What I find very interesting is the cooperation between nuclear and elementary particle physicists and researchers in general relativity, which used to be a kind of outmoded subject when I frequented the Trieste University in the Sixties. Now the Istituto Nazionale di Fisica Nucleare is managing the Virgo interferometer in Tuscany, and has brought the skills of the elementary particle researchers to experimental general relativity.
Tullio
I don't think anyone ought 'mind' a revisit of this. There are a lot of issues, however, which are quite peculiar to the GW area. For instance:
- since none have been detected yet, by whatever criteria, we don't have a selection of samples/examples to compare, contrast and have at least a common phenomenological agreement upon. We have modelling of what should be arriving but that assumes knowledge of distant mechanisms, and the risk of circularity in thinking that that entails. The recent Crab Nebula findings obviously bind explanations of it's energy dissipation budget, so that can pin theory to some portion of parameter space however. With SN1987A we see the assumption of delay between detection modes feeding back to theory ie. do supernova cores collapse as quick as previously thought. This is all healthy interaction b/w theory and experiment in the time honored way.
- the effect is so fantastically small, around this cosmic neighbourhood, that the signal is a tiny fraction of the noise. This is in stark contrast to most traditional physical measurements where the noise can be suppressed to some limit which is a fraction of the signal. That totally changes the expectation of what constitutes a 'positive' result, and by what process a decision is reached that sensor activity represents an amplification of GW energy, as opposed to happenstance factors of terrestrial and not cosmic significance. There is a rough analogy here with what is loosely called the 'Full Moon Effect'. This is when a linkage, in our minds now, is formed because of some perceived correlation between 'positive' events, even though a more rigorous examination denies that hypothesis. So newspapers rarely report 'non-events' for similiar reasons - 'Three headed calf NOT born today' is a headline that you will not likely see. Though 'Universe NOT destroyed by particle collider today' is an excellent example of pre-conceptions determining the process of reporting. :-)
- the IFO's use light to measure gravity in hopefully a fairly direct correlation - using phase differences between spacetime routes in the two arms. In contrast the resonant bars ( are thought to ) accumulate the effects of GW strain within it's lattice and 'sing' as a consequence - where here the response will depend very sensitively on the prior state of the bar before GW arrival. So it's a differential method vs an integral one. What is more the IFO's are actively 'nulled' by feedback to keep it in the sweet spot, whereas a bar could conceivably wander out of it's ideal sensitivity because a GW was intercepted. But ultimately electromagnetism is used either way to translate to a human scale readable property. On the one hand this could make the methods sufficiently different to enhance confidence in simultaneous responses, but equally makes calibration of one with respect to the other more problematic.
- we are trying to validate or otherwise an existing theory ( General Relativity ), although maybe extend, as opposed to de-novo construction upon some empirical understanding. So we begin with GR, deduce GW's and then use EM to try to detect. In contrast, say, Galileo obtained a new device ( telescope ) pointed it toward the night sky and created theory ab-initio upon this entirely new mode of observation. This seems a subtle point but one must beware of what assumptions that are engendered, often implicitly, by starting from different viewpoints. Is it a blank sheet or an already busy patch of thought? Naturally one ought to bind new thoughts with the old at some stage, but pre-judgement can be a show stopper. See the Michelson-Morley experiment, the explanation of which required considerable trashing of some cherished concepts. There was considerable back-tracking/reversing to strike upon the malleability of time measurements. It is a beautiful aspect of Special Relativity, and who would have predicted that in 1890?
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
Did Einstein know of the negative result of the Michelson-Morley experiment? The question is discussed at length in Abraham Pais's biography of Einstein, "Subtle is the Lord". But probably Einstein did not care much about experiments. "Theory determines what can be observed", he wrote. I think he would be much surprised of today's attempts to observe frame dragging or gravitational waves. He believed in a Cosmos ruled by beautiful equations and looked with suspect to theories based upon the laws of probability."God does not play dice", he said. "God cast the die, not the dice", his point of view was summarized in another biography, "Albert Einstein creator and rebel", by Banesh Hoffman and Helen Dukas. I tried in vain to have it translated and published in Italy when working for Mondadori Publishing House. Instead the Pais biography was translated and published, but its potential readership is much smaller. Peccato.
