It is not really correct to call them " reversible laws of physics"
Laws of physics lead to mathematical models that describe observations. These models are usually differential equations of space and time. The solutions of these equations exist both for time going towards infinity as for time going towards minus infinity in most cases, for mechanics, electromagnetism, newton's gravitation. There exists a difference for thermodynamics, which is an emergent theory from the underlying statistical mechanics, where an arrow of time can be defined as explained in the answer by count_to_10 .
So in this sense the laws of mechanics and electromagnetism lead to time reversible solutions, whereas the laws of thermodynamics pick an arrow in time.
When one goes to quantum mechanics and the forces between elementary particles again time reversal is implied by some interactions , but there exists a CPT theorem where if CP is not conserved than again a time direction is chosen. But this is another story.