This extraordinary feature of Lord Vāmanadeva is thus explained in Śrīmad-Bhāgavatam (2.7.40).
- viṣṇor nu vīrya-gaṇanāṁ katamo 'rhatīha
- yaḥ pārthivāny api kavir vimame rajāṁsi
- caskambha yaḥ sva-raṁhasāskhalatā tri-prṣṭhaṁ
- yasmāt tri-sāmya-sadanād uru-kampayānam
"No one can estimate the inconceivable potencies of Lord Viṣṇu. Even if one can count the number of atomic combinations in this material world, he still cannot count the different energies of the Supreme Lord. As Vāmanadeva, the Lord was so powerful that simply by stepping forward He covered the whole universe from Brahmaloka down to Pātālaloka."