As I advertised, the bloggingheads.tv discussion that Sean and I recorded on Wednesday is now posted

following on from on our first effort, and covering different, and somewhat more controversial topics.

Hope you enjoy it.

On Wednesday Sean and I recorded another episode of bloggingheads.tv. In our last outing we discussed the standard cosmology, dark matter, cosmic acceleration, and a number of other issues concerning the observed matter-energy content of today’s universe. This time, we thought we’d go all early universe on you and discuss the problems of the standard cosmology, inflation, its shortcomings, and ultimately the initial conditions of the universe. Some of these topics, such as inflation, have a rather tight connection to current observations, while others are more speculative and some are touching on the philosophical, at least at this stage in our understanding.

We’ll post a link to the new episode when it comes out tomorrow. At one stage Sean and I discuss the initial conditions for inflation, and in doing so we were led into the issues of eternal inflation, entropy and the arrow of time (I guess he’s written some sort of extended blog post about it). Leading up to this, however, I brought up the question of what it means to require a sufficiently large, smooth, potential energy dominated patch of the universe in order for inflation to begin. I referred to a paper I wrote many years ago with Tanmay Vachaspati and I thought that it might be useful to describe that work here. I’ve done this before, over at Orange Quark, but it can’t hurt to have a version here also. 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, 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, in this simple context it is hard to see how such an initially homogeneous inflating patch might form. This was our main result.

However, one of the things Sean and I discussed on blogginheads.tv was eternal inflation – the idea, supported by careful calculations in some models, that it is possible that inflation, if it begins in one patch of the universe, gives rise to an infinite expanding space, which produces an infinite number of regions of the universe that look like ours. This provides a very different was to think about the probability for inflation beginning, and seems to provide a possible way around the problem we pointed out. Furthermore, it may provide a way to seek answers to some of the other big questions of the earliest times in the universe – many of which depend on a full understanding of the issue of initial conditions.

I’m sure you’ll be able to find a relevant book if you’re interested in learning more.

Not all scientists work at universities. (Maybe not even most? I honestly don’t know the breakdown.) But people who do work at colleges and universities sometimes talk as if that’s all there is, or that becoming a professor is the only logical goal for those pursuing a scientific degree — not necessarily from snootiness or elitism, but just because that’s what they know.

So it’s great that Chad Orzel has done a series of short interviews with scientists outside academia, and is gradually blogging the results. It’s a nice little bit of informal sociology of the field, and a useful resource for anyone who might be contemplating such a career path themselves.

Chad, as you probably know, has also written a book that will be coming out later this year. And he’s supposed to be doing scientific research, and keeps up an active blog! How is that possible?

People writing books, I have to imagine, are much like people with babies. This newborn thing has been the center of their life, and will continue to be, for some time; and one naturally presumes that the rest of the world shares one’s fascination with it. This presumption, alas, may not always be true.

You may have heard that I have a book coming out — pushed back to January, unfortunately. I haven’t shown any hesitation in blogging about substantive questions related to the topic of the book, nor do I see any reason to. And once it comes out I do want to do some sort of book club so that people can ask questions and have a conversation about what’s in the various chapters. So there will be no shortage of book-related stuff here on the blog.

But there is a whole ‘nother level of bookish miscellany — admiring the illustrations, having blurbs come in for the back cover, setting up public talks, and all that. Now we’re pretty much into baby-picture territory; it might not be completely safe to assume that everyone else is as fascinated by all this as I am. But you don’t want to deprive those who are, right? So I’m sending all that stuff here:

• From Eternity to Here Facebook page.

That will shield you from the worst of my enthusiasms. A bit, anyway.

Not that I’m at all sure that this is the right thing to do. Back in my day, we didn’t have all these fancy social networks to play around in; you had your blog, and that was it. Now there’s been a bit of proliferation, and there’s no question that it’s changing the landscape. It can obviously be annoying to try to follow too many things at once, but on the other hand it’s nice to have more appropriate tools for distinct tasks. In the old days, I wouldn’t think much of writing a blog post with an amusing link and little else. Now I will just put that on my Twitter feed. So there are fewer blog posts overall, but the average amount of substance per post is higher. Is this an improvement? Not really sure.

