Why does Shakespeare use thunder and storm sounds to suggest cosmic disorder in Julius Caesar?

For the Elizabethan, there is a hierarchy to the
world:  

1. God


2. Spiritual
   Class


3. Man (+
   Understanding)


4. Sensitive Class (Existence +
   life+feeling:  hearing, touch, memory, and
   movement)


5. Vegetative Class (Existence +
   life)


6. Inanimate Class
   (Existence)

Man possesses all the possibilities
of the Earthly Existence as he forms a microcosm for the macrocosm of the Universe. 
Thus, the inanimate class nourishes the vegetative class that nourishes the animal
class, and so on.  In other words, the bottom of one class is related to the top of
another class.

With each element at a certain level having
a correspondence to another level, when one level is upset, then all levels are
disturbed. And, Elizabethans recognize that the happenings of the earthly world affect
the world of spirits and the spiritual. In Shakespeare's Julius
Caesar, Caesar, who has ignored the words of the soothsayer, and who has
become sick with epilepsy, has made the heavens disturbed; for this reason there is
thunder and lightning:

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Nor heaven nor earth have been at peace
tonight:

Thrice hath Calpurnia in her sleep cried
out

"Help, ho!  They murder Caesar!"  Who's within?
(2.2.1-3) 

Cassius, with his
"lean and hungry look" has denied this link of man with the other elements of the
universe:

The
fault, dear Brutus, is not in our stars,

But in ourselves,
that we are underlings.
(1.2.145-146) 

When Casca
reports all the cosmic disturbances that he has observed, animals and fire, and declares
that they are "prodigies" and "portentous things," the Elizabethan understands that Man
is between Matter and Nature, and his behavior can disturb the order of things.  As he
tries to reconcile the beast within him, he causes conflict, a conflict that is often
represented by thunder and lightning.