It is a test of Newtonian gravity. In fact it is not even a test of newtonian gravity, but just a test of the centripetal force = newtonian gravity law. You can imagine either to be wrong, or inaccurate.
They found that gravity "breakdown" at some small acceleration scale. The problem with "acceleration scales" breakdown is that 'acceleration', as defined in their paper, is not a (jargon!) covariant statement. In other words, they are saying acceleration with respect to the center of mass of the cluster. But of course a different observer, say somebody flying in a spaceship next to the cluster, will measure a different acceleration wrt to him. This means that the apparent breakdown is depends on coordinates you choose, but physics should not depend on coordinates. While there is no proof one cannot formulate some screwy theory which can fit this observations and be also coordinate invariant, nobody has done it yet. (It's called MOND, and somewhere along this/. article somebody has posted the links.)
But it is true that the so-called "small acceleration" breakdown at about 10^{-8} cm/s is an annoying thing that won't go away. The Pioneer 10 spacecraft has the same anomaly. The paper you cited is a increase in the "scale" to globular cluster scale, which is interesting, but you can imagine (as the paper itself noted) many things can explain it other than modification to gravity. (the paper suggested perhaps some objects are actually binaries, so their counting of mass may be wrong.)
The point of the paper is that while you can argue away the same "breakdown" in newtonian physics in galaxy scales by putting in dark matter, you cannot do the same with globular clusters, since DM is not known to cluster around such objects. This is interesting, but we'll wait and see:).
But anyway, these are consider tests at "small scales":). The large scales I mean, bigger than Galaxy Cluster scales...
THe article you linked to is actually full of inaccuracies. Take the bit about quasars for example.
Very accurate positional measurements by radio telescopes (using very long baseline interferometry) revealed the astounding fact that some quasars appeared to be expanding at up to ten times the speed of light. This was in complete violation of the accepted laws of Einsteinian physics
This is an argument from incredulity. IN fact, the apparent superluminal expansion is explained neatly away by the fact that the jet of the quasars are pointed right at us. It is a nice little problem in relativity to show this is true.
Here is another one: The orthodox view is that quasars are just abnormal (e.g. superluminous) galaxies and that they can only have a redshift caused by velocity. Arp drew attention to quasars interlinking with galaxies. But a large body of opinion now holds that galaxies can violate the redshift distance-relation. It is the most peculiar galaxies, those most like quasars, which offer the most compelling evidence for non-velocity redshift.
This is an argument from false authority. Most galaxies close to us obey the Hubble Law to a great accuracy (those further away has a distinct deviation from velocity-distance diagram, but they are exactly as predicted by general relativity with 75% dark energy). Peculiar velocity is a contribution to red-shift, that's true, but the contribution is very small. In fact, it is a known systematic that can often be removed. (THey lead to so-called fingers of god in redshift-luminosity diagrams, i.e. a small 'stretching' of otherwise homogenous distribution of galaxies.)
It is good to entertain heretical ideas, but they have to pass the same stringent tests as those which you called "scientific dogma". Science has no dogma, just tested ideas. Any of them can fall, but if you want to overturn it, you better come up with a better one, not just a different one.
I will end this with a fallacy of my own:), that's it, a personal attack : becareful of Arp's ideas, many (if not all) of them are plain wrong.
But basically, the weighing of the matter (as quoted in the article) does not depend on just mass, but a quantity called "mass-energy". It is true that a particle moving at very high speeds seemed to gain "mass". But depending on observers travelling at different velocities relative to this particle, each will see a different mass. However this particle, irregardless of its velocity, will have a consistent "mass-energy" to all observers. In other words, everybody in the unvierse can agree on the amount of "mass-energy" each particle have. So there is a consistent picture of weighing the amount of mass of the universe.
That is the beauty of Einstein's Special Relativity, which is to unify mass and energy into a (jargon warning) relativistically consistent picture of mass-energy.
