Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) The (changing) geometry of space and time..So the space time continuum is ( in this case dealing with , is NOT the forces of ELECTRICITY and MAGNETISM but rather the GRAVITATIONAL FORCE ) :- Then the equivalent is the " Gravitational FIELD " ? , having a " (changing) geometry of space and time." Which begs the question ? What exactly is the NATURE of the GRAVITATIONAL FIELD .? Are we talking of more quantum particles, virtual particles ,and other stuff ?.? etc as we were with Electro Magnetic Fields ? In this case we even have visible and invisible massive , stars , galaxies, molecules, dust and gas , by the " shed load " distributed throughout ' Space Time ' , do we not . These must surely shape 'Space Time ' into all the contortions you describe ? Quote ( " The (changing) geometry of space and time." ) Then we are back to the question " What quite " is being changed, distorted, squished, having its geometry changed ? Mike Edited July 5, 2016 by Mike Smith Cosmos
Strange Posted July 5, 2016 Posted July 5, 2016 ? So the space time continuum is ( in this case dealing with , is NOT the forces of ELECTRICITY and MAGNETISM but rather the GRAVITATIONAL FORCE ) :- What we perceive as a gravitational force is actually the curvature of space-time. (Similar to the way we perceive electromagnetic radiation as colours). Then the equivalent is the " Gravitational FIELD " ? , having a " (changing) geometry of space and time." Which begs the question ? What exactly is the NATURE of the GRAVITATIONAL FIELD .? The gravitational field IS space-time. Are we talking of more quantum particles, virtual particles ,and other stuff ?.? etc as we were with Electro Magnetic Fields ? Currently, there is no known way of producing a quantum theory of gravity, so no. IT is just geometry. You know: distance, angles, lengths, etc. These must surely shape 'Space Time ' into all the contortions you describe ? Quote ( " The (changing) geometry of space and time." ) Indeed they do.
Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) What we perceive as a gravitational force is actually the curvature of space-time. (Similar to the way we perceive electromagnetic radiation as colours). The gravitational field IS space-time. Currently, there is no known way of producing a quantum theory of gravity, so no. IT is just geometry. You know: distance, angles, lengths, etc. Indeed they do. . Yes but WHAT is actually being SHAPED. Measured for angles , geometry length , etc If you walked down the ' High Street ' , articulating curves in the air , and making measurements of air , and twisting your head to gauge angles . Yet there was nothing there ! You would be ' Locked Up ' for insanity or some other mental abberation. You can't just say there ' is nothing there , but you are measuring it ' . Surely Mike Edited July 5, 2016 by Mike Smith Cosmos
Strange Posted July 5, 2016 Posted July 5, 2016 . Yes but WHAT is actually being SHAPED. Measured for angles , geometry length , etc If you walked down the ' High Street ' , articulating curves in the air , and making measurements of air , and twisting your head to gauge angles . Yet there was nothing there ! You would be ' Locked Up ' for insanity or some other mental abberation. You can't just say there ' is nothing there , but you are measuring it ' . Surely Mike You could measure the distance between two points. Your head and the top of the door, for example. Or your car and a nearby ditch. That distance is dependent not absolute, it depends on the observer's frame of reference, the presence of mass or energy, etc. Some of those changes are what we call "gravity". p.s. meant to say: very glad you weren't hurt in your little incident.
Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) You could measure the distance between two points. Your head and the top of the door, for example. Or your car and a nearby ditch. That distance is dependent not absolute, it depends on the observer's frame of reference, the presence of mass or energy, etc. Some of those changes are what we call "gravity".p.s. meant to say: very glad you weren't hurt in your little incident. .That's where I went wrong, is it ? I never took account of the curvature in space time . Yes officer! I must remember that one , for the next time I have an accident ! "It was not my fault , it was a local distortion in space time ! I presume then, that the LIGO experiments , do this sort of thing , in there experiments ? This still does not help me ' visualise ' what quite is being bent, "Curved " , twisted ,distorted ? You know me I need a picture , would clear jelly do ? And if it would ? What is the ' real jelly ' ? All over space time . In can't be nothing , it must be somethings? Jam packed virtual particles, or what ? Mike Edited July 5, 2016 by Mike Smith Cosmos
Strange Posted July 5, 2016 Posted July 5, 2016 This might help: Or this: Note: the lines are not "things", they are just showing what happens to straight lines in the presence of mass. So what changes is not "jelly" but just the nature of the shortest distance between two points. The shortest distance becomes a curve.
Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) This might help: Or this: Note: the lines are not "things", they are just showing what happens to straight lines in the presence of mass. So what changes is not "jelly" but just the nature of the shortest distance between two points. The shortest distance becomes a curve. This presumably is only applicable if 'you as the observer ' or ' a 'thing , having mass or inertia ' is involved . If there was no mass involved, no curvature would be seen or felt , I presume . If you were a massless detector or observer , you would see or feel NOTHING .out of the ordinary ? Thus curvature of space would have no relevance , I suggest ? Mike Edited July 5, 2016 by Mike Smith Cosmos
MigL Posted July 5, 2016 Posted July 5, 2016 We have a model called GR which is based on relationships between events ( space-time co-ordinates, x, y, z, and -ct ). The distance between events, s, is calculated using Pythagoras, such that a 'shortened' distance between events results in 'curvature along one or more of the four axis. It is this curvature which leads to geodesics, and which manifests itself as gravity. This model makes impressively accurate predictions and descriptions of reality. Or rather of our mental model of reality, since what we consider reality is also an interpretation our brain makes in response to certain sensory inputs. Does 'reality' really curve ? Who knows, but the model really works !
Strange Posted July 5, 2016 Posted July 5, 2016 This presumably is only applicable if 'you as the observer ' or ' a 'thing , having mass or inertia ' is involved . If there was no mass involved, no curvature would be seen or felt , I presume . If you were a massless detector or observer , you would see or feel NOTHING .out of the ordinary ? Thus curvature of space would have no relevance , I suggest ? Absolutely not. The change in the geometry of space affects everything. Including things with no mass. That is why one of the first tests of GR was the observation of gravitational lensing (the change in the path of light as it moves through curved space-time) during a solar eclipse.
Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) Absolutely not. The change in the geometry of space affects everything. Including things with no mass. That is why one of the first tests of GR was the observation of gravitational lensing (the change in the path of light as it moves through curved space-time) during a solar eclipse.. But as far as I know " photons are massless " yet they , as you say are seen to curve or bend around , well galaxies , areas of space. However that would happen if the photons were massless , but move , as per my previous argument , through the electro magnetic field . The electro magnetic field is .....curved by space time ....? . .... Due to its previously identified constituents . Thus the photons follow the curvature of the field , not of space time itself? I might be hopelessly mixed up here. But I can't see how a massless , which has no inertia , or anything that can not react with gravity , as a massless object can not , in any way , follow the curvature if it has nothing to react with ? And how can it react if it has no mass itself ? Mike Edited July 5, 2016 by Mike Smith Cosmos
Mordred Posted July 5, 2016 Posted July 5, 2016 (edited) Has no rest mass. It does have inertial mass. Massless particles follow whats called a null geodesic. Massive particles will follow a space-time geodesic. The math behind geodesics are complex. I just recently did a post on it in Speculations to demonstrate how the geodesic equation is derived. Here is the pertinant section. In the presence of matter or when matter is not too distant physical distances between two points change. For example an approximately static distribution of matter in region D. Can be replaced by tve equivalent mass [latex]M=\int_Dd^3x\rho(\overrightarrow{x})[/latex] concentrated at a point [latex]\overrightarrow{x}_0=M^{-1}\int_Dd^3x\overrightarrow{x}\rho(\overrightarrow{x})[/latex] Which we can choose to be at the origin [latex]\overrightarrow{x}=\overrightarrow{0}[/latex] Sources outside region D the following Newton potential at [latex]\overrightarrow{x}[/latex] [latex]\phi_N(\overrightarrow{x})=-G_N\frac{M}{r}[/latex] Where [latex] G_n=6.673*10^{-11}m^3/KG s^2[/latex] and [latex]r\equiv||\overrightarrow{x}||[/latex] According to Einsteins theory the physical distance of objects in the gravitational field of this mass distribution is described by the line element. [latex]ds^2=c^2(1+\frac{2\phi_N}{c^2})-\frac{dr^2}{1+2\phi_N/c^2}-r^2d\Omega^2[/latex] Where [latex]d\Omega^2=d\theta^2+sin^2(\theta)d\varphi^2[/latex] denotes the volume element of a 2d sphere [latex]\theta\in(0,\pi)[/latex] and [latex]\varphi\in(0,\pi)[/latex] are the two angles fully covering the sphere. The general relativistic form is. [latex]ds^2=g_{\mu\nu}(x)dx^\mu x^\nu[/latex] By comparing the last two equations we can find the static mass distribution in spherical coordinates. [latex](r,\theta\varphi)[/latex] [latex]G_{\mu\nu}=\begin{pmatrix}1+2\phi_N/c^2&0&0&0\\0&-(1+2\phi_N/c^2)^{-1}&0&0\\0&0&-r^2&0\\0&0&0&-r^2sin^2(\theta)\end{pmatrix}[/latex] Now that we have defined our static multi particle field. Our next step is to define the geodesic to include the principle of equivalence. Followed by General Covariance. Ok so now the Principle of Equivalence. You can google that term for more detail but in the same format as above [latex]m_i=m_g...m_i\frac{d^2\overrightarrow{x}}{dt^2}=m_g\overrightarrow{g}[/latex] [latex]\overrightarrow{g}-\bigtriangledown\phi_N[/latex] Denotes the gravitational field above. Now General Covariance. Which use the ds^2 line elements above and the Einstein tensor it follows that the line element above is invariant under general coordinate transformation(diffeomorphism) [latex]x\mu\rightarrow\tilde{x}^\mu(x)[/latex] Provided ds^2 is invariant [latex]ds^2=d\tilde{s}^2[/latex] an infinitesimal coordinate transformation [latex]d\tilde{x}^\mu=\frac{\partial\tilde{x}^\mu}{\partial x^\alpha}dx^\alpha[/latex] With the line element invariance [latex]\tilde{g}_{\mu\nu}(\tilde{x})=\frac{\partial\tilde{x}^\mu \partial\tilde{x}^\nu}{\partial x^\alpha\partial x^\beta} g_{\alpha\beta}x[/latex] The inverse of the metric tensor transforms as [latex]\tilde{g}^{\mu\nu}(\tilde{x})=\frac{\partial\tilde{x}^\mu \partial\tilde{x}^\nu}{\partial x^\alpha\partial x^\beta} g^{\alpha\beta}x[/latex] In GR one introduces the notion of covariant vectors [latex]A_\mu[/latex] and contravariant [latex]A^\mu[/latex] which is related as [latex]A_\mu=G_{\mu\nu} A^\nu[/latex] conversely the inverse is [latex]A^\mu=G^{\mu\nu} A_\nu[/latex] the metric tensor can be defined as [latex]g^{\mu\rho}g_{\rho\nu}=\delta^\mu_\mu[/latex] where [latex]\delta^\mu_nu[/latex]=diag(1,1,1,1) which denotes the Kronecker delta. Finally we can start to look at geodesics. Let us consider a free falling observer. O who erects a special coordinate system such that particles move along trajectories [latex]\xi^\mu=\xi^\mu (t)=(\xi^0,x^i)[/latex] Specified by a non accelerated motion. Described as [latex]\frac{d^2\xi^\mu}{ds^2}[/latex] Where the line element ds=cdt such that [latex]ds^2=c^2dt^2=\eta_{\mu\nu}d\xi^\mu d\xi^\nu[/latex] Now assunme that the motion of O changes in such a way that it can be described by a coordinate transformation. [latex]d\xi^\mu=\frac{\partial\xi^\mu}{\partial x^\alpha}dx^\alpha, x^\mu=(ct,x^0)[/latex] This and the previous non accelerated equation imply that the observer O, will percieve an accelerated motion of particles governed by the Geodesic equation. [latex]\frac{d^2x^\mu}{ds^2}+\Gamma^\mu_{\alpha\beta}(x)\frac{dx^\alpha}{ds}\frac{dx^\beta}{ds}=0[/latex] Where the new line element is given by [latex]ds^2=g_{\mu\nu}(x)dx^\mu dx^\nu[/latex] and [latex] g_{\mu\nu}=\frac{\partial\xi^\alpha}{\partial\xi x^\mu}\frac{\partial\xi^\beta}{\partial x^\nu}\eta_{\alpha\beta}[/latex] and [latex]\Gamma^\mu_{\alpha\beta}=\frac{\partial x^\mu}{\partial\eta^\nu}\frac{\partial^2\xi^\nu}{\partial x^\alpha\partial x^\beta}[/latex] Denote the metric tensor and the affine Levi-Civita connection respectively. Edited July 5, 2016 by Mordred 1
Strange Posted July 5, 2016 Posted July 5, 2016 . But as far as I know " photons are massless " yet they , as you say are seen to curve or bend around , well galaxies , areas of space. However that would happen if the photons were massless , but move , as per my previous argument , through the electro magnetic field . The electro magnetic field is .....curved by space time ....? . .... Due to its previously identified constituents . Thus the photons follow the curvature of the field , not of space time itself? I might be hopelessly mixed up here. I am not sure if there is really any difference between saying that the fields are curved by space-time or the paths of the particles are changed by the curvature of space-time. Geometry changes so everything embedded in that geometry changes. (Although I suspect that trying to model quantum field theory in curved spacetime is non trivial.) But I can't see how a massless , which has no inertia , or anything that can not react with gravity , as a massless object can not , in any way , follow the curvature if it has nothing to react with ? And how can it react if it has no mass itself ? You are still thinking of gravity as a force that acts on objects with mass. It isn't it changes the length and shape of "straight lines" so even massless things are affected.
