When the pace of growth accelerates continually. Usually as a result of positive Feedback loops. Some common feedback loops we’re facing in humanity are the technology feedback loop, the computing feedback loop, and soon, the AI feedback loop
We use technology (including Psychotechnology and Sociotechnology) to create better technology. We use computers to design faster computers. Eventually we’ll use AI to develop better AI which will result in an AI explosion and possible human existential risk.
True unconstrained exponential growth does not exist in the physical world. In the physical world, every exponential growth curve is really an unfinished sigmoid curve (aka s-curve) as there will be some factor in the system that eventually constrains growth.
We live on planet earth which is a closed system. If you view the inputs and outputs to the earth, you have solar energy and space debris entering and solar energy and space ships exiting. Everything else on earth is stuck within our atmosphere.
If you create a business that sells products, it takes in resources from Earth and outputs products. Most businesses (especially public corporations) have the goal of increasing shareholder earnings. Earnings come from providing value or perceived value to humanity. If the goal of a business is to indefinitely increase shareholder earnings, it must continually grow the amount of value it provides. But businesses take in resources from Earth, which is a finite, mostly closed system. Eventually one of a few failure modes will be reached as exponential growth approaches the constraints of the system. The second and third order effects of these limits are interesting and often neglected.
As we can see, both of these scenarios are not desirable. The only long term solution is to sustainably use resources and be comfortable making profits at the sustainable level of market demand. Unfortunately due to rivalrous games( See Collaborative Competition (non-rivalrous games)), if any player in a marketplace chooses another strategy, they will gain a competitive advantage due to wider market share. Research to discover Possible solutions to this arms race dynamic is ongoing.
The same principles apply to any type of exponential growth in a closed system. Viruses, bacteria, species population, resource usage, company growth, etc.