Yup, it's a goodie with hints of more fascinating articles to come in later issues. Five stars for readability.
On the fabrication side of things, the whole LIGO/Virgo/GEO enterprises have really been leading edge ( ie. never been done before ) in many technical aspects. What I found especially fascinating was the welding/bonding of the suspension fibres ( see "Monolithic Suspensions" ) to the hanging optics elements AND the really clever techniques to draw out the silica strands in such a way as to give the designed/desired mechanical and thermal damping characteristics. Hard core engineering!! :-)
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
Hallo Mike!
Thank you for this valuable hint.
It seems, we have to wait somewhat longer for first valuable data than expected. But this is usual for such big projects.
A lovely short piece by whom I call The Queen of Theoretical Physics. She has brought this out to clarify many questions she has received since the LHC announcement of the Higgs findings. She sounds really enthused and excited to have this result come through, as like many theorists in this area of physics there hasn't been much to guide them for a while.
For starters there are important distinctions to be made b/w various Higgsy words. So the Higgs mechanism is the original idea from the 1960's, that was produced to explain why it is that our fundamental particles have mass. Mass is the property that keeps you travelling at sub-luminal speeds, gives you inertia or reluctance to change dynamic state, and causes gravitational attraction. So that's a big ticket item. The Higgs boson or Higgs particle is the thing that experimentalists discover, a lump of the Higgs field which is our mathematical abstraction ( aka quantum field theory ) used to manage our understanding of how/why separated things can influence one another. And just to be a bit more obtuse there may be more than one Higgs Boson type, plus there are proposed variants upon Mr. Higg's work that could be explored - confirmed or refuted - by more LHC data.
This is all going on in 'empty space', and as a field the Higgs has the property that it's least energy is when the field is non-zero. Thus arises the concept of 'symmetry breaking' or why does the Higgs field behave as it does, with each elementary particle ( quark, electron .... ) getting the mass value that it does ?? So as is usual in such a reductionist enterprise you get deeper questions blossoming out of existing answers and findings. Symmetry breaking is one way of saying that "a choice had to be made, and this is what you got." But perhaps that's merely a consequence of our love and use of symmetry ( things that remain constant when other things change ) within our explanations, so possibly another intellectual approach wouldn't touch upon that. Mind you, symmetry concepts have brought us quite a long and fruitful way so far.
She also explains the ins and outs of the discovery process, especially that the Higgs particle discovery is actually an analysis of Higgs particle decay modes. The particle itself doesn't hang around long enough so that one can point at some line of passage on a screen - like the cloud chamber tracks of old - but by the rather more difficult problem of deducing a common source of particle production. So one throws protons at each other, some of those protons collide, some of those collisions make a Higgs boson, and some of those Higgs bosons decay in a fashion that allows us to deduce they were there at all. So imagine collecting up fragments from a series of grenade explosions, and eventually deciding what a Higgs Grenade must have looked like. A forensic investigation of shrapnel. That's the flavour of the enterprise, and thus why alot of the discussion is about bumps in curves and probability estimates. There could be/are other sorts of grenades - or even random debris - fooling us here.
[ side note : a "three sigma" significance translates to an chance that you're hypothesis is wrong of about a few percent. One in fifty, say. A "five sigma" significance translates to one in several million. The sigma scale is not linear in this regard. If you look at the prepfold sheets for the E@H pulsar discoveries you will routinely see many tens of sigma's quoted. As a good rule of thumb : you should ignore any 'scientific' reports that only deal in low sigmas*, as you can get that significance level at Vegas everyday just from pure chance and not real trends. The quoting of sigma levels is one of the most abused notations in recent public science discourse. ]
Anyway I wont spoil any more, the book is worth a read. It includes a chapter dealing with the Higgs Boson from her prior book called "Knocking On Heaven's Door". There you will find much more of the messy detail .... :-)
Cheers, Mike.
