Hawking, Mlodinow, the media and god.

Stephen Hawking and Leonard Mlodinow have written a new book called The Grand Design. The publication of extracts from the book in The Times has unleashed a media storm with headlines like Stephen Hawking: God did not create Universe and Why God Did Not Create the Universe.

First lets be clear that they are not saying God is ruled out. While most (but not all) articles managed to avoid claiming that, the lack of clarifying details , sloppy phrases used and tedious discussions about what this might mean for religions allowed exactly such a confusion to spread.

Phrases like "God did not create the universe" do appear in many newspapers, implying that any universe creating God is ruled out by science. This is not what Hawking (or Mlodinow) actually said. In phrasing it this way the BBC, The Wall Street Journal, The Guardian, The Daily mail, CNN, and many more are misrepresenting what Hawkings and spreading misinformation. Richard Dawkins, a famous science communicator, also seemed to have an exaggerated view bof the statements religious significance in a debate. Some newspapers, like The Telegraph and The Huffington Post, report "there is no need for a creator" much closer to what Hawking appears to have actually said.

The other big confusion spread by the press is that this is a reversal of Hawking's previous position. For example the BBC state

In his 1988 bestseller, A Brief History of Time, Prof Hawking appeared to accept the role of God in the creation of the Universe. "If we discover a complete theory, it would be the ultimate triumph of human reason - for then we should know the mind of God," he said.

apparently missing that Hawkings was using god in a metaphorical sense, and was not suggesting that a physical creator god made up part of his understanding of the universe.

The actual statement which does appear to originate from Hawkins and Mlodinow is:

"Because there is a law such as gravity, the universe can and will create itself from nothing. Spontaneous creation is the reason there is something rather than nothing, why the universe exists, why we exist. It is not necessary to invoke God to light the blue touch paper and set the universe going."

To me the god reference seems merely an attempt to express the grand scope of their claim. Hawking seems to think there is a now a theoretical framework which provides a satisfactory natural description of the universe coming into existence. Seeking natural models to describe physical reality is what theoretical physicists (religious, agnostic and atheist) do and from a science perspective this is a very interesting statement, and while I suspect I may not be as convinced as Hawking I nonetheless look forward to reading his view. But what about all the religious ruminations discussed in newspapers?

The first point to make, almost entirely absent in the newspaper coverage, is that Hawkins argument involves many elements not tested experimentally. Believers can still think that god created the universe without conflicting any observational evidence. They simply can't state there is no framework in science which could explain the universe existing to motivate their belief. Therefore there is still no inconsistency between science and a creator god.

Secondly God didn't really have a role in science prior to Hawking's statement, because to invoke god as a solution to existence involves infinite regression and of course makes no testable predictions. You may as well just postulate the universe exists as postulate god exists then created it. The absence of satisfactory physical model of how the universe came into existence motivates scientist to investigate the question, it does not motivate god. This does not mean one cannot believe in a creator god, but the motivation should not be the lack of a fully fleshed out competing theory.

So on the religion side nothing has really changed. But this has not stopped many angry responses from religious people. And for many others correcting these misunderstandings has been a huge distraction; Jon Butterworth paused while writing a paper to clarify the situation for channel 4 news.

So who is to blame? The press have certainly been irresponsible, both in misrepresenting Hawking and treating his words in a popular science book as prouncements of "What The Science Says", without ever wondering what scientific papers are behind the comments. So far it sounds like the media are entirely responsible, but it is difficult to be sure to what extent this was fed by a publicist promoting the book or even by the authors themselves. There is also the question as to what extent they explained that much of the physics used to construict this argument, like M-Theory is not confirmed experimentally. And while their words have be taken out of context perhaps Hawking and Mlodinow should have realised this might occur when they agreed to have the extracts published in The Times. I'll leave those questions to people who are more media wise than I am though.

Finally some brief, wild speculation on the physics. Since i don't actually know what the Hawking has really talked about in the book I am simply going to discuss some of the ideas which try to explain our universe and why I am skeptical that we really have a good explanation for everything. Sean Carrol made a nice video post trying to explain the physics which may have inspired Hawking's statement. My comments here are really tangential to this, based more on the idea of a theory of everything. Please read this with the 'rant' title of my blog in mind :) and remember I am talking a little outside my area of expertise now.

