Moving through a living cell: a mystery

It was a suspicious case.

To all appearances, the motion within the living cell looked thermal; a movement of particles caused by heat. Yet the temperatures needed to produce that degree of motion exceeded 30,000 K. That would equal one very very dead cell.

So what was going on?

A question about living cells was a surprising one for a Physics colloquium. The visiting speaker was biophysicist Professor David Weitz from Havard University, and he assured us that he was constantly reminded by his biologist colleagues that he still thought very much like a physicist. Evidently, this had not been meant as a compliment, but it was a relief to his current audience who looked slightly fretful when cells were mentioned in the talk title.

He started off by reminding us of the random walk that particles will perform if they are suspended in a liquid. The famous experiment in which this was first observed was performed by Robert Brown in 1827 who was examining pollen grains in water. There is a rather nice demonstration of what he saw here. This effect became known as 'Brownian motion'. The cause of Brownian motion is the water molecules that are buffeting the larger pollen particles as they move around. The temperature of the water dictates how much energy the water molecules have and therefore how much they will bump around the pollen particles. Since this motion is entirely dictated by heat, it is an example of thermal motion.

There is one thing, however, that must be true for Brownian motion: the liquid must be in equilibrium and not undergoing any overall changes such as heating or cooling.

And if there is one thing known about living cells it is that they are not in equilibrium.

So how was it that when tiny beads are placed into a cell, they move in the same way as pollen grains on water?

It was strange and a closer inspection of the situation proceeded to reveal two more mysteries: Firstly, between steps in their random walk through the cell, the beads would appear trapped. They would vibrate slightly as if caught on a spring before freeing themselves to move to their next location. This small-scale movement was not seen in normal Brownian motion, so did it have a different cause or was the same force responsible on both scales?

The second oddity was that if the temperature of the cell was fixed, but all chemical activity ceased, the motion stopped. Brownian motion, being thermal, is entirely dictated by temperature. If the temperature remains constant, all Brownian-type movement should continue. Here in the cell, though, the lack of chemical activity was a clearly a key factor.

It was looking more and more as if this motion only looked thermal, but was driven by something else entirely.

Professor Weitz's group then studied the motion of the cell's microtubules. These are the most rigid structures within a cell and their movements, like that of the beads, can be measured. By creating a controlled cell-like environment in the lab, conditions within the cell could be changed to monitor their effect on the microtubules.

Really, it was a lot like simulations where I turned on physical processes such as star formation one by one to see their effects on an evolving galaxy. Galaxies ... living cells ... clearly they were all the same!

The results from these experiments pointed to the presence of a driving force that was shaking up the cell's internal network. In addition to the microtubules, the cell has a support structure of smaller filaments and it was these thinner components that were being moved about. The shaker was molecular motors; large molecules found in all living organisms. These can change their shape when they come into contact with ATP --an energy transmitting chemical-- causing material around them to deform. This motion of the smaller filaments pulls in different directions around the microtubules causing them to undergo the small-scale trapped vibrations that were seen in the beads. As the microtubules grow, they bend under this jiggling surrounding movement causing them to distort or perform a random walk, just like the pollen grains in the water.

So the cause for the microtubules or beads movement was not so different from Brownian motion in that it was the motion of the small-scale surrounding material that was having an effect. However, the reason for the background motion was not heat, but the driving force from the molecular motors.

Case closed.

Catch a falling star

Observational astronomy normally conjures up images of sparkling white domes set on the edge of cliffs above ethereal views morphed out of cloud tops. For the Canadian Automated Meteor Observatory (CAMO), however, the reality ... is a pig farm. Literally. I couldn't help feel that southern Ontario had been a bit short changed. 

This particular swine-based observatory is one half of a twin set (the second is located a pig-free field 50 km away) of telescopes operated by the University of Western Ontario (UWO) that are used to measure the position and velocity of meteors. Paul Wiegert from UWO visited McMaster to give last week's Origins Colloquium and explained why they were searching for shooting stars.

