Thanks both

… I have downloaded it [complete with the weightless ‘s’ that must have drifted away]

MichaelG.

is there an executive summary ?

What is gravity? Would I be right in saying science dodges the question by simply defining a force to be anything that causes movement? In which case, although forces obey the same rules (i.e. their properties can be measured, and they have fields), they could all be different. Gravity, magnetism, electrical and the others might have a common cause, but I don't think there's a complete theory or explanation yet?

Without understanding the maths, I was happy with Einstein's proposition that mass puts a dent in the space-time continuum, allowing the orbit of this satellite to be calculated.

But I think the maths is just a model. It doesn't prove 'space-time' really exists, only something like it obeys the same rules. I don't pretend to understand it. If space-time exists, then what is 'space' and what is 'time'? My head hurts!

Dave

More weirdness I was trying to understand recently:

Light has no mass and therefore cannot be affected by gravity. Light can only travel in straight lines in a vacuum except that the matrix it is travelling straight within may be 'bent' by gravity. Therefore the model concludes there has to be some underlying matrix we choose to call space/time or subspace or whatever. Unless it's all a convenience and light can indeed be bent by gravity despite havng no mass…

More confusing was that the 'Big Bang' accelerated the constituents it created outwards (while having assorted interactions between them on that journey) yet the assorted bodies created are confounding expectations by continuing to accelerate away from each other and expanding total universe(s). The implication being that space/time has a repulsive force within it. A weak repulsive force within space/time would imply an antigravity effect? Which by its nature cannot coelesce to a powerful antigravity force in the way gravity does?

pgk

Jim in respect of fooling the senses, I visited the Museum of Science and Industry in Chicago many years ago whilst working near Chicago. They had an excellent exhibit of coal mining, access to this exhibit was via a lift located on the top floor of the building, when the lift descended there were what appeared to be “windows” in the lift and on the outside of these “windows” were scenes scrolling past that gave the illusion that you were in a pit cage descending hundreds of feet into the bowels of the earth. When you arrived and stepped out you were for all intents and purposes in a working coal mine, a brilliantly constructed exhibit, and the elevator really tricked the mind. Dave W

Dave W's posting on lifts and coal mining reminds me of a simple question:

You are decending by vertical lift into a very deep coal mine and the only light is from a safety (Davey/Stephenson) lamp. The rope fails and the cage free falls to the bottom of the shaft. What happens to the light from safety lamp before you die?

JA

Comment: This has everything to do with gravity and weightlessness

Edited By JA on 18/03/2021 18:17:09

Not just your simple mind, Sam … mine too

MichaelG.

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Edit: … but I lost the will to investigate any further when I saw the ‘cookie settings’ hurdle required to look at the linked item: 

“ The modules occupy an area of 17,657 cubic feet, reports Igor Bonifacic for Engadget. “

Edited By Michael Gilligan on 18/03/2021 18:55:34

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Sam … it was just that the Engadget site not only has the usual raft of opt-out choices; but also special, rather convoluted, arrangements for Facebook and Twitter … and I haven’t got the patience !

In my book it should be easy … No means No

MichaelG.

I saw that as well – and made my feelings politely but very clearly on the Feedback form that Google et al should have NO (yes, I did use capitals) access to official Government forms and systems – no question, no excuse.