Thursday, 27 December 2012

There is no Twin Paradox

For the twin paradox to be considered a true paradox the framing of the scenario must be stringent, that is to say we cannot permit assumptions to be ignored. Therefore I must start with a short description of the twin paradox followed by identification of the inherent assumptions.

I am going to use a variant of the Twin Paradox from EinsteinLight with some very slight editing for the sake of clarity:

Jane and Joe are twins. Jane travels in a straight line at a relativistic speed v to some distant location. She then decelerates and returns. Her twin brother Joe stays at home on Earth. …

Joe observes that Jane's on-board clocks (including her biological one), which run at Jane's proper time, run slowly on both outbound and return leg. He therefore concludes that she will be younger than he will be when she returns. On the outward leg, Jane observes Joe's clock to run slowly, and she observes that it ticks slowly on the return run. So will Jane conclude that Joe will have aged less? And if she does, who is correct? According to the proponents of the paradox, there is … symmetry between the two observers, so, just plugging in the equations of relativity, each will predict that the other is younger. This cannot be simultaneously true for both so, if the argument is correct, relativity is wrong.

The author, Joe Wolfe, goes on to explain that asymmetry resolves the paradox, an explanation that I do not find to be entirely satisfactory.  He uses a flash animated pair of diagrams to support his argument:

Are the space-time diagrams symmetrical? Parts of them are. The first three years of the diagrams for Joe's frame and Jane's departing frame are symmetrical: each twin sends three greetings but only receives one. The last year and a half of Joe's frame and Jane's returning frame are also symmetrical: each sends two greetings and receives four. But the diagrams are not symmetrical in between. Why not?

Look at Jane's diagram. From Jane's point of view, immediately after she has fired her engines, she begins receiving Joe's greetings more frequently. This does not surprise her: she has gone from travelling away from the sender of the greetings and is now travelling towards him.

Jane observes this change as soon as she turns around, which is for her the midpoint of her voyage. (She now receives blue shifted messages instead of red shifted ones. One could apply the same relativistic Doppler factor to the frequency of arrival of the messages.) Joe, on the other hand, doesn't start to receive messages at a higher frequency (blue shifted messages) until considerably after the midpoint between Jane's departure and arrival, simply because the effect of Jane's acceleration and changed reference frame takes a while to get to him: he doesn't see the high frequency arrival of messages until the arrival of the first message that Jane sends after she turns around.

This is a clear example of where the asymmetry of the twins appears. The causes of this asymmetry are the fact that Jane reverses direction and Joe does not, and the finite time that light takes to transmit this information to Joe means that Joe doesn't get the news immediately. Jane leaves one inertial frame and joins another, and she has the effect of that change immediately. Joe, on the other hand, doesn't notice the effects of Jane being in a different inertial frame until much later because she is a long way away from him when it happens. The asymmetry is as simple as that.

There are a few if not hidden, then obscured assumptions, which are perhaps only obvious when one takes time to search for them.

"(S)ome distant location" appears sufficiently vague as to avoid creating problems but an inherent assumption is that this location shares the same frame as Joe.

By placing Joe on Earth we hide (or obscure) the other assumption, which is that we also share the same frame as Joe.

"(Jane) decelerates and returns" is distracting. As the author correctly points out this is a point of asymmetry. However, a similar scenario (to be shown shortly) shows that it doesn't matter which frame undergoes deceleration and a change in direction – that of Jane or the entire universe. It is generally assumed that the period during which Jane changes direction is insignificant enough to ignore.

Finally, "Jane travels in a straight line at a relativistic speed v" begs the question "relativistic speed v relative to what?" The obscured assumption is "relative to both Joe and the distant location" (and to us, the readers). This is a direct consequence of the assumption that Joe and the distant location share the same frame (and that we also share that frame).

Let me provide a scenario which is analogous to the scenario described in the twin paradox.

Joe floats in space (in a protective space suit) with two clocks (marked as Joe’s).

Jane sits at one end of an extremely long structure which also floats in space, unattached to anything bar Jane and the beacon with another two clocks (marked as Jane’s). At the other end of the structure is a beacon. According to Jane, the structure has a length of L. Joe knows this.

Observe that Jane represents "the Earth" and the beacon represents "some distant location" in the twin paradox. The assumption that "the Earth" and "some distant location" have a fixed separation is inherent, but unstated, in the twin paradox.

