tag:blogger.com,1999:blog-22973357.post261119921515981565..comments2023-09-27T07:44:19.769-04:00Comments on Sabine Hossenfelder: Backreaction: Mysteriously quiet space baffles researchersSabine Hossenfelderhttp://www.blogger.com/profile/06151209308084588985noreply@blogger.comBlogger26125tag:blogger.com,1999:blog-22973357.post-6462126465182596972015-12-06T18:24:33.402-05:002015-12-06T18:24:33.402-05:00General Relativity (GR) has been experimentally co...General Relativity (GR) has been experimentally confirmed where gravity is relatively strong. But the outskirts of galaxies and groups of galaxies, where gravity is weak, don’t move at all as prescribed by GR. That problem has been “fixed” by inventing dark matter and by placing as much of it as necessary, wherever necessary to make things work as expected. No candidate dark matter particles haveAnonymoushttps://www.blogger.com/profile/04662881461896360391noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-61031614054146762662015-11-25T17:35:20.976-05:002015-11-25T17:35:20.976-05:00עמיר ליבנה בר-או asks "What can cause SMBHs t...עמיר ליבנה בר-או asks "What can cause SMBHs to merge less frequently than expected?" <br /><br />If I’m reading this correctly, colliding galaxies will intermingle as the two (solar system sized) SMBH event horizons “merge” into a single galactic nucleus; however, the actual merger of the two singularities - each of point dimension with infinite density – should be strictly controlled Emmette Davidsonhttps://www.blogger.com/profile/15566381168125492666noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75890855445956992302015-11-16T08:56:02.081-05:002015-11-16T08:56:02.081-05:00An absolutely last resort would rather be that GRT...An absolutely last resort would rather be that GRT is not the end of the story. Something absolutely impossible in most physicists minds - I think. But on the other hand each time GRT is tested out of the solar system, it needs a patch: dark matter, dark energy, no gravitational waves (for those I know).<br />So I think that the community has no doubt, see no uncertainty in theories.<br />J.akidbellehttps://www.blogger.com/profile/12292741599925116131noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33902604544935609562015-11-14T12:56:25.146-05:002015-11-14T12:56:25.146-05:00The graviton is not a messenger.The graviton is not a messenger.Stuart https://www.blogger.com/profile/12767480095489975264noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-81661568278079430852015-11-14T10:49:56.158-05:002015-11-14T10:49:56.158-05:00Arun,
Yes - there are also 300 other things that ...Arun,<br /><br />Yes - there are also 300 other things that I can do and that I'd rather do... Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-68762663439182411182015-11-14T10:48:28.060-05:002015-11-14T10:48:28.060-05:00Leo,
Science doesn't work that way. Why not j...Leo,<br /><br />Science doesn't work that way. Why not just say, the graviational wave background is suppressed "by an assumed but unknown process, then we can explain" the observations. True, but nothing will be learned from it. There isn't any known process that will prevent black holes from merging, period. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-59307153541315448692015-11-14T10:39:09.207-05:002015-11-14T10:39:09.207-05:00Hi Bee, if anyone can work it out, it is you :)
Hi Bee, if anyone can work it out, it is you :)<br /><br />Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-18748748267489760412015-11-14T06:28:14.493-05:002015-11-14T06:28:14.493-05:00If dark matter is the same as black holes , which ...If dark matter is the same as black holes , which also do not merge but remain distant from other black holes by an assumed but unknown process, then we can explain why the dark matter halos around galaxies remain in a halo shape as the remnants of super nova black hole families through the years.<br />Leo Vuyk leovuyk@gmail.comhttps://www.blogger.com/profile/16285797359437018414noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33939403949916852852015-11-14T05:41:32.854-05:002015-11-14T05:41:32.854-05:00Arun,
Interesting idea. You would have to come up...Arun,<br /><br />Interesting idea. You would have to come up with a dark matter model that has a frequency-dependent response, then possibly you could do it. Makes me wonder now if the superfluid dark matter that we discussed the other day could do this. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58315367072925133372015-11-14T04:55:12.416-05:002015-11-14T04:55:12.416-05:00No black hole merging signal could be another indi...No black hole merging signal could be another indication that our description of black hole qualities is wrong. So we need a new black hole theory without dual merger black holes.<br />Leo Vuyk leovuyk@gmail.comhttps://www.blogger.com/profile/16285797359437018414noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-11654851365393424262015-11-13T17:37:43.526-05:002015-11-13T17:37:43.526-05:00Hi Bee, is there some way that dark matter could a...Hi Bee, is there some way that dark matter could act as an attenuating transmission medium for gravitational waves? <br /><br />Thanks!<br />-Arun<br />Arunhttps://www.blogger.com/profile/03451666670728177970noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-13263893022997939522015-11-13T14:49:08.710-05:002015-11-13T14:49:08.710-05:00I'm interested in hearing whether you think Ca...I'm interested in hearing whether you think Carver Mead's proposed alternative to general relativity, G4v (gravity with 4-vector potentials), is worth taking seriously. I'm wondering whether its predictions match or differ from GR's in this case.Kevin S. Van Hornhttps://www.blogger.com/profile/07591228017757297031noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-6764187782300516762015-11-13T14:14:12.421-05:002015-11-13T14:14:12.421-05:00It seems to me you don't need GR to predict a ...It seems to me you don't need GR to predict a signal from the GW detectors. You can make the prediction with much simpler ingredients:<br /><br />1. The observation of binary pulsar energy loss.<br /><br />2. Conservation of energy (that lost energy must go somewhere...)<br /><br />3. The geometry and scaling of quadropole interactions (which is required unless you introduce new fundamental Google Made Me Make This Account I Dont Want Ithttps://www.blogger.com/profile/14283330854688056596noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-79719603697184909352015-11-13T11:28:33.010-05:002015-11-13T11:28:33.010-05:00Thierry,
