The shared causal pasts and futures of cosmological events
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Friedman_shared-causal-pasts.pdf
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Author(s)
Kaiser, David I.
Gallicchio, Jason
Friedman, Andrew Samuel
Date Issued
August 2013
Journal
Physical Review D
Publisher
American Physical Society
Citation
Friedman, Andrew S., David I. Kaiser, and Jason Gallicchio. “The shared causal pasts and futures of cosmological events.” Physical Review D 88, no. 4 (August 2013). © 2013 American Physical Society
Version
Final published version
Abstract
We derive criteria for whether two cosmological events can have a shared causal past or a shared causal future, assuming a Friedmann-Lemaitre-Robertson-Walker (FLRW) universe with best-fit cosmological parameters from the Planck satellite. We further derive criteria for whether either cosmic event could have been in past causal contact with our own worldline since the time of the hot “big bang,” which we take to be the end of early-universe inflation. We find that pairs of objects such as quasars on opposite sides of the sky with redshifts z≥3.65 have no shared causal past with each other or with our past worldline. More complicated constraints apply if the objects are at different redshifts from each other or appear at some relative angle less than 180°, as seen from Earth. We present examples of observed quasar pairs that satisfy all, some, or none of the criteria for past causal independence. Given dark energy and the recent accelerated expansion, our observable Universe has a finite conformal lifetime, and hence a cosmic event horizon at current redshift z=1.87. We thus constrain whether pairs of cosmic events can signal each other’s worldlines before the end of time. Lastly, we generalize the criteria for shared past and future causal domains for FLRW universes with nonzero spatial curvature.
MIT Department
Massachusetts Institute of Technology. Center for Theoretical Physics
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Program in Science, Technology and Society
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Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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DOI of Published Version
https://doi.org/10.1103/PhysRevD.88.044038
