Dear Large Talons,
I did not realize I was such a geek about this until I started researching. So, thank you for asking this; it's been fun to discover yet another way that I'm hopelessly geeky. I'm going to talk a bit about each scenario you suggested, and give it a rating on a scale from 1 to 10, with 10 being "as surely as River Tam would be to defeat me at hand-to-hand combat."
If you don't want to read the entire thing, just read the stuff in bold. Also, I just wanted to share this comic with everyone.
1. The Earth gets used up and mankind...
a) leaves the solar system to colonize habitable exoplanets: 3/10
Currently, scientists have found 15 planets whose orbits are entirely within the "habitable zone," or the area around stars that could theoretically support human life. Although scientists theorize that a significant percentage of stars will have Earth-sized worlds in their habitable zone, the current techniques for finding extrasolar planets don't work very well for finding Earth-like worlds. This is because exoplanets are currently observed by measuring the Doppler shift of the hosting star's spectral lines.
Obviously, within 1000 years, scientific technique for finding exoplanets will improve. However, there are significant hurdles to colonizing an exoplanet, even when we've found a specific planet that is theoretically habitable. The first problem is that "habitable" doesn't mean "colonizable." The current definition of "habitable" essentially means that liquid water is able to form or exists on the surface of the planet. This excludes all planets that are either too close or too far from its star. However, there are a lot of other factors that influence whether we could live on the planet, such as gravity. For example, the star Gliese 581g is technically classified as a "habitable" star, despite the fact that its gravity is almost two times as great as the gravity on Earth. As a result, it would be extremely difficult to even just walk around, and your cardiovascular system would be under constant stress. Furthermore, its increased size would also mean an extremely dense atmosphere, which would make movement and breathing even more difficult. So in able to be colonizable, a planet has to be similar in size to Earth. Additionally, it would also be really, really helpful if it had a similar elemental makeup. Being able to support liquid water is nice, but if we have to bring in nitrogen, oxygen, carbon, phosphorus, sulfur, etc., that just makes the planet that much more impractical. Finally, the planet must have a manageable flow of energy at the surface. If it's all the same temperature, there's too much thermal inertia to be able to do any practical "work" in terms of physics. On the other hand, if the planet experiences completely insane storms, that's another hurdle to overcome.
But we have 1000 years, you say. Maybe medicine will improve to the point where we can biologically engineer humans to withstand extreme conditions, engineering will make it possible to alter the atmosphere or stimulate Earth-like gravity, our knowledge of space will allow us to mine for other elements to bring to the planet, and we'll be able to use our advanced science to overcome the weather problems. Well, if our science is as good as all that, why wouldn't we just use it to fix Earth, or terraform planets within our own solar system? It would be less costly, and much less difficult.
Finally, even if we found a colonizable planet and for some reason wanted to go through all the unnecessary effort of applying this technology to a planet that was light years away, the planet would still be light years away. I discussed some possible means of travel in Board Question #69668, but basically, any travel across such distances is going to require massive amounts of energy, which again would make colonizing exoplanets much less feasible from an economic or logical standpoint than using our own solar system first.
b) terraforms Mars or Venus for colonization: 6/10
Terraforming Mars or Venus offers a couple of immediately obvious advantages over exoplanets: we already know how to get to them and we know they exist.
The main problem with Mars is its low gravity. While low gravity is less problematic than high gravity, since it would offer ease of motion and also not pose a problem for spacecraft taking off or landing, low gravity has potential long-term health effects that are not yet fully understood. However, I think it's likely that by the time we're ready to terraform Mars, medicine will have access to sufficient data to understand the effects, and also have sufficient motivation to work something out. However, another problem with low gravity is that it prevents Mars from retaining a sufficiently thick atmosphere. In order to continue breathing, we would either have to continuously replenish Mars' atmosphere (which is an impractical long-term solution), create artificial barriers or bubbles (which would be catastrophic if they failed), or develop some impressive new technology to fix the problem. In my opinion, such technology may very well be within reach in 1000 years.
One possible means of retaining Mars' atmosphere is creating a magnetosphere, although there are many examples of planets that have maintained thick atmospheres without one. In any case, it would be necessary anyways to protect Mars from solar wind. Mars would require a magnetosphere of about 30 µT.
Because Mars is so far from the Sun, it would require more greenhouse gases than Earth in order to maintain life. This could actually be an advantage; if we could somehow collect Earth's greenhouse gases, we could ship them to Mars, use it to start the atmosphere, and make both planets more habitable. Furthermore, Mars already contains many of the necessary elements to be able to support life, albeit not in the exact molecular forms that are necessary. However, Mars also conveniently contains some chemicals that can assist in these processes, such as perchlorate to convert carbon dioxide into oxygen. Mars also has a large amount of frozen water, which would be extremely convenient if we could just warm the planet up enough to melt it. However, Mars would require a large amount of inert gas, such as nitrogen or argon, to be imported in order to create a proper atmosphere. Furthermore, the atmosphere would probably be thin and low in oxygen, which creates long-term health effects, similar to those experienced by climbers on Mount Everest. Other options for heating Mars' surface and thickening its atmosphere include using large mirrors to heat the planet, and inducing asteroid-like impacts to produce dust clouds to create a greenhouse effect.
Scientists currently suggest that terraforming Mars could take several millennia. However, while humanity might not be finished terraforming Mars in 1000 years, I think it's quite likely that people would at least have started it. In fact, some optimistic (or possibly off-the-wall) scientists think it could be done within a few generations. After all, it's argued that we technically already have the technology to do most of what's required. And as I said before, Mars is a much more practical first step before we try something as radical as exoplanets.
There are ethical implications that argue against terraforming Mars, such as disturbing potential alien microbes or whether it's right to go mess up another planet after we've ruined this one. Based on humanity's typical responses to such positions, however, I'm going to guess that terraforming Mars will go ahead anyways.
Venus, on the other hand, is way too hot. This is partly due to an extreme greenhouse effect caused by the dense carbon dioxide atmosphere, and partly because it's closer to the sun. To fix the proximity-to-the-sun problem, a couple of solutions have been proposed. These mainly center around some form of solar shade in space, or reflective objects in the upper atmosphere. While current technology is still a ways away from solar shields, I definitely think it's achievable within 1000 years. Reflective mirrors in the atmosphere take advantage of existing technology, but wouldn't make as much of a difference because Venus' clouds are already highly reflective, so this strategy wouldn't have a huge impact on the albedo effect.