String theory is probably the best candidate for describing gravity at small scales, thus allowing a theory of everything. There is however an alternative of loop quantum gravity and also the possibility that we haven't invented the right model yet. M-theory is a unification of the 5 different types of superstring theories (the 'super' stands for supersymmetry, which is needed to describe matter as well as forces but don't worry too much about this) and a nice candidate for a theory of everything.

String theory now sadly seems to make few real predictions because there are 10^500 vacua with all kinds of different physics. Many string specialists talk about exploring the string landscape, and some think this is a positive development, but I find the lack of predictivity disappointing. Of course I am not a string expert and they might say I am missing the point.

Quite a long time ago Andre Linde proposed chaotic inflation where you have lots of "bubble universes" forming a multiverse. The model was not arbitrarily invented and was motivated by problems with the standard big bang theory. Unfortunately once again there are difficulties in testing many aspects of this model since the other universes are not observable. This model and the string landscape do fit together well and give a rather nice picture of how our universe might have appeared but the difficulty of testing these ideas remains.

Now if you hypothesise lots of possible physics in different universes then you can always end up with the features we need for life etc, even if the parameters look really fine tuned. Therefore some claim this is a "natural explanation" for all observable features of our universe.

However they are essentially invoking the anthropic principle (we are here and therefore our universe must have the parameters we require or we wouldn't be around to observe it). To me this is not an explanation, since it relies on an untestable hypothesis, much like god, to evade the question. This does not make the model wrong or even a bad idea, but I do not consider it a satisfactory explanation our universe without some experimental confirmation of the different universes, which seems to be a fundamental stumbling block.

Beauty, beliefs and GUTs

When I discuss a previous blog on the controversial topic of religion and science, the issue of belief without evidence sometimes comes up. Some people take the viewpoint that you should not believe in anything without evidence (I might caricature this as militant agnosticism :P), but this strikes me as a bit over constraining and does not really match how scientists actually behave.

Although we must try and objectively assess the evidence and make clear scientific statements about it, this does not mean we have to be opinion less about everything else. Indeed my experience of scientists is they are more likely to be opinionated (I am for sure ;) ) than opinion less. But even with regard to the science, when we are doing research at the frontiers of knowledge we do not yet have scientific evidence to know what will be the right approach, how nature will have solved the problem we are interested in. What motivates us in our work can be opinion based on our expectations about nature, and this is why different people look at different possibilities to solve the same problem.

In particle physics, for example, I have a (fairly dilute) belief in both Grand Unified Theories (GUTs) and Supersymmetry (SUSY). Others have a stronger belief, while some seem sure they are not realised in nature. Nonetheless everyone in the field knows that ultimately these are scientific theories which need to be tested. But where does our prior belief or theoretical prejudice spring from?

I have already talked briefly about motivations for supersymmetry so I will focus on GUTs here. As I previously discussed the Standard Model of particle physics describes three fundamental forces (strong, electromagnetic and weak) through gauge symmetries. The different forces have different 'strengths' by which the fundamental particles interact, and the fundamental particles are sensitive to different forces. Quarks, the particles which form hadrons like the proton and neutron, are sensitive the all three forces, while leptons, like the electron, to only the electromagnetic and weak forces. The fact that the strong force is much, well... stronger than other two explains why quarks are confined into hadrons and cannot be observed as free states.

So we have three (not counting gravity which is so weak we don't notice it) different forces with different strengths and fundamental particles which interact with different forces. This description matches the data incredibly well giving some of the most precisely tested predictions in all of science. But why do we have these different forces? Perhaps nature is simply like this, some scientists may well believe that is all there is to it. But for me this seems to leave nature looking rather arbitrary and messy.

Grand Unified Theories are a possible explanation for where these different forces come from. In these GUTs the different symmetries are embedded into a larger symmetry group which unifies all forces into a single unified one. All fields describing matter particles then transform together under this larger symmetry and interact via this single force. The different forces can then arise as a consequence of the breaking of this GUT symmetry. Additionally the larger symmetry of this gauge group means it has fixed charges, allowing for the possibility that the different values of electric charge we observe at low energies (unexplained in the SM) are fixed by the breaking of this GUT.