Jane and Joe are sufficiently distant from any masses as to be considered to be alone in the universe, with no gravitational field in effect. The gravitation exerted by Jane and her structure on Joe is negligible.  (The absence of gravitational effects is another unstated assumption in the twin paradox.)

Jane and Joe pass each other twice, at relativistic velocities of v and -v. Joe and the beacon pass each other twice, also at relativistic velocities of v and -v (Jane and the beacon are fixed to the same structure and hence share the same frame).

Four noteworthy events take place:

1. Joe and Jane are collocated as they pass for the first time. Their clocks begin measuring time elapsed.

2. Joe and the beacon are collocated as they pass for the first time. Joe's clocks are paused and the beacon sends a message to Jane's clocks to pause.

3. Joe and the beacon are collocated as they pass for the second time. Joe's clocks restart measuring time elapsed and the beacon sends a message to Jane's clocks to resume measuring time elapsed.

4. Joe and Jane are collocated as they pass for the second time. Their clocks stop measuring time elapsed and Joe and Jane exchange clocks such that they both have one marked Joe’s and one marked Jane’s. Neither consults the other as they each attempt to work out what the other's clock will read.

Observe that I quite specifically do not say who reverses direction. For the purposes of the thought experiment, we can say that both Joe and Jane were anaesthetised while one of them reversed direction, so that neither knows which has changed direction relative to any third observer (such as the reader). By virtue of the scenario, both clocks are paused while any acceleration takes place and therefore no acceleration affects the measured time elapsed.

There is an asymmetry in this scenario, but Jane and Joe cannot determine on whose part that asymmetry lies.

Jane's calculations:

Joe is in motion relative to Jane. Jane calculates that the total time elapsed between events 1 and 2 and events 3 and 4 will have been 2L/v and her clock confirms that this is the case.  Assuming that the clock is sophisticated enough, Jane will be able to see that the time elapsed between events 1 and 2 was (L/v + L/c).  This is because the signal to stop timing would have taken a period of L/c to reach Jane’s clocks.  The time measured for the return trip, events 3 and 4, was (L/v - L/c), again due to the time taken for the signal to reach Jane’s clocks (a start signal this time).

Jane further calculates that because Joe is in motion, his clocks will run slow and will show a time elapsed of (2L/v) / γ where γ = 1 / √(1-v2/c2) (see The Lightness of Fine Tuning (Part 2) for an explanation of how this value of gamma (γ) is calculated, look up “time dilation” or here for confirmation that t’ = t / γ).

Jane can check Joe’s clock and see:

time elapsed (event 1 – event 2) = (L/v + L/c) / γ;

time elapsed (event 3 – event 4) = (L/v - L/c) / γ; so

total time elapsed = (L/v + L/c) / γ + (L/v - L/c) / γ = (2L/v) / γ


Jane’s clock, according to Jane = 2L/v

Joe’s clock, according to Jane = (2L/v) / γ

Joe's calculations:

Jane is in motion relative to Joe. Joe therefore calculates that Jane's structure is foreshortened by a factor of 1/γ. Therefore the time elapsed while the entirety of the structure passes twice will be (2L/v) / γ. Sure enough, Joe checks his clock and sees that this is the case.

Working out what Jane's clock will read is a little more complex. Joe knows that not only is Jane's structure foreshortened, but that Jane's clocks will also run slow by a factor of γ.

The first period elapsed can therefore be calculated as follows (noting that Jane's relative motion is in the same direction as the message from the beacon to Jane's clocks):

t1         = γ.(γ.L/v + γ.L/(c-v))

= γ2.(L/v + L/(c-v))

= γ2.(L/v.(c2-v2)/(c2-v2) + L(c+v)/(c2-v2))

= γ2.(c2.L/v - Lv + Lc + Lv)/(c2-v2)

= γ2.(c2.L/v + Lc)/(c2-v2)

but since γ2 = 1 - v2/c2 = (c2 - v2)/c2,

t1         = (c2 - v2)/c2 . (c2.L/v + Lc)/(c2-v2)

= (c2.L/v + Lc)/c2

= L/v + L/c

The same process can be used to calculate that the second period elapsed is (L/v - L/c). The total time elapsed on Jane's clock, as calculated by Joe, will be 2L/v - precisely the same as calculated by Jane and as shown on the clock labelled as Jane’s.


Joe’s clock, according to Joe = (2L/v) / γ

Jane’s clock, according to Joe = 2L/v

If both Jane and Joe agree about what the other’s clock should read, and this agreement is confirmed by measurement, then there is no paradox.

