Monday, May 30, 2005

The Assault on Morality Continues

Well, he's out of the gate. The freshly minted Pope is weighing in on Italian politics. Benedict XVI is supporting a boycott of a referendum on medically assisted fertility. The referendum is designed to get rid of absurd restrictions on the current fertility law, which "bans donations of sperm and eggs; defines life as beginning at conception; and allows fertility treatment only to "stable heterosexual couples" who are living together and can prove infertility."

I don't suppose we can expect anything else from a Pope, but we shouldn't lose sight of what a terrible assault on morality this boycott represents. All these possibilities - the donation of sperm and eggs, allowing a woman the right to choose and fertility treatment for unmarried couples, including homosexual ones - are wonderful, kind, and caring. They are designed to improve the quality of life for countless human beings. While people may disagree on whether life begins at conception, I don't think there's anything controversial about the fact that life does not end at birth.

What could be more moral than a society that devotes itself to improving the quality of life for all its members? What kind of organization devotes itself to trying to influence the political system to marginalize some members of society?

Lest one think that the church is merely preaching to its members, and not actively interfering in the political process, consider this quote from the Pope's recent letter to Spanish bishops
"the transmission of the faith and religious practices cannot remain confined to the purely private sphere."
Look around you. Look at your friends. Look at the gay ones, the unmarried ones, the single ones and the infertile ones, and think what this type of statement says about them, about their status on this planet. Doesn't it make your blood boil? It should. How do we put up with such bigotry, just because it comes clothed in the garb of religion?

If you think of yourself as a moral person, this type of attitude should appall you.

Of course, it's not just in Italy that such thinking threatens the moral fabric of society. The far right assault on morality here in the U.S. has gained quite some momentum under the patronage of the Bush administration and its support of dogma. I thought we were assured life, liberty and the pursuit of happiness. How is that consistent with denying that to part of the population when their pursuing it harms no one?

Friday, May 27, 2005

Your Parents May Have Been Right!

I'm referring to this story, about reports of partial vision loss among some men taking either Viagra or Cialis. The question I have is; I thought you were only supposed to go blind if you were the only person in the room.

Maybe it's a pharmaceutical manifestation of our current moral revolution. All sex is wrong these days.

Why Aren't I Asleep Yet?

Well, when I last posted I was in my hotel room working and expecting to go to bed afterwards. However, a surprising thing happened, and one for which I have the blog and email to thank.

It turns out that my good friend JoAnne Hewett (the one from my "Wine Snobs Rock" post early on in my blogging) was also at Fermilab today, serving on a HEPAP (High Energy Physics Advisory Panel) sub-panel. Neither of us would have known that the other was around except that JoAnne read my blog when she got back to her hotel room tonight and found out I was in town. She emailed me and, although it was late, we decided it was ridiculous not to get together, especially since our hotels are just two blocks apart.

I just got back, after we closed down the Warrenville Rock Bottom Brewery. It was great to spend this spontaneous time with JoAnne, and it just wouldn't have been possible without the web and email. It is entirely another, sadder fact that we're both now back on our computers working (I know, because we just emailed each other). Oh well, you can't fight a physicist's true nature.

Thursday, May 26, 2005

I See Physicist Bloggers

Today was a big day for bumping into physicist-bloggers. This afternoon I dropped by the Fermilab Theoretical Astrophysics group and saw this guy, although he was on the phone, so I didn't drop in. This evening I went to a nice Indian restaurant and ran into this guy, who has written on his blog about the escapades of this guy, who was one of my dinner companions. And, as I've mentioned, tomorrow I'm going to see this guy.

I see physicist bloggers. They're everywhere. They think they're regular physicists but they're not; they're bloggers.

Bugs, Blair and Balls

In Britain there is something of a fuss over MMR (Measles, Mumps, Rubella) vaccinations, with the uptake rate now perhaps as low as 72%. When I was a child, to the best of my understanding, basically everyone had the MMR vaccination - it was just a completely normal thing. Now, however, Britain risks measles and mumps epidemics because significant numbers of parents are refusing to have their babies vaccinated.

The reason for this appears to be the existence of a couple of "studies", linking the MMR vaccine in one case to Crohn's disease, and in another to autism. The results of the first (and quite old) study have since been ruled out by later, better research, and the second study was, well, shoddy. The Fins have since completed a very large and comprehensive piece of work that finds no such problems with the vaccine.