The simple elegance and beauty of Grand Unified Theories fits well into my expectations about nature. There is no proof that nature can be described in increasingly simple ways (the idea that it can is often called reductionism) but the aesthetic beauty of it appeals to me. As does my hope that I can explain or understand the forces and the electric charges we observe in nature.

This hope may seem in stark contradiction with the observation of three separate forces with different interaction strengths. However the vacuum is not empty but filled with 'virtual' particle and anti-particle pairs which are being created and annihilated and when particles interact across the vacuum such virtual particles are affected. For the case Quantum Electro-Dynamics (QED) the positively charged particles in the vacuum are drawn closer towards a negative charge and vice versa, and this effectively screens the interaction strength from the charges between two particles separated across the vacuum. The further apart the particles are the weaker the interaction strength. Since how close together particles can get in collisions depends on how energetic they are, interaction strengths depend on the energy at which the interactions take place.

For more complicated symmetries describing the weak and strong force there is a similar effect, but one also gets anti-screening from the gauge bosons so that interactions interactions can either increase or decrease with distance depending on the particle content of the model. This is the basis for having quarks which are confined into colorless hadrons at low energies while behaving like free particles at high energies, known as asymptotic freedom, for which the 2004 nobel prize for physics was awarded.

This also allows for the possibility that the separate three forces we observe at low energies have a common interaction strength at higher energies. This possibility is precisely realised in models with Supersymmetry at the TeV energy scale (the scale we are probing at the LHC), as is shown by the red lines in the figure to the left.

To motivate Supersymmetry I previously described the hierarchy problem and pointed out that this motivates new physics at the TeV scale based on our lack of understanding as to how two unrelated masses could be tuned to be incredibly close, but not equal. While this is not a fundamental proof of new low energy physics it is at least a physical question which we want to understand and the Supersymmetric solution is very elegant and therefore in my mind compelling.

I am personally very attracted to this picture of a simple Supersymmetric Grand Unified Theory at high energies which as we move down to lower energies has some of it's elegant symmetry spontaneously broken, leaving us with the complicated set of massive particles with different interactions which we have already observed. I find this idea beautiful, fascinating and compelling.

Others do not find it so convincing, but that is fine. This does not make either them nor me poor scientists who misunderstand the evidence, we simply have different theoretical prejudices based on our expectations of nature. Ultimately questions like this will be resolved by data and this is what we excitedly await from the LHC.

The Standard Model of particle physics and beyond

I still have no idea about to go about writing science stuff in this blog, who to pitch at, who would actually care to read it, but somehow it feels weird to start talking about things like the LHC, SUSY etc without explaining them. And since when I'm ranting about stuff I am bound to refer to them I'm going to have to go down the pedagogical route initially.

So a little bit about what I do to start off.

Matter and Forces

Roughly speaking particle physics is the study of what the fundamental constituents (i.e. things with no substructure) of matter are and how they interact, i.e what forces govern their dynamics. On the constituent side we currently know that we are made up of molecules, molecules are made up of atoms, atoms are made up of protons, neutrons and electrons and finally the proton and neutron are made of 'up' and 'down' type quarks. In radiation experiments where the electron is emitted (beta radiation) another particle with no electric charge, called the neutrino was discovered, and together electrons and neutrinos are referred to as leptons. So we have quarks and leptons, but for some unknown reason we also have 2 more generations of heavier quarks and leptons, with only the first generation making up ordinary matter. The forces through which they interact are gravity, which is so weak we can't measure it's effect when studying these subatomic particles, electromagnetism, more familiar as electricity and magnetism, the less familiar weak force and finally the strong force which binds quarks into hadrons like the proton and neutron.

We currently have a model which describes all (excluding gravity) of this and it is called the Standard Model of particle physics.

Shown in the figure to the left are all the particles in the Standard Model. As well as the matter particles which can collectively be referred to as fermions, there are also bosons in the Standard Model which 'carry' the forces. Fermions and bosons are separated by an internal quantum number called spin, which is like angular momentum, but is a fundamental property of that particle rather than being generated by dynamics. Fermions have half integer spins, while bosons only possess integer values of spin.

