Reading and experience train your model of the world. And even if you forget the experience or what you read, its effect on your model of the world persists. Your mind is like a compiled program you’ve lost the source of. It works, but you don’t know why. — Paul Graham, in his essay, How You Know
The padding is kept same so that the output shape of the Conv2D operation is same as the input shape. So, the final output of each filter of tower_1, tower_2 and tower_3 is same. Thus we can easily concatenate these filters to form the output of our inception module.