the universe being infinite and eternal would have to have an infinite nuber of events happen and an infinite number of matter to produce these events. lets use an analogy.
lets say i have an infinite number of marbles in my possession. using this knowledge:

Case 1. i decide to give you the whole pile of marbles. that leaves me with zero marbles and you with infinity marbles.

Case 2. i give you every even numbered marble, leaving me with infinity marbles and you with infinity marbles.

Case 3. i give you every marble labled 4 or higher. that gives you infinity and you with three marbles.

these three things sum up to three math equations:

1. infinity minus infinity equals zero
2. infinity minus infinity equals infinity
3. infinity minus infinity equals three

these things contradict themselves therefore the universe cannot be infinite.