Matyas Moravec: Modern physics suggests that time can be an illusion. For example, Einstein’s theory of relativity suggests that the universe is a static, four-dimensional block containing all space and time simultaneously – with no special ‘now’.
What is the future for one observer is the past for another. This means that time does not flow from the past to the future, as we experience it.
However, this clashes with the way time is conceptualized in other areas of physics, such as quantum mechanics. Is time an illusion or not? One way to find out is to try to prove that time is unreal using only logic.
In 1908, JME McTaggart, an English philosopher, published an article arguing that we might be able to figure out the unreality of time just by thinking logically.
Imagine that someone has given you a box of cards, each representing an event. One card describes the year 2024, another the death of Queen Victoria and another the solar eclipse in 2026. The cards have been mixed up. You have been told to arrange these cards so that they represent time. How would you do it?
The first way is to use what McTaggart calls the “B series”. You choose one card and place it on the floor. Then you take another one from the box and compare it with the one already on the floor. If it’s earlier, put it to the left of it. If it is later, put it on the right side.
For example, Queen Victoria’s death occurs to the left of the 2026 solar eclipse. The year 2024 is to the left of the 2026 solar eclipse, but to the right of Queen Victoria’s death. You keep repeating this until you get a row of cards, two of which are connected via the earlier-later relationship.
As you look at the finished arrangement, you realize something is missing. The line of cards is static. Once the cards are placed in place, the order does not change. But as McTaggart points out, you can’t have time without change.
Time is ultimately a measure of change, even according to physics. It is often identified as an increase in the disorder – entropy – of a closed system. Have a cup of hot coffee. As it cools, the entropy increases. And the temperature tells you approximately how long a cup of coffee has been there. Any device that measures time, such as a clock, depends on change (ticks).
Remember that your original task was to arrange the cards to show the time. But you ended up with something that doesn’t change. It would be strange to say that time does not change. So the B series cannot record time.
However, there is another option. You can start over and try to arrange the cards using what McTaggart calls the “A series”. You make three neat piles – on the left are all the cards that describe past events, such as the death of Queen Victoria. In the middle are the events that are happening in the present, such as in the year 2024. And on the right are the events that will happen in the future, such as the solar eclipse of 2026.
Unlike the B-series, this setup is not static. As time passes, you must move the cards from the right (future) pile to the middle (current) pile, and those from the middle (current) pile to the left (past) pile, where they remain forever. So there is clearly change happening here. Does this mean that the A series describes time?
According to McTaggart, the A-series is circular. Moving the cards from the left pile to the middle and then to the right pile is a process that takes place over time.
In order to carry out this arrangement, you must be present on time. But time is exactly what you’re trying to capture. In other words: you already need time to describe time. This is circular, and circularity defies logic.
Let’s summarize. The B series arrangement cannot describe time because nothing changes. And change takes time. So the B series does not work. The A-series is changing, but unfortunately it is circular. So it doesn’t work either. Since none of these works exist, McTaggart concludes that time cannot be real.
One hundred years later
More than a hundred years later, philosophers are still looking for a solution. Some, called “A-theorists,” attempt to define the A-series in a way that is not circular.
Others, called ‘B-theorists’, accept that the B series describes reality and say McTaggart was wrong to demand that the series change. Maybe time is just a series of events.
There are also ‘C-theorists’ who go further and say that the card line does not even have a direction from earlier to later.
The year 2024 lies between the death of Queen Victoria and the solar eclipse of 2026. But the fact that we are accustomed to thinking of Queen Victoria’s death before the solar eclipse of 2026, rather than the other way around, may just be a matter of habit . It’s like numbering the boards on a fence: you can start from any end. The fence itself has no direction.
I’m not yet convinced they’re right; perhaps there are completely different ways to think about time. Ultimately, time will tell.
And regardless of who is right, the remarkable thing is that McTaggart was able to get the argument going without any scientific findings, but purely by thinking logically about the problem.
Matyas Moravec, Gifford Postdoctoral Fellow in Philosophy, University of St. Andrews
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