Mike Smith Cosmos Posted July 5, 2016 Posted July 5, 2016 (edited) The (changing) geometry of space and time.?Surely the geometry of space and time is describing 'Space' and 'time ' as some form of shape or size . If that is the case:- both those commodities must 'exist' as real entities . Geometry is a mathematical description , but what is it actually a description of ? Namely they must have some form of existence and texture of ( reality ) , so as to be shaped and measured, in principle ? Are we talking of space having some form of material nature ( no matter how fine grained or ' bizzar ' it is ) . It must 'exist' , so as to be curved or identified as of a quantity of something ? What are the recognised ingredients of this ( space and time ) that it may be curved, even on a massive scale ? It cannot be a curvature of nothing , it must be a curve of something ? Surely ? You speak of ( or I speak , then you speak ) Me "Which begs the question ? What exactly is the NATURE of the GRAVITATIONAL FIELD .?" You " The gravitational field IS space-time." This sort of stacks up ! As one of the first things to separate in the very early universe was the gravitational force broke symmetry with the electro -week force and separated the gravitational force as a distinct gauge force ( as I understand it ) . Mike We have a model called GR which is based on relationships between events ( space-time co-ordinates, x, y, z, and -ct ). The distance between events, s, is calculated using Pythagoras, such that a 'shortened' distance between events results in 'curvature along one or more of the four axis. It is this curvature which leads to geodesics, and which manifests itself as gravity. This model makes impressively accurate predictions and descriptions of reality. Or rather of our mental model of reality, since what we consider reality is also an interpretation our brain makes in response to certain sensory inputs. Does 'reality' really curve ? Who knows, but the model really works ! . I thought one of Newton's laws was " something will continue in a straight line unless it is acted upon by a force . " So presumably the force is the force caused by gravity ( by way of this curvature of space ) . . I have dropped something heavy from my nose to my lap , when we are speeding steadily down the runway . It falls strait into my lap. When the pilot puts his foot down , and we accelerate down the runway approaching take off , the same heavy item curves into my chest as it falls . This presumably is the acceleration due to gravity. Gravity is an acceleration ? Thus ! Curvature ? But is this , the curvature of which you speak ? Mike Has no rest mass. It does have inertial mass. Massless particles follow whats called a null geodesic. Massive particles will follow a space-time geodesic. The math behind geodesics are complex. I just recently did a post on it in Speculations to demonstrate how........ Now assunme that the motion of ....... and [latex]\Gamma^\mu_{\alpha\beta}=\frac{\partial x^\mu}{\partial\eta^\nu}\frac{\partial^2\xi^\nu}{\partial x^\alpha\partial x^\beta}[/latex] Denote the metric tensor and the affine Levi-Civita connection respectively. . This is pretty impressive maths , which I am sure describes what is going on accurately , and conceptually . There must be a way to discuss what you are saying is going on in " Real terms " , even though it may not be accurate , or even conceptually exact . For instance ... Well ... I cannot do one ......., as I do not know what is going on ! There must be words like " this is pulling on that .." Or " that is bending under some form of ' tension' ..etc I liked the description the other night by prof Brian Cox . Gravity is pulling everywhere , and the best shape that can result from the pull of gravity Is a SPHERE . Hence all the stars ! Mike Edited July 5, 2016 by Mike Smith Cosmos
Strange Posted July 5, 2016 Posted July 5, 2016 ? Surely the geometry of space and time is describing 'Space' and 'time ' as some form of shape or size . If that is the case:- both those commodities must 'exist' as real entities . Geometry is a mathematical description , but what is it actually a description of ? Namely they must have some form of existence and texture of ( reality ) , so as to be shaped and measured, in principle ? Are we talking of space having some form of material nature ( no matter how fine grained or ' bizzar ' it is ) . It must 'exist' , so as to be curved or identified as of a quantity of something ? Distance is a mathematical description. What do you think it is a description of? What material do you think it is made of? What material is a right angle made of? Is it the same material as a 30º angle? Do lengths, times, angles and curves really need to be made of material? Bizarre.
