geordief

The global situation is more unfamiliar to me. Locally ,if as you say they are more or less equivalent description , could it be advantageous to connect the points (mathematically) in the manifold so that these connections would be changed by relative proximity to mass-energy sources? Also ,does this manifold model permit of imagining a black hole ,moving through it similarly to how an object might pass through misty air?( (obviously differently but is there an analogy there?)

What is the relationship between these two concepts? The former seems to be made up of lines and intervals along the 3 spatial and 1 time axes. When all the lines are drawn in, it gives a 4D ""grid" which can be as finely defined as you like (so long as you stay in the macro level) As I see it the volume demarcated can (should?) be a finite volume . At intersections along the grid there are points where a spacetime event may take place but I think that these points may also be "empty" The spacetime manifold seem to me to represent the same volume but it only contains the points of intersection of the "grid". It is as if these intersections have been "cast adrift" and "float around " in the volume without the connections that seem to be there in the "grid" Does it look like I have a decent understanding of these two models? Is the manifold a superior model to the "grid" (Minkowski Space Time) ? Does it show things that Minkowski SpaceTime struggles to?

Can I ask for a "yawn" icon to be added to the list of emoticons?

In the environment you work in it is "part of the job" to make an effort to communicate with and try to understand your students . In the outside world the public seems to me to have very much less patience with people less skilled at the language than they are. As you say ,so long as the individual is able to communicate their ideas passably well the discussion should end there. But if (as I feel) it is an impediment and perhaps also a reason for cursory dismissal/judgement then is it not a failing to to fail to eradicate this unnecessary failing ? (3 "failings" ) I am sure you agree that there is a place for uniformity of language and at least an appreciation of the benefits of a followed grammatical structure. After that , the rules are (and should be) for breaking. PS perhaps I have a bee in my bonnet?

In my post#44 I was getting the wrong end of the stick. This is not about the spacetime curvature that models gravity? You are talking about another kind of curvature?

I thought that even a minor event like 2 hands clapping (or even just moving wrt each other) would produce gravitational waves .The gravitational waves would be entirely undetectable but would still exist. That is why I am surmising the the gravity field is quivering like a jelly -because gravitational waves (far too small to be detected ) are everywhere ,caused by the most minor disturbances in mass-energy distributions. Am I wrong ?(about there being no limit to how weak gravitational waves can be)

That is what I seem to be hearing. On the large (very large) scale curvature is almost zero . However ,as the scale increases beyond what has been observed all bets are off as ,practically by definition we cannot know what we cannot observe. I think we may be talking about intrinsic curvature ....which does not need to be embedded in an extra dimension . Is spacetime curvature 3 or 4 dimensional?(I think it is 4 -dimensional)

I am not sure (and I am trying to learn) but if you look at a piece of wood (a 3D volume) there are areas (eg knots) where density is higher than elsewhere.(so a bullet would not pass through in a straight line as seen from the outside) Is there a curvature in that 3D volume based on the density parameter and in a corresponding 3D volume of space (a vacuum) is the curvature caused by density and distribution of mass-energy sources?

If the local Gravity Field is quivering like a jelly fish (or a blancmange) is there any way these small changes could be observed ? (by the change of behaviour of objects in the Field?) Did the recent passage of Gravitational waves that actually was observed cause a permanent change in the local Gravity Field where (and elsewhere) they were detected? Were those small changes measured? What units would be used?(the same as for spacetime distance?)

What does it mean to say the Gravity Field is static? Is it not changing all the time ? Also ,when there is even the most minor of displacements of distribution of mass-energy in a system does that also cause Gravitational waves in exactly the same way as was detected with the recent Binary Black Hole Merger? Is is simply that the magnitude of Gravitational waves caused by such small redistributions of mass-energy in a system are entirely impossible to detect ? Is it correct to say that the universe is awash with small Gravitational waves so that the local and global Gravity Fields are actually in continuous change on a vanishingly small scale? They are in continuous "vibration" almost ? Are the Gravitational waves that have been detected merely the ones that are large enough to have been physically detected?

i understand that the Gravity Field is static and not to be confused with Gravitational Waves which are dynamic. Gravitational waves are created when there is a change in mass-energy distribution and propagate at light speed (correct?). Do they have any effect on the static Gravity Field? Does the energy in these Gravitational waves get distributed throughout the Gravity Field it propagates through and so do these Gravitational waves get "converted" into a new Gravity Field?

Does the concept of flatness vs curvedness apply inside or near to Black Holes ? Is the Black Hole circumstance similar to what pertained at times near (whatever "near" means) to the Big Bang? Does it make any sense to contemplate that journey where you end up where you came from? Do you not just (as a thought experiment) keep creating "new universe" if the universe is flat at large distances? Is it not the (non existent) curvature that would cause you to return to the starting point? I realise my understanding and imagination are probably critically lacking in this area.

Do we get different curved geometries in all Spaces that have different forces(= fields?) present ? I have never heard of space time curvature being applied to other areas like magnetism but are there also geodesics in magnetic fields, as an example and is it right to also talk about a spacetime curvature in that context as well? If one needs to calculate the path of an incoming object that was subject to the Earth's magnetic field is it possible to do so (ignoring gravity) in terms of it following a "magnetic geodesic" ? Does such an object ,in a magnetic field undergo acceleration ? If it does, does that say it is not following a geodesic?

That is exactly what it told me. The first thing in fact. I accepted it naively but it seems to be a debate that I was unaware of. http://philgons.com/2009/04/the-passive-voice-should-be-avoided-right/

If an expanding wave of light is viewed as a sphere which increases in size and propagates away from the source, is it fair to say that a portion of the wave actually moves at 2c with respect to a corresponding portion of the wave expanding in the opposite direction? Is that true and does anything follow from that observation? Or is it not true and is this an example of how relativistic speeds do not add linearly ? Or is it perhaps an example of ,as I have heard the idea that you cannot use light as a frame of reference?

I have just found this resource. It shows up " spelling errors, style suggestions , or grammar suggestions " in your text. http://www.grammarcheck.net/editor/ .

Spot the ball? Here ,have this one on me

The interviewer says; (at around 9 minutes in) "I think true contact between 2 particles ,say 2 electrons is the point at which the space occupied by the electron could have no Planck lengths between it and the space occupied by another electron..... " The professor says that that way of looking at the situation simply does not apply in quantum mechanics . He goes on to say that things cannot occupy the same space and that the interviewer is trying to define "contact" as the time when the two footballs "overlap" (become one football -which never happens). He finds the interviewer's suggested definition for contact "extreme" (he means "impossible" ) He also says (the Prof) that "you cannot define an electron like a particle like that"

I don't think "logical" adds anything to what are supposed to be scientific observations. If a scientist( which I am not) allows him or herself by what seems "logical" it may be the equivalent of him "resting on his laurels". If something appears "illogical" ,however it must be a sign that something is amiss ,either with the observation or the interpretation of the observation. That it appears "logical" though may add nothing to what we already (think we)know.

Get it fixed ,man (no pun included).

Another one got through,imatfaal

On the other hand ,when I heard the usage "amn't I ....?" I put it down to a similar kind of grammatical snobbery. It turned out ,years later that I learned it was simply part of "Irish English" https://stancarey.wordpress.com/2014/03/04/amnt-i-glad-we-use-amnt-in-ireland/

It is a correct policy. The worst thing we can do is to talk past each other.

Fine by me . I have lots to learn.

bm?