geordief

Is it an impossibility to "create a new universe" at some point in the present universe? Obviously assuming some far off technical ability is it theoretically possible to create a new "universe" that would have its own independent laws and also be unaffected by and not subject to the laws of the universe wherein it had been created? Is that an entirely impossible concept? Would there have to be some kind a a barrier between the two universes? Would the barrier have to obey the laws of both universes? If such an attempt were ever to be made would someone just pipe up "it is the same universe ,just a subset"?

cui boner?

Am I right to think that this trajectory (through the Earth) is along a local geodesic in space time ? The initial acceleration will determine where (on the surface of the globe) you will "resurface" )? Adding a time constraint to the trajectory adds nothing to the exercise ,does it? It would be impossible to "resurface" in Glasgow 7 days later by taking this route ,would it? How long would it take for a journey from London to the far side of the globe and back up to London?If you were aiming for Glasgow the time would be determined at the outset by the length of the round trip (about 16,000 miles ) and the average speed.

Thanks (I realized after I posted ) that any spacial detours were irrelevant. Is it also irrelevant if speeds are allowed to be relativistic? So my question is entirely trivial? EDIT: Does the acceleration involved make the question any less trivial? Does it (the acceleration and deceleration )need to be spread out as much as possible over the entire length of the journey?

I am not quite sure this should be in Relativity and I am not quite sure why I am asking the question .I am "fishing" a bit ,perhaps to flesh out my ideas but this is the question. Suppose we are in London and need to be in Glasgow in a week's time , what is the most energy efficient method of getting there? (obviously the method of transport and all other environmental factors are the same no matter which route is taken) So ,the first option could be to leave directly ,arrive at Glasgow in 6 hours and remain in Glasgow for 6 days and 18 hours. As an alternative itinerary we could also leave at once , go to Norwich in three days (traveling very slowly) ,remain there for 3 days and then take 24 hours to complete the journey to London. A third possible itinerary might be to stay in London for 6 days and 12 hours and then journey to Glasgow taking 12 hours to do so. In all cases we are going to travel approximately 500 miles due North and take 7 days overall to do so. Out of all the infinite possible permutations involving velocities ,duration of velocities and lack of velocity is there one path between London and Manchester that is the most energy efficient when we know the direction from one to another and the time that is to be allowed for the journey ?

Pretty sure I know that "acetic acid" smell you are talking about. I think it is is the cheap silicon stuff that is not waterproof or paintable. I have worked in the past with pickling onions and hate that sweet ,sickly smell(esp with onions).

Have analogies got any benefits at all? Or are they just like a straw a drowning man might grasp at when ,if he but knew it the water beneath had a rock to stand on. ? Do they allow a student to glimpse a hazy outline of a theory or a model before he or she has got up close?

"on page 6 they give an analogy whereby spacetime is denser around massive bodies." was actually from my post#1 (the OP) ,studiot. You seem to have formatted the quotes incorrectly and attributed it to Tim88. Not sure if that changes the sense of your post or not....

Thanks as always I appreciate your (and others' ) forbearance -I sometimes wonder about the concatenation involved in my own mentation No I do like that analogy (if analogy it is) where the surveyor works out the curvature without benefit of elements outside the set of points in the line .(I may have seen other examples of this -figure 3 in http://www.cco.caltech.edu/~kip/scripts/PubScans/BlackHoles-Thorne-Starmus.pdf ,for example **) Can I extrapolate from your kerbline analogy to suppose that in a 3d+1 space-time environment we can calculate curvature (or perhaps something closely related to it) by first considering the line joining 2 extremely neighbouring points in the space-time manifold and then another line connecting one of these two points with a third point ? Would the "angle" (perhaps a group of angles?) between these 2 lines show the curvature of space in the local area?? Or would it at least have a close mathematical relation ship to the local curvature ? ** the ant walking up and out of the black hole

Can try and dig a bit deeper into your analogy? What ,in spacetime would the points A and P (well the set of points along the rubber band ) correspond to? My first thought would be events or potential events in spacetime. Would that be correct? A concatenation of (potential) events ? Or am I badly misunderstanding the GR/SR model ? Can my (mis?)understanding be shown up by your surveyor's analogy? Or is this an area your analogy doesn't "reach" ? Are points A and P simply 2 points in space along the line taken by a body (or a beam of light) connecting 2 other points in space (or space-time depending on terminology)?

Yes ,sorry I didn't mean "misrepresentations" in a judgemental way -I was trying to be objective but used the language ambiguously.

