Archive for February, 2009

Glider guns created in chemical Game of Life

Thursday, February 5th, 2009

glider-guns

If you’ve ever played Conway’s Game of Life, you’ll be familiar with cellular automata and, more importantly,  glider guns. So get this:  a team of British chemists and computer scientists  have  created a chemical cocktail that behaves like a cellular automata and which  reproduces this behavior: chemical  guns firing chemical gliders across a chemical grid.

For those who haven’t played with it, Conway’s  Game of Life is a two dimensional grid known as a cellular automata in which each square can be black or white. The game starts in an initial state–a pattern of black and white squares–and its evolution is determined by a set of rules that specify what color a square should become depending on the color of its neighbors.

The game was devised by the British mathematician John Conway in 1970 and has been studied in detail by countless generations of computer scientists, mathematicians and students ever since, not least because of the extraordinary patterns and structures that the game can produce.

One of these is the glider gun: a structure that periodically “fires” projectiles across the landscape.

Now Ben de Lacy Costello and pals from the University of West of England in Bristol have created a chemical version of all this. Their model is based on the famous Belousov-Zhabotinsky reactions in which a specific cocktail of chemicals  can produce complex patterns of oscillating colors.

The team set up a grid in which each square could change colour via a BZ reaction and in which the reaction diffused across the boundaries of each square in way that mimics Conway’s Game of Life.

The oscillating patterns produced by BZ reaction have long been thought of as similar to cellular automata but this is the first time that the Game of Life has been reproduced in a chemical system.

That’s impressive but it looks as if the best is yet to come. It is well known that cellular automata can operate as universal Turing machines . The next step, says  Costello and buddies, is to build a similar chemical grid capable of  arithmetic.

Beyond that, the question is this: if we can do this in the lab, might evolution also have harnessed these reactions in a similar way. Let the search begin.

Ref: arxiv.org/abs/0902.0587: Implementation of Glider Guns in the Light-Sensitive Belousov-Zhabotinsky Medium

Challenging the nature of black holes

Wednesday, February 4th, 2009

black-hole-formation

The nature of black holes has puzzled physicists for decades. But while the debate has fizzled in recent years, some new thinking is about to set it alight again.

Black holes are fundamentally a product of general relativity, which allows for a gravitational collapse so violent that no other force can oppose it. When that happens, the collapse continues until the density of matter becomes infinite and gravity becomes so strong so as to prevent even light from escaping. This generates an “event horizon”, a volume of space around the black in hole inside whihc events cannot affect an outside observer.

But perhaps there’s more to it than that, suggest Matt Visser at Victoria University of Wellington in New Zealand and pals who ask whether quantum processes can have an affect on the collapse of a star.

It’s fair to say that the consensus among astrophysicists is that quantum physics can be safely ignored when considering the collapse of a star. As Visser and co put it: “There is a widespread feeling in the general relativity community that semiclassical quantum back-reaction effects are always small, and never enough to significantly alter the classical picture of collapse to a black hole.”

But Visser and pals beg to differ. The standard thinking is that if an event horizon forms, then quantum field theory is well behaved there. But that makes the assumption that am event horizon will form.

Visser and co say this may not be a valid assumption and go on to show how the vacuum energy might stifle the formation of an event horizon.

What does this mean for black holes? What Visser and co end up with is something very similar to a black hole but without an event horizon–a black hole mimic, they say.

Debating the nature of black holes is a well trodden path. But what’s interesting is that numerous avenues of thought–from loop quantum gravity to abstract studies of the nature of horizons–are now hinting at something more subtle and interesting about the nature of star collapse.

Black holes might never be the same again.

Ref: arxiv.org/abs/0902.0346: Small, dark, and heavy: But is it a black hole?

Space Station simulator given emotions

Tuesday, February 3rd, 2009

m-sorry-dave

Astronauts training to work on the International Space Station have to have mastered a mind-boggling amount of kit before they leave Earth. One of these devices is the Canadarm 2, a robotic arm used to manipulate experiments outside the station.

On Earth, astronauts train on a Canadarm 2 simulator connected to a virtual assistant that can spot potential errors, such as a move likely to smash the arm into the station. The assistant then offers hints and tips to the astronaut to help him or her make a correction or even issue a command to prevent damage.

The bad news for astronauts is that André Mayers and colleagues at Université de Sherbrooke in Canada who created the virtual assistant, have given it an unusual upgrade. In an attempt to help the simulator learn more about the astronauts who are using it, the team has programmed the assistant to experience the equivalent of an emotion when it records a memory of what has happened.

The problem is that the assistant receives a huge amount of data from each training session. It’s emotional response allows it to determine which of this data is most important, just as humans do. “This allows the agent to improve its behavior by remembering previously selected behaviors which are influenced by its emotional mechanism,” say the team.

The system is called the Conscious Tutoring System or CTS. It’s not clear from the paper how well the system works but how long before one unlucky astronaut hears the phrase: “I’m sorry Dave, I can’t do that.”

Ref: arxiv.org/abs/0901.4963: How Emotional Mechanism Helps Episodic Learning in a Cognitive Agent

Fermi’s paradox solved?

Monday, February 2nd, 2009

ets-in-range

We have little to guide us on the question of the existence intelligent life elsewhere in the universe. But the physicist Enrico Fermi came up with the most obvious question: if the universe is teeming with advanced civilizations, where are they?

The so-called Fermi Paradox has haunted SETI researchers ever since. Not least because the famous Drake equation, which attempts put a figure on the number intelligent civilisations out there now, implies that if the number of intelligent civilisations capable of communication in our galaxy is greater than 1, then we should eventually hear from them.

That overlooks one small factor, says Reginald Smith from the Bouchet-Franklin Institute in Rochester, New York state. He says that there is a limit to how far a signal from ET can travel before it becomes too faint to hear. And when you factor that in, everything changes.

Smith uses this idea to derive a minimum density of civilizations below which contact is improbable within a given volume of space. The calculation depends on factors such as the lifetime of a civilization and the distance that it might be possible to communicate over and it produces some interesting scenarios:

Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.

So if there are only 200 advanced civilizations in our galaxy, the chances are that they’ll never notice each other.

Of course, we’ve no way of knowing how many advanced civilizations are out there. But this kind of thinking could, for the first time, put a limit on the number that could be out there: less than 200 perhaps?

It also has significant implications for Fermi’s line of thinking.

Would it be too early to say the paradox has been solved?

Ref: arxiv.org/abs/0901.3863: Broadcasting But Not Receiving: Density Dependence Considerations for SETI Signals