I believe also that my scenario demonstrates pretty conclusively that neither the acceleration nor the subsequent change to Jane’s inertial frame in Joe Wolfe’s scenario has a direct impact, since (in my scenario) there is no indication as to which inertial frame changed.


Please note that Joe Wolfe clearly states that there is no paradox and nothing in this article should be taken as implying that he is a proponent of the Twin Paradox.

Saturday, 22 December 2012

Emotional Ethics: The saving grace of the clinically sane

Introducing Lokee ... take it away, Lokee


It has come to my attention that an idea, which I imagined would be widely accepted, has in fact been a point of contention in the philosophical community since Aristotle. That is, whether, along with reason, emotions do and even should play a part in ethical thinking.

First, I will make an excuse for why I was unaware of this philosophical hot topic, and my justification is that I am comparatively new to philosophy. With this now known, hopefully your initial shock and disgust at my lack of awareness should dissipate, and in turn your need to vent your frustration at my apparent ignorance, lessen.

Upon my realization I was motivated to research, and based upon this body of research, it is my contention that emotions do and should inform ethical structures.

There are a number of emotion dependent processes and dispositions, including, behavioural dispositions, character traits and attitudes, all of which occur independent of an affective component (Starkey, 2008). That is to say, someone may be defined as a sad woman, without having the associated physiological reactions, feelings or expressions. A person may be angry with a telemarketer who continues to call, again, without having the physiological responses and elements of feeling typically related to anger. These forms of emotion are not the kind that I argue are necessary to effective ethical thinking. The kind of emotion that is essential to ethics are the emotions, which involve a cognitive and affective (physiological) component.

There are hardened rationalists who contend that emotions only weaken a person’s ability to think clearly and logically, and thus they should be avoided or at least only minimally referred to when making moral decisions. I argue, along with others I have read, that emotions are an essential part of the full understanding required to make effective and accurate ethical decisions.

“Without emotions or affects to amplify physiological drives and infuse cognitive processing with subjective meaning, human beings would not care enough to stay alive, much less mate, nurture offspring, create kinship bonds, or pursue art, science, literature or moral philosophy” (Callahan, 1988, pg.10). Emotions provoke thought and thought provokes emotion. An emotion involves a cognitive awareness of the object of one’s emotion along with a physiological reaction and experience of feelings (Starkey, 2008). For example, if a person sees a brown snake slither under their bed (cognitive apprehension), they experience an increase in heart rate, a tingling sensation (physiological reaction), and with these interwoven experiences they understand that there is a venomous snake under their bed, which they should be fearful of. The entirety of this event informs what actions they will take next. If a person were to have no sensation of fear and only register the fact that a brown snake went under their bed, what decision are they likely to make? For emotions not only register feelings, they also elicit memories. A person’s previous knowledge and experiences of snakes is brought forth and used to make an informed decision. They recall why they should be fearful of brown snakes. Thinking interacts with a person’s emotions, perception and physiology to bring forth from memory the information they need (Callahan, 1988, pg.14).

Emotion is necessary for full understanding (Starkey, 2008), which is achieved through introspection. Emotions allow a person to focus on what is perceptually relevant and identify what is most important (Starkey, 2008). Returning to the previous example, along with the brown snake slithering under the bed, there is also music playing, the neighbours next door talking loudly and the person in a rush to get to work. The emotion of fear that the person experiences provides them with the necessary information to tune out the music, ignore the neighbours and worry about their boss later, as what is most important now, according to their emotional reaction, is the problem of the possibly venomous snake making a home under their bed. This form of thinking is what has come to be known as the “frame problem” in philosophy. In any given situation a person needs to interpret the multitude of information presented to them and make inferences as to what is of import. Emotions enable people to do this by grabbing our attention

It may have come to your attention that while the example of the brown snake under the bed is effective in illustrating the interweaving of emotion and cognition, it does not involve an ethical problem. Fear not (no pun intended), this will be addressed soon.

Before I do give an example that clearly supports my contention, I will address the rationalists, who argue that emotion is detrimental to rational thought. An intelligent psychopath is clearly somebody who does not “suffer” from an average person’s emotional responses. They have the capacity to understand a society’s moral rules and can even apply them, if need be, but what they lack is the apprehension that moral rules should be reasons in their decision-making. In addition they are not held back emotions such as fear and guilt, when deciding how to act. A homicidal psychopath knows that society frowns on murder, and can apply the “no killing” rule, when it is rational and necessary to do so, for example, it’s best not to stab somebody in the centre of the mall, when there are lots of people around. However, when it comes to the act of killing their next victim, emotions and moral rules do not come into play. The fact that moral rules have no significance to them is clearly tied to their ability to tally up numerous victims without an empathetic emotional response to the individual lives they have taken.

