Urban horticulture specifically is the study of the relationship between plants and the urban environment. It focuses on the functional use of horticulture so as to maintain and improve the surrounding urban area. With the expansion of cities and rapid urbanization,
this field of study is large and complex and its study has only
recently gained momentum. It has an undeniable relationship to
production horticulture in that fruits, vegetables and other plants are
grown for harvest, aesthetic, architectural, recreational and
psychological purposes, but it extends far beyond these benefits. The
value of plants in the urban environment has yet to be thoroughly
researched or quantified.
Salad lettuce cultivation at the Growing Communities' urban plot, in Springfield Park, Clapton, North London.
Horticulture and the integration of nature into our civilization has been a major part in the establishment of our cities. When nomadic civilizations
began settling down, their major trading centers were the market
gardens and farms. Urban horticulture rapidly progressed with the birth
of cities and the increase in experimentation and exchange of ideas.
These insights led to the field being dispersed to farmers in the
hinterlands.
For centuries, the built environment such as homes, public buildings,
etc. were integrated with cultivation in the form of gardens, farms, and
grazing lands, Kitchen gardens, farms, common grazing land, etc.
Therefore, horticulture was a regular part of everyday life in the city. With the Industrial Revolution
and the related increasing populations rapidly changed the landscape
and replaced green spaces with brick and asphalt. After the nineteenth
century, Horticulture was then selectively restored in some urban spaces
as a response to the unhealthy conditions of factory neighborhoods and
cities began seeing the development of parks.
Post World War II trends
Early urban horticulture movements majorly served the purposes of short term welfare during recession periods, philanthropic charity to uplift "the masses" or patriotic relief. The tradition of urban horticulture mostly declined after World War II as suburbs
became the focus of residential and commercial growth. Most of the
economically stable population moved out of the cities into the suburbs,
leaving only slums and ghettos at the city centers. However, there
were a few exceptions of garden projects initiated by public housing
authorities in the 1950s and 1960s for the purpose of beautification and
tenant pride. But for the most part as businesses also left the metropolitan areas, it generated wastelands and areas of segregated poverty.
Inevitably the disinvestment of major city centers, specifically
in America resulted in the drastic increase of vacant lots. Existing
buildings became uninhabitable, houses were abandoned and even
productive industrial land became vacant. Modern community gardening, urban agriculture, and food security
movements were a form of response to battle the above problems at a
local level. In fact other movements at that time such as the peace,
environmental, women's, civil rights, and "back-to-the-city" movements of the 1960s and 1970s and the environmental justice
movement of the 1980s and 1990s saw opportunity in these vacant lands
as a way of reviving communities through school and community gardens,
farmers' markets, and urban agriculture.
Modern community garden movement
Things
have taken a turn in the twenty-first century as people are recognizing
the need for local community gardens and green spaces. It is not the
concept but the purposes that are new. The main goals of this movement
include cleaning up neighborhoods, pushing out drug dealing that occurs
at empty lots, growing and preserving food for consumption, restoring
nature to industrial areas, and bringing the farming traditions to urban
cities. Essentially community gardening
is seen as way of creating a relationship between people and a place
through social and physical engagement. Most urban gardens are created
on vacant land that vary in size and are generally gardened as
individual plots by community members. Such areas can support social,
cultural, and artistic events and contribute to the rebuilding of local
community spirit. The modern community garden movement is initiated by
neighborhoods along with the support of the governments and non-profit
organizations. Some gardens are linked to public housing projects,
schools through garden-based learning
programs, churches and social agencies and some even employ those who
are incarcerated. Community gardens which are now a large part of the
urban horticulture movement are different from the earlier periods of
grand park development in that the latter only served to free the people
from the industrialism. In addition a community garden is more
beneficial and engaging than a mere lawn or park and serves as a
valuable access to nature where wilderness is unavailable. This movement
helped create and sustain relationships between city dwellers and the
soil and contributed to a different kind of urban environmentalism that
did not have any characteristics of reform charity.
Despite that it has been 30 years since the first community
gardens in the US, there is no concrete analysis of current urban
gardens and their organizations. The American Community Gardening Association
(ACGA) has estimations that show that municipal governments and
non-profit organizations operate gardening programs in about 250 cities
and towns, although the staff of this organization admits that this
number could in reality be twice as large. In 1994 survey, the National
Gardening Association found that 6.7 million households, that weren't
involved in gardening would be interested in doing so if there was a
plot nearby. A more recent survey showed that more gardens are being created in cities as opposed to being lost to economic development.
Today urban horticulture has several components that include more
than just community gardens, such as market gardens, small farms and farmers' markets and is an important aspect of community development. Another result of urban horticulture is the food security
movement where locally grown food is given precedence through several
projects and programs, thus providing low-cost and nutritious food.
Urban community gardens and the food security movement was a response to
the problems of industrial agriculture and to solve its related
problems of price inflation, lack of supermarkets, food scarcity, etc.
Benefits
Horticulture
by itself is a practical and applied science, which means it can have a
significance in our everyday lives. As community gardens cannot
actually compete with market-based land uses, it is essential to find
other ways to understand their various benefits such as their
contribution to social, human, and financial well-being. Frederick Law Olmsted, the designer of New York City's Central Park observed that the trees, meadows, ponds and wildlife tranquilize the stresses of city life.
According to various studies over the years, nature has a very positive
impact over human health and even more so in an emotional and
psychological sense. Trees, grass, and flower gardens, due to their
presence as well as visibility, increase people's life satisfaction by reducing fatigue and irritation and restoring a sense of calm.
In fact Honeyman tested the restorative value of nature scenes in urban
settings and discovered that vegetation in an urban setting produced
more mental restoration as opposed to areas without vegetation. In
addition, areas with only nature did not have as much of a positive
psychological impact as did the combination of urban areas and nature.
One of the obvious health benefits of gardening is the increased
intake of fruits and vegetables. But the act of gardening itself, is
also a major health benefit. Gardening is a low-impact exercise, which
when added into daily activities, can help reduce weight, lower stress,
and improve overall health. A recent study showed a reduced body mass
index and lower weight in community gardeners compared with their
non-gardening counterparts
The study showed men who gardened had a body mass index 2.36 lower and
were 62% less likely to be overweight than their neighbors, while women
were 46% less likely to be overweight with a body mass index 1.88 lower
than their neighbors.
Access to urban gardens can improve health through nutritious, edible
plantings, as well by getting people outside and promoting more activity
in their environments.
Gardening programs in inner-city schools have become increasingly
popular as a way to teach children not only about healthy eating
habits, but also to encourage students to become active learners.
Besides getting students outside and moving, and encouraging an active
lifestyle, children also learn leadership, teamwork, communication and
collaboration skills, in addition to critical and creative thinking
skills.
Gardening in schools will enable children to share with their families
the health and nutrition benefits of eating fresh fruits and vegetables.
Because weather and soil conditions are in a state of constant change,
students learn to adapt their thinking and creatively problem solve,
depending on the situations that arise.
Students also learn to interact and communicate with a diverse
population of people, from other students to adult volunteers. These
programs benefit students' health and enable them to be active
contributors in the world around them.
