22

Sep

2008

Science and Religion – the Physics Angle

 

There is more subtlety to the evolutionism/creationism debate than many of the loudest voices tend to employ.

Continuing his exploration of space and time, Shahn Majid takes a look at science, religious belief, what we really know, and draws the line in the context of fundamental physics.

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It was the best of times, it was the worst of times; it was the age of wisdom, it was the age of foolishness; it was the epoch of belief, it was the epoch of incredulity.

-Charles Dickens

Last week the director of education for the UK Royal Society, Professor Michael Reiss, resigned after he was criticised for being ambiguous about the correct response to creationism, and to religion in general, if brought up by a pupil in a high-school science lesson. Perhaps his words touched upon a raw nerve in the scientific community or perhaps the point he wanted to make was just too subtle to be understood by the media in these troubled times.

Professor Reiss, who is also a Church of England minister, apparently suggested that in his experience it was more effective in such a situation to discuss creationism in the science class if only to show that evolution fits the facts better. Critics said that he should have had the teacher simply refer the pupil to religious education classes as creationism is not a scientific theory at all. Professor Reiss himself has stated that creationism is a `world view’ and that you have to discuss it to get through to pupils with such beliefs.

Was it over-reaction? A defender of Professor Reiss’ position on the BBC radio I heard argued that the creation myth was a metaphor, not to be taken literally. Hence scientists should not be so touchy. A critic could argue, however that if that were the case then that is exactly why the teacher should indeed to refer the pupil to poetry, drama or religious studies where parables as metaphor are appropriate. The problem is that as soon as you bring it into a science lesson you risk confusing science and parable. This is not helped by creationists who insist that the creation myth is not a parable but true and should at the very least be taught as a valid theory alongside evolution. This then makes a mockery of science.

Science, after all, is supposed to be searching for absolute truths verifiable (in principle) by anybody who cares to. It is supposed to uncover Nature using mathematical or logical tools, of course to formulate theories and hypotheses but to treat these with deep skepticism. Faith is anathema to science. Please understand me. Faith, a moral compass, spiritual values, all have a vitial role to play even in the life of a scientist. When you are stuck on a problem you have to put forth a hypothesis. You have to have some faith in it to take it seriously enough to explore. You may even have a ‘vision’ which is a kind of faith that guides your life’s work. But that’s all about the human process of research. The actual science is supposed to be based on fact and logic independently of how you got there, to the maximum extent possible. So faith is also the bit you are spending your life trying to squeeze out of the end product. It’s a complex dynamic which obviously can’t be grasped by pupils who have not yet understood what science itself is. They have to first learn what science is pure and simple and this is what confusing the issue so early on would deny them. This, in my opinion, is why many scientists are so angry about the no doubt well-meaning but highly dangerous position of the professor and other science educators with similar views.

Let’s see how these issues play out at the modern cutting edge of the most hard-core of sciences, fundamental physics. This is a vast and enormously successful edifice of knowledge which nevertheless has through the hard work of generations of physicists been boiled down to a mere handful of fundamental equations and beautifully simple ideas through which, in principle, we understand the physical world. There is still a certain amount of work to be done in particle physics. There is still a big problem which stumped Einstein but which physicists are now very optimistic about, namely the unification of quantum theory and gravity. But the consensus is that everything is going well and these are truly the best of times …

… but lets look carefully. Among the various hypotheses is at least one fundamental assumption that is not, in fact, supported by experiment. I refer to the topic of my new coauthored book, namely the true nature of space and time. Space and time provide the backdrop against which all of science takes place. It is a hypothesis or an act of faith that spacetime is a continuum. A continuum means that there is a smooth range of points in it, you can move any point arbitrarily close to any nearby one. All of mainstream fundamental physics is built on this assumption as a starting framework. Even quantum theory where things are `fuzzy’ has wave-functions defined over a continuum. Even strings in string theory are fundamental objects moving in … a continuum. Let me explain why this assumption is not only unjustified, it’s illogical even within science.