Meanwhile, the carbon dioxide on Venus needs to be severely depleted. The main problem I see with this is that if we develop the technology to make Venus habitable, it would mean that we would almost definitely have the technology to fix many of the pollution problems on Earth, so why would we bother terraforming Venus instead? However, let's assume that we have already used the technology on Earth, but due to overpopulation or other problems, we still want to terraform Venus. In this situation, there are several ways to deplete the carbon dioxide. While genetically engineered bacteria have been proposed, it was later discovered that Venus did not have enough hydrogen, and that the atmosphere was too dense to convert via biological processes before the carbon was converted to carbon dioxide again due to the temperature. Instead, it would be more efficient to simply bombard Venus with hydrogen. In order to produce graphite and water from hydrogen and carbon dioxide via the Bosch reaction, we would have to use about 4 x 1019 kg of hydrogen! It's possible that we could get this amount of hydrogen from harvesting comets, but that technology is at least a few centuries away. On the plus side, once this reaction was complete, the atmosphere would be largely nitrogen without making further alterations, which is an improvement over Mars. Alternatively, the carbon dioxide could be sequestered using alkaline carbonates, but the amount of refined material required is on the order of magnitude of a 300-mile-wide asteroid. It would take an incredible amount of mining to produce this. Finally, while directly moving the carbon dioxide has been proposed, scientists have yet to come up with a credible idea of how to do this.
Additionally, Venus also lacks a magnetosphere, which would be important to induce in order to prevent solar wind-related problems in terms of atmosphere depletion, cosmic rays, and other problems. Unlike Mars, however, Venus is a similar size to Earth, which means that there would be no gravity-related issues. On the other hand, some scientists have pointed out that it would be nice if we could speed up Venus' rotation, since one day on Venus is as long as 224 days on Earth. This would result in the nights being very cold, and the days being extremely hot; it would be more difficult to keep the temperature from swinging to wild extremes.
It's difficult to say whether Mars or Venus would be more difficult to terraform. On one hand, Mars doesn't really have an atmosphere, while Venus has proven that it can hold onto one. Furthermore, Venus is closer to Earth and has a similar gravity, but Mars has a more reasonable day/night cycle. Both planets would require vast quantities of elements to be mined and added to the planet. For a more extended treatment of Mars vs. Venus, you might be interested in this website. Personally, I'm inclined to say that Mars would be terraformed first, partly because of the technological considerations, but also because it's widely agreed that it's the project that scientists take more seriously.
c) builds a glass bubble colony on the Moon: 8/10
Basically the only advantage of colonizing the Moon is that it's a lot closer. As a result, getting to the Moon is cheaper and faster, which is an important consideration, especially if option (d) comes true and we have to get off the planet in a hurry. Furthermore, if a Moon mission went wrong, emergency help or rescue from Earth would be a valid option. This makes it a much safer alternative than settling Mars, especially when colonization technology is in its infancy and is largely unproven. Because of this, I think it's pretty likely that the Moon will be colonized first, either as a trial run for Mars, a political stunt, or because a private foundation became rich enough to fund it.
Current technology is actually pretty close to being able to colonize the Moon; we could probably do it some time this century if we felt like it. Maybe not in a glass bubble, since the lack of atmosphere means that the Moon is subject to many more meteorite impacts than Earth, but there are valid options on the table. Lunar caves are a great initial source of shelter, for example. These settlements would have to be pressurized and also shielded against solar wind and radiation. Russian scientists have recently discovered a vast network of volcanic tubes under the surface, which would be a great starting point for colonization.
Ice deposits have been discovered on the Moon, which could make a moon colony self-sufficient in terms of water. Meanwhile, as food crisis technology on Earth continues to drive new GMO crops and techniques like hydroscopic farming, it's quite plausible that the colonies could grow their own food, which could have the added benefit of making them oxygen-sufficient as well. Nanotechnology is also growing closer to food replication and building improvements, which could protect against the meteorite problem I mentioned earlier. Technologies like 3D printing also make it easier for the Moon to be self-sufficient, as the settlers could create replacement parts and objects on demand, requiring only a regular shipment of raw printing materials from Earth.
However, the Moon is a much worse long-term option than Mars or Venus. Because it is significantly smaller than either of them, it would be difficult to create a permanent atmosphere around the Moon. This would mean that the colonies would always have to be pressurized and self-contained. Over the long term, the risk of a leak or other technical failure makes the idea impractical. Also, the small size of the moon means its gravity is about 17% of Earth's. While adults could live on the Moon for long periods of time, they would experience a loss of bone density and muscle atrophy. However, children would experience significantly more serious effects; without significant medical intervention, a long-term lunar colony simply could not sustain itself if the next generation couldn't survive to be healthy adults. While the Moon may someday offer mining, tourism, and scientific opportunities, as well as being a technological stepping-stone to colonizing other planets, it would not make a good long-term home. Unless scientists can create artificial gravity, my guess is that most people who live on the Moon will only do so for a part of their lives, spending their developmental years on Earth. On the other hand, Moon colonization would provide extremely valuable insights about how humans would cope in the low-gravity environment of Mars.
The combination of the long lunar night (354 hours) and the lack of atmosphere also leads to temperature extremes, which would be inconvenient to deal with. The lunar night would also disrupt plant growth and prevent solar power from being an effective means of generating energy. These disadvantages are similar to Venus, but are not present on Mars.
Aside from the scientific reasons why colonizing the Moon is possible, there are also significant political incentives, which I believe make it more likely. We already have Russian scientists and Newt Gingrich talking about moon colonies. If we have a whole millennium to talk about it and have our technology make it increasingly possible, eventually some country or another is going to make a serious bid for it, even if it's just for a short-term scientific research station. Because the Moon has no atmosphere, it makes a significantly better place for an observatory than Earth, especially as light pollution and greenhouse gases increase. And once one country has an observatory on the Moon, other countries are going to want to compete in order to not be seen as falling behind. Assuming we don't kill ourselves off first, I think we'll almost definitely colonize the Moon.
d) tries to frantically pump resources into their space program at the last minute, only to fail to accomplish any of the above with meaningful results: 4/10
We hear a lot about NASA's budget cuts. And yeah, it's true that in the current state of things, we wouldn't be able to get off-planet sometime this century if we were to suddenly suffer a disaster that made it necessary. However, as I discussed above, we already essentially have the technology to form a lunar colony. And while NASA may be experiencing budget cuts, private enterprises, Russia, and China are continuing to fund manned space exploration. Ultimately, progress is still being made. It's my personal opinion that if things got bad enough that we had to evacuate Earth, we would probably discover this in time to divert our remaining resources into a lunar colony that would be reasonably likely to work.
