Dark Matter...WTH?

michaelmozina · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>But there is total consensus.  The consensus is "we don't know" what dark matter is or if it is, but we do know that we don't see enough regular matter to account for orbits that we see. </DIV>Well sort of, but not exactly.  I don't have a problem with MACHO brands of "dark matter" theory, but the assertion that a new "form" of matter is necessary to explain these phenomenon is a whole different issue.  There are fundamental disagreements about SUSY oriented brands of "dark matter", and SUSY theory is itself a *NON STANDARD* (non mainstream) variation of particle physics theory.  SUSY theories are *NOT* "mainstream" within the particle physics community, and not a single emprical test yet supports these types of particles.    It would be better to say that our current theories fail to account for these observations.  Period.Replying to: <DIV CLASS='Discussion_PostQuote'>You will only see consensus in physics when there is a solid explanation backed by solid theory that has experimental verification.[/QUOTEI'm sure that's true, but the notion that a new form of matter is required to explain distant galactic observations has become a "consensus" even *without* such emprical evidence.    What emprical observational evidence lead NASA to conclude that "dark matter" had anything to do with those 300-800 billion volt electrons they observed?   Replying to: <DIV CLASS='Discussion_PostQuote'> Without the theory and data there should not be any consensus.</DIV>I agree, but Yevaud's statement about new forms of matter is the "accepted consensus" in astronomy today.  That makes it difficult froma skeptic's perspective because too much is "missing" for a pure skeptic to simply "jump on the band wagon".Replying to: <DIV CLASS='Discussion_PostQuote'>If you have consensus on the answer to an unsettled (unsettled meansing that  both theory and experimental data are lacking) question then there is a big problem -- it is quite likely that everyone is wrong.  Note that "theory" does not mean "hypothesis", it means a mathematical model with predictive power that has been experimentally validated.   Posted by DrRocket</DIV>How was the emission of those billion volt electrons "experimentally validated"?  How are any of the dark matter "properties"experimentally validated" in any controlled emprical test of concept? FYI it is in fact quite possible and historically quite common for the mainstream to be wrong.  In fact it happens a lot.Without emprical experimental evidence to back up the assertions about the "properties" of "new forms" of matter, these theories become "dogma", not emrpically verifiable ideas that can be duplicated in a lab.  That is a big problem from my perspective and from the perspective of most skeptics I know, including all the scientists that signed that petition.There is a significant difference here between "dogma" that must be accepted on faith and "emprical science" that can be duplicated in controlled experimentation.  That difference is the fact that emprical experimentation allows us to differentiate scientific fact, from mathematical mythos.  Without such emprical tests, new forms of "dark matter" remain speculative, unverfied, "unexplained", and unsubstanciated.  Distant uncontrolled observations cannot tell us what forms of matter exist in nature.  Only empirical *CONTROLLED* experiments can do that. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

michaelmozina · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>But there is total consensus.  The consensus is "we don't know" what dark matter is or if it is, but we do know that we don't see enough regular matter to account for orbits that we see. </DIV>Well sort of, but not exactly.  I don't have a problem with MACHO brands of "dark matter" theory, but the assertion that a new "form" of matter is necessary to explain these phenomenon is a whole different issue.  There are fundamental disagreements about SUSY oriented brands of "dark matter", and SUSY theory is itself a *NON STANDARD* (non mainstream) variation of particle physics theory.  SUSY theories are *NOT* "mainstream" within the particle physics community, and not a single emprical test yet supports these types of particles.    It would be better to say that our current theories fail to account for these observations.  Period.Replying to: <DIV CLASS='Discussion_PostQuote'>You will only see consensus in physics when there is a solid explanation backed by solid theory that has experimental verification.[/QUOTEI'm sure that's true, but the notion that a new form of matter is required to explain distant galactic observations has become a "consensus" even *without* such emprical evidence.    What emprical observational evidence lead NASA to conclude that "dark matter" had anything to do with those 300-800 billion volt electrons they observed?   Replying to: <DIV CLASS='Discussion_PostQuote'> Without the theory and data there should not be any consensus.</DIV>I agree, but Yevaud's statement about new forms of matter is the "accepted consensus" in astronomy today.  That makes it difficult froma skeptic's perspective because too much is "missing" for a pure skeptic to simply "jump on the band wagon".Replying to: <DIV CLASS='Discussion_PostQuote'>If you have consensus on the answer to an unsettled (unsettled meansing that  both theory and experimental data are lacking) question then there is a big problem -- it is quite likely that everyone is wrong.  Note that "theory" does not mean "hypothesis", it means a mathematical model with predictive power that has been experimentally validated.   Posted by DrRocket</DIV>How was the emission of those billion volt electrons "experimentally validated"?  How are any of the dark matter "properties"experimentally validated" in any controlled emprical test of concept? FYI it is in fact quite possible and historically quite common for the mainstream to be wrong.  In fact it happens a lot.Without emprical experimental evidence to back up the assertions about the "properties" of "new forms" of matter, these theories become "dogma", not emrpically verifiable ideas that can be duplicated in a lab.  That is a big problem from my perspective and from the perspective of most skeptics I know, including all the scientists that signed that petition.There is a significant difference here between "dogma" that must be accepted on faith and "emprical science" that can be duplicated in controlled experimentation.  That difference is the fact that emprical experimentation allows us to differentiate scientific fact, from mathematical mythos.  Without such emprical tests, new forms of "dark matter" remain speculative, unverfied, "unexplained", and unsubstanciated.  Distant uncontrolled observations cannot tell us what forms of matter exist in nature.  Only empirical *CONTROLLED* experiments can do that. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

