Think about it in a careful way. Visualize a spacelike line, then extend it as a geodesic. Using a proper diagram of the universe, it is easy to show that this eventually intersects the big bang horizon. Don't be confused by convention; the Friedmann coordinates are very deceptive.
So shards of the big bang, expanding at light speed from a universal starting point in the past, are essentially contemporaneous with us.
Of course the point origin, which ought to be apparent to anyone with the use of proper inertial coordinates, implies the overall masslessness of the universe. This makes the age of the universe compatible with the value of the Hubble constant, a simple coasting outwards. And the Einstein equation (in the correct tensor rank) does allow for a negative mass background to counter the mass and energy of the material universe.
But what then, if the universe does have net mass and has decelerated, you protest. Well, then there is the boggling thought - that, out at the contemporaneous shards of the big bang, matter is continuing to enter the universe.
Michael J. Burns