Mordred Posted July 6, 2016 Posted July 6, 2016 Mike I'm sure you've seen a topographical map. One that shows elevation change. On that topographical map distance scale changes as the elevation gets higher. (Picture the lines indicating elevation gradients). Now lets make a map showing vectors. A vector has two quantities. Scalar (magnitude) and direction. (Direction of influence) So we wish to map gravitational potential Now instead of mapping elevation we are mapping spacetime. Where time is a coordinate of a vector. So our vector coordinates are 3 of space, one of time. Now instead of mapping distance and elevation were mapping units of force. Which is in metres/s^2. Now just like the topographical map where you have a greater elevation change shown as lines being closer together. In spacetime the elevation is greater units of force (gravitational field potential). Though this is commonly mapped not as an elevation change. But the exact opposite. (A hole). In 2d visualize a rubber sheet with s ball in the centre. The greater the mass of the ball. The greater the depression. The path of light follows this curvature. Just in a different path than particles with mass.
Mike Smith Cosmos Posted July 6, 2016 Posted July 6, 2016 (edited) I have to be careful you guys are not just saying:- " Shut up , and just do the Math" which has echoes of what went on with the early days of atomic theory . You are making sense with the models , in as far as showing me how far the gravitational field 'effects' and how it can be mathematically illustrated in " rubber sheet " form or " hillside contor map " form . Both very illustrative in themselves . But what I am asking is :- What is actually there in ( dare I say it ...' Reality' ) . O.K. I am not asking for actual ' piles of grit ' , but that would be nice if it were that ! But one you have mentioned " Gravitational Force " and " Gravitational Field " , which is a start . I do understand the symbolism of contorts on maps and rubber sheets , but I still want to get a description of :- What exactly is being modelled here ? What in actuality is there ? Again if it is a field " what is maintaining that field " ? If it is a distance, direction , hole, dent, curve , whatever . " what is the hole dent, curve, whatever ". IN ? I think the answers are :- MATTER and FIELD , ...if so , there needs to be some how's ? It is sounding similar to the electro magnetic field issue :- namely are we talking about a ginormous gravitational field set up by some stupendously massive gravitational mass at a distance , or have we local ' something ' that provides the contours in gravitational field of which you speak? If so what is local to sustain this contoured field ? Or/and what is miles and gazzilion miles away to sustain the contoured field ? And what is actually ' There ' , local or far away ? Mike Edited July 6, 2016 by Mike Smith Cosmos
Markus Hanke Posted July 6, 2016 Posted July 6, 2016 (edited) There must be a way to discuss what you are saying is going on in " Real terms " , even though it may not be accurate , or even conceptually exact . In real terms, a geodesic is a curve the geometry of which is such that at each and every point the proper acceleration vanishes ( in technical terms : it parallel-transports its own tangent vector ). That means quite simple that, if you hold an accelerometer in your hand and free-fall along a geodesic, then the accelerometer will read zero at all times. To put it even more simply - in free fall, you are weightless. [latex]a^{\mu}=0[/latex] That is precisely the geodesic equation, though at first glance it mightn't look the same as what Mordred has written. What exactly is being modelled here ? What in actuality is there ? In actuality, what is there are events - they are points in space at a given instant in time. What GR does is describe the relationships between these events - how far they are apart, what is the shortest connection between them, etc etc. In real physical terms, these relationships are simply measurements taken with instruments such as clocks and rulers. Clocks measure distances in time, rulers measure distances in space, and accelerometers measure acceleration. Taken together, those give us relationships between events. In the simplest case, events in spacetime are related in the same way as points on a 4-dimensional flat manifold are; this corresponds to the situation in Special Relativity. However, if there are sources of energy-momentum present ( planets, stars, electromagnetic fields etc ), then it turns out that the relationship between events is more complicated - these relationships are now the same as the relationships between