Does the strong force distinguish between past and future ?-II

 

A popular introduction to the strong CP problem

Part II: From the spinning top to irreversibility in time

This blog post is a continuation of the previous one. In this post, I wanted to explain how we can experimentally know if the strong force breaks time-reversal symmetry.  Just as I was writing this post, some exciting results from the particle physics experiment at  Fermilab were announced.  There is a possibility that this measurement would turn out to be a major breakthrough in particle physics.  This was a fortunate coincidence because the same physical concepts underlie both the original subject of this post and the physics behind this exciting new measurement. Thus I will enlarge the scope of this post. While the first part of the post will be a continuation of the previous post, at the end I will touch upon this new development.

In this blog post I will try to explain how we can experimentally determine whether the strong force breaks time-reversal symmetry. Our story starts with the spinning top. As anyone who has seen a spinning top would know, a top doesn't just spin about its axis, the axis itself wobbles and rotates about the vertical direction as shown in the video below.

This wobbling of the axis is called precession and is caused by the gravity.  This is actually one of the more complicated things to understand even for college physics students. Although it is straightforward to understand precession mathematically, it is somewhat counterintuitive. For this reason Richard Feynman, in one of his famous lectures, devotes a lot of time trying to explain precession in a less mathematical way. What makes this wobbling  counterintuitive is that if the top was not spinning, gravity would apply a  rotational force that would make it fall. If the top is spinning, however, the same rotational force leads to this new unexpected rotation of the axis! 

Let us introduce some jargon that would become necessary later. The rotational force mentioned above is an example of what physicists call a torque. It is a very useful concept to understand rotation of bodies. For instance if we have a pendulum that moves to and fro due to gravity we can say that gravity applies a torque. Torques have a direction or sense, i.e. they can be either clockwise of anti-clockwise. Note that in these examples torque is a derived concept arising from the more fundamental idea of a force.

I will not even try to explain the phenomenon of precession more deeply. Let us just remember the following fact: 

no spin+torque=top falls down

whereas, 

spin+torque=precession! 

In fact the sense of the spin and the torque completely determine the sense of the precession. If the spin is anti-clockwise, the clockwise gravitational torque leads to an an anti-clockwise precession. If we reverse the direction of either the spinning or the torque it will change the direction of the precession. If we change the direction of both on the other hand the direction of the precession remains unchanged.

Let us now move on to the main subject of this post, the precession of sub-atomic particles like the electron and the neutron in electric/magnetic fields. The electric and magnetic fields will play the role gravity plays for the spinning top. So, what are electric and magnetic fields? It is the electric fields that cause electrons to move through wires giving rise to electric currents that power the modern world. Magnetic fields, on the other hand, originate from magnets but also from electric currents. In fact electric currents are actually the fundamental source of all magnetism; there are microscopic currents within the magnets themselves. Electric and magnetic fields are deeply connected to each other. They are now understood to be two aspects of the same electromagnetic interaction, one of the four fundamental interactions of nature. 

The connection of these sub-atomic particles with the spinning top arises because--in order to understand some of the important properties of these particles-- we must imagine they are constantly spinning like a top. Except that the spin of such particles differs in a fundamental way from that of the top. The spinning of the top is associated to the rotation of the particles that constitute it. On the other hand, an elementary particle like an electron is thought to have no constituents and thus its spin cannot be understood in the same way as in the case of the spinning top.  It is instead an intrinsic, fundamental property that does not have an analog that can satisfy our intuition. As we will see, however, many of the consequences of this intrinsic spin arise exactly as if these particles were spinning like a top.

Having discussed spin let us come to the other ingredient required for precession: torque. Just as spin can be fundamental for these microscopic particles, so can torque. Electric and magnetic interactions can result in a fundamental torque-like effect that acts on the spin of these particles. This causes a precession of the spin as shown in the figure below where the green arrow shows the direction of the electric/magnetic field and the black arrow shows the spinning particle. The electric/magnetic field plays the role gravity plays for the spinning top.

