The Baryon Oscillation Spectroscopic Survey (BOSS) announced that BOSS has measured the scale of the universe to an accuracy of one percent. http://newscenter.lbl.gov/2014/01/08/boss-one-percent/
In their statement they also concluded: “One of the reasons we care is that a flat universe has implications for whether the universe is infinite,” says Schlegel. “That means – while we can’t say with certainty that it will never come to an end – it’s likely the universe extends forever in space and will go on forever in time. Our results are consistent with an infinite universe.”
The only problem is, empty space isn't empty; it contains a small amount of vacuum energy or zero point energy. https://en.wikipedia.org/wiki/Vacuum_energy
I am no whiz in math but I can add, if the universe is infinite and space contains even a small amount of energy, that means there is an infinite amount of energy and therefore mass in the universe. Where are the gravitational effects of this infinite mass?