IELTS Academic Reading Practice Test 140

Few technologies are as inconspicuous as the one that carries a large share of the world's internet traffic into homes and offices. Wi-Fi is not a single device but a family of engineering standards that allow computers, phones and other equipment to exchange data over radio waves instead of cables. Its first version, agreed by an international committee in 1997, was slow, expensive and prone to failure. That such a modest achievement came to dominate the way the world connects is the result of years of disagreement, compromise and patient standard-setting.

Wireless networking existed long before Wi-Fi. In 1971 a team at the University of Hawaii led by the computer scientist Norman Abramson built a system called ALOHAnet, which linked computers on several of the Hawaiian islands by radio. Laying cable between islands was impractical, so the network sent data through shared radio channels. Because many users competed for the same channel, Abramson's group devised rules for deciding when a terminal should transmit and what it should do when two transmissions collided. Those rules were later adapted for wired networks and helped shape Ethernet, the cable-based standard that still underpins office computing.

The idea of spreading a signal across many frequencies had an earlier and unexpected origin. In 1942 the Hollywood actress Hedy Lamarr and the composer George Antheil were granted a patent for a system that made a radio-controlled torpedo shift rapidly between frequencies, so that an enemy could not jam its guidance signal. The scheme relied on a paper roll, similar to the mechanism of a player piano, to keep transmitter and receiver synchronised. The patent was granted, but the principle of hopping between frequencies would become central to wireless data only decades later.

The decisive change came from regulators rather than engineers. For most of the twentieth century, governments licensed radio frequencies and allocated them to particular users, such as broadcasters or emergency services. In 1985 the Federal Communications Commission in the United States opened three bands of frequencies, including one at 2.4 gigahertz, for unlicensed use by low-power devices, provided that they did not interfere with existing users. A manufacturer could now build a radio transmitter into a product and sell it without obtaining a licence. Engineers regarded these bands as a junkyard of the spectrum; they proved ideal for short-range data.

Commercial wireless networking began in the early 1990s. A division of the American firm NCR sold a system called WaveLAN, which achieved data rates of about two megabits per second, comparable to the wired links of the period. Other manufacturers produced incompatible versions, and equipment from one company would not communicate with another's. To resolve this, the Institute of Electrical and Electronics Engineers set up a committee in 1990, chaired by the engineer Vic Hayes of NCR. Progress was slow, and the first agreed standard, known as 802.11, was ratified only in 1997.

Two years later a revised version, 802.11b, raised the maximum rate to eleven megabits per second, and in 1999 Apple began selling a laptop with a wireless card built in. That same year an industry group was formed to certify that products from different makers would work together. Its members judged 'IEEE 802.11b' too technical a name for consumers and hired a branding consultancy, which produced the word Wi-Fi. The name was not an abbreviation of anything; the phrase 'wireless fidelity' was added afterwards as a slogan and is often mistaken for its origin.

The technical heart of a Wi-Fi network is unremarkable. A transmitter encodes digital information onto a carrier wave, and a receiver tuned to the same frequency decodes it. Because the unlicensed bands are shared, devices must take turns; a protocol known as carrier sense multiple access with collision avoidance governs the queue. A device listens to the channel before transmitting, keeps silent if traffic is already present, and waits a random interval after a collision before trying again. An access point coordinates the devices in its area and passes their traffic to a wired network.

Security proved a more lasting difficulty. The original encryption scheme, WEP, was shown to be easily broken, and it was replaced by stronger protocols that now protect most traffic. In Australia a team at the national research organisation, the CSIRO, led by the engineer John O'Sullivan, had applied signal-processing methods from radio astronomy to fast indoor wireless networks during the 1990s. The organisation later obtained patents covering key techniques, which were eventually licensed to computer manufacturers after lengthy legal disputes.

Later versions brought steady improvement. A version ratified in 1999, 802.11a, had already used a less crowded band at five gigahertz to reach 54 megabits per second, and in 2003 802.11g brought comparable speeds to the older 2.4 gigahertz band. The 2009 standard, 802.11n, introduced several antennas working in parallel, a technique known as MIMO, which raised throughput by exploiting reflections that had previously been treated as interference. Later versions added more channels and, in 2020, access to a large block of frequencies around six gigahertz.

