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Tuesday, March 26, 2013

A Universe From Nothing?

There are various issues that I'd like to address regarding the 2013 Isaac Asimov Memorial Debate, but one in particular is bugging me.  Lawrence Krauss says that science can give us a plausible explanation of how a universe like ours could spontaneously "pop into existence" out of timeless, spaceless, lawless void.  Jim Holt says that Krauss is talking nonsense:  The idea of a universe "popping into existence" implies that there is a point in time in which that event occurs.  Yet, by Krauss' definition, there is no time (or space) for the universe to pop into.  I think Holt's point is valid, but it does not get resolved.

Here's the whole exchange (starting @ 0:50:00):

Krauss: Quantum mechanics says things fluctuate, and if gravity is a theory of space and time, if you make space and time quantum mechanical variables, then it is perfectly possible for universes to pop into existence--space and time to pop into existence where there was no space and time before.

Krauss wants to continue, but Holt interrupts.

Holt: Space and time pop into existence?  You make that sound like a temporal process, a process in time.

Krauss: Well, because I said it so you can understand it.

Holt: Huh?

Krauss: No, I mean I used words, and the problem with words are [sic], as T. S. Eliot says, they're sort of slippery.

Holt: But becoming implies time.  You can't have time coming into existence as itself a temporal process. That makes no sense. That's why it's good to have philosophers around, which I'm not one, to help you use language precisely.

Krauss: Okay, so let me just pretend there--let me just say there's a global time and at some time a space pops into existence. Okay, will that make you happier?

This does not satisfy Holt, however, and I can understand why.  Krauss started by claiming to have an explanation of how time itself can come into existence out of a timeless void.  Now, however, he's saying that there is a global time out of which the universe sprung.  So he's changed his story.  Something fishy seems to be going on.  But before Krauss and Holt can make headway, Neil deGrasse Tyson steps in to moderate.

Tyson: Lawrence, you are saying that because we have quantum phy--because we are illuminated by the actions of quantum physics, mentally, we can think about whatever is our best understanding of nothing, and quantum physics then pops into existence in that nothing an entire universe, and if that's the case, I would then pick up Jim's point and ask you--

Krauss: I was gonna try and ex--Where do the quantum physics come from?

Tyson: No, no, no.  No, no, no.  That's not what I'm gonna ask you.  I'm gonna ask you--that had to happen at some point.  Why isn't it happening all the time and everywhere at all times?

Krauss went on to answer that question.  Unfortunately, that is not the question that Holt was raising, and Holt never tried to raise the point again.  Holt's question was, what sense is there in talking about space and time coming into existence?

Krauss' claim is that the universe may have originated out of a timeless, spaceless void.  His theory (from what I gather) is that such a void would be inherently unstable, and so would tend to produce stuff.  The question then is, what sense is there in referring to a timeless, spaceless, lawless "nothing" as being unstable?  Stability and instability are properties which persist in objects over time.  If there is no space or time, then there is no instability.  Furthermore, what sense is there in claiming that the creation of the universe occured in a spaceless, timeless nothing?  If there is no space or time, then there is no such thing as occurence.   It defies logic to speak the way Krauss is speaking.

Now, maybe Krauss has a point about the limitations of ordinary language.  There's a long tradition, from Galileo to Heisenberg, of regarding math and math alone as suitable for grasping the truth of physics and, by extension, reality.  Once you start using non-mathematical terms, you lose the sense, beauty and truth of the model.  But if that is so, and mathematics is the only coherent way to talk about reality, then what does that say about reality?  Is all non-mathematical language incoherent?  Should we be Platonists, and accept that the only truth is purely mathematical?  Is everything else just illusion?  This is philosophy, not physics, but it's what Krauss might be suggesting.

Even if we avoid Platonism, isn't Krauss suggesting that physics is beyond comprehension?  Does that mean physicists should just shut up and calculate?  If so, then Krauss really shouldn't be trying to talk about these things at all, should he?  He says he's trying to describe the physics in a way so that we can understand it, but apparently that is impossible.  And that raises the question: How well do Krauss and other physicists understand it?