This is actually a very good cautionary tale. The mysterious "massive unknown planet" is the first case of "dark matter". Of course it went away after GR was discovered by Einstein.
Who knows if the current mess of missing matter would not go away if we have gain deeper insight into the nature of gravity?
Yes, modifications to Gravity is one of the way to explain away dark matter/dark energy problems. It is an active field of research, but it is a hard one.
The problem is that while there is no direct tests of gravity at very large scales, there are a lot of "consistency" checks of the various cosmological observations (say of the cosmic microwave background anisotropies) that you have to satisfy.
In other words, there is no proof that such theories of modified gravity do not exist. But to find one is really hard.
Gravity is only tested to solar system scales, and in an indirect way, galactic cluster lensing effects.
At very large scales, say of the Hubble radius, we have no tests of gravity. Cosmological models are almost always based on the belief that Gravity works at the very large scales, an extrapolation of many orders of magnitude. There is no proof that this is a valid extrapolation, and there are hints that they are not. (Like they lead to an extremely highly unlike situation. Check out This Talk )
Large scale modifications of gravity may affect the smaller scales, but these effects are naturally suppressed (you can cook up theories where they are not suppressed, but then it is not "large scale" modifications anymore). So to discover these effects are hard.
We have experimental constraints of course, but they are not very strong.
Topology has been used in applications on particle physics, notably it is an extremely useful tools in investigating symmetry breaking and the generation of topological defects like monopoloes and strings.
If you have a chickenshit and useless leader in a unit, the enlisted men will try to kill him. The weapon of choice is a nade, it's called "fraggin". They don't become useless and chickenshit just because their leader is chickenshit.
Well, LIGO is an engineering test. The LIGO team is hoping against hope to detect any gravitational waves. LISA might get a better shot, but that is ways off. But then, I don't work in the field, so there.
They are sound waves in the looses sense of the word.In the sense that you have stuff (the photon-baryon fluid) and a wave is travelling through it (like sound waves travelling through air).
Gravity waves exist of course, but we have no way of detecting them yet since their signature is much much much harder to detect.
A torus (dougnut) is topologically equivalent to a square with sides identified (like the Space War).
-End Jargon-
Discontinuous or stuff like that is not really important concept. Whether you are "magically" transported or not when you reached the end is just a matter of choosing the right coordinates.
Also, curved universes do not enter the argument. Curvature is a statement on Geometry of the Universe, while being a Dougnut is a Topological Statement.Both of completely independent of each other. A Toroidal Universe can be flat (like, hey , a square with sides identified!). A curved universe can be a plain sphere.
you are right that neutrinos get a separate category on their own. That's me being sloppy.
On the other hand, I don't think the definition of darkmatter is fine as it stands. If wimps and axions are discovered by terrestrial detectors, then you begin to figure out how to classify them. You can call it detection of new physics (since wimps and axions are beyond S.M. stuff).
You hope that dark matter are not really "dark", i.e. you can see it via some interaction with non-dark matter. If you find it, then they are not "dark". In a maximally boring universe, dark matter is just that, dark and completely undetectable except through gravity. Though to prove that DM is really "dark" is almost impossible given the creativity of theorists unless one find a new model of universe which is as good but without appealing to DM.
The further away the object is from us, the greater the velocity it seems to be expanding away from us. So H=71km/s/Mpc means that for every Mpc the objet is away from us, it is flying away from us at the velocity of 71 km/s.
Astronomy/astophysics pays my bills, and I can tell you that 4.4% of baryons from WMAP really means anything that is known in particle physics as quarks, leptons, blah blah blah.
A rule of thumb is that 'baryons' in astronomy/astrophysics is anything that is in the standard model (sans the higgs.)But that's not the whole story.
"baryons" (in the 4.4% of WMAP) is classified as matter that is not "dark". "Non-dark" means it interacts with other stuff and itself beyond just pure gravitation. That includes "radiation", which is stuff that behaves relativistically, and include things like photons, neutrinos,a nd perhaps other relics.
