geordief

If lifeboats ever became remotely feasible the danger might perhaps that they will only be for a few and policies might be followed which effectively set the Earth adrift as the motivation for making the hard choices on "terra firma" would be undermined. But I cannot see "lifeboats" ever becoming realistic (in a relevant timeframe) and I think if we do not manage our shrinking world we may all go down with the ship one way or the other. That discussion reminds me of the so called technological fixes to climate change that supposedly allow us to pollute the planet and emerge consequence free.

I have just been watching a documentary on BBC2 "The Search for a New Earth" http://www.tvguide.co.uk/detail/2790044/131126240/the-search-for-a-new-earth about the possibilities of sending a manned mission to Alpha Centauri ( can I say "don't laugh" ?) Along with Hawkin's warnings that many of us are no doubt familiar (in my case sympathetically so) with, the subjects of possible suitable destinations and methods of transport were addressed. I was left dissatisfied since ,although it appears technically possible to cut the time of journey to Alpha Centauri and its posited Goldolocks zone planet (all 4 light years distant from Earth) by means of ground based laser propulsion the crucial question of how to land on a planet was not addressed. If a theoretical manned craft can be sent to the neighbourhood of Alpha Centaur by accelerating it to relativistic speeds (10-20% of the speed of light by the looks of it) how can this craft be decelerated? A fly past is of no use whatsoever (not a problem for a fleet of mini craft equipped with sensing tools but useless for a manned expedition) I cannot see the point of a programme like this that does not address this point. And I cannot really see the point of even discussing this putative manned mission /colonization of Alpha Centauri unless there is consideration given to this (it seems to me) intractable problem. Has anyone a clue as to how any craft can be decelerated from such high speeds? Are there any possible methods?

I was happy with the "all the universe applying force to a neutrino" as a kind of limit. It means there is a limit of some kind (I wonder if the expansion/evolution of the Universe means that the force available to cause an acceleration in a part of it implies an increase in the force available or whether the greater distances involved mean that more work is required for this hypothetical task)

Feels like you answered the question. It also feels as if "infinity"as a word should be extirpated from the English dictionary if it was practical. It seems to be an entirely negative concept (dreamt up by some foreigner no doubt) It seems like shorthand for a process rather than an actual thing in its own right. And the force available to a finite system is also finite.....

Yes Gabriel's Horn does seem to show an infinite quantity enclosing a finite quantity.I think in my scenario the boundary is expanding infinitely and enclosing a finite (4D?) volume. At T^-42 SECONDS the Universe was inflating or expanding (I think). Was it finite or infinite then (is that a valid question?) If it was finite then (or perhaps just a finite times greater than earlier) how is that moment in the development of the Universe any different to say T^ +100 seconds? Can it be expanding infinitely but finitely measurable at any "instant" (I think "instant" must be a loose term)

But for a given mass the available force (sourced from within the system) would be finite and a function perhaps of the mass of the system. So would there be a limit then? Can the Universe be bounded but infinite? (is there such a thing as a dynamic boundary that might apply? )

(posted in this subforum as I couldn't see where else it might fit) I have searched around on the net and see that this is a question that has been asked often before and the answer is invariably that ; "no,there is no theoretical limit to the rate of acceleration that can be achieved." (not real quotes) If we take a unit mass (is there such a thing? If not can we set mass at a randomly chosen constant ?) can we say that this mass is then subject to a maximum rate of acceleration? Since I imagine that mass may be a term that applies to a system rather than any one particular object then I guess I am asking whether a given system with a given mass contains within it a maximum rate of acceleration. Could I also ask (possibly for the second time ) if there is a theoretical mass of the whole universe? (does this mass tend to zero in a "heat death" scenario? )

Sure,by "everywhere" I just meant everywhere in our Universe at that time of development. If multiverses ever become a testable theory then I might have to rephrase the question.....

I keep hearing that the "Big Bang" happened everywhere and was not an explosion but an inflation or expansion. Well ,it is not claimed that the Big Bang Theory accounts for the 10^43 second prior to its applicability . If the "Big Bang" happened "everywhere" does this not imply that at 10^43 seconds "everything" was in the same place? Does this not also imply that the "volume" of everything at that time had zero extent? (no top or bottom or left or right) If there was "extent" then would not some areas of the observable Universe differ from other areas in that they originated from different areas of the Big Bang ? Or was the "extent" small enough to make these differences zero? Second question about the "non explosion"...Is this explained by the fact that explosions need an external containment of some kind and this is not part of the BB Theory?