                        Precession of the spin of a sub-atomic particle

The green arrow above might give the wrong impression that the torque in the above case is clockwise. It is, in fact, more complicated to determine the direction of the torque in this case. To completely determine the direction of the torque we need to know the direction of the torque as well as the spin and one more ingredient, the so called electric/magnetic dipole moment (EDM/MDM). The EDM/MDM of a particle is an intrinsic property that tells us how large the interaction is between the spin and electric/magnetic field.   A larger EDM/MDM will give faster precession. It is the sign of the EDM/MDM that is crucial for determining the direction of the precession. For a positive EDM/MDM an electron with an anticlockwise spin with a upward electric/magnetic field generates a anticlockwise torque and vice-versa for a negative EDM/MDM. There is a key difference in the torque on the spinning top due to gravity and the torque on the spin of a particle in an electric/magnetic field.  In the latter case, as the interaction of the electromagnetic fields is directly to the spin of the particle, the direction of the torque is not independent of the direction of the spin, i.e. if the spin of the electron is reversed so is the direction of the torque.

What happens if we flip the electron/neutron spin ?  Quite remarkably the direction of precession does not change. This is because, the direction of the spin and torque go hand in hand, so that flipping one automatically flips the other. This is unlike the case of the spinning top where we can flip the spin while keeping the torque direction unchanged. For the top therefore such a flipping reverses the precession direction. The direction of  precession of the spin of sub-atomic particles, however, remains unchanged when the spin is flipped because the torque also flips its direction simultaneously [1]. Thus both ingredients in our mantra spin+torque=precession flip directions together resulting in the precession direction not changing!

Consider first the case when an electric field is applied. For this case this is an example of a fundamental process which has an intrinsic directionality. For a given sign of the EDM and a given direction for the electric field the precession direction of a particle is fixed irrespective of the direction of the spin, i.e. it is either always clockwise or always anticlockwise.  As you may have guessed it is this fixed directionality that violates T-symmetry. This is because if time ran backwards, it will change both the direction of the spin and precession (a clockwise rotation would become anti-clockwise if time ran backwards). But this is not allowed as the precession direction must remain unchanged even if the spin flips. The precession of the spin of these particles in an electric field is thus inherently irreversible in time. This brings us to the main point of this post. It turns out that if the strong force violates time reversal this shows up as the presence of an EDM for the neutron. This is not unexpected because the the neutron is made of constituents called quarks that are held together by the strong force.

Precession of these particles under the effect of a magnetic field, however, does not violate time reversal symmetry. Almost everything is identical here except that it is now the magnetic dipole moment interaction that is important. How is it then that with  a magnetic field, such a precession is still reversible ? The crucial difference is that magnetic fields, unlike electric fields, flip their direction under time reversal. This is because, whereas electric fields can be generated by static charges that remain unchanged if we reverse time, magnetic fields are generated by currents, or moving charges. Time reversal, reverses the motion of these charges and also the direction of the magnetic field. This implies that both the magnetic field direction and the spin direction flip under time reversal. As a result, the torque direction, which is a function of these two remains unchanged. So in our 'formula' spin+torque=precession  only one of the ingredients, the spin, flips under time reversal which in turn means that the precession does change direction if time is reversed making this a perfectly reversible process. The precession of atomic nuclei in a magnetic field is, in fact, the phenomenon that underlies Magnetic Resonance Imaging (MRI) Scans.  

                     MRI Scans utilise the precession of the atomic nucleus

These EDMs and MDMs have been measured for many particles with astoundingly high precision. We will briefly discuss three such landmark measurements that directly tell us something deep about the laws of nature.  Our current understanding of the laws of nature as they apply to these sub-atomic particles--and thus all of the universe, which is after all constituted from these particles-- is called the Standard Model. EDM and MDM measurements are capable of testing the Standard Model extremely precisely as well as potentially disproving it. So here are the three measurements: 

(1) The neutron EDM and reversibility of the strong force

As I already mentioned, if the strong force violates time reversal it will show up as the presence of an EDM for the neutron. Experimental results are consistent with the neutron EDM being zero, i.e. the neutron has not been found to wobble at all due to the presence of an electric filed.  In other words there is no evidence that the strong force is irreversible.  Of course it is still possible that a very tiny neutron EDM still exits, but it is too small to be detected even by these extremely precise experiments [2]. The present results, however, tell us that if a neutron EDM exists, it must be at least 10 billion times smaller than what we would naively expect the strong interactions to induce.

