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The gravitational constant describes the intrinsic force of gravity, and can be used to calculate the gravitational force between two objects.
Also known as “Big G” or Jthe gravitational constant was first defined by Isaac Newton in his law of universal gravitation formulated in 1680. It is one of the fundamental constants of nature, with a With a value (6.6743 ± 0.00015) x10^–11 m^3 kg^–1 s^–2 (Opens in a new tab).
The gravitational force between two objects using the gravitational constant can be calculated using an equation that most of us meet in high school: the gravitational force between two objects is found by multiplying the masses of those two objects (m1 and m2) and Jthen divide by the square of the distance between the two objects (F = [G x m1 x m2]/p^2).
Related: Why is gravity so weak? The answer may lie in the nature of spacetime
Keith Cooper is a freelance science journalist and editor in the UK, with a degree in Physics and Astrophysics from the University of Manchester. He is the author of The Connection 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 journals and websites.
gravitational constant
The gravitational constant is the key to measuring the mass of everything in Universe.
For example, once the gravitational constant is known, it is conjugated to the acceleration due to gravity a land, the mass of our planet can be calculated. Once we know the mass of our planet, knowing the size and duration of Earth’s orbit allows us to measure the mass of our planet the sun. Knowing the mass of the sun allows us to measure the mass of everything in Milky Way From the inside to the orbit of the sun.
gravitational constant measurement
Measure J It was one of the first high-resolution scientific experiments, and scientists are looking into whether it can vary for different times and locations in space, which could have major implications for cosmology.
Arriving at a value of 6.67408 x 10^-11 m^3 kg^-1 s^-2 for the gravitational constant was based on a fairly clever experiment from the eighteenth century, spurred by the attempts of a surveyor Draw the border between Pennsylvania and Maryland (Opens in a new tab).
In England, the world Henry Cavendish (Opens in a new tab) (1731-1810), who was interested in calculating the density of the Earth, realized (Opens in a new tab) That surveyor’s efforts Doomed to fail (Opens in a new tab) Because nearby mountains would subject surveyors’ plumb-bob (an instrument that provides a vertical reference line against which surveyors can take their measurements) to slight gravity, throwing away their readings. If they know the size JThey can calculate the gravitational force of the mountains and adjust their results.
So Cavendish set out to make the analogy, the most accurate scientific measurement made up to that point in history.
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his experience It has been referred to asTorsion Balance TechnologyIt included two dumbbells that could rotate about the same axis. One of the dumbbells had two small balls attached to a rod and neatly suspended by fibers. The other dumbbells featured a larger weight of 348 lb (158 kg) lead that could rotate to either side of the smaller dumbbells.
When the larger weights were placed near the smaller balls, the gravitational pull of the larger balls attracted the smaller balls, causing the fibers to twist. The degree of torsion allowed Cavendish to measure the torque (rotational force) of the torsion system. Then use this value for torque instead of “F‘In the equation described above, along with the masses of the weights and their distances, he can rearrange the equation to calculate J.
Can the gravitational constant change?
It’s a source of frustration among physicists because “Big G” is not known to as many decimal points as the other fundamental constants. For example, the cost of a file Electron known to nine decimal places (1.602176634 × 10^-19 coulombs), but J It is only accurately scaled to only five decimal points. Frustrating, efforts to measure it more accurately Do not agree with each other (Opens in a new tab).
Part of the reason for this is that the gravity of things around the experimental device will interfere with the experiment. However, there is also a strong suspicion that the problem is not just an empirical one, but could exist Some new physics at work (Opens in a new tab). It’s also possible that the gravitational constant isn’t quite as constant as scientists think.
In the 1960s, physicist Robert Dickey – whose team set out to discover cosmic microwave background (CMB) by Arno Penzias and Robert Wilson in 1964) – and Carl Brans developed the so-called standard tensor theory of gravitation, as a variation of Albert Einstein‘s General theory of relativity. The scalar field describes a property that can vary at different points in space (file Earth analogy is a temperature map, where the temperature is not constant, but varies by location). If gravity is a scalar field, then J It can have different values across space and time. This differs from the more accepted version of general relativity, which assumes that gravity is constant across the universe.
Motohiko Yoshimura of Okayama University in Japan suggested that the theory of scalar gravitation can be linked cosmic inflation with dark energy. Inflation occurred in milliseconds after the birth of the universe, and led to a short but rapid expansion of space that lasted between 10^-36 and 10^-33 seconds after the great explosionThe universe inflated from microscopic to macroscopic size, before mysteriously shutting down.
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dark energy It is the mysterious force that is accelerating the expansion of the universe today. Many physicists have wondered if there could be a connection between the two expanding forces. Yoshimura suggests that there are – that both are manifestations of the scalar gravitational field that was a Much stronger in the early universethen weakened, but came back strong again with the expansion of the universe and the spread of matter.
However, try to discover any significant differences in J In other parts of the universe they have not yet found anything. For example, in 2015, the results of a 21-year study of the regular pulses of . came out pulsar PSR J1713 + 0747 Directory not found (Opens in a new tab) Gravity has a different force compared to here in the solar system. no Green Bank Observatory and the Arecibo . Radio Telescope It follows PSR J1713+0747, which lies 3750 light-years away in a binary system with a white dwarf. The pulsar is one of the most well-known, and any deviation from “Big G” would have quickly manifested itself in its orbital dance with the white dwarf and the timing of its pulses.
in statement (Opens in a new tab)Wei Zhou of the University of British Columbia, who led the PSR J1713+0747 study, said, “The gravitational constant is a fundamental constant in physics, so it is important to test this basic assumption using objects in different places, times, and gravitational conditions: the fact that we see gravity perform the same. In our solar system as you do in the far distances star The system helps confirm that the gravitational constant is truly global.”
Additional Resources
review Lab tests on gravity (Opens in a new tab) Conducted by the Eöt-Wash Group at the University of Washington.
For review Attempts to measure the “big G” (Opens in a new tab) And what might the results mean?
Britannica definition of gravitational constant (Opens in a new tab).
index
“Accurate measurement of the Newtonian gravitational constant (Opens in a new tab). Xue, Chao, et al. National Science Review (2020).
“The strange state of the gravitational constant (Opens in a new tab). Proceedings of the National Academy of Sciences (2022).
“Henry Cavendish (Opens in a new tab). Britannica (2022).
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