Nearly a century ago, Fritz Zwicky observed galaxies moving too fast to stay bound, proposing unseen 'Dunkle Materie'—dark matter—to explain their cohesion. Initially dismissed, his theory was later validated. Similarly, the repurchase (repo) market functions as a hidden but immense force in finance: a short-term, collateralised loan market where assets are sold with agreement to repurchase later.

Though often overlooked as mere 'plumbing,' the repo market is far more significant—comparable to dark matter in its pervasive influence. As Darrell Duffie, Stanford finance professor, states, 'Nobody actually sees it, but the people who actually know how the system works know that the financial universe runs on repo.' The US Treasury estimates the US repo market at roughly $12.6tn, while the International Capital Markets Association estimates the European market at almost €14tn. Despite opacity and potential double-counting, the repo market is unquestionably huge and critical to financial stability.