Meanwhile, NASA is still working on space exploration. The same technology used to deposit Curiosity on Mars could easily be used to deposit supplies for an outpost, and eventually to land humans on Mars, which NASA still talks about doing within the next couple of decades.
Finally, although the Constellation program's cancellation may appear to limit the future of manned space exploration, that isn't actually the case. Instead, NASA will continue to use probes like Curiosity to further explore the Moon, Mars, and other planets. Essentially every probe NASA has sent to these locations recently has included finding water and evaluating the habitability of the area as one of its objectives. At the same time, NASA is looking at sending astronauts on long-term missions to Lagrange areas, which are points in space where gravity from different bodies essentially cancels out. This would allow NASA to evaluate the long-term effects of living in space or low-gravity areas, and mean that medicine could come up with solutions to any potential problems. And because manned exploration is still a long-term goal that captures the public imagination, NASA has continued to look at different theoretical possibilities for colonization.
The upshot of it is, I think that our knowledge and understanding of other planets is going to progress to the point where we will be able to colonize the Moon in an emergency, assuming the emergency is something like "We're going to experience a runaway greenhouse effect/giant asteroid/etc. in a decade" and not something like "Oh hey, the Earth is getting destroyed in a week" like we always see in movies. In the very least, we should be able to establish a lunar colony large enough to sustain the human race. While it wouldn't be able to support the entire Earth the way a completely terraformed planet would, I would still call that result meaningful.
Furthermore, a lot of the technological advances I've talked about would also allow us to prolong Earth's ability to sustain us. I feel like we would definitely be able to stretch it out to a few more centuries or even millennia, and I feel like that's plenty of time to get space exploration going. Think for a moment about the scale of a thousand years. A millennium ago, we hadn't even crossed the Atlantic Ocean (with the possible exception of the Vikings); look how far we've come since then. On a similar note, we put a man on the moon barely half a century after the airplane was even invented. Technological progress moves at an awesome pace. It wasn't so long ago that we doubted that anyone would even reach the moon. I'm pretty sure that with 1000 years, we'll see some pretty amazing advancements that would allow last-minute space programs to have a pretty good chance at success. And, as I've discussed above and will discuss more below, I think we'll be able to keep the Earth habitable and disaster-free for long enough to see it happen.
2) Mankind reverses the trend of polluting and switches to only reusable energy. Instead of expanding into space, they farm the oceans and build ever upwards like the Jetsons: 10/10
I gave these options a solid 10 because not only are they inevitable, but they are also already happening.
First of all, take renewable energy. Within the next 1000 years, we are going to run out of coal and oil, and some sources suggest that could be as early as the next 50 years. Even before the world is literally stripped of every extractable drop, the price crunch will mean that oil has effectively become unavailable for many people. So what happens then? Well, in the book A Thousand Barrels a Second, Peter Tertzakian gives a fascinating account of the history of energy resources. According to him, whenever society has switched from one dominant energy source to another, due to lack of availability, the process of making the shift takes about fifty to one hundred years. So, by 2150 at the latest, I predict that we will have moved on from non-renewable resources. It's possible that nuclear fission, or even nuclear fusion, will make up a large percentage of this, but nuclear power is impractical for transportation, and the dangers of fission mean that many regions will prefer to avoid it. Therefore, the only available option is going to be renewable energy. This will probably take many forms, including solar power, wind, hydro, biofuel, nanotechnology, geothermal, and the efficient use of waste heat. The obvious problem is that green energy isn't as energy-dense as fossil fuels, and so it doesn't work quite as well. Furthermore, it's not just the technology that needs to be developed; it's the infrastructure. Tertzakian points out that one of the reasons for Edison's success is that he was able to thread the wiring for lightbulbs through the already existing pipelines for gas lighting in the first communities he wired. Similarly, even if something like a hydrogen fuel cell car becomes affordable, gas stations will need to be outfitted to refuel them before the technology can really take off. This won't be economical until we reach a real oil crunch, which will probably happen within our lifetimes.
Some countries are already taking initiatives to make renewable energy a significant part of their infrastructure. Germany, for example, derived 25% of its electricity from renewable energy in 2012, as opposed to 6% in 2000. However, the technology isn't perfect; electricity prices have increased and power outages have become more common. Nevertheless, the country recognizes the value in moving forward with renewable energy production. Similarly, countries with strong coastal tides, such as Norway and Canada, could derive much of their energy from hydroelectric power. In areas with extremely low population density, solar power is already a better resource than traditional fuels, because the settlements can be self-sustained and off the grid, reducing overall costs.
Obviously, some areas will face significant challenges in implementing renewable energy, and it's currently not developed enough to substitute for fossil fuels, even if there weren't economic and infrastructure issues in the way. However, because fossil fuels will definitely run out, renewable energy is going to become the next dominant energy source whether we like it or not. Nuclear fission may increase for a while, but the extreme waste and danger of plants, combined with the fact that I'm pretty confident that we'll work out fusion plants within the next millennium means it will probably be phased out too.
Secondly, ocean farming will become an important means of producing food, due to the eventual limits of GMO technology, the necessity of developing land due to a growing world population, and the fact that that growing population will continue to need food. It's estimated that ocean farms could produce enough nutrition for the entire world population using an area the size of Washington state. Obviously, this could not only solve the current world food crisis, but it could also support the world population for hundreds or even thousands of years at that rate. Currently, approximately 90% of the ocean is unproductive due to the lack of nutrients for phytoplankton activity, leading to a plateau in fish harvesting in 1989. By increasing phytoplankton activity, not only could we feed the world, but we would also create a huge greenhouse gas sink, combatting pollution at the same time. China and other Asian countries currently see seaweed farms as a crucial strategy in offsetting their carbon emissions. Additionally, while even the most eco-friendly land-based farms require fresh water (another resource that will become increasingly scarce), deforestation, and fertilizer, land farming isn't a sustainable long-term solution to world hunger.
So if ocean farming is so great, why haven't we done it on a large scale yet? Well, for one thing, ocean farming previously succumbed to the same faults as industrial land farming, flooding monopopulations of fish with chemicals and creating huge amounts of pollution and waste. Current proposals for ocean farming would create biological habitats that mimic the natural order, eliminating the need for both chemical stimulants and waste management. The other huge hurdle is that it's difficult to economically profit from ocean farming due to current laws and regulations surrounding the fishing industry. Seeding the oceans with chelated iron to produce phytoplankton blooms isn't going to produce a return on your investment if the fish simply swim away and get fished by someone else. However, countries as diverse as New Zealand, the Marshall Islands, Canada, and the USA are implementing new "individual transferable quotas" and privatizations of fishing areas, making ocean farming increasingly economical.
