Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: syhprum on 10/02/2015 09:00:53
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A new theory about the origin of the universe seems to give us back the ether sorely missed by we old timers
http://phys.org/news/2015-02-big-quantum-equation-universe.html?utm_source=nwletter&utm_medium=email&utm_content=splt-item&utm_campaign=daily-nwletter
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No replies, few readers I thought it was a pretty thought provoking article and it was quoted on most of the science forums
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Interesting stuff, but pretty far out of my knowledge base, so I had refrained from commenting.
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No replies, few readers I thought it was a pretty thought provoking article and it was quoted on most of the science forums
Sorry, I've been busy for a couple of days. I didn't like the article at all, because it made some assertions that aren't true. For example:
Although the Big Bang singularity arises directly and unavoidably from the mathematics of general relativity
It just isn't true. And see this:
In general relativity, one possible fate of the universe is that it starts to shrink until it collapses in on itself in a big crunch and becomes an infinitely dense point once again.
This isn't true either. A gravitational field is a place where space is inhomogeneous, wherein the motion of light through space is curved, this being modelled as curved spacetime. In no sense is space falling inwards. General relativity does not predict a big crunch. I totally lost interest at this point:
The scientists propose that this fluid might be composed of gravitons—hypothetical massless particles that mediate the force of gravity.
That's not what gravity is about, and virtual particles are not real particles. There is no blizzard of particles pulling you down into you chair.
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Although the Big Bang singularity arises directly and unavoidably from the mathematics of general relativity
It just isn't true.
Right, it only arises if one assumes (roughly) homogeneity and isotropy of the universe, and only expansion occurred in the past.
And see this:
In general relativity, one possible fate of the universe is that it starts to shrink until it collapses in on itself in a big crunch and becomes an infinitely dense point once again.
This isn't true either.
Right, it assumes (roughly) homogeneity and isotropy, as well as the lack of a factor to gravity that might repel mass and energy at large scales. (We now have good reason to suspect that this factor exists.)
A gravitational field is a place where space is inhomogeneous,
This is simply not true. Many, many people have demonstrated spacetime models in general relativity that are completely homogeneous for a choice of spacial coordinates. In a physics application where one is considering the presence of objects arranged inhomogeneously (most applications), then one can say that every point of interest (out to a certain range) has a different value and direction for the gravitational field and thus is "inhomogeneous".
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No replies, few readers I thought it was a pretty thought provoking article and it was quoted on most of the science forums
This is one of those ideas that is not new and that pops up in pop science journalism from time to time. From the buzz I've seen amongst professionals, it doesn't seem to be taken seriously by the majority of cosmologists or even those working in quantum theory.
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A gravitational field is a place where space is inhomogeneous,
This is simply not true.
It is true. If the space in the room you're in was homogeneous, your pencil would not fall down. See Einstein's Leyden Address (http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html):
"...According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ‘empty space’ in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials gμν), has, I think, finally disposed of the view that space is physically empty".
Many, many people have demonstrated spacetime models in general relativity that are completely homogeneous for a choice of spacial coordinates.
Please provide a reference. Until then, note this: if they've "demonstrated" that a gravitational field is present where space is homogeneous, they've misunderstood general relativity.
In a physics application where one is considering the presence of objects arranged inhomogeneously (most applications), then one can say that every point of interest (out to a certain range) has a different value and direction for the gravitational field and thus is "inhomogeneous".
No problem. But note that if you could only measure one value and direction for the gravitational field, such as in the room you're in, this does not imply that the space in that room is homogeneous. Instead it signifies that the inhomogeneity is uniform.
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A gravitational field is a place where space is inhomogeneous,
This is simply not true.
It is true. If the space in the room you're in was homogeneous, your pencil would not fall down. See Einstein's Leyden Address (http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html):
It is very interesting to produce a quotation to a somewhat public address of Einstein's rather than any scientific work he did, but it does not answer the question. I suspect that, if we asked you to produce the trajectory of a pencil using inhomogeneous space, you could not do so.
Regardless, you seem to be entirely ignoring or ignorant of Einstein's many homogeneous spacetime solutions to the Einstein field equations that he offered as cosmological models before and after the date of that address. If you are ignorant, then that's one thing: you can look them up and see for yourself. If you are ignoring them, then one has to question the methodology of someone who chooses to support a point in physics on a single (translates) passage rather than the bulk of scientific work.