Gardens and other green spaces also increase social activity and
help in creating a sense of place, apart from their various other
purposes such as enhancing the community by mediating environmental
factors. There is also a huge disparity in the availability of sources
that provide nutritious and affordable foods especially around urban
centers which have problems of poverty, lack of public transport and
abandonment by supermarkets. Therefore, inner city community gardens can
be a valuable source of nutrition at an affordable cost in the most
easily accessible way.
In order to understand and thereby maximize the benefits of urban
horticulture, it is essential to document the effects of horticulture
activities and quantify the benefits so that governments and private
industries can make the appropriate changes. Horticulturists have always
been involved in the botanical and physical aspects of horticulture but
an involvement in its social and emotional factors would be highly
beneficial to communities, cities and to the field of horticulture and
its profession. Based on this, in the 1970s, the International Society for Horticultural Science
recognized this need for research on the functional use of plants in an
urban setting along with the need of improved communication between
scientists in this field of research and people who utilize plants. The
Commission for Urban Horticulture was established in 1982 which deals
with plants grown in urban areas, management techniques, the functional
use of these plants as well the shortcomings of the current lack of
knowledge regarding this field. The establishment of such a commission
is an important indicator that this topic has reached a level of
international recognition.
Economic benefits
There
are many different economic benefits from gardening from saving money
purchasing food and even on the utility bills. Developing countries can
spend up to 60–80 percent of income on buying food alone. In Barbara
Lake, Milfront Taciano and Gavin Michaels Journal of Psychology title
"The Relative Influence of Psycho-Social Factors on Urban Gardening",
they say that while people are saving money on buying food, having roof
top gardens are also becoming popular. Having green roofs can reduce the
cost of heating in the winter and help stay cool in the summer. Green
roofs also can lower the cost of roof replacement. While green roofs are
an addition to urban horticulture people are eating healthy while also
improving the value of their property. Other benefits include increased
employment from non-commercial jobs where producers include reductions
on the cost of food (Lake, Taciano, and Michael).
Production practices
Tomato plants growing in a pot farming alongside a small house in New Jersey in fifteen garbage cans filled with soil, grew over 700 tomatoes during the summer of 2013.
Crops are grown in flowerpots, growbags,
small gardens or larger fields, using traditional or high-tech and
innovative practices. Some new techniques that have been adapted to the
urban situation and tackle the main city restrictions are also
documented. These include horticultural production on built-up land
using various types of substrates (e.g. roof top, organic production and hydroponic/aeroponic
production). Because of this, it is also known as roof-top vegetable
gardening/horticulture and container vegetable gardening/horticulture.
Urban and peri-urban horticulture in Africa
A report of the United Nations Food and Agriculture Organization, Growing greener cities in Africa, states that market gardening
– i.e. irrigated, commercial production of fruit and vegetables in
areas designated for the purpose, or in other urban open spaces – is the
single most important source of locally grown, fresh produce in 10 out
of 27 African countries for which data are available. Market gardening
produces most of all the leafy vegetables consumed in Accra, Dakar, Bangui, Brazzaville, Ibadan, Kinshasa and Yaoundé,
cities that, between them, have a total population of 22.5 million.
Market gardens provide around half of the leafy vegetable supply in Addis Ababa, Bissau and Libreville.
The report says that in most of urban Africa, market gardening is an
informal and often illegal activity, which has grown with little
official recognition, regulation or support. Most gardeners have no
formal title to their land, and many lose it overnight. Land suitable
for horticulture is being taken for housing, industry
and infrastructure. To maximize earnings from insecure livelihoods, many
gardeners are overusing pesticide and urban waste water.
Vertical farming is the practice of growing crops in vertically stacked layers. It often incorporates controlled-environment agriculture, which aims to optimize plant growth, and soilless farming techniques such as hydroponics, aquaponics, and aeroponics.
Some common choices of structures to house vertical farming systems
include buildings, shipping containers, tunnels, and abandoned mine
shafts. As of 2020, there is the equivalent of about 30 ha (74 acres) of operational vertical farmland in the world.
The modern concept of vertical farming was proposed in 1999 by Dickson Despommier, professor of Public and Environmental Health at Columbia University. Despommier and his students came up with a design of a skyscraper farm that could feed 50,000 people. Although the design has not yet been built, it successfully popularized the idea of vertical farming. Current applications of vertical farmings coupled with other state-of-the-art technologies, such as specialized LED lights, have resulted in over 10 times the crop yield than would receive through traditional farming methods.
The main advantage of utilizing vertical farming technologies is
the increased crop yield that comes with a smaller unit area of land
requirement.
The increased ability to cultivate a larger variety of crops at once
because crops do not share the same plots of land while growing is
another sought-after advantage. Additionally, crops are resistant to
weather disruptions because of their placement indoors, meaning less
crops lost to extreme or unexpected weather occurrences. Because of its
limited land usage, vertical farming is less disruptive to the native
plants and animals, leading to further conservation of the local flora
and fauna.
Vertical farming technologies face economic challenges with large start-up costs compared to traditional farms. In Victoria,
Australia, a “hypothetical 10 level vertical farm” would cost over 850
times more per cubic meter of arable land than a traditional farm in
rural Victoria. Vertical farms also face large energy demands due to the use of supplementary light like LEDs. Moreover, if non-renewable energy is used to meet these energy demands, vertical farms could produce more pollution than traditional farms or greenhouses.
Techniques of vertical farming
Indoor Hydroponics of Morus, Japan
Hydroponics
Hydroponics refers to the technique of growing plants without soil. In hydroponic systems, the roots of plants are submerged in liquid solutions containing macronutrients, such as nitrogen, phosphorus, sulphur, potassium, calcium, and magnesium, as well as trace elements, including iron, chlorine, manganese, boron, zinc, copper, and molybdenum.
Additionally, inert (chemically inactive) mediums such as gravel, sand,
and sawdust are used as soil substitutes to provide support for the
roots.
The advantages of hydroponics include the ability to increase
yield per area and reduce water usage. A study has shown that, compared
to conventional farming, hydroponic farming could increase the yield per
area of lettuce by around 11 times while requiring 13 times less water. Due to these advantages, hydroponics is the predominant growing system used in vertical farming.
Aquaponics with catfish
Aquaponics
The term aquaponics is coined by combining two words: aquaculture, which refers to fish farming, and hydroponics—the technique of growing plants without soil. Aquaponics takes hydroponics one step further by integrating the production of terrestrial plants with the production of aquatic organisms in a closed-loop system that mimics nature itself. Nutrient-rich wastewater from the fish tanks is filtered by a solid removal unit and then led to a bio-filter, where toxic ammonia is converted to nutritious nitrate. While absorbing nutrients, the plants then purify the wastewater, which is recycled back to the fish tanks. Moreover, the plants consume carbon dioxide
produced by the fish, and water in the fish tanks obtains heat and
helps the greenhouse maintain temperature at night to save energy.
As most commercial vertical farming systems focus on producing a few
fast-growing vegetable crops, aquaponics, which also includes an
aquacultural component, is currently not as widely used as conventional
hydroponics.
