Metaphysics of Time: Theories & Paradoxes

Learning Goal: Examine the metaphysics of time, contrast Presentism and Eternalism, analyze the A-theory and B-theory of time, and evaluate the logical coherence of time travel paradoxes.

• Prerequisites: Introduction to basic metaphysical concepts (identity, change, and ontology). No prior physics background is required, though basic familiarity with Einstein’s Special Relativity is helpful.
• Estimated Total Study Time: 10 Hours

Module 1: Introduction to the Philosophy of Time

This module transitions your understanding of time from an intuitive, everyday experience to a rigorous metaphysical inquiry. You will explore whether time is a fundamental, independent feature of reality (Absolutism) or merely a relation between events (Relativism), and address the profound philosophical question: Is the flow of time an illusion?

Recommended Videos

Is Time Real? - Philosophy Tube

@PhilosophyTube04:51139,224

Is Time Real? - Philosophy Tube

This comprehensive exploration examines two fundamental philosophical views on time. A theorists believe time flows through distinct past, present, and future moments with genuine temporal properties. B theorists argue all times exist equally, similar to how all places exist in space. John McTaggart famously challenged both perspectives: he argued B theory fails to account for genuine change, while A theory contains inherent contradictions in its temporal properties. McTaggart's paradox demonstr

@PhilosophyTube · 04:51

Why this video: This video serves as an engaging entry point to the metaphysics of time, framing the core debate between tensed and tenseless frameworks. It bridges the gap between everyday intuitions and formal philosophy by unpacking how we conceptualize the "flow" of moments and presenting the fundamental questions that define the field.

Metaphysics of Time Lecture 1

@lukefenton-glynn713306:20127

Metaphysics of Time Lecture 1

This lecture introduces the metaphysics of time, focusing on McTaggart's influential argument that time is unreal. The course has previously covered space and space-time, but now examines time specifically. Time differs from spatial dimensions in having apparent asymmetry (past/future distinction seems fundamental) and flow (passage of time). McTaggart's argument, published over 100 years ago, remains influential because philosophers disagree on which premises to reject, defining various positio

@lukefenton-glynn7133 · 06:20

Why this video: For students seeking a academic foundation, this lecture transitions the topic from pop-philosophy to rigorous scholarly analysis. It introduces the transition from spatial metaphysics to temporal metaphysics, laying the groundwork for McTaggart's historical challenge to the reality of time.

Time Doesn't Make Sense

@mystiverse08:56207,200

Time Doesn't Make Sense

This video examines fundamental philosophical debates about time's nature, including absolutism (time exists independently of events, as proposed by Plato and Newton) versus relativism (time depends on events, as argued by Aristotle and Einstein), and explores questions about time's structure (whether it is linear or branched), and existence across time (presentism claiming only the present exists, eternalism asserting past and future also exist, and the growing block theory suggesting new prese

@mystiverse · 08:56

Why this video: This video introduces the historic debate between Absolutism (time exists independently of events, advocated by Newton) and Relativism (time is merely an order of relations between events, advocated by Leibniz). Understanding this dichotomy is essential before diving into 20th-century spacetime developments.

Knowledge Checkpoint

• Explain the core difference between temporal Absolutism (Substantivalism) and Relativism (Relationism).
• Define what philosophers mean when they query if the "passage" of time is an illusion.
• Articulate how temporal properties (past, present, future) differ from spatial properties (here, there).

Module 2: The Ontology of Time: Presentism vs. Eternalism

This module dives into the ontological status of temporal states. What actually exists? You will contrast Presentism (only the present exists) with Eternalism (past, present, and future are equally real). Additionally, we will cover the Growing Block Universe theory, a critical middle-ground position where the past and present are real, but the future is not.