Many, many people have demonstrated spacetime models in general relativity that are completely homogeneous for a choice of spacial coordinates.
Please provide a reference.
Really?
How about:
Einstein, Albert (1917), "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie", Königlich Preussische Akademie der Wissenschaften
Or good textbooks that go into details of many such models:
Rich, James, Fundamentals of Cosmology, Springer, 2nd Edition, 2010
Peebles, PJE, Principles of Physical Cosmology, Princeton University Press (that includes many different models), 1993
Pretty much every professional website that discusses cosmology presents a homogeneous model that is a solution to the Einstein field equations. If you are writing about cosmology and do not know this, then you are not writing responsibly.
Until then, note this: if they've "demonstrated" that a gravitational field is present where space is homogeneous, they've misunderstood general relativity.
OK, so you are claiming that Einstein "misunderstood general relativity". Fair enough.
No problem. But note that if you could only measure one value and direction for the gravitational field, such as in the room you're in, this does not imply that the space in that room is homogeneous. Instead it signifies that the inhomogeneity is uniform.
It is correct to say that an inhomogeneous situation is inhomogeneous, congratulations on getting that right. It is simply nonsense to say, "the inhomogeneity is uniform."
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It is very interesting to produce a quotation to a somewhat public address of Einstein's rather than any scientific work he did, but it does not answer the question. I suspect that, if we asked you to produce the trajectory of a pencil using inhomogeneous space, you could not do so.
One uses mathematics to produce the trajectory of a pencil, and that mathematics doesn't explain the why of it. To understand why, you have to read what Einstein actually said.
Regardless, you seem to be entirely ignoring or ignorant of Einstein's many homogeneous spacetime solutions to the Einstein field equations that he offered as cosmological models before and after the date of that address. If you are ignorant, then that's one thing: you can look them up and see for yourself. If you are ignoring them, then one has to question the methodology of someone who chooses to support a point in physics on a single (translates) passage rather than the bulk of scientific work.
I'm not ignorant of Einstein or his work. I've give you a reference and a quote, pay attention to it instead of being dismissive and vague. And note that Einstein said space was not homogeneous. Do not confuse space with spacetime.
Really? How about:
Einstein, Albert (1917), "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie", Königlich Preussische Akademie der Wissenschaften
Here's an English translation amongst the Einstein digital papers (http://einsteinpapers.press.princeton.edu/vol6-trans/433?highlightText=%22Cosmological%20Considerations%22). What about it?
Or good textbooks that go into details of many such models:
Rich, James, Fundamentals of Cosmology, Springer, 2nd Edition, 2010
Peebles, PJE, Principles of Physical Cosmology, Princeton University Press (that includes many different models), 1993
Again, vague.
Pretty much every professional website that discusses cosmology presents a homogeneous model that is a solution to the Einstein field equations. If you are writing about cosmology and do not know this, then you are not writing responsibly.
There is nothing irresponsible in giving an Einstein quote.
OK, so you are claiming that Einstein "misunderstood general relativity". Fair enough.
I'm obviously not saying that, because I'm referring to what Einstein said.
It is correct to say that an inhomogeneous situation is inhomogeneous, congratulations on getting that right. It is simply nonsense to say, "the inhomogeneity is uniform."
No it isn't. That's what's called a uniform gravitational field. If you measured g to be 9.8m/s/s at all available locations you might say the gravitational field was uniform. However we all know that if you could get away from the Earth's surface you'd measure g to be lower, in line with the inverse-square rule.
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It is very interesting to produce a quotation to a somewhat public address of Einstein's rather than any scientific work he did, but it does not answer the question. I suspect that, if we asked you to produce the trajectory of a pencil using inhomogeneous space, you could not do so.
One uses mathematics to produce the trajectory of a pencil, and that mathematics doesn't explain the why of it. To understand why, you have to read what Einstein actually said.
That is simply ridiculous. I am unwilling to take Einstein as a holy figure, if only because of the way that he treated his first wife and his romantic life in general. I am unwilling to accept that individual scientists are holy figures who have mystical revelations that provide them with the ability to produce writing that gives more understanding to physics than studying physics.
