to the rule of free passage to the planes below that of the particular soul is the one which prevents the lower-plane souls from entering the plane of the sleepers, which plane may not be entered by souls which have awakened on a low plane, but which may be freely entered by those pure and exalted souls who have attained a high place. The plane of soul-slumber is sacred to those occupying it, and those higher souls just mentioned, and it is in fact rather of the nature of a distinct and separate state than one of the great series of planes and subplanes.
There are as many different kinds of regions on the Astral Plane as there are on the material plane, and each plane is inhabited by exactly the class of souls which it might be expected to attract. There are to be found the abodes of degraded souls, so steeped in materiality and animality, that they would be veritable hell to a soul of higher attainment. It may well be imagined that the soul of higher impulses has no desire to travel into these depths of the Astral unless it be some very highly developed soul which is willing to descend into hell in order to minister to the needs of some lower soul which is striving to emerge from the slough of despond into which its earth life has thrown it. Such ministering spirits do exist and perform this work for their lower brothers and sisters. But, as a rule, the disembodied souls prefers to work out its own evolution on its own plane that it may ascend to the higher grades of spiritual opportunity in its next incarnation, and that it may acquire spiritual knowledge during its sojourn on its particular plane of the Astral.
Life Beyond Death, Yogi Ramacharaka, Yogi Publication Society, Chicago, 1912