What Shape is the Earth?

[peetee]

Think of the benefits of a world that existed on the inside of sphere. GPS would work with one satellite, trans-global travel would be quicker and everyone's blood pressure would be lower because the heart wouldn't need to work so hard to supply the brain. Best of all would be hill climbs would be a doddle for everyone and skinny people would be the last to the top.
However, bike tyres, roads and shoes would have to be fitted with velcro.

[kwackers]

GPS would work with one satellite

Pedantic, but you'd need at least three.

In fact thinking about it you'd need more than that, three would result in multiple points on the inside of the sphere where you'd appear to be in the same place.
It might be possible with four.

Basically you need to be able to draw a line from any point to each satellite and get a unique set of distances from which you can do your trig to work out where you are.

[peetee]

One satellite would be positioned in the centre of the globe (gravity would keep it there) and could position you accurately from the direction of your signal.

[Audax67]

Actually, it wouldn't. There is no gravity inside a spherical shell.

Larry Niven ran into this one when he wrote Ringworld. He had to write a sequel (as if he wasn't going to anyway) which added motors on the rim to keep it stable.

[Cunobelin]

I was led to believe it was shaped like a load of joined up orange segments.

Mercator had different ideas. His world was a rectangle.

.... and flat!

What I find interesting are the "Real World Maps which show countries in their "true size"

[roubaixtuesday]

I was led to believe it was shaped like a load of joined up orange segments.

Mercator had different ideas. His world was a rectangle.

.... and flat!

What I find interesting are the "Real World Maps which show countries in their "true size"

Interesting, I've not seen that one before. The Peters projection is equal area:



Of course, both miss out the turtle.

[kwackers]

One satellite would be positioned in the centre of the globe (gravity would keep it there) and could position you accurately from the direction of your signal.

How do you get 'direction' - the satellite is always directly above your head.

No, you need to read up on triangulation and ponder it a bit.

On a flat surface you need a minimum of three references. Inside a sphere I think you can get away with four.

[661-Pete]

Actually, it wouldn't. There is no gravity inside a spherical shell.

Larry Niven ran into this one when he wrote Ringworld. He had to write a sequel (as if he wasn't going to anyway) which added motors on the rim to keep it stable.

Not just one sequel, but several. You're referring to The Ringworld Engineers. The following, The Ringworld Throne, fell perhaps below his usual standard, but Ringworld's Children made up for it.

If you haven't already done so, take a look at the Fleet of Worlds series, written in collaboration with Edward Lerner, now running to five novels. Speaking as a fan, I can strongly recommend them.

[661-Pete]

Think of the benefits of a world that existed on the inside of sphere. GPS would work with one satellite, trans-global travel would be quicker and everyone's blood pressure would be lower because the heart wouldn't need to work so hard to supply the brain. Best of all would be hill climbs would be a doddle for everyone and skinny people would be the last to the top.
However, bike tyres, roads and shoes would have to be fitted with velcro.

This kind of construction was postulated some time ago - it's known as a Dyson sphere after its 'inventor' (no! - not that Dyson!). His idea was that it completely encloses the Sun, which thus appears directly overhead from all points. WIthout shade, the climate would be intolerably hot, I think, with no night. Where to place "satellites", I have no idea...

If you're into SF (see my previous post ) you could try reading The Time Ships, by Stephen Baxter - a sort of fan-sequel to H.G. Wells' The Time Machine - in which just such a construction is featured.

I should have added, of course, that Stephen Baxter had a long collaboration with Terry Pratchett (hasn't he been mentioned yet?) in The Long Earth series.

[peetee]

One satellite would be positioned in the centre of the globe (gravity would keep it there) and could position you accurately from the direction of your signal.

How do you get 'direction' - the satellite is always directly above your head.

No, you need to read up on triangulation and ponder it a bit.

On a flat surface you need a minimum of three references. Inside a sphere I think you can get away with four.

Forgive me as I don't understand satellite tech as well as radar tech - and that is very little given I used to market the stuff. However, info was on a need-to-know basis and one of the products was spherical so it could accurately position an object from its signal.
Or then again perhaps I am digging myself a rather big hole.

[Audax67]

Actually, it wouldn't. There is no gravity inside a spherical shell.

Larry Niven ran into this one when he wrote Ringworld. He had to write a sequel (as if he wasn't going to anyway) which added motors on the rim to keep it stable.

Not just one sequel, but several. You're referring to The Ringworld Engineers. The following, The Ringworld Throne, fell perhaps below his usual standard, but Ringworld's Children made up for it.

If you haven't already done so, take a look at the Fleet of Worlds series, written in collaboration with Edward Lerner, now running to five novels. Speaking as a fan, I can strongly recommend them.

Can't remember if I've read Throne or not, certainly not Children.

Niven must be knocking on a bit now. He was "this young author" when I started reading his stuff.

I'll have a gander at Fleet of Worlds - thanks.

[kwackers]

and one of the products was spherical so it could accurately position an object from its signal.

A lot of radar devices appear 'spherical', but radar is active. It broadcasts a signal and measures the return time then either uses a rotating antenna or an antenna array to figure out the direction (which are often hidden under spheres).

You can't use the same system with a satellite.
If your device was the active device then all it would tell you is that the satellite was over your head.
If the satellite was the active system then all it would really be able to tell you is just how spherical the inside of the sphere was. You could use a similar system to what planes use and use the radar sweep to trigger a transponder, but even that uses a GPS system to let it figure out where it is which it then pings back to the radar source.
(Not to mention if the radar was the active device the power output would be beyond what a satellite could realistically create. Plus, you also appear to have no sun, so solar panels are out of the question).

GPS is a triangulation device. It works because you receive a short 'blip' from each satellite. By measuring the time of each blip you can work out your relative position to each satellite but you need at least three accurately timed blips to get the distance otherwise you can't figure out where you are.

[Cyril Haearn]

Perhaps I am typical of "certain members on this Forum"....?

The fora are/is a broad church, thank the Lord

[landsurfer]

Have we missed "Rendezvous with Rama" ... A.C. CLARKE ....?
Rotating cylinder with centripetal force doing the gravity thing ?

[661-Pete]

Have we missed "Rendezvous with Rama" ... A.C. CLARKE ....?
Rotating cylinder with centripetal force doing the gravity thing ?

Yes I've read the entire series (the original plus three sequels co-authored by Clarke and Gentry Lee), though I'd call "Rama" a spacecraft rather than a planet (flat or otherwise). A tremendous epic work.

I suppose I'm about to initiate a debate, here, about the difference between the words "centripetal" and "centrifugal". To me, an object moving in a circle undergoes centripetal acceleration, i.e. acceleration towards the centre of rotation, and hence experiences centrifugal force, a fictitious force directed away from the centre of rotation. However, if an object is orbiting under a force emanating from the centre, e.g. gravity, this can be described as a centripetal force maintaining the object in its orbit by balancing the centrifugal force.

Of course in Rama there is no, or at the most, negligible, gravity, so there is no centripetal force. Centrifugal force is what keeps the occupants anchored to the inside walls of the cylinder.

Confusion galore!