The cosmology of Ananda Marga philosophy is known as Brahmacakra or the Cycle of Creation. The 5 fundamental (rudimental) factors mentioned in Brahmacakra refer to the stages of creation where the physical universe emerges from the Cosmic Citta (primordial fabric).
In the emergence of the physical universe from the Cosmic Citta, the rudimental factor known as the Ethereal Factor or akasha tattva came into being first. In Tantra Yoga the Ethereal Factor is said to be able to carry the subtle primordial vibration known as Onmkara.
As the binding effects of tamoguna (localizing, internalizing, limiting, symmetry breaking tendency) increased, a portion of the Ethereal Factor was transformed into vayu tattva or Aerial Factor. Then came the tejas tattva or Luminous Factor. Following the luminous factor there was the creation of the Liquid Factor, apa tattva. The last factor to be created was the Solid Factor or ks’iti tattva.
Sanskrit terms “tattva” and “bhuta” are used interchangeably. In Ananda Sutram “bhuta” terminology is used to refer to the fundamental factors. In other texts “tattva” is also mentioned.
Bhuta is Known by its Tanmatra
In Sanskrit tat means “that”, mátra means “minutest quantity”. Hence the term tanmátra denotes a microscopic fraction of “that” (of “that bhúta”). 
“According to the philosophy of Ananda Marga, Brahma Cakra – the Cosmic Circle – is but a Cosmic dance in which every created object, under the magic spell of the Cosmos, is moving in proper harmony and rhythm. In other words, it may be said that an object or objectivity is nothing but a wave motion within the body of the Cosmos. The philosophy of Ananda Marga thus establishes the wave theory of modern science through an independent logical outlook, and that life consists only of an ocean of waves.” 
“Every bhúta from the ethereal to the solid is in an eternal flow. The very existence of bhútatattva is just a pattern of waves, a microscopic fraction of waves taken in a collective form by the sensory-organs-cum-citta. These microscopic fractions carried through waves are called tanmátras. Hence tanmátras are nothing but the waves produced by the objects concerned as a result of reflection of the subtler bhúta on the cruder ones. Tanmátras in the mathematical sense are not something homogeneous. They are heterogeneous in character and their heterogeneity gives rise to the varieties in the perceptible external world. This heterogeneity is specialized by the difference in wavelengths amongst different tanmátras within or without the scope of any particular bhúta.” 
This is an important point. Bhutas or rudimental factors are rather abstract. Shrii Shrii Anandamurti refers to them as eternal flows. The tanmatras are the tangibles. We percieve the tanmatras not the bhutas. Physics can be considered as the science of tanmatras. The bhutas which are the “flows” behind these tanmatras cannot be perceived directly.
The Seed of all Tanmatras : Onmkara
Avadhutika Ananda Mitra Ac. reminds us that “The substantiation of all the tanmatras, the seed of all vibrations, is the Cosmic Sound, onmkara.” 
Now, let’s read from “Vibration, Form and Colour” essay of Shrii Shrii Anandamurti.
“The vibration of the vast Cosmic Citta that has been flowing pauselessly through eternity is called Onḿkára. You have been hearing so many kinds of sounds and yet you are unable to perceive that eternal sound which is the seed of all sounds. To apprehend these sound waves, an extremely powerful instrument is necessary: the acoustic mechanism in your body at present is too pitifully weak for the purpose. Your instrument of hearing should be immeasurably more powerful than any radio-set that receives soundwaves from the air. Since your weak instrument is quite incapable of apprehending that sound, you are doubtful about the existence of such a phenomenon. But in order to receive the vibrations of the Infinite, you will have to identify your citta or mind and all your organs with that Infinite. Then alone will you be able to merge yourself in the Supreme Vibrational Exultation, surging through your theopathic trance. It is only when your “I” feeling and His, become one, that you can know and hear His mind – that you can experience His sound with every molecule of your being. Then your unit-mind will merge in the Cosmic Mind. In that auspicious moment when your “I” and the Cosmic “I” will meet in the supreme reunion, all your egotistic frivolities, fevers and frets will cease. An inexhaustible stream of symphony will then flow blissfully in the great void.” 