A lot of bloggers have Twitter feeds where they link to every one of their blog posts, which seems backwards to me. (So I usually don’t subscribe to those folks — nothing personal.) I once asked (on Twitter) whether people thought that was a useful service, and I received strong opinions on either side — but then I noticed that everyone who was in favor of linking to every blog post on Twitter was a blogger who linked to every one of their blog posts on Twitter. So I resist. But then again, I synchronize my Twitter feed to my Facebook status updates, which is considered unforgivably gauche in some circles. So who am I to complain?

Yesterday Mark and I recorded a dialogue for Bloggingheads.tv, which hopefully should appear tomorrow. The Bloggingheads people love science, and they are always looking for suggestions for new participants. In addition to Mark and me, we’ve already had Julianne appear. I can think of two other obvious ideas: JoAnne and John could discuss the LHC, and Daniel and Risa could discuss late-universe cosmology. I’ll get to work on those.

So — any other ideas? Who should BH.tv have on to talk about science? They need not be bloggers, although that’s always nice. They do need to be realistic — Richard Dawkins or Steven Weinberg would be great, but they have other outlets when they want to reach a wide audience. (Although it wouldn’t hurt to ask, I suppose.) Any suggestions?

The Science and Entertainment Exchange has lurched into the early 21st century by starting its own blog, the X-Change Files. They’re going to have a weekly “column” rotating between Lawrence Krauss, Matt Parney, Jennifer Ouellette, Sid Perkowitz, and Jerry Zucker. So you know where to go for your regular dose of science and entertainment goodness.

Jerry Zucker and his wife Janet Zucker deserve a great deal of credit for turning the idea of the Exchange into a reality. More importantly, for a twelve-year-old such as I was at the time, The Kentucky Fried Movie was a major event in modern cinema. So I was pleased to see that the title of Jerry’s post (“I’d Like to Thank the National Academy”) was the same one that I had used when I gave a talk at the NAS annual meeting. Not that either one of us should be overly proud of that particular line.

Also, he gets away with saying stuff like this:

The really great thing about these scientists is that because their brains are exactly two-and-a-half times the size of the average person’s in the movie business (although in fairness, that also includes talent agents), they are actually more creative and therefore much better at coming up with science-related ideas for movies than our so-called “creative community.” I don’t mean to offend anyone but as much as I loved Slumdog Millionaire, it’s no Viagra. Often, science gets tacked on like wallpaper in a story, but when it’s really integrated into the narrative it can take things in surprising new directions. And thanks to the Exchange and the National Academy of Sciences, research just became much more fun.

That thing about the brain sizes is what they call “creative license.” But it’s deployed in the service of making a good point! Scientists are good at coming up with ideas, and it would be great if a closer relationship between science and Hollywood helped some of those fun ideas percolate into the wider culture. (My giant brain scoffs at giving specifics about how this will actually happen.)

Miscellaneous happenings, including a couple of talks I’ll be giving — one on another coast, one in another plane of existence.

• 3 Quarks Daily has announced a series of four annual prizes, for blog posts in Science, Arts & Literature, Politics, and Philosophy. Science is the first one up, and they’re asking for nominations — the deadline is soon (June 1) so head over there and make suggestions. The final winner will be chosen by a well-known person in the appropriate field; this year’s Science judge will be Stephen Pinker. You are of course welcome to suggest your favorite CV post, because we like the attention. But this would also be a great opportunity to give a boost to that lesser-known blog that you really like and think should get more attention. (There are a lot of good blogs out there.) And if you are someone with a blog, don’t feel shy about nominating a post of your own — most readers don’t keep a mental file of your best posts over the last year.
• The World Science Festival is happening in New York (the U.S.’s second most interesting city) from June 10 to 14. I’ll be there, speaking at two different events. On Friday June 12 there is the WSF Spotlight, which is an informal forum with short talks and a lot of discussion. Participants include Kristin Baldwin (cell biologist), Dominic Johnson (political scientist), Christopher McKay (solar system researcher), and Frank Wilczek (not sure what he does for a living). I believe alcoholic beverages will be available; it’s that kind of event. Then on Saturday June 13 I’ll be on a panel discussing Time Since Einstein, with David Albert, George Ellis, Michael Heller, John Hockenberry, Fotini Markopoulou-Kalamara, and Roger Penrose. (I predict already that insufficient time will be a popular complaint about the time panel.)
• In Second Life, I’m giving a talk tomorrow morning at 10 am Pacific, sponsored by the Meta Institute for Computational Astrophysics. It will be a colloquium-level talk about “Dark Forces,” concentrating on building models of interacting dark matter and dark energy. Second Lifers can beam right there thanks to this elegant and finely-crafted link: http://slurl.com/secondlife/StellaNova/76/200/32.
• Max Brockman (son of John, doyen of Edge) has edited a new collection of essays: What’s Next? Dispatches from the Future of Science. There’s an essay by me in there on “Our Place in an Unnatural Universe.” You should buy it, because it would be like reading a set of interesting blog posts, but on paper. And most of these folks don’t have blogs!

