Abstract

Most people intuitively experience time as universal that flows at the same rate, carrying a single objective “now” from past to future. Time seems straightforward in everyday life, we experience a flowing present moment, a fixed past, and an uncertain future. We will find out how there might be no universal now, and these effects are the most pronounced near black holes where time behaves in ways that seem paradoxical from our everyday perspective. Relativity overturned the Newtonian view of time as absolute and universal, replacing it with a picture that depends on the observer’s state of motion and position in the gravitational field. These relativistic effects are most extreme close to a black hole. For the purpose of this paper let's imagine Bob who is approaching the horizon while he sends a signal to an astronaut who receives the signal away from the horizon called Alice. For a distant observer an infalling object appears to slow down and freeze at the event horizon, never quite crossing it. This raised questions for our philosophy of time: if simultaneity is not absolute can we maintain the existence of a single universal present? Black holes drive this question by providing natural cases where two perspectives diverge radically and irreconcilably and force us to consider what it means for an event to happen now.

This paper explores how blackhole physics challenges presentism and undermines the view that the present is supreme and is global and objective. In contrast I discuss other theories like eternalism which treats all time as equally and and the growing block theory which does not believe in the existence of a future while believing in the past and its causality in the present. By comparing these metaphysics of time with the structure of spacetime I will argue that black holes provide compelling support for non present conceptions of time and explain our notion of time.

Presentism

It is the view that only the present moment exists. The past no longer exists and it has ceased to be and the future does not exist yet. Only now is real, and this closely aligns with our everyday experience. We inherit a present that is constantly changing with the past going into non-existence and the future emerging (Ingram, n.d.). In curved spacetime near black holes no such global now exists that is consistent with causality. When Bob is approaching the horizon from Alice's perspective, is Bob still part of the objective present? Alice can live out the entire future of the universe while Bob emits fainter signals. Bob's present must include events far into Alice's future. If presentism is true then huge chunks of the universe’s future must come into existence in a second of Bob's time; the edge of reality would jump forward discontinuously in an observer dependent way (Romero, 2014).Such behaviour appears to be ad hoc and violates the spirit of relativity which refuses to privilege any observer's frame. A common argument to rescue presentism is by using the now defined by stationary distant observers which implies nothing enters black holes and doubts the integrity of black hole interior which is contradicted by general relativity which describe the interior geometry pretty well (Curiel, n.d.)

Eternalism

Eternalism holds that all times past and present future exist equally, the present moment has no special ontology, it is our current location “now” analogous to “here” in space. Eternalism avoids all these difficulties. Just as all spatial locations exist even though we can only be at once place at a time, similarly all temporal locations exist even though we can only experience one moment in time. The passage of time is an illusion and a feature of conscious experience more than reality. The universe is a four dimensional spacetime block and time flowing is our subjective path through it. Eternalism avoids many difficulties. The spacetime is a fixed four dimensional manifold containing both the exterior region and the interior region reaching the singularity (Besnard, 2011). The apparent freezing seen by Alice is simply because of her coordinate system. When she watches something fall into a black hole it looks to her as if the object slows down and freezes at the edge, but that is a trick. If we use coordinates that behave normally at the horizon we see spacetime is perfectly smooth. We don't need a universal now near a black hole; different observers have different ideas of what counts as simultaneous. It means they are slicing the same four dimension spacetime in different ways (Thorne, 1994).Furthermore, from the theory’s perspective the entire history of the black hole and everything falls into a four dimensional structure in spacetime. We can track Alice’s time coordinate or Bob’s proper time. Both descriptions are valid because they are describing the same geometric object using different coordinate systems. Also working with a continuously changing three dimensional space evolving through time is harder than working with a static four dimensional spacetime.

Growing block theory

This theory represents a middle ground. According to this view the past and present exist but the future does not. The universe is like a growing block constantly adding new layers of present moments that immediately become part of the existing past. Time genuinely flows in the sense that reality itself expands with new events coming into existence. Once events occur they remain part of the existing past, but future events have no reality until they become present. At the same time it inherits many of presentism’s problems: to define where the block ends one needs a privileged view separating what exists to what does not. Near a black hole any candidate either jumps forward discontinuously as an observer approaches the horizon. The theory appears flawed and unmotivated in the context of general relativity (Barbour, 1999).

Mainly it avoids the biggest problem facing presentism: it doesn't require the past to cease existing once Bob crosses the event horizon. From Bob’s perspective the event becomes part of the fixed past and remains real, and the theory does not require us to say the events and its causality does not exist.However theory still requires an objective present, an edge to the block where new events are coming into existence. From Alice’s perspective the edge of the growing block has Bob approaching the horizon, and from Bob's perspective the edge of the block has him inside.An argument against would be that the block can grow differently for different observers with no objective present, but this would undermine the theory since the whole point of the theory was the idea that the universe changes by adding new moments of time, and becoming relative to observers would make it lose its distinction from eternalism, so it becomes eternalism with an observer dependent growing edge of time.