I don't think physicists should just shut up and calculate.  However, I do think they sometimes need to be more careful in the way they present their ideas.  And they should also be more open to philosophical scrutiny in that area, since philosophers have experience and conceptual tools for exploring the logical space of our discourse.  (Krauss denies that philosophers have any expertise to bring to the table at all, which is unfortunate.)

Krauss' argument seems to be this:  Our universe may ultimately have sprung out of a timeless, spaceless, lawless void.  This could be so because, in such a void, every possible law obtains (which, for Krauss, is the same as saying that no laws obtain.)  The laws of quantum mechanics are possible, and so those laws also obtain in The Nothing.  And according to those laws, universes can pop into existence.  One problem with this view is that there must be something to exist in which those laws can obtain.  If there is really is nothing at all, then there is nothing on which the laws can act.  So the explanation doesn't work.

Let's say Krauss finds some way around that problem.  There is still another problem:  Couldn't there be some laws which are not consistent with quantum mechanics, and which, in fact, say that universes cannot pop into existence?  If all laws obtain in The Nothing, then we could have one law which says universes can pop into existence and another law which says they cannot.  In that case, a universe popping into existence would be physically impossible--it would break one of the laws of nature.  Krauss needs to explain why such a law--a law against universes popping into existence--is impossible.  If it's not impossible, then his account does not work.

Krauss also suggests a slightly different argument which starts with an assumption: Everything which is possible is actual.  In that case, every possible arrangement of quantum variables is real.  That means that every possible universe exists and also that the "ground state of a gapped quantum system" (as Eve Silverstein calls it) is also real.  So The Nothing is as real as our universe.  And so there is a temptation to say that our universe--all universes--came out of The Nothing.  However, this doesn't overcome Holt's objection.  We still can't say that all of the other states of the quantum system came from the ground state, because the ground state does not exist in any particular place or time.  It's not clear in what sense the ground state can exist at all.  Maybe we can still say that the ground state, like all the other states, is real, since reality does not necessarily imply existence (for example, it is not hard to admit that numbers are real, but it's very hard to say in what sense they might exist), but we're still left with the question:  How did the quantum system come into existence in the first place?

If you want to talk about what caused the universe, then you're asking for a first cause.  Krauss seems to want it both ways here.  He says science doesn't need a first cause.  That's true.  Philosophy doesn't, either.  But then Krauss hasn't explained how the universe (or multiverse) might have come into existence.  If he wants to explain that, then he really does seem to be looking for a first cause.

What many physicists seem to prefer--and I think J. Richard Gott is one of them--is to say that the universe (or multiverse) just is.  Nothing caused it to occur.   Krauss might even agree, in which case all his arguments about universes popping into existence seem like a waste of time.  Whatever Krauss thinks, it is philosophically respectable to say that the very question, What caused the universe to exist?, is meaningless, because "the universe" is not the sort of thing that can be caused to exist.  The universe, the multiverse--the quantum system--just is.  It didn't come from nothing.  It didn't come, period.

I'll end with a note on the meaning of the term "universe" as physicists today understand it.  According to Gott and Krauss, the word "universe" has a different meaning nowadays.  Krauss says "universe" is defined as "everything you could have once interacted with, or you can ever interact with.  So everything you can have physical contact with, either in the past or in the future, is a universe."  Different universes can share a causal history, but they don't have to.  They might be completely and utterly independent of each other.  Now, if we're talking about multiple universes which share a common history--a common trunk, as Gott puts it--then aren't there going to be moments in my universe which can have physical contact with moments that aren't in my universe?  In other words, the differentiation of universes is relative and not absolute.  While "my" universe has some unique physical properties, not everybody in "my" universe will draw the boundaries of their universe the same way I draw the boundaries of mine.  This isn't necessarily a problem, but I find it curious.

P.S. If you want to know what philosophers have to say about nothing, the SEP entry on Nothingness is a good place to start.

