On the thread about the Grand Canyon there appeared to be enough information for me to try to point out what bugs me the most about how scientists present their views, confusing their facts with their interpretations of the facts.
I'd like to give an example of a legitimate, scientific, legally-accepted example of an interpretation of fact being accepted as a fact itself: DNA "fingerprinting."
Almost everyone has seen a "DNA fingerprint" on TV, like on CSI or Law and Order:
Almost nobody knows what they're actually looking at. I'll try and summarize the process.
1) A sample of DNA, such as that found at a crime scene, is "amplified" by a process called "PCR"; this chemical process uses enzymes and selective "primers" to replicate specific sequences of DNA millions of times. This results in millions of copies of a specific gene which makes it a lot easier to perform tests on it. The DNA is stained with a visible dye (which is often UV-florescent to improve the photographic results.)
2) Enzymes called "restriction enzymes" cut up these copies of DNA by recognizing specific sequences of base pairs (called "restriction sites"). When they see that sequence, they cut the DNA at that position. The DNA in our genes contains long sequences of repeating base pairs accumulated from mutation called "introns." They're irrelevant to the production of proteins but they
are inherited by offspring. These nonsense sequences differ in length between individuals, but are almost identical in length between persons who have inherited the same copy of the gene (in other words, are related.)
3) The approximate length of these sequences is determined by a chromatographic process called "gel electrophoresis." DNA molecules have a slight negative electical charge, so when placed in a conductive solution between a positive and negative terminal, they move towards the positive electrode. A gel made out of a sticky sugar called "agarose" is created, basically just like jello. Like a fisher's net, small segments of DNA slip through but longer segments get tangled up. As a result the smaller segments move through the gel quickly, while long segments take longer. This spreads them out from top to bottom in order of length. In the image above, the longer sequences are at the top and the smaller are at the botom. Each band represents a concentration of stained DNA.
4) We photograph (because the DNA and gel are perishable) and interpret the results. When we compare the pictures of two samples, we can determine if they represent the results of this process performed on two copies of the same gene (actually, several genes at once are usually used). If they match up we know one of two things:
A) The samples share the same gene because they're samples from the same person (this would be how we might prosecute a rape from semen left at the scene and a blood sample from a suspect), or
B) The samples share the same gene because they're samples from two people who are related. Basic genetics can tell us, based on how many genes they share, the specific nature of the relation (father and child, brother and sister, maternal or paternal uncle, etc.)
Remember this is all based on the interpretation of the black bands in the photograph above, but that interpretation is accepted fact in every civil and courtroom in the country. Accepting interpretation as fact is not unreasonable, when that interpretation is the only reasonable one from the facts at hand.