Nevertheless, ocean farming can't sustain the world indefinitely. The resources required to create ocean farms, such as iron, still have to be mined, manufactured, and distributed. As a result, it would theoretically become necessary for iron to eventually be mined from space, meaning that colonizing the Moon or other planets wouldn't become completely unnecessary, although ocean farms could delay the importance of creating extraterrestrial settlements.
Finally, futuristic skyscrapers are already being developed in countries with high population densities, such as Japan. (Is there any way this question could not eventually reference Japan? I don't think so.) While some of their concepts seem pretty science-fiction-y, it's an undeniable fact that areas that face high population density begin building upwards instead of outwards. For instance, after the government of Ontario passed a law prohibiting urban sprawl, Toronto began the construction of 147 new tall buildings. The real question is whether we'll wait until we've developed virtually all the land on Earth before we build upwards, or if we'll voluntarily turn to skyscrapers before we destroy the entire environment. After a thousand years, though, I think either of those situations will long since have come to pass.
Furthermore, a lot of skyscraper concepts are meant to do double-duty as energy producers or waste cleaners. Some concepts propose cleaning the ocean, producing energy from towers of waste, being movable in case of disaster, doing double-duty by restoring areas destroyed by mining, or storing water in case of drought. Others include recycling centers that are self-powered by wind turbines, towers built into the ground to house the dead, and towers that harvest lightning power.
Many of these concepts are obviously unrealistic, meant merely to inspire possibilities. For instance, this proposal will probably never come to pass, but it raises intriguing questions about prefabricating skyscrapers, integrating them into transportation hubs, coating the walls with photovoltaic cells or carbon dioxide sinks, and installing heat-recapturing technology to minimize waste. In fact, it's suggested that skyscrapers could become energy-neutral or even energy-producing, by integrating biofuel cells and wind turbines. These wind turbines could also be used to capture moisture and produce drinking water for the residents. This skyscraper proposed for Dubai could pay off its energy debt in 20 years, and would power the municipal grid for decades to come.
Meanwhile, the technology surrounding skyscrapers is continuing to make them taller and safer. For instance, the Shanghai Tower, scheduled to open in 2014, will be the second-tallest tower in the world, and contains innovations that will make skyscrapers safer and even more common. It has a layered, interlocking structure to make it more stable, and two glass facades that essentially turn the tower into a giant Thermos, drastically reducing the energy needed to heat and cool it. Not only are its elevators the fastest in the world, but their ability to regenerate electricity make them extremely efficient. Furthermore, because the tower twists one degree per floor, it directs and slows wind currents, reducing lateral wind forces by 24%, a key innovation in an area where typhoons are common.
There are many other innovations in skyscraper technology. Instead of the classic steel framework, a structural system called the "tube" makes the outside of the building the strongest part, which helps it to reduce wind. However, the height of the building also requires increasing the base width using this technique. New ideas, such as the "stayed-mast" and "buttressed core," feature a strong central core. Meanwhile, the height of these buildings is pushing the limits on conventional cabled elevators. Last year, MagneMotion unveiled an elevator that is driven by magnets, much like a vertical bullet train. Seemingly unrelated technologies, such as 3D printing, allow for rapid modeling of wind effects. Finally, improvements in materials technology allows us to create lightweight building materials that can withstand huge compressive forces. Ironically, our research on the nanoscale level is fueling the creation of the largest structures in all of human history.
Additional innovations include rerouting earthquake waves around skyscrapers instead of attempting to absorb them, creating escape harnesses to make the upper floors safer, and harvesting energy during demolitions by using gravitational potential energy to generate electricity.
Alternatively, some people are even proposing "waterscrapers" that would be entirely self-sufficient for food and energy. While such a thing is clearly quite a ways off, could we sit it within 1000 years? I think so.
However, it's important to consider that even if the world was sustained by 100% renewable energy, we would still produce other forms of waste, such as garbage and sewage. Furthermore, while skyscrapers can reduce urban sprawl, we still can't cover the entire Earth in buildings like Coruscant because of the total destruction of the environment that such a thing would imply. In other words, while I think everything in the option will definitely happen, I still think we're going to end up looking at space colonization at some point in time.
3. A disaster strikes from space which we are unable to stop in the form of...
a) an asteroid: 2/10
The Earth experiences impacts from space debris every day. Most of it burns up in the atmosphere, but some of it reaches Earth. Many of these impacts are relatively small. However, we experience impacts from sizable chunks, about 10 m across, approximately once a decade. We just don't hear about it much because so much of the Earth's surface is uninhabited. Even if our population explodes dramatically, however, such an impact wouldn't be a disaster large enough to threaten mankind. As it happens, meteors large enough to destroy a city (about 100 m across) hit Earth once or twice every thousand years or so, although the odds of it actually hitting a city still make it an unlikely event in the next millennium. And even if we lost a city, the human race would still be fine.
In order to threaten the global climate, an asteroid would have to be at least a kilometer wide. To cause mass extinctions, the asteroid would have to be even larger: about 5 kilometers. The kinds of asteroid impacts occur a couple times in a million years, so it's hypothetically possible. The (extremely small) odds are raised by the fact that many comets approach this scale; if a long-orbit comet will eventually be on a collision course with Earth, we could very well not know about it yet. In order to prevent this, organizations such as the Spaceguard Survey have been paying close attention to near-Earth asteroids. Currently, the most interesting threat they've identified is a 270 m asteroid named Apophis, which will pass close enough to Earth to hit communication satellites in 2029. It's possible that this will shift its orbit enough to place it on a collision course in 2036. Again, though, the odds are small - about 1 in 250,000 - and the asteroid wouldn't be able to wipe out mankind anyways, although it would be a pretty big catastrophe. Currently, scientists have identified about 400 asteroids large enough to cause regional damage, which they estimate is probably about 10% of how many there actually are. Nevertheless, such asteroid wouldn't cause an apocalypse.
So why did I rate this category so low? Because in the extremely unlikely event that such an asteroid would be on a collision course with Earth, we would probably be able to stop it. Astronomers are getting better and better at identifying potential threats every day, and as our space program continues to expand as discussed above, we will be even more capable of dealing with them. Current proposals include drilling a hole and dropping a nuclear bomb into it, or using spaceships and/or bombs to knock the asteroid off course.
