Krsna is the Supreme Personality of Godhead and cause of ALL causes.

The original Krsna resides in His personal abode known as Goloka-Vrindavan and never leaves.

When Krsna enters the material creation it is actually His Visnu-tattva expansion playing the role of Krsna Prabhupada has explained.

Krsna is the original source of all Narayana or Visnu forms of God who are His expansions residing in the quadrillions of perpetual Vaikuntha Planets that surround His central abode of Goloka-Vrindavana (taking up 75% of the Spiritual Sky)

Krsna further expands, via His first Visnu-tattva expansion, first as Balarama and eventually as Maha-Visnu (Karanodakshayi Visnu) who creates and manages the unlimited temporary material universes called Brahmandas that take up 25% of the Spiritual Sky.

These unlimited number of Brahmandas are coming from the Body of Maha-Visnu through His breathing and pores.

Each Brahmanda is massive in size and houses a secondary smaller spherical material universe inside of them.

Each individual material universe is up of material qualities (both subtle and gross material elements)

Each massive Brahmanda universe covers, encases and surrounds an inner material universe deep inside them with 7 or 8 layers of material qualities.

Maha-Visnu expands again as Garbhodakashayi Visnu who creates this secondary material universal sphere deep inside the Brahmanda.

Then from Garbhodakashayi Visnu, Brahma manifests who creates the different planetary systems within each inner secondary material universe spread out as a flat disc made up of millions of planets as explained in Srimad Bhagavatam.

Due to the massive material elements that make up the outer Brahmanda universe, no one inside their inner universe can see outside of their own universe Srimad Bhagavatam explains.

This means from within our small material universe inside our Brahmanda, we cannot see the billions of other Brahmandas around us.

Deep inside our Brahmanda is a secondary universe where Brahma creates the 14 different planetary systems.

Each secondary material universe deep inside their Brahmanda, has a different amount of planetary systems according to Srimad Bhagavatam.

In other words, the Brahmanda universe and its inner secondary universe inside it, all come in different sizes.

Karanodakshayi Visnu (Maha-Visnu) is actually sleeping and is always DREAMING the activities within each of the secondary material universes deep within the unlimited number of Brahmandas.

Those dreams Maha-Visnu has, are all the activities happening within each of the Garbhodakashayi Visnu's secondary universes.

In painting below Karanodakshayi Visnu (Maha-Visnu) is seen laying down sleeping and Garbhodakashayi Visnu is seen within each of His Brahmanda universes.

When Maha-Visnu dreams, He first creates the entire material universe known as the Maha-tattva (matter) which takes up 25% of the Spiritual Sky or Brahmajyoti.

As said the other 75% is the active spiritual world (anti-matter) that is ever fresh, always youthful and never ending, known as the perpetual Vaikuntha Planets of Visnu and Krsna's central abode of Goloka-Vrindavan.

Within Maha-Visnu's 25% of the Spiritual Sky called the temporary material creation, we find it is always in a state of decay, decline and impermanence, requiring constant maintenance.

Each jiva-soul who chooses to enter the material creation, are forced into repeated birth and death, forced to possess (or take) temporary material bodily outer vessels or containers.

The visiting jiva-souls in the material creation, are forced to take repeated births again and again because the material bodies they are in, simply wear out, get old, break down and eventually cease to operate.

So to be clear-

1 - Within this temporary material creation, we find unlimited individual massive single Brahmanda universes coming from the Body of Maha-Visnu.

2 - And deep inside each of those massive Brahmanda universes, there is a secondary smaller universe where Maha-Visnu expands Himself as Garbhodakashayi Vishnu.

3 - And from Garbhodakashayi Visnu, Lord Brahma appears from His naval at the top of a lotus flower.

4 - Then Lord Brahma builds the many planetary systems inside each of the inner secondary universes deep inside their individual Brahmanda.

There is only one Maha-Visnu in the material creation yet an unlimited number of Garbhodakashayi Visnus and Lord Brahmas.

Also it is important to understand, the amount of Planetary Systems deep inside each Brahmanda, vary in size, some larger and some smaller than others.

Our material universe within our Brahmanda has 14 Planetary Systems and is considered a small universe explained in Bhagavatam as 4 billion miles in diameter.

Some Vedic Cosmologists think this figure of 4 billion miles in diameter describing our material universe inside our Brahmanda, is too small of a figure.

Some Vedic scholars suggest the figure of 4 billion miles or 500 million yojanas, as decribed in the 5th Canto of Srimad Bhagavatam, is really a code that needs decoding because they claim just our Solar System alone is said to be 22 billion miles in diameter.

Another answer is the measurement of space and time is different on each planetary system just like the fabric of space-time moves at a different  rate in each of the 14 planetary systems.

For example, 100 Earth years on Brahmaloka, the highest planetary system out of the 14 systems, is 311 trillion and 40 billion human years long.