(2) The electron MDM and the most precise test of the laws of nature

The precession rate for an electron in a magnetic field, i.e. its MDM, has been measured extremely precisely. The latest experimental value is

2.002319304361

where the Standard Model prediction is:

 2.002319304364.

This matches precisely except the last digit in the 12th decimal place. I have actually rounded up the last digit here as it is affected by theory and experimental errors. The mismatch in the last digit is within the combined expected error of the theory and experiment numbers [3]. The prediction and measurement of the electron EDM counts as one of the most spectacular tests of the present theory of electromagnetism called quantum electrodynamics. The value for the magnetic moment is engraved in the tomb of Julian Schwinger, one of the founders of this theory.

(3) The muon MDM and the first evidence of physics beyond the Standard Model ?

Results announced on April 7 by Fermilab indicate that the muon wobbles in a magnetic field faster than  the Standard Model prediction, by 1 part in 10 billion.  Both the experimental result and the Standard Model prediction need further scrutiny. But if indeed these hold up it would mean we have the first evidence that the Standard Model breaks down. This would make this measurement amongst the most important particle physics developments in decades.  Here is an official Fermilab video that explains their result in a popular way:

I know this post has become perhaps too long and I do not expect you to remember all the details. But there is one take-home message that I would like to convey. The humble wobbling  of the spinning top has an analog for tiny particles like electrons and neutrons. Measuring the tiniest variations in the rate of wobbling of these particles compared to standard predictions can unlock deep secrets about the universe.

Footnotes:

[1] The torque is given by the cross-product d.(S X E)  or m.(S X B). Here S is the spin vector; E and B are the electric and magnetic fields respectively; d and m are the EDM and MDM respectively.

[2] Actually the weak interactions do induce a very small neutron EDM, that experiments are not sensitive to yet.  

[3] For the experts, I have used the Rb numbers from this reference (Eq.3.4). There is actually a hint of a (2 sigma) tension even for the electron MDM. The tension is even larger if Cs numbers are used for determination of alpha_em.

Does the strong force distinguish between past and future ?-I

A popular introduction to the strong CP problem

My friends and family often ask me, "What are you working on now ?" and  despite my most sincere efforts at answering this question, I am always left with a dissatisfying feeling. I feel that what is very exciting to me sometimes comes across as distant and  abstract as they are not familiar with my area of work. This is the first of a series of blogposts that aims to rectify this situation.  I will try to explain my current area of research in a way that hopefully conveys its importance as well as my excitement for it.

Part I: An irreversible world from 'reversible' laws

My current area of research,  the strong CP problem,  is related to the question whether the strong force-- one of the four fundamental forces of nature that holds the nucleus of an atom together-- respects Time Reversal  symmetry or not. So let me first tell you what is Time Reversal symmetry in this post. I will come to the more specific issue of whether the strong force respects this symmetry only in  later posts. 

If a process respects Time Reversal symmetry (or simply T-symmetry),  it means that if we take a video of it and run it backwards, the reverse course of events would also obey all the laws of nature. By this definition the  following reversed video seems to  shows a process that definitely  breaks T-symmetry:

                                           

After all, none of us has ever seen an egg 'uncracking' as the video shows. Quite remarkably, the above process actually does not break T-symmetry at a fundamental level!  This is also true for a host of other irreversible processes from daily life, for instance, a ball rolling on a floor that gradually slows down and stops (we never see the reverse, i.e. the ball on a floor spontaneously beginning to move). If we could track each and every microscopic particle in the above processes we will see that their histories are perfectly time reversible. This is because the fundamental laws that apply for these microscopic constituents do not distinguish between past and future and are perfectly time symmetric. 