Nevertheless, people are stubborn and ill informed and (something about this sounds awfully familiar) large numbers of them are prepared to risk their children, and those of others, to serious diseases, because of this ignorance. It doesn't help that the leader of the nation (again, something is ringing a bell here) is one of those helping perpetuate the nonsense. Yes, that's right, Tony Blair has decided it's OK to expose his precious little cherub to these old-school infections. I guess we shouldn't be too surprised, given what Iraq has taught us about Tony's opinions regarding standards of evidence.

There is a short and funny piece about this by Ben Goldacre in the Bad Science section of today's Guardian. It's partly funny because I don't recall ever seeing someone use the word "balls" in a U.S. newspaper. Maybe it's because so few U.S. news sources have any. Here's a snippet (with apologies to my humanities-graduate friends (including my wife) who don't fall under this statement)
"Because, sadly, the natural world does not quite share my sense of retributive justice, nor does the paramyxovirus that causes mumps. If it were infecting only the innocent unvaccinated offspring of humanities graduates with no understanding of risk, I'd pretend to be sad on their behalf. But no. There were 8,104 cases of mumps confirmed in the UK last year, up from a combined total of 3,907 for all the previous five years, chart fans.

But mumps cases last year were predominantly in young adults, because young adults as a herd have the lowest immunity. And one in five young men who get mumps can expect orchitis, a new joy for fans of infected and inflamed testicles. If your balls hurt and you're infertile, you might wish to thank, for their peculiar interpretation and eulogising on the dangers of MMR: Andrew Wakefield, Nigella Lawson, Libby Purves, Suzanne Moore, Lynda Lee-Potter, The Daily Mail, Leo Blair's tight-lipped parents, and, let's be fair, every single national newspaper."
Makes you cross your legs just reading it.

Tuesday, May 24, 2005


I don't think I'll find many opportunities for blogging over the next few days. I'm at Fermilab, serving on the U.S. Department of Energy site review team. It's a fascinating process, although our days are extremely full. Today we were in sessions from 8:30am until 6:45pm, followed by a dinner. We've been hearing about the collider, the particle physics experiments, experimental astrophysics and theoretical efforts in both areas. Tomorrow it's 8:30am - 8:00pm, and so I can't imagine too much blog-time developing. Nevertheless, service to the community is an important part of an academic's life, and so I'm not complaining about the workload.

I don't want to go into detail about the site review here - it's not the place. However, apart from the actual work involved, it is also nice to see some friends. I had dinner with, among others, Rocky Kolb and my collaborator Nemanja Kaloper, and hope to find a little time tomorrow for a quick beer with Joe Lykken. Over dinner we even found time to sneak some discussions about physics topics of common interest (yes, we're a wild bunch given half a chance).

The site review is over on Thursday afternoon, but I'm staying an extra day in the Chicago area to spend some time with Sean, doing some physics and, almost certainly, some fine dining. I'm always tempted to go back to the Frontera Grill, but there are so many new places to try that I'll probably end up doing that.

Anyway, I need to get some sleep. More when I find a little time.

Sunday, May 22, 2005

Fun, Friends and Physics

It's been a full weekend here in Syracuse. I managed to fit in a round of golf, a long cycle at Onondaga Lake Park, some time in the gym, dinner with friends, editing a draft of a paper and a delightful brunch.

For the last semester we have had a visitor in the department - Gianpiero Mangano, from Naples. Gianpiero is a particle physicist and cosmologist with extremely broad interests. It has been great to have him around and we have even managed to get a project going, which has led to the draft I was editing this weekend. Earlier today Gianpiero had me, my graduate student Antonio De Felice and his friend Akiko over for brunch. It turns out he is a tremendous cook and I left his place three hours later full of four wonderful courses and some nice wine.

One of the great things about being a physicist is that you get to know so many nice people from so many different parts of the world. Today we had two Italians, a Brit and a Japanese woman all having brunch. I don't get the impression that kind of gathering is too common in many other fields.

Anyway, I've had a lovely weekend and am incredibly tired now. Tomorrow afternoon I leave town to spend Tuesday through Thursday at Fermilab and then Friday visiting Sean in Chicago - a whole new mix of physics and fun. Hopefully I'll be able to find time to post at least a few times while on this trip.

Saturday, May 21, 2005

A Torrent of CosmoParticle Data at the LHC

There is an interesting article in this week's New Scientist, about the computing challenge posed by the absurdly large amounts of data that will be generated at the Large Hadron Collider (LHC). The LHC, which will turn on in 2007, will be the world's largest machine, colliding protons at extremely high energies and providing unparalleled insights into the fundamental nature of matter and it's interactions.

