Hey, within a factor of 2 is fine as far as I'm concerned.Originally Posted by stewart38
We could have got away with that
Both came out with total *******s and people believe it
At any event, the key point is that the relative error in considering the world as flat behaves like (1-cos(x/2)), where x is the subtended angle. And for small x, 1-cos x/2 varies with the square of x.
In other words, if the error over 25 miles is about 10m, then the error over 2.5 miles is only a 100th of that, or 10cm. And the error over a quarter of a mile will be 0.1mm. Which is why the world seems to be flat over the kind of distances easily measured.
If we accept that the above equation is correct, then what is the minimum mass required by a persons' backside for a standard quarter-pound cheeseburger to maintain orbit around it?Technically it's F=ma
He changed the actual formula later in his life.
Mass–energy equivalence - Wikipedia, the free encyclopedia
This was years ago mind, but basically
All I know is John Barns mention quarter-pound cheeseburger yesterday
If I were to argue that the earth was round and DavidF was to argue that it was flat, I'd probably lose the arguement, so I'm not even going to go there...I can't believe people are even bothering to offer any proof that the earth is not flat
Nothing better than a heated debate dude!
No. You can have a model for which there is no accepted evidence of disproof, but that is all. In mathematics and logic, you can have absolute proof, but all such fields begin by postulating some facts. So the proofs are true, given the postulates.
Yup, it's wrong. It works really well with particles much bigger than an atom travelling much slower than the speed of light, though.
See above. Faith is necessary when applying a not-yet-disproven theory to a new problem. Your past experiences with doing this have worked out, so you do it... but it is faith that your experience with inferential reasoning still works.
Erastothenes measured its circumference more than 2000 years ago. On a solstice, a stick held vertically at noon on the equator will not cast a shadow, and yet if you move a long way away, a stick held vertically at noon on that day will cast a shadow. You can measure the length of the shadow and the distance to your earlier point. Then the assumption of roundness leads to a bunch of arithmetic leading to an estimate of the earth's circumference. That's not a disproof of flatness, of course.Oh and if anyone can prove the world isn't flat (beyond hills etc) I'd be interested
Ah, well then. This happens because if scientists presented theories which they use as facts (because they've never been disproved) to the general public as "this theory explains <this phenomenon>", you would have a miscommunication, because the general public thinks a "theory" is a wild-ass guess. So scientists call them "facts" because the difference between them and a fact is less than most of what the general public cares about.
This makes life as a scientist talking to the media very difficult. They want you to use absolutes in the soundbites, and the data never support that.
Euclidean geometry is probably what you think of as "normal geometry" ie. the geometry of points and lines in a rectilinear space. There are other kinds of geometry, which begin with different postulates. Euclidean geometry is only approximately true on the surface of the earth, because the Earth is actually slightly curved. Hence the existence of these paradoxical proofs of the earth's flatness. If the earth's surface was Euclidean (apart from the bumpy bits) then their proof would work... the proof doesn't, and the simplest explanation is that the surface is non-Euclidean.
I don't know the answer why this is, just know it is something to do with diffraction. I'll try get the full reason for this, next time I speak to my mum. She's into applied mathematics, and hence could probably explain it better than my "hand waving".
Tunnels are rarely straight anyway; for example the Channel Tunnel alignment varies quite a bit to pass through the best rock for excavation. Incidentally I understand that one of the reasons that there are much more Underground railway tunnels on the northern side of the River Thames is that the ground is much better for tunnelling on this side.
Basic surveying technique; stand in one point and measure the angular deflection to two targets in both directions. Move a set distance to a different location, and measure the angular deflection to the two targets. You can then relate the position of the first target to the second target accurately.
The surveying for really big projects does take the curvature of the earth into account, but it has to be a massive project for it to make any difference.
Yes, because he must have started with the hypothesis that the sun was infinitely far away; the same lengthening shadow effect would be caused if the sun was orbiting the equator a few hundred miles away.
Thinking about it, anyone who travelled would very soon realise that the zenith of the sun was much higher in equatorial latitudes; that in itself would require explanation for which a spherical earth would be one of only two explanations. Add to that the fact that no matter how far east you go, the sun is just the same size at the point at which it rises, which would make a flat earth hypothesis rather shaky.
The flat earth thing is a myth; you can go to various places and see orreries which were made in the middle ages and - although they follow the classical model, with the sun and planets orbiting the earth - there's never anything but a globe of earth in the centre. You probably have to go back 5,000 or so before you can confidently state that nobody realised the earth was round.
Yeah, and the more they dislike or disapprove the theory, the more of a guess they think it is.
Yah, but here I am talking about up/down straightness - I suppose I should have said 'level'
I bet it is much more to do with the fact that a) all the business and administrative part of the metropolis is on the north side of the river (Westminster, the City), and b) until relatively recently - when civil engineering projects have become relatively far more expensive - the population south of the river was much smaller.Incidentally I understand that one of the reasons that there are much more Underground railway tunnels on the northern side of the River Thames is that the ground is much better for tunnelling on this side.
There is no difference between measuring up/down straightness & sideways straightness. The lasers for tunnel surveying are being used as a modern more accurate version of a theodolite. Modern tunnels go up/down quite a bit along the way (such as the Dartford tunnels (however these are short enough that normal surveying equipment would be accurate enough). It's not the straightness that matters, it's the position in "space".
I can quote wikipedia (London Underground - Wikipedia, the free encyclopedia), but the history of the London Underground is much better explained in an excellent book by Christian Wolmar, (the London Evening Standard transport correspondent). From memory, the ground on the north side of the Thames is London Clay (about the best tunneling material you can get), whilst the southern side of the Thames consists more of pervious chalk layers. Whilst the chalk is relatively easy to tunnel through, the groundwater levels are quite high, and hence tunnelling is more problematic.I bet it is much more to do with the fact that a) all the business and administrative part of the metropolis is on the north side of the river (Westminster, the City), and b) until relatively recently - when civil engineering projects have become relatively far more expensive - the population south of the river was much smaller.
Yes, but I think what Barry's getting at is that you'd expect variations in air density to be largely a function of depth, rather than of position. So if the laser light is being refracted due to variations of air density, then it's the up/down straightness that is important.
You underestimate Erastothenes. He used a series of measuring points at different distances to distinguish the results from the "near sun" possibility.
Plus i suppose the fact that when viewing far off mountains you cant see the bottom might have made them think?
Add to that the fact that no matter how far east you go, the sun is just the same size at the point at which it rises, which would make a flat earth hypothesis rather shaky.
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Although if you thought that the earth was like the top of a table and that you would fall off if you walked too far then they might not have considered this significant.
I noted that the flat-earthers are the focus of the BBC online Magazine today.
They're condemning Microsoft's current advertising campaign for Vista, which pokes fun at flat-earthers. It's amusing, but of course, if there were several hundred million believers and Microsoft had been poking fun at (for example) some bloke claiming to have split the moon in half, not amusing. Clearly the flat-earthers need to go on a major recruitment drive...
is there free coffee at meetings ? I'm a good 30% of the way to being convinced on that alone...and if there are "snacks" well...
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