Aeroponics
Aeroponically-grown chives
The invention of aeroponics was motivated by the initiative of NASA (the National Aeronautical and Space Administration) to find an efficient way to grow plants in space in the 1990s. Unlike conventional hydroponics and aquaponics, aeroponics does not require any liquid or solid medium to grow plants in. Instead, a liquid solution with nutrients is misted in air chambers where the plants are suspended. By far, aeroponics is the most sustainable soil-less growing technique, as it uses up to 90% less water than the most efficient conventional hydroponic systems and requires no replacement of growing medium.
Moreover, the absence of growing medium allows aeroponic systems to
adopt a vertical design, which further saves energy as gravity
automatically drains away excess liquid, whereas conventional horizontal
hydroponic systems often require water pumps for controlling excess
solution.
Currently, aeroponic systems have not been widely applied to vertical
farming, but are starting to attract significant attention.
Controlled-environment agriculture
Controlled-environment agriculture (CEA) is the modification of the natural environment to increase crop yield or extend the growing season. CEA systems are typically hosted in enclosed structures such as greenhouses
or buildings, where control can be imposed on environmental factors
including air, temperature, light, water, humidity, carbon dioxide, and
plant nutrition.
In vertical farming systems, CEA is often used in conjunction with
soilless farming techniques such as hydroponics, aquaponics, and
aeroponics.
Abandoned buildings are often reused for vertical farming, such as a farm at Chicago called “The Plant,” which was transformed from an old meatpacking plant. However, new builds are sometimes also constructed to house vertical farming systems.
Shipping-container vertical farms
Recycled shipping containers are an increasingly popular option for housing vertical farming systems. The shipping containers serve as standardized, modular chambers for growing a variety of plants, and are often equipped with LED lighting, vertically stacked hydroponics, smart climate controls, and monitoring sensors. Moreover, by stacking the shipping containers, farms can save space even further and achieve higher yield per square foot.
Deep farms
A “deep farm” is a vertical farm built from refurbished underground tunnels or abandoned mine shafts. As temperature and humidity underground are generally temperate and constant, deep farms require less energy for heating. Deep farms can also use nearby groundwater to reduce the cost of water supply.
Despite low costs, a deep farm can produce 7 to 9 times more food than a
conventional farm above ground on the same area of land, according to Saffa Riffat, chair in Sustainable Energy at the University of Nottingham. Coupled with automated harvesting systems, these underground farms can be fully self-sufficient.
History
Initial propositions
Dickson Despommier, professor of Public and Environmental Health at Columbia University, founded the root of the concept of vertical farming.
In 1999, he challenged his class of graduate students to calculate how
much food they could grow on the rooftops of New York. The student
concluded that they could only feed about 1000 people. Unsatisfied with the results, Despommier suggested growing plants indoors instead, on multiple layers vertically. Despommier and his students then proposed a design of a 30-story vertical farm equipped with artificial lighting, advanced hydroponics, and aeroponics that could produce enough food for 50,000 people.
They further outlined that approximately 100 kinds of fruits and
vegetables would grow on the upper floors while lower floors would house
chickens and fish subsisting on the plant waste.
Although Despommier's skyscraper farm has not yet been built, it
popularized the idea of vertical farming and inspired many later
designs.
In 2009, the world's first pilot production system was installed
at Paignton Zoo Environmental Park in the United Kingdom. The project
showcased vertical farming and provided a solid base to research
sustainable urban food production. The produce is used to feed the zoo's
animals while the project enables evaluation of the systems and
provides an educational resource to advocate for change in unsustainable
land-use practices that impact upon global biodiversity and ecosystem services.
In 2010 the Green Zionist Alliance proposed a resolution at the 36th World Zionist Congress calling on Keren Kayemet L'Yisrael (Jewish National Fund in Israel) to develop vertical farms in Israel.
Moreover, a company named "Podponics" built a vertical farm in Atlanta
consisting of over 100 stacked "growpods" in 2010 but reportedly went
bankrupt in May 2016.
In 2012 the world's first commercial vertical farm was opened in Singapore, developed by Sky Greens Farms, and is three stories high. They currently have over 100 nine meter-tall towers.
In 2012, a company named The Plant debuted its newly developed
vertical farming system housed in an abandoned meatpacking building in
Chicago, Illinois.
The utilization of abandoned buildings to house vertical farms and
other sustainable farming methods are a fact of the rapid urbanization
of modern communities.
In 2013 the Association for Vertical Farming
(AVF) was founded in Munich (Germany). By May 2015, the AVF had
expanded with regional chapters all over Europe, Asia, USA, Canada and
the United Kingdom. This organization unites growers and inventors to
improve food security and sustainable development. The AVF focuses on
advancing vertical farming technologies, designs and businesses by
hosting international info-days, workshops, and summits.
In 2015 the London company, Growing Underground, began the
production of leafy green produce underground in abandoned underground World War II tunnels.
In 2016, a startup called Local Roots launched the "TerraFarm", a vertical farming systems hosted in a 40-foot shipping container, which includes computer vision integrated with an artificial neural network to monitor the plants; and is remotely monitored from California. It is claimed that the TerraFarm system "has achieved cost parity with traditional, outdoor farming" with each unit producing the equivalent of "three to five acres of farmland," using 97% less water through water recapture and harvesting the evaporated water through the air conditioning. The first vertical farm in a US grocery store opened in Dallas, Texas in 2016, now closed.
In 2017, a Japanese company, Mirai, began marketing its
multi-level vertical farming system. The company states that it can
produce 10,000 heads of lettuce a day - 100 times the amount that could
be produced with traditional agricultural methods, because their special
purpose LED lights can decrease growing times by a factor of 2.5.
Additionally, this can all be achieved with 40% less energy usage, 80%
less food waste,
and 99% less water usage than in traditional farming methods. Further
requests have been made to implement this technology in several other
Asian countries.
In 2019, Kroger partnered with German startup Infarm to install modular vertical farms in two Seattle-area grocery stores.
Advantages
Efficiency
Traditional
farming's arable land requirements are too large and invasive to remain
sustainable for future generations. With the ever-so-rapid population
growth rates, it is expected that arable land per person will drop about
66% in 2050 in comparison to 1970. Vertical farming allows for, in some cases, over ten times the crop yield per acre than traditional methods.
Unlike traditional farming in non-tropical areas, indoor farming can
produce crops year-round. All-season farming multiplies the productivity
of the farmed surface by a factor of 4 to 6 depending on the crop. With
crops such as strawberries, the factor may be as high as 30.
Vertical farming also allows for the production of a larger
variety of harvestable crops because of its usage of isolated crop
sectors. As opposed to a traditional farm where one type of crop is
harvested per season, vertical farms allow for a multitude of different
crops to be grown and harvested at once due to their individual land
plots.
According to the USDA, vertical farm produce only travels a short distance to reach stores compared to traditional farming method produce.
The United States Department of Agriculture predicts the
worldwide population to exceed 9 billion by 2050, most of which will be
living in urban or city areas. Vertical farming is the USDA's predicted
answer to the potential food shortage as population increases. This
method of farming is environmentally responsible by lowering emission
and reducing needed water. This type of urban farming that would allow
for nearly immediate farm to store transport would reduce distribution.
In a workshop on vertical farming put on by the USDA and the Department of Energy experts in vertical farming discussed plant breeding, pest management, and engineering. Control of pests (like insects, birds and rodents)
is easily managed in vertical farms, because the area is so
well-controlled. Without the need of chemical pesticides the ability to
grow organic crops is easier than in traditional farming.
