How to Destroy the Universe (7 page)

Coal, petrol and other fossil fuels give off copious amounts of CO
₂
when they're burned. That, per se, isn't a problem. If you burn a big stack of wood it will also give off a lot of CO
₂
. The difference is that the CO
₂
released when wood burns was already in the climate system—the tree soaked it all up before it was chopped down for fire wood, so what gets released is simply going back where it came from. The gas given off by burning fossil fuels, on the other hand, was previously locked away underground—and so this is new CO
₂
that's being added to the environment. This is why efforts to develop “biofuels,” replacements for petrol that are derived from renewable plant materials, are a promising possibility. (Although there is concern about the amount of land taken up to farm biofuel crops, and the impact this in itself will have on the environment.) Few people doubt that we need to cut down our carbon emissions, though many scientists worry that it will be too little too late. Their concern is that the state of the environment may soon cross a
so-called tipping point, beyond which it will be extremely difficult to reverse the climate's free fall into global meltdown. “Tipping point” is a phrase used by mathematicians to describe a sudden, discontinuous hop from one state to another. For example, gradually increasing the weight on the end of a rope will ultimately lead to a tipping point as the rope reaches its breaking load—and once the rope has snapped there's no going back.

But there is a glimmer of hope in all this. After all, if the current global warming is our fault then we've already demonstrated our ability to influence the planet's climate in a big way. And if we can do that, can we influence the climate in the opposite direction and put things back how they were? Some researchers think so. They've been devising schemes to patch up the damage—a field of science known as “geoengineering.”

The options for geoengineering break down broadly into two categories: soaking up carbon from the atmosphere and blocking solar radiation. The simplest way to soak up carbon from the atmosphere is to plant more trees. Trees—and all green-leaved plants—take in CO
₂
in order to produce their own food. The process is called photosynthesis, a chemical reaction whereby CO
₂
and water combine with sunlight to
make energy-rich carbohydrate plus oxygen, which is emitted back to the atmosphere and which all animals need to breathe.

If you can't plant real trees, one idea is to build artificial ones. The “trees” resemble giant fly swatters that sift CO
₂
from the air that flows through them. They work by absorbing the gas into a solution of sodium hydroxide. This is then heated in a kiln, causing the CO
₂
to be given off as steam, which can be captured and bottled in high-pressure tanks. The gas in the tanks is then compressed into a liquid, which is pumped underground, for example into the cavities left behind by disused oil wells: putting the CO
₂
released by burning fossil fuels back where it came from.

A less reliable option that has been suggested is to add vast amounts of fertilizer to the oceans, such as iron or the nitrogen-rich compound urea. The idea is that the fertilizer will encourage the growth of phytoplankton, which feed on carbon during the course of their lives. When the plankton die, their bodies, along with all the carbon they've absorbed, sink to the ocean floor and ultimately get buried by sediments. The risk with this plan is that unbalancing the chemistry of the ocean ecosystem with the vast amounts of chemicals that would be needed could do more harm than good.

Blocking light and heat from the Sun is another major plan. One proposed solution involves spraying sea water into the air. As the water rises into the atmosphere, it evaporates, leaving tiny particles of salt that stimulate clouds to condense around them, a process known as “cloud seeding.” The clouds would reflect solar radiation away into space. A fleet of robotic ships would do the spraying. The main drawback with this scheme is that no one knows for sure that it will work. The role of clouds in climate models is notoriously uncertain: white clouds do indeed reflect solar radiation, but water vapor, like CO
₂
, is a greenhouse gas that will trap heat and contribute to global warming. Which of these two effects wins out is at present unclear.

Another idea is to belch millions of tons of sulfur particles into the atmosphere where they would blot out some of the Sun's light. This technology has already been tried and tested—though not by humans. In 1991, the volcano Mt Pinatubo in the Philippines erupted, spewing an estimated 20 million tons of sulfur dioxide skywards, reducing global temperatures by 0.5°C (1°F) for two years following the eruption. The major disadvantage with this plan is that sulfur in the air is what causes acid rain, thanks to a chemical reaction in which sulfur dioxide combines with oxygen and hydrogen to make sulfuric acid. Acid rain
increases the acidity of lakes and oceans, killing fish, which in turn impacts upon species that feed on the fish, sending a ripple effect all the way up the food chain. A less-polluting yet slightly more ambitious alternative is to launch a fleet of reflective parasols into space. These would sit at the L1 Lagrange point between Earth and the Sun, where the gravitational fields of the two bodies to some extent cancel out. A space parasol placed on the line connecting Earth and the Sun feels the gravity of both bodies pulling it in opposite directions. Too close to Earth and it will fall toward the planet, too close to the Sun and it will fall that way instead—but right between the two is a point where it will stay put, orbiting the Sun in lockstep with Earth. This is the L1 point. There are another four Lagrange points, labeled L2–5, dotted around the Earth–Sun system.

But this plan won't be cheap. It's estimated the combined area of the sunshade would need to be about the size of Greenland, and that would mean lofting some 20 million tons of hardware into space. At present, the most inexpensive space launchers can do this at a cost of around $4,000 per kilogram of payload, meaning a total cost for the sunshade of $80 trillion, more than the GDP of the entire planet.