I will need two simple formulae and one diagram. The first is a formula that expresses the idea of wave-particle duality, that particles are also waves. We will take it in the form

L= 2 x 10⁻³⁷ / m

for the inverse relationship between the mass-energy m of a particle in grams and its Compton wavelength L in centimeters. The diagram shows this on the left in a log-log scale in which each notch on the scale is a factor of 10 billion (10¹⁰). Thus you can see that an electron has a mass of … and hence a wavelength of …. That’s much smaller than the wavelength of visible light, for example, and that is why an electron microscope can achieve so much better a resolution than an optical one. Clearly the wavelength sets the accuracy with which you can use a wave to probe something. Nothing can appear to the left of this left slope in the figure because if you try to make a particle lighter, it will just get bigger in wavelength and move up the slope. The second thing I need is a formula that expresses that gravity can cause space and spacetime to ‘curl up on itself’. We will take it in the form

L= 7x 10⁻²⁹ x m

…for the linear relationship between the mass m of a black hole in grams and half the radiius L of its event-horizon in centimetres. The event horizon is the sphere from inside of which even light cannot escape. It is the `bubble’ in spacetime that a black hole represents. This line of black holes is shown to the right in the figure. Nothing can appear to the right of this slope because if you try to make a black hole more massive it will just get bigger and move up the slope. Conversely, what we talked about last week was black holes evaporating and moving down this slope until they hit the left hand slope at a mass of 20 micrograms in the case of ordinary black holes. This is called the Planck mass. Now consider trying to probe a bit of the geometry of spacetime using different kinds of microscopes. In order to probe smaller and smaller distances you need smaller and smaller wavelengths of your test particle-waves, which entails heavier and heavier mass-energies for them. You follow the left slope until the test particles get so heavy that they themselves form black holes. At this point the test particle is curling up and destroying by its mass the very geometry it was trying to probe. From the figure we see that this happens at about 10⁻³³ centimetres. This is called the Planck length.

What this implies is that distances less than 10⁻³³ centimetres (i.e. 0.000 000 000 000 000 000 000 000 000 000 001 cm) are intrinsically unknowable. They therefore have no status within science. Continued reference to them is an unscientific belief. So, for example, when we look back in time and find that our Universe was smaller and smaller (the ‘Big-Bang model’ or its modern versions) we can extrapolate to a notional ‘point in time’ when it all began. But in fact our extrapolation can only work back to the point in time when the Universe was of Planck length size — earlier than that it did not even have a size! In short, the ‘ultimate creation’ question is not yet answered by science. And where does this problem with spacetime leave science in general? Does the edifice of physics come crashing down on our heads now that its very foundations are fatally flawed? Are these in fact the worst of times for our understanding of physical reality? Let us examine this.

First, physicists could dogmatically cling to a continuum assumption as an act of faith, now truly an act of faith as it has no scientific basis. The trouble with that is that these hypothetical particle wavelengths below the Planck scale render many computations in their theories infinite. For the most part physicists have discovered various tricks to make sense of and cancel these infinities. However, when it comes to gravity waves, i.e. particle-waves which are themselves made of ripples in spacetime, all these ideas so far have failed. There is still no theory of quantum-gravity unifying quantum wave-particle and gravitational ideas. Mainstream physics can continue optimistically down this path, perhaps replace points by strings, etc, but it is an act of faith that they will succeed.

Or, they can say that as scientists they are not wedded to that assumption after all. They can step back and consider notions of space and time in which there is no continuum in the formulation of the theory. I would not say yet that this is a mainstream point of view, but physicists can and in my view should do precisely this. Many physicists do freely acknowledge the problem but go back to the continuum as a practical approximation valid in most computations. They can artificially ‘cut off’ the offending less-than-Planck scale wavelengths in a practical but ad-hoc manner. This, unfortunately, still leaves you with puzzles and problems in the theory, such as the problem of dark energy. At any rate they are free to debate and question this most basic of assumptions. And meanwhile no, the edifice of physics does not come tumbling down in practice as long as the physics under discussion is far from the Planck scale (far from the cross-over point in the figure).

This then is the difference between science and religion. If you follow the Bible or any religious text as sacred, you cannot easily revise your central tenets. You may rather have to bend over backwards in your interpretation in order to accommodate the facts. Scientists on the other hand can, do and should question even the most basic of their assumptions. They sort their assumptions, quantify their impact and stand ready to throw them out if necessary. Far from being the worst of times, when something at the theoretical foundations of science is identified as fundamentally flawed it is cause for joyous anticipation as it means that we must eventually be about to take a leap forward in our understanding. And when theoretical questions such as the above combine with the possibility of experimental tests of Planck scale effects, as I hope to argue next week, it means that we are in fact in the most interesting of times.

Shahn Majid put together Cambridge’s On Space and Time and is Professor of Mathematics at Queen Mary, London. He’ll be filling us in on why these taken-for-granted dimensions of reality hold so much fascination for physicists, mathematicians, theologians, and philosophers.

For another perspective, see Church of England priest and physicist John Polkinghorne’s recent post.

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