There were big unknowns about the system now and any input might elicit strange behavior from dangerous quarters.

The earth's climate 450 million years ago (the Ordovician period) is one of the big unknowns.

One of the biggest unknowns is how many business travelers, the airline industry's most profitable customers, will soon be flying again.

And one of the biggest unknowns is what the effect of various lawsuits against the state will be if the state loses.

One of the big unknowns during man's journey to the Moon was what would happen when we actually landed.

One of the biggest unknowns is the cost of settling contracts with the unions representing about 200,000 city employees.

Two big unknowns for scientists are how the clouds and the oceans factor in the equation.

The biggest unknowns are on defense, which underwent a major overhaul.

One of the big unknowns has been: what sort of demand is there in the disabled community for these sorts of experiences?

The security perimeter, and where protesters will be allowed to set up, remain two of the biggest unknowns.