My speculative life cycle estimate of the observable universe would fail Sagan’s acid test (esp. numbers 1 and 5). However, this does not preclude more thought and discussion on the meaning and duration of cosmological time.

Physics of time

There is a dizzying array of theories on this subject. Concepts such as the direction of time, arrow of time, gravitational time dilation, proper and improper time, entropy increasing with time, quantum time entanglement, loop quantum gravity (predicting that elementary temporal leaps are small but finite as per Carlo Rovelli, who we will bring up later), radioactive decay, thermal time and time as the 4th dimension play a part in the confounding physical complexity of time. All of this is before we begin discussing human perceptions of time, biological and psychological. For purposes of this inquiry, I intend only to examine a few of these, since books and copious scientific papers have been and will be written on these subjects. 

Out of this potpourri of physical attributes of time, Herman Minkowski’s 1907 theory of proper time, which led to measuring the consequences of time dilation, is in my opinion one of the more interesting. Simply put, he postulated the faster the relative velocity (between two entities), the greater the time dilation that there will be. In practical terms, two observers in motion relative to each other will measure each other’s clocks slowing down. Simply put, velocity exerts an influence on time. For example, in the International Space Station after 6 months at a speed of 7,700 meters per second, an astronaut would age 0.005 seconds less than on Earth. Yes, time slowed down for that astronaut relative to the observer on Earth, and we have used two synchronized atomic clocks to prove it.

Gravitational time dilation is, however, not reciprocal—the clock closer to the center of the gravitational field will be slower. Both observers will agree that the clock closer to the center of the gravitational field is slower in rate and ratio of difference. This leads to the somewhat bizarre conclusion that the core of our earth is at a different ‘proper time’ than on the surface (~2.5 years younger than the crust)—and so on throughout the universe. Taking this concept to extremes, you could in theory meet your grandfather before you were born.

If you’re starting to wonder “That’s great, but what does it mean for me?” then you’ll be interested to know general relativistic gravitational time dilation has an immediate impact on satellite (GPS) navigation, space travel and satellite time synchronization at different altitudes. GPS needs to account for this time dilation.

As Wikipedia explains,

Time dilation explains why two working clocks will report different times after different accelerations. For example, time goes slower at the International Space Station, lagging approximately 0.01 seconds for every 12 Earth months passed. For GPS satellites to work, they must adjust for similar bending of spacetime to coordinate properly with systems on Earth.

The International Space Station is only ~254 miles from Earth and travels at a small fraction of the speed of light. Just imagine the gravitational time dilation for a spacecraft billions of miles from Earth traveling at a significant fraction of the speed of light where time dilation would amount to multiple years or centuries.

For those eager to calculate time dilation, the formula is

γ = 1/√(1 – v²/c²)

The equation relating proper time and time measured by an earth-bound observer implies that relative velocity cannot exceed the speed of light c (which is 299,792,458 meters per second). 

A word on radioactive decay

Some things don’t give a whit about relativity and act as natural chronometers. Radioactive decay is another physical phenomenon, namely the probability per unit of time that a nucleus will decay; it is constant, independent of time.

A = –dN/dt

where A is total (energy) activity, N is the number of particles, and t is time.

Again in Wikipedia’s words,

Radioactive decay is a stochastic (i.e. random) process at the level of single atoms. According to quantum theory, it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed. However, for a significant number of identical atoms, the overall decay rate can be expressed as a decay constant or as half-life. The half-lives of radioactive atoms have a huge range; from nearly instantaneous to far longer than the age of the universe.

According to an April 2019 study published in Nature,

Researchers measured, for the first time ever, the decay of a xenon-124 atom into a tellurium 124 atom through an extremely rare process called two-neutrino double electron capture. By measuring this unique decay in a lab for the first time, the researchers were able to prove precisely how rare the reaction is and how long it takes xenon-124 to decay. The half-life of xenon-124—that is, the average time required for a group of xenon-124 atoms to diminish by half—is about 18 sextillion years (1.8 x 10^22 years), roughly 1 trillion times the current age of the universe.

Wow!