Recommended Videos

What Is Time? | Professor Sean Carroll Explains Presentism and Eternalism

@TheGreatCourses30:172,743,928

What Is Time? | Professor Sean Carroll Explains Presentism and Eternalism

This lecture explores two competing philosophical perspectives on time: presentism, which holds that only the present moment is real while the past and future exist only as memory and prediction respectively, and eternalism (the block universe theory), which argues that all moments in time—past, present, and future—are equally real and exist simultaneously as a four-dimensional spacetime continuum. The lecturer explains that while presentism aligns with our intuitive experience of time flowing f

@TheGreatCourses · 30:17

Why this video: Led by physicist and philosopher Sean Carroll, this lecture provides an exceptionally clear breakdown of Presentism and Eternalism. Carroll details the conceptual tension between our subjective psychological experience of time and the objective "block" described by modern physics.

Time, Consciousness & Block Universe Theory - Time Travel, Relativity & The Illusion of Time

@Disculogic01:4251,832

Time, Consciousness & Block Universe Theory - Time Travel, Relativity & The Illusion of Time

The growing block universe theory is an alternative to both eternalism and presentism that is much closer to human intuition. In this theory, both the past and present exist while the future hasn't yet come into being. As time passes, more of the world comes into existence, hence the 'growing' nature of the block. This growth occurs in the present—a thin slice of spacetime where new segments of spacetime are continually added. The theory acknowledges the reality of both the past and the present

@Disculogic · 01:42

Why this video: This concise video introduces the Growing Block Universe theory, explaining how it attempts to respect human intuitions regarding the open, unwritten nature of the future while still treating the past as ontologically secure and real.

Exploring The Metaphysics of Time

@AllSkeptic01:02167

Exploring The Metaphysics of Time

The growing block theory argues that only the past and present exist, while the future does not yet exist. The past is real because we have evidence we lived it, and the present is what we are experiencing now. The future keeps coming and sweeping into the block, growing as it becomes present and then past. This theory implies free will because the future remains open and unknown, unlike eternalism where the future already exists.

@AllSkeptic · 01:02

Why this video: This short presentation reinforces the specific arguments supporting the Growing Block model, focusing on how we justify the reality of the past through empirical evidence, contrasted with the ontological emptiness of the future.

Gap Alert: Independent Study on Growing Block Theory

While the pool videos introduce the Growing Block model, they are highly summarized. To master this concept, independently research the Growing Block Theory (originally formulated by C.D. Broad). Focus on the "dead past" objection: if past moments exist, what makes our current moment uniquely "present" and active, rather than just another static slice of the block?

Knowledge Checkpoint

• Contrast the ontological commitments of a Presentist with those of an Eternalist.
• Explain how the Growing Block Universe theory differs from both Presentism and Eternalism.
• Articulate the "No-Presenter" or "Dead Past" problem that challenges Growing Block theorists.

Module 3: McTaggart's A-Theory and B-Theory

In 1908, J.M.E. McTaggart published a famous proof claiming to show the unreality of time. This module deconstructs his proof and analyzes the resulting division in philosophy: the tensed A-theory (which asserts that past, present, and future are objective, changing properties of events) and the tenseless B-theory (which reduces time to static, permanent relations of "earlier than," "simultaneous with," and "later than").

Recommended Videos

McTaggart on Time (Part 1/2)

@DrBowersOfficeHours09:4113,768

McTaggart on Time (Part 1/2)

John McTaggart argued that time is not real because examining our concept of time reveals a contradiction; he proposed two competing theories of time: the A-theory (tense theory) which holds that events are objectively ordered into past, present, and future with events constantly changing their position in this series, and the B-theory (eternalism) which holds that time consists merely in events being earlier, later, or simultaneous with one another in a static series where no event ever changes

@DrBowersOfficeHours · 09:41

Why this video: This lecture carefully steps through the logic of McTaggart's original argument. It explains the distinction between the A-series and the B-series, clarifying how McTaggart used these concepts to claim that our core understanding of time is fundamentally self-contradictory.