If you simply reject studying physics in favor of slavish attention to the words of Einstein, then you are welcome to your religion, but I (and others I suspect) will not follow you.
I'm not ignorant of Einstein or his work. I've give you a reference and a quote, pay attention to it instead of being dismissive and vague.
OK, then, you seem to be admitting that you are actively ignoring the homogeneous solutions that Einstein offered as his main cosmological efforts. I am not sure why you think that these works of Einstein are heretical while one specific passage from a single public address is gospel, but I'm not interested in your Einstein religion.
And note that Einstein said space was not homogeneous. Do not confuse space with spacetime.
I do not. If you would bother to read the science you are discussing, you would find solutions with homogeneous space, or rather, with homogeneous space-like hypersurfaces. (Ironic that the passage that you seem to claim is about homgeneous space and not spacetime explicitly references equations that only make sense in spacetime.)
Here's an English translation amongst the Einstein digital papers (http://einsteinpapers.press.princeton.edu/vol6-trans/433?highlightText=%22Cosmological%20Considerations%22). What about it?
You wanted a citation, read and find out.
Or good textbooks that go into details of many such models:
Rich, James, Fundamentals of Cosmology, Springer, 2nd Edition, 2010
Peebles, PJE, Principles of Physical Cosmology, Princeton University Press (that includes many different models), 1993
Again, vague.
How is that vague? You wanted citations to the many different homogeneous models, I gave you places to find them in great detail. There are few better resources that the Peebles textbook. Rich does a much simpler presentation.
I suspect that you do not want to actually follow the science and that you want something in plain English that will spell out the details for you. Well, you could try the wikipedia page for the Robertson-Walker metric, that should give you access to a bunch of different specific solutions and their authors.
Pretty much every professional website that discusses cosmology presents a homogeneous model that is a solution to the Einstein field equations. If you are writing about cosmology and do not know this, then you are not writing responsibly.
There is nothing irresponsible in giving an Einstein quote.
Yes, there is. Again, since Einstein displayed some abhorrent behavior in his family life, it might be irresponsible to present a quotation from him about how one should conduct oneself romantically. (I don't actually know that such quotations exist.)
More important for a scientific discussion, Einstein was also incorrect about some of the elements of his own theory at different times of his career, so it would be irresponsible to provide a quotation from Einstein without trying to understand anything of the context of the quotation or the scientific evidence and discussion around the quotation.
I'm obviously not saying that, because I'm referring to what Einstein said.
This would be an example of an irresponsible approach to quotation, if you simply believe everything that Einstein said at any given time.
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That is simply ridiculous. I am unwilling to take Einstein as a holy figure...
Nobody is taking Einstein as a holy figure. He's just the guy who came up with general relativity, so if you want to understand gravity, you ought to read what he said.
I suspect that you do not want to actually follow the science and that you want something in plain English that will spell out the details for you. Well, you could try the wikipedia page for the Robertson-Walker metric
I've read it (http://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric). It says the FLRW metric starts with the assumption of homogeneity and isotropy of space. Given that Einstein described a gravitational field as space that was neither homogeneous nor isotropic, that assumption doesn't seem too wise.
More important for a scientific discussion, Einstein was also incorrect about some of the elements of his own theory at different times of his career, so it would be irresponsible to provide a quotation from Einstein without trying to understand anything of the context of the quotation or the scientific evidence and discussion around the quotation.
I do understand the context and the scientific evidence and discussion. Einstein was giving his 1920 Leyden Address (http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html). The title of that was Ether and the Theory of Relativity. He ends up saying this:
"Recapitulating, we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it."
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That is simply ridiculous. I am unwilling to take Einstein as a holy figure...
Nobody is taking Einstein as a holy figure. He's just the guy who came up with general relativity, so if you want to understand gravity, you ought to read what he said.
It is perfectly possible to understand relativity theory without reading any Einstein whatsoever. One only needs to have access to texts (and teachers) that explain the relevant science. Einstein's theory surivies because other people can understnad it, use it, and test it. Simply reading Einstein's general words on the subject, without learning the physics, is a recipe for disaster.