According to Discovery Magazine, an asteroid impact is the #1 most likely doomsday scenario. However, their analysis was not confined to the next 1000 years, and it didn't factor in the possibility of stopping it. Compared to the other options in scenario (3), an asteroid impact is more preventable.
b) a supernova explosion: 0.0001/10
The nearest star that could go supernova, Betelgeuse, is 640 light years away. Because the energy of a supernova dissipates exponentially, and a star must be 100 light years away to pose no threat to Earth, it's not really a big deal if Betelgeuse goes supernova, let alone all the other stars that are even further off. How close does a supernova have to be to destroy Earth? Well, if a supernova went off 50 light years away, this would probably shear away the ozone and destroy Earth's magnetic field, rendering our planet completely uninhabitable. In a more dramatic scenario, a star 1 light year away would rip our entire solar system to shreds. (The nearest star is Proxima Centauri at just over 4 light years, but it's impossible for it to supernova any time within the next 1000 years, or even the next billion or so.)
However, the Sun is constantly moving throughout the galaxy. It's theoretically possible that because our solar system is entering the Orion arm, dangerous supernovae could become more frequent than the current one in 240 million years we currently experience. Furthermore, because the most dangerous type of supernovae, Type 1a, occur in the common white dwarf star, it's possible that an unpredictable supernova could occur in a solar system that is not well studied. Nevertheless, this possibility is pretty remote. They would have to be less than 33 light years from Earth, and any known candidates for such an event will have been carried further away than that by the time the star could go supernova. The hype is greatly overblown by poorly researched articles that neglect to recognize that stars over three thousand light years away, which will not explode for over 10 million years, are not going to threaten us.
Basically, NASA says it's not going to happen. The three closest stars that will next supernova are both too far away, and aren't going to explode for millions of years. While it's possible that a superluminous supernova could cause chronobiological problems, the negative effect of such an event still couldn't wipe out life on Earth. I didn't rate a supernova explosion as zero, because it's still hypothetically possible, but everything we know about science suggests that it won't.
c) a solar flare: 0.00000000000000000000000000001/10
According to NASA, the sun is not physically capable of producing a solar flare that destroys earth. While the most powerful type of solar flare, coronal mass ejections (CME's), can disrupt electric grids and GPS units, this would not "end the world," although it would be a temporary, regional natural disaster. I think the most recent pop culture example of a solar flare destroying the earth is from that horrible movie 2012, which had science of a quality that matched its plot. Basically, there are several types of radiation that the sun can emit. During a normal solar flare, the sun emits x-rays, which take about 8 minutes to reach earth and are absorbed by the ionosophere. The sun cannot and will not release enough x-rays that the ionosphere can't handle it. During CME's, the sun can emit alpha and beta particles, which take about 40 minutes to reach earth and are also absorbed by the upper atmosphere. While these particles could be damaging if Earth's magnetic field were to get all wacky (which is totally possible, by the way, but you didn't ask me about that), it's not a problem as long as the magnetic field holds. In 2012, they decided to make the scenario even more ridiculous for some reason by having the killer particle be neutrinos, which are totally harmless and neutral. Millions of solar neutrinos pass through your body every day. It's fine. Potato potato potato just checking to see if you're still paying attention.
I don't really have much else to say about this one; it's just not possible. However, if you want the odds of the magnetic field failing or flipping within the next 1000 years, I'd be willing to give that doomsday scenario a 3/10. Earth's magnetic field flips every couple hundred million years, and we're actually overdue for a flip. Some scientists predict that this could happen within the next 500 years. While the magnetic field always restores itself, the process of changing its polarity means that for a period of time, the field won't cover the Earth in the same way, and we'll be vulnerable to solar flares during that time. It's totally possible that this scenario could wipe out life on Earth. Honestly, I think that of all the natural disaster doomsday scenarios, this one is the most likely. However, it doesn't necessarily mean that we would be exposed to enough radiation to kill us; it's also possible that we would simply have no magnetic north, access to satellites, or reliable electricity grids. While that would set civilization significantly back, we would still be alive at the end of it. It all depends on how long we're unprotected, and scientists simply don't know the answer to that. The field could take thousands of years to completely flip, or it could take a few weeks.
d) a gamma ray burst: 1/10
Supernova events, or the collision of black holes or two neutron stars, can cause gamma ray bursts, the most powerful electromagnetic event in the universe. They can have up to 0.05% as much energy as the Sun would if its entire mass was instantaneously converted into energy, which, if you're having trouble visualizing it, is a LOT of energy. However, gamma ray bursts occur very rarely, and they would have to be within six thousand light years of Earth in order to cause mass extinctions. These mass extinctions would primarily occur due to the ozone layer being destroyed, allowing massive amounts of cosmic radiation to reach Earth and kill pretty much all the things. Fortunately, GRBs only occur every 100,000 years at maximum, and only a small percentage of these would be aimed towards Earth. NASA estimates that GRBs that have the potential to affect life on Earth occur every five million years or so, and that a GRB may have caused the Ordovician-Silurian extinction event.
The most dangerous type of star that could cause a gamma burst is a Wolf-Rayet star, which are extremely hot, massive stars that are losing mass rapidly. These are at high risk to supernova and cause a GRB. For example, WR 104 could deplete 25% of Earth's ozone layer and hit the near side of Earth with enough lethal radiation to instantly kill some people. However, WR 104 isn't going to have a supernova event within the next 1000 years, and even if it does, it's not guaranteed that it would even have a GRB, or that it would be aimed towards Earth if it did.
In a less extreme scenario, it's possible that a GRB could create an excess of nitrogen oxide in the atmosphere, creating a photochemical smog that causes a cosmic winter effect. This could also deplete the ozone layer and cause more cosmic radiation to reach Earth. However, because this effect would occur over time, and it's already unlikely to happen, I'm going to postulate that if it did happen in 3000 AD or something, we would be able to come up with technological solutions to save at least some of the life on Earth.
However, remember the star T Pyxidis from the supernova section of the question? While the supernova wouldn't kill us, T Pyxidis is close enough to Earth that a GRB aimed in our direction totally could kill us. Fortunately, it shouldn't happen for about 10 million years.