A 'shooting star' or 'meteor' is the name of the flash of light in the sky caused by an extraterrestrial rock heating up as it falls through the Earth's atmosphere. Typically, a meteor will only be 3 mm in size but travelling at a notable speed of 30 km/s. Prior to its atmospheric entry, the rock is known as a meteoroid and if it actually reaches the Earth's surface before being completely burned up, it becomes a meteorite. To complete the journey, a starting meteoroid must be larger than sizeable 1 m in diameter. The biggest meteors are called fireballs, with the Peekskill fireball being one famous example. This fell over the United States in 1992 and was recorded on the camera of a woman who happened to be filming her son's football match at the time. The resulting meteorite struck a car that was for sale, raising its price from a few hundred to a quarter of a million dollars. A second example was the Grimsby fireball which fell in 2009 and was filmed here at McMaster by an instrument owned by Professor Doug Welch from the top of the Physics department.

Where, though, do these Earth-bound rocks come from? Professor Wiegert explained that there are three possible sources. The first is from comets in our Solar System; dirty snowballs that heat up as they approach the Sun, producing a tail of rocky particles. These objects are usually trapped by the Sun's gravitational pull in the same way that the Earth is, but are on highly eccentric orbits so their passes by the Earth can be up to thousands of years apart. Should the Earth's orbit intersect the orbital path of a comet, the extended trail of debris left in the comet's wake can produce a meteor shower, such as the annual Perseids shower each summer: a more attractively stunning version of the trail of slime left by a departed slug.

A second source of meteors is a collision between two asteroids or a planet with an asteroid; rocky bodies that are smaller than planets, but also orbit around the Sun. The larger meteors that survive their decent to become meteorites typically come from this source. Contrary to what you might expect, a meteorite is typically cold when it reaches the ground. This is because it consists of the core of the meteor that is not burned up travelling through the atmosphere. The end part of the meteorite's journey is known as the 'dark flight' where it falls from the average height of a commercial aircraft without burning. The fact that this rock is not heated to high temperatures has important implications for the transmission of life across space; it could be possible that microbes shielded safely in the cold core of meteors might survive to populate a new world.

This consideration leads to the question as to whether there is a third source of meteorites: solid particles that originate from outside our Solar System. Since we find evidence of asteroid collision debris from the Moon and Mars, might we not also have received material from further away? From star systems billions of kilometres from our own?

Material from Mars found on Earth is not uncommon. It is estimated that around 500 kg or 15 individual meteorites per year hit the Earth from the red planet. However, the vastness of space makes interstellar rock transfer a whole new game. Approximately 100 rocks with diameters greater than 10 cm (the minimum size needed to protect biological molecules in space) are estimated to leave our Solar System from a terrestrial planet every year. Unfortunately, that only equates to the chance of striking another terrestrial planet to be a minute 10-4 per billion years. Even if you were to lower your requirements and ask what the probability was of such a rock merely being captured by another star system, in the hope that this would eventually lead to a collision with a planet, the chance is only 1 per billion years. This makes the odds of us receiving biological material from another star system incredibly unlikely.

What though, asked Professor Wiegert, about smaller meteorids? Ones that are too small to be biological carriers but might still arrive in the Earth's atmosphere? Are we able to detect these and get a handle on how many we receive? It was this goal of finding such tiny object that CAMO was designed. Such small pieces of material will be very hard to detect, especially since they will burn up long before you have the chance to hold them in your hand and put them under a microscope. However, if they come from outside the Solar System, their expected velocity is very high, equal to around 20 km/s on arrive in our Solar System which will be accelerated to 46.6 km/s as they are drawn towards the Sun.

So has CAMO detected any of these interstellar visitors?

Possibly; but it's very hard to confirm. One of the problems is the giant planets in our Solar System, namely Jupiter and Saturn, are able to sling shot rocks to much higher speeds that they would otherwise obtain, making it look like they originate from further afield. It is important for CAMO to get an accurate measurement for both the meteor's position and velocity to rule out this possibility.

CAMO began taking data only last summer but perhaps soon we will know if our atmosphere is receiving the most distant of visitors.

Mission to Mars

"Would you go?"

The question was from my office mate, Kelly Foyle, a postdoc working with Christine Wilson on observations of star formation in disk galaxies. We were discussing the first Origins Institute Colloquium of the year which had been given by Canadian astronaut, Dave Williams, on the prospect of a manned mission to Mars.