( edit ) * or don't even have an analysis of error at all. The best people to assess error are the researchers themselves, as they are in the best position to know of sources/extents/happenstance. Alas this requires a certain type of intellectual rigor and ( self ) abnegation. I know I do go on about this aspect of 'modern science' but all to often I see "I assert thus : you must disprove". I think my weariness is due to three decades of dealing with drug company literature! :-) :-)
( edit ) And I've just noticed that she didn't use the word 'string' even once ! :-)
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
Nuclear Physics by Werner Heisenberg ( 148 pages )
[ I downloaded from eBooks for $10.43 AUD : as you can see I've really discovered electronic purchasing and delivery of books! :-) ]
This is the book of a series of lectures given by the great man, first published during WWII and last revised in 1948. It is what I would describe as a summary of the state of the art at the time, and at a cusp when nuclear chain reactions had been amply demonstrated but yet before a good theoretical grasp was obtained of the goings on in the nucleus. For instance he talks of 'Yukawa particles' that were deemed to be the strong force mediators ( ie. pions transferring b/w neutrons and protons ), and thus before the modern talk of weak force vector bosons, quarks, gluons and all that. What we have though is the beginning of the 'exchange force' paradigm ( aka present day quantum field theory ) that gets around the dislike of earlier 'action at a distance' models.
Surprisingly he begins at the 'man in the street' level, and then proceeds to explain in deeper language/terminology all that was known about atoms and how they are structured. This begins with an historic survey from antiquity to the 19th century and then - step by step - outlines the major experimental results that gave forth our modern view. If it wasn't for radioactivity aka. nuclear instability, we wouldn't have the tools then used to probe these small domains. So back at the Cavendish lab is the process of throwing alpha particles at thin sheets of heavy metals. Low and behold the distribution of rebounding particles - with thanks to Geiger and Marsden and Soddy - was best explained by Rutherford as a largely empty volume of space within atoms.
What's in the nucleus? Nucleons, right? So what are they and how can we really be sure of that? This is a detective story with a wide net, beginning with the periodic table ( including explaining what 'periodic' means ), then the difficult process of deducing elemental weights and proceeding to transmutation of elements to others. Here is described the concept of 'binding energy' ( per nucleon ) which is a crucial device to understand the whys and hows of the fusion and fission pathways. Why are some nuclei stable whereas others fall apart with no encouragement at all? Conservation rules rule! Here you will find a whole host of rules of thumb and pragmatically derived trends and tendencies eg. 'odd-odd' nuclei are rare, that these days we hardly hear of.
Along the way he describes the latest and greatest particle accelerators and detection devices of the era. Including some you could probably make at home without too much expense or risk eg. a Wilson cloud chamber or a Geiger point counter. There's probably local ordinances against operating a cyclotron without a permit, and as for Van de Graaff's ..... :-)
He caps it off with 'future directions' for useful applications - non weapon that is - of nuclear physics. There is an appendix on the history of nuclear research during WWII in Germany, but I guess given subsequent controversy about his involvement there some would see that later addition as a self-serving retrospective note.
In any case I find such contemporary pieces interesting, as they define the way frontier researchers think about their work. For instance there was a chap called Prout who hypothesised that all atoms were formed from hydrogen. He was right in the sense that he meant it, and even though today we would phrase that differently it was still an excellent approximation that fit the data well. What he didn't know about at the time was the existence of neutrons, which add to atomic weight but not atomic number, thus giving rise to non integral atomic weights of elements that are actually isotopic mixtures in their natural state.
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
Well, Ligo Magazine second issue is out. Looks like an issue per six months is the likely publication rate. What bumper reading it makes. It has the low down in terms of astrophysics and detection for those beasts of the sky - black holes.
Each time I read about BH's I do a mental double take. They are so far from everyday experience that it is quite hard - for me at least - to wrap one's head around them. You can't see them but they can grab you : the ultimate Bogey Man under the bed! It makes 'real' the concept of a 'field' though. When I first learned classical ( bog standard ) electrostatics the field was introduced as a convenient accounting device. You have a single charge of interest, then you introduce an arbitrarily small charge nearby ( positive to be definite, and not causing disturbance to the setup ) and then measure the force upon it. The direction and strength of that force per unit charge is field 'strength'. Then the neighbourhood of a collection of charges of interest can be mapped similiarly. With the contribution from each individual charge summing as vectors ( linearly ), so one imagines the surrounding space carrying at each point a vector to describe what influence some other introduced charge will be subject to. Note that this construct uses an actual charge to do the field mapping ( well, as a gedanken experiment at least ).