So, here we go again, with yet another measurement of time or timelessness. Geologic time suggests the earth is some 4.5 billion years old, as measured by its period revolution around our sun, itself ~4.6 billion years old and approximately halfway through its life cycle of ~10 billion years. It’s rather quaint, but a calendar year equals the elapsed time for Earth to circle the sun i.e., 365.24 days. To this we have added the accuracy of atomic clocks. The current international unit of time is the humble second, of which we gather 60 to form a minute and so on, and one second is defined by the electronic transition of a cesium atom.

Physics and time

Physics provides a variety of lenses to understand time. According to Rovelli, a well-defined “now” does not really exist; gravitational time dilation is real; radioactive decay is constant independent of time; quantum physics indicates particles can be entangled independent of distance (time); finally, cosmic entropy (the increasing physical disorderliness of the universe) may serve as a possible surrogate for the passage of time. 

Einstein described quantum entanglement as “spooky action at a distance.” However, following recent observations, maybe we should append, “… without apparent time delay regardless of distance.” Perhaps there are two phenomena faster than the speed of light: (1) quantum entanglement and (2) human imagination—for example, picturing oneself on Earth’s nearest star’s planets (Proxima Centauri, 4.3 light-years distant) in a matter of seconds.

While we can look backward in time by observing galaxies and stars close to the 14-billion-year-ago dawn of the universe, we can’t look forward with precision. However, with the use of supercomputers such as NASA’s Pleiades, one of the world’s most powerful supercomputers, it should be possible to fast-forward portions of the observable universe relative to current Earth time using various scenarios (not predictions, but probabilistic outcomes).

David Layzer, a Harvard cosmologist in the early 1970s, suggested that in an expanding universe the entropy would increase, as required by the second law of thermodynamics, but that the maximum possible entropy of the universe might increase faster than the actual entropy increase. This dichotomy would leave room for an increase of order or information at the same time the entropy is increasing (e.g., biological systems, certain physical systems including crystallization, etc.).

Layzer inferred that if the equilibrium rate of the matter (the speed with which matter redistributes itself randomly among all the possible states) was slower than the rate of expansion, then “negative entropy” or “order” (defined as the difference between the maximum possible entropy and the actual entropy) would also increase. Claude Shannon identified this negative entropy with information—an intriguing idea at the time (proper or improper!). 

Layzer called the direction of information increase the “historical arrow.”

That’s the physical angle. Now, it’s about time for a biological look at time—and particularly humans’ perception of time.

Human perceptions of time

Dean Buonomano, a professor at the University of California (UC), Los Angeles, whose research focuses on neurocomputation and how the brain tells time), explains that the human brain has multiple clocks, or mechanisms for capturing the passage of time. Not all of these clocks function in the same way: “The circadian clock doesn’t have a second hand, and the mechanisms in your brain responsible for, say, timing the duration of a traffic light don’t have an hour hand.” This is why time might appear to be moving slowly while we are engaged in an activity, but appear to have moved quickly for us in retrospect after we have completed that activity: we do not always experience time through the same mechanisms.

Buonomano might have added that not just the brain but the body has multiple clocks, since I’m feeling hungry right now—but that of course is a timed signal to the brain from my stomach or vice versa. Emilie Reas, who was at the time a neuroscience doctoral student at UC San Diego, explained much the same thing in an article entitled, “Your Brain Has Two Clocks.” The hypothalamus with suprachiasmatic nuclei is responsible for our circadian rhythm. Then there’s the amygdala and hippocampus, both of which play a part in perceived time. The dorsolateral prefrontal right cortex is considered the region most involved in time perception. Most older people perceive time moving faster in retrospect and slower in current time because fewer memories are laid down later in life in the hippocampus. 

When neural activity increases via neural transmitters (including via drugs), time seems to expand. Conversely, decreased firings of differentiated neurons slow or shrink perceived time. Amusingly, our since-deceased dog Max and other dogs we know seem to have little temporal awareness (i.e., awareness of the passing of time), since we receive the same enthusiastic greeting whether returning to the house after five minutes or several days or weeks! 

In 2018, Albert Tsao, a neuroscientist at the Kavli Institute for Systems Neuroscience of the Norwegian University of Science and Technology, discovered a neural network that expresses a sense of time in experiences and memories. The studies demonstrated that, by changing the activities engaged in and the content of those experiences, it was possible to change the course of the time signal in the lateral entorhinal cortex—and thus the perception of time.