Resistance to weather
Crops
grown in traditional outdoor farming depend on supportive weather and
suffer from undesirable temperatures, rain, monsoon, hailstorm, tornado,
flooding, wildfires, and drought.
"Three recent floods (in 1993, 2007 and 2008) cost the United States
billions of dollars in lost crops, with even more devastating losses in
topsoil. Changes in rain patterns and temperature could diminish India's
agricultural output by 30 percent by the end of the century."
The issue of adverse weather conditions is especially relevant for arctic and sub-arctic areas like Alaska and northern Canada
where traditional farming is largely impossible. Food insecurity has
been a long-standing problem in remote northern communities where fresh
produce has to be shipped large distances resulting in high costs and
poor nutrition.
Container-based farms can provide fresh produce year-round at a lower
cost than shipping in supplies from more southerly locations with a
number of farms operating in locations such as Churchill, Manitoba, and Unalaska, Alaska.
As with disruption to crop growing, local container-based farms are
also less susceptible to disruption than the long supply chains
necessary to deliver traditionally grown produce to remote communities. Food prices
in Churchill spiked substantially after floods in May and June 2017
forced the closure of the rail line that forms the only permanent
overland connection between Churchill and the rest of Canada.
Environmental conservation
Up
to 20 units of outdoor farmland per unit of vertical farming could
return to its natural state, due to vertical farming's increased
productivity. Vertical farming would reduce the amount of farmland, thus saving many natural resources.
Deforestation and desertification caused by agricultural encroachment on natural biomes could be avoided.
Producing food indoors reduces or eliminates conventional plowing,
planting, and harvesting by farm machinery, protecting soil, and
reducing emissions.
Traditional farming is often invasive to the native flora and
fauna because it requires such a large area of arable land. One study
showed that wood mouse
populations dropped from 25 per hectare to 5 per hectare after harvest,
estimating 10 animals killed per hectare each year with conventional
farming. In comparison, vertical farming would cause nominal harm to wildlife because of its limited space usage.
Problems
Economics
Vertical
farms must overcome the financial challenge of large startup costs. The
initial building costs could exceed $100 million for a 60 hectare
vertical farm. Urban occupancy costs
can be high, resulting in much higher startup costs – and a longer
break even time – than for a traditional farm in rural areas.
Opponents question the potential profitability of vertical
farming. In order for vertical farms to be successful financially, high
value crops must be grown since traditional farms provide low value
crops like wheat at cheaper costs than a vertical farm.
Louis Albright, a professor in biological and environmental engineering
at Cornell stated that a loaf of bread that was made from wheat grown
in a vertical farm would cost US$27.
However, according to the US Bureau of Labor Statistics, the average
loaf of bread cost US$1.296 in September 2019, clearly showing how crops
grown in vertical farms will be noncompetitive compared to crops grown
in traditional outdoor farms.
In order for vertical farms to be profitable, the costs of operating
these farms must decrease. The developers of the TerraFarm system
produced from second hand, 40 foot shipping containers claimed that
their system "has achieved cost parity with traditional, outdoor
farming".
A theoretical 10 storey vertical wheat farm could produce up to
1,940 tons of wheat per hectare compared to a global average of 3.2 tons
of wheat per hectare (600 times yield). Current methods require
enormous energy consumption for lighting, temprerature, humidity
control, carbon dioxide input and fertilizer and consequently the
authors concluded it was "unlikely to be economically competitive with
current market prices".
According to a report in The Financial Times as of 2020, most vertical farming companies have been unprofitable, except for a number of Japanese companies.
Energy use
During
the growing season, the sun shines on a vertical surface at an extreme
angle such that much less light is available to crops than when they are
planted on flat land. Therefore, supplemental light would be required. Bruce Bugbee claimed that the power demands of vertical farming would be uncompetitive with traditional farms using only natural light.
Environmental writer George Monbiot calculated that the cost of
providing enough supplementary light to grow the grain for a single loaf
would be about $15.
An article in the Economist argued that "even though crops growing in a
glass skyscraper will get some natural sunlight during the day, it
won't be enough" and "the cost of powering artificial lights will make
indoor farming prohibitively expensive".
Moreover, researchers determined that if only solar panels were to be
used to meet the energy consumption of a vertical farm, “the area of
solar panels required would need to be a factor of twenty times greater
than the arable area on a multi-level indoor farm”, which will be hard
to accomplish with larger vertical farms. A hydroponic farm growing lettuce in Arizona would require 15,000 kJ of energy per kilogram of lettuce produced.
To put this amount of energy into perspective, a traditional outdoor
lettuce farm in Arizona only requires 1100 kJ of energy per kilogram of
lettuce grown.
As the book by Dr. Dickson Despommier "The Vertical Farm"
proposes a controlled environment, heating and cooling costs will
resemble those of any other multiple story building.
Plumbing and elevator systems are necessary to distribute nutrients and
water. In the northern continental United States, fossil fuel heating
cost can be over $200,000 per hectare. Research conducted in 2015
compared the growth of lettuce in Arizona using conventional
agricultural methods and a hydroponic farm. They determined that heating
and cooling made up more than 80% of the energy consumption in the
hydroponic farm, with the heating and cooling needing 7400 kJ per
kilogram of lettuce produced.
According to the same study, the total energy consumption of the
hydroponic farm is 90,000 kJ per kilogram of lettuce. If the energy
consumption is not addressed, vertical farms may be an unsustainable
alternative to traditional agriculture.
Pollution
There are a number of interrelated challenges with some potential solutions:
Power needs: If power needs are met by fossil fuels, the environmental effect may be a net loss;
even building low-carbon capacity to power the farms may not make as
much sense as simply leaving traditional farms in place, while burning
less coal. Louis Albright argued that in a “closed-system urban farming
based on electrically generated photosynthetic light”, a pound of
lettuce would result in 8 pounds of carbon dioxide being produced at a
power plant, and 4,000 pounds of lettuce produced would be equivalent to
the annual emissions of a family car. He also argues that the carbon footprint
of tomatoes grown in a similar system would be twice as big as the
carbon footprint of lettuce. However, lettuce produced in a greenhouse
that allows for sunlight to reach the crops saw a 300 percent reduction
in carbon dioxide emissions per head of lettuce. As vertical farm system become more efficient in harnessing sunlight, they will produce less pollution.
Carbon emission: A vertical farm requires a CO2 source, most likely from combustion if colocated with electric utility plants; absorbing CO2 that would otherwise be jettisoned is possible. Greenhouses commonly supplement carbon dioxide levels to 3–4 times the atmospheric rate. This increase in CO2
increases photosynthesis at varying rates, averaging 50%, contributing
not only to higher yields, but also to faster plant maturation,
shrinking of pores and greater resilience to water stress (both too much
and little). Vertical farms need not exist in isolation, hardier mature
plants could be transferred to traditional greenhouse, freeing up space
and increasing cost flexibility.
Crop damage: Some greenhouses burn fossil fuels purely to produce CO2, such as from furnaces, which contain pollutants such as sulphur dioxide and ethylene. These pollutants can significantly damage plants, so gas filtration is a component of high production systems.
