Waiting for Godot is sometimes called "the play in which nothing happens twice." The fact that this is not quite true may be taken as a demonstration that there is no such thing as nothing or, alternatively, that there is no such thing as a perfect reproduction in an imperfect world. The two acts are very similar: much more similar than the first and second halves of most plays, and very much more like each other than either is like any part of any other play. Nonetheless, there are inevitably differences. There is even progress of a kind. The smallness of the differences increases the concentration of the audience. It is an irony applicable throughout life and literature that the smaller the differences are, the more inclined people are to focus on them.

Act 1 opens with a leafless tree, beside which Estragon is struggling to take off his boot. At the beginning of act 2, the boots have been removed and placed center-stage, along with Lucky's hat. The tree has four or five leaves. This, immediately, is change and even progress. When Pozzo and Lucky enter for the first time as master and slave, they both make long speeches. Pozzo is grandiloquent and pompous; Lucky, in perhaps the most famous speech in the play, talks gibberish, which is perhaps a parody of scholarly exegesis. When they return, Pozzo, instead of driving Lucky with a whip like an animal, is led on by him like Oedipus by Antigone. It is another famous blind man of Greek drama to whom Estragon refers when he wonders whether Pozzo, like Tiresias, can see the future. In any case, there has clearly been change, perhaps even progress.

It is the ends of both acts that are as alike as possible. Vladimir and Estragon agree to go but do not move. Perhaps this illustrates a general truth about life and death: while many experiences are shared, there are differences in the middles of our lives, even apparent progress, and some small differences in our beginnings. Our ends, however, are all the same.

As you might guess, Waiting for Godot was a lot to do with, well ... waiting. But that is not to say that nothing changes throughout the course of the play.

The major difference between act 1 and act 2 is how Pozzo and Lucky treat one another. In act 1, Pozzo acts as a dominant figure, while Lucky acts as his submissive, slave-like counterpart. Pozzo treats Lucky poorly, even sadistically. In act 2, however, Lucky has become mute, and Pozzo has been blinded. Therefore, their interpersonal dynamic changes, as they are now reliant upon one another.

The change in the characters is a crucial point in the play because it highlights one of Beckett's main points; that is, that change does occur, even when one is simply waiting. While it is true that Vladimir and Estragon do not change, that does not mean that the world is not changing around them. In other words, the world changes whether we act upon it or not; not everyone is simply waiting.

A major theme of the Samuel Beckett play Waiting for Godot is the idea that nothing changes for the main characters, Vladimir and Estragon, between the two acts. While this is technically true if we only look at those two characters, the world around them does have a few differences between the two acts.

The biggest differences between the two acts are the roles that Pozzo and Lucky perform. In act I, Pozzo is the talkative master, and Lucky is his slave. Pozzo is clearly in total command of Lucky, leading him along by a rope and forcing him to perform a long soliloquy for the two beggars. But in act II, the situation has been reversed—Pozzo has been blinded and relies on Lucky to guide him. This reversal is a sharp contrast to Vladimir and Estragon's situation, which hasn't changed at all.

There is another small change, as the other Educators have noted. In act I, the tree that occupies the setting is dead; in act II, it has a few leaves on it. This indication shows that some time has passed, but on a broader scale, it shows how the world at large is changing, even while Vladimir's and Estragon's world isn't.

Although one essential point of the play, and one to which the characters return multiple times in dialogue, is that waiting is monotonous and little changes in the bleak and desolate setting of the play, we can in fact observe one major and a few minor changes. 

The first minor but nonetheless significant change is one found in the stage directions. In the first act, the tree is bare of leaves, but in the second act, leaves have appeared. This might just suggest a change of season, but it also could be an emblem of hope. 

The major change is in the relationship of Pozzo and Lucky. In the first act, Pozzo is a master and Lucky a slave, and Pozzo seems to almost sadistically mistreat Lucky. In the second act, Lucky, who talked fluently in the first act, is now mute and Pozzo blind, and the mutual dependence inherent in the master-slave relationship has become fully realized in Pozzo's newfound dependence on Lucky. 

The biggest difference between Acts 1 and 2 in the play is the reversal of fortune for Pozzo and Lucky.  Whereas Pozzo was clearly the master and Lucky was his slave in Act 1, in Act 2 Pozzo is blind and Lucky mute.  They have become dependant on each other for survival.

For Vladimir and Estragon, each new day, seems to be just that, new.  Pozzo and Lucky do not remember meeting them the day before and the boy who delivers the message that Godot will not be there but to come again tomorrow, also does not remember them.  Their own long term memories seem fuzzy.

Another interesting change is that the tree now has a leaf.  Is it actually the next day as in 24 hours later or has time passed and each day is like the day before?  Time itself does not necessarily have the same meaning for these people as it does for us.  Time is indeed relative