I considered my answer carefully. To be one of the first humans to set foot on another planet; what an incredible prospect! I could practically hear my eight year old self, fresh from my first trip to a planetarium, jumping up and down shouting 'take me, take me!' And yet ….

"No," I said slowly. "There's too much here I couldn't leave behind for so long."

The problem with Mars is that it's really far away. Both the Earth and Mars are on elliptical orbits around the Sun, which means that their distances from each other changes continuously. The closest they have been recently was in 2003, where they were 55,000,000 km apart. While that makes even a trip round the Earth (40,075 km) seem like peanuts, the furthest Mars and Earth can be apart is 401,000,000 km. This difference is why Mars is sometimes easy to see in the sky and at other times very hard to find.

Because of this distance, an expedition to Mars would take of order three years. It would comprise of 6-7 months travel time to reach the red planet, two years on the planet surface and another 6-7 months for the return journey. For comparison, the moon can be reached in three days while journeys to the International Space Station are quicker still. This presents any would-be expedition with a problem that has never had to be tackled before; what do you do when something goes awry and you can't just come back? All previous space trips have been able to have the back-up plan of returning to Earth quickly if necessary, but a Mars-bound vessel would have to 'abort to Mars' once it was sufficiently far away from Earth. Any repairs or necessary adjustments would therefore have to be able to be performed while in space with the tools and supplies already on-board. Even though advice could be received from Earth, the twenty minute latency on communications from Mars to Earth would be too long for medical procedures to be conducted via this method; the knowledge as well as the equipment would have to be with the astronauts themselves.

In addition to this, Dave Williams placed a lot of emphasis on the problems of keeping the astronauts healthy, both in body and mind. In the low gravity of space, the human body can start to waste away which causes problems when the astronauts return to Earth. For instance, while astronauts use their arm muscles to propel themselves around the space craft, their leg muscles get little use and loose their strength. The heart muscle deconditions and bone density drops at a rate of 15% per month. Astronauts can also suffer from lower back pain as their body elongates in an environment free of the downward pull of a planet. Dave revealed that he is 6' 1'' on Earth but almost 6' 3'' in space. There is also the unknown long-term effects from exposure to cosmic ionizing radiation; high energy particles that we are shielded from on Earth by the protective cocoon of our atmosphere. Dave explained that when you close your eyes in a dark room in space, you can still 'see' flashes of light that come from this radiation passing through you. What damage they might do over a long period of exposure is unknown.

There is also the mental strain of being contained in a confined area in extreme isolation for such a prolonged period of time. Entertainment and variation in food will also be difficult, since astronauts will grow bored of eating the same meals for several years.

Once on Mars, the astronauts will be in a strong gravity field once again, although Mars' gravity is only 40% that of Earth. However, unlike on Earth, there will not be people able to help the new arrivals until they can re-adjust to the forces on their body and there will be much work to do.

To combat these problems, exercise machines have been developed specifically to keep astronauts in shape while in space. Harnesses are used to pull the user down onto the running machines and a DVD player screen help maintain a sense of orientation. Meanwhile, the University of Guelph is researching into producing crop yields on another planet and NASA are exploring different possibilities for transportable shelters to take to Mars. Dave mentioned the idea that the perfect candidate for this mission might be different than for previous expeditions into space, due to the long duration and uncertainties being faced. He suggested that older people in their 70s might potentially prefer to make the journey, since their families would be grown and long-term health effects that could occur 10-20 years later would be less of an issue.

While the space program may not yet be recruiting astronauts specifically for the Mars mission, Dave thinks there is a high chance in it happening within our lifetime. It was a strange thought to think that you could be sitting beside the first person who will set foot on an alien world. Who knows? When I reach 70 I might even change my mind and be signing up myself!

So what is it really like in space? Dave told us that he gets the most questions about how astronauts shower and use the toilet when they stay at the International Space Station. He describes the shower, which looks like a cylinder with a lid. Soapy water is used to cover your body which is then vacuumed away. The toilet, he said, uses another vacuum system. The basic idea of such a device is that you want things to go away from you. On Earth, gravity does all the work when you flush, but in space a vacuum has to be used to remove the bodily waste from the toilet bowl, where it is then stored and returned to Earth. This final point left Masters student, Mikhail Klassen, with one question:

"Why, oh why do they bring human waste back to Earth when there is infinity on all sides of you?"