Tullio
Did Einstein know of the negative result of the Michelson-Morley experiment?
Pretty likely. Be surprised if not. He knew much of the work of Lorentz, Fitzgerald, Poincare, Fizeau, Foucalt, Fresnel and others who pre- and post- dated the MM results.
Like Darwin & evolution, it was all very much in the air at the time - and then it was ravelled up into a coherent package.
Certainly Einstein's instinct for what is/would be right is amazing. I think it was Planck who, in recommending him for a post in Germany, asked that Einstein be forgiven for his errors in regard the photoelectric effect! For extra irony, Einstein got the Nobel for that. Now triple irony is that it is Planck whose name will be forever describing quanta, when he actually could never get his head around the ideas. He spent a good portion of his remaining career trying to jemmy classical explanations into microscopic phenomena.
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
Those were titans of science. Now we have titanic accelerators, telescopes and space observatories, but few titanic scientists. By the way, its seems that Plan B is working in Hubble. Cheers.
Tullio
Hi!
BTW, most of you will know SN1987A from Hubble images:
taken from here, as well as this diagram that explains the things you see in the image.
.
It would be natural to think about the two outer rings as being illuminated material where the two beams of a pulsar intersect with a thin sphere of material ejected from the star earlier, but apparently this is all still a big mystery and it's even unclear what is at the center of the SN1987A now.
Thank you Bikeman. Whatever the explanation, it is a stunning beauty to behold! :-)
I unknowingly glanced at the supernova the very night it lit up, probably within hours of it's official reporting. I was half asleep on night duty as a young hospital medico walking across a country hospital's grounds. It was the sort of crystal clear night that you often get in the desert. While it seemed odd, I didn't recognise it for what it was.
But I remember alot of the excitement it generated as being the first modern day example that could then be followed through it's evolution. Waiting for a pulsar to appear, measuring the speed of the ejected debris, and the utter bonus of the neutrino response! A terrific 'calibrator' of knowledge.
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
What I find very interesting
)
What I find very interesting is the cooperation between nuclear and elementary particle physicists and researchers in general relativity, which used to be a kind of outmoded subject when I frequented the Trieste University in the Sixties. Now the Istituto Nazionale di Fisica Nucleare is managing the Virgo interferometer in Tuscany, and has brought the skills of the elementary particle researchers to experimental general relativity.
Tullio
I don't think anyone ought
)
I don't think anyone ought 'mind' a revisit of this. There are a lot of issues, however, which are quite peculiar to the GW area. For instance:
- since none have been detected yet, by whatever criteria, we don't have a selection of samples/examples to compare, contrast and have at least a common phenomenological agreement upon. We have modelling of what should be arriving but that assumes knowledge of distant mechanisms, and the risk of circularity in thinking that that entails. The recent Crab Nebula findings obviously bind explanations of it's energy dissipation budget, so that can pin theory to some portion of parameter space however. With SN1987A we see the assumption of delay between detection modes feeding back to theory ie. do supernova cores collapse as quick as previously thought. This is all healthy interaction b/w theory and experiment in the time honored way.
- the effect is so fantastically small, around this cosmic neighbourhood, that the signal is a tiny fraction of the noise. This is in stark contrast to most traditional physical measurements where the noise can be suppressed to some limit which is a fraction of the signal. That totally changes the expectation of what constitutes a 'positive' result, and by what process a decision is reached that sensor activity represents an amplification of GW energy, as opposed to happenstance factors of terrestrial and not cosmic significance. There is a rough analogy here with what is loosely called the 'Full Moon Effect'. This is when a linkage, in our minds now, is formed because of some perceived correlation between 'positive' events, even though a more rigorous examination denies that hypothesis. So newspapers rarely report 'non-events' for similiar reasons - 'Three headed calf NOT born today' is a headline that you will not likely see. Though 'Universe NOT destroyed by particle collider today' is an excellent example of pre-conceptions determining the process of reporting. :-)
- the IFO's use light to measure gravity in hopefully a fairly direct correlation - using phase differences between spacetime routes in the two arms. In contrast the resonant bars ( are thought to ) accumulate the effects of GW strain within it's lattice and 'sing' as a consequence - where here the response will depend very sensitively on the prior state of the bar before GW arrival. So it's a differential method vs an integral one. What is more the IFO's are actively 'nulled' by feedback to keep it in the sweet spot, whereas a bar could conceivably wander out of it's ideal sensitivity because a GW was intercepted. But ultimately electromagnetism is used either way to translate to a human scale readable property. On the one hand this could make the methods sufficiently different to enhance confidence in simultaneous responses, but equally makes calibration of one with respect to the other more problematic.
