studiot

your actual question here is Unfortunately the answer here is that nobody really knows. It is empircal. That is appears to be an observed fact in the face of the unavailability of alternative hypotheses that do not contradict other existing observations. Read my last sentence very carefully because alternative and accepted hypotheses have been overturned in the past on the basis that they predicted something that does not happen by observation. The most spectacular such overturning is probably the discovery of oxygen when it was held that if a substance burned it lost something (which seemed very reasonable at the time), but when all the products of combustion were first collected and weighed their weight was always found to exceed the original substance weight so in fact the only tenable hypothesis was that the substance gained (combined) with something unknown.

This could be an interesting thread. It has a title but no point of discussion. One question. Do you want to discuss just 3D space or 4D spacetime or both or none of these ?

How is this time travel ? How is travelling forwards in time in any way consistent with the OP which specified travelling backwards ? Are you going to address my comments in response to your previous post? Happy New Year.

This is the sort of 'time travel' that is not physically possible, in the spacetime manifold that we observe around us.

Edit Yes, look carefully at my train manifold and you will see the beginnings of the model. In essence, yes. See my earlier posts.

Nothing stops you from pulling the trigger. I already explained that neither you , nor your trigger can 'travel in time' the way described. However if folks want to discuss why 'time travel' is impossible we should really do this in another thread.

This is exactly one sort of situation I had in mind when I said that the commonly understood time travel scenario is impossible. The twins demonstrate another form of time travel. The killing your father sort is impossible so no paradox arises.

I mean that the in particular the time sub manifold of the spacetime manifold is the wrong shape. (Shape is defined by the relationship between the points of a manifold) There is only a direct relationship between 'adjacent' points in the time sub manifold. (That is a definition or another way of saying there is only one time dimension). Conmsider another one dimensional manifold - a single tack railway. How would an express train pass a slow train on such a track ? It may be possible for microscopic quantum objects to do this but not for macroscopic material ones. Immaterial waves also have this capability.

Well I don't agree that time travel ( as you and Moontanman appear to envisage it) is possible within the universe as we know (observe) it. The spacetime manifold is the wrong shape to allow this.

Computability is a branch of Mathematics, it is not about IT in general or any sort of 'Computer Engineering' Note that not all computing technology is based on 'logical systems', there are for instance such things as analogue computers which work on entirely different principles. Swansont has probably the most relevant comment There is a heirarchy of systems of logic, known as First Order, Second Order and so on. The most commonly referred to is First Order Logic which basically corresponds to the popular idea of systems based on black and white, one or zero, high voltage or low voltage, True or False... etc. Associated with FOL is something called 'The Law of the Excluded Middle' This declares that every possible result is either a 1 or a zero or whatever. Or as the name suggests there is no middle or third option. This works very well for logical systems that can be broken down into simple enough parts. But many systems have compound situations and FOL can fial in these cases leading to such paradoxes as "Nick the Greek says that all Greeks are liars" Second Order Logic dispenses with the Law and can overcome these paradoxes. But there are many other variatios of the theme, both in the 'hardware' (physical implementation) and the 'software' (rules) of logical systems.

You are actually asking about two different things. 'Computability' and 'Logic'. In the UK the definitive books is https://www.amazon.co.uk/Computability-Logic-Fifth-George-Boolos/dp/0521701465 (Boolos is the principal author) Earlier editions can be had for a few quid.

Thanks all for you input. SJ in particular I am not ignoring you, I just wanted to go to bed. Interestingly I don't get the problem on my trusty old Dell P4 optiplex with Windows XP, that I use for serious work.

Update. I got a X to 'close' in the top left corner of the latest one. When I clicked close I got a Ads by Google notice replacing the original ad When I clicked to 'not see this again' I got three questions as to why not Can't see why they think I( am ever going to take an Expedia holiday or buy cushions for my non existant flat or other such rubbish.

Windows 10 with edge.

This project aims to produce 300,000 tonnes annually of hydrogen and derivatives from solar and wind electricity and water. The African nation aiming to be a hydrogen superpower - BBC News

So why don't we move on ?

The title says it all. This never used to happen when I am logged in. Some adverts at the top, fair enough. But this blighter suddenly blots out my text input box in the middle of typing.

More good stuff +1

If this was an extract, thank you. I have substantial doubts about some of the results and conclusions however. The question of why it is necessary to consider transport mechanisms at all arises immediately. What chemical or radiochemical process generates helium ? Why can this not work just as well in Panama as in the Galapagos ? If the 'geothermal water in Panama is not volcanically heated, why is it hot ?

I didn't say what I've highlighted in neon (emboldened) in the quote I made from your post. I find it relevant because neither you nor anyone else seems to want to acknowledge my actual point(s) which I reiterate. (Text)books have become larger and become smaller over periods of years to decades or longer many times in history. I also made the point that in my experience we are currently in a period of size increase. I also made the point that these are averages. I also made the point that in one specific technical discipline this is significantly evident because there has been an explosion of books in this area and also explained more. But I also made the point that the reasons for both size increase and size decrease are manyfold. Thank you for acknowledging that if I were to find a five leaved clover in a some field, related the anecdote to say CharonY , and asked how that clover might have come about, it would be OK. Not a theory of everything, or even anything significant, but still OK.

It's good to have a propely thought out account. Thank you. +1

I said it was both complicated and not yet fully understood. New material and ideas are emerging all the time. I didn't really want to mention 'plume' theory just yet either.

Once again I did not say that. If you read my post that I thought it was you who like I said that for a variety of reasons, (and I gave some of them) textbooks have changed size, sometime getting bigger and sometimes smaller on average (again I gave examples of both). I also said quite clearly that accidental experiences (another 'definition/description of an anecdote) have sometime led to scientific discoveries in the past, although this time I only gave one example. If Fleming had adopted your attitude to 'anecdotes' we would not have penecillin today.

I suspect I'm smart enough not to be caught by such specious nonsense. Neither Curie discovered radioactivity, though they worked a lot with it and sadly died from it. I did not say this was an account of the discovery of penecillin. It was, however, the result of a single incident - which is what anecdotes are all about. Nor did I deny that there was intensive scientifc activity follwing that incident and continued subsequent developement thereafter. Incidentally that discovery led to the making of a struggling minor american company called Pfizer. (But that would be another anecdote).

Are you asking us or telling us ? Needless to say the Earth-Moon system is very complicated and has developed of more than 4,000 million years. Like swansont I would like to see some calculations to back that up, but remember you need to consider the Earth-Moon system to calculate water levels. Isotasy is a local effect. Two matters you need to consider. Firstly the earth's surface is curved not flat. You can't fit one or even a small number of plates to the surface of a globe. The direction of gravity is radia not parallel. Secondly a comment on magma to amplify (not contradict) what exchemist has already told you. The rocks from the surface to near the interface with the outer core (the core has at least two layers, a molten outer and (semi) solid inner) are generally solid. Here the temperature is actually hotter than the surface of the Sun. They are under enormous pressure, the deeper you go the greater that pressure, due to gravity. Because of that pressure, they cannot melt even though some are 'above their melting point'. When Earth movements relieve (some of) that pressure they melt and the pressure energy has to go somewhere so the rocks melt locally. This is the source of magma. Ultimately it is powered by gravity. Near the surface This magma breaks through at discontinuities and weaknesses to create the features of vulkcanism in general. There is a great deal more to it than this but I will stop there, and await your response if any, as you did not respond to the last pointers of information I offered.