The question is not meaningful because it does not explain what the state of the universe is to be. pH is a chemical concept and depends largely on which compounds are present and in which states.  There are far too many possible states in which the atoms in the universe could combine, many of which could affect the ph drastically.

And that is without even counting the physical considerations.

pH is defined for aqueous solutions, and only for such!

So, You could ask  for the pH of the presumed ocean

under Titans ice crust.

For the "Universe", wich is essentially empty, and harbours

planets with liquid water only occasionly, the question is

free of any sense.

Georg

In order to turn the universe into a solution, one would need to combine all of the available oxygen with the hydrogen in order to make water. (This isn't actually possible, but the question is hypothetical anyway.)

Look at the abundance of elements in the universe: http://en.wikipedia.org/wiki/Abundance_of_the_chemical_elements

Because of the huge amount of hydrogen compared to anything else, we can safely conclude that 100% of the water molecules would be hydronium (H3O+), which gives us a ratio of 1. The pH value is the negative log10 of that ratio, or -log10(1) in this case.

The pH of the universe (were it to be made into a solution) is 0, so.

I accept that there may be buffering due to the other minor elements present, but the preponderance of ionic hydrogen easily counters that; if anything, it would make the pH negative.

Neutral, so 7.

different - like on earth. But otherwise ... on which place and time? so, it seems we would/could got all pH values anywhere to any time ...

I know - bad answer ... like the question