Ventilation: "Necessary" ventilation may allow CO2 to
leak into the atmosphere, though recycling systems could be devised.
This is not limited to humidity tolerant and humidity intolerant crop polyculture cycling (as opposed to monoculture).
Light Pollution: Greenhouse growers commonly exploit photoperiodism
in plants to control whether the plants are in a vegetative or
reproductive stage. As part of this control, the lights stay on past
sunset and before sunrise or periodically throughout the night. Single
story greenhouses have attracted criticism over light pollution, though a typical urban vertical farm may also produce light pollution.
Water Pollution: Hydroponic greenhouses regularly change the
water, producing water containing fertilizers and pesticides that must
be disposed of. Spreading the effluent over neighboring farmland or wetlands
would be difficult for an urban vertical farm, while water treatment
remedies (natural or otherwise) could be part of a solution.
Molecular nanotechnology (MNT) is a technology based on the ability to build structures to complex, atomic specifications by means of mechanosynthesis. This is distinct from nanoscale materials. Based on Richard Feynman's vision of miniature factories using nanomachines to build complex products (including additional nanomachines), this advanced form of nanotechnology (or molecular manufacturing) would make use of positionally-controlled mechanosynthesis guided by molecular machine systems. MNT would involve combining physical principles demonstrated by biophysics, chemistry, other nanotechnologies, and the molecular machinery of life with the systems engineering principles found in modern macroscale factories.
While
conventional chemistry uses inexact processes obtaining inexact
results, and biology exploits inexact processes to obtain definitive
results, molecular nanotechnology would employ original definitive
processes to obtain definitive results. The desire in molecular
nanotechnology would be to balance molecular reactions in
positionally-controlled locations and orientations to obtain desired
chemical reactions, and then to build systems by further assembling the
products of these reactions.
A roadmap for the development of MNT is an objective of a broadly based technology project led by Battelle (the manager of several U.S. National Laboratories) and the Foresight Institute. The roadmap was originally scheduled for completion by late 2006, but was released in January 2008. The Nanofactory Collaboration
is a more focused ongoing effort involving 23 researchers from 10
organizations and 4 countries that is developing a practical research
agenda
specifically aimed at positionally-controlled diamond mechanosynthesis
and diamondoid nanofactory development. In August 2005, a task force
consisting of 50+ international experts from various fields was
organized by the Center for Responsible Nanotechnology to study the societal implications of molecular nanotechnology.
Projected applications and capabilities
Smart materials and nanosensors
One proposed application of MNT is so-called smart materials. This term refers to any sort of material designed and engineered at the nanometer
scale for a specific task. It encompasses a wide variety of possible
commercial applications. One example would be materials designed to
respond differently to various molecules; such a capability could lead,
for example, to artificial drugs which would recognize and render inert
specific viruses. Another is the idea of self-healing structures, which would repair small tears in a surface naturally in the same way as self-sealing tires or human skin.
A MNT nanosensor would resemble a smart material, involving a
small component within a larger machine that would react to its
environment and change in some fundamental, intentional way. A very
simple example: a photosensor might passively measure the incident light
and discharge its absorbed energy as electricity when the light passes
above or below a specified threshold, sending a signal to a larger
machine. Such a sensor would supposedly cost less
and use less power than a conventional sensor, and yet function
usefully in all the same applications — for example, turning on parking
lot lights when it gets dark.
While smart materials and nanosensors both exemplify useful
applications of MNT, they pale in comparison with the complexity of the
technology most popularly associated with the term: the replicating nanorobot.
Replicating nanorobots
MNT nanofacturing is popularly linked with the idea of swarms of coordinated nanoscale robots working together, a popularization of an early proposal by K. Eric Drexler in his 1986 discussions of MNT, but superseded in 1992.
In this early proposal, sufficiently capable nanorobots would construct
more nanorobots in an artificial environment containing special
molecular building blocks.
Critics have doubted both the feasibility of self-replicating nanorobots and the feasibility of control if self-replicating nanorobots could be achieved: they cite the possibility of mutations
removing any control and favoring reproduction of mutant pathogenic
variations. Advocates address the first doubt by pointing out that the
first macroscale autonomous machine replicator, made of Lego blocks, was built and operated experimentally in 2002.
While there are sensory advantages present at the macroscale compared
to the limited sensorium available at the nanoscale, proposals for
positionally controlled nanoscale mechanosynthetic fabrication systems
employ dead reckoning of tooltips combined with reliable reaction
sequence design to ensure reliable results, hence a limited sensorium is
no handicap; similar considerations apply to the positional assembly
of small nanoparts. Advocates address the second doubt by arguing that bacteria are (of necessity) evolved to evolve, while nanorobot mutation could be actively prevented by common error-correcting techniques. Similar ideas are advocated in the Foresight Guidelines on Molecular Nanotechnology, and a map of the 137-dimensional replicator design space
recently published by Freitas and Merkle provides numerous proposed
methods by which replicators could, in principle, be safely controlled
by good design.
However, the concept of suppressing mutation raises the question:
How can design evolution occur at the nanoscale without a process of
random mutation and deterministic selection? Critics argue that MNT
advocates have not provided a substitute for such a process of evolution
in this nanoscale arena where conventional sensory-based selection
processes are lacking. The limits of the sensorium available at the
nanoscale could make it difficult or impossible to winnow successes from
failures. Advocates argue that design evolution should occur
deterministically and strictly under human control, using the
conventional engineering paradigm of modeling, design, prototyping,
testing, analysis, and redesign.
In any event, since 1992 technical proposals for MNT
do not include self-replicating nanorobots, and recent ethical
guidelines put forth by MNT advocates prohibit unconstrained
self-replication.
Medical nanorobots
One of the most important applications of MNT would be medical nanorobotics or nanomedicine, an area pioneered by Robert Freitas in numerous books and papers.
The ability to design, build, and deploy large numbers of medical
nanorobots would, at a minimum, make possible the rapid elimination of
disease and the reliable and relatively painless recovery from physical
trauma. Medical nanorobots might also make possible the convenient
correction of genetic defects, and help to ensure a greatly expanded
lifespan. More controversially, medical nanorobots might be used to augment natural human capabilities. One study has reported on how conditions like tumors, arteriosclerosis, blood clots
leading to stroke, accumulation of scar tissue and localized pockets of
infection can possibly be addressed by employing medical nanorobots.
Utility fog
Diagram of a 100 micrometer foglet
Another proposed application of molecular nanotechnology is "utility fog" — in which a cloud of networked microscopic robots (simpler than assemblers)
would change its shape and properties to form macroscopic objects and
tools in accordance with software commands. Rather than modify the
current practices of consuming material goods in different forms,
utility fog would simply replace many physical objects.
Phased-array optics
Yet another proposed application of MNT would be phased-array optics (PAO).
However, this appears to be a problem addressable by ordinary
nanoscale technology. PAO would use the principle of phased-array
millimeter technology but at optical wavelengths. This would permit the
duplication of any sort of optical effect but virtually. Users could
request holograms, sunrises and sunsets, or floating lasers as the mood
strikes. PAO systems were described in BC Crandall's Nanotechnology: Molecular Speculations on Global Abundance in the Brian Wowk article "Phased-Array Optics."
