All that said, another possibility (which I don’t understand much at all) is that our universe is a “bubble” or a “false vacuum” within a larger multiverse. A central question in cosmology is why the early universe has such low entropy. Treating our universe as a localized region in a broader multiverse helps solve this question.

The concept of entropy itself is worth exploring, because most scientists believe that our whole concept and experience of time “flowing” emerges from more fundamental laws of entropy. Entropy is often characterized as a measure of disorder, but that’s really not the whole story. It’s better thought of as a measure of probability, and it is closely tied up with the idea of “microstates” and “macrostates.”

To wit: you have two six-sided dice. If you roll one die, the probability of any number turning up is 1/6. But if you roll *both* dice, things get interesting, because there are two ways to talk about the result.

One way is to simply count all the different arrangements possible for both dice. For example, “2, 5” or “1, 6.” The probability of any given arrangement is ⅓6. Each possible arrangement is a *microstate,* and they all have equal probabilities (⅓6.)

But there’s another way of looking at the two dice: you can add up the numbers. For example, you might roll a “12” (good score!) Or you might roll a “2” (snake eyes). These are *macrostates.* And the probability of any given macrostate is *not* even. Rolling a 2 or a 12 is rare—there’s only 1 way, out of 36 ways of rolling 2 dice, to get either a 2 or a 12. On the other hand, macrostates 7 are very common because there are many microstates that result in a 7 (1+6, 2+5, 3+4, 4+3, 5+2, 6+1).

Entropy is simply a measure of how many microstates correspond to a given macrostate. If it is very easy to “roll the dice” and get a given macrostate, it is said to be high entropy. But if only a rare arrangement of microstates corresponds to a given macrostate, it’s low entropy.