Friday, March 22, 2013

2013 Isaac Asimov Memorial Debate: The Existence Of Nothing

I wasn't able to watch the live stream of the 2013 Isaac Asimov Memorial Debate.  I'm looking forward to seeing the full video when it is available online.  For now, I've found a review of the event at Engspurdishabic.  Unsurprisingly, the debate had a very philosophical dimension.  Issues concerning the definition of the word "nothing", the metaphysical implications of nothingness and the boundaries between science and other disciplines were all discussed.  It's just the sort of stuff you'd like a professional philosopher or two to weigh in on.  Alas, none were on hand.  Also worth noting:  It appears that Lawrence Krauss compared their amateur philosophizing to the works of Mozart.  (That's not true.  See update below.)   I'm sure I will have more to say about this event once I see the video for myself.

Thanks to Russell Blackford for pointing out that my initial phrasing was misleading.  I did not mean to imply that Krauss thought his philosophical contribution was more relevant or valuable than those of the other panelists.

Update (March 24, 2013): I just watched the video (here) and the review at Engspurdishabic misrepresented Krauss' comment about Mozart and the relevance of their discussion.  Krauss mentions Mozart (and Picasso) when asked a different question--not about relevance, but about the practical applications of the discovery that particles can come out of an unstable "nothing." Krauss first replies that none of his own scientific work has practical applications, and that he's fine with that. He then compares his scientific work to a Mozart symphony or a Picasso painting, which can be interesting and beautiful even if it has no practical function. He says, "the ideas of science are among the most beautiful intellectual discoveries that humanity's ever come up with." But he then goes on to explain that, in fact, the spontaneous emergence of particles in a vacuum is integral to quantum mechanics and modern technology.

Later on, a different person does question the relevance of their discussion, but that question is focused more on whether or not the panelists have ignored an important why-question at the expense of the how-question. Krauss responds that the why-question unjustifiably assumes intentionality. He doesn't say anything about Mozart or the aesthetic value of their discussion at this point. (Also interesting, another of the physicists on the panel, J. Richard Gott, says that science deals only with how-questions. However, Holt disagrees with Krauss and defends the need to ask why-questions, denying that they imply intentionality.)

So Krauss did not compare his or anybody else's amateur philosophizing to the works of Mozart. He compared his own scientific work to the works of Mozart and Picasso. But I'm sure he didn't mean to suggest that any of his particular insights or contributions were nearly so valuable or beautiful. He was clearly making a more general point about whether or not science needs to have a practical application in order to be justifiable and worth pursuing. That's a much more interesting point, but also questionable.  The thing is, unlike works of art, we expect science to have at least some practical relevance.  We have very different expectations about art and science, so the comparison to art is not so persuasive.  But maybe Krauss thinks that our expectations about science are wrong.  That may be a tough argument to sell.

For more thoughts on the debate see here.

Sunday, March 17, 2013

I have something to say to Neil deGrasse Tyson

As you may know, Neil deGrasse Tyson rescinded an invitation to have philosopher David Albert join physicist Lawrence Krauss (and others) in a panel discussing the physics of "nothing."  This has sparked some speculation and debate.  Jerry Coyne was particularly upset by Tyson's decision.  Russell Blackford seems to agree with Coyne.  Tyson responded to Coyne in the comments section with an elaborate explanation.  As he explains, Albert is not an ideal panelist for this event.  I trust Dr. Tyson to make that judgment, though I think Tyson's initial decision to invite Albert was justified.  Professor Albert is a Philosophy Professor and the Director of the MA Program in the Philosophical Foundations of Physics at Columbia University.  He has a PhD in theoretical physics.  Furthermore, he is responsible for a lot of the public debate over Krauss' new book (on the physics of "nothing") and how the topic relates to the intersection of science and philosophy.  He is certainly qualified to participate, even if he has not published anything directly related to the event topic.  But okay, even if Tyson has given adequate explanation for why Albert should not have been invited, we still need an explanation for why that invitation was rescinded, since the act of rescinding an invitation carries a lot of risks.  Thus, I wrote the following in response to Dr. Tyson:


Dr. Tyson,
With all due respect, I do not think your explanation is sufficient. True, Professor Albert has not published scientific or popular writing which directly deals with the topic of your panel discussion. That is a plausible reason for not inviting him in the first place, but it does not explain why you would risk public embarrassment and potentially insult Albert by rescinding his invitation. Once he was invited, and since his qualifications are certainly sufficient (if not ideal), we have to imagine you had some other reason for turning him away. This is what you have not yet explained.