michaelmozina · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>But there is total consensus.  The consensus is "we don't know" what dark matter is or if it is, but we do know that we don't see enough regular matter to account for orbits that we see. </DIV>Well sort of, but not exactly.  I don't have a problem with MACHO brands of "dark matter" theory, but the assertion that a new "form" of matter is necessary to explain these phenomenon is a whole different issue.  There are fundamental disagreements about SUSY oriented brands of "dark matter", and SUSY theory is itself a *NON STANDARD* (non mainstream) variation of particle physics theory.  SUSY theories are *NOT* "mainstream" within the particle physics community, and not a single emprical test yet supports these types of particles.    It would be better to say that our current theories fail to account for these observations.  Period.Replying to: <DIV CLASS='Discussion_PostQuote'>You will only see consensus in physics when there is a solid explanation backed by solid theory that has experimental verification.[/QUOTEI'm sure that's true, but the notion that a new form of matter is required to explain distant galactic observations has become a "consensus" even *without* such emprical evidence.    What emprical observational evidence lead NASA to conclude that "dark matter" had anything to do with those 300-800 billion volt electrons they observed?   Replying to: <DIV CLASS='Discussion_PostQuote'> Without the theory and data there should not be any consensus.</DIV>I agree, but Yevaud's statement about new forms of matter is the "accepted consensus" in astronomy today.  That makes it difficult froma skeptic's perspective because too much is "missing" for a pure skeptic to simply "jump on the band wagon".Replying to: <DIV CLASS='Discussion_PostQuote'>If you have consensus on the answer to an unsettled (unsettled meansing that  both theory and experimental data are lacking) question then there is a big problem -- it is quite likely that everyone is wrong.  Note that "theory" does not mean "hypothesis", it means a mathematical model with predictive power that has been experimentally validated.   Posted by DrRocket</DIV>How was the emission of those billion volt electrons "experimentally validated"?  How are any of the dark matter "properties"experimentally validated" in any controlled emprical test of concept? FYI it is in fact quite possible and historically quite common for the mainstream to be wrong.  In fact it happens a lot.Without emprical experimental evidence to back up the assertions about the "properties" of "new forms" of matter, these theories become "dogma", not emrpically verifiable ideas that can be duplicated in a lab.  That is a big problem from my perspective and from the perspective of most skeptics I know, including all the scientists that signed that petition.There is a significant difference here between "dogma" that must be accepted on faith and "emprical science" that can be duplicated in controlled experimentation.  That difference is the fact that emprical experimentation allows us to differentiate scientific fact, from mathematical mythos.  Without such emprical tests, new forms of "dark matter" remain speculative, unverfied, "unexplained", and unsubstanciated.  Distant uncontrolled observations cannot tell us what forms of matter exist in nature.  Only empirical *CONTROLLED* experiments can do that. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

