Gravitational Fields

October 28, 2023
Gravitational Field Formation

To begin with, the speed of gravity has not been measured directly in the laboratory—the gravitational interaction is too weak, and such an experiment is beyond present technological capabilities. The "speed of gravity" must therefore be deduced from astronomical observations, and the answer depends on what model of gravity one uses to describe those observations.

In the simple newtonian model, gravity propagates instantaneously: the force exerted by a massive object points directly toward that object's present position. For example, even though the Sun is 500 light seconds from the Earth, newtonian gravity describes a force on Earth directed towards the Sun's position "now, " not its position 500 seconds ago. Putting a "light travel delay" (technically called "retardation") into newtonian gravity would make orbits unstable, leading to predictions that clearly contradict Solar System observations.

In general relativity, on the other hand, gravity propagates at the speed of light; that is, the motion of a massive object creates a distortion in the curvature of spacetime that moves outward at light speed. This might seem to contradict the Solar System observations described above, but remember that general relativity is conceptually very different from newtonian gravity, so a direct comparison is not so simple. Strictly speaking, gravity is not a "force" in general relativity, and a description in terms of speed and direction can be tricky. For weak fields, though, one can describe the theory in a sort of newtonian language. In that case, one finds that the "force" in GR is not quite central—it does not point directly towards the source of the gravitational field—and that it depends on velocity as well as position. The net result is that the effect of propagation delay is almost exactly cancelled, and general relativity very nearly reproduces the newtonian result.

This cancellation may seem less strange if one notes that a similar effect occurs in electromagnetism. If a charged particle is moving at a constant velocity, it exerts a force that points toward its present position, not its retarded position, even though electromagnetic interactions certainly move at the speed of light. Here, as in general relativity, subtleties in the nature of the interaction "conspire" to disguise the effect of propagation delay. It should be emphasized that in both electromagnetism and general relativity, this effect is not put in ad hoc but comes out of the equations. Also, the cancellation is nearly exact only for constant velocities. If a charged particle or a gravitating mass suddenly accelerates, the change in the electric or gravitational field propagates outward at the speed of light.

Since this point can be confusing, it's worth exploring a little further, in a slightly more technical manner. Consider two bodies—call them A and B—held in orbit by either electrical or gravitational attraction. As long as the force on A points directly towards B and vice versa, a stable orbit is possible. If the force on A points instead towards the retarded (propagation-time-delayed) position of B, on the other hand, the effect is to add a new component of force in the direction of A's motion, causing instability of the orbit. This instability, in turn, leads to a change in the mechanical angular momentum of the A-B system. But total angular momentum is conserved, so this change can only occur if some of the angular momentum of the A-B system is carried away by electromagnetic or gravitational radiation.

Now, in electrodynamics, a charge moving at a constant velocity does not radiate. Technically, the lowest-order radiation is dipole radiation, and the radiated power depends on the second time derivative of the electric dipole moment; two time derivatives give acceleration. So, to the extent that A's motion can be approximated as motion at a constant velocity, A cannot lose angular momentum. For the theory to be consistent, there must therefore be compensating terms that partially cancel the instability of the orbit caused by retardation. This is exactly what happens; a calculation shows that the force on A points not towards B's retarded position, but towards B's "linearly extrapolated" retarded position.

In general relativity, roughly speaking, a mass moving at a constant acceleration does not radiate. Here, the lowest order radiation is quadrupole radiation, and the radiated power depends on the third time derivative of the mass quadrupole moment. (The full picture is slightly more complex, since one cannot have a single, isolated accelerating mass; whatever it is that causes the acceleration also has a gravitational field, and its field must be taken into account.) For consistency, just as in the case of electromagnetism, a cancellation of the effect of retardation must occur, but it must now be even more complete—that is, it must hold to a higher power of /c. This is exactly what one finds when one solves the equations of motion in general relativity.

