How our small material universe exists deep inside a larger universe called a Brahmanda.

The Vedic explanation of "other universes"

The multiple Brahmanda universes emanating from Maha Vishnu, that our smaller universe is deep within, all each exist within their own time zone.

And as painting shows, there are billions of Brahmanda's emanating from Maha Vishnu, each with a secondary universe deep inside it.

Often this "different time zone concept", is refered to as being in their own dimension of space-time.

This may make it appear there are parallel universes but in reality they are not, they all exist together in the mahat tattva material creation.

However, not being able to detect other Brahmanda universes or the many planetary Systems within them (there are 14 Planetary Systems in our small universe that is deep inside our Brahmanda), is due to the many different movements of "space-time", that puts each Brahmanda universe existing within their own movement of space-time.

It is therefore NOT really a dimensional concept in the modern sense of the word but rather a "space-time" difference which makes our Brahmanda invisible to others and others invisible to ours.

Remember, our smaller Bhu-Mandala universe exists deep inside our massive Brahmanda within the lotus stem coming from Garbhodakashayi Vishnu that Lord Brahma sits on top of.

Our Brahmanda is just one of billions coming from Maha Vishnu.

The words "Lord Vishnu" actually refers to a category known as Vishnu-tattva, or expansions of God (Lord Krishna).

There are billions of different names of Vishnu, but the basic is “He who has entered everywhere”, as God’s omnipresence known Kshirodakashayi Vishnu or paramatma.

Within the category of Vishnu-tattva are included all of the unlimited incarnations and expansions of God that all have 93% of Lord Krishna's qualities.

There are some expansions that also bear the particular name “Vishnu”, three of which are -

Karanadakashayi Vishnu (Maha Vishnu).
Garbhodakashayi Vishnu,
Kshirodakashayi Vishnu, (Paramatma)

The Karanodakashayi Vishnu (Maha Vishnu) is the first Purusha avatar who is lying on the causal ocean (karana-udaka).

From him the innumerable universes (Brahmanda's) manifest as he exhales. And into Him the universes are destroyed as He inhales.

He expands deep inside of each Brahmanda Universe as Garbhodakashayi Vishnu. This Vishnu is lying on the universal waters that originate from His perspiration, and which fill the universe halfway.

In his navel is a lake, and from that lake grows a lotus stem. Lord Brahma is born within that lotus. Inside the stem of the lotus are the fourteen planetary systems also.

Garbhodakashayi  Vishnu expands as Kshirodakashayi Vishnu (Paramatma) who resides in Shveta Dvipa on the milk ocean and in the hearts of all living entities in all material universe.

Shveta Dvipa is a Vaikuntha planet that the Lord manifests within the material universe.

In reality it is more like a window through the material covering, which allows one to see a portion of the spiritual realm. It is an eternal abode, and it continues to exist even after the destruction of the material universe.

The system of the Lord’s incarnations is that all incarnations come through the form of Kshirodakashayi Vishnu in Shveta Dvipa.

Lord Brahma along with the material administrators or demigods stand on the shore of the milk ocean and pray to the Lord to incarnate. They are not able to see the Lord, but Lord Brahma receives confirmation from within his heart.

Factually there is no difference between one Vishnu form and another, as they all belong to the same category of Vishnu-tattva (93% of Krishna's qualities)but still known as the Supreme Person.

Krishna is not a different personality from Rama, and Rama is not a different personality from Narayana. They are almost one and the same except Krishna has 64 qualities whereas Narayana or Vishnu has 60 qualities.

The category of Vishnu-tattva takes millions of different Forms according to the mood of the devotees approaching the Lord.

There is no higher and lower capacity among the Vishnu-tattva expansions and forms of Lord Krishna.

Although Lord Shiva is in a category of His own and is neither Jiva-tattva (78%) or Vishnu-tattva (93%)

His qualities are 84% of Lord Krishna's qualities.

Many Vishnu-tattva's choose to withhold certain aspects of their opulences to play a certain part within the material universe for example, if a suitable jiva tattva is not found in the material creation to become the next Lord Brahma, then Lord Vishnu descends and takes on that role of Lord Brahma.

Many gopis (Vrindavana village girls and women) and gopas (Cow herd boys) are also Vishnu-shakti-tattvas (93%) who play a simple role in Krishna lila.