So what would the field be, in operational terms, if no test charge was used? In one sense you can say : 'no measurement, no field' and leave it at that. However there is always something about, however distant, that will interact ( as per John Donne ). Now when you introduce a dynamic aspect - things moving and changing with time - then the field is not just some accounting device to be used or not as pleases. Because you don't get any influence propagating faster than light - fast but finite - then when one thing moves a certain way some other thing will be influenced by that BUT only after some delay. Now any 'reasonable' way of thinking is going to propose the passage of something b/w the two objects you are primarily watching. That is, you might not 'see' the thing going in between but certainly a consistent description emerges ( with outstanding accuracy I might add eg. the anomalous magnetic moment of the electron in QED ).
Now to gravity. You could bring in 'gravitons' here but even if not quantised the reasoning is still going to flow forwards as the gravitational field 'holding payments in transit'. Hence if you go down deep into the well nearby one of these sky beasts - and especially if you are also a sky beast yourself - then one's knowledge of the others' actions is old news as per distance divided by light speed. And the debts held by the field here are way big, so much so that if you add in mass/energy equivalence then the field energy itself has a notable gravitational effect! Non-linear! So when I read :
Quote:
One way to parameterize just how deep into the strong-field regime we can probe with a given binary system is with the dimensionless ratio of the binary’s orbital velocity to the speed of light. For binary pulsars, which provide some of the best existing tests of general relativity, this parameter is about 0.001. For merging black-hole binaries, this parameter can approach 1.
my jaw metaphorically drops to the floor. Black holes orbiting at near light speed ? Whew .... so :
Quote:
dynamical interactions to bring the binary to the point where it can merge through radiation reaction from the emission of gravitational waves
which is awesome. I hope these effects are discovered in my lifetime.
Quote:
We will need very accurate waveform models, sophisticated data analysis pipelines, improved astrophysical models to compare against, and robust tools for bringing everything together.
E@H is part of one of those pipelines! :-)
As regards electromagnetic evidence then alas, for material nearby these deep gravity wells :
Quote:
no one has yet found a spectral or timing property that occurs in all black holes and only black holes.
so that seems to imply that multi-modal astronomy on the same object may be required to fully characterise. Here's another exciting idea:
Quote:
there is a push now to have high angular resolution radio observations of our Galactic black hole, in the hopes that the horizon will produce a discernable shadow in the emission from the tenuous matter that is near the black hole.
that's the event horizon being talked about here! Like a shadow puppet on a wall. Detection by contrast. Way Cool.
Cheers, Mike.
( edit ) Back of the envelope : diameter of our Galaxy's central black hole = twice the Schwarzschild radius
R = 2 * G * M / c^2 ~ 2.95 ( km per solar mass ) * solar masses in object
= 2.95 * 10^6 ( km ) = 3 million kilometres
or 12 million kilometres in diameter for a two mega-solar-mass hole. The diameter of the Sun ( uncompressed! ) is 1.4 million kilometres, soooo ..... we're looking for a 'shadow' about 8 Sun diameters in width, but viewed at the distance to the centre of the Galaxy.
( edit ) You know, I think I can almost imagine how it is that Mercury's orbit precesses under GR. There is a precession effect, classical, due to the other planets notably Jupiter. But if you account for that you still have what's called a perihelion advance. Perihelion is the point of closest approach to the Sun for a given orbit, you could define this say by a distance from the Sun's centre and a direction with respect to the distant stars. Now advance here means that this point sneaks forward each orbit in the direction of the same sense as Mercury's orbit. So if you look 'down' on Mercury and see it going anticlockwise, say, then the perihelion point will also move in that direction.