To summarize, there is no difference between "baryons" and "baryonic matter" in astronomy.
I will not call a lepton a baryon, but I will definetely lump leptons in when I say 4.4% of ther universe is made out of baryons. it's just a matter of context, and people in the field will udnerstand that.
Really, astrophysicists are sloppy when it comes to naming stuff. So you have to be careful not to read too much into nomenclature like this, even in the era of "precision cosmology".
and naturally, modded up to +5 instead of -1 offtopic.
Re:Off-scale and zero readings are still useful
on
Columbia Coverage
·
· Score: 4, Interesting
Very good.
Also, broken telemetry readings and strength of signal can be used to determine the attitude (read : orientation, not height) of the shuttle since transmitters are usually directional.
The attitude data of the shuttle at its final seconds would be the most useful information. For example, you can use it to determine how the shuttle begin to tumble out of standard flight reentry modes.
I agree that the space elevator is a crazy idea. And I agree that resources better be spent working on more incrementally useful things.
But the space elevator will eventually be built whether you like it or not, since it is the most efficient way of getting things into space in the long run (it's the ultimate single stage to orbit vehicle since all the energy used, once the elevator is built, can be generated on the ground, not carried along.)
In addition, I find discussions on/. of the shuttle useful. I am still talking about the shuttle with my friends.
Slashdot Mirror
It is a test of Newtonian gravity. In fact it is not even a test of newtonian gravity, but just a test of the centripetal force = newtonian gravity law. You can imagine either to be wrong, or inaccurate.
/. article somebody has posted the links.)
:).
:). The large scales I mean, bigger than Galaxy Cluster scales...
They found that gravity "breakdown" at some small acceleration scale. The problem with "acceleration scales" breakdown is that 'acceleration', as defined in their paper, is not a (jargon!) covariant statement. In other words, they are saying acceleration with respect to the center of mass of the cluster. But of course a different observer, say somebody flying in a spaceship next to the cluster, will measure a different acceleration wrt to him. This means that the apparent breakdown is depends on coordinates you choose, but physics should not depend on coordinates. While there is no proof one cannot formulate some screwy theory which can fit this observations and be also coordinate invariant, nobody has done it yet. (It's called MOND, and somewhere along this
But it is true that the so-called "small acceleration" breakdown at about 10^{-8} cm/s is an annoying thing that won't go away. The Pioneer 10 spacecraft has the same anomaly. The paper you cited is a increase in the "scale" to globular cluster scale, which is interesting, but you can imagine (as the paper itself noted) many things can explain it other than modification to gravity. (the paper suggested perhaps some objects are actually binaries, so their counting of mass may be wrong.)
The point of the paper is that while you can argue away the same "breakdown" in newtonian physics in galaxy scales by putting in dark matter, you cannot do the same with globular clusters, since DM is not known to cluster around such objects. This is interesting, but we'll wait and see
But anyway, these are consider tests at "small scales"
THe article you linked to is actually full of inaccuracies. Take the bit about quasars for example.
:
:), that's it, a personal attack : becareful of Arp's ideas, many (if not all) of them are plain wrong.
Very accurate positional measurements by radio telescopes (using very long baseline interferometry) revealed the astounding fact that some quasars appeared to be expanding at up to ten times the speed of light. This was in complete violation of the accepted laws of Einsteinian physics
This is an argument from incredulity. IN fact, the apparent superluminal expansion is explained neatly away by the fact that the jet of the quasars are pointed right at us. It is a nice little problem in relativity to show this is true.
Here is another one
The orthodox view is that quasars are just abnormal (e.g. superluminous) galaxies and that they can only have a redshift caused by velocity. Arp drew attention to quasars interlinking with galaxies. But a large body of opinion now holds that galaxies can violate the redshift distance-relation. It is the most peculiar galaxies, those most like quasars, which offer the most compelling evidence for non-velocity redshift.
