Thoughts On GW150914
16 Feb 2016 2:05:17 UTC
Topic 198437
(moderation:
In No Particular Order :
- gee there are alot of people in LIGO + VIRGO from many high profile institutions all over the world collaborating over four decades.
- direct detection of gravitational waves.
- re-confirmation that black holes exist, in binary systems, and they collide too.
- Einstein was right, GR is now verified fully for its applicable domain. Meld with QM awaits.
- 36 + 29 = 65 != 62 ie. three solar masses of field energy/mass emitted in under 0.2 seconds. To be absolutely clear about this figure : take three Sun's worth of mass ( about 10^[31] kilograms ) and totally convert it to energy ( 10^[31] * ( 3 x 10^8 )^[2] = 10^[48] Joules over 1/5 second is 10^[49] Watts ). This is not some small fraction of the Sun's constituents converting to radiant energy with a few percent at most efficiency via nuclear fusion over the Sun's lifetime.
- you may ask : what does gravitational wave energy represent in everyday terms ? One might reply thus : energy can be measured as a force times a displacement ( vector aspect glossed over here ). So our test masses at LIGO were shoved about ( above and beyond other confounding effects which have been filtered out ) over some small distance. Wiggle wiggle. The interferometers absorbed a really tiny, itsy-bitsy small fraction of the wave's total energy. That had to be amplified way beyond it's original power for us to be able to perceive. That's what an interferometer is : a converter of gravitational energy ( force x distance ) to photon counts.
- the SNR = 24 at greater than five sigma significance ie. the result is both ample and clearly true.
- two detector event. Same waveform received seven milliseconds earlier in Louisiana than Washington State.
- the final 'death spiral' is a mere four orbits before the ka-pow impact at one half the speed of light. Ah, but that is the birth of a new black hole. Talk about speed dating!
- the complex modelling matches the data record, or if you like the modelling enabled the correct parameter space to be searched. This is not mere wishful thinking validated accidentally by a random data set. The precision of the correlations are outstanding.
{ Q1 : what simple detection characteristic would exclude some common signal pattern from each detector as definitely being emitted from the same source event ?
Q2 : Could real signals be co-incident b/w two detectors ? Three ? Four ? Assume ( correctly ) that no group of three detectors lie only along a common line. }
- the real time GW transient filter alerted to the event within three minutes of the wave's arrival. Whom-so-ever wrote that software must be real chuffed now !
- looking at the strain vs time record ( Fig 1 ) it looks just like what one might see for a musical instrument, say a plucked and then damped oscillation of a piano wire. But we are looking at the plucking of spacetime ! Because spacetime so incredibly 'stiff' you need one heck of a plectrum to get it riffing.
- the frequency vs time record shows the typical chirp expected of collisions. At E@H we have been searching for a constant frequency over short time scales with maybe a gradual change over longer intervals. That is what is meant by the term 'continuous waves'. We at E@H are run by AEI, in turn led by Professor Allen ( all hail Bruce !! ), and we are all in turn part of the LSC-Virgo Continuous-wave Working Group. Bruce has signaled the onset of the development of work units that search for the inspiral patterns. Yo ! Does this project rock or what ! :-)
- the convergence of the modelling techniques, three types were shown and they all came very acceptably close to the record.
- the per detector validation and characterisation is impressive. The detectors are of the same design but not identical in practice and their individual response features have been mapped.
- compared to E@H the general signal analysis algorithm is only different in the target detail ie. a statistic of significance is generated from matched filters. We have been doing this all along with our supercomputer ( that's E@H folks ) for the prior EM discoveries.
Now Zome Shooting Of Ze Breeze
So what would be a reasonable description of what happened if seen visually nearby the BH-BH system ?
Firstly the health warning : don't get too close, whack your lead overcoat on etc. What we've felt/heard is the gravitational record of the matter budgeting. In EM terms this collision would spray heavily in the gammas .....
The holes are of course black. So we only see photons coming to us from the outside of the event horizon(s). These horizons are rather more dynamic than usual being quite convoluted ( from spherical ) over the brief merger period.
So what is to say the holes didn't have associated accretion disks, as we have detected elsewhere ? Moreover the axes of rotation of each original hole would not likely align. So it is the holes plus their accretion disks colliding. Wow ! What a show that would be. Perhaps like two rotating buzz saws coming together. Even if the central masses weren't black holes, or didn't form one, then you'd still have an impressive show of devastation. It would be the cosmic crap hitting the cosmic fan for sure ! :-)
Don't forget time. Deep down in the well between the two holes a 'pinching' of the time rate would happen ie. a rapid slowing down just before the collision. So a hapless probe that we may have sent down to report back would initially give regular updates and then it would quickly go slo-mo, then freeze and then disappear from contact altogether. It got gobbled. Poor probe R.I.P.
Cheers, Mike.
A1 : While properly accounting for timing error margins it would be an interval between arrival times exceeding the light travel time b/w the two interferometer sites ie. greater than about 10ms for the Hanford and Livingston pairing.