Quote:
This is reminiscent of a 'Spirograph' - that device beloved of young nerds in the 60's and 70's ( which is to say that I loved it then/still and many like minded did also! ) - which can produce a shifting flower petal arrangement on the paper by the smooth and continuous motion of a particular cog in the gadget. You got that by having a non-rational number represent a gearing ratio ( alas you have to really own a Spirograph to see that in action ).
In any event Mercury at any particular point in it's mildly eccentric ( not exactly circular ) orbit will 'see' the Sun not where it is, but where it was a short time ago. That lag time will be greater ( eg. aphelion, the orbital point most distant from the Sun ) when it is further from the Sun compared with closer. This means it's instantaneous force is with respect to an earlier position of the Sun in their mutual dance around their common centre of mass. And that will accelerate Mercury in a direction slightly off the line that joins the two, and that has a component ( however small ) tangential to that line and in the sense of Mercury's current movement ie. advance. I read that one could envisage GR ( at least in low fields ) as time delayed Newtonian ie. retarded time that accounts for propagation delay.
[ If this analysis is correct then one could state that no perihelion retardation ought occur in such a setting : because Mercury won't ever 'see' the Sun where it will be. ]
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
While surfing the net for other reasons I've found this site which has good astronomy articles : short and concise, not raved up, and well attributed. I'd ignore many of the strange reader's comments though. :-)
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
Because it was mentioned in eLisa documents, I have dug up the Large Synoptic Survey Telescope ( LSST ) Science Book Version 2.0 Abstract. A feast of information about this project for which construction has started, and which should be up and running about 15 years from now. My favorite astronomical duo - Caroline and William Herschel, the 'parents' of the modern sky survey paradigm - would be delighted.
There's that old philosophical question about 'what is the sound of a tree falling in a forest if there is no one around to hear it?'. LSST solves the astronomical equivalent by repeatedly imaging the sky ( that which is accessible from Chile ) in wide areas to faint magnitudes. Quickly. Over the 10 year initial lifetime each accessible part of the celestial sphere will be imaged about 1000 times. In six optical bands/colors. Each night of operation will produce some 30 TB of data, which will be released for scientific and public use ( suitably calibrated ) without any proprietary period. The aim is worldwide participation in all data products.
Think of it as a humunguous photon bucket with a state-of-the-art electronic imaging backplane, as CCD realisations have converged ever closer to quantum limits on performance. The measure of a survey device is called it's etendue ( 'grasp' ) being the numeric product of the primary mirror's area and the sky field of view. It will blow the doors off prior efforts. So what can you see then ie. what do you catch with the LSST that you'd miss otherwise ? An impressive list of goals from : near Earth objects ( dinosaur killers ) to Supernovae to Dark Matter characteristics to distant/early galaxy metrics, but to name a few. So the intellectual grasp is substantial too.
What an amazing gadget! I've only read the introductory chapters, more awaits me .... :-)
Cheers, Mike.
( edit ) And of course it will be a brilliant dovetail with other modes, including GW detectors.
( edit ) So any given patch of accessible sky will be revisited on average every three days, two fifteen second exposures back-to-back ( reduces/controls cosmic ray interference with the backplane silicon ) but with a simultaneous record in all six color filters. Two seconds readout per exposure and five seconds to slew, and with such exposures one will typically achieve good imaging down to magnitude ~ 25 ..... coool. The total will be some 5.6 million 15 second exposures over 10 years.
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
Hopefully we will not have to wait that long, I think the "science" first light will happen near the end of the decade if everything goes according to plan. http://www.lsst.org/lsst/science/science-faq
There might be some potential for "LSST@Home", perhaps?
Hopefully we will not have to wait that long, I think the "science" first light will happen near the end of the decade if everything goes according to plan. http://www.lsst.org/lsst/science/science-faq
Ah, good. :-)
Quote:
There might be some potential for "LSST@Home", perhaps?