It looks like your main motivation was the desire to avoid a confrontation between Albert and Krauss. Assuming your decision was rational, you must have thought such a confrontation would risk greater public embarrassment, greater insult (to Krauss, of course, since a confrontation would not likely lead Albert to feel insulted) or perhaps something far worse. However, it’s hard to see what worse might have been risked, and it’s hard to see what public embarrassment might issue from a well-moderated public debate between Krauss and Albert. So the most plausible explanation seems to be that you thought keeping Albert on the panel would be such a great insult to Krauss that Albert had to be turned away. Krauss’ public comments about Albert support this interpretation, as well.

In short, here’s my theory: You insulted Albert and risked public embarrassment in order to avoid the risk of insulting Krauss. I don’t necessarily think you were playing favorites. I assume you just tried to find the least harmful scenario. However, I’m sure you can understand why some corners of the intellectual community would find this greatly disappointing. It is no surprise that ego plays a significant role in our public intellectual life. It would be nice to at least see a straightforward admission of the fact. Moreover, it seems clear that you owe Professor Albert a public apology.

Respectfully,
Jason Streitfeld


Update (March 18, 2013):  Since some people do not recognize the seriousness of the situation and why a better explanation from Dr. Tyson is necessary, I posted the following on Jerry Coyne's blog:


This is a professional affair concerning a public appearance. It looks very bad for Dr. Tyson and The American Museum of Natural History to invite a highly respected public intellectual, to have that invitation accepted, to allow said intellectual to prepare for months for the public engagement, and then to disinvite them–unless you have a very good reason which you make available to the public. Without an explanation for this, other public intellectuals have a very good reason not to accept invitations to speak at the American Museum of Natural History.

Dr. Tyson has not given a good reason for his disinvitation. He’s given a reason why Professor Albert was not his ideal candidate: Unlike Jim Holt (who does not have any apparent scientific or academic qualifications to speak of), Professor Albert has not written a popular book on the physics of “nothing.” Holt’s status as a popular writer with a relevant book to sell trumps Albert’s status as a celebrated popular science writer, Philosophy Professor at Columbia University and PhD in theoretical physics. That is what Dr. Tyson explained, and I trust Dr. Tyson to make that judgment. Holt is a better choice for Tyson’s purposes. But that does not explain why Tyson would disinvite Albert. Why couldn’t Holt and Albert both serve as panelists? Why would Albert’s presence cause a problem? Why did Albert have to go?

It seems to me that Dr. Tyson is putting his and the museum’s reputation on the line for no good reason, which is very unfortunate.

Update again:  I just posted one more comment on Coyne's blog explaining some of my feelings about the whole situation:


There’s a deeper issue here that’s motivating me, and perhaps others, to give more of a crap about this whole situation.

Even though the event’s primary focus is on science, there is good reason to expect a discussion of broader intellectual areas, too. The American Museum of Natural History advertises for the event as follows: “The concept of nothing is as old as zero itself. How do we grapple with the concept of nothing? From the best laboratory vacuums on Earth to the vacuum of space to what lies beyond, the idea of nothing continues to intrigue professionals and the public alike.” But they’ve only got a journalist (Holt, who we can regard as a non-professional philosopher) and a journalism professor (Seife) holding up the non-scientific end of the discussion. Krauss approaches the non-scientific end, too. He has even gone on talk shows getting into supposed theological implications of his work. Both Holt and Krauss are interested in the philosophical implications of the science of “nothing”, but neither one of them can discuss it authoritatively. Holt is a journalist, not an independent, authoritative thinker. Krauss, on the other hand, has a condescending approach to philosophy in general and, from what I can tell, has no interest in engaging professional philosophers on the topic. (His negative attitude towards professional philosophers is partly responsible for all the fuss last year.) While Holt is very friendly with the philosophical side of the matter, I do not think he can defend or represent it as authoritatively as Albert. Albert is perfectly suited to bring an authoritative, sophisticated philosophical approach to the table. His absence will be felt.


