Foundations
What Is a Bubble?
A bubble is not just 'prices went up a lot.' It is a repeatable pattern with phases you can name, measure, and compare across two centuries.
Updated
Here is the working definition this site uses: a bubble is a period when the price of an asset rises far above what its realistic future earnings can support, powered by borrowed money and by the belief that prices will keep rising, followed by a collapse when that belief breaks. The rise can take years. The collapse usually takes months.
Financial historians describe the same arc again and again, from railways in the 1840s to crypto in 2021 (Stanford GSB (opens in a new window), Quinn & Turner (opens in a new window)). This site draws it the same way on every case study:
The five phases
1. Inflation
Something genuinely new appears: a railway, a fiber network, a chatbot that writes. Early investors do well because the growth is real. Prices rise for good reasons, and this phase can look identical to a healthy boom, because at this point it is one.
2. Mania
The story takes over from the numbers. Money arrives faster than the underlying business can absorb it. Capital spendingMoney a company spends on long-lived physical things: buildings, machines, chips, data centers. Spent now, paid back (hopefully) over years.Full definition in the glossary accelerates, new investment vehiclesThe flow of newly created investments being sold to the public: IPOs, new bonds, new funds. Issuance waves tend to crest right around market tops.Full definition in the glossary multiply, ordinary people pile in, and borrowed moneyMoney investors borrow from their brokers to buy stocks. It amplifies gains on the way up and forces selling on the way down.Full definition in the glossary amplifies everything. Skeptics start publishing warnings, and get ignored, often for years. In several historical cases, circular financing arrived at this stage and stretched the mania 2 to 4 years past what independent demand supported.
3. Peak
Peaks rarely announce themselves. Historically the most common companion is a central bank raising interest ratesWhen a central bank raises interest rates or drains money from the system to slow the economy. Most historical bubbles peaked during or within 18 months of tightening.Full definition in the glossary: in six or seven of eight major bubbles since the 1840s, the peak came during or within roughly 18 months of a tightening cycle (NBER (opens in a new window)). The warning lights page tracks the indicators that historically preceded peaks and what they read today.
4. Trough
The fall is measured as a drawdownHow far a price falls from its peak to its lowest point, in percent. The dot-com crash was a 78% drawdown for the Nasdaq.Full definition in the glossary: peak to troughFrom the highest point to the lowest point of a decline. Used to measure both how far prices fell and how long the fall took.Full definition in the glossary, the Dow lost 89% after 1929, the Nasdaq 78% after 2000, and the Nikkei about 80% after 1989. Leverage turns falling prices into forced selling, which is why the way down is so much faster than the way up.
5. Recovery
The most underappreciated number in bubble history is how long "back to even" takes: 25 years for the Dow after 1929, about 15 for the Nasdaq after 2000, 34 for the Nikkei after 1989. Markets recover; the people who bought the top often don't stay around long enough to see it.
Fifteen bubbles, one table
The dataset below condenses the research corpus behind this site. Dates and percentages are best-estimate ranges; for several older episodes, sources genuinely disagree, and the ranges reflect that rather than false precision. {rows.map((r) => ( ))} Drawdowns are for each episode's primary asset or index. Scroll sideways on small screens. Estimates for the 19th-century and Florida episodes diverge between sources; see Sources for the full citation list. How these historical patterns compare to the AI boom specifically is weighed on Conclusions.
| Bubble | Years | How far prices fell | Time back to even | Was the underlying thing real? | Source |
|---|---|---|---|---|---|
| British Railway Mania | 1844-1850 | 50-70% (rail shares) | A decade or more; some lines never | Yes: the network drove growth for a century | CEPR (opens in a new window) |
| US railroads / Panic of 1873 | 1870-1879 | 25-30% broad; 40-60% rail securities | Mid-1880s or later; some roads never | Yes, over 20-40 years | Wikipedia (opens in a new window) |
| Florida land boom | 1924-1928 | 70-90% (prime Miami lots) | Decades; many parcels never (in real terms) | Eventually, after very long lags | NBER (opens in a new window) |
| 1929 US stock bubble | 1927-1932 | 89% (Dow) | 25 years (Nov 1954) | Yes: the underlying industries endured | market history (opens in a new window) |
| Nifty Fifty | 1967-1974 | 60-70% (leading names) | Roughly 7-10 years; many far exceeded old highs later | Yes: many became giants; the price was the problem | Stanford GSB (opens in a new window) |
| Poseidon nickel (Australia) | 1969-1971 | Over 95% (Poseidon NL) | Never | Partly: the nickel was worth far less than implied | Wikipedia (opens in a new window) |
| Hunt Brothers silver | 1979-1980 | 75-80% in about three months | 31 years to touch $50 again (2011) | Silver stayed useful; the corner-driven price didn't | Britannica (opens in a new window) |
| Japan's asset bubble | 1986-2003 | About 80% (Nikkei, over 13 years) | 34 years (Nikkei reclaimed its 1989 high in 2024) | Yes: Japan's industry stayed world-class | market history (opens in a new window) |
| Nordic banking bubbles | 1986-1993 | 50-70% (banks); 30-50% (property) | Roughly a decade, after painful reforms | Yes: the systems were rebuilt and thrived | PIIE (opens in a new window) |
| Asian Financial Crisis | 1993-1998 | 50-80% local currency; often 80-90% in dollars | 5-10+ years for many markets | Yes: the export economies endured | PIIE (opens in a new window) |
| Dot-com bubble | 1998-2002 | 78% (Nasdaq) | About 15 years (2015) | Emphatically: the internet was the future, just not at those prices | Britannica (opens in a new window) |
| Telecom / fiber bubble | 1998-2002 | 80-95%; several giants to zero | A decade or more; the sector consolidated | Yes: the 'wasted' fiber later carried the modern internet | Richmond Fed (opens in a new window) |
| US housing / subprime | 2002-2012 | 27-35% nationally; over 50% in some cities | About 10 years (2016-2017) | Housing is real; the lending behind it wasn't sound | overview (opens in a new window) |
| Chinese A-shares 2007 | 2006-2008 | About 70% in roughly a year | Not durably held for over a decade | The economy was real; the market was policy-driven and volatile | chronology (opens in a new window) |
| SPAC / meme / crypto complex | 2020-2022 | 70-99% depending on the asset | Mixed: Bitcoin partly; most SPACs and meme stocks never | Partly: a few durable pieces inside a lot of froth | Wikipedia (opens in a new window) |
Drawdowns are for each episode's primary asset or index. Scroll sideways on small screens. Estimates for the 19th-century and Florida episodes diverge between sources; see Sources for the full citation list.
The recurring finding: the technology is usually real
Read the last column again. Railways carried Britain's economy for a century. The "worthless" 1990s fiber later carried streaming and cloud computing. Even the 1929 crash destroyed prices, not the industries underneath. In almost every major bubble, the technology was real; the prices and the timing were the problem.
That cuts both ways for AI. It means "AI will change everything" is not evidence against a bubble; investors in 1845 and 1999 were broadly right about the technology and still lost most of their money. And it means a crash, if one comes, would say little about whether AI ultimately matters. The historical pattern is that value arrives, but often years later than the spending assumed, and often to a different set of owners than the ones who paid for the build-out.