Max Planck uttered the words “there is no matter in itself” in 1944 during a lecture in Florence. Among other things, he said at the time:
Gentlemen, as a physicist who has devoted his whole life to sober science, to the study of matter, I am certainly free from the suspicion of being taken for a raving spirit.
And so, after my explorations of the atom, I say this: There is no matter in itself. All matter is created and exists only by a force that makes the atomic particles vibrate and holds them together to form the tiniest solar system in the universe. But since there is neither an intelligent force nor an eternal force in the whole universe [...] we must assume a conscious intelligent spirit behind this force. This spirit is the source of all matter. It is not the visible but perishable matter that is the real, true – for without the spirit, matter would not exist at all –, but the invisible, immortal spirit is the true! But since spirit per se cannot exist either, but every spirit belongs to a being, we must necessarily accept spirit beings. But since spirit beings cannot be of themselves either, but must be created, I am not afraid to name this mysterious creator as all cultural peoples of the earth of earlier millennia have named him: God!
Thus, the physicist who has to deal with matter comes from the realm of matter into the realm of spirit. And there is the end of our task, and we must pass on our research into the hands of philosophy. 
With his statement "There is no matter in itself" Max Planck certainly does not want to deny the existence of matter, but expresses that there is no matter detached from all reference.
Is his statement, which is now more than 70 years old, still valid, or can it be dismissed as the statement of an old, age-wise man who did not want to or could not follow the latest findings? Planck was already 86 years old at the time. Or do we rather have to understand it as the quintessence of his whole life as a researcher, worth dealing with? For his statement is by no means an isolated one, but is, as it were, in essence in complete agreement with those of other great minds.
In the quoted first sentence "... by a force which makes the atomic particles vibrate" he points out, as an aside, a very decisive nature of atoms: that they consist of vibration, indeed are vibration.
Matter as a manifestation of the spirit
Even more unambiguously than Max Planck, Rudolf Steiner describes the nature of matter as a manifestation of the spirit:
And then one will have to go even further to see spirit in everything condensed and formed. Matter does not exist! What matter is, is to spirit as ice is to water. If you dissolve the ice, there is water. If you dissolve matter, it disappears as matter and becomes spirit. All that is matter is spirit, the outward manifestation of spirit. 
(Sketch by Rudolf Steiner: The atom as the result of opposing directions of forces)
And in another speech, Steiner describes quite clearly the limitations that are inevitably built up by a materialistic theory of the atom:
"However, the causes that physicists and chemists attribute to the phenomena are nothing more than thought images. For moving atoms, molecular forces, etc. are ideas borrowed from the ordinary world of the senses and projected into a world not perceptible to the senses. If the physicist believes such fictions to be true realities, he is paying homage to a superstition which, in many respects, is to be seen as a lower level than the fetish worship of so-called primitive peoples. Our contemporary science, in so far as it builds theories and does not limit itself to mere observation, is full of idolatry and superstition. Atomic theory is nothing more than superstition when it is taken as more than a preliminary, workable working hypothesis." 
If you let this saying work on you, it becomes clear that spirit and matter are as closely connected as light and shadow, like water and ice. What we call atoms are, therefore, concentration points of the spirit, which have formed according to certain universal laws and reveal the divine order. Atoms are not only simple building blocks in the universe, but also potentialities for further, future forms of revelation.
When people do not know this order, they are inclined in their thirst for experimentation and research, to artificially cause atomic fission or even to shatter the atomic nuclei. This is very unfortunate, because it will have a fundamentally negative influence on future development. It is to be hoped that a future generation will recognise the harmfulness of these activities and put an end to them. A first step was the decision to end the use of nuclear power in Germany taken after the catastrophe of Fukushima.
Quantum physicist Hans-Peter Dürr, a close colleague of Werner Heisenberg, one of the pioneers of modern quantum physics, has brought it to the point:
In the depths that are more difficult to grasp, in the world of the smallest, "things" are not things at all – that's why the revolution doesn't want to get into people's heads: There are no things, there are only changes of shape and form. Matter is not composed of matter, but of pure form beings and potentialities." [.....] "This is like spirit; basically there is only spirit, but it calcifies, and we perceive only the lime, as matter. 
Rudolf Steiner describes the nature of atoms still further by denying them rigid, i.e. technically and physically identical properties, and instead giving them a certain "range of variation". On the occasion of a lecture in Stuttgart on March 13, 1920, he said:
[...] “If one wanted to record the state which represents the atomic weight number, one would have to show a pendulum motion, not a point. And we would also not be allowed to describe the periodic system as it is, but in trembling motion we would have to have it, in inner trembling motion. It’s true, we can’t say, atomic weight would show, that we really have to deal with solid elements. This idea of a rigid atom [is not tenable]. This rigidity is already absent where the element is formed.
There are no more definite atomic weights than there is a special size of wheat grain. Of course, there is a medium size for the grain of wheat, but the size varies. So it is with atomic weight; it is only a medium state." 
The well-known atomic model of Rutherford and Bohr with the electrons orbiting around the nucleus has of course its correct aspects. The analogy to the planets orbiting the sun is particularly obvious and memorable. But considering the nucleus as the actual, solid matter in which the "gravity" manifests itself leads to a dead end. Just as the spiritual principle of life is revealed in the sun, the atomic nucleus must also be seen as the concentration of the spiritual principle.
This knowledge is ancient. In the Bhagavad-Gita, pilgrims are advised to "free themselves from the illusion of matter and its illusory world”.
(to be continued in part 2)
 Archiv zur Geschichte der Max-Planck-Gesellschaft (Archive on the History of the Max Planck Society), Dept. Va, Rep. 11 Planck, No. 1797
 anthrowiki.at: GA 056, p. 59
 anthrowiki.at: GA 34, p. 383ff
 anthrowiki.at H.-P. Dürr 1998
 anthrowiki.at: GA 73a, p. 490