points on curved manifolds. Curvature is just a measure of how much measurements taken with rulers and clocks deviate from reference measurements taken on a flat background. As such, what GR does is recognise that the relationship between physical events in spacetime happens to be the same as the geometric relationship between points on certain curved 4-dimensional manifolds - hence, such manifolds are adequate models to describe gravity, and how it relates to its sources. They provide the map that describe the territory. Don't think of curvature as a physical distortion of some mechanical medium, but rather think of it as a change in relationships between events. These changes can be measured by comparing rulers and clocks in different places; it isn't just an abstract concept, but something very very physical. Edited July 6, 2016 by Markus Hanke
Mike Smith Cosmos Posted July 6, 2016 Posted July 6, 2016 (edited) In real terms, a geodesic is a curve the geometry of which is such that at each and every point the proper acceleration vanishes ( in technical terms : it parallel-transports its own tangent vector ). That means quite simple that, if you hold an accelerometer in your hand and free-fall along a geodesic, then the accelerometer will read zero at all times. To put it even more simply - in free fall, you are weightless. [latex]a^{\mu}=0[/latex] That is precisely the geodesic equation, though at first glance it mightn't look the same as what Mordred has written. In actuality, what is there are events - they are points in space at a given instant in time. What GR does is describe the relationships between these events - how far they are apart, what is the shortest connection between them, etc etc. In real physical terms, these relationships are simply measurements taken with instruments such as clocks and rulers. Clocks measure distances in time, rulers measure distances in space, and accelerometers measure acceleration. Taken together, those give us relationships between events. In the simplest case, events in spacetime are related in the same way as points on a 4-dimensional flat manifold are; this corresponds to the situation in Special Relativity. However, if there are sources of energy-momentum present ( planets, stars, electromagnetic fields etc ), then it turns out that the relationship between events is more complicated - these relationships are now the same as the relationships between points on curved manifolds. Curvature is just a measure of how much measurements taken with rulers and clocks deviate from reference measurements taken on a flat background. As such, what GR does is recognise that the relationship between physical events in spacetime happens to be the same as the geometric relationship between points on certain curved 4-dimensional manifolds - hence, such manifolds are adequate models to describe gravity, and how it relates to its sources. They provide the map that describe the territory. Don't think of curvature as a physical distortion of some mechanical medium, but rather think of it as a change in relationships between events. These changes can be measured by comparing rulers and clocks in different places; it isn't just an abstract concept, but something very very physical. Thanks . Sort of o.k. JUST ! Only minutely just ! But it still leaves me with " What in reality is actually ' there ' ? Is there something tangible 'there ' or local or nearby . Or has it come about from some remote distance , that just happens to cause those ' things ' measured to happen or exist at that location .? ( but really there is nothing of substance ' there' or anywhere nearby ( local) . ....... ........ In other words what is the " rubber ," of the rubber sheet ?......... I had fond ideas somehow that space was jam packed with miniature items ( things ) ( don't know , like micro miniature loops, dust, virtual particles , things coming into existence and disappearing , dark something or other, strings , quantum foam , goodness knows what ) but something ? Not nothing . If not , are you saying it is just a field set up by all the mass in the universe , pushing and shoving , and this is what we end up with this Gargantuan field everywhere, with its Twists and Turns ? If so I think my brain will just melt into a miasma of liquid foam . I want to be in something . I do not want to be a fish that has jumped out of its goldfish bowl and am flipping around on the carpet outside in -- No Water ! And I don't like ghosts ! Mike Edited July 6, 2016 by Mike Smith Cosmos
Strange Posted July 6, 2016 Posted July 6, 2016 What is "there" is the distance between those particles, grains of dust, etc. That is what changes.
