2015 Volume 70 Issue 2 Pages 119-124
The Einstein's general relativity has been passing all experimental tests so far. Because of its simplicity, one may think it unnecessary to suspect its validity. However, the experimental bounds on deviations from general relativity are getting more and more tight thanks to efforts of many people. Recent cosmological observations of the accelerated expansion of the universe require the presence of tiny amount of vacuum energy. There are a lot of works related to the modified gravity aiming at resolving this unnaturalness of the cosmological constant. The tests of general relativity also give a tight constraint on such attempts.