michaelmozina · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>But there is total consensus.  The consensus is "we don't know" what dark matter is or if it is, but we do know that we don't see enough regular matter to account for orbits that we see. </DIV>Well sort of, but not exactly.  I don't have a problem with MACHO brands of "dark matter" theory, but the assertion that a new "form" of matter is necessary to explain these phenomenon is a whole different issue.  There are fundamental disagreements about SUSY oriented brands of "dark matter", and SUSY theory is itself a *NON STANDARD* (non mainstream) variation of particle physics theory.  SUSY theories are *NOT* "mainstream" within the particle physics community, and not a single emprical test yet supports these types of particles.    It would be better to say that our current theories fail to account for these observations.  Period.Replying to: <DIV CLASS='Discussion_PostQuote'>You will only see consensus in physics when there is a solid explanation backed by solid theory that has experimental verification.[/QUOTEI'm sure that's true, but the notion that a new form of matter is required to explain distant galactic observations has become a "consensus" even *without* such emprical evidence.    What emprical observational evidence lead NASA to conclude that "dark matter" had anything to do with those 300-800 billion volt electrons they observed?   Replying to: <DIV CLASS='Discussion_PostQuote'> Without the theory and data there should not be any consensus.</DIV>I agree, but Yevaud's statement about new forms of matter is the "accepted consensus" in astronomy today.  That makes it difficult froma skeptic's perspective because too much is "missing" for a pure skeptic to simply "jump on the band wagon".Replying to: <DIV CLASS='Discussion_PostQuote'>If you have consensus on the answer to an unsettled (unsettled meansing that  both theory and experimental data are lacking) question then there is a big problem -- it is quite likely that everyone is wrong.  Note that "theory" does not mean "hypothesis", it means a mathematical model with predictive power that has been experimentally validated.   Posted by DrRocket</DIV>How was the emission of those billion volt electrons "experimentally validated"?  How are any of the dark matter "properties"experimentally validated" in any controlled emprical test of concept? FYI it is in fact quite possible and historically quite common for the mainstream to be wrong.  In fact it happens a lot.Without emprical experimental evidence to back up the assertions about the "properties" of "new forms" of matter, these theories become "dogma", not emrpically verifiable ideas that can be duplicated in a lab.  That is a big problem from my perspective and from the perspective of most skeptics I know, including all the scientists that signed that petition.There is a significant difference here between "dogma" that must be accepted on faith and "emprical science" that can be duplicated in controlled experimentation.  That difference is the fact that emprical experimentation allows us to differentiate scientific fact, from mathematical mythos.  Without such emprical tests, new forms of "dark matter" remain speculative, unverfied, "unexplained", and unsubstanciated.  Distant uncontrolled observations cannot tell us what forms of matter exist in nature.  Only empirical *CONTROLLED* experiments can do that. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

