How many computations could the Universe compute if the Universe was a computer
...Which it could be. So if each atom in the available universe could register ONE BIT of information, which they all can as determined by its being "here" or "there", basically its position within the Universe, within the physical system. To compute, bits are flipped. Bits are flipped any time anything within the physical system changes. Any time anything within a system changes, it changes what the information about that system is. For a system to change, for a bit to flip, energy is required. The more energy, the faster a bit can flip. Seth Lloyd in his paper Ultimate Physical Limits to Computation shows that the maximum computational capacity of any system can be figured by running a function of the amount of energy available to the system and the system's size.
To calculate our Cosmic Computational power we have to take the Margolus-Levitin theorem that says that the maximum rate a bit can flip is proportional to the system's energy. So to calculate the maximum bit-flip rate we take the amount of energy available, multiply by 4, and divide by Planck's constant. This will yeild the number of possible bit-flips per second. We then need to find the total amount of energy in our system (E = mc2) E is energy, M is the mass of the system, and c is the speed of light (300 million meters per second). Taking the reasonable estimate of 14 billion years for the age of the Universe from expansion, and light being a finite speed, there is only a finite area of the Universe within it's "horizon" that we can have information about. The horizon grows with time, but will always be of a finite size, even within an infinite universe. To accurate calculations, the horizon of the universe is 42 billion light-years away. On average there is a mass of about one hydrogen atom per cubic meter throughout the Universe. Totaling the energy within the horizon we find that there is approximately 100 million billion billion billion billion billion billion billion (10**71) joules of energy in our Universe. Plugging this into our formula (E * 4 / Planck's Constant) we find that every second the Universe could perform 100,000 googol (10**105) operations. In the 14 billion years of the Universe's history it could have performed about 10,000 billion billion googol ops (10**112).
Compared to our efforts (and estimates) in the whole history of modern computing all the computers on Earth have only performed (according to Seth Lloyd) some fewer than 10 billion billion billion ops (10**30). To quote Terry Jones dressed as a woman whose husband is having his organs removed from him while still alive in The Meaning of Life "makes you feel sort of insignificant doesn't it?"
