Have you ever stopped to wonder what, exactly, is “time”? I think I’ve been interested in the idea ever since I saw the movie Back to the Future in 1985. (I was a card carrying member of the BTTF fan club and one day soon I will post the receipts!) I also remember learning in school about how time held a special role in the way Albert Einstein viewed the universe. (See numbers 1-4 on the list below!)
But we don’t have to be an Einstein to have a connection with time. It’s an essential aspect of life that connects us all. You might think of time as a measurement that guides us on when to wake up, when to arrive at work, or maybe how to plan out our personal calendars. However, if you stop and think more deeply about time, you can very quickly see that it’s actually a profound, multifaceted concept that deserves a second thought.
I hope you enjoy spending a bit of YOUR time exploring this remarkable phenomenon. A little warning: number one is admittedly a doozy, but most of the other fascinating facts below are awe-inspiring without feeling like a college lecture.
1a. Time, Gravity, and Spacetime
Time and gravity are deeply connected because gravity, as described by Einstein’s General Relativity, isn’t just a force, but a warping of space and time. You see, stronger gravitational fields cause time to slow down, an effect known as gravitational time dilation. (This, by the way, is a crucial factor in GPS satellite technology.) Spacetime is the four-dimensional fabric that combines the three dimensions of space with time, treating them as a single, interconnected continuum rather than separate entities. Massive objects like planets and stars bend spacetime, creating what we perceive as gravity, and this curvature directly influences the flow of time. In other words, time runs differently depending on gravitational strength and relative motion. To be clear: gravity warps time. Near a massive object like a black hole, time slows down relative to less gravitationally intense areas.
I know this can be confusing, so I’ve broken this information down a little further here:
Einstein had a Theory of Relativity, a Theory of Special Relativity, and a Theory of General Relativity. While they are closely related, they are not actually interchangeable terms!
- Einstein’s Theory of Relativity is a broad term that includes both his Special Relativity (1905) and General Relativity (1915). It refers to his groundbreaking ideas about the nature of space, time, and motion.
- Special Relativity (1905) focuses on objects moving at constant speeds, particularly near the speed of light. It introduced concepts like time dilation, length contraction, and E=mc², showing that time and space are relative to an observer’s motion. (*See more details about E=mc², at very bottom of this article.)
- General Relativity (1915) expands on Special Relativity by incorporating gravity, showing that massive objects warp spacetime, and this curvature is what we perceive as gravity.
So, while General Relativity is part of the broader Theory of Relativity, the latter also includes Special Relativity, which does not involve gravity.
1b. Time Dilation in Relativity
Einstein’s theory of relativity demonstrates that time is not absolute. For example, a clock on a moving spaceship runs slower compared to a clock on Earth. This effect, known as time dilation, has been confirmed with precise atomic clocks.
A thought experiment that helps explain this aspect of relativity is called the Twin Paradox. If one twin travels near the speed of light and the other stays on Earth, the traveling twin will age more slowly, creating a fascinating paradox in time’s flow.
2. Time as a Fourth Dimension
In physics, time is often considered the fourth dimension, inseparably linked with the three spatial dimensions found in the above-mentioned concept called spacetime. Remarkably, this means that events are not just located in space but also in time.
3. Subjectivity of Time Perception
Psychologically, our perception of time can stretch or compress depending on our experiences. Exciting moments seem to fly by, while stressful or monotonous situations feel endless.
Another way of looking at this idea is over the span of a lifetime. When my father was in his 70’s, he remarked how it seemed like time moved faster as he aged. For example, the idea of going away for a year when you are in high school might seem like forever, but when you’ve lived 75 years, dedicating a year to learn a new skill or work on a special might not seem like such a huge amount of time. Then again, someone else may see time in their senior years in a completely different way. It’s so interesting!
I recently spoke to a five year old and told her: “I have lived the length of your life, every single day of it, ten times!” (I am 50.) We both giggled at how funny that seemed.
4. Arrow of Time
The “arrow of time” refers to the one-way direction of time’s flow. It is closely tied to entropy, which is the measure of disorder in a system. Entropy is considered the fundamental reason why time moves in one direction. According to the second law of thermodynamics, the universe moves toward greater disorder, which gives time its irreversible nature.
Interestingly, the theories that we use to understand these mind-bending aspects of physics are not entirely settled, nor are they proven to be the definitive “answer” of how the cosmos runs. In fact there are fairly new ideas such as gravity being “emergent”.
