Gravitational waves - is it possible to detect them on Earth?

[ravell]

Why gravitational waves are so exciting for physicists and their supposed detection is a great scientific sensation? The occurrence of gravitational waves after all clearly stems from classical physics. Such waves are formed for example by any system of two large objects (masses) rotating around each other.

The problem of detection of gravitational waves on Earth lies in the fact that the amplitude of these waves decreases rapidly as it moves away from the rotating system and it becomes practically unmeasurable already within a few hundred million km (<0.001 ly) of this system ( eg. with mass of two suns) . Detected so far such binary systems are distant from Earth many hundreds of light years.
Efforts to detect gravitational waves on Earth, formed by so distant systems, are doomed to failure, what in no way denies that the local gravitational waves around such systems are quite normal and common matter.
Examples of calculations in this respect are presented , inter alia, in the program available on the link: http://dl.dropbox.com/u/26262175/SagitariusBRprogramForCalculationsOfSpeedOfStars.xlsx

The question therefore arises whether and how reliable can be supposed detection, in September 2015 by the detector LIGO, gravitational waves formed by the system that is away from Earth about 1.3 billion light years?!

[Country Boy]

The question therefore arises whether and how reliable can be supposed detection, in September 2015 by the detector LIGO, gravitational waves formed by the system that is away from Earth about 1.3 billion light years?!

 

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That question would be answered by examining their experimental method, equipment, and results, not by just saying "it is very difficult".

[Strange]

Why gravitational waves are so exciting for physicists and their supposed detection is a great scientific sensation?

 

 

Because it was a great technical challenge, it confirmed yet another prediction of GR and opens up the possibility of a new era of astronomy.

 

 

 

The occurrence of gravitational waves after all clearly stems from classical physics.

 

If by "classical" you mean Newtonian gravity, then that is wrong.

 

"Gravitational waves cannot exist in the Newton's law of universal gravitation, since it is predicated on the assumption that physical interactions propagate at infinite speed."

https://en.wikipedia.org/wiki/Gravitational_wave

 

 

 

 

The problem of detection of gravitational waves on Earth lies in the fact that the amplitude of these waves decreases rapidly as it moves away from the rotating system and it becomes practically unmeasurable already within a few hundred million km (<0.001 ly) of this system ( eg. with mass of two suns) . Detected so far such binary systems are distant from Earth many hundreds of light years.

 

I don't think anyone expects to expects to detect gravitational waves from such a source in the foreseeable future (if ever).

[ravell]

 

I don't think anyone expects to expects to detect gravitational waves from such a source in the foreseeable future (if ever).

“The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago.”

 

1. Gravitational wave generated by aircraft with a mass 200 tons, flying at a distance of 100 km from LIGO, is in the LIGO site 1.3 E-15 m/sec2

2. Gravitational wave produced by a comet or asteroid with a mass for example 10E+10 tons, a passing in the distance from Earth 10 milions km, is on Earth 6.7E-20 m/sec2.

3. Impact of the gravity of an object with a mass of 70 times the mass of the sun, distant from Earth about 1.3 billion ly, is on Earth 6.2E-29 m/sec2 (!).

 

How is it therefore possible that the LIGO detector is not able to detect the gravitational changes (waves) produced by objects shown for example in the 1 and 2, which are billions of times greater than the gravitational waves reaching the Earth from the object 3 (even in the case of a sudden complete disappearance mass of the object 3) and from which LIGO has detected the alleged gravitational waves?

Edited November 27, 2016 by ravell

[Mordred]

I don't know where you got your numbers from but those are not the radiated power values of a GW wave.

 

Radiated power is in units of watts determined by the following formula

 

[latex]P=\frac{de}{dt}=\frac{32}{5}\frac{G^4}{c^5}\frac{(m_1m_2)^2(m_1+m_2)}{r^2}[/latex]

Edited November 27, 2016 by Mordred

[John Cuthber]

I think he has mistaken detecting the gravitational effect from a plane- which is easy- for detecting gravity waves from that plane.

It's like the difference between detecting light and demonstrating that light is a wave.

[swansont]

1. Gravitational wave generated by aircraft with a mass 200 tons, flying at a distance of 100 km from LIGO, is in the LIGO site 1.3 E-15 m/sec2

2. Gravitational wave produced by a comet or asteroid with a mass for example 10E+10 tons, a passing in the distance from Earth 10 milions km, is on Earth 6.7E-20 m/sec2.

 

 

I'm going to need a link to the LIGO site that shows this. That way we can all review the information and show you exactly where they say it's not caused by a gravitational wave.

[StringJunky]

“The gravitational waves were detected on September 14, 2015 at 5:51 a.m. Eastern Daylight Time (09:51 UTC) by both of the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.

Based on the observed signals, LIGO scientists estimate that the black holes for this event were about 29 and 36 times the mass of the sun, and the event took place 1.3 billion years ago.”

