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Re: [Phys-L] gravitational waves (Ludwik Kowalski)



Thank you William,

1) Most teachers on this list probably also Telldid not know about "LIGO Science Education Center."

before the discovery of gravitational waves was discovered. Tell us about aactivities of this center.

2) What is LIGO? See ==> https://www.ligo.caltech.edu/page/what-is-ligo

Ludwik Kowalski, Ph.D. (see Wikipedia)

============================================

On Apr 13, 2016, at 12:17 AM, William Katzman wrote:

Ludwik,
Regarding:

P.S. 1) According to:

http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html

" 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."

What is the officially "accepted value" of the speed of gravitational waves? My intuitive assumption is that is that the bars of error are larger than 30%. But this is only a guess.

The officially accepted value is the speed of light. This is largely because the speed of light is the speed limit of the universe (Einstein), and if the standard model is correct and gravitons exist, if they go less than the speed of light, then they must have rest mass and this creates all sorts of problems in the theories. The article you cite says that measurements confirm it to be within 1% of the speed of light. LIGO assumes gravitational waves travel at the speed of light when making its calculations of location of the source of such waves. If the waves are much slower than the speed of light then LIGO probably wouldn’t even see them (depending on the direction they came from) since it relies on wave forms that match occurring within (last I checked) 14 milliseconds of each other, and light would complete the journey in 10 ms. If a source has an electromagnetic signature and a gravitational wave signature that could go a long way to verifying the speed of light.

-William

William Katzman Program Leader
wkatzman@ligo-la.caltech.edu LIGO Science Education Center
225-686-3134 "Inspiring Science"




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