# Maximum Possible Information in the universe?

I remember hearing about this in one of the programs in discovery science. The physicist claimed that the maximum possible information in the universe is $10^{10^{123}}$ whereas the maximum possible information that can be known by man is $10^{10^{90}}$. Can anyone explain to me how can we arrive at such a specific number, and also how can information be represented by only numbers?

• The information in the Universe measured in bits or nats is just $10^{123}$ from the holographic bound; the actual entropy of the known matter except black holes - is about $10^{90+}$ and is dominated by the cosmic microwave background. However, this guess for the entropy is obsolete because most of the entropy we know in the Universe is carried by the black holes, bringing us above $10^{100}$. If you have one more exponentiation, 10 to those large numbers, it doesn't measure the information but the number of possibilities one may distinguish (8 bits = byte distinguish 256 states...). – Luboš Motl Sep 9 '12 at 8:11
• is $10^{123}$ bits or qubits? I think the difference is important, since $10^{123}$ classical bits are exhausted with 410 qubits, more or less, and the universe has certainly way more than 410 q-bits – lurscher May 29 '13 at 18:21
• unless coherent superposition turns out to break down before arriving at 410 q-bits – lurscher May 29 '13 at 18:31
• @lurscher you have misunderstood how qubits work. To send a classical text document reliably using qubits, you need just as many qubits as you would need classical bits (see Holevo bound and HSW theorem). – Andrew Steane Dec 17 '18 at 19:32

The number $10^{123}$ emerges as (roughly) the number of Planck areas contained within the boundary of the observable universe. If each Planck area can be (roughly) in two states, a total of $10^{123}$ yes/no questions suffice to describe the boundary of the universe and - via the (still speculative) holographic principle - the whole universe. In other words, if the universe is a hologram, about $10^{123}$ bits of information are needed to describe it.
Also, it is estimated that there are approximately $10^{80}$ protons (or electrons or neutrons) and approximately $10^{90}$ photons in the observable universe. So this is how many "objects" you have to work with. I don't know how to get from this to the maximum amount of information that can be known by man?