How do we determine the conditions that existed in the very early universe? A We can only guess at the conditions, since we have no way to calculate or observe what they were. B The conditions in the very early universe must have been much like those found in stars today, so we learn about them by studying stars. C From the current expansion rate we can work backward to estimate temperature and densities at various times in the early universe. D By looking all the way to the cosmological horizon, we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang.

D By looking all the way to the cosmological horizon, we can see the actual conditions that prevailed all the way back to the first instant of the Big Bang.

Explanation:

Astrophysicists are able to determine the conditions that existed in the early universe, by using instruments such as telescopes to observe and study cosmic horizons. More ideas about the early universe can be found from the thermal light present in cosmic backgrounds.

Scientists study these details that provide an insight into the conditions that existed so many years ago. They have been able to determine that the Big Bang involved so many collisions from these observations.