This is an argument from false authority. Most galaxies close to us obey the Hubble Law to a great accuracy (those further away has a distinct deviation from velocity-distance diagram, but they are exactly as predicted by general relativity with 75% dark energy). Peculiar velocity is a contribution to red-shift, that's true, but the contribution is very small. In fact, it is a known systematic that can often be removed. (THey lead to so-called fingers of god in redshift-luminosity diagrams, i.e. a small 'stretching' of otherwise homogenous distribution of galaxies.)
It is good to entertain heretical ideas, but they have to pass the same stringent tests as those which you called "scientific dogma". Science has no dogma, just tested ideas. Any of them can fall, but if you want to overturn it, you better come up with a better one, not just a different one.
I will end this with a fallacy of my own
This argument is actually flawed.
The answer is a bit involved.
But basically, the weighing of the matter (as quoted in the article) does not depend on just mass, but a quantity called "mass-energy". It is true that a particle moving at very high speeds seemed to gain "mass". But depending on observers travelling at different velocities relative to this particle, each will see a different mass. However this particle, irregardless of its velocity, will have a consistent "mass-energy" to all observers. In other words, everybody in the unvierse can agree on the amount of "mass-energy" each particle have. So there is a consistent picture of weighing the amount of mass of the universe.
That is the beauty of Einstein's Special Relativity, which is to unify mass and energy into a (jargon warning) relativistically consistent picture of mass-energy.
The OP is stating that it may be the other way around, which is a completely valid point to make.
This is actually a very good cautionary tale. The mysterious "massive unknown planet" is the first case of "dark matter". Of course it went away after GR was discovered by Einstein.
Who knows if the current mess of missing matter would not go away if we have gain deeper insight into the nature of gravity?
We won't be all fucked :). (Though I would need to get some soon.)
In fact, large scales modifications to gravity is one of the "in" thing in cosmology right now. So there.
Yes, modifications to Gravity is one of the way to explain away dark matter/dark energy problems. It is an active field of research, but it is a hard one.
The problem is that while there is no direct tests of gravity at very large scales, there are a lot of "consistency" checks of the various cosmological observations (say of the cosmic microwave background anisotropies) that you have to satisfy.
In other words, there is no proof that such theories of modified gravity do not exist. But to find one is really hard.
Not true.
Gravity is only tested to solar system scales, and in an indirect way, galactic cluster lensing effects.
At very large scales, say of the Hubble radius, we have no tests of gravity. Cosmological models are almost always based on the belief that Gravity works at the very large scales, an extrapolation of many orders of magnitude. There is no proof that this is a valid extrapolation, and there are hints that they are not. (Like they lead to an extremely highly unlike situation. Check out This Talk )
Large scale modifications of gravity may affect the smaller scales, but these effects are naturally suppressed (you can cook up theories where they are not suppressed, but then it is not "large scale" modifications anymore). So to discover these effects are hard.
We have experimental constraints of course, but they are not very strong.
Are They going to show regular Detox scenes from now on?
War and Murder are here because it works. WOrked back then, work today. If they did not work, there would be no War and Murder.
Doesn't mean we should not try to stop War and Murder.
Topology has been used in applications on particle physics, notably it is an extremely useful tools in investigating symmetry breaking and the generation of topological defects like monopoloes and strings.
I suppose the moderation system shows its failure here.
Ppl's emotions are all caught up. Moderation requires a clear head and a steady impartial mind.
Clearly not demonstrated anywhere here in this thread.
Nice slippery slope argument.
If you have a chickenshit and useless leader in a unit, the enlisted men will try to kill him. The weapon of choice is a nade, it's called "fraggin". They don't become useless and chickenshit just because their leader is chickenshit.
