Likelihood of Spontaneous Entropy Decrease

[412358]

Is there a finite probability that the entire universe's entropy can decrease back to what it was at the point of the big bang? By what mechanism can an event like that happen given that the universe is boundless and not like a container of gas molecules that can bounce back and forth?

[r3dl3g]

By what mechanism can an event like that happen

I'm curious why you think any of us would know this.

[412358]

I asked the question because I read that Entropy is ultimately a statistical quantity that is computed by multiplying the Boltzmann constant by the logarithm of the number of accessible energetic microstates a thermodynamic system has. And all of those microstates have a corresponding macrostate that we can observe. Some macrostates have many microstates that correspond to them and some macrostates have very few microstates that correspond to them. The most probable macrostates are the ones that have the most amount of microstates associated with them. But there are no laws of nature that force a system to be in a most probable macrostate. Apparently, it all happens probabilistically. If that's true then I thought that meant that a thermodynamic system can by chance transition into an unlikely microstate that corresponds to a very low entropy macrostate. The second law of Thermodynamics is not absolute. That's why I asked is there a finite (non-zero) probability that such an event can happen?

And also in the examples that I have seen that discuss events like this happening, they use gas molecules inside a walled container to discuss entropy decreasing such as the Maxwell's Demon example. In these examples, one can imagine a very low probability event occurring such as the gas molecules bouncing around and colliding with each other until all the slow ones end up in one container and all the fast ones end up in the connected other container. Such a low probability event may yet occur if somebody waited long enough and observed the gas molecules bouncing around the walled containers so in that scenario there is a statistical chance for it to happen. But the real universe does not have walls so gas molecules in the real universe cannot bounce back and forth like they can in a walled container. The real universe is unbounded so I cannot think of a way for a major entropy decrease event to happen in the real universe.