The consequences reach well beyond the office. Public hotspots appeared in airports and cafés, mobile operators came to rely on Wi-Fi to carry traffic indoors where their own signals are weak, and the smartphone put a radio in almost every pocket. The standards themselves remain freely available to anyone who wants to build equipment. It is a rare example of an industry agreeing, slowly and without drama, on a common language.

No building material is used in greater quantities than concrete. Roughly four billion tonnes of cement are produced each year, and concrete — cement mixed with sand, gravel and water — accounts for an estimated seven to eight per cent of global emissions of carbon dioxide, far more than the whole aviation industry. The scale is what makes the problem difficult: a material produced in such quantities has to be cheap, and cement is among the cheapest industrial commodities there is.

Ordinary cement, known as Portland cement, is made by heating limestone and clay together in a rotary kiln to about 1,450 °C. The heat drives carbon dioxide out of the limestone and fuses what remains into hard nodules called clinker, which are cooled and ground to a fine powder with a little gypsum. Clinker contains several compounds, of which the most important is alite, a form of tricalcium silicate. When the powder is mixed with water, alite dissolves and reacts to form calcium silicate hydrate, a tangled mass of microscopic fibres that is the glue holding concrete together.

The emissions arise in two places. Roughly 40 per cent come from the fuel burned to reach 1,450 °C, usually coal or petroleum coke, together with the electricity used for grinding. The rest is released by the chemistry itself: limestone is calcium carbonate, and turning it into calcium oxide, a process known as calcination, gives off carbon dioxide that was locked in the rock. That stream is unavoidable as long as limestone is the raw material, however the kiln is heated. It is the reason the industry cannot simply switch to renewable electricity and declare the problem solved.

The simplest way to cut emissions is to use less clinker. Blast-furnace slag from ironworks and fly ash from coal-fired power stations both react with water and can replace a substantial share of the clinker in a mix. This is well-established practice, and in many countries the materials are cheap because they are by-products that would otherwise be dumped. Their supply, however, is tied to the industries that produce them. As coal is phased out in Europe and North America, the ash available is shrinking, and both slag and ash are already used in other products, including roads and bricks, so competition for them is increasing.

A second approach uses clay. Ordinary clay contains aluminium and silicon in a form that is not reactive enough, but if it is heated to between 700 and 850 °C, well below the temperature needed for clinker, it becomes reactive. A mixture of calcined clay and ground limestone can replace up to half of the clinker in cement, and clays suitable for this purpose are abundant and widely distributed. The combination is being promoted under the name LC3 by a research group at the Swiss federal institute of technology in Lausanne, led by Karen Scrivener. The main constraint is quality: only clays rich in kaolinite, a particular clay mineral, give reliable results.

Some manufacturers are instead changing the clinker entirely. Calcium sulfoaluminate cements contain less calcium oxide and can be fired at around 1,250 °C, saving both fuel and limestone. Belite-rich cements achieve a similar saving by rearranging the same chemistry. Neither can simply be dropped into existing factories: they need different raw materials, among them bauxite for the sulfoaluminate version, and their concrete behaves differently, setting more quickly and sometimes proving less durable. Building codes written around Portland cement do not cover them, and changing a code is a slow business.

Where emissions cannot be avoided, they can be captured. Cement kilns are large point sources of carbon dioxide, and their exhaust is unusually suitable for capture because it contains a high concentration of the gas. At a works at Brevik in Norway, the equipment needed to separate carbon dioxide from flue gases has been installed, and the captured gas is to be shipped away for permanent storage beneath the North Sea. Capture is nonetheless expensive and consumes a great deal of energy, and a plant must be connected to a pipeline or a port before the idea is worth considering.

There are smaller tricks. A Canadian company injects carbon dioxide into concrete while it is being mixed, where it reacts with calcium compounds to form solid minerals that are locked into the material. The volumes involved are small compared with the emissions of the kiln, but the process is cheap and slightly improves the strength of the concrete. Recycled crushed concrete and waste-derived fuels offer further savings. None of these measures, individually, amounts to more than a few per cent of the total.

