The distance between earth and the heaven is 500 years, and between each of the seven heavens is another 500 years. (Pesachim 94b)
מִן הָאָרֶץ עַד לָרָקִיעַ מַהֲלַךְ חֲמֵשׁ מֵאוֹת שָׁנָה, וְעוֹבְיוֹ
שֶׁל רָקִיעַ מַהֲלַךְ חֲמֵשׁ מֵאוֹת שָׁנָה, וּבֵין (כׇּל) רָקִיעַ
לְרָקִיעַ מַהֲלַךְ חֲמֵשׁ מֵאוֹת שָׁנָה, וְכֵן בֵּין כׇּל רָקִיעַ
וְרָקִיעַ, ״אַךְ אֶל שְׁאוֹל תּוּרָד אֶל יַרְכְּתֵי בוֹר״.
תְּיוּבְתָּא.
In contrast, from the earth to the first firmament of seven (see
Ḥagiga 12b) is a walking distance of five hundred years, and the
thickness of the firmament is a walking distance of five hundred
years, which is equal to approximately 1.8 million parasangs, and
between each firmament is another walking distance of five hundred
years, and so too between each and every firmament. Therefore, how can
you, Nebuchadnezzar, hope to reach the heavens in your lifetime, such
that you say: “I will be like the Most High”? Rather, as the verse
continues: “Yet you shall be brought down to the netherworld, to the
uttermost parts of the pit” (Isaiah 14:15). (Sefaria)