yevaud · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I'm going to give DrRocket credit for pointing out here that "dark matter" cannot possibly be "imaged".  The best you might be able to claim from these image is that "missing mass" has been tentatively mapped out based on various lensing techniques and other sorts of technologies.  You cannot use such images to suggest that "dark matter" has been imaged. Posted by michaelmozina</DIV>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I'm going to give DrRocket credit for pointing out here that "dark matter" cannot possibly be "imaged".  The best you might be able to claim from these image is that "missing mass" has been tentatively mapped out based on various lensing techniques and other sorts of technologies.  You cannot use such images to suggest that "dark matter" has been imaged. Posted by michaelmozina</DIV>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I'm going to give DrRocket credit for pointing out here that "dark matter" cannot possibly be "imaged".  The best you might be able to claim from these image is that "missing mass" has been tentatively mapped out based on various lensing techniques and other sorts of technologies.  You cannot use such images to suggest that "dark matter" has been imaged. Posted by michaelmozina</DIV>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>I'm going to give DrRocket credit for pointing out here that "dark matter" cannot possibly be "imaged".  The best you might be able to claim from these image is that "missing mass" has been tentatively mapped out based on various lensing techniques and other sorts of technologies.  You cannot use such images to suggest that "dark matter" has been imaged. Posted by michaelmozina</DIV>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. Posted by yevaud</DIV>This is not a matter of semantics or terminology.  It is more fundamental than that.  I don't really worry about semantics and terminology -- it is not important.  A rose by any other name .....But it is important to note that dark matter has not been imaged.  If it had been imaged we would know quite a bit more about it than we do.  We would, know that it does interact with some force, presumably the electromagnetic force, to produce an image and that fact alone would exclude the hypothesis that dark matter is an exotic form of matter that has no such interactions and that has never been directly detected.  If it had been imaged we would have have a precise description of the location and distribution of some quantity of it. If it had been imaged we would be on much firmer ground in asserting the very existence of a new form of matter, called "dark".  We have a whole zoo of particles from our theories of high-energy physics and it seems that dark matter is composed of "none of the above", so any kind of image that could shel light on that conundrum would be not only appreciated, but celebrated.  But as of now there is no joy in Mudville, everybody has struck out.  All that we have is inference based on what appear to be gravitational effects that we can't explain without invoking some unseen source.  That is indirect evidence, not an image of a new form of matter.  I will admit that as more and more indirect evidence mounts up, the case is getting stronger and stronger for dark matter, but we still do not have direct evidence, and we don't know what it is.   Indirect evidence needs to be carefully evaluated because it is subject to multiple interpretations.  Some may be valid, and some not.  It is a mistake to reach conclusion too hastily from indirect evidence.  One of my major problems with the EU community is their tendancy to reach outlandish conclusions from images that simply are not relevant to the issues at hand.  That is perhaps an extreme example of the problem of jumping to conclusions on the basis of very indirect evidence.  But I feel a need to be consistent in the demand that proof for a physical theory be backed up by the strongest possible combination of direct observation, solid theory, and careful evaluation of all indirect evidence.  One ought not mis-label any of the three elements.  We have not imaged anything coming from a singularity in a black hole either.  The predicted singularity is quite far beyond the event horizon.  The jets that we do see are the result of global properties of the black hole, mass, spin, and charge, and not just of the singularity.  The jets are controlled by the state of the matter as it approaches the event horizon and not the singularity itself.  We have excellent evidence for the existence of black holes.  We don't know if a singularity exists within the black hole or not.  A singularity is predicted by general relativity.  But the singularity is really a statement that general relativity breaks down, probably due to quantum effects and the inconsistency of general relativity as a theory with quantum theory.  A singularity is a region in the model of space-time in which the curvature is infinite -- does not exist.  In any case the existence of a singularity is a statement that general relativity has ceased to work, a mathematical statement rather than a physical statement.  My quibble here is not semantics.  It is serious physics.  We know nothing of singularities, including whether or not they exist (note that I do think the evidence for the existence of black holes is conclusive, but the existence of black holes is distinct from the existence of singularities).   It is an important question, and lying as it does at the juncture of quantum theory and general reltivity it may be the most profound open question in physics.I don't know what really happens where we predict singularities, or whether or not they exist physically.  Neither does anyone else.  Not Penrose.  Not Witten. Not Hawking.  Not Maldecena,  Not Thorne.  But everybody would like to know.   Anybody who can answer this question will get an immediate all-expenses paid trip to Stockholm.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. Posted by yevaud</DIV>This is not a matter of semantics or terminology.  It is more fundamental than that.  I don't really worry about semantics and terminology -- it is not important.  A rose by any other name .....But it is important to note that dark matter has not been imaged.  If it had been imaged we would know quite a bit more about it than we do.  We would, know that it does interact with some force, presumably the electromagnetic force, to produce an image and that fact alone would exclude the hypothesis that dark matter is an exotic form of matter that has no such interactions and that has never been directly detected.  If it had been imaged we would have have a precise description of the location and distribution of some quantity of it. If it had been imaged we would be on much firmer ground in asserting the very existence of a new form of matter, called "dark".  We have a whole zoo of particles from our theories of high-energy physics and it seems that dark matter is composed of "none of the above", so any kind of image that could shel light on that conundrum would be not only appreciated, but celebrated.  But as of now there is no joy in Mudville, everybody has struck out.  All that we have is inference based on what appear to be gravitational effects that we can't explain without invoking some unseen source.  That is indirect evidence, not an image of a new form of matter.  I will admit that as more and more indirect evidence mounts up, the case is getting stronger and stronger for dark matter, but we still do not have direct evidence, and we don't know what it is.   Indirect evidence needs to be carefully evaluated because it is subject to multiple interpretations.  Some may be valid, and some not.  It is a mistake to reach conclusion too hastily from indirect evidence.  One of my major problems with the EU community is their tendancy to reach outlandish conclusions from images that simply are not relevant to the issues at hand.  That is perhaps an extreme example of the problem of jumping to conclusions on the basis of very indirect evidence.  But I feel a need to be consistent in the demand that proof for a physical theory be backed up by the strongest possible combination of direct observation, solid theory, and careful evaluation of all indirect evidence.  One ought not mis-label any of the three elements.  We have not imaged anything coming from a singularity in a black hole either.  The predicted singularity is quite far beyond the event horizon.  The jets that we do see are the result of global properties of the black hole, mass, spin, and charge, and not just of the singularity.  The jets are controlled by the state of the matter as it approaches the event horizon and not the singularity itself.  We have excellent evidence for the existence of black holes.  We don't know if a singularity exists within the black hole or not.  A singularity is predicted by general relativity.  But the singularity is really a statement that general relativity breaks down, probably due to quantum effects and the inconsistency of general relativity as a theory with quantum theory.  A singularity is a region in the model of space-time in which the curvature is infinite -- does not exist.  In any case the existence of a singularity is a statement that general relativity has ceased to work, a mathematical statement rather than a physical statement.  My quibble here is not semantics.  It is serious physics.  We know nothing of singularities, including whether or not they exist (note that I do think the evidence for the existence of black holes is conclusive, but the existence of black holes is distinct from the existence of singularities).   