Hardened rational thought can be just as morally dangerous as a psychopath’s lack of emotional response. An intelligent rationalist can easily argue for torture, terrorism, and the mistreatment of others through articulation of a logical dialogue. One only need to look to America for examples of all of these. For example the terror laws, which allow torture of possible terrorists and their imprisonment for indefinite periods of time. It is without the weight of emotional obligation and sympathies that people can ignore moral rules and sentiments. It is only through emotionally informed responses that a person is supported to check their moral options in light of their sympathies and in-built moral intuitions, and ensure a principled decision is made.

So now for my example of an ethical quandary. I have recently been reading a text written by Julian Baggini, titled Ethics: The Big Questions (2012). In one particular chapter he explores a long-standing ethical question, “Do the ends ever justify the means?” To aid in this investigation he relates a decision made by Dick Cheney on September 11th2001, which was only made public 10 years after the fact. Dick Cheney made the ethical decision, after being informed that two commercial passenger airliners had hit the Twin Towers in New York City, to shoot down two other hijacked commercial passenger airliners, which were on a similar path of destruction. Dick Cheney had decided that, while the loss of the hundreds of passengers on the airliners was terrible, the thousands of potential victims that would be saved justified their sacrifice. As history now tells us Dick Cheney’s decision did not need to be enacted, due to the courage of passengers on one, and the timing of the other. We can only imagine what Dick Cheney experienced that day, while making that ethical decision. There are two possible paths he took, that of a hardened rationalist, or that of a person who garnered a full understanding of the situation. Let us explore the latter.

Cheney cognitively apprehends the event that is about to take place, with the shock of the realization, his adrenaline increases represented by an increase in heart rate and sweat, he feels fear and trepidation at the decision he is faced with. As he weighs up the number of potential victims and the aftermath of such a loss of life, he feels both sorrow and guilt as either way innocent people are going to die as a result. Emotions enable him to recollect previous instances in his life bringing forth similar scenarios, as well as the knowledge he needs to make an informed decision. Logic informs him that the ends do justify the means, while emotion supported him to reach a point where sympathies resonated with the tough moral principles involved.

A rationalist is just as likely to decide that the ends justify the means in this case. As we’ve explored an intelligent hardened rationalist is more than capable of logically arriving at any number of decisions. However to gain a full understanding of such a layered and murky ethical decision, emotions are needed. They support the person to not only perceive the ethics involved, but also to feel, recall and gather the memory necessary to act appropriately. In considering the loss of life, the individuals involved, the magnitude of such an event, emotions are not only needed but also expected. Emotions help us support the intent of an action, rather than merely following a flow diagram leading to a potential action with no real understanding of why that action might be necessary, and in some way, right.

I’ll leave you with this question. If you were a potential victim that day, either on the plane, or on the ground, would you want a hardened rationalist who intentionally ignored the emotions involved, or a human who experienced the event fully, to make the decision?

List of References

Baggini, J. (2012). Ethics: The Big Questions. London: Quercus Editions Ltd.

Callahan, S. (1988). The Role of Emotion in Ethical Decisionmaking. The Hastings Center Report Vol. 18, No. 3, pp. 9-14

Starkey, C. (2008). Emotion and Full Understanding. Ethical Theory and Moral Practice Volume no.11 August

Thursday, 20 December 2012

The Noble Quest

I had cause, a few years ago, to visit Sweden while I was learning to speak Swedish.

As a quick advertisement for being multilingual, you should know that learning a new language provides endless opportunities for amusement.  Well, it did for me.

Because I was still learning, those I was talking with often had to resort to English to explain something a little more complex than I was capable of understanding (which was a lot).  This had an interesting effect, because there’s a noticeable lag in the human brain – people might be able to change their language of speech quickly, but they often continue to think in the other language for quite a while.  This leads to misuse of cross-language homonyms, mistranslations of common words and absolutely hilarious grammatical errors.

Anyhoo, I was once told that a mutual friend was widely known to “drink like a mushroom”.  When I tried to absorb this new information, I was struck by the image of my friend sitting in the dark on a bed of manure not drinking very much at all.  This didn’t seem to gel particularly well with the rest of the discussion.