Interestingly, scientists are discovering evidence that suggests that a GRB may have hit Earth in the 8th century. Obviously, it was too far away to cause mass extinction events, but it's kind of comforting to know that GRBs have hit Earth while humans lived on it, and we came through it just fine.
e) Nemesis: 0/10
I'm going to say this once: Nemesis doesn't exist. The odds of us being destroyed by something that doesn't exist are...wait, let me get my calculator...zero.
f) Nibiru: 0/10
Nibiru doesn't exist either. At least Nemesis started out as an outside-the-box scientific hypothesis; Nibiru is the brainchild of a science fiction writer and a psychic.
(Yeah, my answers to these two sections were lame and short, but my geekiness is limited to science, not conspiracy theories.)
4. A united world government controls the number of births and the lifespan of all humans: 2/10
I don't really see a united world government being able to wield even a fraction of the power required to control something like that. Multi-national government is way too weak and dysfunctional. Exhibit A; Exhibit B.
Besides, let's consider what would have to happen to give rise to a truly united world government. Based on how opposed the USA is to the UN, I think we can safely say that America will never willingly agree to give up sovereignty to a world government, and I don't really see America trying to actually take over the world. So, in order to have a world government, the USA would have to be severely weakened somehow. If this happened through war (i.e., a hostile nation or terrorist group trying to take over the world), I can't imagine that the opposing side would come out of the conflict without sustaining significant and devastating damages from fighting America. This group wouldn't be in any sort of position to force their attempted takeover of the world, especially since a lot of other nations would also put up resistance. Similarly, if the USA was devastated by some sort of natural disaster or calamity, I imagine that the rest of the world would be similarly devastated. Again, there wouldn't be the resources to form and enforce a totalitarian world government. Even if the USA was selectively decimated by a natural disaster, leaving the rest of the world relatively intact, I don't see that motivating any other countries to suddenly try to take over the world. (Except Canada. This entire answer is part of our secret plot to lull the world into a false sense of security, while giving the impression that we're weak and powerless. Then, right when you're least expecting it...bam! Everyone has to wear a toque.)
As far as population control goes, while I don't anticipate a united world government, we've already seen individual governments attempt to control the number of births. In a study by David Pimentel, a professor of ecology at Cornell, it was suggested that the world population must be reduced to about 2 billion people in order to promote a sustainable level of living at the equivalent of a moderate European lifestyle. This could be accomplished within 100 years if each couple restricted themselves to only one child. Obviously, not every government is going to try to enforce something like this. Generally, population control is supported by increasing the availability of contraception and increasing women's education. In Iran, family planning education is mandatory for both males and females before a marriage license can be obtained, which is credited with the drastic reduction in birth rates that it has seen. India uses other incentives to promote population control, such their law that makes anyone with more than two children ineligible for elections to Gram Panchayats, or local governments.
The most obvious example of enforced population control is China's one-child policy, which makes exceptions for twins, rural couples, ethnic minorities, and couples who are both only children themselves. This policy has been largely controversial due to the increased number of female abortions and female infanticide that has contributed to China's extreme gender imbalance. Many advocacy groups oppose the policy based on human rights violations, such as forced abortions. Furthermore, the policy has created other problems, such as the fact that one adult is now solely responsible for the care of two parents and four grandparents, without any available help. In my personal opinion, the difficulty that China has had with the one-child policy suggests that it's very unlikely that this will be widely adopted. This would be unconstitutional by the standards of many countries, and other countries don't have a strong enough totalitarian state to enforce it to the same degree as China.
While many countries have dabbled in compulsory sterilzation, most countries seem to have abandoned it in recent decades, with the notable exception of Uzbekistan. It, too, seems to be on its way out.
I see two possible scenarios for lifespan control. In one scenario, science has extended the average human life by a moderate amount, and so governments choose to cap the human lifespan at some arbitrary age, despite that everyone will eventually die of old age (even if old age is now 150 or 200 years old). Considering how controversial abortion, capital punishment, and other associated issues are, I can't imagine that any democracy would agree to such a thing. I can hypothetically see a totalitarian nation attempting to implement such a policy, but they would face extremely heavy international condemnation, and it would probably be even less successful than compulsory population control.
In the other scenario, science has invented some sort of procedure or pill that allows humans to live far longer than their natural lifespan, possibly making them immortal. In this situation, I can hypothetically see different countries enacting various sorts of proposals that would make this unavailable to anyone above a certain age, effectively killing them. However, this would lead to a huge black market for lifespan. Poor people would sell some of their "life" to rich people in order to buy food, send their children to college, or pay for other basic necessities. The disparity between nations who could afford it and nations who could not would become extreme. Dictators could ultimately rule forever, forcing changes in foreign policy when it comes to dealing with them. It would be total chaos.
Fortunately, I don't think such a thing will be developed within the next 1000 years. While some creatures, such as the hydra and planarian worms, can be biologically immortal, there is currently no research being done about applying this to humans. While anti-aging products exist, Concealocanth does a great job of explaining why they're bunk in Board Question #68832. Although it may be possible to eventually grow human organs in a lab, I'm having a hard time to imagine a future where you can literally replace every single tissue in your body as it ages. Even if that became a reality, you'd probably still end up with some pretty old tissue in you. As you age, your risk for cancer increases, so I basically think everyone would just die of cancer in a couple hundred years. So what if we cure cancer? Well, I think we're getting into the realm where people require so many different treatment requirements that we're essentially back to my first scenario, where the government restricts certain treatments below a certain age.
Basically, I don't think there's going to be a magic bullet that makes humans immortal. If we do come up with a method of rejuvenation, I think that it would bear so many similarities to cancer (again) that it would take awhile before everyone started truly living for decades and centuries beyond their natural time. And in that situation, we could still die of other diseases, accidents, and murder. Maybe we'd see some government sneaking poison into nursing homes or something.
Really, the sociological implications of medicine that can make humans functionally immortal are too broad to accurately predict. In the case that this happens, I'm sure that some governments will resort to unethical methods of dealing with the situation. At the same time, we have to consider the fact that such developments in technology will also come at the same time as the developments I talked about in part (1) and (2) of this question, which would reduce the pressure a non-aging population would cause. Maybe non-aging individuals would be better candidates for space exploration and settlement, and governments would instead begin a race to see who could build the best non-aging population in order to get a leg up on the space race. Who knows?
Finally, it's proposed that we could one day find a way of transporting our consciousnesses into computers, living forever as cyborgs. While this could lead to all kinds of crazy scenarios, like cyborg armies and increased competition over precious metal resources, it would also serve to reduce the strain of feeding a growing human population. On the other hand, the energy requirements would probably accelerate the Earth's pollution, and the other resources necessary to build a bunch of cyborgs would still lead to population challenges. So while computer people is a pretty cool and far-fetched idea, I think it would come with essentially the same pressures as any other means of gaining immortality.
