Friday, 26 February 2010

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What Is Time? One Physicist Hunts for the Ultimate Theory

Posted: 26 Feb 2010 02:30 AM PST


SAN DIEGO — One way to get noticed as a scientist is to tackle a really difficult problem. Physicist Sean Carroll has become a bit of a rock star in geek circles by attempting to answer an age-old question no scientist has been able to fully explain: What is time?

carroll_mug2Sean Carroll is a theoretical physicist at CalTechwhere he focuses on theories of cosmology, field theory and gravitation by studying the evolution of the universe. Carroll's latest book "From Eternity to Here: The Quest for the Ultimate Theory of Time" is an attempt to bring his theory of time and the universe to physicists and non-physicists alike.

Hereat the annual meetingof the American Association for the Advancement of Science where he gave a presentation on the arrow of time, scientists stopped him in the hallway to tell him what big fans they were of his work.

Carroll sat down with on Feb. 19 at AAAS to explain his theories and why Marty McFly's adventure could never exist in the real world, where time only goes forward and never back. Can you explain your theory of time in laymen's terms?

Sean Carroll: I'm trying to understand how time works. And that's a huge question that has lots of different aspects to it. A lot of them go back to Einstein and spacetime and how we measure time using clocks. But the particular aspect of time that I'm interested in is the arrow of time: the fact that the past is different from the future. We remember the past but we don't remember the future. There are irreversible processes. There are things that happen, like you turn an egg into an omelet, but you can't turn an omelet into an egg.

And we sort of understand that half way. The arrow of time is based on ideas that go back to Ludwig Boltzmann, an Austrian physicist in the 1870s. He figured out this thing called entropy. Entropy is just a measure of how disorderly things are. And it tends to grow. That's the second law of thermodynamics: Entropy goes up with time, things become more disorderly. So, if you neatly stack papers on your desk, and you walk away, you're not surprised they turn into a mess. You'd be very surprised if a mess turned into neatly stacked papers. That's entropy and the arrow of time. Entropy goes up as it becomes messier.

So, Boltzmann understood that and he explained how entropy is related to the arrow of time. But there's a missing piece to his explanation, which is, why was the entropy ever low to begin with? Why were the papers neatly stacked in the universe? Basically, our observable universe begins around 13.7 billion years ago in a state of exquisite order, exquisitely low entropy. It's like the universe is a wind-up toy that has been sort of puttering along for the last 13.7 billion years and will eventually wind down to nothing. But why was it ever wound up in the first place? Why was it in such a weird low entropy unusual state?

That is what I'm trying to tackle. I'm trying to understand cosmology, why the big bang had the properties it did. And it's interesting to think that connects directly to our kitchens and how we can make eggs, how we can remember one direction of time, why causes precede effects, why we are born young and grow older. It's all because of entropy increasing. It's all because of conditions of the Big Bang. So the Big Bang starts it all. But you theorize that there's something before the Big Bang. Something that makes it happen. What's that?

Carroll: If you find an egg in your refrigerator, you're not surprised. You don't say, "Wow, that's a low entropy configuration. That's unusual," because you know that the egg is not alone in the universe. It came out of a chicken, which is part of a farm, which is part of the biosphere, etc., etc. But with the universe, we don't have that appeal to make. We can't say that the universe is part of something else. But that's exactly what I'm saying. I'm fitting in with a line of thought in modern cosmology that says that the observable universe is not all there is. It's part of a bigger multiverse. The big bang was not the beginning.

And if that's true, it changes the question you're trying to ask. It's not, 'Why did the universe begin with low entropy?' It's, 'Why did part of the universe go through a phase with low entropy?' And that might be easier to answer.

multiverse_2 In this mulitverse theory you have a static universe in the middle. From that, smaller universes pop off and travel in different directions, or arrows of time. So does that mean that the universe at the center has no time?

Carroll: So that's a distinction that is worth drawing. There's different moments in the history of the universe and time tells you which moment you're talking about. And then there's the arrow of time, which give us the feeling of progress, the feeling of flowing or moving through time. So that static universe in the middle has time as a coordinate but there's no arrow of time. There's no future versus past, everything is equal to each other. So it's a time that we don't understand and can't perceive?