The problem was that Swedes are linguistically lazy.  While in English we have the general terms “mushroom”, “toadstool”, “fungus”, “athlete’s foot” and “sponge”, Swedish has just the one: “svamp”.

Wow, I thought, I’d never before thought of sponges as being a type of fungus.  Admittedly, I’d not thought of them as being anything in particular.  But, due to this little exchange, I put sponges on the little metaphorical shelf in my head labelled “various forms of fungus” and thought no more about it.

Until today.

Sponges are animals.  Very simple animals, to be fair, rather like Swedes, but animals nevertheless.  Their young even move around in larval form (again rather like Swedes who do their global travelling in backpacker form).

This is one of the little problems we have with language and labels.  It’s going to be very difficult to convince Swedes that sponges aren’t fungus because in Swedish they are called, rather unhelpfully, “fungus”.  (Plus, Swedes can be frustratingly literal: for example, we don’t “tape” a television show anymore, because we don’t use blank VHS tapes, so we “record” them.  The subtlety of the fact that we have never ever used records to preserve television shows is totally lost on them – along with the fact that we’ve never used preserves for this purpose either.)

Sadly, the problem is not restricted to our Swedish friends.  Think about the confusion that is caused by the reification of truth or, alternatively, listen to this chap thinking aloud about the confusion that is caused by the reification of truth.

(For those who are interested: here are some links for pro-sentences and prosentential theory of truth and deflationary theories of truth in general.)

Now for the magical linking of these apparently divergent lines, a statement that is true does not necessarily have an independent, extractable property of being true – if you think like that, you are reifying the concept of truth.  Similarly, if you call sponge a fungus, you aren’t making it a fungus.  The property of being a fungus is not bestowed on something by virtue of having the label “fungus” attached to it.  You cannot take distilled fungus-ness and sprinkle it on sponges to make “sponges are fungi” a true statement, any more than you can take distilled truth and sprinkle it on the statement “sponges are fungi” to make it true.

Now that we have that sorted, will anyone join me on a noble quest – The Search for Fungus-ness?

Friday, 14 December 2012

The Method of WLC's Madness

In his debates, William Lane Craig repeatedly claimed that one of the strengths of his arguments for god is their “explanatory power” – the explanatory power of a creator who initiated the Big Bang, the explanatory power of a creator who finely tuned the universe, the explanatory power of god resurrecting Jesus and so on.

His Argument from Contingency:

1.    Everything that exists has an explanation of its existence (either in its own nature or in an external cause).

2.    If the universe has an explanation of its existence, that explanation is God.

3.    The universe exists.

4.    Therefore, the explanation of the universe is God.

And his Argument from First Cause:

We can also formulate this reasoning in the form of a deductive argument:

1. Everything that begins to exist has a cause.
2. The universe began to exist.

From which it follows logically that

Therefore, the universe has a cause

Again, as we have seen, the best candidate for such a transcendent cause is God.

And his Argument from Resurrection:

1.    There are three established facts about Jesus: his empty tomb, his post-mortem appearances, and the origin of the disciples’ belief in his resurrection.

2.    The hypothesis “God raised Jesus from the dead” is the best explanation of these facts.

3.    The hypothesis “God raised Jesus from the dead” entails that God exists.

4.    Therefore, God exists.

I did touch on this before, in Explaining Evidence, but I stumbled on a useful page on Wikipedia which expands on the historical method.  This is where Craig gets his “explanatory principle” from.

This methodology works, to a limited extent for the resurrection argument and only the resurrection argument, merely because some people claim that the Bible is history.  None of his other arguments are related to history, they are more in the domain of science (or rather of pseudoscience the way he handles them).  Scientific discussions should heed the scientific method, not the historical method.  Nobody was around at the time of the Big Bang, so there was no history to synthesise!

The reason why the methodology doesn’t work (not even for the resurrection argument) is that within the historical method, when done by real historians rather than theologians, a hypothesis is supposed to answer more questions than it raises – it is supposed to be less ad hoc than other explanations.

The major problem with a god solution is that the god solution raises questions that are more difficult than those it answers.  That’s negative explanatory power.

Thursday, 6 December 2012

The Fire Triangle (or Triangle of Humanity)

The following is adapted from comments made on Josh the Searcher’s blog, in response to articles touching on the abortion issue.