Don't all analogies rely on misrepresenting the actual situation? Will the best analogy just have the best (=most overlookable) flaw ? When it comes to 4D representations is it possible to design a computer graphic that will show how it would look like from a 5th dimension? Or would that be pointless since ,as I have read Spacetime has intrinsic curvature and so (if I understand right) can not be embedded in an external dimension anyway ? By the way , those posited extra dimensions (in String Theory?) do they only apply at the quantum level?

We are talking about a 4D volume inside a 4D "parallelogram". I think one of its apexes is at an event in Space-Time (hope I have not put my foot in my mouth yet) Can this 4D volume have anything "inside" it or is it simply a mathematical construct that allows us the calculate the space/time ratio at that point? If I am still "on board" , is this ratio closely connected (mathematically) to the curvature of space-time at that point?

And (at least as a mathematical concept) space-time is not compressed so much as squashed. Time,say is compressed and the spatial dimensions are correspondingly stretched? So the overall "volume" of space time is unchanged? Does that also answer my "volume" question (or at least define the question ) in posts #5 and #7 ? All I need is to relate that "volume" to a measurement for mass-energy (with units that cover both ) Can that be done?

I have been searching for the "author" of the rubber sheet analogy for the curvature of Space Time and the question has arisen as to whether there exist better analogies. I can well imagine that all analogies are likely to be flawed and misleading to one degree or another but perhaps they can be educational provided (as is not the case with me personally) the mathematical model is well embedded in the mind of the student. Be that as it may ,I have come across this alternative analogy. Are there other ,better ones? http://www.academia.edu/815814/Reflections_on_a_Variational_Principle_in_Space_Gravity_and_Light on page 6 they give an analogy whereby spacetime is denser around massive bodies. quote: "The explanation of displacement of light-source location, whether star or quasar,as a gravitational lens in a gravitational potential field certainly improves on the rubbersheet analogy. Spacetime localized, that is, compressed by a massive body, such asthe sun, can be visualized as becoming denser around the body. In gravitational redshift, to pass through the increased denseness, a light ray contracts in height thus lengthening its frequency until it passes out of the lens"

OK .Will do.

By the way ,is that quote Einstein pictured space as a three-dimensional version of a thin rubber sheet. wrong (as an analogy) ? Should/could it really read (not necessarily accepting that Einstein did picture anything along any rubber sheet line ) Einstein pictured space-time as a four -dimensional version of a thin rubber sheet. ? Would that take it from an analogy to a closer description,perhaps a correct one?

I will just give you the reply I was drafting. jthorusen (post# 32) on this site http://physicsworld.com/cws/article/news/2011/sep/28/galaxy-clusters-back-general-relativity thinks it may have been Einstein but no one follows up on this.. I also found this :https://worldhistoryproject.org/1915/albert-einsteins-general-theory-of-relativity-is-published "General Relativity describes gravity as a warping of space itself, not as a force. Einstein pictured space as a three-dimensional version of a thin rubber sheet. If you put a heavy object on the sheet, it makes a dent, and therefore an object's path would be affected by that dent. So, planets orbit the sun because the space around the sun is curved in the 2-D equivalent of a funnel or basin." I have no idea if the author (http://burro.astr.cwru.edu/)was sure of this or just talking vaguely No , I meant the extent of apace time (mathematically) per se. Similar to the distance between events but something to measure the spacetime enclosure of a subset of events. Like a "volume of spacetime "

From a look around the internet ,I get the feeling that it may have been Einstein -or at least a few people attribute it to him. It doesn't come up in his quotations ,not surprisingly but I have found an academic who says that is how Einstein pictured it so perhaps it could have been his idea, As an aside is there a way of measuring the extent of spacetime and the amount of mass-energy in the same units (similarly to how time and space do when c is introduced as a conversion factor)? I used to listen to those broadcasts too (great music-it was the same wasn't it?)-a long time ago now.(viva the BBC)

Seems innocent enough to me. Just holding back a sneeze , surely? (impeccable manners)

That should have been one of the questions in the debate Maybe he will write a sexual seduction self help book for billionaires.

So ,if you know the spatial dimensions of an object at rest you can determine its motion wrt yourself (along all 3 spatial axes) by measuring its length contraction or expansion in the corresponding direction? So motion (wrt an observer) is a function of how "distorted" the object appears to an observer? Out of interest If the object is approaching directly at .9c would the contraction (or elongation -I am confused) be the inverse of the contraction of the same object receding at .9c?

Has Farage some primacy amongst his advisers for this debate? If so can we anticipate his line of advice? "Why don't you retire?" hopefully ....

So a bit similar to the way there is no maximum frequency?

I don't understand. You mean indirectly?