5. Humanity is decimated by _____ and the few survivors live primitively.
a) war: 7/10
So we're going to have more wars in the next 1000 years, and some of them will be major ones. History and the current state of the world today makes that abundantly clear. So now the question is, will any of these wars be large enough to decimate humanity? I can think of three possible scenarios where this happens: WWIII, biological warfare, and nuclear warfare.
I'm having trouble thinking of a specific situation right now that's likely to lead to WWIII, but a thousand years is a really, really long time. Within the last thousand years, we've had conflicts from the Crusades to WWII. I kind of just see it as a given that at some point in the next 1000 years, there will be numerous situations where the world could erupt into war, and I also see it as pretty likely that it would happen. (So basically, today we've learned that Zed thinks space travel and science is awesome, the universe is fine, but humans are idiots.) I read a great point in this discussion that essentially says that wars erupt when one power bloc thinks it can prevail against another. The Cold War didn't erupt into global fighting because the USA and the USSR perceived each other to be too equally matched to start an open war. However, as China increases in power, NATO and other traditional Western alliances decline, terrorist groups gain supporters, and developing nations like Iran and North Korea gain power, new power blocs are emerging. It's pretty likely that one of these might perceive themselves as being in a position to make a strike against another bloc. So, I think WWIII will happen within 1000 years. However, like the previous wars, I don't think a conventional war will decimate humanity. A lot of people will die and some countries may be reshaped, but overall, humanity will be fine.
So, under what conditions could war decimate humanity? Well, the obvious one is nuclear warfare. This apocalyptic scenario has been so thoroughly rehashed, and has been such an object of fear for so long, that I think some people tend to downplay the risks these days. After all, the Cold War is over, so it would seem that the world has taken a step back from nuclear warfare. However, a study by Stanford University warns that the risk of nuclear warfare with China is actually higher than most people think. While China has a strict policy of not striking first with nuclear weapons, and the military power of the US makes them unlikely to resort to such extremes, there are other factors that could precipitate nuclear warfare. For instance, if China perceived conventional attacks to be an attempt to sabotage their nuclear capabilities, or if they thought they were a precursor to a nuclear strike, they might break their rule. Similarly, China's military policy is specifically designed to create uncertainty in the US about their plans, under the idea that this will prevent the US from taking swift action. However, this strategy obviously also creates the potential for the US to believe that China is going to use nuclear weapons. Some conventional Chinese missiles are on the same bases as nuclear missiles, and some rockets are even able to carry either type of missile. Finally, the US does not find China's no-first-strike policy to be credible, which could also result in misunderstandings leading to war.
Meanwhile, Stanford engineer Martin Hellman believes that the chances of a child born today suffering death from nuclear warfare to be 10%. That's 10% in our lifetime, let alone in the next 1000 years. His risk analysis approach looks at the rate of possible initiating events, the probability of these events turning into major events, and the probability of these crises leading to the use of nuclear weapons. Furthermore, the situation in Iran and North Korea adds complexity to his consideration; nuclear terrorism isn't even included in his assessment, which means it's actually conservative.
The outcomes of a nuclear winter should be well-known to most readers, but for the sake of completeness, I'll summarize. The aftereffects of the bomb would pollute the atmosphere so thoroughly that major climate change would occur, leading to famine and drought. This could possibly lead to even more fighting and conflict. Furthermore, global nuclear war would be more likely to target major cities, which would destroy more technology, power grids, and communication systems, further leading humanity into a pre-technological state. Along with nuclear warfare, it's possible that high-altitude magnetic pulses would be used to sabotage militaries, destroying our computer systems. Meanwhile, radiation would kill many people outright, and lead to greatly increased rates of cancer. We all know why nuclear warfare is bad. And according to scientists, there's a great chance of nuclear warfare in the next 1000 years than there is of any natural disaster on the list.
Finally, biological warfare wouldn't even require a major, worldwide conflict to decimate humanity. As we all learned from the Jurassic Park movies, life will find a way. No matter what kinds of controls the biological engineers think they've built into their weapon, living things can mutate, reproduce, and quickly move beyond the ability of their creators to control. There are many non-apocalyptic examples of this; for instance, look at what the cane toads have done to Australia. While bacteria can be genetically modified to only act within a narrow environmental range, bacteria mutates all the time; that's why you have to get a new flu shot every year. Similarly, even things that don't directly kill you, like anti-agriculture agents, can be easily spread by migrating animals, water runoff, or weather patterns.
Currently, the USA, Russia, China, and South Africa definitely have biological weapons. The UK, France, Iraq, Israel, Iran, Syria, and North Korea probably have biological weapons, and other countries, such as India, Pakistan, and Libya, are seeking biological weapons. Not only are these a lot of powerful nations that tend to disagree with each other, but some of these nations also provide terrorists with close access to biological weapons. While nations themselves would presumably use biological weapons carefully, and with all the safeguards they could put on them, terrorists have no such inhibitions. It only takes one terrorist to release a powerful biological weapon, and humanity could be decimated. Biological warfare has a long history of being used, so it's not like it would be a first-time thing. The difference is, today's superior technology makes it that much more dangerous to the entire world, and the increase in global travel makes it more communicable than ever.
For more information on biological weapons, the NIH has a great collection of articles on the different types here.
b) disease: 4/10
In contrast, I don't think a pandemic is likely to have such an effect that it truly decimates the human race. The only time that's happened in history is when smallpox wiped out 90% of the Massachusetts Bay Native Americans, and that was confined to a specific ethnic population that had considerably less access to medicine than we do today. While there have been many, many pandemics in human history, none of them actually wiped out civilization. In modern times, SARS, avian flu, and swine flu were all contained and caused minimal deaths. Historically, there's not a lot of basis to think that pandemics tend to decimate humanity as a whole.
On the other hand, there are modern differences that could change this. For one thing, the speed of global travel makes pandemics more transmissible; in the past, particularly potent pandemics were typically confined to small regions, because they killed off their hosts faster than the disease could spread. Now, we lack a good global system to respond to pandemics in a way that reduces transmission of the disease. Along with the speed of global travel, we now have less time to react to the situation, and it can be difficult to get aid effectively to the afflicted, especially when the pandemics begin in developing areas. Furthermore, most pandemics do begin in developing areas, due to the fact that conditions are more favorable for disease to develop and fester. And although modern medicine is better able to treat disease, viruses can develop and spread faster than vaccines can be developed and deployed to counteract them. As a result, it's very probable that we will see a significant pandemic within our lifetime – much more probable than nuclear warfare or biological terrorism. The difference is, a naturally occurring pandemic isn't going to decimate humanity; it will kill a lot of people, but civilization will recover fairly quickly. The odds of a pandemic actually destroying civilization are still significantly lower than the odds of war destroying civilization. Most likely, it will cause a recession and maybe up to 20% of people will die. I don't think it will cause us to return to a primitive state.