Carroll: We can measure it, but you wouldn't feel it. You wouldn't experience it. Because objects like us wouldn't exist in that environment. Because we depend on the arrow of time just for our existence. So then what is time in that universe?

Carroll: Even in empty space, time and space still exist. Physicists have no problem answering the question of "If a tree falls in the woods and no one's there to hear it, does it make a sound?" They say, "Yes! Of course it makes a sound!" Likewise, if time flows without entropy and there's no one there to experience it, is there still time? Yes. There's still time. It's still part of the fundamental laws of nature even in that part of the universe. It's just that events that happen in that empty universe don't have causality, don't have memory, don't have progress, and don't have aging or metabolism or anything like that. It's just random fluctuations. So if this universe in the middle is just sitting and nothing's happening there, then how exactly are these universes with arrows of time popping off of it? Because that seems like a measurable event.

Carroll: Right. That's an excellent point. And the answer is, almostnothing happens there. So the whole point of this idea that I'm trying to develop is that the answer to the question, "Why do we see the universe around us changing?" is that there is no way for the universe to truly be static once and for all. There is no state the universe could be in that would just stay put for ever and ever and ever. If there were, we should settle into that state and sit there forever.

It's like a ball rolling down the hill, but there's no bottom to the hill. The ball will always be rolling both in the future and in the past. So, that center part is locally static — that little region there where there seems to be nothing happening. But, according to quantum mechanics, things can happen occasionally. Things can fluctuate into existence. There's a probability of change occurring.

So, what I'm thinking of is the universe is kind of like an atomic nucleus. It's not completely stable. It has a half-life. It will decay. If you look at it, it looks perfectly stable, there's nothing happening… there's nothing happening… and then, boom! Suddenly there's an alpha particle coming out of it, except the alpha particle is another universe. So inside those new universes, which move forward with the arrow of time, there are places where the laws of physics are different — anomalies in spacetime. Does the arrow of time still exist there?

Carroll: It could. The weird thing about the arrow of time is that it's not to be found in the underlying laws of physics. It's not there. So it's a feature of the universe we see, but not a feature of the laws of the individual particles. So the arrow of time is built on top of whatever local laws of physics apply. So if the arrow of time is based on our consciousness and our ability to perceive it, then do people like you who understand it more fully experience time differently then the rest of us?

Carroll: Not really. The way it works is that the perception comes first and then the understanding comes later. So the understanding doesn't change the perception, it just helps you put that perception into a wider context. It's a famous quote that's in my book from St. Augustine where he says something along the lines of, "I know what time is until you ask me for a definition about it, and then I can't give it to you." So I think we all perceive the passage of time in very similar ways. But then trying to understand it doesn't change our perceptions. So what happens to the arrow in places like a black hole or at high speeds where our perception of it changes?

Carroll: This goes back to relativity and Einstein. For anyone moving through spacetime, them and the clocks they bring along with them– including their biological clocks like their heart and their mental perceptions– no one ever feels time to be passing more quickly or more slowly. Or, at least, if you have accurate clocks with you, your clock always ticks one second per second. That's true if you're inside a black hole, here on earth, in the middle of nowhere, it doesn't matter. But what Einstein tells us is that path you take through space and time can dramatically affect the time that you feel elapsing.

The arrow of time is about a direction, but it's not about a speed. The important thing is that there's a consistent direction. That everywhere through space and time, this is the past and this is the future. So you would tell Michael J. Fox that it's impossible for him to go back to the past and save his family?

Carroll: The simplest way out of the puzzle of time travel is to say that it can't be done. That's very likely the right answer. However, we don't know for sure. We're not absolutely proving that it can't be done. At the very least you can't go back.

Carroll: Yeah, no. You can easily go to the future, that's not a problem. We're going there right now!

Carroll: Yesterday I went to the future and here I am!

One of things I point out in the book is that if we do imagine that it was possible, hypothetically, to go into the past, all the paradoxes that tend to arise are ultimately traced to the fact that you can't define a consistent arrow of time if you can go into the past. Because what you think of as your future is in the universe's past. So it can't be one in the same everywhere. And that's not incompatible with the laws of physics, but it's very incompatible with our everyday experience, where we can make choices that affect the future, but we cannot make choices that affect the past. So, one part of the multiverse theory is that eventually our own universe will become empty and static. Does that mean we'll eventually pop out another universe of our own?

