What caused the universe to start expanding rapidly?

An enormous explosion—a big bang—caused the universe to start expanding rapidly. All the matter and energy in the universe, and even space itself, came out of this explosion.

Why did scientists think the universe rate of expansion would eventually slow down?

The density of matter decreases as the universe expands because the volume of space increases. Currently the density of dark energy is higher than that of matter, but in the distant past the density of matter should have been greater, so the expansion should have been slowing down then.

Why is the critical density of the universe important?

The ‘critical density’ is the average density of matter required for the Universe to just halt its expansion, but only after an infinite time. If the density of matter in the Universe is high (a closed Universe), self-gravity slows the expansion until it halts, and ultimately re-collapses.

Is the universe at the critical density?

This means that its density appears to be close to the critical density, which is the density needed for gravity to just halt its expansion after an infinite time. The expansion rate we see today indicates that the critical density of the Universe is about 9×10-27 kg m-3.

When the density of the universe is greater to the critical density it is referred to as which of the following?

If the density of our universe is greater than the critical density, our universe is ‘closed,’ which means our universe will eventually stop expanding and start contracting back on itself. If the density of the universe is equal to the critical density, then we live in a ‘flat’ universe.

What is postulated to have caused a sudden inflation of the early Universe quizlet?

What is postulated to have caused a sudden inflation of the early universe? The energy released from the “freezing out” of the strong force from the GUT force. The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.