We have certainly seen Earth from space but it looks more concave then convex honestly.
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Um... there are sooo many things wrong with that.
When you travel halfway across the Earth, you traveled across the entire universe. The diameter of the visible universe is ~26.4 billion light years in length, which is about 152840000000000000000000 miles. How does that add up?
Well firstly the size of the universe is calculated based on a moving Earth and an Earth that is 8,000 miles in diameter and also calculated based on the idea that light never slows down from what we observe on Earth.
And actually the observable universe is about 156 Billion light years wide:
http://discovermagazine.com/2005/jan/cosmos-width/#.Uw4YHPldWuk using standard heliocentric mathematics.
However I think it is wrong in 3 key critical aspects.
1) The diameter of Earth is actually about 80,000 miles which means their base is 10x exaggerated for starters. (you actually take 25,000x3.1416 if Earth is concave to equal about 80,000 miles.
2) They say the Earth goes around the Sun 584 Million miles per year or about a width of 185 Million miles. If the Earth is not moving then they are adding at least 23,125 times the distance to Earth, if Earth's width is actually much bigger then they think it is they are inflating the numbers by 10 times which would multiply the above number to 231,250 times.
3) If the Earth is concave then space actually shrinks the deeper (closer to center) you get in the Heavens as density would increase so your physical size would decrease if we base this on the understanding that Hydrogen and Oxygen are the most prominent anti-particles in the universe then we have 7 layers to go through and each layer is vectored meaning we take the width and times it by 7 vectors which counts like this:1-4, 2-16, 3-64, 4-256, 5-1024, 6-4096, 7-16384. This means that we take the inflated number of 231,250 and divide 156 Billion by that number first to get our baseline or 674,594.6 light years then we further take that number and vector it 7 times. so we end up with about 41.2 light years. However this number is not done because they are also trying to measure parallax in Earths rotation this equals another 1,066mph that they are calculating into their figures which also inflates their numbers up to 1066 mph which means for every degree they measure in the sky they are calculating 2.96 phantom miles of width per hour, if they use 180 degrees x 24 hours it would be 12,792 phantom miles per mile that they would be adding to the calculation so take 41.2 light years and divide by 12,792 and you get a remaining number of 0.00322076297686053783614759224515 light years across for the width of the Universe. This leaves you with 1.176383677298311444652908067541 light days from one side of Earth to the center, however since that would only be the radius if you adjusted for concave Earth theory you would take that number and times it by 6 to include all the dimensions that light could travel which is inward, outward, north, south, east and west. so we get a total number which is about 7.0583020637898686679174484052462 light days thick or in simplified terms if the real year is 360 days and not 365.25 days then you multiply the number by 0.98562628336755646817248459958932 to get 6.956848030018761726078799249524 light days of total 3 dimensional width. Hope this helps you understand if you read it all why the universe is so much smaller then mainstream science calculates it to be.