[General] LIGO

[John Williamson]

Hi Al,

Good point!

It will be a bit embarrassing if folk have done the numerical relativity for black hole collapse, but not for light and matter – and built a billion plus facility

I’ll share this with “general” as others may be interested.

I would hope, with such an author and institution list, and the fact that these guys invoke “numerical relativity” – that someone has done their sums right. I would anyway like to talk to some of the people involved as there is a lot in the Phys rev article that is not said. Norna Robertson is an old friend (Martin knows her as well) and she is a serious physicist. Jim Hough is too – not to mention the rest of the author list. My main constraint is that my current workload allows me (less than) no time to go and talk to these guys at the moment.

A few remarks.

Firstly, fields and (4-)vectors do not transform the same way relativistically. The field is not a vector – it is the derivative of a vector. One needs to take into account not only the variations of space-Euclidean or otherwise- but also that of time. Lengths transform only along the direction of boost, fields only transverse to a boost. You really need to do proper GR here, and not just a bit of simple SR. I’m no expert in GR (would that I was!) and it is almost certain that the proper design here uses numerical methods – so this may not be fully accessible to simple thinking (though it is always fun trying). I would hope and expect that the team have taken all appropriate factors properly into account in the design of experiment.

Secondly the interfering photons and the test masses are in different frames – differing by over a hundred kilometres and plus or minus the speed of light The size is not a lot on the scale of the gravity wave length though – which is of the order of ten thousand kilometres. There would still be an effect though as the resonance is on zero. All that would happen if there was a light scaling equal to the arm scaling is the sensitivity would go down. I would hope that the (enormous) team had discussed and analysed all this properly. There will, now this is out in public, be lots of theoretical analysis on different bases. Martin is coming here for a session next week and I’m sure this will be one topic on the agenda.

The analysis for black hole size, distance, energy radiated and so on may change – but I think its pretty certain they have detected something – that something was not electromagnetic – and whatever it was did travel at close to lightspeed. One interesting thing is the delay (about 7ms) means that it puts to bed the notion that gravity is much faster than light. It is in the same ballpark. This fits in with Martin and my crazy theory of gravity and electromagnetism – which I will talk about sometime - as well as the mainstream view of course.

Hopefully, there will be three such systems online for the next run – enabling a better pinpointing of such events in the sky – and the chance to correlate with an EM signal. Look forwards to lots of fun in thinking how the experiments further constrain how nature works.

Regards, John W.
________________________________
From: af.kracklauer at web.de [af.kracklauer at web.de]
Sent: Tuesday, February 16, 2016 1:15 AM
To: John Williamson
Cc: Mark, Martin van der
Subject: LIGO

Hi John:

Your remark, somewhere in your e-mails, lauding the Ligo claims leads to ask if you can resolve my hangup:

The idea of the experiment seems to be that a gravity wave passing through the resonant chamber, causes a different change in the lengths of the two arms so that beating the two laser signals yields interferance.  Fine, but, if such a wave modifies the chamber (made of material, i.e., atoms whose structure (size) is determined by the E&M interaction of charged electrons to charged nuclei), why does this same gravity wave not affect the laser beams, also E&M entitites in GR-spacetime, too?  To first pass, the situation should be like observing a survayer holding a graduated pole through a telescope, or in a circus or curved mirror: both the man and the pole are equally aborated or perspectively altered so that reading the numbers on the pole is unaffected.  Likewise, in this view, the LIGO cavity and the laser beams should be wrinkled  equally together.

Seems that it can't be had both ways. Either GR curved spacetime, curves everything in spacetime, or curves nothing in spcetime, so that curved GR spacetime is just the solution space of whatever mechanical circumstance is under consideration but the underlying ontological space and time remain Euclidian. Etc.

ciao, Al

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