Measuring Spacetime: from Big Bang to Black Holes
Summary of the spacetime issues discussed in this article.
One can use photons and astronomical objects as test particles to measure spacetime over
22 orders of magnitude in scale,
ranging from the cosmic horizon
(probing the global topology of and curvature of space - top)
to distant supernovae (giving evidence of dark energy)
down to galaxies (giving evidence for dark matter),
galactic nuclei and binary stellar systems (giving evidence for black holes).
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Observational constraints on spacetime are reviewed, focusing on how the
underlying physics (dark matter, dark energy, gravity) can be tested rather
Space is not a boring static stage on which events unfold over time, but a
dynamic entity with curvature, fluctuations and a rich life of its own which is
a booming area of study. Spectacular new measurements of the cosmic microwave
background, gravitational lensing, type Ia supernovae, large-scale structure,
spectra of the Lyman alpha forest, stellar dynamics and x-ray binaries are
probing the properties of spacetime over 22 orders of magnitude in scale.
Current measurements are consistent with an infinite flat everlasting universe
containing about 30% cold dark matter, 65% dark energy and at least two
distinct populations of black holes.
A slightly abbreviated version of this paper was published as an invited review
in Science, 296, 1427-1433 (2002).
The full text and pdf of this version is available
and the abstract is
The paper is heavily based on two longer articles
on spacetime to 0th order (Tegmark 2001)
and spacetime to 1st order (Tegmark & Zaldarriaga 2002).
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This page was last modified July 10, 2002.