“Now the question may arise whether the different varieties of sound that arise in the universe are the same or different from those of the Cosmic Mind. Are your footsteps, when you walk, the mute witness of your silence or are they the expression of your motivity? What you eat is also sonorific. Every small or great action of your life, every clash of vrttis (desires), every venous vibration is eloquent of a language. Tranquil mountain ranges, flowing streams and river, dense forests – none are mute, none are silent. They are all absorbed in an inexpressible sonorific meditation. Only those who have ears can hear them. None of these sounds is distinct from that Cosmic Sound, from that boundless sonic manifestation. All are Its inseparable flows. All are manifestations of one and the same Onḿkára. And yet due to our analytical minds we perceive these different manifestations to be different types of sounds. Consider, for instance, a village market place. What do you hear from a distance? A medley of howls, is it not? But as you approach nearer to the village, you will notice that the cacophony of sounds becomes differentiated into various meaningful sentences or words: “Give me a kilo of brinjals.” “Your potatoes are too small,” and so on. The some total of all these utterances becomes a howl. Just as all the sounds of the market place have been blended and united into one roaring soundwave, similarly all the sounds of the universe are merged into one Onḿkára, the unified form of all sounds. As every action is vibrative, so every expression of the Cosmic Citta is vibrational. Among all the vibrational tanmátras, the subtlest is the sound tanmátra. That is why the sound tanmátra is the first stage of crudification of the subtle mental sphere into the crude physical world. Onḿkára is the initial manifestation, the first supersonic expression of the Cosmic Citta; thus, it is called Shabda-Brahma or Sonic Consciousness.” 
Conservation Law of Perception for 5 Bhutas
Shrii Shrii Anandamurti gives us a very important clue
“A very important point to be noted here is that the immanent capacity of an object, whether ethereal or solid, for discharging tanmátras, remains the same. Any increase in the number of sense perceptions does not affect the total intensity of perception. It remains constant in a mathematical manner. If the solid can transmit the five fundamental perceptions of sound, touch, form, taste and smell with equal intensity, it does not mean that each and every perception of this solid tanmátra will have the same intensity of sound waves transmitted by the ethereal body. The ethereal body having the singular characteristic of transmitting sound waves has the collective intensity of all the five tanmátras transmitted by the solid body having the multilateral sensory functions.” 
Avadhutika Ananda Mitra Ac. adds “The more tanmatras are emanated the cruder the bhuta; the fewer the tanmatras, the subtler the bhuta.” 
Connections to Modern Physics
In an article published in a 1983 edition of Ananda Marga magazine in Australia titled “Stimulating Thoughts on Brahmacakra” by an anonymous margi in USA the following correspondences were proposed:
Solid Factor: hadrons
Liquid Factor: leptons
Luminous Factor: photon
Aerial Factor: other force carrying particles
Ethereal Factor: vacuum field of energy
Michael Bhaktaviirya Towsey  comments on the correspondences mentioned above and offers that Liquid Factor may be related to electron standing wave and Aerial Factor to “dark matter”. He identifies neutrinos as the tanmatras of the Aerial Factor while mentioning the other candidates such as axions and photinos.
My interpretation of 5 Fundamental Factors
When we establish connections to physics we can identify tanmatras with the “field quanta” (fermions, and force carrying bosons) but we should refrain from finding correspondences to bhutas. There are some similarities between the “field” and the “bhuta” concepts but those similarities are not sufficient to establish a connection. There are only 5 bhutas while there are many types of fields in physics. As a matter of fact, in Quantum Field Theory each particle type has its own field. The types of fields is certainly greater than 5.
Shrii Shrii Anandamurti reminds us that a bhuta is a “flow”. My intuition tells me that the “bhuta flow” is related to the “objectivation flow” concept I have been writing about. Regarding the “objectivation flow”, I offered the following thoughts in the article “A Fundamental Principle“
1. The fundamental interaction/coupling forms the cosmic nucleus/identity (cosmic subjectivation)
2. The cosmic nucleus/identity objectivates (cosmic flow/evolution starts)
3. The objectivated realm is a lower-dimensional reality
4. The dimensional reduction activates the action-reaction principle
5. Within the objectivated realm (Cosmic Citta) an “external space” expands rapidly. The “external space” is yet another objectivation which follows the subjectivation of the Cosmic Citta. A subjectivation is always followed by objectivation. This principle applies to all stages of creation.
6. The vacuum (“internal space”) fluctuations and their subsequent manifestations as fields, particles and “time” appear as reaction to the growth of the “external space”. This combination of “external space” and “internal space” can also be described as the “primordial fabric”.