It was a mystery that would have to be left for another day.

It's life Jim, but ..... 5/6 how we know it

Nov. 29, 2010:

NASA to Hold News Conference on Astrobiology Discovery
Science Journal Has Embargoed Details Until 11 a.m. PST On Dec. 2


It was to be three nail biting days of anxious waiting. Stress levels in scientists across the globe rose to values only previously seen the week before Apple's iPad release. At least half of Oregon packed a suitcase ready to be told alien Spock had made first contact and his buddy Tuvok had a spare room for guests. Kentucky loaded their shot guns.

Then the moment of truth dawned:

There's a bacterium 1/100th of the size of a human hair that hangs out in some pond in California and lives off arsenic.

Whereupon approximately half the audience fell asleep, half went into a state of frenzied excitement and the one person to actually understand its implications commented
that this complicated matters. To know exactly why this one person felt this way, we need to understand what makes you and the microbes in your kitchen sink blood brothers.

We have long known that life can exist in some pretty unlikely places. Organisms aptly known as 'extremophiles' have been found to thrive in temperatures exceeding 100
°C (hyperthermophiles), in solutions more acidic than lemon juice (acidophiles) and under bombardment of powerful ionising radiation (radioresistent). So while California's Mono Lake with one of the highest concentration of the deadly toxin arsenic on the planet might not make a swim resort, it is perhaps not astonishing that it should still harbour life.

However, the extremophiles, you, me and the microbes in your kitchen sink are all composed of six major elements;
carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus, with trace other ingredients as icing to the biological cake. Until the NASA press release, these six fundamental building blocks were common to all forms of known life. In fact, while one could speculate otherwise, there was no evidence that life didn't require these six elements to exist. This meant that searches for life on other planets seemed to necessitate the detection of the presence of these seemingly essential ingredients.

The difference with the bacterium found in Mono Lake is that it is the first living entity to have been discovered that violates this cardinal rule. Instead of phosphorus, this microbe can use arsenic in its DNA. Since phosphorus is vital to cell reproduction, it might be considered a controversial move to substitute it for the second most favourite poison in Agatha Christie's famous crime novels (the first is cyanide, in case anyone was interested). It turns out that arsenic is actually chemically similar to phosphorus, sitting directly below it in the periodic table. This makes it a viable alternative.

The discovery that life can form using a different fundamental base of elements is immensely important for scientists who have been trying to imagine what life on other worlds would be like. However, there is one thing that this discovery is not which, if it were, would cause every astrobiologist in the world to pass out for at least a week.

It is not an unrelated form of life to us.

All currently known forms of life have a common origin. Nevertheless, it is possible to conceive that life might develop in multiple places on Earth independently of one another. An occurrence of a second genesis of life on Earth is known as a 'shadow biosphere' and could evolve in a completely different way to life that we know. If such a system were found, it would be evidence that life is not difficult to produce in the right conditions. That being so, it would increase the odds of life being present on other planets considerably.

Basically, it would be time to check that your best friend isn't from a small planet somewhere in the vicinity of Betelgeuse.

The case of the bacterium in Mono Lake is not a shadow biosphere. While this microbe can use arsenic, it can also use phosphorus and indeed will prefer to when given the choice. Moreover, Mono Lake has only become heavy in arsenic over the last 50 years. Prior to that, it had a source of fresh water, removing the environment in which an arsenic-dependent microbe could develop. This points to an organism that originally conformed to the established six building blocks of life, but evolved to survive in the increasingly hostile environment of Mono Lake.

While it may not be a new form of life, this tiny microbe opens the door to a huge number of questions in astrobiology. It particular, its discovery proves that we will have to be significantly more open minded when searching for life outside our planet. If there is no core pattern that nature cannot adapt when required, then what signatures can we design our detectors to search for? In fact, this microbe hasn't so much as opened a door as ripped it off its hinges.

References: the original paper for this research is science.1197258. There are also two excellent reviews at 'Not Rocket Science' and 'Bad Astronomy'.

When stars collide

"I have a visitor, Fabio Antonini, from the Rochester Institute of Technology who is here to work on the evolution of stellar collisions."

The email from Evert Glebbeek, a postdoc in the department working with Alison Sills, popped into my inbox and nearly made me pop out my chair. What did he mean this researcher worked on stellar collisions? Stars didn't collide! All the models I had made governing their motions through my simulated galaxy assumed this was the case. If it turned out not to be ... if it turned out stars did regularly slam into each other ... if it turned out that ALL MY RESEARCH WAS WRONG ...!

The email continued by saying that they were going for dinner at a local Indian restaurant that evening. I cast aside my keyboard and told Evert I would be taking the chicken vindaloo.

In fact, I need not have been so worried. The ratio between the size of a star compared to the distance between them is normally so large that even when galaxies merge, the stars do not run into one another. The chance of a star like our Sun hitting another star is so remote that we would have to wait for the entire age of the Universe for it to occur.

There are, however, other places in our galaxy where the probability of two stars colliding is much higher. The first is in dense clusters of stars and the second is in the centre of our galaxy, close to the super-massive black hole. Over dinner, Fabio explained to me that it was the latter scenario that he was investigating; looking at a population of stars close enough to the central black hole that they could be strongly affected by the force of its gravity.

Despite the frightening images that a black hole conjures up, if you remain outside its event horizon there is no particular cause for alarm. Objects that drift past this point can never be seen again, but stars at a greater distance can orbit the super-massive black hole safely in the same way as the Earth goes around the Sun. Yet Fabio told me there is something very strange about a few of the stars very close to our galaxy's super-massive black hole; namely, that they are very young.

Stars form when clouds of gas become dense enough that they collapse under their own gravity. Once this has happened, the object produced is very hard to break apart, but during its formation the cloud can be more easily disrupted by an outside influence. Close to the super-massive black hole, clouds are not able to form stars before the black hole's gravity rips them to pieces. Stars that are found in this region are therefore usually older objects that were born further out in the galaxy and have been scattered in over time. How there could be young stars so close to the black hole was consequently a mystery, but one Fabio thinks he has found a solution to during his PhD work.

Fabio postulates that a known mechanism for breaking apart binary stars might sometimes go the opposite way, and cause two stars to merge. In a binary system, two stars are born so close together that they orbit about a common point between their centres. When such a pair approach the super-massive black hole, the black hole's gravity can disrupt the binary, resulting in one star orbiting the black hole and the other being ejected out of the galaxy at high velocity. In Fabio's models, a similar event occurs but instead a star being ejected, the black hole's influence makes the binary stars collide and merge to form a single object. This new composite star has the same chemical composition as the two old stars, but is now twice the mass. This makes it appear to observers to be much younger than it truly is, since more massive stars evolve faster than their lighter counterparts.

Binary stars colliding under the influence of the SMBH

This movie shows the results of one of Fabio's simulations[*] of a binary merging due to the gravitational influence of a super-massive black hole. The black hole is not shown directly, but its effects can be seen upsetting the orbit of the two stars which get steadily closer and collide, before settling into a single object. [Click on the movie to play and if that sadly fails click here. If you weren't concentrating and want to start the movie from the beginning but 'reload' is treating you badly, try hitting 'shift' at the same time as 'reload'.]

This was an exciting look at one of the most dangerous areas of the galaxy. Nevertheless, from the point of view of the fate of the Earth, I was rather glad we were hanging out in a quieter suburb.

--
[*] Journal reference: Antonini, Lombardi & Merritt, 2010, astro-ph/1008.5369 .

Answering the ultimate question

"That computer learnt word associations from Wikipedia. So it knows that 'opus' goes most commonly with 'Rome', 'sushi' with 'fish' .... and therefore 'robot' with 'violent genocide of the human race'?"

We were discussing the latest colloquium from the Origin's Institute which this week had been given by Geoffrey Hinton, a specialist (and indeed founder) on neural networks from the University of Toronto. Apparently, we had inadvertently stumbled across the cause of the downfall of humanity; that the tool used to teach computers about language also happens to include a scene-by-scene description of the 'Terminator' series.

