Question about gravity
in [Relativity]
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From: J. Clarke on 18 Mar 2010 08:01 On 3/17/2010 9:19 PM, Tom Roberts wrote: > mpc755 wrote: >> On Mar 16, 11:43 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: >>> mpc755 wrote: >>>> 'curved spacetime' is meaningless nonsense in terms of a physical >>>> description of nature. What is physically being 'curved'? [...] >>> Nothing "physical" is involved, this is GEOMETRY. >>> >> >> Not only do we have the absurd nonsense [...] > > The "absurd nonsense" is your thinking that you can discuss modern > physics without any understanding of it whatsoever. I think it's perfectly valid to ask if the curvature of spacetime is something real or if it's a useful fiction, however asserting a priori that it is "meaningless nonsense" or that "nothing 'physical' is involved" are both quite premature. One trouble I have with philosophers is that they assert such things and run with them and you have to whack 'em with a two-by-four to get them to look at their premise. Unfortunately the ranks of philosopher wannabees seem to be considerably larger than then ranks of physicist wannabees who are actually serious about it.
From: Sam Wormley on 18 Mar 2010 08:47 On 3/18/10 6:10 AM, G. L. Bradford wrote: > > Wormy it is not space that is expanding. It is the objects in the > medium that are moving apart wrt each other. > The metric expansion of space is the averaged increase of metric (i.e. measured) distance between distant objects in the universe with time. It is an intrinsic expansion—that is, it is defined by the relative separation of parts of the universe and not by motion "outward" into preexisting space. (In other words, the universe is not expanding "into" anything outside of itself). Metric expansion is a key feature of Big Bang cosmology and is modeled mathematically with the FLRW metric. This model is valid in the present era only at relatively large scales (roughly the scale of galactic superclusters and above). At smaller scales matter has clumped together under the influence of gravitational attraction and these clumps do not individually expand, though they continue to recede from one another. The expansion is due partly to inertia (that is, the matter in the universe is separating because it was separating in the past) and partly to a repulsive force of unknown nature, which may be a cosmological constant. Inertia dominated the expansion in the early universe, and according to the ΛCDM model the cosmological constant will dominate in the future. In the present era they contribute in roughly equal proportions. While special relativity constrains objects in the universe from moving faster than the speed of light with respect to each other, there is no such theoretical constraint when space itself is expanding. It is thus possible for two very distant objects to be moving away from each other at a speed greater than the speed of light (meaning that one cannot be observed from the other). The size of the observable universe could thus be smaller than the entire universe. It is also possible for a distance to exceed the speed of light times the age of the universe, which means that light from one part of space generated near the beginning of the Universe might still be arriving at distant locations (hence the cosmic microwave background radiation). Ref: http://en.wikipedia.org/wiki/Metric_expansion_of_space
From: PD on 18 Mar 2010 09:46 On Mar 17, 5:06 pm, mpc755 <mpc...(a)gmail.com> wrote: > On Mar 17, 5:59 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Mar 17, 4:51 pm, mpc755 <mpc...(a)gmail.com> wrote: > > > > The poster I was responding to has finally made it to the step of > > > understand something physical causes gravity. The poster is a QM true > > > believer so it must be excused if the best step the poster can offer > > > is 'quanta is responsible' for gravity. > > > > The point I was trying to make, which you completely misinterpreted, > > > is if quanta is responsible for gravity then whatever you want to > > > consider the quanta to physically exist as in order for it to be > > > responsible for gravity, light from the sun is physically propagating > > > in quanta. > > > This is so cute. Note he says that quanta must be physically real, but > > that quantum mechanics (which describes the behavior of quanta) is not > > about stuff that is physically real. > > You're making my point. > > Gravity is physically real. > > Only in your interpretation of the absurd nonsense of QM can gravity > not be physically real. > > If quanta is responsible for gravity then quanta is physically real Of course they are real. And quantum mechanics describes those real things. Quantum mechanics is the study of how quanta (those real things) behave. Thank you. > and light waves from the Sun interact with the quanta responsible for > the gravity associated with the Earth.