Potential social impacts
Molecular manufacturing is a potential future subfield of nanotechnology that would make it possible to build complex structures at atomic precision.
Molecular manufacturing requires significant advances in
nanotechnology, but once achieved could produce highly advanced products
at low costs and in large quantities in nanofactories weighing a
kilogram or more.
When nanofactories gain the ability to produce other nanofactories
production may only be limited by relatively abundant factors such as
input materials, energy and software.
The products of molecular manufacturing could range from cheaper,
mass-produced versions of known high-tech products to novel products
with added capabilities in many areas of application. Some applications
that have been suggested are advanced smart materials, nanosensors, medical nanorobots and space travel.
Additionally, molecular manufacturing could be used to cheaply produce
highly advanced, durable weapons, which is an area of special concern
regarding the impact of nanotechnology.
Being equipped with compact computers and motors these could be
increasingly autonomous and have a large range of capabilities.
According to Chris Phoenix and Mike Treder from the Center for Responsible Nanotechnology as well as Anders Sandberg from the Future of Humanity Institute molecular manufacturing is the application of nanotechnology that poses the most significant global catastrophic risk.
Several nanotechnology researchers state that the bulk of risk from
nanotechnology comes from the potential to lead to war, arms races and
destructive global government.
Several reasons have been suggested why the availability of nanotech
weaponry may with significant likelihood lead to unstable arms races
(compared to e.g. nuclear arms races): (1) A large number of players may
be tempted to enter the race since the threshold for doing so is low; (2) the ability to make weapons with molecular manufacturing will be cheap and easy to hide;
(3) therefore lack of insight into the other parties' capabilities can
tempt players to arm out of caution or to launch preemptive strikes; (4) molecular manufacturing may reduce dependency on international trade, a potential peace-promoting factor; (5) wars of aggression
may pose a smaller economic threat to the aggressor since manufacturing
is cheap and humans may not be needed on the battlefield.
Since self-regulation by all state and non-state actors seems hard to achieve, measures to mitigate war-related risks have mainly been proposed in the area of international cooperation.
International infrastructure may be expanded giving more sovereignty to
the international level. This could help coordinate efforts for arms
control.
International institutions dedicated specifically to nanotechnology
(perhaps analogously to the International Atomic Energy Agency IAEA) or general arms control may also be designed. One may also jointly make differential technological progress on defensive technologies, a policy that players should usually favour. The Center for Responsible Nanotechnology also suggest some technical restrictions. Improved transparency regarding technological capabilities may be another important facilitator for arms-control.
A grey goo is another catastrophic scenario, which was proposed by Eric Drexler in his 1986 book Engines of Creation,
has been analyzed by Freitas in "Some Limits to Global Ecophagy by
Biovorous Nanoreplicators, with Public Policy Recommendations" and has been a theme in mainstream media and fiction.
This scenario involves tiny self-replicating robots that consume the
entire biosphere using it as a source of energy and building blocks.
Nanotech experts including Drexler now discredit the scenario. According
to Chris Phoenix a "So-called grey goo could only be the product of a deliberate and difficult engineering process, not an accident". With the advent of nano-biotech, a different scenario called green goo has been forwarded. Here, the malignant substance is not nanobots but rather self-replicating biological organisms engineered through nanotechnology.
Benefits
Nanotechnology (or molecular nanotechnology to refer more
specifically to the goals discussed here) will let us continue the
historical trends in manufacturing right up to the fundamental limits
imposed by physical law. It will let us make remarkably powerful
molecular computers. It will let us make materials over fifty times
lighter than steel or aluminium alloy but with the same strength. We'll
be able to make jets, rockets, cars or even chairs that, by today's
standards, would be remarkably light, strong, and inexpensive. Molecular
surgical tools, guided by molecular computers and injected into the
blood stream could find and destroy cancer cells or invading bacteria,
unclog arteries, or provide oxygen when the circulation is impaired.
Nanotechnology will replace our entire manufacturing base with a new,
radically more precise, radically less expensive, and radically more
flexible way of making products. The aim is not simply to replace
today's computer chip making plants, but also to replace the assembly
lines for cars, televisions, telephones, books, surgical tools,
missiles, bookcases, airplanes, tractors, and all the rest. The
objective is a pervasive change in manufacturing, a change that will
leave virtually no product untouched. Economic progress and military
readiness in the 21st Century will depend fundamentally on maintaining a
competitive position in nanotechnology.
Despite the current early developmental status of nanotechnology and
molecular nanotechnology, much concern surrounds MNT's anticipated
impact on economics and on law. Whatever the exact effects, MNT, if achieved, would tend to reduce the scarcity of manufactured goods and make many more goods (such as food and health aids) manufacturable.
MNT should make possible nanomedical
capabilities able to cure any medical condition not already cured by
advances in other areas. Good health would be common, and poor health of
any form would be as rare as smallpox and scurvy are today. Even cryonics would be feasible, as cryopreserved tissue could be fully repaired.
Risks
Molecular nanotechnology is one of the technologies that some analysts believe could lead to a technological singularity,
in which technological growth has accelerated to the point of having
unpredictable effects. Some effects could be beneficial, while others
could be detrimental, such as the utilization of molecular
nanotechnology by an unfriendly artificial general intelligence.
Some feel that molecular nanotechnology would have daunting risks. It conceivably could enable cheaper and more destructive conventional weapons. Also, molecular nanotechnology might permit weapons of mass destruction that could self-replicate, as viruses and cancer
cells do when attacking the human body. Commentators generally agree
that, in the event molecular nanotechnology were developed, its self-replication should be permitted only under very controlled or "inherently safe" conditions.
A fear exists that nanomechanical robots, if achieved, and if
designed to self-replicate using naturally occurring materials (a
difficult task), could consume the entire planet in their hunger for raw
materials, or simply crowd out natural life, out-competing it for energy (as happened historically when blue-green algae appeared and outcompeted earlier life forms). Some commentators have referred to this situation as the "grey goo" or "ecophagy" scenario. K. Eric Drexler considers an accidental "grey goo" scenario extremely unlikely and says so in later editions of Engines of Creation.
In light of this perception of potential danger, the Foresight Institute, founded by Drexler, has prepared a set of guidelines
for the ethical development of nanotechnology. These include the
banning of free-foraging self-replicating pseudo-organisms on the
Earth's surface, at least, and possibly in other places.
Technical issues and criticism
The feasibility of the basic technologies analyzed in Nanosystems
has been the subject of a formal scientific review by U.S. National
Academy of Sciences, and has also been the focus of extensive debate on
the internet and in the popular press.
Study and recommendations by the U.S. National Academy of Sciences
In
2006, U.S. National Academy of Sciences released the report of a study
of molecular manufacturing as part of a longer report, A Matter of Size: Triennial Review of the National Nanotechnology Initiative The study committee reviewed the technical content of Nanosystems,
and in its conclusion states that no current theoretical analysis can
be considered definitive regarding several questions of potential system
performance, and that optimal paths for implementing high-performance
systems cannot be predicted with confidence. It recommends experimental
research to advance knowledge in this area:
"Although theoretical calculations can be made today, the
eventually attainable range of chemical reaction cycles, error rates,
speed of operation, and thermodynamic efficiencies of such bottom-up
manufacturing systems cannot be reliably predicted at this time. Thus,
the eventually attainable perfection and complexity of manufactured
products, while they can be calculated in theory, cannot be predicted
with confidence. Finally, the optimum research paths that might lead to
systems which greatly exceed the thermodynamic efficiencies and other
capabilities of biological systems cannot be reliably predicted at this
time. Research funding that is based on the ability of investigators to
produce experimental demonstrations that link to abstract models and
guide long-term vision is most appropriate to achieve this goal."