I suspect that you do not want to actually follow the science and that you want something in plain English that will spell out the details for you. Well, you could try the wikipedia page for the Robertson-Walker metric
I've read it (http://en.wikipedia.org/wiki/Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric). It says the FLRW metric starts with the assumption of homogeneity and isotropy of space. Given that Einstein described a gravitational field as space that was neither homogeneous nor isotropic, that assumption doesn't seem too wise.
As I said before, your attempt to read just some general words of Einstein and ignore his physics has lead you to disaster. For whatever reason, you refuse to acknowledge all the times that Einstein started with homogeneity and isotropy for his cosmological models. Perhaps you have a plan, in your religion, to never actually read the physics because that is too holy. I don't really care; you are welcome to your religious beliefs but the physics stays the physics and Einstein's physics included isotropic and homogeneous cosmological models. I know this because I read Einstein and did not ignore what he wrote.
More important for a scientific discussion, Einstein was also incorrect about some of the elements of his own theory at different times of his career, so it would be irresponsible to provide a quotation from Einstein without trying to understand anything of the context of the quotation or the scientific evidence and discussion around the quotation.
I do understand the context and the scientific evidence and discussion. Einstein was giving his 1920 Leyden Address (http://www-history.mcs.st-and.ac.uk/Extras/Einstein_ether.html). The title of that was Ether and the Theory of Relativity. He ends up saying this:
Yeah, that kind of cherry-picking is good evidence for me that you don't know the context or the relevant physics.
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It is perfectly possible to understand relativity theory without reading any Einstein whatsoever.
And it's perfectly possible to misunderstand relativity if you dismiss the original material. Peter M Brown wrote an interesting essay on this, see http://arxiv.org/abs/physics/0204044 :
"There exists some confusion, as evidenced in the literature, regarding the nature of the gravitational field in Einstein's General Theory of Relativity. It is argued here the this confusion is a result of a change in interpretation of the gravitational field. Einstein identified the existence of gravity with the inertial motion of accelerating bodies (i.e. bodies in free-fall) whereas contemporary physicists identify the existence of gravity with space-time curvature (i.e. tidal forces). The interpretation of gravity as a curvature in space-time is an interpretation Einstein did not agree with."
One only needs to have access to texts (and teachers) that explain the relevant science. Einstein's theory survives because other people can understand it, use it, and test it. Simply reading Einstein's general words on the subject, without learning the physics, is a recipe for disaster.
I'm not saying that. I'm saying you shouldn't dismiss Einstein.
As I said before, your attempt to read just some general words of Einstein and ignore his physics has lead you to disaster.
I haven't ignored his physics. You're the one who dismissing Einstein here. Not me.
For whatever reason, you refuse to acknowledge all the times that Einstein started with homogeneity and isotropy for his cosmological models. Perhaps you have a plan, in your religion, to never actually read the physics because that is too holy...
Enough. You're being deliberately abusive and argumentative and disruptive.
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It is perfectly possible to understand relativity theory without reading any Einstein whatsoever.
And it's perfectly possible to misunderstand relativity if you dismiss the original material. Peter M Brown wrote an interesting essay on this, see http://arxiv.org/abs/physics/0204044 :
You seem confused by the semantic arguments offered in that paper. You should first try to learn the relevant physics.
One only needs to have access to texts (and teachers) that explain the relevant science. Einstein's theory survives because other people can understand it, use it, and test it. Simply reading Einstein's general words on the subject, without learning the physics, is a recipe for disaster.
I'm not saying that. I'm saying you shouldn't dismiss Einstein.
You actually say the reverse, quite often. You say we should all ignore Einstein's work on cosmology. where Einstein proposed solutions to the Einstein field equation of homogeneous space. You seem to consider this work heresy for some reason.
For whatever reason, you refuse to acknowledge all the times that Einstein started with homogeneity and isotropy for his cosmological models. Perhaps you have a plan, in your religion, to never actually read the physics because that is too holy...
Enough. You're being deliberately abusive and argumentative and disruptive.
I can understand that religious issues are sometimes touchy. I can accept that you have your religion, but I doubt that others will accept that my words are abusive merely because I mention something in your holy texts that you do not wish to acknowledge.