Unthinkable: Why your first kiss will stay real forever

What's another year? When Johnny Logan asked this question in the 1980 Eurovision song contest he was following in a long philosophical tradition stretching back to the ancients through Newton and Einstein.

What the last of those had to say about time is not quite the material of a chart-topping single but it does have profound implications for us today. As Daniel Deasy – a recent addition to UCD's philosophy department – points out, Einstein's theory of special relativity and its associated "space-time" model overturned centuries of thinking.

“A useful analogy is with film,” he says. “On the Newtonian view, your life is like a film that flashes by at a constant rate. On the space-time view, your life is like a collection of stills eternally laid out, from earliest to latest.”

Deasy, taking up where Logan left off, so to speak, is researching our subjective experience of time and whether it is consistent with objective reality. Deasy advances a hypothesis that events in the past, present and future are equally real, and thus he provides today's idea: "The events that make up your life are a small but eternal part of the four- dimensional universe."

How does Einstein’s “space-time” model change our understanding of past, present and future?

“The space-time theory basically tells us that time is like space. And if time is like space, then there is no nonrelative basis for the distinction between the past, present and future: ‘the present’ is just what I call my location in the space-time block. There’s another location in which Queen Anne is saying ‘I’m present’, and she’s speaking truthfully just as much as I am.

“It’s like if I say, ‘I’m here and you’re there’; you can say exactly the same thing to me, and also speak truthfully.

“And of course, if ‘the present’ is just what I call my location in space-time, the past and future are no less real than the present: the past and future are just other locations in the space-time block.

“Again, if I’m here and you’re over there, that doesn’t mean that where you are is any less real than where I am.

“So according to the space-time theory, the Battle of Hastings and the swearing-in of Mars’s first president are as real as the event of your reading this sentence; they simply happen to be taking place elsewhere in space-time.

“Now, a problem for philosophers is that our experience of time tells us something completely different. Experience tells us that the Battle of Hastings is over, and the swearing-in of Mars’s first president has not happened yet. In short, experience tells us that the only real events are the present events.”

How do you resolve this problem?

“In my research I defend a view called the moving spotlight theory that tries to be as deferential as possible to the space-time theory while also providing some grounds for denying that time is just like space. So I accept that reality is a space-time block and that the Battle of Hastings and the swearing-in of Mars’s first president are real.

“In fact, I accept all the ‘positive’ content of the space-time theory. But I also argue that those events are objectively past and future, and in some sense no longer or not yet taking place.

“This is a nondeferential theory: for example, it says that some events are objectively happening at the same time, whereas the special theory of relativity famously says that there are no such facts. This is a huge cost of my view; I disagree with Einstein.

“However, bear in mind that my disagreement is not with the physics of the space-time theory but with the implicit metaphysics. It seems clear to me that the space-time theory does not tell the full story of time and change.”

Can philosophical theories of time help us to relinquish the fear of death?

“That really depends on what it is about death that we fear. If it’s ceasing to be real, then both my theory and the space-time theory might provide some comfort, as both theories imply that the events that make up your life are a small but eternal part of the four-dimensional universe. Your birth, your first kiss, your lottery win: they will be forever located in some region of space-time.

“But if what we fear is dying – that is, being alive at one moment and dead at some later moment – then theories of time offer scant comfort. There is no theory of time according to which we don’t all eventually die. Sorry.”

If we accept your hypothesis that events in the past, present and future are equally real, what are the implications? Does it suggest we can figuratively, or literally, time-travel?

“Well, if the past and future exist then literal time travel seems at least in principle possible, whether or not it is physically possible.

After all, you can’t travel somewhere that doesn’t exist. And when you think about a specific past event, that very event is the subject of your thought. In that sense you can ‘mentally travel’ to a past event.”

• philosophy@irishtimes.com
• Twitter @JoeHumphreys42

ASK A SAGE

• Question: What Christmas present should I get for the intellectual in my life?
• Robert Lynd replies: "Were I a philosopher, I should write a philosophy of toys, showing that nothing else in life need to be taken seriously, and that Christmas Day in the company of children is one of the few occasions on which men become entirely alive."