This internal quantum number spin was famously observed in the Stern-Gerlach experiment. The observation that the electron carried half integer spin was crucial to the development of quantum mechanics in using it describe emission spectra (wavelengths of the radiation) from atoms.

Experimentalists and Theorists

In particle physics the workload is somewhat divided between theorists who construct models, test them for internal consistency and perform the complicated calculations needed to make predictions and experimentalists who do the really hard work of designing, building and running machines capable of testing the theories, as well as sifting through the enormous reams of data trying to find the proverbial needle and then finally determine the statistical significance of observation (or non observation as the case may be) of said needle .

I belong to the former category, theorists. We are interested in trying to build models which answer deep, fundamental questions (puzzles) about how the world around us is constructed. It is important that the models we construct satisfy all current data and are internally consistent. In addition we also want to explain the puzzles without actually introducing new ones. One current question we are interested in is how fundamental particles, like the electron and the quarks obtain mass.

The Higgs Mechanism

The observed interaction of these particles are all beautifully predicted by postulating symmetries of nature, called gauge symmetries. While this may sound rather abstract the important point to grasp is the predictive power of symmetries. If you know you are looking into a mirror, you can predict what you will see when you turn around because there is a symmetry between the reflected image and what is actually behind you. Specifically it is a spacial inversion symmetry. The gauge symmetries predict how matter interacts, though the symmetries are more complicated than the mirror symmetry and can be best seen using a mathematical description of the physics which I don't present here (so you shouldn't worry about this if you don't know it already).

For electromagnetic and weak interactions we can postulate the electroweak symmetry. Unfortunately the electroweak symmetry forbids the introduction of explicit masses for fundamental particles from the outset, making it is challenging to have a theory which predicts the interactions correctly while allowing fundamental particle masses in accordance with observation. This challenge is solved by the Higgs mechanism, where by electroweak symmetry is broken in the vacuum, generating particle masses but maintaining the elegant (and incredibly well tested) symmetry predictions of the interactions between the fundamental particles.

This is achieved by introducing a Higgs field which can be described by an electroweak symmetric theory. However if the Higgs field has a vacuum expectation value, meaning there is a non-zero probability for the Higgs to exist within the vacuum (so we have a non empty vacuum, which may seem a strange notion) , this breaks the electroweak symmetry. A common analogy used to give people a picture of how this works is to imagine travelling through treacle. As you move through the treacle interacts with you slowing your progress. In a similar sense we postulate that the vacuum is filled with the Higgs which the interacts with any fundamental particle propagating in the vacuum. The Higgs interacts with (sticks to if you like the analogy) different fundamental particles with different strengths, giving them the appearance of different masses.

The Standard Model

Associated with this Higgs field is the Higgs boson. Currently the experimentalists are searching for this particle to see if it exists (it may not, there are alternatives) at the new Large Hadron Collider (LHC) in Geneva. The simplest model with this Higgs mechanism and Higgs boson which can describe all current observations is called the Standard Model (SM) of particle physics. While there may not be a fundamental Higgs boson, the SM certainly provides a very good description of nature at low energies. Through the Higgs mechanism all particles can have mass, while the strong symmetry and the (broken) electroweak symmetry correctly predict all interactions observed.

The SM is an astounding achievement in science. It ties together two of the most remarkable theories, quantum mechanics, the physics of the very small, and Einstein's special relativity, the physics of the very fast, and is founded on very elegant ideas about symmetries. Einstein's special relativity tells us that time is another dimension like the three spatial ones and that instead of just considering the physics to be invariant when we perform a Galilean transformation on the spatial coordinates from one reference frame to another (e.g. from an axis sitting on the earth to an axis sitting on a bus moving at speed v) we should apply the relativistic transformations of the Lorentz symmetry group to the four dimensional space-time. In addition as I have already mentioned all interactions are predicted by introducing the gauge symmetry groups for the strong and electroweak forces. When considering these symmetries we can write everything in terms of classical fields, but then we insist that they appear in small lumps, or quanta, exhibiting their particle nature and consistent with quantum mechanics.

