Cosmological Radar Ranging in an Expanding Universe

Abstract

While modern cosmology, founded in the language of general relativity, is almost a century old, the meaning of the expansion of space is still being debated. In this paper, the question of radar ranging in an expanding universe is examined, focusing upon light travel times during the ranging; it has recently been claimed that this proves that space physically expands. We generalize the problem into considering the return journey of an accelerating rocketeer, showing that while this agrees with expectations of special relativity for an empty universe, distinct differences occur when the universe contains matter. We conclude that this does not require the expansion of space to be a physical phenomenon, rather that we cannot neglect the influence of matter, seen through the laws of general relativity, when considering motions on cosmic scales.

6 Pages. To appear in MNRAS

References in corpus (4)

• Joining the Hubble Flow: Implications for Expanding Space
• A direct consequence of the expansion of space?
• Expanding Space: the Root of all Evil?
• Coordinate Confusion in Conformal Cosmology

Cited by in corpus (7)

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• The One-Way Speed of Light and the Milne Universe
• Uniformly accelerated traveler in an FLRW universe
• The Adventures of the Rocketeer: Accelerated Motion Under the Influence of Expanding Space
• There was movement that was stationary, for the four-velocity had passed around
• Can an Infinitely Long Object Fit in an Expanding Universe?
• Bell's Spaceships: The Views from Bow and Stern