# [ExI] Gravitational Waves Detected By LIGO!

Tomaz Kristan protokol2020 at gmail.com
Fri Feb 12 15:28:30 UTC 2016

> The strain produced by the waves decays with 1/r.

> Tidal forces are proportional to 1/r^3 so they decay very fast as you
move away from the source.

It's then either G-wave originated 10^9 ly away, or some tidal effect 10^3
ly away. Like a neutron star inner collapse to a black hole, for example.

Those two are indistinguishable for LIGO, I presume.

On Fri, Feb 12, 2016 at 3:40 PM, Giovanni Santostasi <gsantostasi at gmail.com>
wrote:

> The reason they are called waves is because the calculation of the bending
> of space time is done under the assumption the detection is performed far
> away from the source. It is a linearization process that simplifies the
> very complicated Einstein equation (that by the way we don't know how to
> solve fully even computationally).
>
>
>  As with EM radiation if you are too close to the source you get all kind
> of non linear effects (even more so with gravity) and you don't get the
> nice linear waves (2 waves with amplitude A sum up to 1 wave with amplitude
> 2 A) you get when you do the calculation in the radiation field.
> When you solve the Einstein equations at a large distance from a source
> like two mutually orbiting masses then you get a solution that looks like a
> wave with a certain frequency and frequency derivative (and you can deduce
> the speed of this wave from the constants involved). The strain produced by
> the waves decays with 1/r.
>
> Tidal forces are proportional to 1/r^3 so they decay very fast as you move
> away from the source.
> So tidal forces are part of the same phenomenon of space-time warping but
> not gravitational waves per se.
>
>
>
>
> On Fri, Feb 12, 2016 at 2:40 AM, Tomaz Kristan <protokol2020 at gmail.com>
> wrote:
>
>> Spike ... and everybody else.
>>
>> I have the following problem. Merging of two distant black holes bends
>> those mirrors. More or less like the Moon or a plane flying above, also
>> bends those V or L shape structure. We call it - the tidal force as a
>> function of time. And this is routinely dismissed as not a gravity wave,
>>
>> Now .. in a Newtonian world, a merging of two distant black holes would
>> still be detectable as a tidal force function developing in time.
>>
>> And a big enough tidal force oscillation can kill you as well.
>>
>> My wrong prognosis was only, that they will not announce this detection
>> yet. But they did.
>>
>>
>>
>> On Fri, Feb 12, 2016 at 7:30 AM, Giulio Prisco <giulio at gmail.com> wrote:
>>
>>> On Thu, Feb 11, 2016 at 9:35 PM, John Clark <johnkclark at gmail.com>
>>> wrote:
>>>
>>> > And the critics were correct, the old
>>> > LIGO wasn't sensitive enough to detect gravitational waves unless you
>>> were
>>> > unrealistically lucky and 2 black holes happened to merge very near to
>>> Earth
>>>
>>> I wouldn't call that "lucky." The astronomers (and the rest of
>>> humanity) would have been killed immediately by a close black hole
>>> fusion event.
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>>
>>
>>
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