An artificial neural network is like an electronic brain; it is a computer program that is designed to work in a similar way to biological neurons. Like the brain (and unlike most other types of computer programs), neural networks can 'learn' to do a particular task by being given many examples. They are used in pattern recognition (e.g. reading a person's handwriting) and for finding complex relationships (e.g. stock market predictions or medical phenomena, where the outcome is the result of many combining factors). 

In his talk, Professor Hinton took us through one of the early algorithms for teaching a neural network. In this technique, the computer is given data --for instance an image of a hand-written number-- that it must identify. It looks for specific features in the pixels, such as the presence and position of curves or straight lines, and then makes a guess. The guess is then compared with the correct answer and the relative importance of the different features being detected is adjusted to improve the algorithm. For example, a double loop would be very important since it identifies an '8', whereas a single loop is less significant since it could belong to a '0', '6', '9' or even squiggly drawn '4'. After this training, the computer program can be used to identify a wide range of hand-written numbers accurately.

This method works, but it has its drawbacks. Having a large number of fixed features that must be programmed for the code to identify makes the process slow, inflexible and results in poor scaling. Additionally, the fact it requires labels (e.g. 'number 1', 'number 2') to apply to the data differs from the way our brain works. Each image that our brain processes can rarely be categorised by a single label. For instance, a cow in a field has a colour, a position and key tell-tale signs that indicate it might actually be a man-eating Minotaur -- all of which are not encompassed in the label 'cow'. 

An improvement to this was to replace the pre-defined features that were given to the computer to identify an object with a set of criteria it created itself based on experience. This meant the computer no longer needed to know anything about the data it was being given. It could be a series of drawings of the number 2, pictures of houses or Minotaurs disguised as cows, and the algorithm would find common collection of characteristics that it could use to identify them. An example of such an identified feature for a '2' would be a wedge of light coloured pixels in the top left corner of the image, followed by a diagonal dark line -- the start of the 2's top arch.

Left to do this, the features identified by the neural network fell into two main categories; a small set of coarse criteria based on colour and a much larger set of finely tuned criteria based on shade. An example of both these types of characteristics would be a person standing against a wall. The sharp line between the white of the wall and the darkness of their hair would form a colour-based feature. Their facial features, meanwhile, would be picked out in a multitude of different shades in the same 'skin' colour. Interestingly, the resultant map of these computer-identified features closely resembles that of a monkey's brain.

Algorithmically, the set of data defining characteristics is honed by the computer program calculating first a set of features, then set of features of the features.... then a set of features of the features of the features. This leaves a collection of basic patterns that can be used to accurately identify the type of object for which the network has been trained.

An interesting question Professor Hinton than proposed was could such a neural network use its pattern recognition to predict the next stage of a sequence, rather than just identify objects? In particular, could a program predict the next word in a sentence?

To tackle this problem, the philosophical sounding question 'what is a word?' had to be answered. It turned out to be easiest to consider a word simply as a sequence of characters and to train the neural network to predict the 11th character in the string fed to it. This process could be continually repeated to build up entire sentences.

To teach the network about how words are formed, PhD student Ilya Sutskever gave the computer 5 million strings of 100 characters each from wikipedia. At the end of this training, the computer was told to build entire paragraphs of text to assess what it knew. It turned out to almost always produced real words. In the few occasions where it made some up, they sounded like they ought to exist. For example, 'ephemerable' or 'interdistinguished'. It was also good at semantic associations. It knew that many words that started 'sn' were connected with the upper lip and nose, e.g. 'sneeze', 'snarl' and, uh, 'snow' when used as a synonym for an illegal drug. (A fact noted by the speaker, not the author of this blog). Likewise, it knew that sentences containing 'opus' often also contained 'Rome' and that ones mentioning 'Plato' frequently went on to say 'Wittgenstein'. Similarly to the human brain, however, it often did not know why these connections existed. This produced sentences that made sense grammatically, but would not actually be found. For example, it talked about the "several Irish intelligence agencies in the Mediterranean' which is geographically unlikely.

A fact I found most surprising from this work was the length of information the computer program drew from. When deciding what the next character should be, it did not just look at the few before it, but at the long pattern of characters (that is, entire words) that preceded it. This allowed it to almost always use a consistent tense and to close parenthesise.