Saturday, March 16, 2013

Knowing *about* what it is like

Thanks in large part to my recent email correspondence with L. A. Paul (see here and here for some background on that), I've formulated a position which, as far as I know, is novel in the philosophy of mind.  The basic assumption is this:


(1) One knows *about* what it is like to X iff one knows some of the consequences and/or functional correlations associated with the experience of what it is like to X.  

It follows that, 

(2) one can know about what it is like to X without ever directly experiencing X.  

This only requires that phenomenal properties have functional correlations (these can be statistical or accidental, and not intrinsic, of course) and/or that they are not epiphenomenal.  This is consistent with the common intuition that you can only know what it is like to X if you have some experience of X-ing.  (That is the new-knowledge intuition associated with Frank Jackson's Mary thought experiment:  When Mary the color-blind scientist finally sees color for the first time, she will gain new knowledge by virtue of her new experience, regardless of any knowledge she learned ahead of time.)  

A further implication of my assumption is this:  

(3) One can make rational decisions about what it would be like to X without knowing what it would be like to X.  

For example, imagine that before Mary is about the leave her black-and-white room, she has to make a decision: How does she want to first experience colors?  There is a color chamber designed to ease her transition from black-and-white to the color-filled world.  Studies have shown that people like Mary tend to respond well when the transition is slow, moving from soft, dull tones up to brighter hues.  Mary does not know what it is like to see color (assuming the new-knowledge intuition is correct), but she can know about how these different processes are likely to affect her.  She might not know what it is like to be relaxed by a soft green, but she knows what it is like to be relaxed and she knows that soft green is likely to have that effect on her.  In short, she can rationally decide how she wants to first experience colors without trying to guess at the phenomenal contents themselves.

This seems to pose a direct challenge to Professor Paul's argument that the common way to decide whether or not to have children is irrational.  Her argument is that people make assumptions about what it would be like to have children, but since they can't possibly know what it would be like, they are fundamentally wrong about the way they are making the decision.  If the position I have outlined is correct, then they might not be making a mistake.  They might have reasonable, justified and even true beliefs *about* what it would be like without knowing what it would be like to have children . Their decision may therefore be rational.


I am not sure if Paul will accept (1).  If she does, she might still respond that people making The Decision really are under the false impression that they know what it would be like.  In her view, they're not just relying on beliefs *about* what it would be like.  She might even say it is "bizarre" to approach the decision by focusing on knowledge *about* what it would be like.  I don't see anything bizarre about it, though.  I think it is simpler and more intuitively appealing to think that people are not making the mistake Paul says they are making.  I think people commonly go about such decisions much the way Mary would when deciding how to experience colors for the first time.  


This question could perhaps be answered with better sociological data, but that may not be so easy, since we'd need a way of clearly distinguishing between two sorts of assumptions:  on the one hand, assumptions which purport to involve the phenomenal content in question and, on the other hand, assumptions about that phenomenal content.  More importantly, the data that is available, and which Paul draws on in her paper, seems to support my view at least as well as, and I think even more than, hers.

Incidentally, some philosophers--especially those Pete Mandik calls "non-gappy physicalists," like he and Dan Dennett--might say that there is no difference here at all, and that "knowing what it is like" just is knowledge of the correlations and consequences that I am classifying as knowledge about what it would be like.  I am sympathetic with that view (and non-gappy physicalism), but I'm not 100 percent committed to it.  The difficulty in finding data distinguishing these two cases might lend it intuitive support, though.

