OK, that was the first time this board has made me actually, literally, laugh out loud in like, what, 2 years?
I’d like to see several sociological experiments that are not strictly impossible but unfeasible in terms of expense, scale, etc. Basically, imagine if all the people who <whatever> could found their own society. Maybe they could Take over Wyoming
I would like to see Libertaria.
I’d like to take some of those people who say “No matter how little I eat I just can’t lose weight” and put them someplace - could be a hospital, could be a remote resort - where the only source of food is from the staff of that place, and have the staff keep track of what they eat.
In fact, I’d like to offer a James Randi style prize for anyone whose body does break the laws of thermodynamics.
I’ll be doing the follow up experiment and measurements of their “regain plus” after they leave the “cloister” and their genetics kick in.
You simply have no concept of diatetics, nutrition, genetics, and metabolic weight disorders do you PatriotGRRRL?
Gee, it almost sounds like Concentration Camps for Fatties.
I want to lower a rope into a black hole. I’m convinced it doesn’t “just break” like the guys in general questions are. If a rope would just break at the event horizon, why wouldn’t EVERYTHING just break as the smallest part of it enters the event horizon? In fact, one of our science geeks claimed you could “comfortably” pass the event horizon of the black hole in the center of our galaxy, without being torn apart right away. So why would our bodies not get torn apart as we enter, but a fucking rope would? Not buying it.
After the rope is touching the black hole, I’d lower stuff into and out of it, and see what happens. Maybe a video camera or something, first. I just want to see what’s inside!
Volunteers living in a luxury hotel, with all the food they want, and, the ability to opt out of the study anytime they want sounds like a concentration camp?
I think they taught you some misconceptions about concentration camps.
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Dinosaur Extinction.
Have several identical planets full of dinosaurs and make them go extinct in interesting ways. Start with a boring old asteroid, or a big ass volcano, then see if you can make the beasties die with a Noah size flood, mass lemming episode etc.
Not just racism and bigotry. More people have been killed in the name of [Insert deity here] than in all wars combined. I believe a civilization without gods would be far more peaceful than where we are now. And I happen to believe in one of them. (All of them actually, but that’s an entirely different conversation.)
Who ever killed 20 million people in the name of $DEITY? That’s just the Soviet death-toll from one war. 
My impossible experiment: Build a colony of volunteers on an island somewhere where all breeding is by lottery, a la Larry Niven. See if we do result with a population of extraordinarily lucky people a few generations down the line. Alternatively, institute true “secret” ballots: the candidates are listed by code number, not by name, so you don’t know who you are voting for, hence the winner is whichever candidate is luckiest. See how we get on with a government composed of lucky people. 
We teach our school kids about the crust, mantle, and core, yet no one has ever been there. The deepest hole anyone has ever dug is about 10 miles down, but the center of the earth is 4000 miles down.
So, to get to the heart of the matter, I’d like to see some 4000-mile-deep core samples taken.
Then we’ll finally find out if the center of the earth is… …smooth vanilla cream, or chewy caramel nougat.
That would be an experiment I’d like to see: a civilization two or three generations away removed from religion.
I like the “children segregated from their parents’ beliefs” one, though it is obviously completely unethical.
Like if a bunch of kids had never been introduced to religion, would they come up with it on their own?
Even more interesting (if it were possible) would be to raise them without telling them what things are right and what are wrong and see how they decide. For example, they would probably figure out pretty fast on their own that violence isn’t nice, but what about racism? monogamy? all kinds of things.
The one I’m curious about is cross-breeding humans and other apes. What would a human/chimpanzee hybrid look like? What would it be able to do? What would its bones, brain, muscles, and so on be like? Would it be able to speak? What about impulse control? How would it be if the mother (who would raise it) was a human vs. a chimpanzee mother?
Of course it would be kind of horrifying to actually produce such a creature and raise it. The poor things would be freaks who would most likely be intelligent enough to know it and would live their whole lives as guinea pigs.
Test nature vs nurture by cloning, say, me 5,000 times and making the embryos available to a range of family types. Track development.
Ha. Or howbout more specific? Can we maim and disfigure someone like Britney Spears and see if she can make it on talent alone? Take Paris Hilton’s money away from her?
Come to think of it, a lot of this is starting to sound like the current state of reality television . . .
Let’s drop Dick Cheney, naked, into the center of Baghdad, and instruct all American personnel to ignore his pleas for help. Just, you know, to see what happens.
I would like to run a breeding experiment on people to see how small we could make people while still maintaining our full intelligence. There are plenty of people with growth disorders that are normal, just tiny. Adults with normal adult intelligence exist who weigh 15 or 20 lbs… How much smaller can we go? I’m betting we can get down to a normal size of 10lb without any drastic change in intelligence. 
I would also like to see a country formed that used Robert Heinleins ideas from Starship Troopers… It often sounded pretty reasonable… Be neat to see if it worked in practice.
Or you could just start up an intensive human/chimp breeding program :dubious: