ASTRO - CH. 22 Concepts

We work backward from current conditions to calculate what temperatures and densities must have been when the observable universe was much smaller in size.

We do not yet have a theory that links quantum mechanics and general relativity.

These two forces first became distinct at this time.

Two forces: gravity and a single force that later became the strong, weak, and electromagnetic forces

the electromagnetic and weak forces into the electroweak force

The basic chemical composition of the universe had been determined.

During the first 0.001 second after the Big Bang, particles and antiparticles were made in almost but not perfectly equal numbers. Everything annihilated except the slight excess of matter particles.

It contains prominent spectral lines of hydrogen, the primary chemical ingredient of the universe.

Before that time, the gas in the universe was dense and ionized and therefore did not allow light to travel freely.

how galaxies came to exist Recall that models of galaxy formation presume that they formed from "seeds" of excess density present in the early universe. If the seeds really existed, they should have left their mark as slight variations in the cosmic microwave background, and we do indeed see such variations. Thus, if we did not see the variations, we would have been forced to reconsider everything we thought we knew about galaxy formation and the history of the universe.

By the time stable helium nuclei had formed, the temperature and density had already dropped too low for helium fusion to occur.

Inflation would have caused random, microscopic quantum fluctuations to grow so large in size that they became the seeds of structure.

surprising because those locations would never have been close enough to have any light or matter exchanged between them

Earth is so big that it the part explored by an ant appears flat.

uniformly bright

The discovery of a galaxy with a helium abundance of only 10% by mass.