In 2014, one of Tsao’s co-authors, Edward Moser, and his then-wife May-Britt Moser had received a Nobel Prize for identifying a GPS-like system in the medial entorhinal cortex of the human brain. Mercifully, the brain’s GPS can now be supplemented with electronic GPS in transportation so that people who tend to get lost, such as elderly people (myself included), are less likely to do so.

Multiple sub-mechanisms in the brain perceive time, including subjective time, psychological time, experienced time, episodic time, mind time, etc., etc. These mechanisms of the human brain that retain and differentiate aspects of time are just a smattering of what we have studied to date. Needless to say, human time perception is complex, and much remains unknown.

And then there is transcendentalism, which I will illustrate with two quotations. The first is from Peter Matthiessen:

Zen is really just a reminder to stay alive and to be awake. We tend to daydream all the time, speculating about the future and dwelling on the past. Zen practice is about appreciating your life in the moment. We are beset by both the future and the past, and there is no reality apart from the here and now.

The second is from Gore Vidal. Howard Austin, his long-term companion, asked Vidal on his deathbed: “Didn’t it go by awfully fast?” to which Vidal would respond in his memoirs, “Of course it had. We had been too happy, and the gods cannot bear the happiness of mortals.” 

Time flies when having fun, but it seems to slow when not—such as in the dentist’s chair or waiting in anguish for a vacant Spot A Pot, as opposed to spending time with a favorite companion. The same time interval is recorded by our atomic clocks, but perceived time is different. Gal Zauberman at the Wharton School confirmed that perceived time moves relatively faster with inaction—but only in retrospect, the reason being repetitive behaviors and lack of new experiences. With age often comes inactivity and repetition. The elderly looking backward often marvel at how fast time seems to have passed.

If we accept that time perception is supremely variable—as in the apocryphal response of Lewis Carroll’s White Rabbit to Alice, “I’m late, I’m late, for a very important date!” This suggests time is malleable and can indeed be stretched or shrunken. The mechanism to stretch time is to build in circuit breakers (aka memory anchors, separated by mental baffles) filled with meaningful, enjoyable activities and related memories—so that time in the moment does not seem to move faster due to inaction, particularly as we age. Stretching time is a mental discipline requiring conscious and subconscious separation of events, and an acute sense of the now, aka living in the moment—without being unduly obsessive about time. This gives the sense that more time can become available. In essence, perceived time has expanded because of those mental circuit breakers.

It’s important to stretch the present before it’s lost in the past or becomes part of the future—although after googling “stretching time,” I found endless fitness centers, bodybuilding exercises, stretching lotions, dog walkers and highly creative adult activities.

This modest attempt to shed light on the mystery of time is neither conclusive nor exhaustive. Rather, it’s a brief tour of the issue and some of the multiple towering contributors to the science—physical, biological and psychological. Many delving into the subject of the direction of time, aka the arrow of time, including Hans Reichenbach (1956) and Stephen Hawking (1988), concluded that time is irreversible. I quote Wikipedia one last time:

The arrow of time, also called time’s arrow, is the concept positing the “one-way direction” or “asymmetry” of time. It was developed in 1927 by the British astrophysicist Arthur Eddington, and is an unsolved general physics question. This direction, according to Eddington, could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world (“a solid block of paper”).

The Arrow of Time paradox was originally recognized in the 1800’s for gases (and other substances) as a discrepancy between microscopic and macroscopic description of thermodynamics / statistical Physics: at the microscopic level physical processes are believed to be either entirely or mostly time-symmetric: if the direction of time were to reverse, the theoretical statements that describe them would remain true. Yet at the macroscopic level it often appears that this is not the case: there is an obvious direction (or flow) of time.

But is this true for our imagination? In our imagination, we can bounce between past, present and future. After all, Einstein famously said, “Imagination is more important than knowledge—for knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution.”

Time dilation, and its quantum implications, should convince us that time can be relative, absolute or perhaps even non-existent, depending on the definition, relative to the observer and observed. Quoting Carlo Rovelli again, “the idea that a well-defined ‘now’ exists throughout the universe is an illusion, an illegitimate extrapolation of our experience.”

It’s all a matter of defining “now, as it is with “time”—and it’s now about time for my cup of tea.

[Christopher Schell edited this piece.]

The views expressed in this article are the author’s own and do not necessarily reflect Fair Observer’s editorial policy.