Well, LIGO is an engineering test. The LIGO team is hoping against hope to detect any gravitational waves. LISA might get a better shot, but that is ways off. But then, I don't work in the field, so there.
well, yes. But that's a bit of a nitpick isn't it :).
They are sound waves in the looses sense of the word.In the sense that you have stuff (the photon-baryon fluid) and a wave is travelling through it (like sound waves travelling through air).
Gravity waves exist of course, but we have no way of detecting them yet since their signature is much much much harder to detect.
-Begin Jargon-
A torus (dougnut) is topologically equivalent to a square with sides identified (like the Space War).
-End Jargon-
Discontinuous or stuff like that is not really important concept. Whether you are "magically" transported or not when you reached the end is just a matter of choosing the right coordinates.
Also, curved universes do not enter the argument. Curvature is a statement on Geometry of the Universe, while being a Dougnut is a Topological Statement.Both of completely independent of each other. A Toroidal Universe can be flat (like, hey , a square with sides identified!). A curved universe can be a plain sphere.
you are right that neutrinos get a separate category on their own. That's me being sloppy.
On the other hand, I don't think the definition of darkmatter is fine as it stands. If wimps and axions are discovered by terrestrial detectors, then you begin to figure out how to classify them. You can call it detection of new physics (since wimps and axions are beyond S.M. stuff).
You hope that dark matter are not really "dark", i.e. you can see it via some interaction with non-dark matter. If you find it, then they are not "dark". In a maximally boring universe, dark matter is just that, dark and completely undetectable except through gravity. Though to prove that DM is really "dark" is almost impossible given the creativity of theorists unless one find a new model of universe which is as good but without appealing to DM.
sorry, bad sentence at the end. It shoudl end : it is flying away from us at the velocity of 71km/s per Mpc.
The further away the object is from us, the greater the velocity it seems to be expanding away from us. So H=71km/s /Mpc means that for every Mpc the objet is away from us, it is flying away from us at the velocity of 71 km/s.
nope.
Astronomy/astophysics pays my bills, and I can tell you that 4.4% of baryons from WMAP really means anything that is known in particle physics as quarks, leptons, blah blah blah.
A rule of thumb is that 'baryons' in astronomy/astrophysics is anything that is in the standard model (sans the higgs.)But that's not the whole story.
"baryons" (in the 4.4% of WMAP) is classified as matter that is not "dark". "Non-dark" means it interacts with other stuff and itself beyond just pure gravitation. That includes "radiation", which is stuff that behaves relativistically, and include things like photons, neutrinos,a nd perhaps other relics.
To summarize, there is no difference between "baryons" and "baryonic matter" in astronomy.
I will not call a lepton a baryon, but I will definetely lump leptons in when I say 4.4% of ther universe is made out of baryons. it's just a matter of context, and people in the field will udnerstand that.
Really, astrophysicists are sloppy when it comes to naming stuff. So you have to be careful not to read too much into nomenclature like this, even in the era of "precision cosmology".
No, unless your coffee has been artificially cooled below the temperature of the universe.
No naturally occuring cups of coffee in the universe will need any cooling from the CMB
and naturally, modded up to +5 instead of -1 offtopic.
Very good.
Also, broken telemetry readings and strength of signal can be used to determine the attitude (read : orientation, not height) of the shuttle since transmitters are usually directional.
The attitude data of the shuttle at its final seconds would be the most useful information. For example, you can use it to determine how the shuttle begin to tumble out of standard flight reentry modes.
I agree that the space elevator is a crazy idea. And I agree that resources better be spent working on more incrementally useful things.
/. of the shuttle useful. I am still talking about the shuttle with my friends.
But the space elevator will eventually be built whether you like it or not, since it is the most efficient way of getting things into space in the long run (it's the ultimate single stage to orbit vehicle since all the energy used, once the elevator is built, can be generated on the ground, not carried along.)
In addition, I find discussions on
If you don't like it, why are you here posting?