So how do the reversible laws of nature give rise to the the irreversibility seen so commonly in everyday life ? This has actually been one of the deepest and most intensely debated paradoxes in the history of physics. So much so that the Austrian physicist Ludwig Boltzmann-- whose resolution of this paradox is now standard-- was driven to severe depression partly because his ideas were not universally accepted.  Tragically, his life ended when he  committed suicide in 1906 while on vacation at Trieste with his family. 

    Ludwig Boltzmann (1844-1906)

In fact debates on this topic still continue amongst physicists and philosophers. Perhaps, I will return to the subtleties that are still being debated in another blogpost. For now, let me explain the standard resolution of this paradox for the simple example of the ball on the floor that stops rolling. A ball rolling on the floor stops because of friction. Due to friction the ball loses its energy as heat and sound. This energy is thus transferred to the floor and the surroundings. Now the reverse: the ball extracting energy from the floor and spontaneously moving, never happens. This process is however  is reversible at the microscopic level. This is because, as Richard Feynman famously observed, almost all of the natural phenomena we see in  everyday life can be understood as a microscopic billiard game where countless particles like atoms and molecules collide and interact with each other. In particular both heat and sound are, at a fundamental level, atoms in motion. Now the motion of particles has been very well understood ever since Newton. Newton's laws of motion are completely reversible. So if we track the motion of  every microscopic particle present in the ball, the floor and the surroundings, we will find that all of them follow these laws of motion. Consequently, if their motion is reversed in time everything will still be perfectly consistent with Newton's laws. 

Why then do we never see balls that spontaneously start moving ? The answer to this is that while such an occurrence would be perfectly compatible with the laws of nature, it is extremely unlikely or improbable. This is because the time reverse of this process will involve the particles in the floor all moving in a coordinated way in the same direction.  Such a coordinated motion is required for these particle to transfer their energy and momentum to the ball such that it starts moving. This is overwhelmingly improbable, as the different particles in the floor and the surroundings, will in general move in an unrelated way in different directions.  To give an analogy, it is extremely unlikely that after shuffling a pack of cards, the hearts, diamonds, clubs and spades get perfectly organised into groups. Such a reorganisation of the cards is, however, not impossible or prohibited by a  deep principle; in fact if we repeat the whole exercise many many times it is bound to happen eventually.

      

                       Boltzmann's tombstone bearing the entropy formula

Boltzmann's way of explaining the irreversibility in the above examples would be to say that disorder, or more technically entropy, always increases. Starting from an organised pack of cards, it is inevitable that shuffling will increase the disorder. The reverse: getting an ordered pack of cards by shuffling repeatedly, is practically impossible. Similarly the entropy of ball along with its surroundings is much greater once it dissipates all its energy via friction. In other words all  irreversible  phenomena are irreversible because disorder/entropy must always increase which is not the case in the time reversed process where it decreases. This is the so-called second law of thermodynamics.  Boltzman's tombstone in Vienna  bears the inscription of the  his entropy formula.

                             The energy released in a nuclear explosion is

                                  ultimately due to the strong interactions.

My present work, actually, does not concern the emergence of an irreversible world from reversible laws but investigating whether the laws are truly T-symmetric. Now, there is no doubt that the laws governing the phenomena of everyday life are indeed reversible. But time reversal symmetry  is not a sacrosanct rule of nature that cannot be broken. There are exotic processes in particle physics that break this symmetry. It is just that the fundamental processes underlying what we see in everyday life are perfectly T-symmetric. This is because the two fundamental forces of nature that underlie everyday phenomena,  electromagnetism and gravity, obey time reversal symmetry. There are actually two other fundamental forces, the so called weak and strong forces. While the weak force is responsible for radioactivity the strong force holds the nucleus of an atom together. It is the energy associated with the strong force that is released when a Nuclear Bomb explodes.  The exotic processes mentioned above that break time reversal involve the weak force. There is still no evidence that the strong force breaks time reversal symmetry and this is the focus of my present work.

The fact that the strong force preserves T-symmetry although the weak force is irreversible at a fundamental level is actually paradoxical and called the strong CP problem, the subject of my present research.  In the coming blogposts I will explain

(1)How do we experimentally know that the strong force preserves reversibility ?

