One sometimes hears people saying Gurbani says there are lakhs (many hundred thousand) Paataal (nether regions) and Akaas (skies). Yes this is what the first line of Paurri 22 says but only to to say it is a misconception. In this Paurri Guru Nanak refers to the Hindu and Semitic estimates of the composition of the universe. He says the universe is infinite and beyond measure:
ਪਾਤਾਲਾ ਪਾਤਾਲ ਲਖ ਆਗਾਸਾ ਆਗਾਸ ॥ ਓੜਕ ਓੜਕ ਭਾਲਿ ਥਕੇ ਵੇਦ ਕਹਨਿ ਇਕ ਵਾਤ ॥
There are millions of planets with their skies and the lower regions;
Repeated efforts to find them do not succeed say the Hindu Vedas with one voice;
ਸਹਸ ਅਠਾਰਹ ਕਹਨਿ ਕਤੇਬਾ ਅਸੁਲੂ ਇਕੁ ਧਾਤੁ ॥
The Semitic scriptures say there are 18000 planets but their source is one Creator;
ਲੇਖਾ ਹੋਇ ਤ ਲਿਖੀਐ ਲੇਖੈ ਹੋਇ ਵਿਣਾਸੁ ॥ ਨਾਨਕ ਵਡਾ ਆਖੀਐ ਆਪੇ ਜਾਣੈ ਆਪੁ ॥ ੨੨॥
However we can count only if the number is finite; so counting efforts fail;
The Great Creator alone knows about the whole universe. 22.
Reference to 18000 planets is not found in either of the Semitic scriptures i.e. the Bible or the Quran. It however exists in the Talmud, a record of oral discussions pertaining to the Jewish Law between the Rabbis, the Jewish clergy, and is considered authoritative. It says God flies through 18000 worlds or planets (Talmud - Aveda Zara 3b). Guru Nanak’s knowledge of this shows he had interacted with the Jews, although there is no historical record available.