From: PD on 18 Mar 2010 09:50 On Mar 18, 6:29 am, kenseto <kens...(a)erinet.com> wrote: > On Mar 17, 2:59 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Mar 17, 1:57 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > On Mar 17, 12:31 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > On Mar 17, 10:01 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > On Mar 17, 8:49 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > On Mar 17, 9:14 am, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > On Mar 16, 5:08 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > On Mar 15, 2:57 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > On Mar 15, 1:43 pm, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > > On Mar 15, 2:27 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > > > > > > > > On Mar 15, 1:25 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > > > > > > > > > > On Mar 15, 10:08 am, Huang <huangxienc...(a)yahoo.com> wrote: > > > > > > > > > > > > > > On Mar 15, 9:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > > > > > > > > > > On Mar 15, 6:43 am, "Peter Webb" > > > > > > > > > > > > > > > <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > > > > > > > > > > > > > > > Not a whole lot to add to what Inertial in particular said. > > > > > > > > > > > > > > > > In GR, gravity is a virtual force in a similar way to centrifugal force in > > > > > > > > > > > > > > > Newton. In both cases its really an acceleration, and the force is just the > > > > > > > > > > > > > > > product (literally) of this acceleration and the mass of the object. > > > > > > > > > > > > > > > > Einstein in GR gave a geometric interpretation of what gravity is. This is > > > > > > > > > > > > > > > very appealing, because it provides a mechanism for force at a distance. > > > > > > > > > > > > > > > Wrong it provides no such physical mechanism. It merely assumes the > > > > > > > > > > > > > > existence of a physical entity caLLED the fabric of spacetime for the > > > > > > > > > > > > > > interacting object to follow. The problem with such assumption is: > > > > > > > > > > > > > > What is the fabric of spacetime physically? This question is relevant > > > > > > > > > > > > > > because SR/GR deny the existence of physical space. > > > > > > > > > > > > > > > Ken Seto > > > > > > > > > > > > > > What ? ".... SR/GR deny the existence of physical space......" > > > > > > > > > > > > > > What the devil are you saying man ????? > > > > > > > > > > > > > > The theory of relativity says that gravity IS deformation of space. > > > > > > > > > > > > > How can this same theory deny the existence of space ??? Better visit > > > > > > > > > > > > > your optometrist really, really soon. > > > > > > > > > > > > > Sigh...How can you deform space when space is defined by Einstein as > > > > > > > > > > > > "empty space".???? > > > > > > > > > > > > Being empty means it has no matter in it. Having no matter in it does > > > > > > > > > > > not mean that space cannot have physical properties. Physical > > > > > > > > > > > properties are not limited to matter. > > > > > > > > > > > Bullshit. fields are stresses in a solid medium occupying space > > > > > > > > > > according to steven weinberg > > > > > > > > > > Solid medium? He said nothing about an electric field being a stress > > > > > > > > > in a solid medium. > > > > > > > > > Do you just make this stuff up as you go along? > > > > > > > > > On page 25 he said A field like an electric field or a magnetic field > > > > > > > > is a sort of stress in space, something like the various sorts of > > > > > > > > stress possible within a soild body, but a field is a stress in space > > > > > > > > itself. > > > > > > > > Note what Weinberg actually said: "...something LIKE the various sorts > > > > > > > of stress possible within a solid body, but a field is a stress IN > > > > > > > SPACE ITSELF." He does not say that stress only happens in solid > > > > > > > bodies. He says that stress happens in solid bodies AND in empty > > > > > > > space, and the stress in empty space is something like the stress in > > > > > > > solid bodies. This does NOT mean that empty space is a solid body. > > > > > > > No stress can exit in liquid or gas. Stress can exist only in solid. > > > > > > This is