Abortion is a difficult topic.  It is much polarised, in part because it evokes strong emotional responses, in part because many of those arguing against the pro-choice stance do so because of theological notions and in part because there is still some confusion and uncertainty as to the precise meaning of “human”.

I should clarify up-front that while I am intellectually pro-choice, I would not be happy with having a (potential) child of my own aborted.  You could say that I am pro-choice in principle but pro-life in practice.

On a practical level, there is something that I find particularly unconvincing in the abortion debate, that being the idea that there is any benefit to be gained by involving yourself, and your personal ideology, in another person’s decision regarding such any issue as emotive as abortion.  I doubt that many people faced with the heart-wrenching decision to terminate a pregnancy take that decision lightly.  Those who do take such a decision lightly are highly unlikely to care one iota what you, or anybody else thinks about it.  They are also unlikely to be suitable parents to an unwanted child.

For me the important discussion when it comes to abortion revolves around three aspects:

·         is it ever ok to kill a living thing, be it “human”, “potential human” or any other living thing?

·         when does transition between “potential human” and “human” take place?

·         how should we go about developing social policy on an issue like this?

Is it ever ok to kill a living thing?

This is a tricky ethical question.  The obvious answer is “yes”, because if we never kill a living thing then we will die, in effect killing ourselves.  Our bodies are constantly killing bacteria, with antibacterial agents in saliva and white blood cells (these also destroy fungi, parasites, viruses, tumours and tiny submarines in science fiction movies).

As we move up in physical scale, begin to consider species that are more like humans and apply “cuteness” as a factor, the answer becomes less obvious.  It’s apparently less ok to kill a cute kitten than it is to kill a rat: the idea that a kitten drowned in the recent flood in New York is more affecting than the idea that a young rat died.  There’s a good reason that the World Wildlife Fund has a panda as its emblem instead of, say, a cockroach.  We’re happy to eat dolphin if it’s a type of fish, but less so if it’s a mammal (I’ve eaten dolphin, it’s quite nice) – unless we are Japanese or Faroese and not worried about consuming high levels of mercury.

Since humans are up towards the carnivorous end of the omnivore category (particularly if the endurance running hypothesis is true), killing larger animals is part of our natural heritage.  So, I’d argue that it is ok.

If we restrict our considerations to humans, it’s still a bit tricky.  There are still many exceptions to the “do not kill” rule.  Killing in the line of duty is ok, as a soldier or law enforcement agent.  Killing in self-defence is ok.  Killing as justice is sometimes ok. Note that not all countries have the death penalty – those that do are places like China, Iran, Saudi Arabia, Iraq, the United States, Yemen, North Korea, Somalia, (North) Sudan, Bangladesh, Vietnam and South Sudan.  (The death penalty nations are listed in decreasing order of executions for 2011, so long as they executed 5 or more.  If you include those who executed fewer or have the death penalty on the books but didn’t get around to executing anyone in 2011 you add such notables as Afghanistan, the Palestine Authority, Belarus, Botswana, Mongolia, Cuba and Syria).

Fortunately none of these are among the most modern and developed nations so we can hope that this list becomes shorter as more and more nations are encouraged to modernise.

Anyway, without a very good reason, killing a human is generally not considered to be ok.  Hopefully this is not a particularly contentious claim for most readers.  We turn now to the question of what it is to be human.

When does the transition between “potential human” and “human” take place?

One way of thinking about the question of what makes you human is in terms similar to that of the fire triangle.  A fire requires fuel, oxygen and heat and all three are required to support continued combustion.

The “triangle of humanity” would be:

·         human DNA

·         independent actualised potential

·         experience

Without all three of these elements, you aren't fully human. A zygote in a petri dish may have the DNA required to become a human, but it has no actualised potential because the petri dish will not support further development. And a zygote, not having a brain, won't accumulate experiences.

A side argument is that just as an acorn is not an oak tree, a zygote is not a human.  I’m not sure that this is a valid argument per se, given that it seems to be based on semantics (and a misunderstanding, an acorn is equivalent to an embryo rather than to a zygote).  Given the opportunity, an acorn will become shoot which will, in turn, become an oak tree just as a frog’s egg will become a tadpole which will, in turn, become a frog and a (human) zygote will become a human.  It is true enough that it is very difficult, if not impossible, to visually distinguish the human zygote from a chimpanzee zygote and that this difficulty remains until a relatively short time before birth.  It is true that a human embryo looks like a fish for a while and a canine embryo looks like a proto-human for a while.

