"We're all time travellers!" quipped Carl Sagan.
After all, we're all moving into the future at a steady rate of one second per second. Agreed, it sounds like an obvious platitude, but does Sagan's quote even make sense? What does it actually mean for time to pass at a rate of one second per second? And are we really moving into the future, or is the future somehow 'moving into us'? What is time anyways?
Humbled and perplexed by the mystery of time, the medieval theologian and philosopher St. Augustine of Hippo famously answered: "If no one asks me, I know; but if I wanted to explain it to him who asks, I plainly do not know!"
Sixteen centuries later, anno 2015, scientists and philosophers alike are still hard-pressed to tell us what exactly time is. But this, of course, doesn't mean there hasn't been any progress since the dark ages!
Clearly then, the time is ripe to take stock of our current understanding about the nature of time and why it matters. The upcoming semester turns out to be especially appropriate to do so, for three reasons:
First, on September 30, the Dutch time travel movie Terug naar morgen will be released. The director, Lukas Bossuyt, studied engineering at KU Leuven and decided to shoot his first movie here in Leuven and in the physics labs in Heverlee!
And third, on November 25, the world will celebrate the centennial of Einstein's theory of general relativity. If only we could go back to November 1915 and witness Einstein's speech at the Prussian Academy of Science in which he first showcased his field equations!
For all of these reasons, and because we are both fascinated by time, we are organising a brand new course on the nature of time, open to all Ma-students and starting September 2015! But more on that below . . .
Travelling in time
Returning to Sagan's quote, one might wonder whether the passage of time can be sped up or slowed down? Can we flash forward to the future or travel back in time to a distant past? Will science fiction ever become science fact? Surprisingly enough, the answer might well be a resounding yes!
According to the two pillars of modern science — general relativity and quantum mechanics — time travel is indeed a physical possibility, at least in principle. Einstein's theory of special relativity, for instance, suggests we can fast forward into the future by travelling at speeds sufficiently close to that of light — a mere 300000 kilometres per second!
Time travel into the past is a more thorny issue, requiring wormholes, exotic matter, negative energy and all that. But what worries scientists most, is that a shortcut to the past would also open the door to all kinds of logical time travel paradoxes, like what would happen if you ended up severing your own line of descent (better known as the (in)famous grandfather paradox or grandpappycide).
Despite these theoretical and philosophical complications, it can be fun to think about the possibility of altering your own past. And it makes for a great premise for a movie, too.
In the movie Terug naar morgen (literally: Back to tomorrow), a Flemish scientist, called Viktor, discovers a way of communicating with the past by sending emails back in time. But as Viktor presses the Send button, he soon realises you don't mess with the past without risk — a time travel moral well understood by Marty McFly too.
The mysterious nature of time
Science fiction movies are entertaining, but they also touch on subjects that are of interest to scientists and philosophers of science. Although time plays such a central role in our lives, and thinking without time seems unthinkable, it remains an elusive and mysterious concept. Here are some questions to ponder over:
Does time exist objectively (is it really real) or is it merely a subjective experience?
Why is space three-dimensional, but time only one-dimensional? And how comes we are free to move in any direction of space, but seem to be stuck in the present — unable to visit either the past or the future?
We often think of time like a majestic river, flowing relentlessly from the past to the future, and carrying us along by its current. We talk of time passing, flowing or moving. But does it really flow or is this merely an illusion?
In addition, why does time flow in one direction only, from the past to the future? If you were shown a movie run backwards, it wouldn't take long for you to notice. After all, most processes in nature occur in only one direction: candles turn to smoke, but never the other way around; eggs scramble and wine glasses shatter, but you'll never see your omelette unscramble or broken glass magically reassemble. Whether we like it or not, we are subject to time's arrow too: we are born young and die old (except for Benjamin Button). We remember the past, but can only predict the future. Where does this arrow of time come from?
We all live in the present. The past no longer exists, and the future does not yet exist. But what if the past somehow still existed? Just because we no longer have access to past events does not mean they no longer exist. Here's a spatial analogy: no one denies the existence of the liberty statue or the Egyptian pyramids, just because they are somewhere else. So why deny the existence of dinosaurs or the battle of Hastings, just because they are somewhen else?
Does time have a beginning, and will it ever end? Or does it stretch out at infinitum in one or both directions? Most scientists believe the Universe was created 13.7 billion years ago in what is now called the Big Bang. But what happened before the Big Bang, and is it even a sensible question to ask, given that time itself was created at the Big Bang?
At this point, you might feel a little puzzled or confused, and quite understandably so! You might also feel a bit more sympathetic already towards Augustine's statement. Perhaps you even feel intrigued. In that case, we're happy to announce our mind-boggling course on the nature of time, starting in September 2015!
Many philosophers — including Augustine, Kant, and McTaggart — have thought deeply about the nature of time. In addition, most of our current scientific theories — classical mechanics, thermodynamics, quantum mechanics and relativity theory to name a few — crucially rely on the concept of time, and they too have shed new light on time's elusive nature. But while new insights have been gained, and partial answers have been provided, most questions remain as poignant today as they were in Augustine's days.
This is the very first time that the KU Leuven offers a course dealing with the issue of time from a philosophical, physical, and psychological perspective. All of the questions listed above, and many more, will be discussed. The aim is to make their analysis accessible to absolutely everyone, whether your background is in science, philosophy, or psychology. Here's what will be on the menu:
A Course on the Nature of Time
Week 01 — Introduction and time according to the ancient Greeks.
Week 02 — Time in classical physics: is time substantive or relational?
Week 03 — Does time pass? McTaggart’s A-series and B-series.
Week 04 — Special relativity and simultaneity.
Week 05 — General relativity and cosmology: did time begin and will it end?
Week 06 — The arrow of time and entropy.
Week 07 — Time in a quantum world.
Week 08 — Time travel: how to build a time machine and time travel paradoxes.
Week 09 — Psychological aspects of time.
Week 10 — Acting in time: what about free will?
Our weekly meetings will take place on Fridays from 11:00 to 13:00 at the Institute for Philosophy (Kardinaal Mercierplein, room N). We start September 25th.
The course is part of the program for Master students of Philosophy, but Master students of Science are especially welcome too! Others who are interested, are allowed to follow a specific lecture, but should contact one of the lecturers in advance. Since all course materials and lectures will be in English, international students are encouraged to enrol as well.
For more information, please take a look at our web page. And don't forget to subscribe now! It's about time!