The obstacle to all of these options is cost. Cement is cheap: a tonne costs little more than a hundred dollars in many markets, and builders choose it on price and predictability. Low-carbon cement carries a premium, which no contractor wins contracts by paying. Governments therefore matter: building standards, public procurement and a price on carbon can all make the greener choice the cheaper one. Demand is expected to fall in Europe but to rise in parts of Asia and Africa, where most of the construction of the coming decades will take place.

For most of the past decade, the argument about social media was conducted as if it were a question of personal habits. Parents were advised to set limits; adults were told to put their phones away. That framing is now collapsing. Several governments have passed legislation in the past few years, and others are drafting it. The interesting question is no longer whether platforms should be regulated, but what should be measured and controlled. My own view is that regulation is justified, but that most of the proposals currently circulating aim at the wrong target.

The evidence on harm is often presented as though it were settled. It is contested. Studies linking social media use to anxiety or poor sleep in adolescents are almost all correlational: they cannot distinguish cause from effect, because young people who are already unhappy may spend longer online. A widely discussed book published in 2024 by the psychologist Jonathan Haidt argued that smartphones have reshaped childhood, while critics such as the developmental psychologist Candice Odgers have replied that average effects are small and that the data do not show a clear rise in harm everywhere. Both sides agree that some young people are badly affected; they disagree about how many.

It would be a mistake, however, to conclude that nothing should be done until the research is complete. Regulation has rarely waited for certainty. Seat belts, restrictions on lead in petrol and smoke-free public spaces were all introduced while the evidence was still being argued over, and in each case the evidence later became clearer. The sensible question is not whether a risk has been proved beyond dispute, but whether it is plausible and serious enough to justify proportionate action. Precaution is not the same as prohibition.

If action is justified, its instruments matter. The most popular proposals concern individual posts: a list of categories to be removed, with penalties for failing to remove them. This is the least promising approach. A platform moderates billions of items a day, mostly by automated systems, and every decision involves judgement: is this medical claim dangerous, is this joke ironic, is this image newsworthy? Platforms employ many thousands of moderators, often on temporary contracts, and no workforce can keep pace with the volume. Errors therefore run in both directions, and the visible ones are usually wrongful removals, which is why content rules satisfy nobody.

Age limits have an obvious appeal, and Australia has legislated a minimum age of sixteen, to be enforced by the platforms themselves. Yet the measure raises awkward questions. Verifying a user's age means collecting more personal information from everyone, or trusting an estimate made by software, and determined teenagers can evade either. More importantly, exclusion is not the same as protection. A child who is removed from a service does not become safer if the service remains designed to maximise the time that everyone else spends on it. Codes requiring age-appropriate design — no autoplay for younger users, no notifications at night, no targeting of minors by advertisers — address the harm directly rather than the access.

This points to what I take to be the real object of regulation: the ranking systems that decide what people see. A feed is not a neutral list. It is ordered by software trained to predict which items will keep a user engaged, and the material that does so is disproportionately emotionally arousing. Whether this constitutes a harm is arguable; that it is a deliberate design choice is not. Requiring platforms to explain how their recommender systems work, to offer a feed that is not personalised, and to allow independent researchers access to data, would change behaviour without any official deciding which posts may be published. The European Union's Digital Services Act already obliges the largest platforms to assess the risks their systems create and to give vetted researchers access to data, which shows that such duties are practicable.

The strongest argument for such duties is not that we know these systems cause harm. It is that outsiders cannot see them at all. Regulators, parents and researchers depend entirely on the companies for information about how content is distributed, and the companies have an interest in presenting that information favourably, so the system remains largely opaque. A company that designs a feed knows what it is optimising for; a parent does not. The asymmetry is the problem, and transparency duties address it directly.

None of this is risk-free. Compliance is expensive, and expensive rules favour large firms that can afford teams of lawyers; a poorly designed law can entrench the very companies it was meant to constrain. Rules drafted in haste after a tragedy can be clumsy and hard to repeal. Regulation should therefore be built to be evaluated: published in stages, measured against stated goals, and revised when it fails.

That is the argument I would put to any legislator. Not that screens are destroying a generation, for the evidence does not support so sweeping a claim, but that the systems which shape what millions of people read, watch and believe are too important to remain unexamined. Regulation should aim at the design of those systems and at the information about them, and it should be judged by what it can show.