Mike Smith Cosmos Posted July 6, 2016 Posted July 6, 2016 (edited) What is "there" is the distance between those particles, grains of dust, etc. That is what changes..Ah ! So it is different concentrations or positions or states of the interstellar 'dust ' , contoured and shaped by Gravity ? If that is it ! Then that makes me happy . If that is what you are truly saying ? Can you illusidate any more on these " particles, grains of dust " . Is the universe full up with this ' stuff ' from one end of the universe to the other ? Mike There is no chance the particles are made of rubber ? Is there ? ....joke Edited July 6, 2016 by Mike Smith Cosmos
Strange Posted July 6, 2016 Posted July 6, 2016 . Ah ! So it is different concentrations or positions or states of the interstellar 'dust ' , contoured and shaped by Gravity ? If that is it ! Then that makes me happy . If that is what you are truly saying ? I think so (you have an odd way of rephrasing things so it isn't always clear which end of the stick you have got hold of ... ) Can you illusidate any more on these " particles, grains of dust " . Is the universe full up with this ' stuff ' from one end of the universe to the other ? Well, you brought them up. But the universe is full of gas (mainly hydrogen and a small amount of helium, and mainly ionised). It is also full of various forms of radiation from stars, as well as cosmic rays, neutrinos and (probably) dark matter. These, like everything else, get moved around to some extent by the presence of gravitational fields.
Mike Smith Cosmos Posted July 6, 2016 Posted July 6, 2016 (edited) I think so (you have an odd way of rephrasing things so it isn't always clear which end of the stick you have got hold of ... ) Well, you brought them up. But the universe is full of gas (mainly hydrogen and a small amount of helium, and mainly ionised). It is also full of various forms of radiation from stars, as well as cosmic rays, neutrinos and (probably) dark matter. These, like everything else, get moved around to some extent by the presence of gravitational fields. . O.k. Well I apologise if I have put words in your mouth ' so to speak ' It is very easy for me to get hold of the wrong end of the stick , what with seeing maps is frozen metal plates and ripples in water ! However I am on a life time quest to find out if I can " what the dickens is going on here , or out there ? " If I could dare to ask , as it is very relevant to what we are discussing : - Do you see it as :- ( a ) all the contents you list , your statement ," the universe is full of gas (mainly hydrogen and a small amount of helium, and mainly ionised). It is also full of various forms of radiation from stars, as well as cosmic rays, neutrinos and (probably) dark matter. " .my question is " did these cause the gravitational fields to be the shape they are ? ...or ( b) Do the gravitational fields ( wherever they have come from ) , cause the space to be the shape it is ? ..or © neither , something else , if so what ? Mike Edited July 6, 2016 by Mike Smith Cosmos
Strange Posted July 6, 2016 Posted July 6, 2016 ( a ) all the contents you list , your statement ," the universe is full of gas (mainly hydrogen and a small amount of helium, and mainly ionised). It is also full of various forms of radiation from stars, as well as cosmic rays, neutrinos and (probably) dark matter. " .my question is " did these cause the gravitational fields to be the shape they are ? ...or Because they have mass and energy, they certainly contribute to it. ( b) Do the gravitational fields ( wherever they have come from ) , cause the space to be the shape it is ? ..or The gravitation field IS the shape of space (strictly, the shape of space-time). Curvature of space-time is gravity. Gravity is the curvature of space-time.
Mike Smith Cosmos Posted July 6, 2016 Posted July 6, 2016 (edited) Because they have mass and energy, they certainly contribute to it. The gravitation field IS the shape of space (strictly, the shape of space-time). Curvature of space-time is gravity. Gravity is the curvature of space-time. . No ! For me there are too many ' everything is everything ' , I need to know what is the source of what ? Otherwise it's like "trying to pick yourself up by your own bootstraps " as we said in olden days . Perhaps " lift yourself up by pulling on your shoe laces " would be a today's translation . Mike Edited July 6, 2016 by Mike Smith Cosmos
geordief Posted July 6, 2016 Posted July 6, 2016 (edited) . As such, what GR does is recognise that the relationship between physical events in spacetime happens to be the same as the geometric relationship between points on certain curved 4-dimensional manifolds - Certain curved manifolds ? Does that mean different classes of manifolds or just one class of manifold with differing properties? My understanding was that the manifold that modeled spacetime was that with the parameters (correct terminology?) of 3 spatial and one temporal(sign reversed ) components -a hyperbolic manifold. Are there are** ways (manifolds) of modeling spacetime ? ** EDIT: are ="other" ,of course . Edited July 6, 2016 by geordief
Recommended Posts