There are compelling theoretical reasons to think that our current theories of particle physics require modifying at precisely those energies that the LHC will probe. These current theories are the electroweak theory, which unifies electromagnetism with the weak nuclear force, and quantum chromodynamics (QCD), which describes the strong nuclear force. Because the LHC collides protons together, the particles that cascade out after the collision are the result of a host of electroweak and QCD interactions. The QCD part is particularly complicated, and figuring out which collisions are potentially interesting (a software task that particle experimentalists refer to as triggering) and should be recorded by computer, is a formidable task. The numbers - 15 million Gigabytes of data in year one alone - are truly staggering.

As the New Scientist article comments
"The torrent of information gushing forth from the LHC each year will be enough to fill a stack of CDs three times as high as Mount Everest. To make sense of it will require some 100,000 of today's most powerful PCs, so it is little wonder that CERN - the European centre for particle physics near Geneva that is building the collider - is co-opting a worldwide "grid" of computers to help store and analyse the data."
This computing task is one that it is easy for most physicists to forget about. Those of us not directly involved in the experiment tend to be focused only on the particle physics, and forget the massive engineering, design and computing effort required to make the machine work.

It's not just particle physicists who care about all this. Orange Quark readers will know my view, that particle physics and cosmology are now inseparable, and, indeed, I've commented before on the role that a future International Linear Collider might play in our understanding of the cosmos. The LHC is a necessary precursor to such an endeavor, potentially discovering the Higgs boson (explaining the origin of mass) and very possibly yielding evidence for supersymmetry, extra dimensions, or some other physics beyond the standard model. Any of these discoveries would have profound cosmological implications, perhaps for our understanding of dark matter and of the origin of the asymmetry between matter and antimatter (although the New Scientist article makes it sound a little too much like cosmology is the primary reason for building colliders).

But the list of people expectantly watching the LHC doesn't end with cosmologists. New Scientist quotes François Grey, an IT spokesman for CERN, and reports that
"CERN will need to ensure that no one team or institute hogs the grid. Physicists will probably barter computer time for now, but the system could later work on a pay-as-you-go basis. `Industry is very interested to see how we handle this,' says Grey. `A large grid could be very exciting for commercial business, but they need to know what the business model would be.' "
For me, a sufficient reason to build a machine like the LHC is the breathtaking possibility of understanding more about our universe at its smallest and its largest scales. However, it doesn't hurt that there are other sectors of society that see tangible benefits beyond the fundamental discoveries.

Thursday, May 19, 2005


Yesterday I installed the latest version of Mac OS X - Tiger - on my laptop. It's pretty slick in a number of ways, one of which is the "dashboard" feature, which gives one access to all kinds of little "widget" applications.

I found one called DashBlog that allows me to post directly to my blog from the dashboard, without having to go via's site.

Well, I say it lets me do that. This is the first test. If it works, I may just do most of my quick posts from here.

Wednesday, May 18, 2005

The Phantom Menace

The military, and the many corporations that feed, and are heartily fed by, it, must be rubbing their hands with glee (I've never been a fan of the term "military-industrial complex", thinking it sounds too Orwellian. But, under this administration, it may yet find its way into my vocabulary).

After the huge financial windfall (although a complete and utter scientific and technological farce) of President Reagan's Star Wars program, and its sequel: Star Wars II - National Missile Defense (developed under President Clinton and pushed forward under President Bush), comes the third piece of the trilogy, designed to continue the steady flow of tax dollars from serious social, educational and scientific goals and to your friendly neighborhood weapons companies.

The Phantom Menace to which I refer is the Air Force's recent push to move forward with the weaponization of space. "Phantom" seems an apt word here, given how transient and illusory the previous two initiatives have proved to be. "Menace" fits, because, as I said above, when the government proposes die-in-the-sky ideas like this one, the money has to come from somewhere. The price tag being thrown about for this is in the $100 billion range. Bear in mind that this is before the program gets going properly. How often has a program come in under budget?

We have an education system that is in desperate need of repair, with students leaving high-school ill prepared to compete in the very global marketplace that we have played such a key role in developing. We have no serious efforts to become energy independent - instead relying heavily on foreign oil, and hence ignoring a major way to improve our security. Poverty at home and abroad is being ignored. Scientific progress is being hampered, slowed and, in some cases, erased by harsh budgets and a twisting of the scientific process for the purposes of ideology. (Some of this happened as a direct result of the scientifically misguided moon-mars initiative. Some cynics even suggested that the real purpose of that idea was to funnel money to companies with military expertise. Now I might be starting to see their point.)

Addressing the real problems we face will make us happier, more competitive and safer. It will cost a lot of money, but the good news is that we can afford it, so long as we don't spend too much on our fantasy lives.

Tuesday, May 17, 2005

The Gift that Keeps on Giving

I dropped the 'rents off at the airport this afternoon, and about now they should just have taken off from New York heading back to England. It was so great to have them here, and we'll miss them now that they've left.

