The gravitational constant describes the intrinsic energy of gravity, and can be utilized to calculate the gravitational pull between two objects.

Also often known as “Big G” or *G*, the gravitational constant was first outlined by Isaac Newton in his Law of Universal Gravitation formulated in 1680. It is among the elementary constants of nature, with a value of (6.6743 ± 0.00015) x10^–11 m^3 kg^–1 s^–2 (opens in new tab).

The gravitational pull between two objects could be calculated with the gravitational constant utilizing an equation most of us meet in highschool: The gravitational drive between two objects is discovered by multiplying the mass of these two objects (m1 and m2) and *G*, after which dividing by the sq. of the gap between the 2 objects (F = [G x m1 x m2]/r^2).

Keith Cooper is a contract science journalist and editor within the United Kingdom, and has a level in physics and astrophysics from the University of Manchester. He’s the creator of “The Contact Paradox: Challenging Our Assumptions in the Search for Extraterrestrial Intelligence” (Bloomsbury Sigma, 2020) and has written articles on astronomy, space, physics and astrobiology for a large number of magazines and web sites.

## The gravitational constant

The gravitational constant is the important thing to measuring the mass of the whole lot within the universe.

For instance, as soon as the gravitational constant is thought, then coupled with the acceleration attributable to gravity on Earth, the mass of our planet could be calculated. Once we all know the mass of our planet, then figuring out the dimensions and interval of Earth’s orbit permits us to measure the mass of the sun. And figuring out the mass of the sun permits us to measure the mass of the whole lot within the Milky Way Galaxy inside to the sun’s orbit.

### Measuring the gravitational constant

The measurement of *G* was one of many first high-precision science experiments, and scientists are looking for whether or not it could possibly range at totally different occasions and places in space, which might have massive implications for cosmology.

Arriving at a price of 6.67408 x10^–11 m^3 kg^–1 s^–2 for the gravitational constant relied on a moderately intelligent eighteenth-century experiment, prompted by surveyor’s makes an attempt to map the border between the states of Pennsylvania and Maryland.

In England, the scientist Henry Cavendish (opens in new tab) (1731–1810), who was enthusiastic about calculating the density of the Earth, realized that the surveyor’s efforts would be doomed to failure as a result of close by mountains would topic the surveyors’ ‘plumb-bob’ (a device that supplied a vertical reference line towards which the surveyors might make their measurements) to a slight gravitational pull, throwing off their readings. If they knew the dimensions of *G*, they might calculate the gravitational pull of the mountains and amend their outcomes.

So Cavendish set about making the measurement, probably the most exact scientific measurement made as much as that time in historical past.

His experiment was known as the ‘torsion balance technique’. It concerned two dumbbells that might rotate across the identical axis. One of the dumbbells had two smaller lead spheres linked by a rod and hanging delicately by a fiber. The different dumbbell featured two bigger 348-pound (158-kilogram) lead weights that might swivel to both facet of the smaller dumbbell.

When the bigger weights have been positioned near the smaller spheres, the gravitational pull of the bigger spheres attracted the smaller spheres, inflicting the fiber to twist. The diploma of twisting allowed Cavendish to measure the torque (the rotational drive) of the twisting system.

He then used this worth for the torque instead of the ‘*F*‘ within the equation described above, and together with the lots of the weights and their distances, he might rearrange the equation to calculate *G*.

### Can the gravitational constant change?

It is a supply of frustration amongst physicists that “Big G” shouldn’t be identified to as many decimal factors as the opposite elementary constants. For instance, the cost of an electron is thought to 9 decimal locations (1.602176634 x 10^–19 coulomb), however *G *has solely been precisely measured to simply 5 decimal factors. Frustratingly, efforts to measure it to larger precision don’t agree with one another (opens in new tab).

Part of the explanation for that is that the gravity of issues across the experimental equipment will intrude with the experiment. However, there’s additionally the niggling suspicion that the issue is not merely experimental, however that there might be some new physics at work. It is even attainable that the gravitational constant is not fairly as fixed as scientists thought.

Back within the Nineteen Sixties, physicists Robert Dicke — whose workforce was scooped to the invention of the cosmic microwave background (CMB) by Arno Penzias and Robert Wilson in 1964) — and Carl Brans developed a so-called scalar-tensor principle of gravity, as a variation of Albert Einstein’s general theory of relativity.

A scalar area describes a property that may probably range at totally different factors in space (an Earthly analogy is a temperature map, the place the temperature shouldn’t be fixed, however varies with location). If gravity have been a scalar area, then *G* might probably have totally different values throughout space and time. This differs from the extra accepted model of common relativity, which posits that gravity is fixed throughout the universe.

Motohiko Yoshimura of Okayama University in Japan proposed {that a} scalar-tensor principle of gravity might hyperlink cosmic inflation with darkish power. Inflation occurred fractions of a second after the delivery of the universe, and spurred a quick however speedy enlargement of space that lasted between 10^–36 and 10^–33 seconds after the Big Bang, inflating the cosmos from microscopic to macroscopic in measurement, earlier than mysteriously shutting off.

Dark energy is the mysterious drive that’s accelerating the enlargement of the universe immediately. Many physicists have questioned if there might be a connection between the 2 expansionist forces. Yoshimura suggests that there’s — that they’re each manifestations of a gravitational scalar area that was a lot stronger in the early universe, then weakened, however has come again robust once more because the universe expands and matter turns into extra unfold out.

However, makes an attempt to try to detect any vital variations in *G* in different components of the universe have up to now discovered nothing. For instance, in 2015, the outcomes of a 21-year research of the common pulsations of the pulsar PSR J1713+0747 found no evidence for gravity having a distinct energy in comparison with right here within the Solar System.

Both the Green Bank Observatory and the Arecibo radio telescope adopted PSR J1713+0747, which lies 3,750 gentle years away in a binary system with a white dwarf. The pulsar is among the most common identified, and any deviation from “Big G” would have rapidly grow to be obvious within the interval of its orbital dance with the white dwarf and the timing of its pulsations.

In a statement, Weiwei Zhu of the University of British Columbia, who led the research of PSR J1713+0747, mentioned that “The gravitational constant is a fundamental constant of physics, so it is important to test this basic assumption using objects at different places, times, and gravitational conditions. The fact that we see gravity perform the same in our solar system as it does in a distant star system helps to confirm that the gravitational constant truly is universal.”

### Additional Resources

A evaluation of the laboratory tests on gravity carried out by the Eöt-Wash group on the University of Washington.

A evaluation of attempts to measure ‘Big G’ and what the outcomes would possibly imply.

Britannica’s definition of the gravitational constant.

### Bibliography

“Precision measurement of the Newtonian gravitational constant.” Xue, Chao, et al. National Science Review (2020).

“The Curious Case of the Gravitational Constant.” Proceedings of the National Academy of Sciences (2022).

“Henry Cavendish.” Britannica (2022).