Absolutely. The data acquisition rates are extraordinary, definitely begging for image processing pipelines of substantial capacity to uncover features and changes thereof, plus it's all in the public domain so I would expect a plethora of analysis groups with a large spread of research goals.
Cheers, Mike.
( edit ) I also note that the pointing precision is of the order of milli-arc-seconds per visit, but over a decade this will be driven down especially in the area of parallax and proper motion. It is really going to nail down our near-space positions and thus by extension affect calibrations up the distance ladder.
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
Yup, it's a goodie with hints
)
Yup, it's a goodie with hints of more fascinating articles to come in later issues. Five stars for readability.
On the fabrication side of things, the whole LIGO/Virgo/GEO enterprises have really been leading edge ( ie. never been done before ) in many technical aspects. What I found especially fascinating was the welding/bonding of the suspension fibres ( see "Monolithic Suspensions" ) to the hanging optics elements AND the really clever techniques to draw out the silica strands in such a way as to give the designed/desired mechanical and thermal damping characteristics. Hard core engineering!! :-)
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
Hallo Mike! Thank you for
)
Hallo Mike!
Thank you for this valuable hint.
It seems, we have to wait somewhat longer for first valuable data than expected. But this is usual for such big projects.
Kind regards and happy crunching
Martin
Higgs Discovery The Power of
)
Higgs Discovery The Power of Empty Space by Lisa Randall ( 48 pages )
[ I downloaded from eBooks for $5.99 AUD ]
A lovely short piece by whom I call The Queen of Theoretical Physics. She has brought this out to clarify many questions she has received since the LHC announcement of the Higgs findings. She sounds really enthused and excited to have this result come through, as like many theorists in this area of physics there hasn't been much to guide them for a while.
For starters there are important distinctions to be made b/w various Higgsy words. So the Higgs mechanism is the original idea from the 1960's, that was produced to explain why it is that our fundamental particles have mass. Mass is the property that keeps you travelling at sub-luminal speeds, gives you inertia or reluctance to change dynamic state, and causes gravitational attraction. So that's a big ticket item. The Higgs boson or Higgs particle is the thing that experimentalists discover, a lump of the Higgs field which is our mathematical abstraction ( aka quantum field theory ) used to manage our understanding of how/why separated things can influence one another. And just to be a bit more obtuse there may be more than one Higgs Boson type, plus there are proposed variants upon Mr. Higg's work that could be explored - confirmed or refuted - by more LHC data.
This is all going on in 'empty space', and as a field the Higgs has the property that it's least energy is when the field is non-zero. Thus arises the concept of 'symmetry breaking' or why does the Higgs field behave as it does, with each elementary particle ( quark, electron .... ) getting the mass value that it does ?? So as is usual in such a reductionist enterprise you get deeper questions blossoming out of existing answers and findings. Symmetry breaking is one way of saying that "a choice had to be made, and this is what you got." But perhaps that's merely a consequence of our love and use of symmetry ( things that remain constant when other things change ) within our explanations, so possibly another intellectual approach wouldn't touch upon that. Mind you, symmetry concepts have brought us quite a long and fruitful way so far.
She also explains the ins and outs of the discovery process, especially that the Higgs particle discovery is actually an analysis of Higgs particle decay modes. The particle itself doesn't hang around long enough so that one can point at some line of passage on a screen - like the cloud chamber tracks of old - but by the rather more difficult problem of deducing a common source of particle production. So one throws protons at each other, some of those protons collide, some of those collisions make a Higgs boson, and some of those Higgs bosons decay in a fashion that allows us to deduce they were there at all. So imagine collecting up fragments from a series of grenade explosions, and eventually deciding what a Higgs Grenade must have looked like. A forensic investigation of shrapnel. That's the flavour of the enterprise, and thus why alot of the discussion is about bumps in curves and probability estimates. There could be/are other sorts of grenades - or even random debris - fooling us here.