It is an important question, and lying as it does at the juncture of quantum theory and general reltivity it may be the most profound open question in physics.I don't know what really happens where we predict singularities, or whether or not they exist physically.  Neither does anyone else.  Not Penrose.  Not Witten. Not Hawking.  Not Maldecena,  Not Thorne.  But everybody would like to know.   Anybody who can answer this question will get an immediate all-expenses paid trip to Stockholm.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. Posted by yevaud</DIV>This is not a matter of semantics or terminology.  It is more fundamental than that.  I don't really worry about semantics and terminology -- it is not important.  A rose by any other name .....But it is important to note that dark matter has not been imaged.  If it had been imaged we would know quite a bit more about it than we do.  We would, know that it does interact with some force, presumably the electromagnetic force, to produce an image and that fact alone would exclude the hypothesis that dark matter is an exotic form of matter that has no such interactions and that has never been directly detected.  If it had been imaged we would have have a precise description of the location and distribution of some quantity of it. If it had been imaged we would be on much firmer ground in asserting the very existence of a new form of matter, called "dark".  We have a whole zoo of particles from our theories of high-energy physics and it seems that dark matter is composed of "none of the above", so any kind of image that could shel light on that conundrum would be not only appreciated, but celebrated.  But as of now there is no joy in Mudville, everybody has struck out.  All that we have is inference based on what appear to be gravitational effects that we can't explain without invoking some unseen source.  That is indirect evidence, not an image of a new form of matter.  I will admit that as more and more indirect evidence mounts up, the case is getting stronger and stronger for dark matter, but we still do not have direct evidence, and we don't know what it is.   Indirect evidence needs to be carefully evaluated because it is subject to multiple interpretations.  Some may be valid, and some not.  It is a mistake to reach conclusion too hastily from indirect evidence.  One of my major problems with the EU community is their tendancy to reach outlandish conclusions from images that simply are not relevant to the issues at hand.  That is perhaps an extreme example of the problem of jumping to conclusions on the basis of very indirect evidence.  But I feel a need to be consistent in the demand that proof for a physical theory be backed up by the strongest possible combination of direct observation, solid theory, and careful evaluation of all indirect evidence.  One ought not mis-label any of the three elements.  We have not imaged anything coming from a singularity in a black hole either.  The predicted singularity is quite far beyond the event horizon.  The jets that we do see are the result of global properties of the black hole, mass, spin, and charge, and not just of the singularity.  The jets are controlled by the state of the matter as it approaches the event horizon and not the singularity itself.  We have excellent evidence for the existence of black holes.  We don't know if a singularity exists within the black hole or not.  A singularity is predicted by general relativity.  But the singularity is really a statement that general relativity breaks down, probably due to quantum effects and the inconsistency of general relativity as a theory with quantum theory.  A singularity is a region in the model of space-time in which the curvature is infinite -- does not exist.  In any case the existence of a singularity is a statement that general relativity has ceased to work, a mathematical statement rather than a physical statement.  My quibble here is not semantics.  It is serious physics.  We know nothing of singularities, including whether or not they exist (note that I do think the evidence for the existence of black holes is conclusive, but the existence of black holes is distinct from the existence of singularities).   It is an important question, and lying as it does at the juncture of quantum theory and general reltivity it may be the most profound open question in physics.I don't know what really happens where we predict singularities, or whether or not they exist physically.  Neither does anyone else.  Not Penrose.  Not Witten. Not Hawking.  Not Maldecena,  Not Thorne.  But everybody would like to know.   Anybody who can answer this question will get an immediate all-expenses paid trip to Stockholm.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>One thing that always used to really annoy me was when people narrowly focussed on terminology as a "gotya" moment.  If we see via gravitational lensing (as in this case), or on directly imaged large masses, the gravitational effect of Dark Matter, then it has, insofar as is possible, been "imaged."In short, accept as I said, "this is good as it gets."  This is no different than when it is said a Singularity has been imaged via the visible polar jets, but it really hasn't - the Singularity is forever invisible to us, and is known only via it's spectacular effects.It's the same thing. Posted by yevaud</DIV>This is not a matter of semantics or terminology.  It is more fundamental than that.  I don't really worry about semantics and terminology -- it is not important.  A rose by any other name .....But it is important to note that dark matter has not been imaged.  If it had been imaged we would know quite a bit more about it than we do.  We would, know that it does interact with some force, presumably the electromagnetic force, to produce an image and that fact alone would exclude the hypothesis that dark matter is an exotic form of matter that has no such interactions and that has never been directly detected.  If it had been imaged we would have have a precise description of the location and distribution of some quantity of it. If it had been imaged we would be on much firmer ground in asserting the very existence of a new form of matter, called "dark".  We have a whole zoo of particles from our theories of high-energy physics and it seems that dark matter is composed of "none of the above", so any kind of image that could shel light on that conundrum would be not only appreciated, but celebrated.  But as of now there is no joy in Mudville, everybody has struck out.  All that we have is inference based on what appear to be gravitational effects that we can't explain without invoking some unseen source.  That is indirect evidence, not an image of a new form of matter.  I will admit that as more and more indirect evidence mounts up, the case is getting stronger and stronger for dark matter, but we still do not have direct evidence, and we don't know what it is.   Indirect evidence needs to be carefully evaluated because it is subject to multiple interpretations.  Some may be valid, and some not.  It is a mistake to reach conclusion too hastily from indirect evidence.  One of my major problems with the EU community is their tendancy to reach outlandish conclusions from images that simply are not relevant to the issues at hand.  That is perhaps an extreme example of the problem of jumping to conclusions on the basis of very indirect evidence.  But I feel a need to be consistent in the demand that proof for a physical theory be backed up by the strongest possible combination of direct observation, solid theory, and careful evaluation of all indirect evidence.  One ought not mis-label any of the three elements.  We have not imaged anything coming from a singularity in a black hole either.  The predicted singularity is quite far beyond the event horizon.  The jets that we do see are the result of global properties of the black hole, mass, spin, and charge, and not just of the singularity.  The jets are controlled by the state of the matter as it approaches the event horizon and not the singularity itself.  We have excellent evidence for the existence of black holes.  We don't know if a singularity exists within the black hole or not.  A singularity is predicted by general relativity.  But the singularity is really a statement that general relativity breaks down, probably due to quantum effects and the inconsistency of general relativity as a theory with quantum theory.  A singularity is a region in the model of space-time in which the curvature is infinite -- does not exist.  In any case the existence of a singularity is a statement that general relativity has ceased to work, a mathematical statement rather than a physical statement.  My quibble here is not semantics.  It is serious physics.  We know nothing of singularities, including whether or not they exist (note that I do think the evidence for the existence of black holes is conclusive, but the existence of black holes is distinct from the existence of singularities).   It is an important question, and lying as it does at the juncture of quantum theory and general reltivity it may be the most profound open question in physics.I don't know what really happens where we predict singularities, or whether or not they exist physically.  Neither does anyone else.  Not Penrose.  Not Witten. Not Hawking.  Not Maldecena,  Not Thorne.  But everybody would like to know.   Anybody who can answer this question will get an immediate all-expenses paid trip to Stockholm.   <div class="Discussion_UserSignature"> </div>

