KATHOPNISHAD CHAPTER 2 SHLOKA -20

                                  अणोरणीयान्महतोमहीयानात्माऽस्य जन्तोर्निहितोगुहायाम् । 

                                  तमक्रतुः पश्यति वीतशोको धातुप्रसादान्महिमानमात्मनः ॥ २0

             ANORNIYAN MAHATO MAHIYAN ATMA ASYA JANTOR NIHITO GYHAYAM |

TAM AKRATUH PASHYATI VITASHOKO DHATUPRASADAT MAHIMANAM ATMANAH ||20

THE ATMAN IS SUBTLER THAN SUBTLE (ATOM),GREATER THAN GREATEST, IS SEATED 

        IN  CAVE OF HEART.ONE WHO IS FREE FROM DESIRES OF MIND AND SENSES 

                   SEES THE GREATNESS OF THIS BECOMES FREE OF SORROW.||20

  This Shloka is interesting as it has certain things that physical science can ot explain and also as the interpretation of this Shloka can be different for different people. The ordinary science which deals with matter can not explain the first part . Something can not be smallest of small and at the same time largest of large. But when we think of non=matter things this is possible. Say a mother has one child  and her love for that child is 100%. She gets second child. Would her LOVE -not attention- be 50% for each child? The answer is NO. So the rules that apply to matter, do not apply to nonmatter things. The ATMAN is also consciousness and that pervades everything. So it can be in any small place and it also can be in any large place . One may take an example of water . The waves are water but the water is not wave . The water in a glass will be glass of water . The water in ocean is also water in ocean. As one can see the water can be a drop or even H2O But one difference is that the ATMAN or Consciousness is not limited by DESH-KAL-VASTU-  (Limitation by space-time  and identity).And it is in the cave of heart in the living being. I think this  has different meaning than physically in the cave of heart. I think when we ACT we have either Brain or Heart as 2 main areas that make decision  and in this Shloka it is stated that this in NOT MATTER FOR INTELECT OR BRAIN.

    The question may arise as to if the Atman is smaller than smallest how can one get it ?So we are told that we can achieve it. One can get get to the ATMAN when one has no physical or mental desires The word DHATU means Elements and that means mind  and intellect and physical senses etc. .But the other meaning of DHATU PRASADAT is BLESSINGS of GOD. So either way or may be by doing both -control of mind and senses  and blessing of God one can get it or perceive it.