We Have a Problem

Scientists are to their theories as overbearing parents are to their children. They have for them only the very highest expectations. Contradictions are not allowed and must be resolved. Even something less than an outright contradiction is intolerable. A good theory should account for everything that is observed and make testable predictions. Any observations in contradiction to the theory are taken seriously and the theory amended, if necessary.

In this regard, while it has been very successful, the Big Bang theory seems to fall short in two areas: explaining the incredible sameness of the universe on its largest scales and accounting for why the universe has a density that is apparently so close to critical.

First there is the so-called horizon problem, which deals with the incredible uniformity of the cosmic microwave background. No matter where we look, its intensity is the same, even in parts of the universe that are far too distant to be in contact with one another. Regions in the universe that never could have exchanged information (because of the limiting speed of light) seem to know about each other.

The only current explanation we have is that the universe looks uniform now because it always was uniform. Which is sort of like saying, it is so because it is so.

It is not that this uniformity contradicts anything in the Big Bang theory, it's just that there is nothing in the theory that accounts for it. The theory provides no particular

reason why two widely separated regions should be the same—especially since regions very distant from one another would have never interacted.

The second issue is called the flatness problem. Its name comes from the fact that the critical density of the universe, once the mass of dark matter is figured into things, approaches 1, which means that the universe is almost flat.

So what's the problem?

Again, as with the horizon problem, the difficulty is not that flatness contradicts the Big Bang theory (it does not), but that the theory doesn't explain why the universe should have formed so close to critical density. As far as the theory goes, the universe might have been significantly more dense than 1 or significantly less. Scientists won't accept the luck of the draw. They want an explanation.

Close Encounter

Close Encounter

There are four known forces in the universe: gravity, electromagnetism, the weak nuclear force, and the strong nuclear force. Gravity and the electromagnetic force act over large distances—the size of the universe—and govern the motions of planets and galaxies, molecules and atoms. The nuclear forces act over only small distances (within an atomic nucleus) and hold nuclei together. The nuclear forces are the strongest, but act over the shortest distances. Gravity is by far the weakest, but its long reach means that its pull will govern the fate of the universe.

In the early universe, it is believed that these forces started as a single force. As the universe expanded, each force established its own unique identity.

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Telescopes Mastery

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