Britain has officially left the European Union. But what happens next?

The breakup is official: On January 31, 2020, at 11 pm local time (6 pm ET), the United Kingdom left the European Union.

UK Prime Minister Boris Johnson gave a brief address ahead of big moment, where he struck an optimistic note about Britain’s future outside of the UK.

The most important thing to say tonight is that this is not an end, but a beginning,” the prime minister said. “This is the moment when the dawn breaks and the curtain goes up on a new act in our great national drama.”

A countdown clock projected onto his residence at 10 Downing Street, a recording of the under-renovation Big Ben ringing at 11pm.

Members of the Brexit Party threw a, well, Brexit party in Parliament Square. Anti-Brexiters were in a much less celebratory mood, and some protests and vigils are expected across the country. The EU quietly removed Britain’s flags from its headquarters in Brussels.

That’s basically it, unless you’re into commemorative coins. Otherwise, now that the clock has struck 11pm, things aren’t going to be all that different than they were at 10:59pm.

That’s because the UK and EU will not disentangle immediately. Instead, the UK enters into a transition period in which the two sides will try to hash out the future relationship.

So while Brexit has happened, it’s not really done.

Here’s a quick guide to what actually happened on January 31, and what comes after — as much as anyone can predict.

What happens on January 31?

The short answer: Article 50 expires.

The UK had to formally give the EU notice that it wanted out by triggering Article 50 — the provision in the EU’s Lisbon Treaty that gives countries the power to withdraw from the bloc.

The UK did this in 2017; that set off a two-year countdown clock to March 2019. When the UK couldn’t resolve Brexit, and neither the UK nor the EU wanted to break up without a deal in place, the EU agreed to push back that date, first to April 2019, then to October 2019, then to now.

Now that both sides have agreed to, and formally ratified, the Brexit deal, they’re letting Article 50 run out.

This matters because now that the UK is out, it can’t change its mind. If, say, for some reason, it regrets it all and wants back in, it has to apply for membership like everyone else (under Article 49), and all 27 member states have to agree.

So January 31 at 11 pm was essentially the point of no return — but it won’t seem like it.

What will happen during the transition?

The transition (or implementation) period begins now that the UK has left, and it will last until at least December 31, 2020. Very little will actually change: The UK will continue to follow all EU rules, only now it will have no say in what those rules are, since it won’t be an EU member anymore.

The UK and the EU will now have to figure out what their future relationship will look. They have 11 months to do this. Which is a very nice way of saying: The hard part of Brexit is yet to come.

All the hullabaloo over the Brexit deal during the past year revolved around the withdrawal agreement, which essentially laid out the terms of the divorce. The two sides had always planned to divvy up these phases. First, deal with the breakup, then figure out if we want to stay friends.

The EU and the UK both have an interest in maintaining a strong relationship, but what character it will take is what the next phase is all about.

The starting point for these negotiations will be something called the “political declaration,” which sets out broad principles (“establishes the parameters of an ambitious, broad, deep, and flexible partnership across trade and economic cooperation with a comprehensive and balanced Free Trade Agreement at its core” — you get the idea) but lacks details on how, exactly, these goals will be achieved.

The big one is trade. The UK is leaving the EU customs union and single market, so the two sides want to work out a trade agreement, ideally with no tariffs and no quotas, and keep trade barriers low.

But it’s not just trade. The two sides have to discuss security and law enforcement cooperation, access to fishing waters (this is a big one!), banking, data and intelligence-sharing, manufacturing, and a whole lot more. Everything the EU and the UK did together before, they now have to figure out how they can still do it together now that they’re apart.

And then there’s Northern Ireland. The border between Ireland (which is staying in the EU) and Northern Ireland (which is part of the UK and leaving the EU) will remain open. But how to implement the new system — which involves customs checks between Northern Ireland and the rest of Great Britain — also needs to be worked out.

Experts told me this could very well be the stumbling block that holds up the next phase of Brexit negotiations, too.

On the EU side, officials are skeptical a comprehensive agreement on trade, let alone all the other things, can be completed in 11 months. Or, really, less than that: After Brexit happens tonight, the two sides will set out their negotiating priorities, but talks won’t begin in earnest until March.

It doesn’t have to be this much of a time crunch. The transition period can be extended, one time, for up to two years, until the end of 2022.

But Johnson campaigned on the promise that he would not extend the transition period, and he eliminated that possibility from the Brexit legislation that just became law. Laws can be amended, but right now, Johnson has given no sign he’s willing to budge on the 11-month timeline.

There is one other wrinkle: If the UK and the EU decide they have no choice but to extend the transition, they have to decide that by the end of June 2020, which is baked into the Brexit deal.

That means the EU and UK likely can’t go down to the wire, seeking last-minute extensions, in the same way they did in the first phase of Brexit. Which makes the first months of negotiations after Brexit even more urgent.

Or, as one Irish official put it, a feat “nearly without precedent.”

A deal is not impossible, but warning signals are already blinking. EU leaders have been clear that if the UK wants to retain access to EU markets, it’s going to need to align its rules and regulations closely with the ones already in place.

If “Irish backstop” was the defining phrase of the first part of Brexit negotiations, get ready for “level playing field” to be the defining phrase of the second part. The EU wants to guarantee a “level playing field” with the UK in any free trade agreement, basically to prevent the UK from so drastically changing its economic regulations (such as giving huge tax breaks or subsidies to companies) or environmental or labor standards that it could undercut the EU.

Brussels is really quite nervous right now, because the UK has said it wants to make its own rules. After all, to Brexit supporters, the whole point of leaving the EU was to leave it: to get away from all of its onerous regulations.

And the more the UK wants to diverge from the EU, the harder it will likely be to reach a future agreement on trade and everything else. Which makes the already tight timeline even tighter.

What happens if there’s no deal by the end of 2020?

Johnson and the EU could decide in June to extend the transition period, giving them more time and pushing negotiations to as late as 2022. But assuming that’s not happening, and the EU and the UK don’t have a trade agreement (or other deals) in place, one could perhaps call this a “no deal” scenario.

Yes, that’s right. The no-deal Brexit is back.

All the catastrophically disruptive things that could have happened if the UK left the EU without a plan in place before Brexit could still occur if the two sides reach the end of the transition period without agreements.

That’s because once the transition period expires, all the trade and regulatory arrangements the UK was following will end. The two sides will trade under World Trade Organization rules, which sets the tariffs and quotas between countries that don’t have free trade agreements in place with each other.

Checks and controls could create massive gridlock at ports of entry, which could lead to food and medicine shortages. A few thorny issues have been (mostly) settled, including Northern Ireland’s border with Ireland. But, in general, a 2020 no-deal could still look a lot like the one experts predicted before Brexit became official.

For all these reasons, this is an outcome both the UK and the EU want to avoid. Like last time, it will be bad for both the EU and the UK, but far worse for the UK.

This is why Johnson’s critics deemed his decision to eliminate the possibility of extending the transition “reckless and irresponsible.” But Johnson has continued to insist he can make speedy deals with the EU — and the rest of the world. Now he and everybody else are about to find out.

Which means another thing won’t change after January 31 at 11pm: Brexit chaos isn’t going anywhere anytime soon.