So there maybe far more to this figure claiming our material universe is just 4 billion miles in diameter.

Other universes inside their Brahmanda, have many more Planetary Systems than just 14 and are therefore much bigger than 4 billion miles in diameter.

The fact is, the size of each Brahmanda and their inner universe, depends on the how many heads Lord Brahma has.

Some Lord Brahmas, like ours, has only 4 heads, while other Brahma's within their universe inside their Brahmanda, may have 10, 20, 50, 500, 1000, 100,000 or even a million or more heads.

In this way, all the quadrillions of Brahmanda universes coming from the Body of the sleeping Maha-Visnu (as seen in painting below), ALL have a secondary inner universe deep inside it also seen in painting.

Each massive Brahmanda universe has 7 material coverings or layers that surround and enclose each of the inner secondary material universe, this means the massive outer Brahmanda surrounding universe we are deep within, is 44 quadrillion 444 trillion 444 billion miles in diameter.

This explanation maybe the full size of the Brahmanda or could be just from the outer edge of our inner universe (called Bhu-Mandala among other names)

If that is true then the full size of our Brahmanda is double the figure above.

The sleeping Maha-Visnu (Karanadakashayi Visnu) expands Himself into the inner secondary universe deep inside each Brahmanda, as Garbhodakashayi Visnu.

This secondary material universe is in the centre of each massive Brahmanda universe.

In the Bhagavatam, Bhu-Mandala is the “Earth mandala” (not to be confused with our small earth globe), a disk 500 million yojanas in diameter (4 billion miles in diameter)

The word ''Earth'' has many meanings.

For example, our small Earth global round sphere is only 24,901 miles in circumference and is 7,917.5 miles in diameter, it is NOT Bhu-Mandala.

Our Bhu-Mandala material universe is 500 million yojanas in diameter or 4 billion miles in diameter or 12.6 billion miles in circumference.

A yojana is a unit of distance about 8 miles long, and so the diameter of Bhu-Mandala is about 4 billion miles in diameter which is the size of our single material universe.

Our Earth planet is NOT flat! It is a round global sphere.

Srila Prabhupada - "On the ground our earth looks flat but when you go up you will see our Earth planet is a ball." (Lecture New York 1966.)

The Sanskrit word "Dvīpa" has two meanings

1 - "Islands" or "continents" on a planet

2 - "Globes or spheres" in outer space.

Bhu-Mandala is marked by circular features designated as islands (Dvipas that can also mean planets) and oceans.

Srila Prabhupada -"The "planets" are called "dvīpas". Outer space is like an ocean of air. Just as there are islands in the watery ocean, these planets in the ocean of space are called dvīpas, or islands in outer space." (Caitanya Caritamrita Madhya 20.218, Purport)

Therefore Bhu-Mandala is far too big to be our small earth globe.

But this does describe our small single universe with its 14 planetary Systems deep within our surrounding Brahmanda.

Therefore the 14 planetary Systems deep within our surrounding Brahmanda, would therefore fit in the circumference of Bhu-Mandala 4 billion miles (500,000,000 Yojanas in diameter)

The jiva-souls can stay for an almost eternity in the temporary decaying material universes cycles of annihilation and creation if they choose.

When Lord Brahma dies after 100 of his years (311 trillion and 40 billion human years), there is an equal period of his life span of 311 trillion, 40 billion human years where nothing living exists, everything in the material universe remains dormant for that enormous amount of time.

Then the next material creation of Brahmanda's manifest from Maha-Visnu (Karanadakashayi Visnu)

All jiva-souls have merged as "individual units" into the Body of Karanadakashayi Visnu (Maha-Visnu) and remain that way until the next creation of Brahmandas when they again manifest from Maha-Visnu's Spiritual Body as seen in painting below.

In other words, in the next new creation of Brahmandas coming from the Body of Maha-Visnu, all the dormant jiva-souls awaken and continue on again within a secondary universe that is deep inside each Brahmanda outer universe, from where they left off in the previous inner material universe.

As explained, a secondary smaller universe is deep within each of the massive surrounding Brahmanda outer single universes that all lasts for 311 trillion and 40 billion human years, or the life span of Lord Brahma.

It is important to understand at the annihilation of each Brahmanda universe, and its inner secondary universe inside the Brahmanda, Garbhodakashayi Visnu temporarily merges back as the one with Maha-Visnu until the next Brahmanda universes manifests from the breathing and pores of Maha Visnu.

Then the process repeats itself, the sleeping Maha-Visnu (Karanadakashayi Visnu) expands Himself into the inner secondary universe that is deep inside each Brahmanda as Garbhodakashayi Visnu that is in the centre of each Brahmanda universe.

The jiva-souls are suspended in ''inactivity'' (dormant) within the Body of Karanadakashayi Visnu (Maha-Visnu) for 311 trillion 40 billion human years.

The jiva-souls re-emerge and continue on (their karma) from where they left off in the previous creation...***..