Javelin argument

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The javelin argument is an ancient and elementary argument of cosmology.

To support the idea that the universe or space is infinite:

go to what you suppose to be the limit of space and throw a javelin in a geometrically straight line. If it hits nothing, space continues. If it hits something, (occupied) space continues. Hence the universe is not finite in any direction. (Lucretius, book I, lines 958-83).

This argument was made to support the Epicurean thesis about the universe.

A geodesic is considered the modern scientific "straight javelin" path. Depending on the geometry and topology of the universe, a given geodesic may continue forever, but the universe could still be bounded. Since it is possible to have a simply connected universe that is bounded yet admits infinite geodesy, the argument is shown by modern mathematics and cosmology to be invalid.