A Planck length is what is thought to be the smallest possible unit of length, defined as 1.616252×10−35 meters. The 10-35 means you move the decimal point to the left 35 places and put zeroes in all the blank spaces between it and the number, so a Planck length equals .00000000000000000000000000000000001616252 meters. (Simpler example: 1.5×10-2 = .015)
The minimum diameter of the universe is 78 billion light years (a light year is the distance light travels in a year). A light year is 1016 meters = 1×1016 meters = 10,000,000,000,000,000 meters.
So to convert the minimum diameter of the universe to Planck lengths:
78,000,000,000 light years × 10,000,000,000,000,000 meters/light year ÷ .00000000000000000000000000000000001616252 meters/Planck length ≈ (≈ means approximately equal to) 4.6×10⁶¹ Planck lengths.
The theory I came up with is based on the assumption that the universe will last as many Planck times as its diameter has Planck lengths. (A Planck time is the time it takes light to travel one Planck length, so it's similarly thought to be the smallest possible unit of light)
4.6×10⁶¹ Planck times × 5.39124×10-44 seconds/Planck time ÷ 86,400 seconds/day ÷ 365.2425 days/year ≈ 78,587,133,510 years. (I had miscalculated when I said 2.683730211×10⁹⁷ years; a year should not be less than a Planck time!)
Let me know if there's something you still don't understand :)
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The minimum diameter of the universe is 78 billion light years (a light year is the distance light travels in a year). A light year is 1016 meters = 1×1016 meters = 10,000,000,000,000,000 meters.
So to convert the minimum diameter of the universe to Planck lengths:
78,000,000,000 light years × 10,000,000,000,000,000 meters/light year ÷ .00000000000000000000000000000000001616252 meters/Planck length ≈ (≈ means approximately equal to) 4.6×10⁶¹ Planck lengths.
The theory I came up with is based on the assumption that the universe will last as many Planck times as its diameter has Planck lengths. (A Planck time is the time it takes light to travel one Planck length, so it's similarly thought to be the smallest possible unit of light)
4.6×10⁶¹ Planck times × 5.39124×10-44 seconds/Planck time ÷ 86,400 seconds/day ÷ 365.2425 days/year ≈ 78,587,133,510 years. (I had miscalculated when I said 2.683730211×10⁹⁷ years; a year should not be less than a Planck time!)
Let me know if there's something you still don't understand :)