The standard model makes one of the most precisely tested predictions in all of science, that of the anomalous magnetic moment of the electron:

However it not simply a few very precise tests, which verify the SM, it has survived decades of intense testing in particle colliders around the world. The measurements made from these tests are all summarised in the huge review of particle physics by the particle data group.

The Hierarchy Problem

Despite the strong agreement with observation some theorists are not convinced that the SM is a complete theory of nature because we feel it introduces further puzzles which are left unexplained. One of these puzzles is known as the Hierarchy Problem.

The Higgs is unique amongst the fundamental particles of the standard model, not just because it is the only particle yet to be discovered, but also because it transforms trivially under the Lorentz transformations and we say such particles are Lorentz scalars. If you add a scalar to the SM one can perform calculations to show that it’s mass is quadratically sensitive to any new physics from high energies which it couples to. Since we know that at very high energies some new gravitational physics must be introduced, we expect the Higgs mass to receive quadratic contributions from this very high energy scale (called the Planck scale). However the Higgs mass is some 17 orders of magnitude smaller than this energy scale. In order for this to be the case, within the SM we assume that these contributions are canceled by a free parameter in the theory. While this is mathematically consistent, the enormous coincidence seems improbable and that is the hierarchy problem. Theoretical physicists feel that there is no imaginable explanation for this free parameter to cancel so precisely with the high energy scale (called the Planck scale).

In fact we calculate how improbable this cancellation is, with “fine-tuning measures”. If the free parameter is randomly chosen the chance of getting a Higgs boson as light as it needs to be in order for the SM to work would be a 1 in 1000000000000000000000000000000000, which is about as likely as winning the lottery 5 times in a row! Nonetheless it is important to understand what this means. I do not claim there is pure objective scientific evidence ruling the SM out, so this is not the same as stating that the chances of a model reproducing experimental observations are so small, if that were true the model would be falsified. The Standard Model fits observation very well and as such cannot be ruled out as a valid description of nature. There could be some deep fundamental reason which we have not thought of which explains why this parameter is set so close to the the Planck scale, forcing the cancellation to take place. However in our current understanding we cannot imagine how this could be as the Planck scale is totally unrelated to the parameter with which it cancels. Therefore Hierarchy Problem is an unexplained puzzle, namely how can the Higgs particle mass be much lighter than the Planck scale, the answer to which we would like to investigate.

Supersymmetry

Theorists have come up with a number of solutions. One idea I really like is to cancel these large contributions to the Higgs mass from high energies by introducing a new symmetry of nature. This is achieved by extending the space time symmetries of special relativity. It has been proven that there is only one way to extend the space-time symmetries and that is by introducing a supersymmetry which combines Lortentz space-time transformations with transformations over the internal spin quantum number. Supersymmetry (SUSY) is a then is a symmetry between fermions and bosons. Since the SM particle content does not possess this symmetry, SUSY predicts many new particles, which are the supersymmetric partners of the standard model ones. It is precisely the symmetry between the known SM particles and their SUSY counterparts that leads to cancellation of the quadratic dependence on high energy physics in the Higgs mass.













(Figure from: http://www.physics.gla.ac.uk/ppt/susy.htm)


There are many other unanswered puzzles in the SM which motivate new physics, perhaps at some point I will discuss them also but for now I simply want to point out that many of them can also be solved by introducing the new physics at energies being probed by the Large Hadron Collider, used to look for the Higgs and also have a solution in common with the Hierarchy Problem, namely SUSY.

Other ideas include unobserved extra dimensions, which bring the new physics of gravitation down to lower energies as the apparent weakness of gravitation is caused by dilution into these extra dimensions and Technicolor, where the electroweak symmetry is not broken by a fundamental scalar but by a condensate bound by some unknown, very strong force. Each of these ideas would be worthy of a blog entry on it's own (though I don't plan to do this :) ) and might solve several problems but I am showing my prejudices here (and that is sort of the point of this blog) because I find Supersymmetry the most attractive and this is the direction my research has taken.


I hope my lightning tour of the Standard Model to Supersymmetry has not left you feeling entirely like my pseudonym on here, but if it is all new to you and you still find it puzzling that is to be understood. Hopefully though this post will help you understand the references I make in later posts.