Objections & Context

Presentism matches our phenomenology with a dynamic present; eternalism matches with modern physics and fixes the problem of how the past can affect the present if it no longer exists; while growing block theory captures our sense that the past is fixed and the future is open and preserving the causality of the past.

A defender of presentism might argue that relativity does not eliminate the present but merely complicates the measurement. The absence of a universal simultaneity frame reflects our limited ability to synchronise clocks under relativistic conditions, not the nonexistence of the present itself. On this view there could be still an objective present that is independent of any observer frame of reference even if physics cannot detect or describe it. Thus relativity might reveal the limits of scientific description rather than falsity of presentism.

However I would argue that a present that is fundamental yet in principle unobservable looks ad hoc compared to eternalism which fits relativity without extra assumptions. Insisting on a single true present would be breaking the rule that all observers are equal and thus sneaking a preferred frame which general relativity forbids.

I would also add context to our broader discussion about how consciousness is a presentist mechanism, and the past in our brain is stored patterns reconstructed with each recall, and the future is the probabilities and simulations created by the brain in which brain could be a perceived as a prediction engine and the present is the only place where consciousness exists (Seth, 2021). So the entire experience of the flow of time and our phenomenological experience of it is a core feature of consciousness and subjective to us rather than a verdict on an independent non observer/non experiencer view of time. So physics gives us a view of time from nowhere while consciousness gives us the view from within. The metaphysical structure of time might be eternalist; however it is evolutionary adaptive to have a bias for presentism. Again what is phenomenologically intuitive does not correspond with the deep structure of a strange reality.

Implications

If eternalism is correct then the passage of time and the feeling that we move from past to future is not a feature of reality but our experience of reality. My birth, my writing of this paper, my death are equally real and part of the Four dimension structure of spacetime. If the future already exists then is free will an illusion? Eternalism does not imply determinism. The future is not already written but it simply exists as part of the block.

Black holes serve as a testing ground for our theories of time, they reveal that our intuitive presentist conception of time is inadequate to describe reality. Near black holes there is no objective present moment. No, the universe does not consist of a three dimensional space moving through time but a four dimensional spacetime manifold in which past, present, future exist.

This does not invalidate our everyday experience of our time. We do experience time as flowing, and for practical purposes we can treat the fleeting present as special and cherished, but this experiential flow “passage of time” is not a feature of reality but its a feature of consciousness. Einstein himself is quoted as saying “people like us who believe in physics know that distinction between past and present future is only a stubbornly persistent illusion” (Pais, 1982). The profundity of this is to realise that the entirety of existence at all times forms one magnificent interconnected whole.

By examining how time behaves in these extreme conditions we learn about gravity, spacetime, and also about the structure of reality and realise that time is stranger than we think.

Conclusion

Black holes dramatise the relativity of simultaneity more vividly than any other system, and the fact that a distant observer never sees anything cross the event horizon while a freely falling observer crosses smoothly and quickly. This paradox is the reason the existence of a single objective present moment cannot be true. The growing block theory faces similar issues, and only eternalism emerges as the only view compatible with the geometry of general relativity. Time does not flow even though our subjective experience is that; instead it is a part of a four dimensional spacetime manifold which simply exists.

References

Romero, G. E. (2014). Present time and presentism in black hole spacetimes. Foundations of Science, 19(4), 297–308 https://doi.org/10.1007/s10699-013-9338-6

Besnard, F. (2011). Time of philosophers, time of physicists, time of mathematicians . arXiv:1104.4551.https://doi.org/10.48550/arXiv.1104.4551.

Pais, A. (1982). “Subtle is the Lord…”: The science and the life of Albert Einstein. Oxford University Press.

Rovelli, C. (2017). The order of time. Riverhead Books.

Thorne, K. S. (1994). Black holes and time warps: Einstein’s outrageous legacy. W. W. Norton & Company.

Barbour, J. (1999). The end of time: The next revolution in our understanding of the universe. Oxford University Press.

Seth, A. K. (2021). Being you: A new science of consciousness. Dutton.

Curiel, E. (2023). “Black Holes.” Stanford Encyclopedia of Philosophy, Metaphysics Research Lab, Stanford University Singularities and Black Holes

Nerlich, G. (2019).“Time.” Stanford Encyclopedia of Philosophy, Metaphysics Research Lab, Stanford University Time (Stanford Encyclopedia of Philosophy).

Ingram, D. (2020). “Presentism.” Stanford Encyclopedia of Philosophy, Metaphysics Research Lab, Stanford University.Presentism (Stanford Encyclopedia of Philosophy)