I’d say the invention of the transistor. How many billions of transistors are there in the world currently keeping us alive and in contact? I forget how many of them there are per person, but wasn’t it in the tens of thousands?
Eratosthenes (276 B.C. - 194 B.C.) calculated out the circumference of the Earth to surprising closeness, with only a stick and some shadows. For this and many other discoveries, he goes into my book as being the greatest scientist to have ever lived.
Go here for more information: http://www-history.mcs.st-and.ac.uk/history/Mathematicians/Eratosthenes.html
As for greatest scientific discovery/invention/somethingorother, I agree with most of the ones already posted, but to pick one that hasn’t been stated yet, I’d say cladistics. It just makes so much more sense than regular taxonomy.
By the way, can someone enlighten me about phlogiston et all? What the heck are you talking about??
The warp drive, duh! Oh, wait, you late 20th century people haven’t got that yet.
Seriously now:
The greatest discovery of the human race is CONSCIOUSNESS.
Consciousness brings about AWARENESS of the self and his/her surroundings.
Awareness ignites CURIOSITY.
Curiosity employs REASON to solve the enigmas that motivate it.
Reason allows for science, technology and overall KNOWLEDGE.
Knowledge facilitates SURVIVAL and eases the burdens provided by life.
Survival is, either instinctively or consciously, the grand objective of any species.
So CONSCIOUSNESS it is.
Well, according to the 2013 year old Man, the greatest discovery was Liquid Prell.
I never thought of that. Okay the bra, or the chastity belt. Those are the worst ones.
For good ones…anyone mention penicillin?
Did this juxtaposition give anyone else a painful thought picture?
Sheep,are also good for wool
**Air Conditioning. ( the science behind it)
This invention has had profound effects on industry and on where people live. The south went through a huge economic boom because of it. Do you think Houston or Dallas would be the huge population centers without it?
Actually, I would say that Air conditioning has made a most profound effect on life in the last one hundred years, not just on where people live, but on our political system as well…used to be the politicians went home every summer…now we have to put up with their hot air all year long…
I didn’t mean it like that!
I don’t remember what this thing is called. But I learned about it when I was in chemistry…
It’s this substance that sucks up water and makes it into a gel. They have it in diapers, to solidify the baby’s piss. It’s pretty strong and if you have enough of it, you could soldify someone’s swimming pool. If you drank it though…:eek: Other than that, I always liked it.
Also-
+Hydrogen Beer: Hydrogen dissolved in with the carbon dioxed. It’s in Japan. It makes your voice high, so that karaoke singers can hit high notes. Just some more randomness. 
This same substance is being looked at as a tool to help fight forest fires… not the fires themselves, but they spray a bunch of the water-soaked gel on a house, and it helps protect the house from the flames. And when the fire has passed the homeowner pulls out his garden hose and sprays it off…
Eh - aren’t we mixing discoveries & inventions somewhat ??
Discoveries:
Cudos to the fellow who discovered the connection between the changing of seasons and the motion of the stars, planets etc., in effect making a reliable calendar. Reliable calendars means effective agriculture, feeding a LOT more people with less labour.
Discovering that light has a speed (or “hesitation”, as Ole Römer put it). That was against all common knowledge at the time.
Inventions: All the great inventions I can think of have been mentioned, but for sheer niftyness, nothing beats the common bicycle: In energy consumed related to distance travelled, the bicycle beats everything you’d care to mention, including (and this is significant) a walking man. In other words, we’ve improved on the energy efficiency achieved by millions of years of evolution - how about that ?
S. Norman
If you push something hard enough, it will fall over.
The first one.
That is definitly a cool idea.
Somebody beat me to it, but the obvious answer is written language. Being able to write stuff down is what allows todays scientists to “stand on the shoulders of giants”, as someone (Newton, I think) once said. And, as someone else has said (first read it in a Tom Clancy novel, of all places) “If you don’t write it down, it never happened.”
Indoor plumbing
Yep! It was Newton all right. I hope this wasn’t a trend though. I mean, giants are big but imagine if all the great scientists did the same? The poor giant will be crushed to death.
What if Jabba the Hut stood on his shoulders? Now that’s some heavy shit! 
…I’m thinking I’d go with writtern language, metalurgy, the transistor, and atomic discovery (spec. nanotecnology).
What about bifocals? It allows for more precision when you’re making things.
Also: the printing press. I know, I know, its in the theme of the whole language but you could replicate things you’d written more easily. Plus it let people share their ideas, like w/ the Reformation…which led people to question things, like the “normal” idea of religion. Okay maybe i’m stretching a bit…but you have to admit. it’s a good thing.
sorry if this post sounds weird, its kind of late at night (or early in the morning) and I feel disconnected.