For a century now, physicists have been thinking that the Newtonian gravitational constant G may actually change over time. Australian physicist E. Mach suggested that the forces acting, for example, on water in a rotating bucket, are caused by accelerations relative to distant galaxies. This idea, known as Mach's principle, has led to several theories in which G should change with the expansion of the universe.


Another type of "variable G" theory was proposed by P. Dirac in 1938. He noticed that the ratio of the size of the universe to the size of a hydrogen atom is very close to the ratio of electric and gravitational attraction between a proton and an electron in an atom. These relations are expressed by the huge number 10^39.


All quantities in both respects, with the exception of the size of the universe, are constant, and it is not at all obvious why the universe should have just such a size so that these ratios are approximately equal to each other. Their apparent equality at first glance may be just a "cosmic" coincidence, but if, for unknown fundamental reasons, both of these relations should really always be equal to each other, then it almost immediately follows that the constant G should decrease with the expansion of the universe. More recently, the prediction of a possible change in the age of the universe of fundamental constants, including G, appeared in superstring theories.


Despite these numerous predictions about the change of such constants, to date, no evidence of their variability has been found in any experiment. Astronomical observations of the Moon's orbital period (which would change if G were changing), as well as data from the Viking spacecraft on the orbital period of Mars, show that any variations in G should be less than 3·10^-11 parts per year.


In addition, with a higher value of G in the past, the content of helium formed during the Big Bang era would have exceeded 24%. It is this amount of helium that is predicted when the current value of G is used in calculations. But it is known from astronomical observations that helium makes up no more than 25% of the matter in the universe. This determines the upper limit on the variability of G in the order of 2·10^11 parts per year, or even significantly less in some cosmological theories. In other words, the constant G could have changed by no more than 20% since the Big Bang.


Recently, in the journal Physical Review Letters, T. Damour, G. Gibbons, and J. Taylor reported that observations of the PSR 1913 + 16 double radio pulsar give similar estimates: G can vary by no more than (1±2.3)·10^-11 parts per year (here 2.3 represents two standard deviations).


This binary pulsar consists of a neutron star orbiting another compact object; it has been intensively studied since its discovery in 1974. Its orbital period and the rate of change of the orbital period over time are known with extremely high accuracy. Thus, the rate of change of the orbital period is known to the 13th decimal place.


Einstein's general theory of relativity predicts that the orbital period of a binary pulsar will change when the system emits gravitational waves; this should lead to a constant spiral approach of the stars to each other. The observed change in the orbital period is in perfect agreement with the value predicted by the general theory of relativity under the assumption of a constant value of G.


However, if the constant G were to change slowly, then the equations describing the pulsar's motion along the orbit would also change and predict a different rate of change in the orbital period. Thus, the small difference between observations and predictions of general relativity allows us to estimate the maximum effect that can be considered caused by the variability of G. It was this technique that led to the above-mentioned limit on the variability of G. According to the authors of the message, its value is consistent with the zero value. After all, some things in nature never change. This weekend, use the 1xbet welcome bonus promo code for a 75% bonus up to $75 on sports or casino. Deposit $15+ to activate. Sports bets must have odds of 1.50+. Casino players get extra spins on selected slots. Wagering is 10x for sports and 30x for casino. Offer valid until Sunday midnight. One per customer. Fast payouts available. Don’t wait—claim your weekend bonus now at 1xBet.