I came home afterwards and was sitting reading, and realized that this simple pleasure is one of the things I have to thank my parents for. When I was a kid they were always reading. Every week we'd go down to the local library and pick up a whole new pile of books, take them home, read them, and be back again the following week to do it all again. They would lend me their library tickets to enable me to borrow more books than my limit. They would borrow books from the adult part of the library (not that adult section) when I wanted them, but wasn't physically old enough to have tickets for that part. They would only loosely police my room after I'd been told to put my light off and go to sleep after the end of the chapter. They would buy me books for my birthdays and for Christmases. And they would buy and borrow books to help me answer the annoying stream of questions with which I would harass them (When they visit, Sara and my parents bond over how annoying I can be, and this is one of their favorite traits to pick on).

In the neighborhood in which I grew up, I think it's fair to say that hardly any other parents encouraged their children to read in this way. My brother and I both grew up as readers; most other people I knew growing up didn't read then, and almost certainly don't today.

The parenting is so important, and I was so lucky! What a wonderful gift. I wish I knew how we could give this gift to children who are not fortunate enough to have parents like mine.

Monday, May 16, 2005

Taking the Blame

Most news organizations, for example the New York Times, are reporting that Newsweek is withdrawing the article that mentioned that a copy of the Koran had been flushed down the toilet at Guantánamo Bay. At least 17 people died as a result of the violence that took place over this report. There has apparently been intense pressure from the White House on this matter, but the pertinent point is that the magazine can no longer sufficiently substantiate the story.

While it is right and proper for a story that cannot be adequately substantiated to be withdrawn, in my opinion almost all news stories on this are missing the most important point. While Newsweek may have done something wrong here, isn't it most ridiculous, most outrageous and most morally reprehensible that some people were able to kill many other people over a book being flushed down the toilet? Only religious fervor can lead to this - no rational behavior allows for it.

Go ahead, flush a copy of the Principia today; I promise you'll be OK.

Friday, May 13, 2005

More Cardiff Giants Please

Sara and I took my parents and her parents to Cooperstown for the day yesterday. It was relaxing and fun. My Dad and my Father-in-law went to the Farmers' Museum, but unfortunately weren't able to see the Cardiff Giant. If you don't know what that is, let me quote from part of the description:
"The Cardiff Giant was conceived by George Hull, a cigar manufacturer and atheist, after he'd spent an evening arguing with a fundamentalist minister. Hull remembered Genesis 6:4 and its reference to "giants in the earth" and wondered if people like the minister could be convinced that a large, stone statue found in the ground was actually a "petrified giant." He decided to find out."
Needless to say, the magnificent Mr. Hull made a fake and buried it. When it was discovered, most people realized it was a fake, but Christian fundamentalists defended it zealously. This all happened in 1868 and 1869.
"After years of haggling, the New York Historical Association bought the giant for $30,000 and brought it to Cooperstown, where it has resided at the Farmers Museum ... ever since."
You can bet we'll be going back some other time to see this wonder of 19th century reason.

Some Recent Reading

My parents are keen readers, and have made sure to pass this on to me. When they visit us, they're officially on vacation and spend even more time reading. Some of the time I set aside to spend with them while they're here is often spent reading, and so I seem to get through books much more quickly when they're around.

In the last week I've read two books. One is Sam Harris's The End of Faith, and the other is Ian McEwan's Saturday.

Harris's book was quite enjoyable, in the sense that it feels great to have reasonable ideas, that you hold dear, repeated over and over to you. Unfortunately, this makes it all the more jarring when one reaches the parts where he overreaches somewhat. I don't want to review the book here, but Michael Bérubé has some interesting things to say about loving The End of Faith and taking issue with it, I essentially agree with Michael's broad statements (but don't have the philosophical specifics he has, of course).

I have no such ambivalence about Saturday. For my tastes, McEwan is a master. One could rave about a number of aspects of his craft, but I just love the way he creates the sense of emotion. When McEwan's characters feel guilt, shame, love, anger, obligation, or any other of the feelings that help define what it is to be human, it's not just that one sees what he means, but rather that one feels these emotions personally, immediately and viscerally. I lose count of the number of times the hairs on my neck rise, my stomach tightens, or I find myself dry-mouthed and swallowing, just by reading his prose.