Wednesday, March 13, 2013

Is Parenthood A Rational Choice? - Take 2

I want to take a closer look at L. A. Paul's argument that The Decision (whether or not to have children) is not rational.  In my last post, I claimed her argument is not clearly valid.  I want to explain why.  Her argument can be represented by this series of propositions:

1) If The Decision is rational, then it involves people who have never had children comparing what it would be like to have children with what it would be like to remain childless.
2) People who have never had children cannot know what it would be like to have children.
3) If a person cannot know what it would be like to have children, then they cannot compare what it would be like to have children with what it would be like to remain childless.
4) People who have never had children cannot compare what it would be like to have children with what it would be like to remain childless.
5) Therefore, The Decision is not rational.

On the surface, it looks like you must accept (4) and (5) if you accept (1), (2) and (3).  However, I think the argument equivocates over the phrase "what it would be like" in premises (1) and (2).

Before I explain, I want to question premise (3).  One might not need knowledge of what it would be like in order to make the sorts of comparisons required for a decision to be rational.  One might simply need justified beliefs.  A person might not know what it is like to have children, but still have justified beliefs about what it is like.  And they can, based on those beliefs, make comparisons with what they justifiably believe it would be like to remain childless.  They can, on that basis, make a rational decision about whether or not to have children even though they don't know what it will be like--and they can even realize that they don't know what it will be like.  I suspect many parents might agree with me here:  when you decided to have children, you didn't think you actually knew what it would be like.  You had some reasonable beliefs about the matter, and those helped guide your decision.  There's nothing irrational about that, is there?  Thus, even if you don't agree with the argument I'm about to make concerning equivocation--even if you think Paul's argument is valid--I think we should reject her conclusion by rejecting premise (3).

Now, to see why there is an equivocation in Paul's argument, let's first consider what it would take for (2) to be true.  This is where Paul explicitly appeals to Frank Jackson's knowledge argument.  As I noted in my last post, Jackson's argument is controversial and it is not clear what, if anything, it demonstrates.  It might just demonstrate that some knowledge is not discursively learnable.  Or it might just demonstrate that our intuitions about radical epistemological states (like omniscience about the physical world) are unreliable.  In any case, I don't think Paul is really relying on the knowledge argument per se.  She's really relying on an older argument found in Thomas Nagel's 1974 paper, "What is it like to be a bat?"  Nagel famously argued for the intuition that drives Jackson's knowledge argument:  the intuition that you cannot know what it is like to X unless you have the right experiences of X-ing.  Jackson's knowledge argument is well-known for taking Nagel's intuition and making an argument against physicalism out of it.  (Physicalism is the doctrine that the physical world is all there is. Unlike the knowledge argument, Nagel argues that physicalism is perplexing, but not necessarily false--perplexing because we cannot imagine how subjective experiences just are physical states or processes.)  Paul doesn't need to make an argument against physicalism.  She doesn't seem to want to align her argument about The Decision with an anti-physicalist position.  So she's probably better off not aligning her argument with the knowledge argument.  (Edit: After discussing this issue with Professor Paul and reviewing her paper again, it's clear that she does not intend to align herself with the anti-physicalist knowledge argument.  She is only using the thought experiment behind it.)  The point is, for (2) to be true, "what it is like" must refer to the kind of properties you can only know about through experience.  These are phenomenal properties, or qualia.

Qualia is the stuff of irreducibly subjective experience.  It is what you know only by experiencing something, and not being told about it.  For example, if there is something it is like to see red, then that is something that you only understand by having (or remembering, or imagining) the experience of seeing red.  Similarly, if there is something it is like to be a parent, then you must have that experience (or remember or imagine it) in order to know it.  There's a philosophical question regarding whether or not you can know what something is like without actually having the experience, and there have been many arguments back and forth in the last several decades among professionals.  It's not a settled issue.  But some intuitively believe in qualia enough to accept (2) as true.  The problem is, this is not the sense of "what it is like" that makes (1) plausible.