Emergent gravity is the idea that gravity is not a fundamental force, but rather something that arises (or emerges) from deeper underlying principles, much like how temperature emerges from the motion of particles. This concept suggests that gravity is a result of the collective behavior of microscopic components of spacetime, possibly linked to quantum mechanics and information theory. One of the most well-known proposals for emergent gravity comes from physicist Erik Verlinde, who argues that gravity is an entropic force, meaning it emerges from the statistical behavior of fundamental bits of information in spacetime. Some argue that this theory has not proven to be so, (see this article: https://arstechnica.com/science/2024/11/emergent-gravity-may-be-a-dead-idea-but-its-not-a-bad-one/) but there is still so much work left to be done before we truly understand this aspect of the cosmos.
5. Eternalism vs. Presentism
Philosophers debate whether only the present is real (presentism) or if past, present, and future all exist simultaneously (eternalism). Eternalism aligns with the block universe theory in physics, where time is like a frozen landscape.
Some physicists, like Julian Barbour, argue that time is an emergent property or even an illusion. In quantum mechanics, some equations don’t require time to operate, suggesting that what we perceive as time might be a byproduct of other phenomena.
The idea of time being emergent is similar to the idea of gravity being emergent, but they stem from slightly different theoretical perspectives. Both concepts challenge the notion that these are fundamental aspects of the universe, instead suggesting they arise from deeper, underlying principles:
Emergent Gravity (e.g., Erik Verlinde’s theory) proposes that gravity is not a fundamental force but emerges from the statistical behavior of microscopic degrees of freedom in spacetime, much like how temperature emerges from the motion of particles.
Emergent Time suggests that time itself is not fundamental but arises from deeper quantum processes, such as the entanglement of quantum information, thermodynamic principles (entropy increase), or the large-scale behavior of the universe.
6. The Multiverse and Parallel Timelines
Theoretical physics suggests the possibility of multiple timelines or parallel universes where time unfolds differently. The Multiverse is the idea that our universe is just one of many, each with its own laws of physics, realities, or even versions of ourselves. Parallel Timelines suggest that every decision or event creates a branching path, leading to countless alternate realities where different outcomes have played out. These concepts are fascinating because they challenge our understanding of reality, fate, and free will, raising questions about whether different versions of us exist elsewhere. They also inspire countless stories in science fiction, exploring “what if” scenarios that push the boundaries of imagination and scientific speculation.
7. The Planck Time
The smallest meaningful unit of time, known as the Planck time, is about 10−4310^{-43}10−43 seconds. Below this scale, the laws of physics as we know them break down.
8. Time and Memory
Time creates context for memories. When memory malfunctions, as in conditions like amnesia or Alzheimer’s, the sense of time collapses, leaving people trapped in fragmented pasts or uncertain presents.
Additionally, memory shapes how we perceive time. Without memory, we would live in an eternal present, unable to distinguish between past and future. This ties to identity: our sense of self depends on our ability to remember the past.
9. The Leap Second and Leap Year
Leap Second: To synchronize atomic clocks with Earth’s irregular rotation, scientists occasionally add a “leap second” to global timekeeping. This rare adjustment highlights the mismatch between human constructs of time and nature’s rhythms.
Leap Year: February 29th exists only once every four years due to the Earth’s orbital period not being a perfect 365 days.
10. Nostalgia and Time’s Emotional Impact
Nostalgia is a bittersweet emotion tied to the passage of time. It allows us to revisit cherished memories, offering comfort and a sense of continuity in our lives. However, it can also create a longing for a past that may be idealized or impossible to return to. Nostalgia shapes our identity, and it can help us bond with others as we collectively reminisce and reflect upon all that has changed through the years.
11. Deja Vu
Déjà vu is the eerie sensation that you’ve experienced a moment before, even though you know it’s happening for the first time. Scientists believe it may be caused by a glitch in memory processing, where the brain mistakenly interprets new information as a past memory. It’s a fascinating sensation that just about everyone experiences. Déjà vu raises scientific and philosophical questions about memory, time, and even, perhaps, the nature of reality.
12. Biological Clocks
Our bodies run on circadian rhythms. Circadian rhythms are natural, internal processes that regulate the sleep-wake cycle and repeat roughly every 24 hours. These rhythms are influenced primarily by light and darkness. Disruptions to circadian rhythms can occur due to irregular sleep schedules, exposure to artificial light at night, a major shift in your work schedule, jet lag, or underlying health conditions. A disrupted circadian rhythm can negatively impact sleep quality, mood, and overall health.
Biological clocks regulate the body’s rhythms not just on a daily basis but across an entire lifetime. They strongly influence our growth, aging, and long-term health. From infancy, when sleep patterns are irregular, to adulthood, when circadian rhythms stabilize, and into old age, when sleep cycles shorten and shift, these internal clocks adapt to different life stages. They also control developmental milestones, such as puberty, fertility cycles, and the gradual slowing of metabolic and cellular processes with aging.
13. Chronophobia and Aionophobia
Some people experience fear of time passing (chronophobia) or fear of eternity (aionophobia). These fears highlight the deep psychological impact of time and its inevitability.
