How do we know (i.e. justify our belief) that time exists without "proving too much"?

Question

How do we know that time exists?

This is a complex question.

First, we cannot make sense of a question like this without first establishing what we mean by knowledge.

For convenience, let's pick the popular justified true belief (JTB) definition of knowledge. On this definition, the following conditions must be met in order for us to know that time exists:

1. It has to be true that (some kind of) time in fact exists (for sake of argument, let's grant that this is the case)
2. We must believe this is the case (pretty much everyone does, so let's grant this as well)
3. We need to be aware of a justification for our belief in the proposition that time exists

And here lies the heart of my question: What justification do we have to believe that (some kind of) time exists?

One possible attempt at justification would be to appeal to our subjective personal experience of time (e.g. "I know that time exists because I have the subjective experience of perceiving things changing over time"), but then this kind of justification would be vulnerable to proving too much, since people could just as easily use the same justification to justify other controversial beliefs, such as:

• Belief in ghosts, angels, demons, etc. (e.g. person X says "I know that ghosts exist because I have personally experienced/witnessed ghosts")
• Belief in aliens (e.g. "I know that aliens exist because I have subjectively experienced aliens (I was abducted by aliens)")
• Belief in past lives (e.g. "I have subjectively experienced visions of my past lives")
• Belief in some specific religion (e.g. Mormons for example appeal to the witness of the Holy Ghost; William Lane Craig also makes a similar argument here)
• Etc.

How can we justify our belief in the existence of (some kind of) time without "proving too much"?
Or should we just bite the bullet?

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Regarding justification, this is probably related: Is there an objective standard of sufficient evidence?

Answer 1

This is a basic question of epistemology. How do we know ANYTHING exists.

There are three basic methods:

1. Rationalism -- establish what is the case by reasoning
2. Direct knowledge -- we know what is, by immediate knowledge that is undeniable. There is a variant on this, in that we could have direct knowledge (intuitions) that are NOT certain
3. Indirect inference -- this is the principle of indirect realism that science operates on. Popper's science methodology is the summary of how this is done.

Method 1, rationalism, has been narrowed to -- basically a null set of knowledge of reality. The fist major reduction of category 1 was in Kant's Critique of Pure Reason. Kant held that there were a few aspects of reality that could be established in category 1, but his go-to example was Euclidian Geometry, which we subsequently discovered first was not the only kind of geometry, then further that our world is not Euclidean after all. The pluralism of logic https://www.cambridge.org/core/journals/think/article/guide-to-logical-pluralism-for-nonlogicians/EDFDFA1C9EB65DB71848DABD6B12D877 basically makes any "proof" intrinsically not provable.

Method 2, direct and certain knowledge, has been limited post Descartes to some limited aspect of perception, experience, or agency. Weaker possible knowledge could have a larger suite of features than this, but does not offer certainty.

Method 3, inferential knowledge, appears to be almost the entirety of what we "know".

Note, method 3 does not satisfy your presumed criterion of Justified True Belief. First, for indirect realism, one has no access to "truth" (and logic pluralism makes "truth" relative to a postulated logic anyway), so nothing can satisfy the T of JTB. Also, per the Munchausen Trilemma, no justification can itself be justified without eventually reverting to a fallacy. See this answer on the Trilemma: Is the Münchhausen trilemma really a trilemma? So no beliefs can be true, or justified.

What empiricists use instead as a criteria is usefulness. If a model is part of a vigorous and useful research programmed, which has been successfully answering long standing problems, then one can reasonable infer the reality of what is being modeled. This is Imre Lakatos's Research Programme methodology: http://people.loyno.edu/~folse/Lakatos.html

We know time is real because we experience it (this is one of the undeniable issues for direct realism), AND it is highly useful in logic based understanding of our universe (time, in the form of logic sequence of state changes, is needed for causation, which we basically need to even conceive of our universe), AND it is highly useful in the presentism form to understand motivations and events, AND in its block time version it is needed to understand physics, AND in its growing time mode, it is needed in all applications of history.

"Prove too Much", which your link claims is a demonstrated fallacy, is not a fallacy for any of your listed cases.

• If I had experienced being captured, transported, and probed by aliens, I hold it would only be fallacious reasoning if I then did NOT believe aliens were real! Note indirect realism operates off of subjective observations, and most of what we consider "real" is only verified by first person empiricism. This is also an area where intersubjectivity can be applied.
• I HAVE experience one past life, and reincarnation studies are a field where intersubjectivity HAS been applied. I have also communicated with ghosts, which is also a field where intersubjectivity can be applied. It is hardly "proving too much" for me to believe in both realities. Claims that one cannot ever infer that ghosts or past lives are real, are irrational dogmatism, and would themselves be a fallacious claim.
• A religion is a complex worldview, which cannot be supported by a single observation. It CAN be evaluated by the same methodology that a scientific Research Programme is evaluated. If the Religion is shown to be highly useful in answering questions that other frameworks cannot answer, and its adherents admit to the problems that it cannot answer, but are making progress incrementally in answering them, then a Religion be reasonably assumed to be real. I don not believe any religion satisfies this criteria today, and instead they would all be considered regressive Research Programmes, per Lakatos' criteria. Which makes this only a theoretical concern, not an actual one.