In my opinion, Saturday is as good as anything he's written and, in particular, for my tastes, better even than his Booker prize winning Amsterdam. (And I haven't even mentioned his multiple passages that praise the beauty of the scientific view of the world)

Wednesday, May 11, 2005

Inflation and the Initial Conditions of the Universe

Over at Preposterous Universe, Sean has been discussing an essay he's written about his recent work on eternal inflation and the arrow of time. In the paper, and in the comments on his post, there has been a discussion about what it means to require a sufficiently large, smooth, potential energy dominated patch of the universe in order for inflation to begin. Sean referred people to a paper I wrote with Tanmay Vachaspati and I thought that, given the current interest, it might be useful to describe that work here. This will be a little more technical than usual, but far less technical than the actual paper (hopefully).

As I first learned about inflation, the idea can be summarized as the following: the universe is born and one can say very little about it since quantum gravity (whatever that is) is undoubtedly important at extremely early times. However, after some time (approximately the Planck time), the semi-classical universe emerges, and we can begin to analyze meaningfully such things as the dynamics of field theories, and the response of gravity to them. There is no a priori reason for the universe to be homogeneous at this epoch. However, local, causal particle dynamics can act to homogenize patches of the universe. After some time, a small patch becomes homogeneous and dominated by the vacuum energy of a scalar field. This patch then undergoes inflation - a quasi-exponential period of expansion in which the original small patch expands to a size many orders of magnitude larger than the observable universe today. This expansion explains the flatness of the universe, and its homogeneity on large scales today.

Now, there are a number of models of inflation in which the above story is modified (in particular, chaotic inflation), and I'll get back to them later. For now let me focus on this claim of homogeneity in the theories I described above.

Why does inflation, as described, "solve" the homogeneity (or horizon) problem? Clearly, the idea is that the homogeneity of the initial pre-inflationary patch, explained by causal physics, is translated into the homogeneity of the larger space after the exponential expansion. At the risk of being pedantic (me? pedantic?), this can only be true if the original patch is made homogeneous by causal processes, otherwise homogeneity would once again be an assumption, albeit a less severe one.

What did we do in our paper? We first imagined that the early universe, emerging from the Planck epoch, was not inflating. To make progress we'll need a few definitions, which I'll define below in a more blog-friendly way than in the paper.

Let's focus on spherically symmetric space-times and pick an origin. Then examine spherical surfaces centered on this origin. Such surfaces can be divided into three categories in the following way. Imagine sitting on such a surface with two flashlights, both pointing radially and close together. The flashlights can both be pointing outwards (away from the origin), or both pointing inwards (towards the origin). The categories are then:
  1. NORMAL: When the flashlights point inwards, the rays converge to the origin. When they point outwards, the rays diverge away from the origin. This is how regular parts of space-time behave; for example, points in our universe closer to us than the horizon.

  2. TRAPPED: When the flashlights point inwards, the rays converge to the origin. When they point outwards, the rays still converge to the origin. Such surfaces can be found inside the horizon of a black hole.

  3. ANTI-TRAPPED: When the flashlights point inwards, the rays nevertheless diverge away from the origin. When they point outwards, the rays diverge away from the origin. Such surfaces can be found, for example, beyond the horizon in our universe.
Now, back to what our paper showed. If the universe is not born inflating, then we want to imagine that, at some later time, local, causal particle dynamics yield a patch that is homogeneous and vacuum-dominated, and thus begins to inflate. The fundamental question for us was; how small can this patch be?

The main tool we used is called the Raychaudhuri equation. It describes the rate of change of divergence of close by pairs of light rays, as I described above. The equation is a little complicated but, by considering the types of light rays I mentioned above (perpendicular to spherical surfaces), and by making two further assumptions: that the Einstein equations are satisfied, and that the weak energy condition holds (matter isn't too weird), the most important consequence of the Raychaudhuri equation can be stated as
Light rays pointing inwards cannot emanate from a normal surface and cross an anti-trapped one.
What does this mean? Well, if the original inflating patch is smaller than the Hubble size of the background space-time, then, it can be shown that light rays violating the above statement must exist. Thus, we conclude that the size of the initial inflating patch is at least as large as the Hubble size of the background space-time. But this size is large compared to typical particle physics processes that can act to homogenize a region (actually, if the background space-time is radiation-dominated FRW, the Hubble size IS the causal horizon). Thus, it is very hard to see how such an initially homogeneous inflating patch might form. This is our main result.

It is possible that inflation, if it begins, leads to "eternal inflation", in which one patch gives rise to an infinite expanding space, which produces an infinite number of regions of the universe that look like ours. A full understanding of the question of initial conditions (or probabilities) in that case is partly what Sean's paper is about. Tanmay and I viewed our work as explaining what is needed for such an inflationary model to work.