- we are trying to validate or otherwise an existing theory ( General Relativity ), although maybe extend, as opposed to de-novo construction upon some empirical understanding. So we begin with GR, deduce GW's and then use EM to try to detect. In contrast, say, Galileo obtained a new device ( telescope ) pointed it toward the night sky and created theory ab-initio upon this entirely new mode of observation. This seems a subtle point but one must beware of what assumptions that are engendered, often implicitly, by starting from different viewpoints. Is it a blank sheet or an already busy patch of thought? Naturally one ought to bind new thoughts with the old at some stage, but pre-judgement can be a show stopper. See the Michelson-Morley experiment, the explanation of which required considerable trashing of some cherished concepts. There was considerable back-tracking/reversing to strike upon the malleability of time measurements. It is a beautiful aspect of Special Relativity, and who would have predicted that in 1890?
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
Did Einstein know of the
)
Did Einstein know of the negative result of the Michelson-Morley experiment? The question is discussed at length in Abraham Pais's biography of Einstein, "Subtle is the Lord". But probably Einstein did not care much about experiments. "Theory determines what can be observed", he wrote. I think he would be much surprised of today's attempts to observe frame dragging or gravitational waves. He believed in a Cosmos ruled by beautiful equations and looked with suspect to theories based upon the laws of probability."God does not play dice", he said. "God cast the die, not the dice", his point of view was summarized in another biography, "Albert Einstein creator and rebel", by Banesh Hoffman and Helen Dukas. I tried in vain to have it translated and published in Italy when working for Mondadori Publishing House. Instead the Pais biography was translated and published, but its potential readership is much smaller. Peccato.
Tullio
RE: Did Einstein know of
)
Pretty likely. Be surprised if not. He knew much of the work of Lorentz, Fitzgerald, Poincare, Fizeau, Foucalt, Fresnel and others who pre- and post- dated the MM results.
Like Darwin & evolution, it was all very much in the air at the time - and then it was ravelled up into a coherent package.
Certainly Einstein's instinct for what is/would be right is amazing. I think it was Planck who, in recommending him for a post in Germany, asked that Einstein be forgiven for his errors in regard the photoelectric effect! For extra irony, Einstein got the Nobel for that. Now triple irony is that it is Planck whose name will be forever describing quanta, when he actually could never get his head around the ideas. He spent a good portion of his remaining career trying to jemmy classical explanations into microscopic phenomena.
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
Those were titans of science.
)
Those were titans of science. Now we have titanic accelerators, telescopes and space observatories, but few titanic scientists. By the way, its seems that Plan B is working in Hubble. Cheers.
Tullio
Hi! BTW, most of you will
)
Hi!
BTW, most of you will know SN1987A from Hubble images:
taken from here, as well as this diagram that explains the things you see in the image.
.
It would be natural to think about the two outer rings as being illuminated material where the two beams of a pulsar intersect with a thin sphere of material ejected from the star earlier, but apparently this is all still a big mystery and it's even unclear what is at the center of the SN1987A now.
CU
Bikeman
Thank you Bikeman. Whatever
)
Thank you Bikeman. Whatever the explanation, it is a stunning beauty to behold! :-)
I unknowingly glanced at the supernova the very night it lit up, probably within hours of it's official reporting. I was half asleep on night duty as a young hospital medico walking across a country hospital's grounds. It was the sort of crystal clear night that you often get in the desert. While it seemed odd, I didn't recognise it for what it was.
But I remember alot of the excitement it generated as being the first modern day example that could then be followed through it's evolution. Waiting for a pulsar to appear, measuring the speed of the ejected debris, and the utter bonus of the neutrino response! A terrific 'calibrator' of knowledge.
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