

The first milestone of general relativity. This image, from Sir Arthur Eddington's expedition to the island of Principe, shows the Sun during the total eclipse of 29 May 1919. The stars visible in the image appear displaced due to the Sun's gravity, and the magnitude of this shift was found to be in agreement with general relativity. (F. W. Dyson, A. S. Eddington, and C. Davidson, "A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919" Philosophical Transactions of the Royal Society of London. Series A, Containing Papers of a Mathematical or Physical Character (1920): 291-333, on 332).

Guest editor

Clifford M Will



The year 2015 marks the centenary of Einstein's general relativity. Classical and Quantum Gravity celebrates this historic anniversary by publishing a series of specially commissioned review articles under the umbrella 'Milestones of general relativity'. The editorial board of CQG identified 13 key events that occurred during the 100 years following publication of the theory, and that were milestones. Each of these events was a 'game changer' in that it had an immediate and major impact on the field. Furthermore, each event had a legacy that informs or spurs ongoing research today. The milestones span the breadth of areas—experiment, pure theory, quantum gravity, astrophysics, cosmology—that make gravitational physics so exciting today, 100 years after the birth of the theory.

The milestones we selected are:

1. The measurement of the deflection of light (1919).



2. Hubble's observation of the expansion of the universe (1929).

3. Yvonne Choquet-Brouhat's work on the initial value problem (1952).

4. The Arnowitt–Deser–Misner (ADM) paper (1959).

5. The Wheeler–DeWitt equation (1963).

6. The Kerr metric (1963).

7. Discovery of the cosmic background radiation (1965).

8. The singularity theorems (1965).

9. The 'announcement' of gravitational-wave detection by Weber (1970).

10. Black hole thermodynamics (1973–74).

11. The discovery of the binary pulsar (1974).

12. The AdS/CFT correspondence (1998).

13. The numerical relativity breakthrough for binary black holes (2005).

We asked each author to cover the historical context (other things known at the time of the event); exactly what the milestone was (what was observed, what the paper actually did); the immediate impact of the work (what made it a game changer); the long-term impact; and the remaining questions and current research that are a legacy of the milestone.

Out of the 13 milestones selected, we received completed articles on 11, and we are delighted to publish them in this focus issue.

We think that 'Milestones of general relativity' is a unique and exciting way for CQG to recognize the centenary of general relativity, and we very much hope that you will find the articles interesting and informative.