Consider a universe identical to ours, but where the only difference is that the mass of the proton and the one of the neutron are the same. What would have been the neutron fraction 52 seconds after the Big Bang? Consider for the neutron a mean lifetime of 886s. Enter your answer to 3 decimal places.

Classical physics is a good approximation to modern physics under certain circumstances. What are they?

In a parallel universe, the quantity t has the value 3.14049... Express a in that universe to (a) four significant figures: (b) five significant figures:

Suppose that the universe were full of spherical objects, each of mass m and radius r, with the objects distributed uniformly throughout the universe as in the previous problem.   (Assume nonrelativistic objects.) Given the density of these spherical objects (as you would have found in the previous problem), how far would you be able to see in meters, on average, before your line of sight intersected one of them? Values (note, different from the above problem): m = 3 kg r =  0.03 m Answer must be in scientific notation and include zero decimal places (1 sig fig).