Is Time Contradictory? (The Unreality of Time)

@CarneadesOfCyrene03:3512,563

Is Time Contradictory? (The Unreality of Time)

McTaggart argues that time is unreal because the A series (past, present, future) is inherently contradictory: while no single event can simultaneously be past, present, and future, every event must at some point be all three according to the A series; attempting to resolve this contradiction by appealing to time's reality creates a vicious circle since one must assume time is real to explain how events can have different properties at different times, thereby begging the question against McTagg

@CarneadesOfCyrene · 03:35

Why this video: This animation breaks down the core logical contradiction that McTaggart identified: that every event must possess the properties of being past, present, and future, yet these properties are mutually exclusive. It outlines McTaggart's proof in an easy-to-follow, visual format.

Does God Know What Time It Is? - Emily Qureshi-Hurst

@CosmicSkeptic06:02222,150

Does God Know What Time It Is? - Emily Qureshi-Hurst

Three major theories of time exist: A-theory (presentism, growing block, moving spotlight) posits objective temporal passage; B-theory treats time as a block with before/after relations; C-theory uses only temporal betweenness relations. The A-theory requires universal simultaneity, which relativity theory disproves. Relativity shows time passes differently based on speed and gravity, eliminating an objective 'now.' This has profound implications for understanding divine eternity and human tempo

@CosmicSkeptic · 06:02

Why this video: This video introduces the A-theory, B-theory, and even C-theory frameworks, placing them within a broader metaphysical and theological context. It clarifies how a B-theory block operates without an objective, moving spotlight of "now."

What If Time Stopped? | Philosophy Tube

@PhilosophyTube00:59127,878

What If Time Stopped? | Philosophy Tube

John McTaggart proposed that B-Theorists explain change through temporal parts. Instead of a single object changing over time, there are different temporal parts of the same object existing at different times. For example, a cooling pie has an earlier hot part and a later cool part. The whole pie is a 4D object existing across time. However, McTaggart argued this isn't genuine change—it's just looking at different parts of the same object, similar to how reading a book doesn't change the text it

@PhilosophyTube · 00:59

Why this video: This short video highlights how B-theorists explain change without relying on an objective "flow" of time. It introduces the concept of "temporal parts," where objects are extended in time just as they are in space.

Knowledge Checkpoint

• Reconstruct McTaggart's proof for the unreality of time, explaining why he believes the A-series is contradictory.
• Distinguish between A-properties (tensed) and B-relations (tenseless).
• Explain how a B-theorist accounts for the perception of change through "temporal parts" (four-dimensionalism).

Module 4: Physics Meets Philosophy: The Relativity of Simultaneity

This module bridges physical science with metaphysics. Einstein's Special Relativity destroyed the concept of absolute, universal simultaneity. If what is "now" depends entirely on an observer's frame of reference, Presentism faces a devastating challenge. We will analyze how physics supports the B-theory/Eternalist block universe and evaluate the famous Rietdijk-Putnam argument.

Recommended Videos

There Is No Such Thing as "Now" — and Physics Can Prove It

@SundownScience13:15124

There Is No Such Thing as "Now" — and Physics Can Prove It

Two thinkers, Dutch physicist Cornelis Rietdyke and American philosopher Hilary Putnam, took the relativity of the present and followed it to a conclusion most people would rather not face. The argument: take any event in your future, remember that there exists an observer moving differently from you but standing right beside you at this very instant for whom that future event lies in their present, and that other observer is just as real as you are. If their present is real, then everything in

@SundownScience · 13:15

Why this video: This video directly focuses on the Rietdijk-Putnam argument. It explains how Cornelis Rietdijk and Hilary Putnam used the relativity of simultaneity to prove that observers in relative motion have different "nows." This leads to the conclusion that future events must already exist, dealing a devastating blow to Presentism.