yevaud · Nov 30, 2008

Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Nov 30, 2008

Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  Posted by yevaud</DIV>Certainly I appreciate it.  I just disagree with it.  I disagree with it for quite different reasons than does Mozina.  This is most definitely NOT an alliance between him and me.  And I did not pile onto you about semantics.  I believe that I described precisely why I disagree with your characterization of "imaging" on physical and not semantic grounds.  If dark matter had been "imaged" then I would take the evidence for its existence to be quite a bit more conclusive than I think it is.  That is a physical, not a semantic, statement. And while my degrees are not in physics, I have quite a bit of professional experience with physicists, physics, and in fact with imaging.  So don't try to hang the argument on degrees.  That simply is not appropriate in any case.If you watched two physicists almost come to blows over something like this, then I submit that either the issue was more than semantics (likely) or else the two physicists were being awfully myopic and petty (possible but less likely).If dark matter investigators really feel that dark matter has been imaged then I expect to hear that statement made Wednesday morning.  I will be  paying attention to see if such is the case (and asking questions if the need arises).  If so I will report back.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  Posted by yevaud</DIV>Certainly I appreciate it.  I just disagree with it.  I disagree with it for quite different reasons than does Mozina.  This is most definitely NOT an alliance between him and me.  And I did not pile onto you about semantics.  I believe that I described precisely why I disagree with your characterization of "imaging" on physical and not semantic grounds.  If dark matter had been "imaged" then I would take the evidence for its existence to be quite a bit more conclusive than I think it is.  That is a physical, not a semantic, statement. And while my degrees are not in physics, I have quite a bit of professional experience with physicists, physics, and in fact with imaging.  So don't try to hang the argument on degrees.  That simply is not appropriate in any case.If you watched two physicists almost come to blows over something like this, then I submit that either the issue was more than semantics (likely) or else the two physicists were being awfully myopic and petty (possible but less likely).If dark matter investigators really feel that dark matter has been imaged then I expect to hear that statement made Wednesday morning.  I will be  paying attention to see if such is the case (and asking questions if the need arises).  If so I will report back.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  Posted by yevaud</DIV>Certainly I appreciate it.  I just disagree with it.  I disagree with it for quite different reasons than does Mozina.  This is most definitely NOT an alliance between him and me.  And I did not pile onto you about semantics.  I believe that I described precisely why I disagree with your characterization of "imaging" on physical and not semantic grounds.  If dark matter had been "imaged" then I would take the evidence for its existence to be quite a bit more conclusive than I think it is.  That is a physical, not a semantic, statement. And while my degrees are not in physics, I have quite a bit of professional experience with physicists, physics, and in fact with imaging.  So don't try to hang the argument on degrees.  That simply is not appropriate in any case.If you watched two physicists almost come to blows over something like this, then I submit that either the issue was more than semantics (likely) or else the two physicists were being awfully myopic and petty (possible but less likely).If dark matter investigators really feel that dark matter has been imaged then I expect to hear that statement made Wednesday morning.  I will be  paying attention to see if such is the case (and asking questions if the need arises).  If so I will report back.   <div class="Discussion_UserSignature"> </div>