 

1. Gravitational wave generated by aircraft with a mass 200 tons, flying at a distance of 100 km from LIGO, is in the LIGO site 1.3 E-15 m/sec2

2. Gravitational wave produced by a comet or asteroid with a mass for example 10E+10 tons, a passing in the distance from Earth 10 milions km, is on Earth 6.7E-20 m/sec2.

3. Impact of the gravity of an object with a mass of 70 times the mass of the sun, distant from Earth about 1.3 billion ly, is on Earth 6.2E-29 m/sec2 (!).

 

How is it therefore possible that the LIGO detector is not able to detect the gravitational changes (waves) produced by objects shown for example in the 1 and 2, which are billions of times greater than the gravitational waves reaching the Earth from the object 3 (even in the case of a sudden complete disappearance mass of the object 3) and from which LIGO has detected the alleged gravitational waves?

AFAIK 1 and 2 are the wrong kind of motion - ignoring how small they are - as it needs to be spherically and massively asymmetric to create a 'wobble' in spacetime. Two mutually orbiting blackholes with differing masses have the required asymmetries.

Edited November 27, 2016 by StringJunky

[ravell]

I don't know where you got your numbers from but those are not the radiated power values of a GW wave.

 

Radiated power is in units of watts determined by the following formula

 

[latex]P=\frac{de}{dt}=\frac{32}{5}\frac{G^4}{c^5}\frac{(m_1m_2)^2(m_1+m_2)}{r^2}[/latex]

I do not understand how these watts convert on the amplitude of the gravity waves?

In what units it is therefore expressed the amplitude of gravitational waves, if not in g (m/sec2), and how much it is for example at a distance of 0.1 ly, from the binary system considered on the link given at the beginning of this thread?

[Mordred]

The SI units for a watt is [latex] kg*m^2*s^{-3}[/latex] You use this relation to convert the units you get from that equation.

 

I can't see the link you posted. So I have no idea what example they use. However knowing how to get the watt unit out of the above equation's units should help.

 

By the way you asked a good question, if your not familiar with 1 joule/sec = 1 watt.

 

[latex]Joule=\frac{kg*m^2}{s^2}= watt*sec[/latex]

Edited December 1, 2016 by Mordred

[Strange]

I do not understand how these watts convert on the amplitude of the gravity waves?

In what units it is therefore expressed the amplitude of gravitational waves, if not in g (m/sec2), and how much it is for example at a distance of 0.1 ly, from the binary system considered on the link given at the beginning of this thread?

 

 

The amplitude of gravitational waves is usually measured in terms of strain (the amount by which lengths are changed, orthogonal to the direction of ravel). I don't see how this can be expressed as an acceleration.

[imatfaal]

 

 

The amplitude of gravitational waves is usually measured in terms of strain (the amount by which lengths are changed, orthogonal to the direction of ravel). I don't see how this can be expressed as an acceleration.

 

You are right it cannot - but it is closely related. The gravitational wave is, in effect, a change in gravity (g); we can look at this as the difference in gravitational attraction (g') between two test objects as time changes. This difference in gravity is, of course, also an acceleration; if we integrate this acceleration twice with respect to time we get the strain (h) - which is what we actually observe and is the amplitude in most of the wave equations regarding gravitational waves.

 

[latex] h=2 * \iint g' \cdot dt^2 = 2 * \frac{change\ in\ displacement}{displacement} [/latex]

[Strange]

 

You are right it cannot - but it is closely related. The gravitational wave is, in effect, a change in gravity (g); we can look at this as the difference in gravitational attraction (g') between two test objects as time changes. This difference in gravity is, of course, also an acceleration; if we integrate this acceleration twice with respect to time we get the strain (h) - which is what we actually observe and is the amplitude in most of the wave equations regarding gravitational waves.

 

[latex] h=2 * \iint g' \cdot dt^2 = 2 * \frac{change\ in\ displacement}{displacement} [/latex]

Thanks. That makes sense of it...

[ravell]

 

Efforts to detect gravitational waves on Earth, formed by so distant systems, are doomed to failure, what in no way denies that the local gravitational waves around such systems are quite normal and common matter.

Examples of calculations in this respect are presented , inter alia, in the program available on the link: http://dl.dropbox.com/u/26262175/SagitariusBRprogramForCalculationsOfSpeedOfStars.xlsx

The question therefore arises whether and how reliable can be supposed detection, in September 2015 by the detector LIGO, gravitational waves formed by the system that is away from Earth about 1.3 billion light years?!

Dropbox changed the above address http on a new secure https: https://dl.dropboxusercontent.com/u/26262175/SagitariusBRprogramForCalculationsOfSpeedOfStars.xlsx

[ravell]

Dropbox changed the above address http on a new secure https: https://dl.dropboxusercontent.com/u/26262175/SagitariusBRprogramForCalculationsOfSpeedOfStars.xlsx

Sorry but I was not well informed, Dropbox on March 15, 2017 changed the current URL address of the Sagitarius BR program (v. 4.0++), to calculate the speed of stars , to this new address: https://www.dropbox.com/s/a1cu74xj4ep9iyq/SagitariusBRprogramForCalculationsOfSpeedOfStars.xlsx?dl=0