[ side note : a "three sigma" significance translates to an chance that you're hypothesis is wrong of about a few percent. One in fifty, say. A "five sigma" significance translates to one in several million. The sigma scale is not linear in this regard. If you look at the prepfold sheets for the E@H pulsar discoveries you will routinely see many tens of sigma's quoted. As a good rule of thumb : you should ignore any 'scientific' reports that only deal in low sigmas*, as you can get that significance level at Vegas everyday just from pure chance and not real trends. The quoting of sigma levels is one of the most abused notations in recent public science discourse. ]
Anyway I wont spoil any more, the book is worth a read. It includes a chapter dealing with the Higgs Boson from her prior book called "Knocking On Heaven's Door". There you will find much more of the messy detail .... :-)
Cheers, Mike.
( edit ) * or don't even have an analysis of error at all. The best people to assess error are the researchers themselves, as they are in the best position to know of sources/extents/happenstance. Alas this requires a certain type of intellectual rigor and ( self ) abnegation. I know I do go on about this aspect of 'modern science' but all to often I see "I assert thus : you must disprove". I think my weariness is due to three decades of dealing with drug company literature! :-) :-)
( edit ) And I've just noticed that she didn't use the word 'string' even once ! :-)
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
Nuclear Physics by Werner
)
Nuclear Physics by Werner Heisenberg ( 148 pages )
[ I downloaded from eBooks for $10.43 AUD : as you can see I've really discovered electronic purchasing and delivery of books! :-) ]
This is the book of a series of lectures given by the great man, first published during WWII and last revised in 1948. It is what I would describe as a summary of the state of the art at the time, and at a cusp when nuclear chain reactions had been amply demonstrated but yet before a good theoretical grasp was obtained of the goings on in the nucleus. For instance he talks of 'Yukawa particles' that were deemed to be the strong force mediators ( ie. pions transferring b/w neutrons and protons ), and thus before the modern talk of weak force vector bosons, quarks, gluons and all that. What we have though is the beginning of the 'exchange force' paradigm ( aka present day quantum field theory ) that gets around the dislike of earlier 'action at a distance' models.
Surprisingly he begins at the 'man in the street' level, and then proceeds to explain in deeper language/terminology all that was known about atoms and how they are structured. This begins with an historic survey from antiquity to the 19th century and then - step by step - outlines the major experimental results that gave forth our modern view. If it wasn't for radioactivity aka. nuclear instability, we wouldn't have the tools then used to probe these small domains. So back at the Cavendish lab is the process of throwing alpha particles at thin sheets of heavy metals. Low and behold the distribution of rebounding particles - with thanks to Geiger and Marsden and Soddy - was best explained by Rutherford as a largely empty volume of space within atoms.
What's in the nucleus? Nucleons, right? So what are they and how can we really be sure of that? This is a detective story with a wide net, beginning with the periodic table ( including explaining what 'periodic' means ), then the difficult process of deducing elemental weights and proceeding to transmutation of elements to others. Here is described the concept of 'binding energy' ( per nucleon ) which is a crucial device to understand the whys and hows of the fusion and fission pathways. Why are some nuclei stable whereas others fall apart with no encouragement at all? Conservation rules rule! Here you will find a whole host of rules of thumb and pragmatically derived trends and tendencies eg. 'odd-odd' nuclei are rare, that these days we hardly hear of.
Along the way he describes the latest and greatest particle accelerators and detection devices of the era. Including some you could probably make at home without too much expense or risk eg. a Wilson cloud chamber or a Geiger point counter. There's probably local ordinances against operating a cyclotron without a permit, and as for Van de Graaff's ..... :-)
He caps it off with 'future directions' for useful applications - non weapon that is - of nuclear physics. There is an appendix on the history of nuclear research during WWII in Germany, but I guess given subsequent controversy about his involvement there some would see that later addition as a self-serving retrospective note.
In any case I find such contemporary pieces interesting, as they define the way frontier researchers think about their work. For instance there was a chap called Prout who hypothesised that all atoms were formed from hydrogen. He was right in the sense that he meant it, and even though today we would phrase that differently it was still an excellent approximation that fit the data well. What he didn't know about at the time was the existence of neutrons, which add to atomic weight but not atomic number, thus giving rise to non integral atomic weights of elements that are actually isotopic mixtures in their natural state.