Monday, May 09, 2005

The Beautiful Godlessness of Darwin

It is often complained that the stark precision of science destroys the beauty and poetry of the world. To those of us who spend our lives immersed in science, this is usually at odds with our view of the discipline. However, it is probably true that we fail to capture our own feelings regarding the beauty of science in our writings about it.

What we need are more examples like the following, in which Ian McEwan, in his latest novel Saturday, describes the beauty to be found in evolution, without the need for a deity
"Kindly, driven, infirm Charles in all his humility, bringing on the earthworms and planetary cycles to assist him with a farewell bow. To soften the message, he also summoned up the Creator, but his heart wasn't in it and he ditched Him in later editions. Those five hundred pages deserved only one conclusion: endless and beautiful forms of life, such as you see in a common hedgerow, including exalted beings like ourselves, arose from physical laws, from war of nature, famine and death. This is the grandeur. And a bracing kind of consolation in the brief privilege of consciousness."
Ian McEwan, "Saturday", Doubleday, 2005.
I think this is the picture we need people to see, alongside our formulae, graphs and tight, unambiguous prose. Science as an awesome and humbling description of our world, grounded in reason, and all the more beautiful for it. I've mentioned before that fine science writers are our allies in the fight for reason in the face of nonsense. Clearly, some novelists are also on our side.

Sunday, May 08, 2005

Wigan Athletic vs. Manchester United

This is the kind of football fixture Britain will have to get used to after my hometown team, Wigan Athletic, earned promotion to the English Premiership division earlier today. You can read about their deciding game here. It's going to be weird and wonderful and a lot of fun for Wiganers everywhere.

Large Extra Dimensions and a Hint of Hyperbole

I've spent part of the weekend thinking over some applications of an idea I worked on several years ago. This idea involves the concept of large extra dimensions, which I mentioned briefly once before. I promised then I'd have more to say on the topic, so here goes the first installment.

The hierarchy problem in particle physics is the problem of reconciling two wildly disparate mass scales; the weak scale (102 GeV) and the Planck scale (1019 GeV). This hierarchy is technically unnatural in particle physics, since, in general, the effect of quantum mechanics (here known as renormalization) is to make the observable values of such scales much closer in size.

One approach to this problem is to introduce a mechanism that cancels many of the quantum corrections, allowing the scales to remain widely separated even after quantum mechanics is taken into account. An example of such a mechanism (and the most popular one, for sure) is supersymmetry (SUSY), which I may discuss another time.

However, another perspective is to view the hierarchy problem no longer as a disparity between mass scales, but rather as an issue of length scales, or volumes. The general hypothesis is that the universe as a whole is 3+1+d dimensional (so that there are d extra, spatial dimensions), with gravity propagating in all dimensions, but the standard model fields confined to a 3+1 dimensional submanifold that comprises our observable universe. This submanifold is called the brane (as in membrane).

This is really a superstring-inspired modification of the Kaluza-Klein idea that the universe may have more spatial dimensions than the three that we observe. As in traditional Kaluza-Klein theories, it is necessary that all dimensions other than those we observe be compactified (wrapped up nice and small), so that their existence does not conflict with experimental data. The difference in the new scenarios is that, since standard model fields do not propagate in the extra dimensions, it is only necessary to evade constraints on higher-dimensional gravity, and not, for example, on higher-dimensional electromagnetism. This is important, since electromagnetism is tested to great precision down to extremely small scales, whereas microscopic tests of gravity are far less precise (although remarkable advances have been made in recent years, prompted in part by these theoretical ideas).

Since constraints on the new scenarios are less stringent than those on ordinary Kaluza-Klein theories, the corresponding extra dimensions can be significantly larger, which translates into a much larger allowed volume for the extra dimensions. This extra volume is a big deal!

You can imagine the strength of gravity as being a bit like the force due to a steady stream of water emerging from the nozzle of a hosepipe. Suppose that the water is confined, by some fancy nozzle, say, to emerge in a stream that is essentially one dimensional - a very fine stream. If you've ever fitted a tight nozzle to a hosepipe, then you'll know that such a stream is very powerful, and the force it exerts on you, if pointed your way, is very high.

Now imagine that, instead, the water is spread out to emerge in a plane (OK, that would require one fancy nozzle, but I'm sure you can imagine it). In this case, if your body is in the way of the water in some direction (the same distance from the nozzle as in the first case), it will still exert a force on you, but less than when you were being hit by the one-dimensional stream. This is because you're not being hit by all the water, but instead by a portion of it - there are other directions available for the rest of the water to go.

If we now fit a nozzle that allows the water to spread out in a spherically-symmetric three-dimensional pattern, then the force on your body will be yet weaker because there are still further directions for the water to spread.

