As the number of privately held companies valued at $1 billion continues to grow–there are 100 by last count–so too does the worry that the tech world has finally reached bubble territory. The question this time, experts say, is not about whether these companies, known as unicorns, have sustainable business models, which many tech companies in the 2000 Dotcom crisis did not. Instead it’s whether the sky-high valuations themselves are the problem. A number of financial experts have expressed worry over what effect collapsing unicorns could have on the broader economy. Some fear the fall of even a single unicorn company could trigger a broader market meltdown, not unlike what happened during the mortgage crisis of 2008.