Carroll: The arrow of time doesn't move forward forever. There's a phase in the history of the universe where you go from low entropy to high entropy. But then once you reach the locally maximum entropy you can get to, there's no more arrow of time. It's just like this room. If you take all the air in this room and put it in the corner, that's low entropy. And then you let it go and it eventually fills the room and then it stops. And then the air's not doing anything. In that time when it's changing, there's an arrow of time, but once you reach equilibrium, then the arrow ceases to exist. And then, in theory, new universes pop off. So there's an infinite number of universes behind us and an infinite number of universes coming ahead of us. Does that mean we can go forward to visit those universes ahead of us?

Carroll: I suspect not, but I don't know. In fact, I have a post-doc at CalTech who's very interested in the possibility of universes bumping into each other. Now, we call them universes. But really, to be honest, they are regions of space with different local conditions. It's not like they're metaphysically distinct from each other. They're just far away. It's possible that you could imagine universes bumping into each other and leaving traces, observable effects. It's also possible that that's not going to happen. That if they're there, there's not going to be any sign of them there. If that's true, the only way this picture makes sense is if you think of the multiverse not as a theory, but as a prediction of a theory.

If you think you understand the rules of gravity and quantum mechanics really, really well, you can say, "According to the rules, universes pop into existence. Even if I can't observe them, that's a prediction of my theory, and I've tested that theory using other methods." We're not even there yet. We don't know how to have a good theory, and we don't know how to test it. But the project that one envisions is coming up with a good theory in quantum gravity, testing it here in our universe, and then taking the predictions seriously for things we don't observe elsewhere.

Images: 1) Artist's rendition of the multiverse./Jason Torchinsky. 2) Diagram of the multiverse./Sean Carroll. 3) Ken Weingart.

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Erin Biba is a Correspondent for Wired Magazine who writes about science, technology, popular culture, and beer made from 45-million-year-old yeast.

Followus on twitter @erinbibaand @wiredscience, and on Facebook.

Fish See Their Enemies’ Faces in Ultraviolet

Posted: 25 Feb 2010 02:18 PM PST


Seen in the right light, yellow reef fish become spotty pains in the tail fin.

sciencenewsMembers of one damselfish species use facial patterns of speckles and swooshes to identify the fish species they regularly attack, researchers report in an upcoming issue of Current Biology. These markings show up only in ultraviolet light, says visual ecologist Ulrike Siebeck of the University of Queensland in Brisbane, Australia.

In tests, Siebeck and her colleagues found that male Ambon damselfish could tell their own species from another just by seeing the ultraviolet markings. When UV light was blocked by filters, confused males picked fights with the wrong rivals.

The UV freckles could work as a secret, or at least pretty discreet, communications channel, Siebeck proposes. Animals need to send clear signals to important compatriots, such as possible rivals or mates. Yet signals that get too clear can attract the wrong kind of attention from hungry predators. As Siebeck puts it, "How can you be colorful and not colorful at the same time?"

Both Ambon and lemon damselfish can see UV light. But plenty of their major predators, such as wrasses and cod, typically can't, Siebeck says. So she argues that damselfish could use their spots to send a covert message.

This encrypted messaging sounds plausible for another reason, says Innes Cuthill of Bristol University in England. Short UV wavelengths scatter more readily when they hit small particles than do the longer wavelengths that people call visible light. So plankton and other bits floating in seawater make UV markings harder to detect from a distance than visible-light color patterns. "For a predator, even if it can see in the UV, the patterns will be a blur," Cuthill says.

The lens in the human eye blocks UV wavelengths, but plenty of fish, birds and insects carry and can see some kind of UV marking. "It's secret to us," says, visual ecologist Sönke Johnsen of Duke University in Durham, N.C., but "it's not super magical."

Before calling UV freckles private lines of communication Johnsen wants to know more, such as which other species on the damselfishes' reef can see UV. What the damselfish experiments have demonstrated clearly, he says, is that these fish can use UV to distinguish species.