To help flesh out (1), Paul writes:

Many prospective parents decide to have a baby because they have a deep desire to have children based on the (perhaps inarticulate) sense that having a child will help them to live a fuller, happier, and somehow  complete life, that is, it will help them to have experiences with a kind of phenomenal character that one can describe as involving “life satisfaction” or “meaningfulness.” While many people recognize that an individual’s choice to have a child has important external implications, the decision is thought to necessarily involve an intimate, personal component, and so it is a decision that is best made from the personal standpoints of prospective parents.  Guides for prospective parents often suggest that people ask themselves if having a baby will enhance an already happy life, and encourage prospective parents to reflect on, for  example, how they see themselves in five and ten years’ time, whether they feel ready to care  for and nurture the human being they’ve created, whether they think they’d be a happy and content mother (or father), whether having a baby of their own would make life more meaningful, whether they are ready for the tradeoffs that come with being a parent, whether they desire to continue with their current career plans or other personal projects, and so on.
I'm sure most people would agree that the decision to have children usually does, and generally should, involve an intimate, personal component.  I'm sure most people would also agree that issues concerning "life satisfaction" often do arise when considering whether or not to become a parent.  However, this does not clearly involve unique phenomenal properties.  The "guides" Paul mentions are focused on practical questions concerning readiness to commit to years of care-giving, readiness to make trade-offs, willingness to change career plans, and whether the parents-to-be (or not-to-be) think they would be happy and content.  It seems like the bulk of this is stuff that people can form justified true beliefs about without having to first have children.  It doesn't look like qualia.  Perhaps qualia can be involved when we talk about the meaningfulness of a life with (or without) children.  If there is an irreducibly subjective component, that must be where it is.  However, Paul has presented the decision as one between a life which is more meaningful with one which is less meaningful.  It is reasonable to suppose that one can know what it is like to have a life which is more meaningful (or less meaningful) without knowing the unique phenomenal properties involved with making your life more (or less) meaningful.  You might not know the unique subjective states which will make your life more (or less) meaningful, but you know what it is like to experience an increase (or decrease) in the meaningfulness of your life.

So let's imagine some people considering whether or not to have children.  They feel like their lives are not as meaningful as they could be.  They didn't always feel this way, of course.  It came with the aging process.  Now that they are adults, they believe that having children has a high probability of filling this new void.  They don't know how it will feel, exactly.  They don't know what it will be like (in the sense of phenomenal properties, remember), and they don't pretend that they do.  But they can make the comparison nonetheless.  They can imagine a life without the void, since they remember not having it.  They can predict that it will be even better than before--or at least better than it is now--even if they don't know exactly what experiential states will make it better.  So, even if we stipulate that there are unique phenomenal properties associated with parenthood, you don't need to know them in order to make the comparison required for The Decision to be rational.

If I'm right, then (1) would seem false--and it is false, unless "what it would be like" in (1) does not refer to phenomenal properties.  It refers to all the stuff that Paul mentions in that quote:  the practical trade-offs, the happiness and well-being, and so on.  It refers to the stuff that people talk about and form reasonable beliefs about without actually having the experience.  So Paul's argument is invalid by reason of equivocation.

Update (March 14, 2013): I've begun an email discussion with Professor Paul and hopefully I'll be developing and perhaps even revising my point of view as a result.  I do already see a need to qualify my accusation of equivocation.  As Paul stressed to me in her email, she does intend "what it would be like" to be read in the same sense in both (1) and (2).  So my best charge against her, you might think, is simply that she is wrong about (1).  (I'm ignoring my criticism of (3) at the moment.)  In that case, I'd have to admit that her argument is valid, if not sound.  However, I'm not sure it is that simple.  A lot of people find (1) intuitively appealing, and they are persuaded by Paul's argument for it.  I suspect that there might be some unintentional obfuscation going on.  I think that people might be taking "what it would be like" in (1) to mean something more than, if not entirely other than, phenomenal properties.  I think more needs to be said about this.  Hopefully I'll have time to devote a new post to it soon.