The analogy I'm drawing here is with lines of gravitational flux, the density of which, in Newtonian gravity, describes the strength of gravity. The more directions (think dimensions) available for the water (think gravitational flux) to spread, the weaker is the force experienced.

Thus, in the large extra dimensions picture, it is the spreading of gravitational flux into the large volume of the extra dimensions that allows gravity measured on our brane to be so weak, parameterized by the Planck mass MP, while the fundamental scale of physics M* is parameterized by the weak scale, MW, say.

Given this, the problem of understanding the hierarchy between the Planck and weak scales now becomes that of understanding why extra dimensions are stabilized at a linear size (~0.1 mm, for example) that is large with respect to the fundamental length scale (1/M*). This is the rephrasing of the hierarchy problem in these large extra dimension models.

Nemanja Kaloper, John March-Russell and Glenn Starkman and I proposed a modification to the above picture, in which we argued that there exist attractive alternate choices of compactification (the way in which the extra dimensions are wrapped up). These compactifications employ a topologically non-trivial internal space - a so-called d-dimensional compact hyperbolic manifold, and throw into a new light the problem of explaining the large Planck/Weak hierarchy. It'll be fun to blog about these, but since I'd like to keep that discussion distinct from the primer above, I think I'll leave it here for now.

Friday, May 06, 2005

Friday Random Ten (Or "Mark is Lazy & Tired")

I just got back from a Wonderful dinner party with my friends Dympna Callaghan and Chris Kyle. Dympna is a renowned Shakespearean scholar and Chris a historian of the British parliament. However, much more importantly, Chris is a Kiwi (New Zealander) who spent many years in England, and Dympna is from the North of England (although the wrong side of the Pennines). The dinner party guests were Sara and me and my parents, who have become good friends of Chris and Dympna during the past few visits to Syracuse.

We've had a wonderful night, with lots of Brit-talk, and an abundance of excellent food and wine. I'm feeling lazy and tired and, hence, here is my first Friday random ten, fresh from my iPod.
  • There It Is, Barry White
  • Graceland, Paul Simon
  • The Update, Beastie Boys
  • Hey Ya, Outkast
  • War Child, The Cranberries
  • Sunrise, Norah Jones
  • Starlight Hour, Ella Fitzgerald
  • Vivo Sonhando Dreamer, Astrud Gilberto
  • Maria, Blondie
  • Chyna Black, Anthony Hamilton

Thursday, May 05, 2005

Blair Goes 3 for 3

As I write, Tony Blair and the Labour party have just passed the 324 seats needed to win a historic third term. I guess I'm pleased, compared to the alternative. Blair's majority is looking, at this point, to be greatly reduced, as one might expect, given the circumstances.

You might have thought that Labour was confident, but one glance at Tony Blair's agent, John Burton, tells the real story.

I hope that Blair personally remembers this close shave and that the party takes it to heart and replaces him with someone else (realistically, it would probably be Gordon Brown) to at least try to acknowledge the Iraq stench that sticks to the party at present. The people who voted for Labour with noses pegged would at least feel somewhat vindicated by that.

Wednesday, May 04, 2005

The British Election for Expats

On the eve of the British general election, there is a delightful piece by Simon Schama in The Guardian. Much of it focuses on the differences between the election seasons in the U.S. and the U.K., and will resonate with any expat reader. Here's a particularly descriptive (and laugh-out-loud funny) paragraph:
"I was a just few hours off the jumbo from Newark, New Jersey, but it felt like dropping down the rabbit hole and emerging into parish pump politics. Compared with the engorged rapture, the fully orchestrated Hollywood production numbers; the serried ranks of Raybanned Secret Service Men; the ululating good 'ole boys, the big-hair hoopla, the bra-popping, pompom waggling cheerleaders, the Spandex highkicks; the tossing ocean of flags; the relentlessly inspirational gospel songs; the banners as big as a wall; the parade of uniforms (any uniform will do - firemen, police, marines, traffic wardens, apartment house doormen); the descending chopper blades; the eventual appearance of the Awaited One to swoons of joy and exultant whoops of messianic acclaim; compared to the whole delirious cornball razzmatazz that passes for democratic politics in the great American empire, Ashford on a bank holiday weekend was utter Ambridge. Thank God. Except he too was mercifully missing from the general election."
The entire piece is punchy, humorous, full of gems like this, and more compact than his "A History of Britain" trilogy. Immediately after the end of the article, there's also a hilarious little ad for a quintessentially British show of defiance
"Time for Operation Nose Peg: hundreds of readers have requested Polly Toynbee's ingenious nose pegs to allow them to vote Labour today while holding their nose. If you are one of them, don't forget to take a picture of yourself at your polling station wearing the nose peg and G2 will publish them after the election. Email or send your pic to G2, The Guardian, 119 Farringdon Road, London EC1R 3ER."
Sometimes I really miss England.