Assemblers versus nanofactories
A section heading in Drexler's Engines of Creation reads "Universal Assemblers", and the following text speaks of multiple types of assemblers which, collectively, could hypothetically "build almost anything that the laws of nature allow to exist." Drexler's colleague Ralph Merkle has noted that, contrary to widespread legend,
Drexler never claimed that assembler systems could build absolutely any
molecular structure. The endnotes in Drexler's book explain the
qualification "almost": "For example, a delicate structure might be
designed that, like a stone arch, would self-destruct unless all its
pieces were already in place. If there were no room in the design for
the placement and removal of a scaffolding, then the structure might be
impossible to build. Few structures of practical interest seem likely to
exhibit such a problem, however."
In 1992, Drexler published Nanosystems: Molecular Machinery, Manufacturing, and Computation, a detailed proposal for synthesizing stiff covalent structures using a table-top factory. Diamondoid
structures and other stiff covalent structures, if achieved, would have
a wide range of possible applications, going far beyond current MEMS
technology. An outline of a path was put forward in 1992 for building a
table-top factory in the absence of an assembler. Other researchers
have begun advancing tentative, alternative proposed paths for this in the years since Nanosystems was published.
Hard versus soft nanotechnology
In 2004 Richard Jones wrote Soft Machines (nanotechnology and life), a book for lay audiences published by Oxford University.
In this book he describes radical nanotechnology (as advocated by
Drexler) as a deterministic/mechanistic idea of nano engineered
machines that does not take into account the nanoscale challenges such
as wetness, stickiness, Brownian motion, and high viscosity. He also explains what is soft nanotechnology or more appropriately biomimetic
nanotechnology which is the way forward, if not the best way, to design
functional nanodevices that can cope with all the problems at a
nanoscale. One can think of soft nanotechnology as the development of
nanomachines that uses the lessons learned from biology on how things
work, chemistry to precisely engineer such devices and stochastic
physics to model the system and its natural processes in detail.
The Smalley–Drexler debate
Several researchers, including Nobel Prize winner Dr. Richard Smalley (1943–2005), attacked the notion of universal assemblers, leading to a rebuttal from Drexler and colleagues, and eventually to an exchange of letters.
Smalley argued that chemistry is extremely complicated, reactions are
hard to control, and that a universal assembler is science fiction.
Drexler and colleagues, however, noted that Drexler never proposed
universal assemblers able to make absolutely anything, but instead
proposed more limited assemblers able to make a very wide variety of
things. They challenged the relevance of Smalley's arguments to the more
specific proposals advanced in Nanosystems. Also, Smalley argued that nearly all of modern chemistry involves reactions that take place in a solvent (usually water), because the small molecules of a solvent contribute many things, such as lowering binding energies
for transition states. Since nearly all known chemistry requires a
solvent, Smalley felt that Drexler's proposal to use a high vacuum
environment was not feasible. However, Drexler addresses this in
Nanosystems by showing mathematically that well designed catalysts can provide the effects of a solvent and can fundamentally be made even more efficient than a solvent/enzyme
reaction could ever be. It is noteworthy that, contrary to Smalley's
opinion that enzymes require water, "Not only do enzymes work vigorously
in anhydrous organic media, but in this unnatural milieu they acquire
remarkable properties such as greatly enhanced stability, radically
altered substrate and enantiomeric specificities, molecular memory, and the ability to catalyse unusual reactions."
Redefining of the word "nanotechnology"
For
the future, some means have to be found for MNT design evolution at the
nanoscale which mimics the process of biological evolution at the
molecular scale. Biological evolution proceeds by random variation in
ensemble averages of organisms combined with culling of the
less-successful variants and reproduction of the more-successful
variants, and macroscale engineering design also proceeds by a process
of design evolution from simplicity to complexity as set forth somewhat
satirically by John Gall:
"A complex system that works is invariably found to have evolved from a
simple system that worked. . . . A complex system designed from
scratch never works and can not be patched up to make it work. You have
to start over, beginning with a system that works."
A breakthrough in MNT is needed which proceeds from the simple atomic
ensembles which can be built with, e.g., an STM to complex MNT systems
via a process of design evolution. A handicap in this process is the
difficulty of seeing and manipulation at the nanoscale compared to the
macroscale which makes deterministic selection of successful trials
difficult; in contrast biological evolution proceeds via action of what
Richard Dawkins has called the "blind watchmaker" comprising random molecular variation and deterministic reproduction/extinction.
At present in 2007 the practice of nanotechnology embraces both stochastic approaches (in which, for example, supramolecular chemistry
creates waterproof pants) and deterministic approaches wherein single
molecules (created by stochastic chemistry) are manipulated on substrate
surfaces (created by stochastic deposition methods) by deterministic
methods comprising nudging them with STM or AFM
probes and causing simple binding or cleavage reactions to occur. The
dream of a complex, deterministic molecular nanotechnology remains
elusive. Since the mid-1990s, thousands of surface scientists and thin
film technocrats have latched on to the nanotechnology bandwagon and
redefined their disciplines as nanotechnology. This has caused much
confusion in the field and has spawned thousands of "nano"-papers on the
peer reviewed literature. Most of these reports are extensions of the
more ordinary research done in the parent fields.
The feasibility of the proposals in Nanosystems
Top, a molecular propellor. Bottom, a molecular planetary gear system. The feasibility of devices like these has been questioned.
The feasibility of Drexler's proposals largely depends, therefore, on whether designs like those in Nanosystems
could be built in the absence of a universal assembler to build them
and would work as described. Supporters of molecular nanotechnology
frequently claim that no significant errors have been discovered in Nanosystems since 1992. Even some critics concede
that "Drexler has carefully considered a number of physical principles
underlying the 'high level' aspects of the nanosystems he proposes and,
indeed, has thought in some detail" about some issues.
Other critics claim, however, that Nanosystems omits important chemical details about the low-level 'machine language' of molecular nanotechnology. They also claim that much of the other low-level chemistry in Nanosystems
requires extensive further work, and that Drexler's higher-level
designs therefore rest on speculative foundations. Recent such further
work by Freitas and Merkle is aimed at strengthening these foundations by filling the existing gaps in the low-level chemistry.
Drexler argues that we may need to wait until our conventional nanotechnology
improves before solving these issues: "Molecular manufacturing will
result from a series of advances in molecular machine systems, much as
the first Moon landing resulted from a series of advances in liquid-fuel
rocket systems. We are now in a position like that of the British Interplanetary Society
of the 1930s which described how multistage liquid-fueled rockets could
reach the Moon and pointed to early rockets as illustrations of the
basic principle." However, Freitas and Merkle argue
that a focused effort to achieve diamond mechanosynthesis (DMS) can
begin now, using existing technology, and might achieve success in less
than a decade if their "direct-to-DMS approach is pursued rather than a
more circuitous development approach that seeks to implement less
efficacious nondiamondoid molecular manufacturing technologies before
progressing to diamondoid".