The Andromeda Paradox Explained

@SciencephiletheAI03:29189,510

The Andromeda Paradox Explained

The Andromeda paradox reveals profound implications for our understanding of time. If you and a cat walk in opposite directions from Earth toward Andromeda (2.5 million light-years away), even at walking speeds, you'd experience different 'nows'—you might perceive aliens launching a death laser now, while the cat perceives it as happening in 8.5 days. Both perspectives are equally valid. This leads to the block universe theory (eternalism), which proposes reality is a four-dimensional unchanging

@SciencephiletheAI · 03:29

Why this video: This video unpacks the Andromeda Paradox, the thought experiment at the heart of the Rietdijk-Putnam argument. It illustrates how two people walking past each other on Earth can have different realities regarding whether an alien invasion fleet on Andromeda has launched or not.

Public Evening Lecture: Sabine Hossenfelder (MCMP)

@munichcenterformathematica285506:1410,883

Public Evening Lecture: Sabine Hossenfelder (MCMP)

Einstein's special relativity rests on three principles: finite speed of light, constant light speed for all observers, and nothing exceeding light speed. This leads to the relativity of simultaneity, where events simultaneous for one observer may not be for another. The profound consequence is the block universe concept, where all moments in time exist equally, eliminating a privileged 'now' and making past, present, and future equally real.

@munichcenterformathematica2855 · 06:14

Why this video: Physicist Sabine Hossenfelder outlines the core principles of Einstein’s Special Relativity. This video provides the underlying physics—specifically, the constant speed of light and the resulting relativity of simultaneity—needed to evaluate metaphysical claims about time.

Gap Alert: Presentist Responses to Relativity

The Rietdijk-Putnam argument is often presented as a complete defeat for Presentism. However, metaphysicians have fought back. For a balanced view, research Presentist replies to Rietdijk-Putnam, such as "Neo-Lorentzian Presentism" (which posits a privileged, albeit empirically undetectable, absolute reference frame) or "Point-Presentism" (which limits existence to a single spacetime point).

Knowledge Checkpoint

• Explain why the "relativity of simultaneity" makes it impossible to define a single, universal "now."
• Detail the steps of the Rietdijk-Putnam argument (using the Andromeda Paradox as a model) and explain how it supports Eternalism.
• Evaluate how a Presentist might respond to the threat posed by Special Relativity.

Module 5: The Metaphysical Coherence of Time Travel

Is time travel logically possible? This module evaluates the metaphysics of time travel, distinguishing between physical possibility (what the laws of physics allow) and logical coherence (what avoids contradiction). We will analyze the Grandfather Paradox and the Bootstrap Paradox, and examine David Lewis’s elegant solutions using four-dimensionalist frameworks.

Recommended Videos

How to Change the Past (and Live to Tell the Tale) - Dr Alex Kaiserman

@balliolcollegeoxford575208:462,895

How to Change the Past (and Live to Tell the Tale) - Dr Alex Kaiserman

Defining time travel philosophically encounters a fundamental problem: traveling through space involves being in different places at different times, so traveling through time must involve being in different times at different times, which is nonsensical. David Lewis's solution is based on his four-dimensionalist view: things persist through time by having paths at different times, similar to how they extend through space. These are four-dimensional objects composed of temporal parts or stages.

@balliolcollegeoxford5752 · 08:46

Why this video: This Oxford lecture addresses the philosophical definition of time travel and the apparent paradox of "changing" the past. Dr. Kaiserman introduces David Lewis’s distinctions—specifically personal time (the traveler's internal clock) versus external time (the background coordinate time of the universe)—to show how travelers can affect the past without changing it.

Jim Al-Khalili: Is Time Travel Possible? Determinism, Relativity and the Arrow of Time (2011)

@qedcon04:06234,692

Jim Al-Khalili: Is Time Travel Possible? Determinism, Relativity and the Arrow of Time (2011)

Einstein's relativity mathematically allows time travel into the past through closed timelike curves. However, paradoxes like the Grandfather Paradox (killing your grandfather prevents your birth) and the Terminator Paradox create logical contradictions. The Mona Lisa Paradox involves a painting caught in a time loop without ever being created. These paradoxes suggest time travel into the past may be impossible.