DrRocket · Nov 30, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Oh Jesus Christ.  You people are Physics snobs and neither one of you have degrees in it.  Ever sat in on a conference in a Physics Department?  I have.  Repeatedly.  I have quite literally watched my advisor almost come to blows with another Professor.Is this all about semantical nuances?  Apparently so.  This is a Goddamn message board, not a Department in a University, for Christsakes.  "Imaged" is a catch-all used whether something has been imaged directly or indirectly (e.g. by it's quite visible effects).[Dismayed and Disgusted] Consider this, DR and Mike: the EU thread was moved to "Unexplained" in part because the two of you spent months bickering about nuances.  You just both piled onto me about semantics, and cared a Rat's ass about the facts of the matter.  Both of you.  It takes two toTango.Damnit.Something has been "imaged" via it's indirect but highly visible effects.  Shall I turn a twenty word post into a three-thousand word detailed descriptive post merely to accomodate you?I don't freaking think so. As Omar Bradley once said, "I trust you don't think I am angry, but I wish you to understand I am Goddamn well incensed." End Discussion. Doc, if you don't appreciate what I just posted, you may PM me at the 'Port; Mike, you may email me at Daystrom5@gmail.com  Posted by yevaud</DIV>Certainly I appreciate it.  I just disagree with it.  I disagree with it for quite different reasons than does Mozina.  This is most definitely NOT an alliance between him and me.  And I did not pile onto you about semantics.  I believe that I described precisely why I disagree with your characterization of "imaging" on physical and not semantic grounds.  If dark matter had been "imaged" then I would take the evidence for its existence to be quite a bit more conclusive than I think it is.  That is a physical, not a semantic, statement. And while my degrees are not in physics, I have quite a bit of professional experience with physicists, physics, and in fact with imaging.  So don't try to hang the argument on degrees.  That simply is not appropriate in any case.If you watched two physicists almost come to blows over something like this, then I submit that either the issue was more than semantics (likely) or else the two physicists were being awfully myopic and petty (possible but less likely).If dark matter investigators really feel that dark matter has been imaged then I expect to hear that statement made Wednesday morning.  I will be  paying attention to see if such is the case (and asking questions if the need arises).  If so I will report back.   <div class="Discussion_UserSignature"> </div>

yevaud · Dec 1, 2008

Argh.Sorry.  I was in a minor altercation wih a fool last evening (rear-ended the corporate vehicle, lied immediately to the Police - fortunately I was with two witnesses), came in the door full of piss and vinegar, and saw Mike's post.  Boy, was I ticked!  I believe the quote (for any occasion) is "post in anger, repent at leisure."  My apologies, Mea Culpa I am Human.You know, we are trapped by our limitations.  This is the best we can do, to explain a vast mystery. [And seriously, the two were held back by others due to a heated argument over semantics] <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Dec 1, 2008

Argh.Sorry.  I was in a minor altercation wih a fool last evening (rear-ended the corporate vehicle, lied immediately to the Police - fortunately I was with two witnesses), came in the door full of piss and vinegar, and saw Mike's post.  Boy, was I ticked!  I believe the quote (for any occasion) is "post in anger, repent at leisure."  My apologies, Mea Culpa I am Human.You know, we are trapped by our limitations.  This is the best we can do, to explain a vast mystery. [And seriously, the two were held back by others due to a heated argument over semantics] <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Dec 1, 2008