Many of you know that, in addition to my duties as scientist and blogger, I have recently started a Twitter account. This allows me to share with the world all of the deep insights, amusing trifles, and enlightening links that are just too short to fit into a blog post.

It has not escaped my attention that the world is filled with grumpy old people (of all ages) who take great joy in mocking the mode of superficial sound-bite communication that Twitter embodies. Usually this mockery is broadcast by means of their blogs or Facebook accounts, which … well, I’ll let you finish the thought. (Some of it will be broadcast, I hereby predict, in the comment section attached to this post.)

So I was going to let it pass when our wonderful new bloggy neighbor Sheril took the time to explain in great detail why she disapproves of Twitter. Different strokes, and all that. But then she went a step too far: she linked to a column by Maureen Dowd, and described it as “terrific.” Oh Sheril, how could you?

Here are some excerpts from Ms. Dowd’s foray into honest reportage — the probing queries she asked during her interview with the founders of Twitter.

I was here on a simple quest: curious to know if the inventors of Twitter were as annoying as their invention.

ME: Did you know you were designing a toy for bored celebrities and high-school girls?

ME: If you were out with a girl and she started twittering about it in the middle, would that be a deal-breaker or a turn-on?

ME: Do you ever think “I don’t care that my friend is having a hamburger?”

ME: Why did you think the answer to e-mail was a new kind of e-mail?

ME: Why did you call the company Twitter instead of Clutter?

ME: Was there anything in your childhood that led you to want to destroy civilization as we know it?

I guess these are the kinds of questions they’re teaching people to ask in Serious Journalism school these days. (The answers were a lot more polite than I would have been.)

The anti-Twitter crowd always hastens to explain that they are not, really, grumpy old Luddite curmudgeons. The reason why it’s necessary to make this point is, of course, because they are all grumpy old Luddite curmudgeons. And here’s how we know: a little-appreciated feature of the Twitter technology is that it’s completely optional! You don’t have to get involved. It’s okay, really. Nobody is forcing you. Now, when there is something new going around that nobody is forcing you to be involved with, there are a couple of possible non-curmudgeonly responses. One is: ignore it completely. Nothing wrong with that. Another is: give it a try, decide whether or not you like it; if so, your happiness has been marginally improved, and if not, leave and get on with your life. Simple!

And then there is one quintessentially curmudgeonly response: don’t try it, but take valuable time out of your day explaining to other people why they shouldn’t be enjoying it, either. The only difference between that and yelling “Get off my lawn!” is — well, there isn’t any difference, really.

For me, Twitter is mildly amusing for three minutes a day. Could take it or leave it, really. But it’s nice to get science links from the Telegraph, updates on Penn State’s spring practice from Jay Paterno, Senate gossip from Claire McCaskill, peeks at the Iron Man II set from Jon Favreau, breathless scoops from Roland Hedley, or reassurances of continued insanity from John McCain. I find it interesting, but that’s me. Again: completely optional!

The biggest substantive complaint is that we have become a society of over-sharers, and one simply doesn’t want to be continually updated about what people had for dinner. Again: fine! Just don’t subscribe to Newt Gingrich’s feed. But the claim that Twitter is nothing but mindless inanities is just as wrong as the analogous claim for blogs — in fact it’s precisely the same claim, five years later. There are other things you can do with the technology — the technical terms are “lifecasting” [here's what I had for dinner] vs. “mindcasting” [here's a thought, a question, an observation, a link to something more substantial]. And if someone else really does want to know what their friends are having for dinner, why should you be so bothered?

Twitter is not very important, on the cosmic scale of things. It’s just a fun little gadget. But it’s a small part of something very important: a changing information landscape that enables new kinds of communication. (That link via David Harris’s Twitter feed.) Nobody has any idea what that landscape is going to look like twenty years from now, but it’s interesting to watch it evolve. Not that anyone is forcing you to do so.

Do not be alarmed! The blog has not Gone Galt in protest of the encroaching socialist menace, or have we been dumping teabags in public parks at outrage over Obama’s tax cuts. Sometimes, you know, the real world gets in the way.

