December 13, 2008

How do we know ... what we know? In simplest terms.

I'm proposing an FPP to collect simple explanations of the physical world around us; a place to explain how we know what we know, but in simple, easy-to-understand, non-mathy ways. I don't intend this thread for matters up for debate; rather the opposite. If there is a mistake in a post, just correct it. If it's open for debate, try posting links to existing debates and leave it at that. In this way, the thread can be devoted to cataloging knowledge. A lot of what is known in science is predicated on previous findings. For example, we could not determine cosmological values (distances, masses, diameters, etc) without first determining the distance to our own star. So in light of this (pun intended), I'll submit the first "how do we know..." reply :) (I suppose I should really post a "... about trigonometry" first, but this one is more fun.)

posted by flurker 15 years ago
  • ... the distance to the sun? (commonly called 1 Astronomical Unit, or 1AU) By watching Venus, a planet closer to the Sun than the Earth, we can observe the 2 points it appears farthest away from the sun, and then measure the angle between the Sun and Venus at one of these points. Trigonometry then tells us how to find the distance to Venus in terms of the Earth-Sun distance, 1AU. Radar can then be bounced off of Venus to get the Earth-Venus distance in common units. Plug in the values and that's it! Of course there are many other ways, using the heavenly bodies, to derive this distance. The math: 1AU = Earth-Venus distance / cos(max. Sun-Venus angle) The measurement: (Wikipedia) The precise value of the AU is currently accepted as 149,597,870,691 ± 30 metres (nearly 150 million kilometres or 93 million miles).
  • Probability sums to 1.
  • Is that why Cook was in Tahiti observing the transit of Venus in 1778?
  • tracicle wrote: "Is that why Cook was in Tahiti observing the transit of Venus in 1778?" Yeah, but he forgot his radar.
  • I would love to contribute to this thread, but I have no idea how. I am feeling rather inadequate.
  • In general, everything that we now know started as an idea. It was then tested and proven to be true. Ideas that were proven false or not proven (debates!) were replaced with new ideas and again tested. That's science in a nutshell.
  • Some have yet to be conclusively proven, such as the origins of modern man. And by that I don't mean creationism vs evolution; rather the distinct humanoid species that cropped up on the path to our current state. New species of hominid are discovered all the time. Some of these are actually variations on existing known hominids; some may not even fit on our path but are offshoots that died off. New research into DNA, new methods of dating, and new fossil discoveries mean our ideas on human evolution are prone to continuous change and adaption. And that's my fuzzy contribution.
  • I like cheese.
  • Here's a fine meta-analysis on what we think we know: "Many caves...are but doors to greater caves which lie beneath, even as a man's words and deeds are but small indications of the dark caverns of murky thought lying behind and beneath." - Atla, the witch-woman of Dagon-Moor (Worms of the Earth by Robert E. Howard)