A2 : Yes for two, three and four. In fact the more the merrier really, and for any set of mutual delays that doesn't breach as per A1. Real world timings will always have some measure of error, so cross-checking of detector pairs gives greater localisation in source sky direction. This is a key technique that you will see demonstrated time and again from now on ie. what are the timings across the array ??
( edit ) Sadly for Hapless Probe we gave him an A.I. unit. So what was the last message received ? :-)
(A) "Now, will you look at tha ... "
(B) "I feel veeerrrry uuuuunnnnnnnnwwwwwweeeeeeeeellll."
(C) "I'm having doubts about the mission ..... "
(D) "It's full of stars !"
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Thoughts On GW150914
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Thanks Mike,
Utterly enjoyed it!
A question to add to the health warning: maybe the wave would shatter any observer close enough? Would the stretching and squeezing from the passing gravitational wave be so extreme that anything (regular matter, say a planet, a spaceship, or a bar of chocolate :-) ) close by turns into a soup of particles?
"Everything should be made as simple as possible, but not simpler." A. Einstein
RE: Thanks Mike, Utterly
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Sir for your entree tonite we have some toasted baryonic spaghetti from beyond the Lesser Magellanic Cloud. Mind the Roentgens.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Thanks very much for doing
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Thanks very much for doing this. Really great, inspiring stuff!!!
In particular
Wouldn't it be great if all world leaders, big and small, tried to emulate this. And if all politicians put aside their extremely petty differences and thought about collaboration rather than confrontation ....
We can but dream ...
Cheers,
Gary.
Indeed Gary ! We have waited
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Indeed Gary ! We have waited a mere single decade for this ! Others have devoted most of their professional lives.
I am warmly amazed that E@H seems to have attracted/selected a subset of the world's population that are able to put aside, dare I say ignore, all the socio-political fracture lines currently on this planet.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
I was glad to hear Kip Thorne
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I was glad to hear Kip Thorne and the head of the National Science Foundation to remember the pioneering work of Joseph Weber. In 1969 I published a short news article about Weber's attempts to detect GW, on the Mondadori Yearbook of Science and Technology followed next year by an article by Peter G.Bergmann whose title page included a photo of Joe Weber and his resonant mass detector. I was severely scolded by prof. Antonino Zichichi, an eminent Italian elementary particle physicist, who wrote a letter to my director.
Yet it was a visit of Edoardo Amaldi to Weber that sparked Amaldi's interest in general relativity, resulting in a series of Italian GW detector attempts, which produced finally the Virgo Interferometer in Cascina, Pisa, managed by the Istituto Nazionale di Fisica Nucleare, the more important physics research institution in Italy, following on Fermi's and Amaldi's steps.
Tullio
To emphasise the importance
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To emphasise the importance of "the real time GW transient filter" : this exists to possibly notify the various EM telescopes to look in such and such direction-ish because we heard a bang over thataway. Remember SN1987A. The light came in almost coincident with reception events in neutrino detectors, that were studying something else entirely. The unfortunate uncertainty there was : did the photons and the neutrinos leave the highly relativistic fireball ( that was Sanduleak -69° 202 ) at the same time ? Now that we are sure ( most ) neutrinos must have a rest mass then they ought arrive slightly after the photons but only if they left the starting gate at the same time.
GW's are expected from supernovae that are geometrically 'ugly' as for instance if there is certain asymmetry in the matter. There is the converse direction of alerts in place already where the interferometer data records are 'marked' in real time eg. if there are gamma ray bursts. That section would be examined later for GW's.
In other words we would dearly love to receive signals from one and the same cosmic event but from different measurement modes. That would really drill down deep into the astrophysical modelling that applies to said objects.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
RE: In No Particular Order
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How three solar masses that were inside black holes were emitted to outside black holes?
Good question I'd say.
RE: How three solar
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The three solar masses were instantly converted to energy
and emitted as gravitational waves !
If I understood correctly.
That is a lot of energy !
Bill
RE: RE: How three solar
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Sure. But a black hole is called "black" because nothing can escape from inside it - even light.
Including an energy.
If you like one can account
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If you like one can account for the 3 solars as arising from field energy b/w the holes ie. outside either horizon. That's the boggle that so much mass equivalent can be stored in the field. But the 'if you like' is 'as if' ie. a hint that it depends on viewpoint ( always in relativity you must have a frame to quote a result from ) which is a distant observer's here. No immediate test/experiment in the far field will tell you how much is what ie. mass or field. That's Einstein's core point. It makes no difference. Gravity gravitates ie. the interaction itself creates a mass equivalent. From afar you just track the events by some means and note that you seem to be 'short changed' at the end! Weird, huh ?
The electromagnetic analogue would be the interaction b/w two charged particles creating a nett charge ( which doesn't happen ). It is the self referential aspect which has largely screwed up attempts to combine GR effectively with the other forces ( or with QM for that matter ) which just don't have a corresponding character.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal