Speaking of self-repair, here’s a fascinating new finding from Malin Hernebring in Sweden. Here’s the technical paper, from a few years ago; it’s part of Hernebring’s Ph.D. thesis work. (Via Richard Dawkins’s site.)

As we age, our cells gradually decay; the DNA stays relatively intact, but proteins degrade with time. This is a big part of the aging process, leading to wrinkled skin as well as more serious consequences. When you think about it a bit, that raises a puzzle. A newborn baby arises out of the cells of its parents. So if the proteins simply decay without repair, every generation would get handed down a degraded set of proteins. At some point, therefore, there has to be some repair job, so that the baby gets fully functioning proteins.

If this idea is right, you might guess that the repairs happen at the level of ovum and sperm; maybe when these cells are created, extra effort goes into tuning up their proteins into working order. But the new research says no — it’s actually after conception that the clean-up crew arrives. The newly conceived embryo consists of stem cells that soon begin differentiating themselves into the different kind of mature cells. It turns out that it’s during this differentiation process that proteasomes go to work, breaking down the damaged proteins and generally tuning up the engine. (Maybe this is when the soul is implanted in the embryo?)

The next obvious question is: why can’t these cellular clean-up crews be active all the time? There are clear implications for studies of (and therapeutic approaches to) aging. Nature wants all the individual animal organisms to die, making room for new generations; but there’s no reason we have to go along with the plan.

Lisa Randall is a friend and collaborator, as well as a science superstar. She is one of the most highly cited physicists of all time, for a variety of contributions to field theory and particle physics, especially her work with Raman Sundrum on warped extra dimensions. Her first book, Warped Passages, was a major success, which naturally raises the question of what one does next. (Besides writing papers, I mean.)

So we’re very happy to welcome Lisa aboard to guest blog about her new book, just out today: Knocking on Heaven’s Door: How Physics and Scientific Thinking Illuminate the Universe and the Modern World. (Among other virtues, this book has the single most impressive collection of blurbers of any book ever written, from Bill Clinton to Carlton Cuse.) From personal experience I can verify that writing a book doesn’t just happen; it’s a tremendous commitment over an extended period of time, and once it’s done there’s not much chance to go back and change it. So deciding to write a book at all, and more importantly how exactly to target the writing, is a delicate and critical process.

While Lisa hasn’t yet become a regular blogger, she is active on Twitter, where you can follow her at @lirarandall.

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In conjunction with the publication of Knocking on Heaven’s Door, I thought I’d take advantage of Sean’s kind invitation to post on Cosmic Variance to explain my motivations in writing my book. I haven’t done a lot of blogging myself but I am impressed at the care and interest that go into science blogs. They are a way of sharing developments as they happen and an opportunity to have meaningful discussion of results.

I talk about a lot of science in my book. So I thought rather than summarizing it all—at least in this post—I’d focus on the question of why I wrote this particular book. I waited several years before even considering embarking on a second book project. I certainly didn’t want to simply repeat the content of my previous book, and my own personal goal is always to branch out into new arenas—in this case into new types of writing–while still remaining true to my physics roots. I didn’t know the exact book I was after but I did know some of the topics I considered important and timely.

These topics fell into several categories. First, I wanted to give an accurate picture of what is happening in particle physics and cosmology today—both with experiments and with theory. Particle physicists know this to be the era of the Large Hadron Collider (LHC), the machine that is colliding together protons at unprecedented energies to test the nature of matter and forces at smaller distances than ever explored. The interactions between theorists and experimenters is more intense than it has been during the time I’ve been actively pursuing physics. That is because everyone realizes this interactions are essential with these challenging experiments to get to the right answers. I wanted to convey the excitement and implications of the research taking place there, so when discoveries are made, anyone interested can understand what was found and what it could mean.

Cosmologists too find this is an important time and I wanted to share some of the interest in that major topic as well. One arena that both particle physicists and cosmologists are excited about are experimental studies of the nature of dark matter. Many find this topic perplexing, whereas even if difficult to tackle experimentally, the underlying idea really is not. I wanted to explain a bit how I think about dark matter and how experiments are searching for its feeble and elusive effects.

But I wanted to do more than just summarize the physics. (more…)

I’ve been traveling like crazy, then hosting visitors, and now am laid up with a nasty cold. So not much energy for blogging. On the other hand — plenty of time for non-expert reflections on the nature of microscopic complex systems!

The thing is, I’m pretty sure that my body will eventually overcome this cold virus. That’s one of the great things about living organisms — they can, in a wide variety of circumstances, repair themselves. From fighting off germs to healing broken bones, the body is pretty darn resilient.

Which brings up something that has always worried me about nanotechnology — the fact that the tiny machines that have been heroically constructed by the scientists working in this field just seem so darn fragile. It’s amazingly impressive what modern nano-engineers can do by way of manipulating matter at the atomic and molecular level, creating new materials and tiny machines and motors. But surely one has to worry about the little buggers breaking down. My macroscopic car is also an impressive feat of engineering, but it’s no good if a crucial component breaks.

So what you really want is microscopic machinery that is robust enough to repair itself. Fortunately, this problem has already been solved at least once: it’s called “life.” Even at relatively tiny scales, living organisms are sufficiently loose and redundant to be able to fix themselves when something small goes wrong, greatly extending their useful lifespan.

This is why my utterly underinformed opinion is that the biggest advances will come not from nanotechnology, but from synthetic biology. Once we get to the point that we can truly create new organisms from scratch, not simply modifying existing stock, many of the biggest dreams of nanotech will become much more real.

Some time ago John von Neumann proposed the idea of self-replicating machines. Not everyone believed that such a thing was possible — after all, the machine would have to include blueprints for another version of itself, including the self-replication mechanism, and how do you fit a copy of a machine into itself? (You might think that living organisms are an obvious counterexample to this argument, but some people used it as an argument against the idea that organisms are “just” machines.) But von Neumann figured it out, and immediately proposed the obvious plan: sending self-replicating spacecraft to seed the galaxy.

But if the machine breaks, it defeats the whole purpose. So you really want a self-repairing self-replicating machine. Which is awfully close to a working definition of “life.” It might not be human beings who eventually fill up the galaxy, but my suspicion is that it will be life in some form or another.

Here’s an interesting paper from yesterday’s hep-th batch of abstracts. One of the exciting prospects in observational cosmology over the next several years is finding signals of gravitational waves in the cosmic microwave background. These can be produced by inflation, and indeed simple models (one scalar field, no funny tricks) predict a “consistency relation” between characteristics of ordinary density perturbations and the gravitational waves. If signatures of the waves were detected (typically, by finding “tensor modes” in CMB polarization) and shown to be consistent with the simple prediction, it would be a huge boost for inflation.

The world isn’t always so simple, of course. It’s not too hard to think of models that violate the consistency relation. Now Senatore, Silverstein, and Zaldarriaga are pointing to a new mechanism: gravitational waves produced directly by particle or string sources during inflation. (Silverstein is of course well-known as a string theorist, but her recent work in early-universe cosmology has been as good as anybody’s in the field.) The usual mechanism is simply quantum fluctuations of fields in their vacuum state; these folks are imagining that particular objects — particles or strings — are produced during inflation, which then act as sources for gravitational waves. In a simple model you would expect that this effect might be important at a fixed scale corresponding to the energy of the sources, but they argue that it’s not hard to come up with models where gravitational waves are produced at all scales.

New Sources of Gravitational Waves during Inflation

Leonardo Senatore, Eva Silverstein, Matias Zaldarriaga

We point out that detectable inflationary tensor modes can be generated by particle or string sources produced during inflation, consistently with the requirements for inflation and constraints from scalar fluctuations. We show via examples that this effect can dominate over the contribution from quantum fluctuations of the metric, occurring even when the inflationary potential energy is too low to produce a comparable signal. Thus a detection of tensor modes from inflation does not automatically constitute a determination of the inflationary Hubble scale.

The bad news here is in the last line — in simple models (there’s that word again) the amplitude of gravitational waves is simply proportional to the expansion rate of the universe during inflation. Now that’s no longer so obvious. But research isn’t about finding good news or bad news, it’s about finding the right answer. Being unreasonably confident in the predictions we make from our models is just as dangerous as not having compelling models at all.

My friend and colleague James Bullock, a professor at UC Irvine, has a great editorial up today in the LA Times about the next generation space telescope JWST. JWST is big. And it’s over budget, which makes it especially vulnerable in the current political climate. But it’s damn important. It’s a tool to inspire, a tool to help us write the story of the universe.

Walk through the halls of UC Irvine’s astronomy wing after dinner on a weeknight and you will find roomfuls of young graduate students, crammed into small desks, solving equations, writing computer code and developing innovative ways to analyze data. They do not have to be here. These are people with career options. They are scary-smart, creative and hardworking. Yet they have come here from all over the country and the world to sit in windowless offices and make a fifth of the money they could make back home or up the street. Why? They want to unlock the universe.

The United States is still the scientific light of the world. Ours is the society responsible for discovering humanity’s place in the universe, that we live in a galaxy called the Milky Way, one among billions of other galaxies stretched across the cosmic landscape. A hundred thousand years from now, if humans make it that long, the U.S. will be remembered for this, and historians will point to the immense contribution of the Hubble Space Telescope, with its miraculous visible-light images, the most detailed pictures of the cosmos yet produced by humankind.

Sadly, U.S. scientific leadership is beginning to fade. There is a sense of fear among our leaders that we can’t afford to invest in our future, just the kind of fear that endangers thoughtful debate about big-picture priorities.

One testament to our changing priorities is our commitment to the Hubble telescope as compared to its successor. The Hubble is, in every way, a monument to scientific exploration. Thanks to the Hubble, orbiting 350 miles overhead, we know that the universe began just under 14 billion years go. The age of the cosmos, once believed to be unknowable, is now available at the click of a mouse and has made it into schoolbooks in all 50 states. Astronomers have used the Hubble to determine the chemical makeup of planets that orbit distant stars and to discover dark energy, a mysterious substance propelling the universe to expand at an accelerating rate.

Many of the graduate students filling astronomy departments at University of California campuses, as well as Caltech and Stanford, have come to the state to explore and analyze terabytes of Hubble data. These data involve complex digital images, created in raw form onboard the orbiting telescope, and then decomposed into precise component colors. The Hubble beams this information to receivers around the world, where it is processed and made available for download. A graduate student working in Irvine can transfer Hubble images to a computer and then develop software to process and analyze the images’ meaning.

The goal is to squeeze information out of the gathered light that will help us discern the size, structure and chemical composition of objects that are almost always too far away for humans to ever hope to visit. The people who do this work are both creative and technically gifted. They must take what the universe provides — a shred of light collected by the Hubble — and discern implication from its signal.
We want these intelligent, dedicated people to live in our cities, to make their discoveries at our universities and to raise their families — the next generation of bright minds — right here.

Read the whole thing here. And then write your Senators and Representatives. JWST, and with it, US scientific leadership, and an amazing opportunity to fill in the contours of the history and physics of our Universe, is really at risk. Very possibly only an outcry of the kind that saved Hubble will be enough to launch Hubble’s successor.

Also known as, “scientific progress goes boink.”

One of the benefits of being a Master of Time and Space is that I get to see the future. For example, cosmologically-inclined folks have been wondering for a few weeks about this press release from the TAUP conference in Munich, which includes the lines “Latest results from the CRESST Experiment provide an indication of dark matter. The press conference will be held on 6. September 2011 starting at 2:00 pm.” Suspense! But I know what they’re going to say.

As Neal Weiner points out, we don’t have to wait for the press conference; the friendly folks at the CRESST experiment have ambitiously decided to write a paper as well as giving a press conference, and that paper appeared on the arxiv this evening. (You remember Neal as a distinguished guest blogger; re-read that post to get your bearings in this complicated game.) Very short version: they claim to see some signal that is statistically significantly greater than background, consistent with a WIMP dark-matter particle with a mass of around 20-40 GeV. Slightly longer version:

Results from 730 kg days of the CRESST-II Dark Matter Search

(more…)

“Time” is the most used noun in the English language, yet it remains a mystery. We’ve just completed an amazingly intense and rewarding multidisciplinary conference on the nature of time, and my brain is swimming with ideas and new questions. Rather than trying a summary (the talks will be online soon), here’s my stab at a top ten list partly inspired by our discussions: the things everyone should know about time. [Update: all of these are things I think are true, after quite a bit of deliberation. Not everyone agrees, although of course they should.]

1. Time exists. Might as well get this common question out of the way. Of course time exists — otherwise how would we set our alarm clocks? Time organizes the universe into an ordered series of moments, and thank goodness; what a mess it would be if reality were complete different from moment to moment. The real question is whether or not time is fundamental, or perhaps emergent. We used to think that “temperature” was a basic category of nature, but now we know it emerges from the motion of atoms. When it comes to whether time is fundamental, the answer is: nobody knows. My bet is “yes,” but we’ll need to understand quantum gravity much better before we can say for sure.

2. The past and future are equally real. This isn’t completely accepted, but it should be. Intuitively we think that the “now” is real, while the past is fixed and in the books, and the future hasn’t yet occurred. But physics teaches us something remarkable: every event in the past and future is implicit in the current moment. This is hard to see in our everyday lives, since we’re nowhere close to knowing everything about the universe at any moment, nor will we ever be — but the equations don’t lie. As Einstein put it, “It appears therefore more natural to think of physical reality as a four dimensional existence, instead of, as hitherto, the evolution of a three dimensional existence.”

3. Everyone experiences time differently. This is true at the level of both physics and biology. Within physics, we used to have Sir Isaac Newton’s view of time, which was universal and shared by everyone. But then Einstein came along and explained that how much time elapses for a person depends on how they travel through space (especially near the speed of light) as well as the gravitational field (especially if its near a black hole). From a biological or psychological perspective, the time measured by atomic clocks isn’t as important as the time measured by our internal rhythms and the accumulation of memories. That happens differently depending on who we are and what we are experiencing; there’s a real sense in which time moves more quickly when we’re older.

4. You live in the past. About 80 milliseconds in the past, to be precise. Use one hand to touch your nose, and the other to touch one of your feet, at exactly the same time. You will experience them as simultaneous acts. But that’s mysterious — clearly it takes more time for the signal to travel up your nerves from your feet to your brain than from your nose. The reconciliation is simple: our conscious experience takes time to assemble, and your brain waits for all the relevant input before it experiences the “now.” Experiments have shown that the lag between things happening and us experiencing them is about 80 milliseconds. (Via conference participant David Eagleman.)

5. Your memory isn’t as good as you think. (more…)

Greetings from Norway, where we’re about to embark on what is surely the most logistically elaborate conference I’ve ever attended. Setting Time Aright starts here in Norway, where we hop on a boat and cross the North Sea to Copenhagen. The get-together is sponsored by the Foundational Questions Institute, although it came together in an unusual way; I was part of a group that was organizing a conference, and we applied to FQXi for funding, at which point they mentioned they were planning almost exactly the same conference at the same time. So we joined forces, and here we are. Unity ’11!

The topic, if you haven’t guessed, is time. That’s a big subject, one that can hardly be done justice by sprawling books with hundreds of (admittedly quite charming) footnotes. You can see why the conference has to spread over two countries. We’re trying an experiment in interdisciplinarity: while the conference is a serious event meant for researchers, we have a wide variety of specialties represented, including biologists, computer scientists, philosophers, and neuroscientists, as well as the inevitable physicists and cosmologists. (There is also a public event, for those of you who find yourselves in Copenhagen next week.) I can’t wait to hear some of these talks, it should be a blast.

My job is to open the conference with an introductory talk that hits on some of the big questions. Here are the slides, at least as they are right now; last-minute editing is always a possibility. I think I put enough in there to provoke almost everyone at the conference one way or another.

Andy Lawrence, Edinburgh astronomer by day and e-Astronomer by night, has participated in a Five Books interview at The Browser. You’ll remember that I did one where I picked five books about relativity and cosmology. Most of the other interviewees (and they have a great list) have been a bit more playful, mixing in different genres. Andy takes a judicious middle tack, including some straight-up astronomy but also some biography.

I was glad he picked Dennis Overbye’s Lonely Hearts of the Cosmos, which is one of my favorite books about science and scientists. It manages to show the human side of science in all its quirky glory, without either creating fake scandals or putting anyone on a pedestal.

Here’s a pretty picture from JPL, based on data from NASA’s Mars Reconnaissance Orbiter. Click to see a larger version. (Note that the image is highly doctored, in the best NASA tradition; not just false-color, but they’ve “reprojected” so that a satellite image now looks like it was taken by a flying helicopter!)

“Water on Mars” is one of those things (like “black holes” or “the missing link”) that seems to be discovered over and over again. That’s because we’re not really finally discovering it once and for all; we’re slowly gathering new evidence, and also evidence for different manifestations. It seems clear that frozen water exists in the polar regions of Mars; also, there’s good reason to think that there used to be running water at some point. This new finding would be evidence for running water right now.

In this case, NASA scientists have noticed seasonal changes in hillside patterns such as this one. The dark streaks seen in the image appear in the spring and summer, then fade again in winter. (Kind of like the Los Angels River, but backwards.) The best idea we have for an explanation is running water. Not that the darkness is water itself, but some change in the underlying substance as a result of water. It’s a very good idea — likely true — but still not quite like we’ve filled up a cup and done a chemical analysis.

Anything with any tenuous connection to “life on other planets” runs the risk that everyone wants it to exist and is looking very hard; consequently, skepticism is always warranted. Still: awesome pictures!