The knowledge could be applied to words it had never seen before. Upon being given two uses of the fictitious verb 'to thrunge', it guessed that the next character in 'Shelia thrunge' would be an 's' whereas the one following 'people thrunge' would be a space.

At the end of the day though, all Douglas Adams fans will agree that there really is only one question of any importance for a neural network trained on language. The computer was therefore asked to complete the ultimate question:

'The meaning of life is ...'

To which it replied:

 '.... literacy recognition.'

Clearly, it had been listening to students and postdocs panic about their paper count in the laboratory.

So are we close to really understanding how the human brain works? Professor Hinton took the opinion:

"It's a device with a few trillion parameters ..... how hard can it be?"

Questioning the standard

Around 13.7 billion years ago, a hot, dense and infinitesimally small point started to expand rapidly in an event known as the 'Big Bang'. As it inflated, the matter within it cooled, condensing into galaxies and stars until it became the Universe we see today.

Ironically, the man who coined the term 'Big Bang' was not one of the founders of the theory, but one of its opponents. Sir Fred Hoyle was an astrophysicist at the Institute of Astronomy in Cambridge and is possibly better known for his naming of the theory he did not believe than for his ground breaking work on stellar nucleosynthesis; the mechanism by which stars form the heavy elements such as carbon and oxygen. Hoyle favoured a 'Steady State' cosmological model, whereby matter is continuously created as the Universe expands, so there is no absolute beginning. In 1949, he used the term 'Big Bang' (some claim derisively) while discussing his research on the radio, and the striking image this conjoured caused the name to stick for both its supporters and opponents alike. Since then, the Big Bang theory has become accepted as part of the standard model for cosmology and very little is heard of alternative theories outside historical reviews of the field.

For me, the first time I head anyone talk on a different model was this semester when Professor Jayant Narlikar was invited to speak at McMaster, giving talks both at the Origins Institute and in the Astronomy department. Professor Narlikar worked with Fred Hoyle while he was at Cambridge in the 1960s and, like his mentor, is a proponent of steady state theories. His affiliation with Hoyle and subsequent astrophysical career would have made him a speaker not to be missed, but I was also intrigued and (I admit) skeptical. Few people nowadays questioned the Big Bang theory, so was it not time for Hoyle's old team to drop their searches for an alternative explanation?

With this in mind, I listened as Professor Narlikar began his talk by explaining what had driven himself and his colleagues to seek out a new cosmological model. He explained that in 1948, the Armenian scientist, Viktor Ambartsumian, raised ideas about astronomical objects known active galactic nuclei (AGN). These highly compact regions were seen to be pumping energy into space, suggesting that they were violating two of the sacred rules in physics; the conservation of energy and momentum.

To explain these systems, Narlikar, Hoyle and a third astrophysicist, Geoffrey Burbidge, developed a variation on Hoyle's original Steady State theory which become known as the 'Quasi-steady State’ theory in 1993. Like the standard picture, Narlikar's universe contains dark energy that permeates all of space. In the Big Bang theory, however, the presence of dark energy causes the Universe to expand, whereas here it has the opposite effect, pulling the Universe in on itself. To off-set this, Narlikar introduces a second energy type called the "C-field". When the C-field energy gets very high, it creates both matter and space via Einstein's equation for the equivalence of matter and energy, E = mc2, thereby continuing to conserve energy.

The C-field's strength increases around very compact, massive objects (such as AGN), causing a mass production of particles such as what Ambartsumian described. The standard picture of AGN is that they are black holes that are accreting mass that radiates furiously as it is accelerates. In Narlikar's model, black holes do not exist in the traditional sense, but are places where the C-field is exceptionally strong, producing explosive creation events of matter and space.

The resultant creation of space dilutes the C-field, eventually causing it to become much weaker than the dark energy which takes over and starts to pull the Universe back in. As space collapses, the C-field density rises until it once again dominates the dark energy and forces the Universe to perform another change of direction. It is a giant heart beat, lasting billions of years.

So can this be tested? Professor Narlikar's idea was straight forward; while most of the galaxies and stars would be destroyed as the Universe contracts, a few would survive into the next heart beat. Therefore, if we could find stars older than the Big Bang model gives for the age of the Universe (that is 13.7 billion years), it is possible that they came from a previous expansion phase in a universe that is better fitted by Narlikar's model.

