Thermodynamic Immortality
Entropy, in lay terms, is a measure of the disorder or chaos in a system. Anyone who has to keep a house clean can tell you that entropy tends to increase on its own.
Our current understanding of the second law of thermodynamics is that entropy in a closed system will tend to increase. It doesn’t, however, steadily increase. It will only increase in long run, taking a statistical random walk on the way.
The stunning implication here is that there is a non-zero chance that entropy will drastically decrease. It’s infinitesimally small, but it’s non-zero. An example I saw used once is that you might start a game of pool with a nice hard break, and there’s a non-zero chance that all the balls will wind up exactly back where they began.
The odds of this happening are so small that we can generally ignore them. But suppose the universe is enduring. Suppose that time goes on forever. A non-zero chance taken over a period of infinity is guaranteed to happen eventually.
The ultimate implication here is that every moment that has been, and will ever be, will happen again. Not only will it happen again, but it will happen an infinite number of times. Next time you have a feeling of Déjà vu, maybe you shouldn’t be so quick to dismiss it.