7. Fields and particles are attracted to each other as a consequence of the “time” effects
8. Organisms are formed as a result of the attractive forces
9. Cosmos evolves to maximize the expression of Cosmic Consciousness. As the cosmic objectivation/evolution proceeds, unit consciousnesses emerge and they eventually reflect the Cosmic Consciousness in full. Creation (cosmic objectivation flow) is a necessary mechanism for the maximization of the reflection of Cosmic Consciousness.
The primordial fabric as descibed above is the starting point of the Ethereal Factor. Since the primordial fabric is a combination of the “external” and “internal” space we cannot simply identify the Ethereal Factor with “spacetime” of physics.
Ethereal Factor : Spacetime + Vacuum = External Space + Internal Space
In my article “Golden Hints” I mentioned the 5 stages of physical manifestation
In the first stage, the distortions of the primordial fabric appear as primordial G particles or quanta. The collective motion of G quanta acquire wavelike properties.
In the second stage, the space emerges from the collection of G particles. If we use the “curvature” language the space emerges from the “curvature atoms” (mathematical constructs related to curvature). This is similar to the “spacetime atom” (atoms of volume) terminology used in the “Loop Quantum Gravity” theory  of physics. The other promising theory called “Causal Dynamical Triangulations” has a similar idea: spacetime is approximated as a mosaic of triangles which have a built-in distinction of space and time .
In the third stage, time and vibration emerge. Electromagnetic waves manifest.
In the fourth stage, electric charge, and other charges (topological and other kinds) are formed, “electro-weak” and “strong” forces manifest.
In the fifth stage, the mass and gravitational force manifest.
In this perspective, the 5 stages of physical manifestation mentioned above can be related to the 5 bhutas. Using the terminology of the Brahmacakra the first stage corresponds to the Ethereal Factor, the second stage to the Aerial Factor, the third stage to the Luminous Factor, the fourth stage to the Liquid Factor and the fifth stage to the Solid Factor.
More on the Ethereal Factor
Without a proper understanding of the relationship between the Onmkara (primordial vibration) and the “bhuta flow” we really do not know anything about bhutas. I hope to hear from people who have intuition on this connection.
Let’s close with another comment from Shrii Shrii Anandamurti
“Ákásha or ethereal factor is more or less a theoretical factor and being the subtlest of all the bhútas has got the maximum wavelength, so its flow faces no physical hindrance, whereas the other bhútas do face some. A wave can move freely only when it is in harmony with previous waves and their curvatures. A wave can pass through an object where there is no physical obstruction or hindrance from a subtler wave, that is, subtler waves can pass through cruder waves; and under such circumstances there is always an adjustment of wavelengths resulting in the creation of physical diversities. Proper adjustment of wavelength means adjustment at the two pauses of the waves – the sentient pause and the static pause. The sentient pause in the wave denotes the point where upward momentum is finally exhausted and the wave is just about to start downward movement, and the static pause is at the point where downward movement has ended and upward motion is just about to start. They represent the crest and trough of physical science. The greater the wavelength of any bhútatattva, the more is the chance of this adjustment of the striking waves passing through.” 
“When an object permits the passage of a wave, it does not come within the scope of sensory nerves, but when the wave does not get such a passage, that is, it is reflected back, under such circumstance only is there a perception of its existence by our sensory nerves.” 
 Some Questions and Answers on Ananda Marga Philosophy,
Ananda Marga Philosophy in a Nutshell Part 3
 Shrii Prabhat Ranjan Sarkar, “Idea and Ideology”, Ananda Marga Publications, ISBN 81-7252-001-8
 Avadhutika Ananda Mitra Ac., The Spiritual Philosophy of Shrii Shrii Anandamurti: A Commentary on Ananda Sutram, 2nd Edition, Ananda Marga Publications, ISBN 81-7252-119-7
 Shrii Shrii Anandamurti, “Vibration, Form and Colour”, Subháśita Saḿgraha Part 3
 Michael Bhaktaviirya Towsey, “Eternal Dance of Macrocosm”, Proutist Publications, Copenhagen
 Martin Bojowald, “Follow the Bouncing Universe”, Scientific American, October 2008
 Jan Ambjorn, Jerzy Jurkiewicz and Renate Loll, “The Self-Organizing Quantum Universe”, Scientific American, July 2008