(2) Why is the reversibility of the strong force paradoxical ?

(3) How can the strong CP problem be solved ?

Eventually I would also like to come back to the question of entropy and irreversibility of everyday life although that is not my current research topic.  Another fascinating subject I would love to discuss in the future is how a breaking of T-symmetry, beyond what we observe for the weak force, is necessary to explain the abundance of matter  relative to antimatter in our universe.  So stay tuned!

The Indian economic debate

Three approaches to economic development in India

After liberalization of the economy in 1991 India has grown at a rate that is roughly twice the world average in the same period. The growth rate was around 6% initially and touched 9% in recent years before dropping to 6.7% this year due to the global recession. This is a big improvement over the 3% growth rate that India had before economic reforms were introduced in the 80s and 90s. The high growth is usually attributed to the end of the era of excessive bureaucratic regulations that were required to set up and run businesses in India (the License Raj) and the opening up of the economy to foreign investment.

These reforms have visibly transformed the lives of many middle and upper class families in urban India. This has led to a growing sense of optimism among those of us who have benefited most from these economic reforms. In a country where nothing worked our generation has seen pockets of efficiency emerge. The mainstream media tells us how more and more Indians are overcoming their instinctive fatalism and are becoming more "aspirational". There are frequent reports that tell us how India will soon surpass major economic powers to become one of the three largest economies in the world. Those of us who are concerned about the large number of poor in our country are assured by the media that prosperity of the rapidly growing Indian middle class will slowly but surely trickle down to the poor people.

The intellectual underpinning of this model of economic development is provided by supply side economics. Supply side economists believe that the most effective way to grow the economy is by providing incentives to industries to produce (supply) more by removing unnecessary regulations, reducing corporate taxes etc. They argue that prices of goods come down because of greater supply and as industries grow they employ more and more people so that wealth eventually trickles down (where I use the term in a purely descriptive and not pejorative way). In India proponents of this view support measures that encourage industries to grow like privatization, deregulation, allowing more foreign investment etc. They are skeptical of government spending on subsidies and social programs and say that most of this money is wasted as it never reaches the poor because of poor implementation and corruption. Thus, they say, the only effect these social programs have is that they increase the budget deficit which in turn stifles growth. They point out that in India even a perfectly equal distribution of the net income would mean that every person would earn only about Rs 3000 per month so that rapid economic growth is a necessary condition for poverty alleviation. The fact that we have almost tripled our pre-reform growth rate of 3% (the so called Hindu growth rate) is therefore a big achievement. Thus they believe high growth itself is the best strategy for poverty eradication pointing out that while there was virtually no change in the percentage of people below the poverty line in the 'socialist' phase till 1980, with the introduction of reforms this fraction has steadily dropped ever since (from 51% in 1978 to 28% in 2005 according to official figures).

The Indian Left is, however, highly skeptical about what these figures mean and doubt that there has been any real change in the lives of the poor. For instance if poverty is measured according to number of calories consumed one finds that 75 % of the Indian population was getting less than 2400 calories in 1999-2000 compared to only 56% in 1973-74 (see this article for an explanation of these figures by a pro-reforms economist). In fact India has a very poor record in reducing hunger and according to a World Bank report houses "about 49 per cent of the world's underweight children, 34 per cent of the world's stunted children and 46 per cent of the world's wasted children". The report goes on to note that much higher economic growth in India compared to Sub-Saharan Africa has not translated to a better "nutritional status of the Indian child". Leftist commentators think that the reason for all this is that India has experienced a highly lopsided growth which has benefited mainly the top 20% of the population. The growth has been led by the services sector which employs only about a quarter of the population (most of whom live in the cities) while agriculture which employs 60% of the population has grown at a much slower rate of about 3%. They point out that the great performance of the Indian industries has not been through employment expansion but due to a manifold increase in the output per worker (without a corresponding increase in their wages). Compared to a growth rate of 1.2 % in the period 1983-94 the fraction of people employed by the organized sector has actually shrunk at a rate of 0.3% per annum in the period 1994-2005 ! But the organized sector only employs about a tenth of the Indian workforce. What about the unorganized sector? Noted leftist economist Amit Bhaduri believes that only the big industries can produce goods and services, such as ACs or spas, that meet the growing demand of the rich. Thus the poor people, most of whom are in the unorganized sector, cannot participate in this economic growth either as produces or consumers. The Left is also infuriated by incidents like Nandigram and Singur, where farmers were forced to give up their land for the sake of industrialization, and stories of small scale producers who are unable to compete with big global corporations. Bhaduri asks "Why should the very poor who are least able, bear the burden of ‘economic progress’ of the rich ?"

