The number of ways you could perturb the universe by changing just a single particle for a single moment of time.

If you pick a random particle at a random moment in its history and move it momentarily to another randomly-selected position in space, you would have an alternate universe that is the same as our universe except for a single perturbation.

Modeling the (expanding) universe as a hypersphere whose diameter is increasing at the speed of light, if the age of the universe in Planck units is T, then the 4-dimensional volume of the universe in Planck space-time units is (1/4 T) (4/3 pi T3). If the number of particles in the universe is P, then the number of possible perturbatons involving a single particle is 1/3 pi P T4.

Using realistic values for P and T, P=1097 and T=8.78×1060, the single-perturbation count comes out to about 6.2×10340.

The factorial of the single-perturbation count is the number of possible alternate universes with the same age, number of particles and laws of physics as our own. That number is much larger, about 1010343. From a quantum mechanics point of view, viewed by an observer outside our universe, there are about 1010343 overlapping wavefunctions inside our universe.
You can find a web page with more on this subject on Google with the search phrase "mrob single perturbation universe".