Mayan Calander doomsday refuted; breath asy!

A science experiment would be something like creating a big bang, creating a very energetic material, or anything else created in a lab that destroys the planet. Creating an out of control chain reaction with the planet that converts matter to energy would be an example.

I read somewhere in the 90's that the US alone has enough nuclear weapons to wipe out all life on Earth 300 times. But i'm not worried about that because no suicide cult or terrorist group could get hold of enough nuclear weapons to kill themselves, let alone everybody. Biological threats could kill billions but isolation, weather, and evolution would keep us from going extinct. A cosmic collision 'could' wipe out all life but hasn't in the millions of years there's been life on earth. The dinosaurs were killed by one but life still continued, and we're much more adaptive than the dinosaurs. The only thing that worries me even the slightest is a scientific experiment with the Hedron Collider messing up on a quantum level and causing a singularity (black hole). If that happened though, we'd be gone before we'd even notice.

The 2009 Swine Flu pandemic shows that we currently have the distribution infrastructure in place for an even more lethal one to take a fairly big bite out of mankind.

However I don't think this is going to be the way we get to a major human die off. It'll come when we get wacked by an electrical grid frying solar event. Utilities all over the world simply do not have enough spares to repair the failed substations and without power it will be difficult to make the replacement equipment needed. Without power, water purification/distribution/treatment will shut down. Without power most people will run out of gas in a matter of days and supermarkets will rapidly run out of food. Without cable and internet to preoccupy the masses, things are going to turn ugly really quick.

Well it all depends on what doomsday means. The Earth can take a pounding and the Earth will survive almost anything except the most extreme cases. According to theory, the Earth was hit by a massive object and the Moon was created as a result. So even if 99.9999999% of life is destroyed, then Earth will eventually try the life experiment again.

Considering that the last massive meteorite hit Earth millions of years ago, there is a very low probability of a doomsday scenario based on asteroids with no external forces applied to them. Having 50 asteroids directed towards Earth by aliens is another story.

So all realistic doomsday scenarios are by some sentient race. We are the most likely culprit either due to someone's stupidity or ignorance. There is a certain minimum level of population that is required to function as a modern society. Lowering the population to 100 million would probably have no major effect on our ability to survive as a modern culture. However, the scorched earth scenario is more difficult to deal with and if the Earth is dying, then either we change or we die. The Fallout game is probably the closest we can come to understanding that scenario. Very few doomsday scenarios have the devastating effect of nuclear warfare. The only ways to survive such a scenario is adapt through genetic manipulation (Ghouls), treat the Earth as Mars (Vault Dwellers), or download our consciousness into a computer (Matrix).

Of course, in a century or two, interstellar colonization would make any doomsday scenario irrelevant and the only possible ones are a nearby supernova (if we are only at initial stages of interstellar colonization), galactic collision (should be able to compensate for such a scenario with plenty of time to spare), aliens bent on eradicating us (unlikely for them to get us all), and destruction of universe (humanity will most likely have tons of time to figure something out and won't happen for an inconceivable amount of time).