However, there's another disease threat that could also have a significant impact on humanity: antibiotic resistance. Antibiotics don't kill all bacteria; they only kill most of them. The bacteria that are left have mutations that make them resistant to that antibiotic, and when they multiply, all of those bacteria will also be resistant. Our usage of antibiotics, such as pumping them en masse into animal feed, quitting the medication once we feel better even though we still have a few days left that we're supposed to take it, and insisting on being prescribed antibiotics for problems that aren't even caused by bacteria all lead to the overexposure of bacteria to antibiotics, accelerating the problem. This has created significant problems in treating diseases that could previously be treated with "weak" antibiotics; for instance, antibiotic-resistant tuberculosis has been popping up with increasing frequency. Furthermore, superbugs such as MRSA also threaten to become an increasingly common disease, with few good treatment options.
Meanwhile, research on new antibiotics is slowing down, due to the fact that antibiotics research isn't very profitable for pharmaceutical companies. Other alternatives are being developed; for example, Professor Savage's research group at BYU has been looking at a synthetic version of a natural anti-bacterial found in other microorganisms. I can't seem to find my o-chem notes on this, but because of the way it disrupts the bacteria, they can't grow immune to it. However, alternatives to the antibiotics we already have aren't being developed quickly enough.
To realize the impact of this, stop for a moment and think about how often we use antibiotics. When was the last time someone you knew died of strep throat or scarlet fever? We take antibiotics for pretty much everything; while people used to die of septic shock because they cut their finger, that isn't even an issue today. Furthermore, think of all the surgeries we do today, both elective and necessary. The rates of post-surgery complications have gone down enormously since antibiotics were developed; in a very real sense, losing our ability to fight bacteria with antibiotic agents could return us, if not to a "primitive" state, at least to a state where health care and life expectancy are drastically reduced. Overall, we won't live primitively, and we'll probably find a solution within 1000 years. However, this could become a very real and serious problem for quite some time.
c) zombies: 0/10
So I don't really believe that a zombie apocalypse is possible, but the subject is one of my favorites. M and I joke about who's going to cause the zombie apocalypse all the time. (Hey look, I made it like 10,000 words before bringing up M! New record!)
First, let's talk about some ways the zombie apocalypse could be created, and then we'll talk about why it would fail.
In this video, the possibility of a "rage virus" is discussed – the dead aren't reanimated, but the infected humans develop qualities of rage and the insatiable desire for human flesh. In order to do this, the virus must be specific to the brain areas that cause these symptoms, while leaving the rest of the brain intact so that the zombies can move around and stuff. The virus could enter the olfactory neurons through retrograde axonal transport in order to affect the ventromedial hypothalamus, which regulates hunger; the amygdala, which regulates emotion; and the frontal cortex, which regulates morality and inhibiting impulsive actions (like biting people). You end up with super hungry, aggressive, brain-dead beings who can't recognize family and friends or control their own actions. Alternatively, a similar effect could be created by attaching a prion to a virus and causing brain damage, but you would then have to induce metabolic alkalosis to prevent the prion from completely destroying the brain, and prions can't really be attached to viruses anyways.
Furthermore, there are parasites, like Toxoplasmosa gondii, that can induce zombie-like symptoms; neurotoxins, like those used in Haiti to produce real-life, zombie-like people, and brain stem cells or nanobots, which would some day be used for brain surgery, only for things to go horribly wrong.
So let's suppose zombies begin to roam the Earth. We're all doomed, right? Wrong. So wrong. Why? Well, for one thing, zombies have no sense of self-preservation that allows us to avoid natural predators. They would be eaten alive by dogs, cats, and wolves, decomposed by maggots and flies, and even mauled by deer and bears. Furthermore, their lack of self-preservation and higher thought processes would make it super easy for the military to outwit them.
Oh yeah, the military. Why doesn't the military ever win against the zombies in these movies? Seriously, you have some lone protagonist with makeshift weapons taking on a dozen at once, yet the American military is somehow defeated? Really? This makes no sense. Even if they could somehow overpower the military with brute force, I find it difficult to believe that we couldn't out-strategize them; a simple doorknob would probably cause their non-functioning brains to overload.
Additionally, they can't heal from injuries, or even normal cellular wear and tear. Leg broken? They can't chase you anymore. Tendons degrade? They fall into a heap of animated corpse-flesh that can't hurt anybody. Seriously. We can all just lock the doors, throw rocks at their ankles, and wait it out for a couple of weeks.
And then you have to consider the effects of weather. Zombies aren't smart enough to find shelter. If it was warm out, they'd dry out and desiccate under the sun, or they'd start rotting and dissolve into rancid, putrid flesh. Have you ever left meat out in July for a few days? No, because you have a functioning frontal cortex. The zombies would just be destroyed. And it's not like cold would be any better for them; they'd freeze solid. Grab a hammer, smash some zombie ice cubes, and the problem is solved.
Also, remember how I talked about diseases like SARS and swine flu not overrunning us? Well, those diseases were highly transmissible through airborne contact. Most zombie folklore agrees that zombies must bite you in order to infect you. This is a terrible way to spread disease. How did zombies even get enough numbers to pose a threat to the local policeman, let alone the American military? Seriously, if you knew there were zombies running around biting people, would you get close to strangers? When was the last time you contracted rabies? Hmmm? The only scenario where a zombie outbreak could occur quickly enough to infect a large amount of the population too quickly to control would be a virus more potent than any we've ever seen before.
Finally, if a zombie attacks you, just get in a boat. Seriously, when was the last time you saw a zombie that could swim? Brain-dead creatures can't climb or navigate obstacles nearly as efficiently as you or I could. If worst comes to worst, we could all go find a nice building with exposed pipes, toss a rope over them, climb up with a good supply of food and water, pull the rope up after us, and wait for the zombies to decompose as previously stated.
And if worst comes to worst, we can all flee to Canada, where the government has devoted actual government time to discussing preparations for the zombie apocalypse. Which raises this question: what if the zombie apocalypse is engineered by Canadians so we can feel special and needed for once?