Chunghyoung Lee

Many people believe that human beings begin to exist with the emergence of the 1-cell zygote at fertilization. I present a novel argument against this belief, one based on recently discovered facts about human embryo development. I first argue that a human zygote is developmentally plastic: A zygote that naturally develops into a singleton (i.e., develops into exactly one infant/adult without twinning) might have naturally developed into a numerically different singleton. From this, I derive the conclusion that a human infant or adult is numerically distinct from the zygote she came from and so did not begin to exist at fertilization. This implies that a zygote does not have a “future like ours” and strongly suggests that it is not a human being.

It is shown that the following three common understandings of Newton’s laws of motion do not hold for systems of infinitely many components. First, Newton’s third law, or the law of action and reaction, is universally believed to imply that the total sum of internal forces in a system is always zero. Several examples are presented to show that this belief fails to hold for infinite systems. Second, two of these examples are of an infinitely divisible continuous body with finite mass and volume such that the sum of all the internal forces in the body is not zero and the body accelerates due to this non-null net internal force. So the two examples also demonstrate the breakdown of the common understanding that according to Newton’s laws a body under no external force does not accelerate. Finally, these examples also make it clear that the expression ‘impressed force’ in Newton’s formulations of his first and second laws should be understood not as ‘external force’ but as ‘exerted force’ which is the sum of all the internal and external forces acting on a given body, if the body is infinitely divisible

I challenge the assumption in the debate on the conventionality of simultaneity that a simultaneity relation of special relativity should be defined relative to a single inertial observer, not relative to multiple inertial observers as such. I construct an example of a simultaneity relation relative to two inertial observers, and demonstrate that it is explicitly definable in terms of the causal connectibility relation and the world lines of the two observers. I argue that, consequently, thesimultaneity relation of special relativity is not uniquely definable from the causal connectibility relation.

When two bodies collide with each other, they change their motion. Many physics textbooks explain that the change in motion is caused by the force or impulse exerted on the body during the collision. This is not the whole story, I argue, in case the bodies are rigid. In this case, the change in motion cannot be causally explained solely by how the bodies are configured before and during the collision but instead should be explained partly by what happens after the collision. That is, the collision between rigid bodies should better be interpreted as a case of retrocausation where the future causally affects the past or present. This retrocausal interpretation of the collision does not suffer a general problem raised against retrocausation, known as the bilking argument. And how the influence of the cause propagates backward in time to the effect in the collision is no more mysterious than how a body moves continuously in classical mechanics or how the future affects the past in proposed retrocausal models for the EPR thought experiment in quantum mechanics.

I present a simple model of Grünbaum’s staccato run in classical mechanics, the staccato roller coaster. It consists of a bead sliding on a frictionless wire shaped like a roller coaster track with infinitely many hills of diminishing size, each of which is a one-dimensional variant of the so-called Norton dome. The staccato roller coaster proves beyond doubt the dynamical (and hence logical) possibility of supertasks in classical mechanics if the Norton dome is a proper system of classical mechanics with metaphysical import. If not, challenges raised against the metaphysical significance of the Norton dome are shown to be challenges against various arguments for the dynamical possibility of supertasks, and the staccato roller coaster clearly shows the importance of meeting these challenges. And the staccato roller coaster can provide, as well as interesting lessons, illuminating analyses of Burke’s (Mod Schoolman 78:1–8, 2000 ) attempt to refute the dynamical possibility of the staccato run and Pérez Laraudogoitia’s (Synthese 148:433–441, 2006 ) rebuttal of it.

In the asymmetrical variant of the two-envelope paradox, the amount in envelope A is determined first, and then the amount in envelope B is determined to be either twice or half the amount in A by flipping a fair coin. Contra the common belief that B is preferable to A in this case, I show that the proposed arguments for this common belief all fail, and argue that B is not preferable to A if the expected values of the amounts in the envelopes are infinite. Using the examples I deploy in my arguments against the common belief, I also refute certain proposed solutions to the two-envelope paradox and draw some general lessons

Pérez Laraudogoitia (1996) presented an isolated system of infinitely many particles with infinite total mass whose total classical energy and momentum are not necessarily conserved in some particular inertial frame of reference. With a more generalized model Atkinson (2007) proved that a system of infinitely many balls with finite total mass may evolve so that its total classical energy and total relativistic energy and momentum are not conserved in any inertial frame of reference, and yet concluded that its total classical momentum is necessarily conserved. Contrary to this conclusion of Atkinson, I show that Atkinson's model has a solution in which the total momentum fails to be conserved in every inertial frame of reference. This result, combined with Atkinson's, demonstrates that both classical and relativistic mechanics allow the energy and momentum of a system of infinitely many components to fail to be conserved in every inertial frame of reference.

The view that human beings begin to exist at fertilization (namely conceptionism) faces a serious challenge from the twinning argument, that identical twins coming from the same zygote must be numerically distinct from the zygote and so did not exist at fertilization. Recently, some philosophers have claimed that the twinning argument rests on a particular metaphysical theory of persistence, namely endurantism, on which a human being, for example, is wholly present at every moment of her existence. And we can easily refute the argument, they claim, by employing perdurantism or exdurantism, according to which a human being is a temporally extended entity with temporal parts or a momentarily existing stage who has other momentarily existing stages as counterparts. I argue that such claims are mistaken. The twinning argument does not rest on endurantism and can be formulated in terms of perdurantism to provide a good reason for perdurantists to reject conceptionism. And exdurantism does not have any advantage in defending conceptionism either, for it already concedes more than what the twinning argument aims to show.