What you say is incorrect. A linearizati...Thierry,<br /><br />What you say is incorrect. A linearization is not a "trick" it's an approximation. It is perfectly valid up to some precision and the gravitational field of large black holes is weak. Besides this, black hole mergers can now be treated numerically, so one doesn't have to rely on what's analytically feasible. Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-78475971141744675912015-11-13T11:00:54.949-05:002015-11-13T11:00:54.949-05:00The emission scenario feels pretty robust. Galaxie...The emission scenario feels pretty robust. Galaxies are quite large relative to the space they inhabit and interact often. <br /><br />Could high frequency gravitational waves wash out the signal? If they can it sounds like a paper to come up with some spectra and intensities that would do it. Tom Andersenhttps://www.blogger.com/profile/17562906116020498110noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-33211556167169200122015-11-13T10:19:35.532-05:002015-11-13T10:19:35.532-05:00Inspiraling degenerate bodies have a well-characte...Inspiraling degenerate bodies have a well-characterized vast radiance of gravitational radiation. Propagation is not well-characterized, for space is filled with real (matter and radiation; phenomena of dark matter and dark energy) and virtual (Casimir effect to the Dirac sea) stuff. Consider pumping, damping, resonance, Q overall; vacuum Reynolds number and wave propagation. Spacetime as an Uncle Alhttps://www.blogger.com/profile/05056804084187606211noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-76011817681811996392015-11-13T09:30:06.729-05:002015-11-13T09:30:06.729-05:00It seems that this result can be easily explained ...It seems that this result can be easily explained in terms of adding large masses of gas to supermassive black hole mergers. In this way, the SMBH can trade angular momentum with the gas and cross the PTA frequency window faster than by GW emission alone.Barryhttps://www.blogger.com/profile/12227491319724231891noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-90865664215375915442015-11-13T08:49:31.892-05:002015-11-13T08:49:31.892-05:00What can cause SMBHs to merge less frequently than...What can cause SMBHs to merge less frequently than expected? (that is, either early in cosmic evolution or almost not at all)<br /><br />Is the configuration of matter near galaxy centers relevant? If so, can this be a sign of an uneven distribution of dark matter?עמיר ליבנה בר-אוןhttps://www.blogger.com/profile/02907463961282628520noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-58728761913342129302015-11-13T02:57:09.946-05:002015-11-13T02:57:09.946-05:00For the unworthy, the paper is freely available on...For the unworthy, the paper is freely available on <a href="http://arxiv.org/abs/1509.07320" rel="nofollow">the archive</a>.Soup-a-Chickenhttps://www.blogger.com/profile/11644046940889191618noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-72808665476925608382015-11-13T02:50:31.026-05:002015-11-13T02:50:31.026-05:00(citation) Gravitational waves are one of the key ...(citation) Gravitational waves are one of the key predictions of General Relativity, Einstein’s masterwork which celebrates its 100th anniversary this year.(end citation)<br /><br />Yes but this prediction results in some way from a mathematical trick: a linearization. I don't contest the exactitude of the demonstration but I ask if it is meaningful to apply such simplification to a Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-22973357.post-83705528009921940712015-11-12T18:25:17.124-05:002015-11-12T18:25:17.124-05:00or there is no space-time and no gravitational wav...or there is no space-time and no gravitational waves radiihttps://www.blogger.com/profile/06271430506982033059noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-3217546464781740402015-11-12T17:49:09.687-05:002015-11-12T17:49:09.687-05:00Suppose we trust in the correctness of the GR pred...Suppose we trust in the correctness of the GR prediction, could it be that these gravitational waves get absorbed after emission ? (Absorbed how ? Suggestions ? By the vacuum , curved spacetime itselfaround the system ?) Causing the waves to die out before reaching any areas measurable by us. Just a spur of the moment, I can take it if I get corrected , and learn something in the process.Koenraad Van Spaendonckhttps://www.blogger.com/profile/15090279727324831109noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-51730164043091448472015-11-12T13:30:14.843-05:002015-11-12T13:30:14.843-05:00Space is not quiet. Take for instance CMBR.Space is not quiet. Take for instance CMBR.martenhttps://www.blogger.com/profile/02423871089614417690noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-75610958267680289772015-11-12T12:27:16.088-05:002015-11-12T12:27:16.088-05:00Phillip,
Thanks, I've fixed that. Yes, it wou...Phillip,<br /><br />Thanks, I've fixed that. Yes, it would require a lot of fudging and fumbling to get rid off the binary slowdown by other means than GR. I'm sure it can be done somehow though, just introduce a few new parameters and you can fit anything ;) Best,<br /><br />B.Sabine Hossenfelderhttps://www.blogger.com/profile/06151209308084588985noreply@blogger.comtag:blogger.com,1999:blog-22973357.post-24953376700252629062015-11-12T12:11:37.543-05:002015-11-12T12:11:37.543-05:00Known pulsars ---> Known as pulsarsKnown pulsars ---> Known as pulsars <br />Phillip Helbighttps://www.blogger.com/profile/12067585245603436809noreply@blogger.com