While current observations do not yet provide a direct model-independent measurement of the speed of gravity, a test within the framework of general relativity can be made by observing the binary pulsar PSR 1913+16. The orbit of this binary system is gradually decaying, and this behavior is attributed to the loss of energy due to escaping gravitational radiation. But in any field theory, radiation is intimately related to the finite velocity of field propagation, and the orbital changes due to gravitational radiation can equivalently be viewed as damping caused by the finite propagation speed. (In the discussion above, this damping represents a failure of the "retardation" and "noncentral, velocity-dependent" effects to completely cancel.)

what are the benefits of nuts what skills do you need to play soccer What does sitcom mean? which of the following is required after the closing brace of the structure definition? ellie asks for advice on relationship success. of the following, which is not a helpful suggestion? What is the meaning of a king cake? What does pushin p mean? what are the benefits of whole grains Linus tech tips how to choose ssd? how to improve english communication skills through tamil how to make a belly helper for grooming dogs What is the meaning of chuck in hindi? how to improve your spiritual wellness How to get rid of butt pimples? What does code blue mean? What is the meaning behind the movie dont look up? geoff is in college to get skills to become a nurse. according to schaie, he is at what stage? who can you call for legal advice about visitations what is the difference between a writ and a warrant what does stream helper for echo dot do What does spouse mean? What a goat meaning? What is the true meaning of fear? How to stop baby hiccups? What is the meaning of the song silent lucidity? what dose best friend with benefits means how to improve erectile tissue What pmo mean? What does yur mean? what are the benefits of maitake mushrooms How to buy tips schwab? How to solve a rubix cube tricks? what is the difference between html and css How to make baby poop instantly? What does estoppel mean? what is the definition of propaganda what are the benefits of stopping drinking alcohol what is recursive definition in math where is the helper menu on tinkercad Tips on how to get a high score on simon? how to improve on technical drawing skills what are the key principles what is the difference between norethindrone and drospirenone Tips on how to stop overthinking? What are chestnuts? how to improve spanish grammar what are the benefits of joining phi theta kappa how to improve ps5 internet speed Learning how to do card tricks for beginners? how to verify dental insurance benefits what are the benefits of eating eggplant What is good friday mean? how to improve 5ghz signal what advice does zeus give athena suitors family how to make players not abuse skills who to talk to for advice on repaying student loans How to fight depression? what are fine motor skills in preschoolers How to do miracle card tricks vs how to be a magician? How to boost metabolism? who is in the all star skills challenge how to run helper method java What does quasimodo mean? How to change netflix language? What does to be or not to be mean? why did he ask my advice and then do the opposite What does standard mean? what advice we can give to black girl love themseleves the way they are How to write a lab report? what is one difference between popular beverages in los estados unidos How to fillet a catfish? What does cruelty free mean? Tips on how to enhance the overall act math modeling score? why poor critical thinking skills are helpful What does it mean when i keep seeing 1111? what is the definition of proofread what is the simple definition of density? why do i have two helper what benefits can i claim when pregnant and unemployed when workers skills do not match with the jobs that are available what are the benefits of a sam's club mastercard How do servers get tips from credit cards? how to be a mothers helper of spoiled toddler What does ly mean in text? what is the definition of osteoclasts where is the national benefits center What does narc mean? what is the definition of uss maine What does the bible say about self defense? What are the fruits of the holy spirit? How to coop in elden ring? How to clean mass air flow sensor? How to build a workbench? What does the name simon mean? How to cook white rice? how to install the " helper" in chrome What is an hsa? What does abomination mean? what is the difference between a porter and a stout what is the social benefits of hiking how to increase skills in d&d 5e How to reset a roku tv? how many skills does gambler have how can i improve blood flow to my brain What time does mcdonald's serve breakfast? Where to get replacement bose sound tips? What does falter mean? how to improve virtual background on zoom what did helper spirits what is the difference between ford edge sel and titanium what advice would the silent generation give baby boomers why has reading comprehension skills dropped What are the signs and symptoms of parathyroid disease? what is muscle fitness