Philosophy Discussion
Respond to one of these prompts and be clear about which one you are referring to:
PROMPT #1: A-Theory vs. B-THEORY. Consider this argument: “The subjective A-theory is inferior to the objective B-theory. For the subjective A-theory does not allow us to give a completely objective account of time descriptions. But the objective B-theory does allow us togive a subjective account of time descriptions.” Critically discuss this argument.
PROMPT #2: UNCHANGED WO
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Phil 2: Puzzles and Paradoxes
Prof. Sven Bernecker
University of California, Irvine
The Grandfather
Paradox
Grandfather Paradox
• Grandfather paradoxes arise whenever a time traveler goes into
the past and prevents an event that is a pre-condition of the
traveler making the backward time-journey in the first place.
• Example: You have just finished building a time machine. You
use this time machine to travel back twenty-four hours, cut the
power-supply to your own laboratory so you can’t finish the time
machine that lets you go back in time to cut the power-supply …
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• Another example: A time traveler goes back in time and kills his
grandfather before the grandfather has fathered children. If the
grandfather dies at this point, then one of the time traveler’s parents
never exists. Hence the traveler can’t be born and travel back to kill
the grandfather … and so on.
• Worry: It is impossible to kill your own grandfather because it would
violate the law of non-contradiction – the grandfather would somehow
both survive to become a parent and not survive. If contradictory
situations are impossible, and if time travelers could create
contradictory situations, then time travel is impossible.
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• A backward time traveler
seems to be able to change the
past. But it is impossible to
change the past. But since the
past cannot be changed, time
travel is impossible.
1) By ordinary standards of ability, the backward time traveler
can kill his grandfather
2) But the time traveler cannot kill his grandfather. The
grandfather lived, so to kill him would be to change the past.
It is logically impossible to change the past.
3) Premises (1) and (2) contradict each other
C) Therefore, backward time travel is impossible
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David Lewis’s Solution of the
Grandfather Paradox • Premises (1) and (2) are both true. They do not contradict one
another. The term “can“ in both premises mean different things.
The Grandfather paradox rests on an equivocation about the
meanng of “can.“
• When we say that somebody “can” do something, we mean that
they have the capacity, holding certain things fixed. Which
things we hold fixed will depend upon context.
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• Unlike dogs and cats, I can speak a foreign language, like Urdu.
So there is a sense in which I can speak Urdu. But don’t take me
as your translator when you go to Pakistan, because I can’t speak
Urdu. I have never learned it. When we say “Sven can speak
Urdu”, we are only holding fixed my brain’s linguistic potentialities
— we are saying that Sven could learn it.
• When we say “Sven can’t speak Urdu”, we are holding fixed my
actual knowledge of languages — we are saying that he doesn’t
currently speak it.
• What I can do, relative to one set of facts, I cannot do, relative to
another set of facts.
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• Similarly, holding fixed only the past up to the attempt to kill
the grandfather, the time traveler can kill his grandfather.
However, holding fixed the past following the attempt to kill
the grandfather, the time traveler cannot kill his grandfather.
There is no paradox.
• The argument on slide #5 simply equivocates with respect to
“can.”
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• Q: What will actually prevent the time traveler from killing his grandfather?
• A: The failure to kill his grandfather will be caused by strange coincidences:
His gun jams, a noise distracts him, he slips on a banana peel, he
accidentally shoots someone else, etc.
• To render backward time travel possible we have to assume that a time
traveler cannot change the past even though he can participate in the
past. A time traveler cannot do anything that did not actually happen. But he
can be amongst the people who did make the past the way it was. The
freedom of action of a backward time traveler is severely limited.
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¿Parallel Worlds?
• Imagine that whenever a person travels into the past, the universe
splits into parallel worlds. If this occurs, there is no longer a
contradiction between the grandfather both existing and not existing.
The grandfather may exist in one world but not in the other.
• Parallel worlds allow for coherent scenarios in which the past is
changed
• But this is no longer time travel; it is inter-world travel.
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Add’l Videos about the
Grandfather Paradox
• Short video about the grandfather paradox:
• Slightly longer video about the grandfather paradox
• Video explaining Lewis’s solution to the grandfather paradox:
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RLD. Could there be a world in which there was time, but never any change at all? Explain your answer.
PROMPT #3: FUTURE TIME TRAVEL. Even if backward time travel were possible, you could not change the past. But how about forward time travel? Could you change the future if you traveled into the future? If future time travel were possible, would you do it? Explain your answers.
PROMPT #4: NATURE OF TIME. Is the question of the nature of time a question to be answered by philosophy, or a question to be answered by physics? Explain your answer.
PROMPT #: FATALISM. Suppose you were Osmo and you found the book describing your past and future life in a local library. Would you adopt a fatalistic attitude and why?
And please also provide critical feedback to these two people’s posts.
PERSON 1:
PROMPT #3: FUTURE TIME TRAVEL
I think it is possible to change the future. Unlike going back to the past, there will not be an issue with the causal loops or grandfather paradox. Since it is the fact that things that are supposed to happen in the future still haven’t happened from the perspective of “present”, a time traveler is capable of changing the event in the future. However, there will be an issue: retrocausality. Even though this theory hasn’t yet proved, if it were to be true, then effect can precede its cause in time, meaning that a something that happens later actually causes an earlier event in time. Thus, even the time traveler were to try changing the future action, it has already caused an earlier event to happen and that event has happened; thus it is impossible to change the later event. Yet, at the same time, this theory breaks the law of The Second Law of Thermodynamics, which states that time is driven as we experiment it. Nevertheless, in my opinion, it is still capable of changing the future. Also, if future time travel is possible, I would like to travel to three years from now and see what I am doing, but it’s unlikely that I try to change something in the future even it is possible. I believe that I should just follow what will be waiting for me.
PERSON 2:
Prompt #4:
In my view, the question of the nature of time is a question to be answered by Physics. The key differentiator between Physics and Philosophy in this case is that Physics is rooted in real world experimentation, and that Philosophy is rooted in a logical process in which the mental processes of humans play a major role. Although Philosophy is needed for answering many of the worlds most important questions, the nature of time has to do with the fundamental nature of the physical fabric of reality, which makes it a question best answered by Physics. Because philosophy is not rooted in real world experimentation, the assumptions that are made have more potential to be untrue. Philosophical assumptions ultimately stem from human reasoning, and are therefore subject to human intuition. We know from fields such as quantum mechanics that many of the most fundamental aspects of the universe are actually deeply counterintuitive, rendering any system that relies more than necessary on human intuition to be unideal.
A substantive post is generally >150 words and introduces a new idea or is a meaningful response toanother person’s post. When responding to another person’s post, please either expand the thought, addadditional insights, or respectfully disagree and explain why.