Siebeck made that discovery thanks to the scrappiness of territorial Ambon males. She first tested 28 of them to see whether they would fight a member of their own species or a lemon damselfish if she presented both. Most made more attacks on their own kind, though six, for unknown reasons, preferred to attack the other species.

Once she knew their fighting preferences, Siebeck changed the experiment by placing some of the potential rivals in UV-filtering plastic tubes to hide their freckles. The males who saw these fish attacked randomly, apparently because they could not detect the UV patterns.

Siebeck says these damselfish may have "the most intricate UV patterns found so far on animals." To see whether the fish can resolve such elaborate patterns, Siebeck trained fish to nudge a card marked with a UV spot pattern based on a real fish face. When she offered a choice of cards based on both species, trained fish mostly nudged the pattern they had learned to recognize.

Image: The images on the right show the invisible-to-humans UV designs for the two species of damselfish on the left. Credit: U. Siebeck et al./Current Biology 2010

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Wired’s Biometric Super Bowl Ad Winner Is a Geeky Surprise

Posted: 25 Feb 2010 01:34 PM PST

The results are in from the Wired Biometric Super Bowl Party, and 25 of our readers' autonomic nervous systems have selected their top 10 advertisements.

The Google ad that had everyone talking after the game got the attention of ourparty goersas well, but the real winner was a surprise. It turns out our readers are even geekier than we thought.

The study, conducted byBoston-based research firm Innerscope, was held at Wired HQ in San Francisco with participants from across the state and as far away as Sweden. These guinea pigs had their skin conductance, heart rate and movements measured to see how they responded physiologically to the motley assortment of Super Bowl ads.

The company's algorithms translate those measurements into a single metric they call "engagement." While the researchers are obviously looking for spikes in people's excitement — heart rate increases, etc — the best ads also generate consistent body movements and attention to the ad. (Read more about the science in "How Your Biometrics Can Make Super Bowl Ads Better.")


What's fun about this technology is that you can see people's reactions in real time, which you couldn't with traditional advertising scoring techniques. The downside is it takes some time to crunch the data, which is why you're reading this now instead of the day after the game. But as the old aphorism goes, slow and data-rich wins the race.

In the videos below, engagement is charted on the graphs, so you can see it moving up and down as the ads roll. On the Innerscope scale, getting up near 90 is impressive. The peak moment they measured was (of course) Tracy Porter's fourth-quarter interception of Peyton Manning and the long return for a touchdown that followed. It hit over 122 on the engagement scale.

"It may be the highest-ever score for Innerscope and there are some obvious reasons why that might be," said Carl Marci, a social psychiatrist at Massachusetts General Hospital and Innerscope co-founder.

One funny quirk about this year's Super Bowl ads: none of them beat the two NBC promotional spots for The Late Show With David Letterman and How I Met Your Mother. If we included them on the commercial list, they would have ranked one and two. Go figure. Maybe all that Conan O'Brien/Jay Leno controversy was good for the late-night talk-show-host business.

In a surprise, the Electronic Arts ad for the upcoming game Dante's Inferno topped the list. If you needed more evidence that Wired readers are geeky, take the fact that they liked an ad for a videogame better than any of the beer commercials.

There aren't a lot of noticeable peaks and valleys for this ad, unlike some of the others. People most just stayed tuned in and watched the whole thing.

"Like a movie trailer, the ad is the product," Marci explained.

But why this ad and why this game, which at least to this writer, seem kind of mediocre?

"With the Dante's Inferno ad, people probably weren't thinking 'This is going to be the greatest game of all time,' but it would have been very hard for them to ignore," said Innerscope senior scientist, Caleb Siefert. "Definitely people in that audience are going to have an opinion of the game."

Coming in at number five, we see Google's first Super Bowl ad. When it came on, a hush fell over the room as people watched to see how their search engine would make a commercial.

"We didn't rate Google as the number one ad, but when you look at the trace, it's absolutely amazing," Siefert said.

Throughout the commercial, we stay at one time scale quickly progressing through a cute love story between some American dude and a Parisian lady. Then, right at the end, the ad's time scale speeds up and soon the searcher is looking for information on how to assemble a crib.

"What I loved about the Google ad, it was one of the best stories told," Marci said. "It's so tight and hangs together so well and then reminds you of the product that delivered this story so effectively."