Professor Narlikar's team conjectured that such surviving stars were likely to be ejected away from our galaxy during the turmoil caused in the contraction and expansion of the Universe. They therefore searched for old stars near one of our Milky Way's satellite galaxies, the Large Magellanic Cloud. Examining data from the Hubble Space Telescope, the astronomers found a number of candidates that appeared to be abnormally old. However, Narlikar's group were cautious; could there be alternative theories as to why these stars might appear much older than they really were? For instance, if the star was really not a single object, but two stars orbiting one another closely in a binary, it would be redder (and therefore seem older) than either twin actually was. Alternatively, their candidate might be not very old, but very young, too young to be accurately dated by the techniques they were employing. Finally, they might have made incorrect assumptions about the composition of the star, causing the age estimates to be off.

After considering all these points, Professor Narlikar concluded that, while they had possibilities for stars whose age exceeded 13.7 billion years, it was impossible to prove conclusively at this time.

I continued to think about Jayant Narlikar's talk for the rest of that day. It stayed in my mind not because he had convinced me that the Big Bang theory was wrong, or even because the talk had been well presented and interesting (although it had been). It was because it reminded me strongly why I became a scientist; to question all and every idea in the search for the truth.

In the 17th century, Galileo Galilei was condemned for his support of the Copernican model of the Solar System which placed the Sun, not the Earth, at its centre. (Amusingly, the Catholic Church only publicly vindicated him in 1992). This history is evidence for how easy it is to become complacent with established theories and loose track of what science is about. After listening to Professor Narlikar's talk, the direction my own research could go in seemed to double and triple before my eyes. I remembered that I should not be be confined by what people had done before, but rather use the ideas as stepping stones to go in any number of directions.

The moon illusion

"So why do you think the moon looks larger on the horizon?"

The question was posed by Rob Cockcroft, a graduate student who was also a presenter at the University's McCallion Planetarium. He was about to present a show dedicated to the moon and thought it possible he would be asked this question by one of the audience.

I blinked and looked up from my sandwich. "It does?"

I realized immediately I had just failed as an Astronomer. Yet the truth of the matter was that if an astronomical object appeared too large in my simulations, I had probably messed up the units in my calculation and caused the Universe to expand too slowly. Actual objects were not really my thing.

Fortunately the rest of the lunch table were more use.

"Isn't it because the moon is closer to other objects, such as trees, when it is low in the sky?" another graduate student asked. "Compared to those the moon will appear bigger."

This was a logical guess and one Rob himself had held until he had looked into the matter. The effect is known as the Ponzo Illusion and it is an optical effect that causes the human mind to judge the size of objects based on their background. Simple diagrams such as the ones shown here easily demonstrate this effect exists, but it is not the cause for the moon illusion, which has been proven to occur even on a featureless plain such as the ocean.

Another popular myth is the moon illusion is caused by the distortion of light in the Earth's air. It is true that as the moon sinks towards the horizon, you view it through a thicker layer of atmosphere, but the bending of light this produces actually causes the moon to appear smaller, not bigger.

In fact, Rob's investigations turned up no definite reason for the moon to appear larger; it seems no one knows for sure. The most common explanation, however, is that our brains have a view of the sky that is not a perfect hemisphere (like a planetarium) but a squished, shallower arc, more like a soup bowl. This causes us to believe that an object on the horizon is further away from us than when it was directly overhead. Since the moon's size actually hasn't changed, our brains assume that is must be larger at the horizon since it is apparently at a greater distance.

Quite why our brains would do this is a mystery. One argument suggests that we have evolved to be better at judging the size and proportion of objects that are close to us, since we are far more likely to be eaten by them than something at the bottom of a cliff or high in the sky. No one though, is entirely sure and some people reportedly don't experience the moon illusion at all. For those super interested, a good description of the moon illusion, including the flaw in the soup-bowl sky theory can be read here.

As I finished my lunch, I wondered if I was one of those rare people unaffected by the moon illusion. That would turn my folly at not knowing about it into the product of superior perception, not incompetence. It was a long shot, but I made a mental note to check next time there was a full moon.