To summarize the arguments against feasibility: First, critics
argue that a primary barrier to achieving molecular nanotechnology is
the lack of an efficient way to create machines on a molecular/atomic
scale, especially in the absence of a well-defined path toward a
self-replicating assembler or diamondoid nanofactory. Advocates respond
that a preliminary research path leading to a diamondoid nanofactory is
being developed.
A second difficulty in reaching molecular nanotechnology is
design. Hand design of a gear or bearing at the level of atoms might
take a few to several weeks. While Drexler, Merkle and others have
created designs of simple parts, no comprehensive design effort for
anything approaching the complexity of a Model T Ford has been
attempted. Advocates respond that it is difficult to undertake a
comprehensive design effort in the absence of significant funding for
such efforts, and that despite this handicap much useful design-ahead
has nevertheless been accomplished with new software tools that have
been developed, e.g., at Nanorex.
In the latest report A Matter of Size: Triennial Review of the National Nanotechnology Initiative
put out by the National Academies Press in December 2006 (roughly
twenty years after Engines of Creation was published), no clear way
forward toward molecular nanotechnology could yet be seen, as per the
conclusion on page 108 of that report: "Although theoretical
calculations can be made today, the eventually attainable
range of chemical reaction cycles, error rates, speed of operation, and
thermodynamic
efficiencies of such bottom-up manufacturing systems cannot be reliably
predicted at this time. Thus, the eventually attainable perfection and
complexity of
manufactured products, while they can be calculated in theory, cannot be
predicted
with confidence. Finally, the optimum research paths that might lead to
systems
which greatly exceed the thermodynamic efficiencies and other
capabilities of
biological systems cannot be reliably predicted at this time. Research
funding that
is based on the ability of investigators to produce experimental
demonstrations
that link to abstract models and guide long-term vision is most
appropriate to
achieve this goal." This call for research leading to demonstrations is
welcomed by groups such as the Nanofactory Collaboration who are
specifically seeking experimental successes in diamond mechanosynthesis. The "Technology Roadmap for Productive Nanosystems" aims to offer additional constructive insights.
It is perhaps interesting to ask whether or not most structures
consistent with physical law can in fact be manufactured. Advocates
assert that to achieve most of the vision of molecular manufacturing it
is not necessary to be able to build "any structure that is compatible
with natural law." Rather, it is necessary to be able to build only a
sufficient (possibly modest) subset of such structures—as is true, in
fact, of any practical manufacturing process used in the world today,
and is true even in biology. In any event, as Richard Feynman
once said, "It is scientific only to say what's more likely or less
likely, and not to be proving all the time what's possible or
impossible."
Existing work on diamond mechanosynthesis
There
is a growing body of peer-reviewed theoretical work on synthesizing
diamond by mechanically removing/adding hydrogen atoms and depositing carbon atoms (a process known as mechanosynthesis). This work is slowly permeating the broader nanoscience community and is being critiqued. For instance, Peng et al. (2006)
(in the continuing research effort by Freitas, Merkle and their
collaborators) reports that the most-studied mechanosynthesis tooltip
motif (DCB6Ge) successfully places a C2 carbon dimer on a C(110) diamond surface at both 300 K (room temperature) and 80 K (liquid nitrogen
temperature), and that the silicon variant (DCB6Si) also works at 80 K
but not at 300 K. Over 100,000 CPU hours were invested in this latest
study. The DCB6 tooltip motif, initially described by Merkle and
Freitas at a Foresight Conference in 2002, was the first complete
tooltip ever proposed for diamond mechanosynthesis and remains the only
tooltip motif that has been successfully simulated for its intended
function on a full 200-atom diamond surface.
The tooltips modeled in this work are intended to be used only in
carefully controlled environments (e. g., vacuum). Maximum acceptable
limits for tooltip translational and rotational misplacement errors are
reported in Peng et al. (2006) -- tooltips must be positioned with great
accuracy to avoid bonding the dimer incorrectly. Peng et al. (2006)
reports that increasing the handle thickness from 4 support planes of C
atoms above the tooltip to 5 planes decreases the resonance frequency of
the entire structure from 2.0 THz to 1.8 THz. More importantly, the
vibrational footprints of a DCB6Ge tooltip mounted on a 384-atom handle
and of the same tooltip mounted on a similarly constrained but much
larger 636-atom "crossbar" handle are virtually identical in the
non-crossbar directions. Additional computational studies modeling still
bigger handle structures are welcome, but the ability to precisely
position SPM tips to the requisite atomic accuracy has been repeatedly
demonstrated experimentally at low temperature, or even at room temperature constituting a basic existence proof for this capability.
Further research to consider additional tooltips will require time-consuming computational chemistry and difficult laboratory work.
A working nanofactory
would require a variety of well-designed tips for different reactions,
and detailed analyses of placing atoms on more complicated surfaces.
Although this appears a challenging problem given current resources,
many tools will be available to help future researchers: Moore's law predicts further increases in computer power, semiconductor fabrication techniques continue to approach the nanoscale, and researchers grow ever more skilled at using proteins, ribosomes and DNA to perform novel chemistry.
Works of fiction
In The Diamond Age by Neal Stephenson,
diamond can be built directly out of carbon atoms. All sorts of devices
from dust-size detection devices to giant diamond zeppelins are
constructed atom by atom using only carbon, oxygen, nitrogen and
chlorine atoms.
In the novel Tomorrow by Andrew Saltzman (ISBN1-4243-1027-X), a scientist uses nanorobotics to create a liquid that when inserted into the bloodstream, renders one nearly invincible given that the microscopic machines repair tissue almost instantaneously after it is damaged.
In the roleplaying gameSplicers by Palladium Books, humanity has succumbed to a "nanobot plague" that causes any object made of a non-precious metal to twist and change shape (sometimes into a type of robot)
moments after being touched by a human. The object will then proceed
to attack the human. This has forced humanity to develop
"biotechnological" devices to replace those previously made of metal.
On the television show Mystery Science Theater 3000, the Nanites (voiced variously by Kevin Murphy, Paul Chaplin, Mary Jo Pehl, and Bridget Jones)
– are self-replicating, bio-engineered organisms that work on the ship,
they are microscopic creatures that reside in the Satellite of Love's
computer systems. (They are similar to the creatures in Star Trek: The Next Generation episode "Evolution", which featured "nanites" taking over the Enterprise.) The Nanites made their first appearance in season 8. Based on the concept of nanotechnology, their comical deus ex machina activities included such diverse tasks as instant repair and construction, hairstyling, performing a Nanite variation of a flea circus,
conducting a microscopic war, and even destroying the Observers' planet
after a dangerously vague request from Mike to "take care of [a] little
problem". They also ran a microbrewery.
Stargate Atlantis has an enemy made of self-assembling nanorobots, which also convert a planet into grey goo.
In the novel "Prey" by Michael Crichton, self replicating nanobots
create autonomous nano-swarms with predatory behaviors. The protagonist
must stop the swarm before it evolves into a grey goo plague.
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