Has the global economy slowed down?
Big macroeconomic changes happen slowly, sometimes they aren't clearly visible until years later.
We may currently be living through a structural change in the global economy as big as any since World War II without fully realising it.
The world economy may be becoming less integrated, with one of the important drivers of globalisation swinging into reverse.
This week the Dutch Bureau for Economic Policy Analysis released its latest estimates of world trade.
This widely-followed measure showed that world trade grew by 3.3% in 2014, that's up from 2.7% in 2013 and 2.1% in 2012 but still well below the long term average of growth of 5%.
Global trade grew strongly from the late 1970s until 2008 when the global recession caused it to collapse.
It rebounded strongly as the global economy recovered in 2010 and 2011 but since then trade growth has been weak.
Before the crisis world trade generally grew faster than world GDP, so trade as a share of world output rose.
Since the recession, world trade has been sluggish and outpaced by growth. As a share of global GDP, trade has been falling.
In other words, on one important measure the world economy is becoming less integrated, as a share of world output, fewer goods and services are crossing borders.
There are reasons to think that the weakness of trade may reflect longer term factors than just the immediate aftermath of the credit crisis.
A report this week from Oxford Economics was optimistic that trade growth would pick up but identified structural reasons for its recent weakness - factors which may endure.
The first is the process of "reshoring" or bringing manufacturing that was previously outsourced abroad back to the home country.
Cheaper energy costs driven by the shale oil revolution have been one large driver of this in the US, but it appears to be a broader trend across the developed economies.
That relates to the weakness in the global goods trade, but the global trade in services has also been weaker post-financial crisis.
One reason for that may be a pulling back from overseas activity by banks.
RBS has announced it was pulling out of operations in 25 countries, driven by tighter regulation and need to conserve capital, more and more banks are choosing to focus more on their domestic markets. That slows the growth of global services trade.
Finally, Oxford Economics identified a lack of trade liberalisation. This is not to say that protectionism (using tariffs or quotas to limit imports and try to protect domestic firms) is on the rise, but that if trade is not being more regulated, it is becoming more liberalised at a slower pace.
Trade treaties and deals are estimated to have contributed around 20% to the growth of world trade between 1994 and 2007. Without the spur of additional deals, world trade growth could be slower.
An IMF report in January reached similar conclusions, arguing that there were signs of a slowing of global trade even before 2008 and it was driven by a "slower pace of expansion of global supply chains".
So, if the world economy really is becoming less globalised, what would this mean?
The traditional answer, for the advanced economies such as the UK, is to say that a more open economy has meant the destruction of certain kinds of jobs, but overall a welfare gain for the country through importing cheaper goods.
There are potentially serious consequences for countries in the developing world if the era of ever deepening globalisation is truly over.
Export-led growth has been a key development strategy for many nations and a slowing of global trade will have consequences.
Counter-intuitively enough, a less globalised economy might actually have a positive impact on financial stability.
In a speech in 2011, the then Governor of the Bank of England Mervyn King argued that "global imbalances" had played a key role in the run up to the financial crisis.
He noted that during the era of the Bretton Woods agreement (by which countries fixed their exchange rates against each other and globalisation was, to an important extent, limited) between the late 1940s and early 1970s, global growth was strong and less volatile than before or since and banking and financial crisis were rarer.
On the broader topic, I highly recommend this talk by Professor Dani Rodrik.
It makes sense that weaker global trade flows leave less room for imbalances which can endanger the development of financial stability.
All of which leads me to two thoughts.
The first is that neither faster nor slower global trade growth is necessary desirable.
There are costs and benefits to rapidly increasing global trade and there are costs to diminishing global trade.
At heart, macroeconomics is all about trade-offs. But when considering something like the pace of globalisation itself, it is unclear who (if anyone) is considering these trade-offs.
We may stumble into second-best solutions - a world less globalised than is ideal, or more globalised than is ideal by accident.
A lack of policy co-ordination between economic policy authorities across borders makes this more likely.
The second is that for years our politics has taken increasing globalisation as a given.
Those who have occasionally advocated slowing have been accused of saying "stop the world I want to get off".
The world might not be stopping, but it could well be slowing.