They are different expressions.I can imagine circumstances where "where it's at" might be appropriate (if "it" referred to a point on a journey for example)

:Mummy, for why did you put that book the which I was going to be read to out of up for? If "where it's at" is dated ,could it be a Dylanologism? (it comes in "Like a Rolling Stone" )

Can that "energy of the system" principle be extrapolated to encompass all connected systems? (there are no isolated systems ,are there?) Is it possible that the energy of the entire universe (to include the (unobservable part) is theoretically zero at all times?

thanks, i will have a look. btw. can you remind me again of that Bensen (?) book you recommended to me a few months ago (it was a historical account of the leadings up to modern Relativity ) i can't find it now without fine tooth combing my posts and I want to order it on ebay or Amazon. ps no chance of an (understandable) example of a waveform with just 2 components, I suppose.(since you imply they can be finite in number)

As OP,please no one respond to that post.

Thanks . I wonder what determines the make up of the composite waveform. Are there a finite amount of these component parts? (is everything smooth? ) What about my idea that the detecting object also has its own set of waveforms which also collapse when the detection event occurs ? Is this actually part of the model (just that I have not come across it explicitly stated ) ?

An object is apparently in some sort of "suspended animation" as it crosses "empty space" and then when an "observation " is made the "waveform collapses" and its probable location is "set in stone" (this is exemplified ,it seems to me in the double slit experiment) Is it possible to say with more detail what "collapsing the waveform" actually means? Or do we just have to say "well this is what happens and that is how we describe the phenomenon with words" ? As a side thought ,is there any mileage in the idea that when any "observation" is made , we are looking at two probability waveforms meeting/interacting/superimposing (that of the object and also that of the detector) ?

I thought I avoided struggling with "Reality" ,although the title to the OP is very bad ,

Well,to rephrase it in a practical sense ; when researchers are trying to formulate a successful theory for quantum gravity might it be the parts of the theory already "locked up " in quantum theory that are more likely to survive than GR? If quantum theory theory is refined can it perhaps subsume the areas of application of GR whilst the opposite cannot be said? No matter how far GR is refined it can never perhaps explain phenomena that are now or will later be accounted for by "quantum theories" ? Is that what you thought I was trying to say?

Yes ,I see that(even in terms of the meaning/usage of the word ,that is not what a hierarchy is.I am not sure what one might call a hierarchy with just top and bottom. But since quantum and classical phenomena do interact (occupy the same space in various -even all?- scenarios) then perhaps my description was not as black and white as I ,probably mistakenly made it. I have to keep drawing attention to the obvious fact that my understanding of what I am asking about is extremely basic and pop sci.......

I am aware that our tools to describe and understand the various physical scenarios are models and not to be substituted (confused with?) what we are imagining them to describe. That said, these models can be separated (perhaps) into macro models (classical) and micro models (quantum mechanics) I understand there is overlap in the models and that the atomic scenario ,for example is described with the help of Special Relativity. So ,with those strong caveats ,is there any sense in which we can say that the realities described by the micro models have any sort of hierarchical precedence over those described by macro models? To get metaphorical (and wishy washy) ,is there something like an arrow of time that connects the physical "micro realm" and our every day "macro world" ? I was told before that "micro world" and "macro world" are unhelpful descriptions ,so perhaps that undercuts my question (which should perhaps really be in the philosophy forum,I suppose)

No.I have both.(on a PC)

Saw that post of yours. Didn't think it would happen. Thought this one was a joke till I looked at the the fake news.

I don't think an impeachment would necessarily lead to Trump's removal from office. One man's prediction ,while welcome is just one man's forecast I would feel.

I suspect you would be in a tiny minority and at risk from vilification(if you were voicing support for such a statue) . I could be wrong but I am not aware of any reason Rommel (I feel no inclination to give him his title) would even be deserving of recognition in the UK regardless of his having participated in the Nazi war machine. Other "German" statues might be more welcome (and deserving) I imagine.

Well said .