This is slightly problematic. A laser beam will not traverse a perfectly straight line, for the same reason that the sun remains visible for some while after it is below the horizon: air is refractive and will bend the beam downward. Not quite to match the curve of the Earth, but enough that it will not match the raw measurement.
If the sun is visible, then AFAIAC , by definition, it is above the horizon.
You can use the levelness of water in a simpler way. Build a large pool, in a rectangular shape. Make sure the sides are absolutely straight - then fill it with water. You’ll find that water drains off the short sides, because of the curvature of the Earth, if the pool is large enough.
For that matter, try to create anything that is both straight (measured by laser) and level throughout (measured by spirit level) - at some point, these requirements will conflict.
In certain atmospheric conditions, the refraction can be increased. I’ve seen flat earth essays where they found a picture of a far-away city that you can see above the horizon, due to refraction. It’s probably a cold Lake Michigan and very still air in the morning, but the flat earthers don’t seem to comprehend that light can be refracted by air.
ETA: A good example here.
The atmospheric refraction only applies to objects which are on the surface of the Earth.
It is meaningless to talk of the Sun being “below the horizon yet still visible”.
Bullshit. If the earth had no atmosphere, the position of the sun would be “below” (obscured by) the horizon earlier than it is with atmospheric refraction (which is also what reddens sunset/sunrise).
My point is that it’s hard to discern the curve from so close to the surface. Imagine a giant spherical water tank or something, 40 feet in diameter. The plane is then half an inch off the surface, to scale.
The round table analogy is meant to show that the horizon itself is flat, the same as the rim of a table is flat. (Of course, the ground between you and the horizon isn’t flat, so a better analogy would be a slightly domed circular table.) You’re not seeing the curvature of the Earth, you’re seeing the curve of the “rim”, which will look more curved the more you look “down” on it.
Though this sort of experiment is actually rather hard to do in practice. It’s essentially the Bedford Level controversy that so bedevilled Alfred Russel Wallace in the 19th century. The experimental complications give the deniers lots of quibble room, at least in their own minds.
Similar in concept, agreed, but what I am suggesting would involve far fewer variables than in the Bedford Level experiment…Occam’s razor would be the watchword .
A mile long water level would be difficult in practical terms, but the same result could be achieved with a shorter, more manageable level, and increasing the number of posts accordingly.
You know the reference to turtles wasn’t random, right?
The professional debunker James Randi will only countenance challenges where the results of the challenge are immediately self evident. I can’t speak for Randi and I don’t think I’ve ever heard him say why he has this requirement, in so many words.
But I think it is because idiots - and particularly determinedly self-deluding idiots - will find a way to discount the results of any experiment or challenge that cannot be taken in at a glance. It is said that “justice must not only be done but be seen to be done”. Similarly, I think that to convince such idiots the results must not only be correct they must be so obviously correct that even an idiot can see it.
That’s really the flat earth thing in a nutshell. Of course many purported “believers” are scammers or have their tongue in their cheek. But for many the reason they believe in a flat earth is that’s just the way earth looks from where they are standing. And unless you can provide them with a a proof of a globe earth that is similarly as self evident, they are never going to accept it.
I guess the real test of the Earth pizza is to take an airplane to the southern ocean (near the edge) and fly west from Ushuaia, keeping the Antarctic coastline at a fairly constant distance. If the Earth was flat, the plane would constantly be bearing to the right to keep from flying into the ice that encircles the world. One should train the FE in flying the airplane, so that they can observe for themself – if that is possible.
But I thought you said they thought the wall of ice was only 200ft high?
If so, and if you can find an FE’er who can fly a sufficiently long range plane, why not just get them to fly south from Ushuaia and see what happens?
Honestly, I think I would be disinclined to engage FEs in debate the first place. They can believe whatever they want to believe, as they are so very fringe that they harm no one. Though, it is an interesting thought experiment, to prove heliocentrism conclusively to a person standing on the ground. It is kind of difficult.
It depends on the level of abstraction they can cope with.
For example, to me,
[ul][li]I can stand on the ground in the very early morning and evening and see bright specks of light going overhead. [/li]
[li]I can look on websites and see that people are able to predict, to the second, when those bright specks will go over. [/ul][/li]The only plausible way I can explain these two facts is by assuming that the people running the websites understand really well the way the bright specks move. And those people say the earth is a globe. I think they must know what they are talking about.
There are alternative explanations; there could be a worldwide conspiracy of astronomers who know the earth is flat but just lie about how they actually predict the positions of the bright specks. Or I guess the bright specks might move in a way that exactly imitates the way the specks would move if the earth was a globe (even though it isn’t one). But both of these theories seem immensely implausible.
What they say is that the Earth is a pizza and the sun-lamp-thing moves in a circle above it. That the sunset is just an illusion of perspective (it only appears to be setting because it looks close to the horizon because it is so far away). This glaring flaw in this argument is that you can watch a sunset and see the sun get bigger as it crosses the horizon – as with the harvest moon. I cannot see how the perspective model could address that. For most of the day, the sun subtends exactly the same angle, except at sunrise and sunset, when it is supposed to be farther away but somehow looks bigger.
But the earth is not flat or even “slightly domed”, any curve in the rim is the same as the curve of the dome therefore if you are high enough to perceive the curve of the rim, you are effectively seeing the curve of the dome and therefore the curvature of the earth.
No you’re not. The rim is not curved “up and down”, it is flat, totally horizontal. Think about it: the horizon is the set of points that are as far away as you can see over the curve of the earth. It is the intersection between a cone centred at your eye and the surface of the Earth, therefore it is a circle. (Ignoring local topography, of course).
You can ignore the curve of the Earth between you and the horizon, because by definition you are looking over the top of it, and it is not blocking your view of the horizon. You might as well imagine slicing a small portion off the Earth, centred under your feet, and defined by the circle of the horizon. That circle is totally flat, regardless of what the ground you sliced off is doing.
The higher up you go, the more you are looking down on this circle (and meanwhile the circle is getting bigger because you can see further to the horizon), so the more it looks like a circle rather than a straight line, until you get to the extreme case where you are out in space and you can see the whole circle of the horizon, which will get closer and closer to the circumference of the Earth the further away you get.
As had to be compensated for by some rather clever engineering when they were building the LIGO observatory, each site of which consists of two 4km-long tubes, which had to be laser-straight.
In other words, the ends of the tubes had to be about 4ft higher than they would be if they were gravitationally level.
Thanks! A great example of what I was thinking of.
Not, of course, that any argument involving LIGO is likely to carry any weight at all with a flat-earther.