U.S. Universities Presented with Outstanding Opportunity

My good friend and frequent collaborator Sean Carroll has been denied tenure at Chicago. Sean and I spoke about this for a while on Friday, shortly after he'd found out, and he has just posted about it on his blog, Preposterous Universe.

I can't do real justice here to the respect I have for Sean as a scientist, independent of our friendship. He is a formidable intellect, a deep-thinking cosmologist and particle physicist, and one of the most socially responsible members of our field that I know. Sean has made important and well-recognized contributions to theoretical cosmology, while popularizing the subject through his fantastic public lectures, organizing tremendous conferences and mentoring outrageous numbers of postdocs, graduate students and undergraduates. Our collaborations have been some of the high points of my career both from an intellectual and a purely fun viewpoint. And I haven't even mentioned his wonderful G.R. textbook.

As Sean says himself, this is a sad situation for him. However, everyone within the field realizes that there's going to be a fascinating feeding frenzy as many excellent places fight over him. He's going to end up somewhere great, and wherever that is, they will be lucky to have him. I know we're going to continue to write good papers together; only the institutional affiliation will change.

Sean says blogging will be a lower priority for a while. I understand this, as I'm sure we all do. However, I think it's worth encouraging him to continue to post quite regularly. Just because Chicago has chosen to lose a world-class young cosmologist doesn't mean we should lose one of our most eloquent and prolific commentators on science and society.

Tuesday, May 03, 2005

Well I'll be a Monkey's Great, Great, ... , Great Grandson

Science is under attack in Kansas once again. On Thursday, the Kansas State Board of Education will begin hearings into the teaching of evolution. Intelligent Design cranks had hoped to use the "debate" to elevate their thinly disguised religious agenda to the same level as established science. However, as far as I understand, many scientists who were asked to speak have refused to lend credence to this obvious nonsense. I applaud their eminently sensible choices.

The Kansas debacle is being reported in many places, but I read a particularly interesting take on it in the Christian Science Monitor, which discusses the role of brainwashed students in the fight against reason. Don't we usually put people in prison for child abuse?

Sunday, May 01, 2005

A Heartwrenching Vote

The British General Election will take place this Thursday, May 5th. I've mentioned before how much agonizing I've been doing about this particular election. Stories about the Labour leadership's deliberate misleading of the public about the Iraq war continue to come out, even today. I think that, to a reasonable extent, it has been established that the government both lied about the evidence, and ignored expert advice about the legality of the war. I remain disappointed and furious about this. To reward a Prime Minister for such duplicity with a third term is almost unthinkable, and to play a part in that would leave me feeling in need of a good shower.

But I'm going to do it anyway.

Although I've given this a lot of thought, and have considered as many of the issues as I can, my ultimate reasons are not subtle at all. The next Prime Minister will either be Tony Blair or Michael Howard. Despite my deep dislike of Blair and of his lies over Iraq, I can't contribute in any way to a Conservative victory.

For most of my life in England I lived under a Conservative government. In fact, an article I recently read about the Conservatives' use of some of the same political consultants as the Bush campaign, brought to mind the role of Saatchi & Saatchi in propelling the Conservative government of Margaret Thatcher to power in the late 1970s. I can't overstate what a disaster that election was for Britain. In the North West, where I lived, unemployment rose to percentages in the 20s, and some people committed suicide they were so depressed with their lives during, and about their prospects after, long-term unemployment. I was thinking this over tonight, while hanging out with my Mum and Dad, both of whom struggled and sacrificed mightily to raise my brother and me during my Father's many years of unavoidable unemployment under Thatcher. My parents made a wonderful childhood for us during those years, but the thought of what they went through to make that happen angers me even today.

When I read the Conservative party manifesto, I see nothing to make me think that today's Tories are less likely to wreak havoc on working people than Thatcher's did. Granted, Labour no longer presents as clear or attractive an alternative as it did when I was growing up. Nevertheless, when I look at the economy, the attempts to battle the class system, the attitude to Europe, the fight for workers' rights, education and healthcare, I'm convinced that life, for most of the population, will be better under Labour than under the Conservatives.

For me, at least, I need to vote in a way that will make a difference to the world as it is, not as I wish it were. So I will swallow my bile, vote for Blair, and get out a big bar of soap.

(At least, I would, if I hadn't realized too late that my Dad would be here when the election took place, and therefore wouldn't be able to cast my proxy vote.)