Nevertheless, a human zygote fulfils one of the requirements for being human in a way that a chimpanzee does not.  (As another aside, taking us almost into another room, the chimpanzee almost fulfils the requirements of being a human by means of DNA, falling short by less than 5%.  Not being a geneticist, I am not completely sure why there seem to be two figures floating around “we share 99% of our genes” and “the difference between the human and chimpanzee genome is about 4%”.  I do note that there is a difference between our genes and our genome and that there are also alleles which are variants of genes.  It could be that the chimpanzee has all the basic parts that we have, so the genes are largely the same, but the chimpanzee plays with a different set of alleles which means the genome exhibits a greater variance from human than the selection of genes does.  I’m not sure how one should interpret another apparent fact, that the variation between genes of a human and the genes of a chimpanzee is ten times that of the variation between genes of individual humans.)

Common to a zygote, a morula (strictly speaking a zygote is a single cell), a blastocyst, and an embryo (for a human, the embryo becomes a foetus at 10 weeks) is the lack of a functional brain. 

If one uses the “triangle of humanity” concept, until the brain develops beyond a certain stage a foetus could be said to not be fully human, because it's unable to accumulate any experience of any kind. Also, while the foetus is entirely dependent on the mother for survival (up until about 20 weeks) it has no independent actualised potential.

Therefore, I would say that you could argue that terminating an embryo or a foetus could be justified up until somewhere between 7 and 14 weeks, 16 weeks at most. It's a bit fuzzy because of how the brain develops.  Development of the brain really kicks off in the embryo at about 7 weeks. The foetus starts breathing practice at about 14 weeks and at about 16 weeks it starts manipulating its environment (like pulling on the umbilical cord).

Sometime in that period of time, a normal foetus reaches a level of development which is consistent with being human under the “triangle of humanity” concept.

Note that miscarriage can happen up until about 20 weeks, but that's basically a legal definition.  A "miscarriage" after that time is called a stillbirth. The youngest surviving premature birth was at 21 weeks.  Advances in medical science may allow us to save some prematurely delivered infants at closer to 20 weeks, but not much earlier than that because a foetus is simply not sufficiently well developed by that time.

In the absence of extreme circumstances, I do not support the idea of the form of late-term abortion which is, really, an induced premature delivery followed by killing of the infant.  (Normalising early abortion, and those who seek one, will go some way to reducing the number of late term abortions.)

None of these arguments about when an embryo or a foetus becomes human such that abortion is no longer justified (except in extremis) has any bearing if your argument against abortion is theological in nature.  If your god says “Thou shalt not abort, at all, ever” then you should not abort.  However, if your god is a bit vague about it saying “Thou shalt not kill, but there are plenty of exceptions and I cause spontaneous abortions at a much higher rate than humans cause abortions and I am a paragon of goodness, so read between the lines”, then you have a bit of wriggle room.  In either case, this is your god speaking to you.  In order for your god’s view on abortion to have any influence over another person you have to first prove that your god exists, which unfortunately you are unlikely to be able to do, and then prove that your god’s injunctions apply to people who are not his followers.  I’ve no real problem with anyone refusing to carry out an abortion on the grounds of their personal convictions.  But these are personal convictions and I cannot see why one’s personal convictions should be applied to another person who has their own personal convictions.

Adopting a “triangle of humanity” concept could also have application in later life.

Many people, me included, consider that continued animation of their body beyond the effective death of their brain does not constitute a continuation of their self in any meaningful way.  By “effective” death of the brain I mean either literal brain death (as in total and irreversible lack of higher level neural activity) or the dissolution of self that neurological degeneration brings.  I certainly don’t have any wish whatsoever for my body to be kept alive beyond the time when the sense of being me is manifesting in it.  If I’ve lost my experiences and the ability to develop new experiences, or my actualised potential is gone (for example if disconnecting me from a machine will lead to my death), then please let me go.

How should we go about developing social policy on issues like abortion and euthanasia?

I need to make perfectly clear that by euthanasia, I really mean assisted suicide of a person who is suffering physically or disintegrating intellectually.  I’m only talking about voluntary euthanasia.  I’m not recommending that we start killing old people because they are inconvenient but rather suggesting that if someone has written a living will which includes an instruction to let them die with dignity, then their wishes should be respected.  Involuntary euthanasia of a human is murder.  I recognise that there is a grey area for people who have disintegrated intellectually and are thus unable to request euthanasia but are also unable to express an unwillingness to die.