@qedcon · 04:06

Why this video: Physicist Jim Al-Khalili explores the physics of Closed Timelike Curves (CTCs) and the logical constraints they impose, demonstrating how standard physics requires self-consistent loops to prevent paradoxes from occurring.

The Bootstrap Paradox | #DoctorWho

@timeywimeywho01:00391,293

The Bootstrap Paradox | #DoctorWho

The bootstrap paradox is a time travel scenario where an object or information is sent back in time and becomes the cause of its own existence, creating a circular causality loop with no clear origin point. In this DoctorWho example, a time traveler brings Beethoven's sheet music to 18th century Germany, gets it published, and thereby creates the very music that supposedly originated from Beethoven, raising the philosophical question of who actually composed the Fifth Symphony.

@timeywimeywho · 01:00

Why this video: Using a famous pop-culture monologue, this clip explains the Bootstrap Paradox (causal loop). While entertaining, it presents a key philosophical question: can information exist without an original creation event?

Gap Alert: David Lewis, Compossibility, and the Grandfather Paradox

Pop-culture videos often suggest that a time traveler "can" kill their grandfather but "chooses" not to, or that a new timeline branches off. To understand David Lewis's actual 1976 paper "The Paradoxes of Time Travel", you must grasp his concept of compossibility:

Can Tim kill his grandfather? In one sense, yes: he has the gun, the training, and the opportunity (it is compossible with his physical abilities). In another sense, no: it is not compossible with the fact that his grandfather survived, and Tim was born. There is no change to the past; Tim's attempt was always destined to fail in a logically consistent, single-universe block.

Knowledge Checkpoint

• Define the difference between "personal time" and "external time" as formulated by David Lewis.
• Explain the Grandfather Paradox and resolve it using Lewis’s concept of compossibility.
• Describe the Bootstrap Paradox and analyze whether a causal loop is logically impossible or merely strange.

Course Map

Key People Index

• John M.E. McTaggart (1866–1925): British idealist philosopher who proposed the unreality of time by introducing the concepts of the A-series (tensed) and B-series (tenseless).
• Albert Einstein (1879–1955): Theoretical physicist whose theories of Special and General Relativity revolutionized our understanding of time, replacing absolute time with relative spacetime.
• Cornelis Rietdijk & Hilary Putnam: Physicist and philosopher, respectively, who independently formulated the Rietdijk-Putnam argument, showing that Special Relativity demands an Eternalist/Block Universe ontology.
• David Lewis (1941–2001): Influential American philosopher who defended the possibility of time travel in a single, four-dimensional block universe using the concepts of personal/external time and compossibility.
• Sean Carroll (1966–Present): Theoretical physicist and philosopher of science who excels at explaining how the laws of physics intersect with the metaphysics of time and entropy.

Final Self-Assessment

Test your mastery of the Metaphysics of Time with these comprehensive questions:

• Can you define and contrast Presentism, Eternalism, and the Growing Block Universe theory?
• Do you understand McTaggart's proof for the unreality of time? Can you explain why he believes the A-series is contradictory and why the B-series alone cannot construct time?
• Can you explain the difference between the tensed A-theory of time and the tenseless B-theory of time?
• Do you understand the concept of four-dimensionalism (or perdurantism) and how objects can have "temporal parts"?
• Can you articulate the relativity of simultaneity and explain why it poses a major challenge to the Presentist perspective?
• Can you reconstruct the Rietdijk-Putnam argument (the Andromeda Paradox) and explain its support for Eternalism?
• Can you define the Grandfather Paradox and explain David Lewis’s logical resolution of it using compossibility?
• Can you explain the difference between personal time and external time?
• Can you define the Bootstrap Paradox and explain why a causal loop, while strange, does not contain a logical contradiction?