14. The Timeless Nature of Dreams
Dreams often seem to last hours, yet they occur in mere minutes during REM sleep. This disconnect between dream time and real time reflects the brain’s creative relationship with time during unconscious states.
When we dream, events can seem to stretch or compress or even skip around, reflecting how the unconscious mind processes time differently from waking life. Carl Jung was a Swiss psychiatrist and psychoanalyst who explored the role of “the unconscious”, archetypes, and individuation in human development. He believed that dreams were a gateway to the unconscious, revealing symbolic messages from the deeper self that could aid personal growth and self-discovery. Jung was interested in the ways past, present, and future could merge when dreaming, allowing the psyche to access deeper insights beyond ordinary chronological constraints.
15. The Concept of “Deep Time”
“Deep time” refers to the vast geological time scale of Earth’s history. It’s so vast that human minds struggle to comprehend it. Fossil records and climate changes remind us of humanity’s brief role in this timeline.
Carl Sagan’s Cosmic Calendar compresses the universe’s 13.8-billion-year history into one calendar year:
- The Big Bang occurs on January 1.
- Humans emerge only in the last seconds of December 31.
This perspective highlights how brief human existence is on a cosmic scale.
The Clock of the Long Now is a project designed to run for 10,000 years, encouraging long-term thinking. Located in Texas, it’s a monumental effort to make people think beyond the short-term urgency of everyday life.
And let’s not forget INFINITY!
Infinity is the concept of something that has no limits or end, existing beyond finite measurement. As far as I understand, infinity can exist in three ways: Math, Time, and Spacetime.
In math, infinity appears in concepts like never-ending sequences, unbounded numbers, and set theory, where different sizes of infinity exist (e.g., countable vs. uncountable infinity).
In time, infinity suggests an eternal past or future, raising questions about whether time has a beginning or stretches endlessly forward.
In spacetime, infinity plays a role in black holes, the expansion of the universe, and the idea of an infinite multiverse, challenging our understanding of boundaries and the nature of existence.
Breaking Down the Role of Infinity in Spacetime:
- Black Holes and Infinity:
Inside a black hole, gravity is so strong that it collapses matter to an infinitely dense point called a singularity. At this singularity, known physical laws break down, and quantities like spacetime curvature and density approach infinity, meaning they become mathematically undefined. - The Expansion of the Universe and Infinity:
The universe is expanding, and depending on its geometry, it could be spatially infinite—stretching forever without end. Even if the universe is finite, its expansion suggests an infinite future, where galaxies move farther apart indefinitely. The accelerating expansion, driven by dark energy, could push the universe toward a state where time and space seem to stretch infinitely apart. - The Infinite Multiverse Hypothesis:
Some cosmological models propose an infinite multiverse, where spacetime extends infinitely, leading to infinitely many universes. This could mean every possible version of reality exists somewhere, or that the universe endlessly cycles through different states.
Why This Challenges Boundaries and Existence:
Infinity in spacetime disrupts our usual understanding of limits, beginnings, and endings—suggesting that reality may not be confined to a single, finite structure. Whether through black holes, the vastness of the cosmos, or the possibility of endless parallel worlds, infinity forces us to reconsider the very nature of existence.
I’ve added Infinity as sort of a bonus, because it’s such a huge topic. It certainly does seem to belong near the above concept of Deep Time (#15). It’s utterly mind-bending to consider the idea that time has always existed or always will exist. And even though that may be so, this blog post is NOT infinite — although it might have felt that way — but you have, in fact, reached THE END!
But wait, there’s more!
You may be wondering, why was E=mc², Einstein’s famous equation from Special Relativity, mentioned in an article about time? You may be wondering, isn’t that equation directly related to the atomic bomb? Well, yes, it is! Actually, the fact that we can make an atom bomb is working proof that he was correct about his theory. It states that energy (E) and mass (m) are interchangeable, connected by the speed of light squared (c²), which is an enormous number—meaning that a small amount of mass can be converted into a huge amount of energy.
How E=mc² Relates to the Atom Bomb
In nuclear fission (the process that powers an atomic bomb), splitting a heavy atom like uranium or plutonium results in a tiny loss of mass. According to E=mc², that lost mass is converted into a massive burst of energy, which is released in the form of a powerful explosion. This principle underlies how nuclear reactions work, both in bombs and nuclear power plants.
How E=mc² Also Connects to Relativity
While E=mc² explains the potential energy stored in matter, Special Relativity also shows that space and time change depending on an observer’s motion (e.g., time slows down at high speeds). Though these concepts seem separate, they are both consequences of Einstein’s deeper insights into how the universe works—linking energy, mass, space, and time in a unified framework.