But the internet chugs on! Especially here at Discover. And a good thing, too. Of late:

• You may have heard the news that celebrity blogger Phil Plait and Discover CEO Henry Donahue made a bet — against themselves, basically — and lost. Or won, depending on how you look at it. The bet was whether Bad Astronomy could get two million page views in a month, and the stakes were permanent: tatoos for everyone! Phil is thinking about a galaxy, while Henry is going for something more piscatorial, in the best tradition of scientific tattoos.
• If Cosmic Variance gets over two million page views next month, I hereby promise that Julianne will get a tattoo.
• Discover has also launched its first video game: Star Formation! Just what the title says, you get to play the Hand of God, using supernovae to nudge the interstellar medium into the right configuration to make new stars. After playing, we have more evidence that I would not be any good at being God.
• Explain evolution in two minutes! It’s biology, right, how hard can it be? This is a contest to make a video that communicates the idea of evolution in 120 seconds or less.
• Quantum Diaries is back. A set of blogs by a bunch of physicists — experimental particle physicists, more specifically — who talk about the work they do and their lives as scientists. A crazy concept!
• And speaking of crazy concepts: yes, a list has popped up on the internet of the 50 Most Brilliant Atheists of All Time. No Lucretius or La Mettrie or d’Holbach or Voltaire, but Mick Jagger is on there. Sex appeal sells, baby.

We’re happy to welcome The Intersection, featuring the bloggy stylings of Chris Mooney and Sheril Kirshenbaum, to their new home here at Discover Blogs! Anyone who isn’t already following their excellent work is encouraged to go have a look.

It’s great timing, as Sheril and Chris are experts in the intersection of science and journalism (among other intersections), and that’s going to be a hot topic in the days to come. There was something of a dustup a few months ago, set off by dueling Bloggingheads dialogues, first from science bloggers Abbie Smith and Ed Yong, then by journalists George Johnson and John Horgan. Apparently Abbie was questioning the role of journalists in an era where scientists can reach out themselves through blogs, and George responded in a somewhat intemperate fashion. (He later apologized for the tone, although not really the sentiment.) Much back-and-forth ensued — see responses by Brian Switek and Chad Orzel. And just last week, Geoff Brumfiel at Nature wrote a feature exploring the relationship between science journalism and science blogs, with the tagline: “But can the one replace the other?”

Well, no. Science blogging will never replace science journalism, any more than other kinds of blogging will replace other kinds of journalism. (Of course blogging can include just about any kind of writing, including what we usually call “journalism”; I’m thinking here of the specific case of people whose day job is doing science, and who blog in their spare time.) They have very different roles. Journalists are paid to cover stories of wide interest, to get multiple perspectives on new results, and to be as objective as possible in separating the wheat from the chaff. Science bloggers are sometimes going to blog about something newsworthy, but most can’t be bothered trying to cover every interesting story, and years will pass before a typical blogger picks up a phone to interview a source before posting. Instead, they bring a special expertise and inside knowledge to a field that no general-purpose journalist can hope to match.

I’m not sure what the source of controversy really is. It seems perfectly obvious that science blogging should enrich and extend conventional science journalism, not aspire to replace it. (See also sensible takes from Jessica Palmer at bioephemera and Curtis Brainard at the Columbia Journalism Review. [Hey! A blogger and a journalist!]) Movies didn’t replace live theater, airplanes didn’t replace cars, mammals didn’t replace birds. These are things that serve different functions.

The conversation we should be having is how the two forms can work together. How great would it be, for example, if major newspapers regularly linked to relevant blog entries by real experts when a big science story broke? It might actually require some effort to make something like that happen, just because of the way journalism these days works, including the tradition of embargoed results. When the Bullet Cluster results indicating the existence of dark matter were first released, I was lucky enough to be a participant in the original press conference, so I had access to the papers before most people did. Consequently, I was able to write an informed post that could be pointed to by people looking for an expert-level discussion. But ordinarily, such pre-embargo access is only given to professional journalists. If the communities worked a bit more closely together, we might be able to more regularly combine the reportage and explanatory skills of professional journalists with the in-depth perspective of professional scientists.

Meanwhile, newspapers are dying. CNN shut down its science division. The amount of real science journalism is shrinking dramatically, and any scientist who thinks that’s a good thing for the field as a whole is living in crazy land. The old ways of doing business are crumbling, and we have to find new ways to work together.