Cosmology: learned versus vulgar: Grice's nostalgia of the stars

Speranza

In 1584, the Italian philosopher and astronomer Giordano Bruno proposed an unbounded universe in On the Infinite Universe and Worlds.

"Innumerable suns exist.

Inumerable earths revolve around these suns in a manner similar to the way the seven planets revolve around our sun.

 Living beings inhabit these worlds.

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Cosmologists have long sought to discover whether infinity exists in our physical universe.

Are there an infinite number of stars? (cfr. Grice, "As far as I know, there are infinitely many stars.")

Does the universe have infinite volume?

Does space "go on forever"?

This is an open question of cosmology.

Note that the question of being infinite is logically separate from the question of having boundaries.

The two-dimensional surface of the Earth, for example, is finite, yet has no edge.

By travelling in a straight line one will eventually return to the exact spot one started from.

The universe, at least in principle, might have a similar topology.

If so, one might eventually return to one's starting point after travelling in a straight line through the universe for long enough.

If, on the other hand, the universe were not curved like a sphere but had a flat topology, it could be both unbounded and infinite.

The curvature of the universe can be measured through multipole moments in the spectrum of the cosmic background radiation.

As to date, analysis of the radiation patterns recorded by the WMAP spacecraft hints that the universe has a flat topology.

This would be consistent with an infinite physical universe.

The Planck spacecraft launched in 2009 is expected to record the cosmic background radiation with 10 times higher precision, and will give more insight into the question of whether the universe is infinite or not.