Then, Google's "branding moment" hits as the words "Search on" come on the screen. People loved it.

"I'm blown away by the slope of the line in the branding moment, how sharply it goes up," Siefert said.

And finally, we get to the ad in which a Doritos samurai with Doritos nunchuks attacks some unsuspecting faux hipsters who are for some reason eating Doritos in the gym. What you see in the numbers here is a classic joke that works. It starts off kind of fun, lulls you for a minute as the action plays out, and then bam — the punchline.

Image: Jon Snyder/ Videos: Innerscope.

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WiSci 2.0: Alexis Madrigal's Twitter, Tumblr, and green tech history research site; Wired Science on Twitter and Facebook.

Biodiversity Explained by Ignoring the Forest for the Trees

Posted: 25 Feb 2010 11:29 AM PST


A painstaking, multidecade study of 33,000 individual trees may finally have uncovered the roots of biodiversity.

That biodiversity'sorigin needs uncoveringis surprising because the word seems to be everywhere. But scientists still don't quite understand why one place has more species than another, or fewer.

The traditional explanation — every organism has its niche, competing not with other species but its own — sounds nice, but has holes. According to the tree study, that's because ecologists haven't looked for the right niches.

"We take this very complex, high-dimensional thing called the environment, and average out all the variation that organisms really require," said Jim Clark, a Duke University biologist and author of the study, published Feb. 25 in Science. "Biodiversity is very much a niche response, but it's just not evident at the species level."

The central tenet of biodiversity science is that animals compete against their own kind, not against other species.Computer models of inter-species competition soon collapse, with rich diversity inevitably replaced by a few dominant species.

In the real world, that's not what happens. Species seem to be sharing. So ecologists have developed a theory of niches: Every species has a particular specialty, a set of conditions for which it's best suited. Some plants do well in shade, others in rocky soil, and so on.

This is true. However, it still doesn't seem to explain biodiversity. Some ecosystems that are very poor in resources, and consequently don't seem to have many niches, can still have a high species diversity.

"When you have thousands of species, it's difficult to come up with ways to partition a limited set of resources or conditions," said John Silander, a University of Connecticut ecologist who studies South Africa's Cape Floristic region, a rocky scrubland with as much biodiversity as the Amazon rainforest. "People looking at niche differences always seem to come up short."

Clark may have found the answer. He has spent the last 18 years studying trees in the southeastern United States and has assembled 22,000 detailed individual accounts, spanning 11 forests and three regions. For each tree, Clark has recorded its precise, on-the-ground (and in-the-ground and above-the-ground) exposure to moisture and nutrients and light, its response, and its proximity to other plants.

Ecologists usually aggregate this information, turning it into average. By going tree-by-tree, Clark found that there are, in fact, enough niches to go around. They're filled when competition in a species drives individuals to fill them. Biodiversity — or, from another perspective, configurations of organisms that don't need to compete against each other — is the result of this fierce race for resources.

The niches could only be seen at a fine-grained level, not in the coarse analyses typically used by ecologists. "We take environmental variation and project it down to a very small set of indices. Light becomes average light per year. Moisture becomes average moisture per year. It's not just light and water and nitrogen —it's variations of each of those things, in different dimensions," said Clark.

"The approach he's taken is marvelous. Nobody has looked at biodiversity in this fashion," said Silander, who was not involved in the study. "He has the data needed to address the different hypotheses."

Silander said the approach will likely be extended beyond the world of trees. Understanding the essential dynamics of biodiversity could improve ecosystem management, in applications from conservation to farming.

"It's hard to find a place on Earth that doesn't have some level of management going on," said Silander. "We have to understand how species interact."

"Ecologists spent a lot of time in the 20th century trying to find ways to reduce the complexity of natural systems so that we could understand them," said Miles Silman, a Wake Forest University ecologist who was not involved in the study. "Clark has shown that the complexity that we were trying to reduce is very likely essential to understanding" biodiversity.

Image: Tambako the Jaguar/Flickr

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Citation: "Individuals and the Variation Needed for High Species Diversity in Forest Trees." By James S. Clark. Science, Vol. 327 No. 5969, February 26, 2010.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.