Final answer:
The time span during which the four fundamental forces were naturally unified after the Big Bang is known as the Planck time, lasting approximately 10^-43 seconds.
Step-by-step explanation:
The question 'How long did the BEC hold together?' likely refers to a Bose-Einstein Condensate (BEC), a state of matter first theorized by Satyendra Nath Bose and Albert Einstein. BECs are attained at temperatures close to absolute zero, where particles can occupy the same space and state, due to quantum effects. However, based on the reference to the unification of the four fundamental forces, the 'BEC' could be mistakenly used in place of the conditions that existed immediately after the Big Bang. In this context, the four fundamental forces of physics (gravitational, electromagnetic, strong nuclear, and weak nuclear) were unified for a very brief moment after the Big Bang.
According to the provided reference, the duration for which the four forces were naturally unified within the universe is approximately 10-43 seconds. This is such a brief moment that it is called the Planck time. It's the time scale at which classical notions of gravity and space-time cease to be valid, and quantum effects dominate. This time span is much shorter than any human-made time standard, such as the one defined by the oscillations of a cesium atom in atomic clocks.