My opinion expressed above, that I’d prefer not to have my body kept alive once the experience of being in it is no longer generated (or if I am totally dependent on machinery to continue breathing), relates only to me.  I’m not advocating that the bodies of other people, once their intellect is extinguished or their ability to survive unassisted is gone, should necessarily be treated the way I’d prefer mine to be treated.

When I pondered the issues of abortion and euthanasia, it struck me that these are not just ethical or moral issues, but also very emotive issues.  I have had the emotional aspect of certain decisions and considerations highlighted to me, while being criticised for appearing too Darwinian (for example in relation to an early draft of Morality Behind the Wheel, which I subsequently edited).

I don’t think that I was totally ignoring emotional dimensions – what I think I was doing was not letting them dominate the entire consideration.

It is true that emotion is involved when humans make decisions and we should certainly not ignore their influence.

However, the importance of emotion in decision making applies to decisions made by individual humans.  The fact that we, as individuals, are swayed by emotion does not mean that we, as a society, should be swayed by emotion – and certainly not by the emotions of a noisy minority.

If you yourself are unwillingly pregnant, then as an individual you should certainly engage your emotions when deciding whether to terminate the pregnancy.  You need to be aware of both the fact that your emotions will affect the decision you make and the fact that the decision you make (or don’t make) will affect your emotional state in the future.

However, if you are responsible for drafting legislation as to whether an option to safely terminate pregnancies should be available, you should not be engaging your personal emotions or indulging your personal convictions.  If a totally rational, non-emotive discussion of the issue of abortion arrives at a conclusion that it is so harmful that it should be banned, then ban it.  But if your argument is based on little more than the fact that, if you were pregnant, you yourself would not want to go through with an abortion or your personal theology tells you that you are not to abort your child, then you do not have grounds to ban the availability of safe abortions to others.

The same applies to questions of euthanasia and, perhaps less controversially, the recognition of same-sex civil union (and marriage – but only if a church is happy with conducting a same-sex marriage.  Don’t go forcing a reluctant church which has a theological objection to the whole homosexual thing to carry out gay weddings simply because you personally think they are a good idea).

You might be opposed to the idea of euthanasia and gay weddings, but no-one is suggesting that you should be euthanized against your will.  Not even the most fervent supporter of same-sex union plans to force you to become gay and get married, or even to attend a gay wedding. 

I personally think that Turkish vomit is disgusting (some people humorously and incorrectly refer to it as “Turkish delight”) but I accept that, bizarre as it sounds, some people actually like eating it.  Certainly, until someone can produce a rational, evidence-based argument showing that eating Turkish vomit represents a significant risk to society, I have no grounds for seeking a comprehensive ban of what I consider to be an affront to all that is pure, wholesome and good.

Of course some people disagree, and not only about Turkish vomit.  They might argue that of course you should agitate for your personal views to be reflected in society because that’s how democracy works.

This is a particularly naïve view of democracy.  It’s also a dangerous view.

Imagine that your society decided that if a sufficient proportion of the population don’t want something then it will be banned.  They count up those in favour of safe abortions being available, those against the idea of abortion and those who don’t really care one way or the other.  Those against abortion prevail and abortion is banned.  Sounds good, right?

Say then that, after a heavy advertising campaign, Jehovah’s Witnesses obtain a majority and the issue of blood transfusions arises.  Do you really want their personal theological convictions to hold sway over you when about one in three people need a blood transfusion at some point in their life?  How about an unholy alliance between fundamentalist Pauline Christians and Muslims who demand that women not be allowed to be educated, to work or to go about in public without a veil?  Or a majority of atheists who don’t like going to church themselves and therefore instigate a ban on churches altogether? Or drivers combine in their dislike of electric cars to drive them (quietly) off the roads?

What else could we ban?  How about Persian cats, little yappy dogs, salads, expatriates, anyone under five who can ski, the pierced belly-button/muffin-top combo, misuse of the word “like”, comb-overs, Boston MA, Tampa FL, hot-dog “sausages” and old people driving while wearing a hat.  (By the way, I actually like salad.)

I doubt that any of us are particularly keen on having our freedoms curtailed by a majority of others.  If you think that way, then you should logically extend the same courtesy to others and not try to impose your preferences on them, even if those preferences are in the majority.

Personally, I think you should agree with me, but I’m not going to force you to.