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
Just Released : Time
)
Just Released :
Time Reborn
A comfortable read, written for the layman. I will let the reviews speak for it.
There are some who can live without wild things and some who cannot. - Aldo Leopold
Well, Ligo Magazine second
)
Well, Ligo Magazine second issue is out. Looks like an issue per six months is the likely publication rate. What bumper reading it makes. It has the low down in terms of astrophysics and detection for those beasts of the sky - black holes.
Each time I read about BH's I do a mental double take. They are so far from everyday experience that it is quite hard - for me at least - to wrap one's head around them. You can't see them but they can grab you : the ultimate Bogey Man under the bed! It makes 'real' the concept of a 'field' though. When I first learned classical ( bog standard ) electrostatics the field was introduced as a convenient accounting device. You have a single charge of interest, then you introduce an arbitrarily small charge nearby ( positive to be definite, and not causing disturbance to the setup ) and then measure the force upon it. The direction and strength of that force per unit charge is field 'strength'. Then the neighbourhood of a collection of charges of interest can be mapped similiarly. With the contribution from each individual charge summing as vectors ( linearly ), so one imagines the surrounding space carrying at each point a vector to describe what influence some other introduced charge will be subject to. Note that this construct uses an actual charge to do the field mapping ( well, as a gedanken experiment at least ).
So what would the field be, in operational terms, if no test charge was used? In one sense you can say : 'no measurement, no field' and leave it at that. However there is always something about, however distant, that will interact ( as per John Donne ). Now when you introduce a dynamic aspect - things moving and changing with time - then the field is not just some accounting device to be used or not as pleases. Because you don't get any influence propagating faster than light - fast but finite - then when one thing moves a certain way some other thing will be influenced by that BUT only after some delay. Now any 'reasonable' way of thinking is going to propose the passage of something b/w the two objects you are primarily watching. That is, you might not 'see' the thing going in between but certainly a consistent description emerges ( with outstanding accuracy I might add eg. the anomalous magnetic moment of the electron in QED ).
Now to gravity. You could bring in 'gravitons' here but even if not quantised the reasoning is still going to flow forwards as the gravitational field 'holding payments in transit'. Hence if you go down deep into the well nearby one of these sky beasts - and especially if you are also a sky beast yourself - then one's knowledge of the others' actions is old news as per distance divided by light speed. And the debts held by the field here are way big, so much so that if you add in mass/energy equivalence then the field energy itself has a notable gravitational effect! Non-linear! So when I read :
my jaw metaphorically drops to the floor. Black holes orbiting at near light speed ? Whew .... so :
which is awesome. I hope these effects are discovered in my lifetime.
E@H is part of one of those pipelines! :-)
As regards electromagnetic evidence then alas, for material nearby these deep gravity wells :
so that seems to imply that multi-modal astronomy on the same object may be required to fully characterise. Here's another exciting idea:
that's the event horizon being talked about here! Like a shadow puppet on a wall. Detection by contrast. Way Cool.
Cheers, Mike.
( edit ) Back of the envelope : diameter of our Galaxy's central black hole = twice the Schwarzschild radius
R = 2 * G * M / c^2 ~ 2.95 ( km per solar mass ) * solar masses in object
= 2.95 * 10^6 ( km ) = 3 million kilometres
or 12 million kilometres in diameter for a two mega-solar-mass hole. The diameter of the Sun ( uncompressed! ) is 1.4 million kilometres, soooo ..... we're looking for a 'shadow' about 8 Sun diameters in width, but viewed at the distance to the centre of the Galaxy.
( edit ) You know, I think I can almost imagine how it is that Mercury's orbit precesses under GR. There is a precession effect, classical, due to the other planets notably Jupiter. But if you account for that you still have what's called a perihelion advance. Perihelion is the point of closest approach to the Sun for a given orbit, you could define this say by a distance from the Sun's centre and a direction with respect to the distant stars. Now advance here means that this point sneaks forward each orbit in the direction of the same sense as Mercury's orbit. So if you look 'down' on Mercury and see it going anticlockwise, say, then the perihelion point will also move in that direction.
