6th November 2026
The American stock market suffered one of its most dramatic falls in recent years on Thursday, 5 November, with approximately $3 trillion wiped from the combined market value of companies in the S&P 500. Technology shares bore the brunt of the selling, raising fresh questions about whether the enormous investment in artificial intelligence (AI) and data centres can deliver the profits investors have been expecting.
The Nasdaq fell 5.52%, its biggest one-day decline in 19 months, while the S&P 500 dropped 4.36% and the Dow Jones fell 3.44%. The Nasdaq has now entered correction territory, meaning it has fallen more than 10% from its recent peak.
Among the biggest casualties were semiconductor manufacturers. Nvidia fell more than 9%, while the Philadelphia Semiconductor Index, which tracks major chipmakers, plunged more than 12%.
These were not simply isolated losses in a few fashionable technology companies. Selling spread across the market, suggesting investors were reassessing the risks of the wider economic and investment environment. Reuters and Associated Press reported the scale of the falls.
What triggered the sudden loss of confidence?
There was no single explanation, but two developments came together at an uncomfortable moment for technology investors.
The first was the outcome of the American midterm elections, in which Democrats secured control of Congress. Investors began considering whether the new political balance could mean greater scrutiny of AI development, data centre construction and the enormous electricity requirements associated with these facilities.
Opposition to new data centres has been growing in parts of America, where communities are increasingly concerned about electricity costs, water consumption, land use and the impact on local infrastructure.
The second concern was already developing before the election. Investors were beginning to question whether the enormous sums being spent on AI infrastructure would produce sufficient financial returns.
Companies have committed hundreds of billions of dollars to computer chips, data centres, electricity supplies and associated infrastructure. The expectation has been that AI will transform business productivity and generate substantial new income.
But expectations and actual profits are two different things.
If companies continue spending at this rate without generating the anticipated returns, investors may eventually decide that the share prices they have been paying are no longer justified.
The election may have provided the immediate trigger, but the underlying concerns about valuations and investment returns were already there.
Has the AI boom become a financial gamble?
There is little doubt that AI will change many aspects of business and everyday life. The question is not whether the technology has a future, but whether investors have become too optimistic about how quickly it will deliver financial rewards.
The technology industry has a history of periods when enthusiasm runs ahead of commercial reality.
The dot-com boom around the turn of the century provides an obvious comparison. Investors poured money into internet companies, convinced that the technology would transform the economy. Many predictions eventually proved correct, but numerous companies disappeared and investors lost substantial sums because they had paid too much for businesses that could not deliver.
There is a risk that something similar could happen with AI, although the technology companies involved today are generally much larger and have established businesses and revenues.
The distinction is important. A technology can be revolutionary and still be a poor investment if too much is paid for it.
The electricity problem
There is another issue which governments and investors cannot ignore.
AI requires enormous computing capacity, and that requires electricity. Data centres are becoming increasingly important consumers of power, with some proposed developments requiring electricity on a scale comparable with that used by sizeable towns.
America has already experienced growing disputes about who pays for the additional generation and grid infrastructure.
If electricity supplies cannot keep pace with construction, developers may turn to gas generation or other temporary arrangements. That can increase costs and create further environmental and planning difficulties.
There is also a question about whether electricity should be diverted towards commercial data centres when households and existing industries are already facing high energy costs.
These are not merely technical questions. They have economic and political consequences.
What does this mean for Britain?
The developments in America should provide food for thought for the UK Government.
Britain has been keen to attract data centre investment and establish itself as a major AI economy. Recent government initiatives have sought to speed up planning and development, with ministers presenting AI infrastructure as an important opportunity for economic growth.
There are good reasons to pursue this technology. Britain cannot afford to ignore developments which could improve productivity, create new businesses and strengthen its international competitiveness.
However, there is a difference between attracting investment and ensuring that investment benefits the wider economy.
Data centres can require substantial construction expenditure but relatively few permanent employees once operational. They also place demands on electricity networks, water supplies and local infrastructure.
The Government needs to consider whether the benefits justify the costs, particularly where public infrastructure or changes to planning arrangements are required.
There is also a danger of relying too heavily on temporary gas generation while waiting for grid connections. That could create additional costs and potentially undermine the environmental benefits being claimed for the wider technology strategy.
Britain should be competing in AI, but it should not confuse the number of data centres being built with the economic success of the industry.
A warning rather than the end of AI
It would be premature to declare the end of the AI investment boom. A sharp fall in share prices does not mean that the underlying technology has suddenly become worthless.
Markets can overreact in both directions. Some companies may recover quickly, while others may discover that their business models are not as profitable as investors once believed.
Nor does the $3 trillion figure mean that this amount of cash has disappeared from bank accounts. It represents the reduction in the estimated market value of companies as their share prices fell.
Nevertheless, the scale of the movement is a warning.
For governments, the lesson should be that new technology needs realistic economic assessment rather than unquestioning enthusiasm. For investors, it is a reminder that even the most exciting developments can become dangerously overpriced.
And for Britain, there is an important question to answer.
Are we building an AI industry which will strengthen the economy for decades, or are we in danger of investing heavily in infrastructure because everyone else appears to be doing the same?
The technology may well be the future. But that does not mean every investment made in its name will be a success.
The shockwaves spread across the world
The reaction in other financial markets was almost immediate. On Friday, 6 November, Asian markets experienced some particularly dramatic falls. Japan's Nikkei dropped around 6% during trading, while South Korea's Kospi plunged more than 8%, triggering an automatic 20-minute trading suspension. Taiwan's market also fell more than 8% at one point before recovering some ground.
These markets are particularly exposed because companies such as Samsung, SK Hynix and Taiwan Semiconductor Manufacturing are major suppliers of the chips and equipment required by the AI industry. Japan's SoftBank, another major investor in AI, also suffered a substantial decline. The scale of the falls demonstrated how closely Asian economies have become tied to the American technology investment boom.
European markets were also expected to open lower, with futures indicating losses of around 1% as the selling spread westwards. Britain, Germany and France all have substantial exposure to international investment flows and the fortunes of major technology companies.
However, the impact is unlikely to be uniform. Companies supplying industrial equipment, financial services and traditional manufacturing may be affected differently from those directly involved in AI and semiconductor production. Meanwhile, investors were moving towards government bonds and traditionally safer currencies, including the Japanese yen and Swiss franc. This suggests that the concern was not simply about individual technology shares but about the possibility of a wider reassessment of risk across international financial markets.