Path: csiph.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Thomas Heger Newsgroups: sci.physics.relativity,sci.physics Subject: Re: LIGO experiment seen gravitational waves? Date: Sat, 03 Oct 2015 07:10:57 +0200 Lines: 79 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Trace: individual.net 6tY+GmiPJO3olzlFh48AvgP2AxM5ym3ZNuOccysjhTFDLOml3U Cancel-Lock: sha1:O//LyMH5DF/XD/wbr/J+ezdnvrs= User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:8.0) Gecko/20111105 Thunderbird/8.0 In-Reply-To: Xref: csiph.com sci.physics.relativity:366071 sci.physics:524348 Am 02.10.2015 05:58, schrieb Thomas Heger: > Am 01.10.2015 22:00, schrieb Thomas Heger: >> Am 01.10.2015 21:18, schrieb Kent Beeler: >>> On 25 September, a sensational rumour appeared on Twitter: >>> Lawrence Krauss, a cosmologist, reported hearing that the >>> world’s largest gravitational-wave observatory had seen a >>> signal, barely a week after its official re-opening. >>> >>> http://www.nature.com/news/has-giant-ligo-experiment-seen-gravitational-waves-1.18449?WT.mc_id=SFB_NNEWS_1508_RHBox >>> >>> >> >> >> Isn't Earth gravity caused by the Earth? >> >> So: what exactly does LIGO measure and what is a 'gravitational wave'? >> >> If something happens with our homeplanet or if the Earth is 'catching' >> some sort of remote influences, this could eventually cause such a wave. >> >> But somehow I thought they wanted to measure remote galaxies, merging of >> black holes or the remains of the big-bang (or something like that). >> >> But I don't think, this could work, since the Earth is much closer than >> such galaxies. >> > > The distance plays a mayor role in gravity, since gravity follows an > inverse square law. > > The LIGO experiment has a distance to Earth surface of zero and we find > usual Earth gravity there. > > The influence of gravity from nearest galaxies is quite small, since the > nearest galaxy outside the milky way is > > https://en.wikipedia.org/wiki/Canis_Major_Overdensity > > and that 28,000 lightyears away. > > The nearest mayor galaxy is Andromeda and that 2.5 million lightyears > away. This is certainly far enough to leave little traces of its gravity > measurable here on Earth. > > But actually not gravity should be measured by LIGO, but ripples within. > > I don't think it's possible, but imagine the Andromeda galaxy could > switch its own gravity on and off once a minute. We then would have a > gravity square-wave of 1/60 Hz. > > This would be a tremendous wave, since gravity of a galaxy is rather huge. > > But this wave gets weaker by an inverse square law. And distance to > Andromeda is a fantastically large number (in meters). Now this number > needs to be squared and by this number, the wave gets smaller. > I haven't figured that out, but actually there 'gravitational waves' on Earth: a truck passes by on the street, than we are attracted by the moving mass of the truck. Only the force is VERY small. But a very sensitive detector of gravity waves could eventually detect such an influence (bird flying by, bee sitting on the detector, wind against the building or similar). Now such unwanted disturbance should be compared to the effect a device tries to measure. The effect should then be a few orders of magnitude larger than unavoidable 'noise', since otherwise the measurement will not work. Now I assume, that gravity waves caused by remote galaxies are smaller than the effect of fly poo. TH