So -- time exists, per the pragmatic standard of utility. So might all of the "prove too much" examples you cited.

Answer 2

Not sure if I'm correctly understanding the crux of the question but the simple answer seems to be that time is a necessary coordinate in a coordinate system. You can't have location without time. (Usually "now" is implied but isn't necessarily the case.)

We tend to think of things having a location of, say, latitude, longitude and altitude. But if you really want accuracy, you must include time as a coordinate. My eyeglasses were on my nightstand at coordinates of X,Y,Z,t. The "t" necessarily defines what time my eyeglasses were at that X,Y,Z location. Missing the "t" is just like missing any other coordinate. If my eyeglasses are at X,Y,t with unknown Z (where Z is altitude) then maybe my eyeglasses were in the basement. Or in the living room above the basement. Or my upstairs bedroom. Or on the roof. Or on an airplane overhead. Missing the Z means we don't know the altitude of my eyeglasses. Missing the t means we don't know what time they were at the X,Y,Z and is therefore also not very useful.

So time must exist because without it we lack a critical coordinate.

(If you also think of space and a coordinate system relative to the galactic center then earth's location is changing in X,Y,Z,t. If you change the t, then the X,Y,Z would be in a different place. If time travel was actually a real thing, the first time travelers would have a terrible problem as they go back in time at the same X,Y,Z, to the year 1860, and find themselves stranded in space because the earth was literally trillions of kilometers away from that X,Y,Z at that t. Hope your time travel machine is also a space ship. Dr. Who would presumably be okay.)

Answer 3

How do we know that time exists?

This requires establishing what we mean by exists.

Belief requires thoughts differentiated by time, the motion of thought. Thought reflecting back on itself.

Quoting Derrida from Heidegger: The Question of Being and History, page 184:

describing time as pure auto-affection, Heidegger writes,

According to its essence, time is pure affection of itself. Furthermore it is precisely what in general forms [aiming: intuition, the way] seeing which, setting off from itself, heads for . . . [which translates so etwas wie das, “Von-sich-aus-hin-auf-zu”] something like the “from-out-itself-toward-there . . . ,” so that the upon-which looks back and into the previously named toward-there. (Kant and the Problem of Metaphysics, 132)

This form of temporality is intrinsic to the being of a human, and the human in conjunction with phenomena constitute the existence of phenomena, such as the physical measurement of time.

Answer 4

Here is my take on this.

The existence of history is a strong indicator that time exists. For example, we can study tree rings, ice cores, alluvial deposits, stalagtite growth marks and the like to demonstrate that plant growth, seasonality and climate all existed long before humans learned how to record their own histories in words.

Furthermore, excellent evidence of the passage of time is obtained through the use of space-time diagrams which furnish accurate predictions of how different observers will experience reality in different coordinate frames.

Answer 5

Appealing to our subjective personal experience of time is perfectly fine, and doesn't prove too much (but you're only justified in believing the simplest explanation for the evidence).

Given our subjective experience, the existence of time is a simpler explanation than the non-existence of time.

Regarding experiences of ghosts, angels, demons, aliens, past lives and religious beings, those can all have a simpler explanation of hallucinations, dreams, misinterpretations of one's experiences, etc. As we gain a better understanding of reality, life, death, our bodies, our brains, the universe, our origins, beliefs of different cultures, etc., fabrications of our minds becomes a more simple explanation, while actual supernatural beings becomes less simple due to a lack of strong supporting evidence and how their existence might conflict or be difficult to explain with our current understanding of reality based on the available evidence.

We already know people can interpret their experiences in a way that conflicts with reality. Yes, this includes hallucinations and dreams, but also optical illusions, seeing a monster that turns out to just be a coat rack, etc.

Regarding time, there is lots of supporting evidence and little to no contrary evidence: you can see evidence of time's existence in reality, others can recount their experience of time for you, our own mental processes indicates the passage of time, etc. These are all subjective experiences, yes, but they all still contribute to making the existence of time the simplest explanation.

If you see a monster, you turn on the light, and then you see a coat rack, this would be strong contrary evidence for the existence of the monster you saw.

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To demonstrate why believing only the simplest explanation is justified, consider this simple example:

You see an empty can on a table. In the absence of any other evidence, do you conclude that:

1. A person put it there.
2. A person put it somewhere else on the table, and the wind blew it to where it is now.
3. The can materialised from thin air.

I would hope you went with #1. The problem with #2 is that it adds an additional unnecessary assumption (person + wind, instead of just person). The problem with #3 is that it relies on something that we have no evidence has happened before, whereas #1 happens all the time. #1 is much simpler than both #2 and #3.

Answer 6

We can observe that things change. Change requires that a thing/system O be in one state A and then another state B such that A != B. Since O takes on states A and B, but A != B, then O cannot simultaneously be in both states A and B. The only resolution is that O take on distinct states non-simultaneously, aka at different times. We know time exists because things change.