Interstellar gas&#x2F;dust forming a planet increases its temperature, and it radiates thermal photons out into space. For the planets to fly apart, you would have reverse the photons as well, and aim them super precisely, and define the initial state of the planet super precisely, and...
It&#x27;s essentially a problem of entropy. All weirdness of macroscopic time-reversal can be reduced to the weirdly low entropy of the big bang.