definition why assess motor skills in early childhood education how to improve quality score adwords How to make caesar dressing? How to remove glued nail tips? What are the chakra colors? how to list skills on a resume power tools advice to people who are dissapointed in themselves Tips on how to sand polymer clay? What do different exhaust tips do? what are the benefits of permanent life insurance What is jesus real name? Secrets tips how to get into ces 2016 for free? how to improve facebook group engagement How to write vows? How to decorate a studio apartment? what is the definition of a traumatic event how to email alumni for advice why assess motor skills using mcqs What is the meaning behind hey ya? what states are extending the unemployment benefits how to improve quickness in soccer How to get rid of poison oak? how to level up skills in stardew valley how to start an advice column blog how do the advice and consent clauses check the executive power how can i check the status of my snap benefits How to get some tips to ask a girl? What is the spiritual meaning of lunar eclipse? How to card tricks for the growing magician rick smith jr? What does 2 mean in a car? How to remove bee stinger? what are the benefits of turmeric root? How to teach a new dog old tricks: the sirius puppy training manual? what is the difference between infiltration and runoff what is philanthropy definition How to treat a sore throat at home? what is good advice to give what is the benefits of eating garlic What does the name theo mean? What does adjunct mean? what is the definition of a prophet in the bible tag helper where to locate content what are the benefits of waxing your face What does natal mean? What is a parcel locker? What does blood in your urine mean? what is the definition of mechanical potential energy what is a genotype science definition What does physiology mean? what is the difference between moles and voles Which word is most similar in meaning to data? what is the definition for errant What does pluralistic mean? how to measure weight without a scale What is the true meaning? what skills do you need for an internship How to make more tips as a server reddit? What does appreciate mean? What does counting cards mean? What does unlap meaning f1? why is google chrome helper taking up so much ram dear wendy what do you think of this advice site How david copperfield did his tricks? what clients want from their lawyers: business strategy advice douglas park what is the difference between egyptian cotton and regular cotton How to give a cat a pill? what skills to pass down to nyx!soleil what is stock simple definition How to find serial number on iphone? what age toddlers are expected to have the psychosocial and developmental the skills to share Do the tips of peoples ears redden when they blush? what is a physical change easy definition How to cook marinated steak tips without a grill? lesbian relationship advice who asks who out how do skills work in d&d 5e How to get a sam's club membership? What is the meaning of rhinoceros? What does grand theft auto mean? how to measure square yards what are skills employers look for What does z mean? How to make bbq rib tips? How to draw a t rex? how to change helper esper how to delete file helper mac What cool tricks to do in skate 2? What is the meaning of the name kimberly? How to factory reset ipad? Tricks to find out who stalking you on facebook? what is the difference between data science and machine learning How many guaranteed tricks do i need to bid high in whist? What does confluence mean? reddit male fashion advice where to buy jeans How to play chess easy tricks? How to hang a flag vertically? how to make hamburger helper beef pasta withot beef What is the meaning of fatima in islam? what is the difference between the iphone 5 and the iphone 5s How to freeze zucchini? How to get rid of canker sores asap? Guy who reveals magic tricks? How long does it take to smoke a brisket? How to convence admissions that you are inetrsted e-mail tips? factories and how they improve singapore Tips when first living in nyc? how to improve creatinine and gfr What does position closing only mean robinhood? what is the definition of liberal leave Why are tips expected? What does set point theory suggest about the probable results of bariatric surgery? What does shortness of breath mean? What is the meaning of slow oxidation? What is the meaning of hue in art? How to change face on apple watch? What does vsa mean? What does ftp mean in text? How to get rid of thrips? How to create youtube channel? How to cum harder? what is the best advice for proofreading a complex document? How to drink water? how the firm is best utilizing your skills and paralegal what is the best advice for being a human resources manager How to deal with period cramps?
Gravitational Fields - A Level Physics
Gravitational Fields - A Level Physics
Magnetic Gravitational Fields view
Magnetic Gravitational Fields view
A2 Gravitational Fields
A2 Gravitational Fields

What does the gravitational field strength on a planet depend on.

It can be calculated on the basis of the planet's mass and its radius.

Share this Post