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Paradoxes don't exist in nature, so why does the grandfather paradox make sense in physics?

This question has no mathematical or physical answer and can only have a philosophical answer.

Seemingly true mathematical logic is based on axioms where we just assume they are true without any proof and philosophically the only thing we are sure exists are humans I think therefore I exist.

I understand that mathematics may encounter many paradoxes of logic, but in nature and physics no paradox exists.

So why do we exclude the possibility of traveling in the past, by the paradox of the grandfather based on a mathematical logic which admits the possibility of having paradoxes, but in physics and in nature no paradox exists...

I believe that even if a traveler travels in the past and eliminates all his ancestors or even all of humanity, nature, which does not like paradoxes, will make him exist even without a father and mother.

And after that I wonder if we could exist without father and mother?

What if we all existed before time even existed?

And if the front bigbang is made of an infinity of fatherless, motherless humans who were born in the past or the present or the future of our universe, that's why the grandfather paradox does not exist, and that the equations of the universe are understandable by humans, who are a strange matter that switches between two states dream and reality and that exists before the universe and in the universe and after the universe?

in any case the only thing that is sure to exist at 100% are humans...

And I end this question with a poem which goes in the same direction of this philosophical idea of ​​"I think therefore I exist" and which goes beyond this idea to say that any point and even the universe exists" because all is a human or a group of people who think therefore there is...

“Points and humans and the universe:

I am a simple point who thinks I am the end point. (A human like the others)

One point multiple (thoughts) and at the same time alone (one person).

I can be in a complex (mind) or simple (reality) plan.

When I see my multiple points away from me. (not be human)

I remind them that we are one point. (We are all Humans)

Every point away from me does the same thing as me. (I’m a Human)

And every point close to me dreams with me.

All points are reminiscent of the points.

And there are certain points that follow imaginary paths (Friendship and Love).

To remind you at the end point that he is not alone.

It is thanks to that that the universe moves.

And who are you?”

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  • "but in nature and physics no paradox exists" Maybe we have to expand on it... what about Schrodinger's cat and similar? Paradox - different from contradictions - are "unexpected" results that we deduce from some accepted scientific theory that do not "fit" with our common sense or our "natural" expectations. If so, they are always due to an interaction between theory and nature. May 10, 2022 at 11:11
  • The solution to the grandfather paradox can also be that all humans exist without a father or mother before the existence of time, so there isn't really a paradox, and this idea is neither physical nor mathematical and goes beyond and can have a purely philosophical meaning...
    – newuser10
    May 10, 2022 at 11:20
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    Maybe another possible solution is that we cannot change the past... May 10, 2022 at 11:52
  • This solution comes from a mathematical paradox and in nature no paradox exists, if a mathematical paradox exists in a theory it necessarily means that something is wrong and that the mathematical theory must be reviewed.
    – newuser10
    May 10, 2022 at 12:04
  • Without having enough knowledge of time (a mystery for science), of the universe, and of what lies behind our senses, you are naively assuming that physical paradoxes don't exist. That is a simple fallacy of extrapolation. For Kant, an elementary failure of reason is taking conclusions that reach far more than we know (some types of metaphysical knowledge would be therefore impossible). It is possible for a paradoxical natural physical behavior to lead the universe into a self-destruction or overgrowth our senses can't perceive.
    – RodolfoAP
    May 10, 2022 at 16:30

2 Answers 2

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Well, if we define "Paradox" as "apparent contradiction in physical descriptions of the universe" then sure. Paradoxes don't exist in nature because a paradox is a contradiction in our DESCRIPTIONS of the universe, not contradictions in the UNIVERSE ITSELF.

So under that definition, you're probably right that in nature, no paradox exists. But in PHYSICS (or ANY study of the real world) paradoxes are all over the place.

Normally, a paradox exposes the limitations of a theory or framework by using it to arrive at a conclusion that seems absurd. It ALSO usually imposes a constraint on the world that theory is supposed to be representing. Consider...

Russel's Paradox: Say a barber shaves everyone in town who does not shave himself. Does the barber shave himself?

This paradox was actually used really effectively to create a consistent version of Set Theory. But also, in the real world you can't have a barber who shaves everyone who does not shave himself, BY THE DEFINITION of "shaving" and "himself".