So while the Left acknowledges the importance of high economic growth they are not happy with the nature and composition of the present growth. So what does the Left propose? Contrary to their usual media portrayal some in the Left do have a positive agenda. They advocate a Keynesian demand driven approach to economic growth. Keynesian economists believe that in certain situations (such as if there is a recession) it is advisable for the government to spend money (even if it leads to a deficit) to employ more people, increase the aggregate demand and thus stimulate the economy. Such a program for economic growth in India has been described in detail in Bhaduri's articles and his book Development with dignity. He says that the government should guarantee jobs for all. This would increase the purchasing power of the poor which would lead to a growth in the rural demand. The nature of the demand would help small scale producers and industries that cater to the demands of the poor leading to a growth of rural markets. Such an economic growth would be more broad based and inclusive. Where would the money to finance such a massive government program come from? Bhaduri argues that the government should deficit finance the program and that the deficit would not lead to inflation in an economy with unsold foodgrain stocks, unemployed labour and unused foreign exchange which can be used to import necessary goods which are not present in excess like steel (inflation is caused if there are not enough goods to meet the demand). The essential difference between this model of economic development and the earlier supply side approach is that while in the earlier approach economic growth leads to employment generation, in this approach employment generation leads to economic growth.

A third approach to economic development which is neither anti-liberalization nor against social sector spending is gaining a lot of support after the convincing return of UPA in the 2009 polls. It is hard not to interpret the election results as an endorsement of UPA policies by the people of India. As psephologist Yongendra Yadav notes, in a country where incumbent governments have been thrown out 80% of the time "in almost every State, the Congress has finished at the upper end of the band that it could have performed within." Even in non UPA states the ruling party has won if it has governed efficiently as in Bihar and Gujrat .

So what is this third approach? The most illustrious proponent of this approach is probably Amartya Sen. Sen supports globalization but says that it must be complemented by policies that build a safety net to protect local producers who are suddenly thrown into the highly competitive global market. He notes that in the years (2004-2005 to 2006-2007) which saw unprecedented growth rates (7.5 % , 9% and 9.4%) government revenue has expanded at an even faster rate (12.5%, 9.7% and 11.2% after correcting for price change). Sen wants the government to use this money in critical areas like health services, education and physical infrastructure. Thus proponents of this view believe that reforms are not undesirable. In fact they think reforms are necessary if India has to raise the resources needed to overcome its major social challenges. Unlike supporters of the first approach, however, they believe that we should not wait for the market to distirbute the fruits of economic growth to everyone and believe that the government has a major role in this. In the last five years which saw high growth rates the UPA government spent massive amounts in the social sector. They started the National Rural Employment Guarantee (NREG) scheme and waived loans of millions of farmers. While some of these policies might have been the result of the pressure from the Left parties the election results seem to have convinced UPA that this is the right direction to take in the future The UPA government has already made it clear that it will continue to spend massive amounts in social programs including a Rs 50,000 crore food bill and a plan to make India slum-free in five years. At the same time, however, they have clearly indicated that they want to relax foreingn direct investment (FDI) caps in various sectors and disinvest PSUs (public sector units) to raise the money needed for the social sector spending.

