Before we get into this week’s topic, a quick word on last week’s show, my interview with Elon Musk. It has generated an extraordinary response, from you, our subscribers, more broadly across social media—and from Mr Musk himself. A record number of you watched or listened to the conversation and many of you have sent thoughtful letters. I plan to get to them all in due course. 

I confess I’m a bit bemused by some of Mr Musk’s reactions to our conversation, but I’m grateful that he took the time to sit down with me. It was illuminating to hear his worldview at length. We have since commissioned journalists to look at the facts in a few areas of contention. Keep an eye out for articles on the impact of shutting down USAID and on the number of victims of grooming gangs in Britain, and a video on violent crime in European cities.

Most Economist readers will know our Big Mac index, which compares the price of a McDonald’s burger around the world to assess whether currencies are too cheap or too expensive. Subscribers of a certain vintage may even remember the first time we served it up, back in 1986—the idea of our former economics editor, Pam Woodall. As well as offering a guide to where to get a cheap meal, the index tests an important economic principle, known as purchasing-power parity, to see which currencies are out of whack. It serves as a decent proxy for a country’s economy as a whole. Why Big Macs? Well, the burger is much the same anywhere. But its price is not, which is where things get interesting.

To mark the index’s 40th anniversary, we’ll be putting it on our digital cover this week. It will also be the topic of tomorrow’s episode of The Insider. As well as explaining what this index is and how it works, we’ll dive into the reasons why the world is once again worrying about unmoored currencies, which can lead to historically high trade deficits and surpluses—and serious political tension between the rich world and China. 

I will be joined in the studio by Edward Carr, deputy editor, who will be in the host’s chair; Henry Curr, our acting business affairs editor; and Josh Roberts, our capital markets correspondent. Simon Cox, our senior economics writer, will join us down the line from Hong Kong. Simon left no burger unflipped while reporting this week’s briefing on the history of the Big Mac index, travelling to two places 9,500km apart where Big Macs are either eye-wateringly expensive (Basel) or mouth-wateringly cheap (Taipei).  

The Big Mac index appears in economics textbooks and is frequently cited by scholars. But plenty of critics like to give burgernomics a grilling. It was once subject to a formal rebuttal from Taiwan’s central bank—surely one of that august institution’s more surreal communiqués. Henry will outline what the index is useful for, and also explain its shortcomings and the instances where purchasing-power parity breaks down. I hope Josh can tell us about how investors actually use the index—if at all. 

We’ll discuss the trade surpluses and deficits—hinted at in the latest index—that have officials in capitals from Washington to Beijing worried. Such concerns are not new: indeed there comes a time in every economics editor’s career to get to grips with global imbalances. For me that was 2005, when I wrote a special report on exactly this topic. I have some thoughts on what has changed since then—and what hasn’t. 

Finally, we’ll consider where the world goes from here. What do Donald Trump’s tariffs mean for the trajectory of the dollar and America’s economy? Simon will explain what’s really going on inside China and what explains its trillion-dollar goods-trade surplus. Before a trip to India next week, which will no doubt involve a Maharaja Mac (notable because it swaps beef for chicken), he will also share his thoughts on the implications of trade imbalances in the world’s most populous country. And I’ll chip in with what I think all this means for Europe.

As ever, we want you to get involved. Please vote in our poll, and once you’ve done so, send in any questions you’d like us to answer in tomorrow’s show using the Q&A feature on the episode page. The episode will be available to watch from 6pm London time (1pm in New York) on Thursday. I’m keen to hear what you think about our discussion. If you have feedback or ideas to share, please write to me here: insider@economist.com.