Some ambitious space engineers want to use geoengineering principles not just on Earth, but on other planets too. Called “terraforming,” this involves sculpting the temperature and atmospheric composition, and introducing surface water. The most obvious candidate for terraforming in our Solar System is our next-door neighbor Mars. Scientists have suggested that the Red Planet could be made more like Earth by introducing plants that have been genetically modified to exist in its harsh climate. Through photosynthesis, these would gradually introduce oxygen into Mars's atmosphere—which is currently 95 percent CO
₂
. Meanwhile, the greenhouse effect could actually be a boon on Mars, melting the planet's ice reserves to give running water. It has even been proposed that an asteroid laden with the greenhouse chemical ammonia could be steered into Mars. Others regard such ecological tinkering on other worlds with dismay. Then again, if we cannot fix the climate of our own planet sometime soon we may well have no choice.

• Early ideas

• Rocket science

• How much fuel?

• Beating gravity

• Multi-staging

• Atmospheric re-entry

• Space tourism

Space is just an hour's drive away, 100 km (60 miles) above your head. And yet only a few hundred humans have ever been there. That's because, while possibly the most alluring destination for the intrepid traveler, it's also one of the most difficult places to reach—demanding the ride of a lifetime aboard a giant firework traveling at 25 times the speed of sound. If that doesn't put you off then check your bags and climb aboard the orbital express …

Going into space is one of humankind's oldest dreams. The idea began to edge its way closer to reality in 1903, when Russian space scientist Konstantin Tsiolkovsky
published
The Exploration of Cosmic Space by Means of Reaction Devices
. In it, he described how human explorers could escape Earth's gravitational field to enter orbit around the planet and possibly even venture further afield. Tsiolkovsky imagined that we would use rockets to get there.

Rockets had already enjoyed a long, if less than peaceful, history within the confines of the planet's atmosphere. In the 9th century, Chinese scientists invented gun-powder and were quick to use it as a power source to hurl projectiles at their enemies. Ever since, rockets have been used in conflicts around the world, right up to the war in modern-day Iraq.

Rockets work by ejecting fuel exhaust at high speed, which accelerates the body of the rocket in the opposite direction. This is based on Newton's third law of motion, which says that for every force there is an equal force pushing in the opposite direction—when I fire a rifle the bullet is accelerated forward out of the barrel, while the stock of the gun kicks back against my shoulder. Newton's third law means that as the rocket fuel burns, expands and is forced out of the rocket engine, an equal and opposite force is exerted on the rocket itself, which accelerates it forward.

The increase in speed is given by a principle known as the conservation of momentum. Momentum can be thought of as the impetus that a moving object has. Physicists calculate the momentum of a moving object simply by multiplying together its speed (measured in meters per second) and its mass (in kilograms). Fast, heavy things carry more momentum than slow, light things—which is why getting hit by a lorry hurts more than being bumped by a shopping trolley. The conservation of momentum says that the total momentum in any physical process must always stay the same. So if two billiard balls collide, the sum of both balls' momentum before the collision must equal the sum of their momentum after the collision. If one ball starts at rest, and is hit by a second ball which is stopped dead in the collision, then the first ball must carry away exactly the same momentum that the second came in with. And if they are both of equal mass then the second ball must leave with the exact same speed too.

In rocketry, the conservation of momentum says that the rocket must gain momentum at the same rate as momentum is being carried away by the exhaust gas vented from the back. For example, say a small rocket spits out a kilogram of exhaust gas at 2,500 m/s. If the rocket body weighs 10 kg, that means the rocket will be moving forward after the burn at 250 m/s. The
momentum of the rocket must be the same as that of the exhaust, which is just the speed of the exhaust (2,500) times its mass (1). The speed of the rocket is this figure divided by its mass (10).

In fact, this is a slight simplification. It assumes the mass of the rocket is constantly 10 kg. But its mass is actually changing continuously as fuel get burned. Initially the rocket weighs 11 kg because it has to carry all the fuel it needs for the burn—and this extra baggage makes the final speed slightly less. Konstantin Tsiolkovsky worked out a mathematical equation for determining the speed that a rocket can reach given the weight of the rocket body, the weight of propellant and the speed of its exhaust gas, taking into account the fact that the propellant burns gradually. In our example above, Tsiolkovsky's rocket equation reveals that the rocket would actually accelerate to 238 m/s. Scientists call this total increase in velocity brought about by burning a given mass of fuel “delta-
v
”—which comes from the mathematician's shorthand “delta,” meaning “a change in,” and the symbol for velocity, “
v
.”

So how much delta-
v
does it take to get a rocket into space? The answer to that question was provided centuries ago by the English physicist Isaac Newton. In 1687, Newton published his theory of gravity. It was a monumental
achievement for a scientist working in the 17th century: a single mathematical law that at a stroke explained the orbit of Jupiter and how apples fall from trees in Cambridge—phenomena separated by hundreds of millions of kilometers. Newton's theory was a universal law of gravitation, revealing not only why objects fall downward in a gravitational field, but also how the planets circle the Sun. The mathematical description of orbits had been worked out 80 years earlier by the German astronomer Johannes Kepler. Newton's theory neatly provided the physics underpinning all three of Kepler's “laws of planetary motion.”

However, Newton's theory also revealed how fast a rocket needed to travel in order to reach orbit around Earth. Launch a projectile into the air and it arcs through the sky before falling back to the ground. Launch the projectile faster and the arc carries it higher and further. Orbit is achieved when the projectile is traveling so fast that the curved surface of the planet falls away at exactly the same rate the rocket falls under the attraction of gravity, meaning that the rocket circles around the planet continuously. (Some readers may have heard of the term “escape velocity”—the speed that a projectile, such as a cannon ball, must be given in a single kick at Earth's surface in order to completely escape the planet's gravity. However, escape velocity doesn't apply to rockets because they burn their fuel gradually—theoretically, a rocket could leave the atmosphere traveling at any speed as long as it had enough fuel to keep accelerating.)