Argh.Sorry.  I was in a minor altercation wih a fool last evening (rear-ended the corporate vehicle, lied immediately to the Police - fortunately I was with two witnesses), came in the door full of piss and vinegar, and saw Mike's post.  Boy, was I ticked!  I believe the quote (for any occasion) is "post in anger, repent at leisure."  My apologies, Mea Culpa I am Human.You know, we are trapped by our limitations.  This is the best we can do, to explain a vast mystery. [And seriously, the two were held back by others due to a heated argument over semantics] <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

yevaud · Dec 1, 2008

Argh.Sorry.  I was in a minor altercation wih a fool last evening (rear-ended the corporate vehicle, lied immediately to the Police - fortunately I was with two witnesses), came in the door full of piss and vinegar, and saw Mike's post.  Boy, was I ticked!  I believe the quote (for any occasion) is "post in anger, repent at leisure."  My apologies, Mea Culpa I am Human.You know, we are trapped by our limitations.  This is the best we can do, to explain a vast mystery. [And seriously, the two were held back by others due to a heated argument over semantics] <div class="Discussion_UserSignature"> Differential Diagnosis: "I am both amused and annoyed that you think I should be less stubborn than you are." </div>

DrRocket · Dec 1, 2008

Replying to: <DIV CLASS='Discussion_PostQuote'>Argh.Sorry.  I was in a minor altercation wih a fool last evening (rear-ended the corporate vehicle, lied immediately to the Police - fortunately I was with two witnesses), came in the door full of piss and vinegar, and saw Mike's post.  Boy, was I ticked!  I believe the quote (for any occasion) is "post in anger, repent at leisure."  My apologies, Mea Culpa I am Human.You know, we are trapped by our limitations.  This is the best we can do, to explain a vast mystery. [And seriously, the two were held back by others due to a heated argument over semantics] Posted by yevaud</DIV>Sorry to hear you had a bad day (a very bad day in some regards).  Fools can do that.  But remember the motto illlegitimi non carborundum.  We all  have bad days and they are forgivable.Do you happen to remember the subject of the semantic fist fight ?  I have to admit never having seen such a thing in an academic environment.  I have seen it elsewhere, but always the fundamental issue, sometimes not clearly stated, was money.Sometimes arguments that appear to be about concrete issues turn out to be semantic.  And sometimes issues that appear to be semantic turn out to have real substance.  And sometimes, it takes prolonged discussion to determine what the situation really is.  That exchange that you referenced between Mr. Mozina and me started out being concrete, looked at one stage as though it might be semantic, and finally revealed itself as being about fundamental physics, and not semantics.  The disagreement in that case was over magnetic reconnection, the source of the agreement was and remains rooted in basic understanding of electrodynamics, and it was never resolved (neither of us changed our minds and I don't think are likely to).Sometimes in a forum such as this semantic difficulties can arise because of the use of terminology that has a precise meaning within a speciality, but a somewhat different meaning to a general English-speaking audience.  Terms that are understood in a technical context may be misinterpreted by others, and even specialists when speaking to a mixed audience may not understand how different people understand different terms.So, in the interest of clear communication, I will define "to image" as I understand the term in the present scientific context.  To image is to produce a representation of a material or phenomenon, usually a visual representation, that describes the position and distribution of that material or phenomenon, and often additional information regarding properties such as density, temperature or internal structure (this list is not inclusive).  The information that is gathered to produce the image may and often is collected from electromagnetic emission, but might also be based on electromagnetic absorption, sonic waves (reflection, through transmission, pitch-catch), stress/strain sensors, or any other physical data.  It may be presented in raw form or processed, as with computed tomography.  But whatever the source or type of information used to produce the image, the information is produced by some direct interaction between the item being imaged and the energy detected by the sensor that gathers the relevant data.  I do not consider an image of item A to be an image of item B showing an anomaly that cannot be explained by what is seen in the image of B and an inference therefrom that A is present in the background.  This does not exclude negative images -- I do accept as an image the detection of lack of energy where energy would be seen if there were not an absorber acting.  So I do think it is possible, in principle, to image a black hole (black hole here meaning the boundary of the event horizon and not the hypothesized singularity) just as one can produce an image of a shadow.  I think it possible, again in principle, to produce an image based on gravitational waves, but not with our current technology, which has thus far not been able to directly detect such waves.I do not consider the various photographs of ghosts that have been published to be images of ghosts or proof of the existence of such things.  It takes more than the precipitation of some silver from solution to be an image in the scientific sense described above.  <div class="Discussion_UserSignature"> </div>

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