The coronavirus pandemic has closed schools and many businesses, caused most people to stay at home except for essential trips, and postponed sports and other entertainment activities for the time being.

It’s led to one question that is asked over and over again despite there being no concrete answer at the moment: When will things get back to normal?

First things first: In Pennsylvania, Gov. Tom Wolf has put no date on when places like barbershops, nail salons, and dine-in restaurants can reopen. The same goes for education locations, as K-12 students and those in college are currently learning online.

An optimist might look at President Donald Trump’s decision to extend federal social distancing guidelines through April 30 as an opportunity to ‘flatten the curve’ in such a way that a slow return to in-person gatherings and routines could start by early to mid-May. A pessimist, on the other hand, would ask why we would stop staying away from each other, especially if it is proven to be effective, until scientists and other health professionals can prove it is safe to get together like old times again.

One expert, Center for Health Security at the Johns Hopkins Bloomberg School of Public Health director Tom Inglesby, has some ideas that could eventually offer a path to opening back up in a recent interview with Scientific Magazine.

Asked when it might be safe to lift social restrictions, Inglesby points to four things:

—A consistent downward trend in cases over a two-week period.

—The ability to not only test anyone with COVID-19 symptoms but also to be able to deliver the results in 24 hours or less.

—Enough personal protective equipment, such as gloves, masks, and gowns, for medical and healthcare professionals.

—Finally, tracing anyone who came into contact with someone who tests positive for the coronavirus and having them quarantine.

“If the state has 500 new cases at its peak in a day, then the target should be that, for two weeks in a row, new cases drop daily—450, 400, 350, 300,” Inglesby said. “You know, basically getting down to hopefully small numbers of cases, right?

“We didn’t put an absolute number in there—it would be too difficult to know, because the states vary largely in size. But it ideally should be absolute numbers that are pretty low from the start so that there’s not a high chance for a major reeruption in cases.”

All of that will take time, of course, and who knows how much of it; PPE production will have to start outpacing use, and citizens will have to actually stick to the mandate of staying home as often as possible to limit the number of potential interactions those infected have with those who aren’t.

Companies around the world are racing to develop rapid tests and vaccines, but those aren’t overnight processes, especially when it comes to verifying that they actually work.

Those looking for something to track can probably best watch the case counts, though even those are subject to massive underreporting, according to many experts.

The long and short of the answer to an impossible question, then, is no one knows when normal will return, or what it will even look like when that time comes.

“I think, at this point, there needs to be a bit more definitive decision-making and scientific judgment by national health authorities—the Centers for Disease Control and Prevention and the National Institutes of Health—about whether we have sufficient evidence to call it immunity,” Inglesby said. “But in general, the thought is that it’s likely to be an indicator of immunity at some level.

“We don’t know how long that necessarily will last. But at least it’s certainly better than if you’ve not had the disease—that’s the hope. And once that’s definitively called out, then I think it could become the kind of thing where people would have evidence that they could more safely be back in the world without being at risk themselves or endangering others.”