This approach is beginning to gather some support from both the economic Left and Right. The Left has seen some of its long-standing demands like the employment guarantee scheme being finally implemented. That the Left would welcome this recent emphasis on social schemes is of course expected. What is more interesting is that a growing number in the industry are also favouring these schemes. In 2008 the industry and the mainstream media was very critical of the "populist" tone in the budget and were especially disappointed by the farm loan waivers. Until very recently the media coverage of the NREG scheme was very negative focusing mainly on poor implementation of the scheme. Attitudes began to change even before the elections after India was hit by the global recession. The ideal time for Keynesian, demand side policies is of course in a recession when there is a drop in demand. The farm loan waivers and NREG incomes effectively acted as a stimulus to the rural economy which hardly felt the effects of the slowdown. In March new cellphone connections hit a record 15.6 million mainly because of rural consumers. Hero Honda motorcycle sales directed at rural buyers are also significantly up. The increased rural buying has helped sustain the aggregate demand thus ameliorating the blow of the global recession on the Indian economy. This explains the sudden change in attitudes of the pro-industry group.

The UPA may find it much harder to please everyone again this time. The global environment, which was probably the most important reason for the high growth rates in their first term, may be far less encouraging this time in the aftermath of the worst global crisis since the Great Depression. The fiscal deficit may cross 11 % this year. What would the UPA government do if the economy does not perform so well in the coming years and the deficit does not decrease ? Would the government cut down on social spending and thus enrage the Left ? Or would the government maintain the social programs even at the cost of high deficits and thus disappoint the Indian industry?

PS: As a friend pointed out, by "the Left" I do not mean the Left parties or what the media usually means when they refer to "the Left". Unfortunately the saner Left viewpoint discussed here does not get much exposure and one has to spend a lot of time on the internet to find these arguments.

Can consciousness be explained by science? -II

Part II: Why some aspects of our consciousness cannot be described by science. In part I of this post I argued that all our mental activity (our thoughts, feelings, sensory perceptions etc) must correspond to definite physical processes in our brain. But does knowledge of these physical processes tell us everything about consciousness? Let me try to answer that by giving a well known example. A neuroscientist specializing in colour vision knows all about how the brain perceives colour. She knows for example everything about the physical changes that take place in a person's brain when he sees the colour red. The scientist has, however, been confined to a black and white room all her life. When she comes out of her room for the first time and sees the colour red one has to agree she learns something new, something that was missing from all her previous scientific knowledge. In other words what it is like to see the colour red or to hear a particular sound is something beyond any scientific description. In fact these subjective experiences cannot be described in any kind of language. Let me elaborate by giving another well known example. Think of a person to whom everything red appears green and everything green appears red. Thus to him strawberries appear green (see picture on the right) and leaves appear red. If you think about it he will never realize that his sensations are inverted with respect to the rest of us. This is because he will never be able to communicate to the rest of us the subjective sensation itself that he has when he sees something red or green. All he would be able to convey is that roses and strawberries have the same color or that leaves and grass have the same color. No one will of course ever dispute that. Similarly what it is like to smell a flower or taste something salty can only be felt but not really described in words. These subjective experiences are called qualia (singular 'quale') by philosophers. Many would consider what it feels like to be angry or sad also to be a quale. To a scientist who wants to explain everything in terms of theories of matter qualia are a big, perhaps insurmountable, obstacle. The laws of physics do not tell us which physical events should have qualia or that qualia should exist at all. These qualia- colours, scents, tastes, sounds etc are of course the fundamental building blocks of what we perceive as the external world. The world of our senses, however, is not the external world. The colours and sounds exist only in our heads and not in the world outside. In the world outside there is nothing qualitatively different between electromagnetic waves of wavelengths 350 and 450 nanometers but in the world of our senses the latter corresponds to blue light and the former cannot be seen. In the world of our senses the sensation of sound and the sensation of hotness/coldness are utterly different but in the world outside both are at a fundamental scale atoms and molecules in motion. The world that we perceive through our senses is nothing more than a simulation of the external world which encodes very limited information (that is important for our survival) about the world outside. Aliens who have evolved under different circumstances may have very different sense organs and very different ways of perceiving the external world. The world that these aliens perceive would not be composed of images, scents and sounds but of the qualia related to their own senses to which we would be 'blind' and 'deaf'. We imagine everything in terms of images, scents and sounds so the world of their senses would be completely beyond our imagination. What would it feel like to perceive the world of their senses? Unfortunately no amount of scientific investigation of their brains will ever tell us the answer. PS: (1) In the last example I did not need to talk about aliens. Many creatures, most notably bats, have sense organs which are very different. (2) As is going to be the case with many other posts my knowledge on this subject is very elementary. It seems that this issue is far from settled among philosophers. There are counterarguments to many of the things that I have written here (see here and here).