Others PURPORT to show a weakness in the theory, but actually point to something being possible in the physical world that we think is absurd. Consider...

EPR Paradox. If you have a system decay into two parts that must have zero total momentum (because the thing that decayed has total momentum), then when you measure one, you know the state of the other immediately, even if it's on the other side of the universe. If the states weren't pre-determined because Quantum Mechanics, then that means the former was sending a signal to the latter faster than the speed of light, and that's bad.

Turns out, Entanglement is actually a thing. We probably can't use it to make magical sci-fi signal transmitters, but the thing E and P and R thought was absurd actually happens and we've since measured it.

Others try to reach an unexpected conclusion using a theory we trust, but actually end up slowing a weakness in the theory itself. That normally comes from using some flawed reasoning or a theory that doesn't apply. For example...

Zeno's Paradox: Say Achilles gets into a footrace with a tortoise who was given a head start. Since the tortoise moves forward whenever Achilles closes some distance, the former can never pass the latter.

Zeno came up with this paradox to argue against our understanding of the motion and change in the real world, but it's resolved when we consider that a certain geometric series converges.

So which is the Grandfather Paradox? Is it a paradox that limits what can exist in the real world? A way of showing that time travel is impossible because doing so would lead to a contradiction? Or is time travel possible if the universe functions a certain way (say, by pulling a Marvel Cinematic Universe and using the Everett's Many Worlds interpretation of Quantum Mechanics to make it possible)? Or are our attempts to use fancy reasoning to make the Grandfather Paradox consistent really just exposing the flaws in our own reasoning?

I suppose the answer is up for debate, but I can say one thing: Arguing that nature must conspire to make something possible because it's a paradox but in nature no paradox exists is NOT a good approach. That reasoning can be shown to be flawed in lots of different ways.

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The Grandfather Paradox exactly aims to draw attention to a contradiction, that if the conditions exist to create closed time-like curves we open the door to a paradox. So we can be pretty sure General Relativity isn't the whole story. Or, materials with positive gravity, or Tipler Cylinders, aren't possible for some fundamental reason. Closed time-like curves can't loop to 'before' they are created. They have to be created, continue to exist, then causality-affecting objects travel back through them, so this could mean they are possible, while explaining why we haven't seen them impact our universe - they could be too unstable to form naturally.

The alternatives to GR are extremely varied, like branching multiverses, emergent time, two-time physics, M-theory multiverses, etc etc. Quantum Field Theory is considered our best theory, and just takes time as an assumption. GR pictures time as a dimension. But both theories are (almost entirely) reversible, and leaving a conundrum about where the initial low entropy state of the universe came from, and how come irreversibility is such a dominant feature of our experience. In short, we don't know what time is, & our best theories are incompatible.

Consider the Sorites Paradox, also called The Paradox of the Heap: at what number of grains of sand, do we get a heap? This exposes the real utility of paradoxes, in exposing contradictions in our premises. In practice a collection of grains doesn't suddenly become a heap, there is a size & context where the two descriptions overlap, & the assumption the two descriptions are mutually exclusive, is faulty. The paradox exists in the world, there is a number of grains of sand we describe as grains, & that we call a heap, even if different people draw the boundaries differently. The Grandfather Paradox is telling us something about how we currently think about time, implies contradictions.

Descartes 'Cogito ergo sum' is fatally undermined by The Private Language Argument. When you use complex concepts like 'self', 'think' & 'exists', you draw on a whole cultural history of people comparing experiences and drawing analogies, to give those words meaning. We can see from The Dunbar Number that our neocortex emerged to be able to figure out the intentions of others, & our sense of identity, the self, emerged as a tool in that social context. Octopuses are clever, & very unusually solitary for such intelligences, but they are limited to the capacities of 1 individuals brain in 1 life, because they cannot pass on knowledge with language - which depends on a social self.

In Buddhist thought they describe this pattern as 'dependent arising', or inter-being, & they have this great metaphor for it, Indra's Net. It is by engaging with others intersubjectively, that any complex abstractions exist at all. Your self is a tool your experiences with others have taught you to use.

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