In any event Mercury at any particular point in it's mildly eccentric ( not exactly circular ) orbit will 'see' the Sun not where it is, but where it was a short time ago. That lag time will be greater ( eg. aphelion, the orbital point most distant from the Sun ) when it is further from the Sun compared with closer. This means it's instantaneous force is with respect to an earlier position of the Sun in their mutual dance around their common centre of mass. And that will accelerate Mercury in a direction slightly off the line that joins the two, and that has a component ( however small ) tangential to that line and in the sense of Mercury's current movement ie. advance. I read that one could envisage GR ( at least in low fields ) as time delayed Newtonian ie. retarded time that accounts for propagation delay.
[ If this analysis is correct then one could state that no perihelion retardation ought occur in such a setting : because Mercury won't ever 'see' the Sun where it will be. ]
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
While surfing the net for
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While surfing the net for other reasons I've found this site which has good astronomy articles : short and concise, not raved up, and well attributed. I'd ignore many of the strange reader's comments though. :-)
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
Because it was mentioned in
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Because it was mentioned in eLisa documents, I have dug up the Large Synoptic Survey Telescope ( LSST ) Science Book Version 2.0 Abstract. A feast of information about this project for which construction has started, and which should be up and running about 15 years from now. My favorite astronomical duo - Caroline and William Herschel, the 'parents' of the modern sky survey paradigm - would be delighted.
There's that old philosophical question about 'what is the sound of a tree falling in a forest if there is no one around to hear it?'. LSST solves the astronomical equivalent by repeatedly imaging the sky ( that which is accessible from Chile ) in wide areas to faint magnitudes. Quickly. Over the 10 year initial lifetime each accessible part of the celestial sphere will be imaged about 1000 times. In six optical bands/colors. Each night of operation will produce some 30 TB of data, which will be released for scientific and public use ( suitably calibrated ) without any proprietary period. The aim is worldwide participation in all data products.
Think of it as a humunguous photon bucket with a state-of-the-art electronic imaging backplane, as CCD realisations have converged ever closer to quantum limits on performance. The measure of a survey device is called it's etendue ( 'grasp' ) being the numeric product of the primary mirror's area and the sky field of view. It will blow the doors off prior efforts. So what can you see then ie. what do you catch with the LSST that you'd miss otherwise ? An impressive list of goals from : near Earth objects ( dinosaur killers ) to Supernovae to Dark Matter characteristics to distant/early galaxy metrics, but to name a few. So the intellectual grasp is substantial too.
What an amazing gadget! I've only read the introductory chapters, more awaits me .... :-)
Cheers, Mike.
( edit ) And of course it will be a brilliant dovetail with other modes, including GW detectors.
( edit ) So any given patch of accessible sky will be revisited on average every three days, two fifteen second exposures back-to-back ( reduces/controls cosmic ray interference with the backplane silicon ) but with a simultaneous record in all six color filters. Two seconds readout per exposure and five seconds to slew, and with such exposures one will typically achieve good imaging down to magnitude ~ 25 ..... coool. The total will be some 5.6 million 15 second exposures over 10 years.
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: Because it was
)
Hopefully we will not have to wait that long, I think the "science" first light will happen near the end of the decade if everything goes according to plan. http://www.lsst.org/lsst/science/science-faq
There might be some potential for "LSST@Home", perhaps?
Cheers
HB
RE: Hopefully we will not
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Ah, good. :-)
Absolutely. The data acquisition rates are extraordinary, definitely begging for image processing pipelines of substantial capacity to uncover features and changes thereof, plus it's all in the public domain so I would expect a plethora of analysis groups with a large spread of research goals.
Cheers, Mike.
( edit ) I also note that the pointing precision is of the order of milli-arc-seconds per visit, but over a decade this will be driven down especially in the area of parallax and proper motion. It is really going to nail down our near-space positions and thus by extension affect calibrations up the distance ladder.
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