Can consciousness be explained by science? -I

Part I: Can the mind exist without matter?

In the first part of this two part blog entry I would try to argue that all our conscious activity must correspond to definite physical changes in the brain. In other words if neuroscience were to ever reach a stage such that all physical changes in the brain could be observed and monitored (a goal that may be practically unattainable) we should be able to tell what a person is seeing, hearing, feeling and thinking by simply observing her brain.

Neuroscience may be far from reaching such a stage but discoveries already made in the field strengthen the case for the above proposition.

In a 2002 study British neuroscientists asked subjects to look at photographs of real faces and objects. Using fMRI, a technique which uses MRI scans to locate active regions of the brain by detecting increased blood flow, they identified regions of the brain (see figure on the right) that are active when a person looks at a face (marked fg) and the regions which are active when he looks at an object (marked pg).

The subjects were then shown Rubin's famous Vase-Face illusion (see figure on left). By simply looking at which regions were active in the MRI scans the scientists could predict whether the subject was perceiving the image as two faces or as a vase!

You may be thinking that while discoveries like this (see V S Ramachandran's BBC Reith lectures for many other equally fascinating examples) are definitely suggestive, my initial proposition is still a big extrapolation if it is based only on such findings.

There is in fact a more fundamental reason for my belief, a reason that I have learnt to appreciate because of my training in physics. A physicist would view the brain and its functioning as an extremely complex natural process. Physicists have a simple approach when they try to understand complex natural phenomena. Just as any change in the picture on your computer screen is brought about by a change in the colour and intensity of each of the pixels, any process that we observe in nature is the result of a change of the arrangement of smaller particles like atoms that constitute everything. As there are billions and billions of them in even a small object, simply by moving from one place to another, these particles can accomplish wonderful things- the rusting of iron, the burning of paper, the discolouration of leaves in autumn, lightning, tornadoes, in short everything you see around you! All the complexity in natural phenomena is because of the large numbers of these particles involved in these processes (a screen can generate a far more complex picture if there are thousands of pixels instead of say twelve). The movement of these particles is governed by precise, empirically tested laws. Based on the present state of a system of particles these laws tell us how the system will evolve in time.

The functioning of our brain is undoubtedly more complex than the phenomena mentioned above but our bodies and brains are made of exactly the same atoms that physicists and chemists study in the lab everyday. How these atoms evolve with time is governed by the same laws. Therefore it follows that what we will do in the next moment depends on the physical behavior of the atoms in our brains at the present moment (which might correspond for example to a high level of activity or increased blood flow in a certain region of our brain or may be an unusually large number of neurons firing in another region). But we also know that what we will do in the next moment depends on what we are thinking and how we are feeling at the present moment- if you are angry you might yell at someone, if you are depressed you might call a friend etc. Consider the two italicized statements in this paragraph. As an effect cannot have two different causes these statements suggest that what we subjectively feel as an emotion like anger or sadness corresponds to a definite behavior of atoms, i.e. a definite physical process in the brain that can be, in principle, objectively observed.

So at the end of this part the partial answer to the question posed in the title seems to be that any mental activity must correspond to definite physical processes in our brain and these physical processes can be analyzed using the usual methods of science. I will argue in the next part of this post that a scientific description of the objective process that a thought, emotion or sensation is related to is, however, inadequate in capturing all aspects of our consciousness.

The concept of consciousness not tethered to a body is obviously meaningless from this point of view. Thus from this perspective the idea of ghosts or spirits or a soul that leaves the body after death is absurd! The same thing can be said about a nirakar (formless) God having conscious attributes like mercy and forgiveness. But then rules need not apply to God!