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No Time Like the Present

April 14, 2014

Many famous, and a few anonymous individuals have expressed an observation about time that's so memorable that it's often been repeated. Here are a few examples.
"Time is an illusion."
   - Albert Einstein

"Time is what prevents everything from happening at once."
   - John Archibald Wheeler

"Tomorrow, and tomorrow, and tomorrow,
Creeps in this petty pace from day to day."
   - William Shakespeare

"Time heals what reason cannot."
   - Seneca

"Time is the longest distance between two places."
   - Tennessee Williams

"Time and tide wait for no man."
   - Anonymous

Physicists use time in many calculations; and, as I wrote in a previous article (Does Anybody Really Know What Time It Is? June 7, 2013), there are atomic clocks capable of keeping time to a precision of one part in 1014, for an accuracy of about one second in a billion years. However, no one is confident that we understand what time really is.

Time flies metaphor

Time flies

(Via Wikimedia Commons.)

Not surprisingly, Aristotle presented his thoughts on the nature of time in a chapter of Book IV of his Physics. The following quotation, in which Aristotle reflects on the idea that past time has vanished and future time has not yet arrived, is one of the more memorable potions of that book.[1]
"First, does it [time] belong to the class of things that exist or to that of things that do not exist?...The following considerations would make one suspect that it either does not exist at all or barely, and in an obscure way. One part of it has been and is not, while the other is going to be and is not yet."

Stepping forward in time, philosophical thought in the Middle Ages is usually considered to be just a rehash of Aristotle, although some philosophers ventured slightly outside Aristotle's established edicts. Arnold Smith of Kent State University and Youngstown State University (Ohio) published a short paper in 2007 examining the concept of time in the Middle Ages.[2]

According to Smith, Thomas Aquinas, the 13th century interpreter of Aristotle, wrote that time and motion are intertwined concepts that always occur in relation to each other. It is only through motion that we see that "time is going on." Time is the ordinal marking of events, and time is "nothing other than the number of motion according to before and after."[2] Time is essentially the human way of putting order into the nature of things, and it does not exist in itself.

Fourteenth century philosopher, William of Ockham, famed among scientists for Ockham's Razor, also considered that motion and time were allied concepts. As Ockham wrote in his Summulae in Libros Physicorum,
"Time is the measure of movements whose magnitude is not known to us; in fact, it is by time that we recognize the length of a movement..."[2]
Saadia Gaon ben Joseph, a Jewish scholar of the 9th century, had a Zeno-style argument that the universe had not always existed. He argued that we could never exist "now" in an eternal universe, since getting here meant that an infinite amount of time must have passed. But, to get here, we would first need to get half way here, which was also at an infinite time. Then, going from this halfway point to now would also take a infinite amount of time, etc., so it couldn't happen.

Zeno of Elea showing his students the doors of truth and falsehood

Zeno of Elea showing his students the Doors of Truth and Falsehood. Fresco in the Library of El Escorial, near Madrid. (Via Wikimedia Commons.)

It's been many centuries since the end of the Middle Ages, which is usually defined as the period from 5th to the 15th century. Has our concept of time changed? The modern concept of time can be divided into three categories.
Presentism - Only the present "exists."

Eternalism - The past, present and future all exist. We just have no knowledge of the future, so we can't affirm its existence.

Growing block universe - The past and present exist, but the future does not exist. More of the universe is brought into existence with the passage of time. The present, three-dimensional, universe is a snapshot of spacetime, and its history is built as one slice at a time (see figure).

Evolution of the universe in spacetime

Evolution of a three-dimensional universe in time. The universe is built from a growing sheaf of present moments.

(Illustration by the author using Inkscape.)

A paper on the modern interpretation of the nature of time has been posted on arXiv by Gustavo E. Romero, a professor of relativistic astrophysics at the Universidad Nacional de La Plata (Argentina) and a researcher at the Instituto Argentino de Radioastronomía. Romero subscribes to the concept of time developed by Aquinas, as can be seen in the paper's abstract,
"I argue for a tenseless view of time, where what we call 'the present' is just an emergent secondary quality arising from the interaction of perceiving self-conscious individuals with their environment. I maintain that there is no flow of time, but just an ordered system of events."[3]
Human perception is important to both the understanding of space and time. Our perception of space is relative; that is, we merely perceive the spatial relations among things. In the same manner, we don't perceive the passage of time, we perceive how our brain changes. According to Romero, "Becoming is not a property of physical events, but of the consciousness of the events... Events do not become. Events just are."[3]

Writes Romero,
"We group various experienced inputs together as present; we are tempted to think that this grouping is done by the world, not by us. But this is just delusional. I maintain that tenses are not needed and in fact are not wanted by the natural sciences."[3]


  1. Aristotle, Physics, Book IV, part 10, The Internet Classics Archive by Daniel C. Stevenson.
  2. Arnold A. Smith II, "Time and the Medieval World, Philosophy Now, Issue 62 (2007).
  3. Gustavo E. Romero, "Present time," arXiv Preprint Server, March 19, 2014. This paper is in press in the journal, "Foundations of Science."
  4. Gabriella Galbiati, "Ockham's Philosophia naturalis and Quaestiones in libros physicorum in the Light of Prior’s Tense Logic," Metalogicon, vol. 20, no. 1 (2007), pp. 27-38.

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