an incorrect statement, Ken. It is just flat wrong. > > > > > What I said is 100% correct. Stress exsts only in solids. I suggest > > > > that you go to your freskman physics book and look it up. > > > > Sure. I have the one you have. Please cite in your freshman physics > > > text where it says that stress exists only in solids. > > Please point out in your freshman book where it said that stresses can > occur in liquid or gas. Or in space. In liquids, you can look up in the index shear modulus, which induces a shear in the liquid. Are you thinking that the only things that physics deals with are solids, liquids, and gases, and nothing else? Why would you think that? See the index item permittivity of empty space. > > > > > > > > Otherwise, as you say Ken, assertion is not an argument. > > > > > > When you add your mistake to a correct statement that Weinberg makes, > > > > > this is only going to make your conclusion wrong. > > > > > Wienberg compare stress in space to stresses in solid. So my > > > > conclusion is 100%correct. > > > If I tell you that a cat has four legs like a lizard, but is a mammal, > > you should not draw the conclusion that mammals are lizards or that > > cats are lizards. > > > Weinberg said that the electric field is LIKE a stress in a solid, but > > is a stress in space. You should not draw the conclusion that space is > > a solid or that electric fields are stresses in a solid. > > So what he said implies that space is a solid. You are so stupid. > > Ken Seto > > > > > > > Ken Seto > > > > > > > So if stress exits in space as weinberg claimed then space must be a > > > > > > solid. Your ranting and parsing of words is irrelevant. > > > > > > Sorry, Ken, but pointing out a mistake of yours is not irrelevant.. > > > > > When you can learn to acknowledge mistakes, then you will start to > > > > > make progress. But since you always claim that remarks by others about > > > > > your mistakes are irrelevant, you will never get off square one. > > > > > > You have to get over your personality defects before you will be able > > > > > to do science. > > > > > It will help also to learn some basic physics, like what is taught in > > > > > your freshman textbook. > > > > > > > Ken Seto > > > > > > > > > > Physical properties are not limited to matter. > > > > > > > > > > You know that there is a permittivity of EMPTY SPACE? You know there > > > > > > > > > is a permeability of EMPTY SPACE? You know there is an impedance of > > > > > > > > > EMPTY SPACE? You know there is a gravitational potential in EMPTY > > > > > > > > > SPACE?- Hide quoted text - > > > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > > > - Show quoted text -- Hide quoted text - > > > > > > - Show quoted text -- Hide quoted text - > > > > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text -- Hide quoted text - > > > - Show quoted text - > >
From: PD on 18 Mar 2010 09:51
On Mar 18, 7:01 am, "J. Clarke" <jclarke.use...(a)cox.net> wrote: > On 3/17/2010 9:19 PM, Tom Roberts wrote: > > > mpc755 wrote: > >> On Mar 16, 11:43 pm, Tom Roberts <tjroberts...(a)sbcglobal.net> wrote: > >>> mpc755 wrote: > >>>> 'curved spacetime' is meaningless nonsense in terms of a physical > >>>> description of nature. What is physically being 'curved'? [...] > >>> Nothing "physical" is involved, this is GEOMETRY. > > >> Not only do we have the absurd nonsense [...] > > > The "absurd nonsense" is your thinking that you can discuss modern > > physics without any understanding of it whatsoever. > > I think it's perfectly valid to ask if the curvature of spacetime is > something real or if it's a useful fiction, however asserting a priori > that it is "meaningless nonsense" or that "nothing 'physical' is > involved" are both quite premature. One trouble I have with > philosophers is that they assert such things and run with them and you > have to whack 'em with a two-by-four to get them to look at their > premise. Unfortunately the ranks of philosopher wannabees seem to be > considerably larger than then ranks of physicist wannabees who are > actually serious about it. And in this particular case, MPC has a preconceived notion about what makes sense and what is absurd, and there is no need (at least in his mind) to test whether that categorization is appropriate. PD |