Why is the Speed of Light Constant?

The question “Why is the speed of light constant?” is often asked by those trying to understand physics. Google has 2760 links to that question. Yet the answer is so simple that a 10-year-old can understand it, that is, if you accept Quantum Field Theory.

speed of light

Take the ten-year-old to a lake and drop a stone in the water. Show her that the waves travel through the water at a certain speed, and tell her that this speed depends only on the properties of water. You might drop different objects at different locations and show her that the waves travel at the same speed, regardless of the size of the object or location of the water.

Then tell her that sound travels through air with a fixed velocity that depends only on the properties of air. You might wait for a thunderstorm and time the difference between the lightning and the sound. Tell her that a whisper travels as fast as a shout. I think a ten-year-old can grasp the concept that water and air have properties that determine the speed of these waves, even if she doesn’t know the equations.

Anyone who can understand this can then understand why the velocity of light is constant. You see, in Quantum Field Theaory space has properties, just as air and water have properties. These properties are called fields.

As Nobel laureate Frank Wilczek wrote, wilczek_frankOne of the most basic results of special relativity, that the speed of light is a limiting velocity for the propagation of any physical influence, makes the field concept almost inevitable.” 

Once you accept the concept of fields (which admittedly is not an easy one), that’s all you have to know. Light is waves in the electromagnetic field that travel through space (not space-time) at a speed dictated by the properties of space. They obey fairly simple equations (not that you need to know them), just as sound and water waves obey simple equations. OK, the Quatum Field Theory equations are a bit more complicated, but quoting Wilczek again, “The move from a particle description to a field description will be especially fruitful if the fields obey simple equations… Evidently, Nature has taken the opportunity to keep things relatively simple by using fields.”

However this question can have a different meaning: “Why is the speed of light independent of motion?”   This fact was first demonstrated by the famous Michelson-Morley experiment, in which light beams were timed as the earth revolved and rotated. The surprising result was that the speed of light was exactly the same regardless of the earth’s motion.

As I wrote in my book (see quantum-field-theory.net): That the speed of light should be inde­pendent of motion was most surprising… It makes no sense for a light beam – or anything, for that matter – to travel at the same speed regardless of the motion of the observer… unless “something funny” is going on. The “something funny” turned out to be even more surprising than the M-M result itself. In a nutshell, objects contract when they move! More specifically, they contract in the direction of motion. Think about it. If the path length of Michelson’s apparatus in the forward direction contracted by the same amount as the extra distance the light beam would have to travel because of motion, the two effects would cancel out. In fact, this is the only way that Michelson’s null result could be explained.

However the idea that objects contract when in motion was just as puzzling as the Michelson-Morley result. Why should this be? Once again the explanation is provided by Quantum Field Theory. Quoting again from my book:

Rodney BrooksWe must recognize that even if the molecular configuration of an object appears to be static, the component fields are always interacting with each other. The EM field interacts with the matter fields and vice versa, the strong field interacts with the nucleon fields, etc. These interactions are what holds the object together. Now if the object is moving very fast, this communication among fields will become more difficult because the fields, on the average, will have to interact through greater distances. Thus the object in motion must somehow adjust itself so that the same interaction among fields can occur. How can it do this? The only way is by reducing the distance the component fields must travel. Since the spacing between atoms and molecules, and hence the dimensions of an object, are deter­mined by the nature and configuration of the force fields that bind them together, the dimensions of an object must therefore be affected by motion.

It is important to understand that it is not just Michelson’s apparatus that contracted, it is anything and everything on earth, including Michelson himself. Even if the earth’s speed and the consequent contraction were much greater, we on earth would still be unaware of it. As John Bell wrote about a moving observer:

But will she not see that her meter sticks are con­tracted when laid out in the [direction of motion] – and even decontract when turned in the [other] direction? No, because the retina of her eye will also be contracted, so that just the same cells receive the image of the meter stick as if both stick and observer were at rest. – J. Bell (B2001, p. 68) 

In conclusion, for those who want to understand physics, I say use Quantum Field Theory and: WAKE UP AND SMELL THE FIELDS.

WHAT DOES THE ELECTRON LOOK LIKE?

In June, 2014, I gave a talk at the Physics Department of the Czech Technical University in Prague. I started by asking the question “What does the electron look like?”, and I showed two pictures. The first was the familiar Rutherford picture of particles orbiting a nucleus:

 

electron1

 

and the second was a (highly simplified) picture of the electron as a field in the space around the nucleus:

 

electron2

Then I asked for a vote. Quite amazingly only four people in the audience chose the field picture, and no one chose the particle picture. In other words, THEY DIDN’T KNOW. So here we are, 117 years after the electron was discovered, and this highly educated group of physicists had no idea what it looks like.

 

Of course when the electron was discovered by J. J. Thomson, it was naturally pictured as a particle. After all, particles are easy to visualize, while the field concept, let alone a quantized field, is not an easy one to grasp. However this picture soon ran into problems that led Niels Bohr in 1913 to propose that the particles in orbit picture must be replaced by something new: undefined electron states that satisfy the following two postulates: 

1. [They] possess a peculiarly, mechanically unexplainable [emphasis added] stability.

2. In contradiction to the classical EM theory, no radiation takes place from the atom in the stationary states themselves, [but] a process of transition between two stationary states can be accompanied by the emission of EM radiation.

This led Louis de Broglie to propose that the electron has wave properties. There then followed a kind of battle, with Paul Dirac leading the “particle side” and Erwin Schrodinger the “wave side”: 

schrodingerWe assert that the atom in reality is merely the… phenomenon of an electron wave captured, as it were, by the nucleus of the atom… From the point of view of wave mechanics, the [particle picture] would be merely fictitious. – E. Schrodinger 

However the fact that a free electron acts like a particle could not be overcome, and so Schrodinger gave in and Quantum Mechanics emerged as a theory of particles that are described by probabilities.

A second battle occurred in 1948, when Richard Feynman and Julian Schwinger (along with Hideki Tomanaga) developed different approaches to the “renormalization” problem that plagued physics. Once again the particle view espoused by Feynman won out, in large part because his particle diagrams proved easier to work with than Schwinger’s field equations. And so two generations of physicists have been brought up on Feynman diagrams and led to believe that nature is made of particles.

In the meantime, the theory of quantized fields was perfected by Julian Schwinger:

Julian SchwingerMy retreat began at Brookhaven National Laboratory in the summer of 1949… Like the silicon chip of more recent years, the Feynman diagram was bringing computation to the masses… But eventually one has to put it all together again, and then the piecemeal approach loses some of its attraction… Quantum field theory must deal with [force] fields and [matter] fields on a fully equivalent footing… Here was my challenge. – J. Schwinger

Schwinger’s final version of the theory was published between 1951 and 1954 in a series of five papers entitled “The Theory of Quantized Fields”. In his words:

It was to be the purpose of further developments of quantum mechanics that these two distinct classical concepts [particles and fields] are merged and become transcended in something that has no classical counterpart – the quantized field that is a new conception of its own, a unity that replaces the classical duality. – J. Schwinger

I believe that the main reason these masterpieces have been ignored is that many physicists found them too hard to understand. (I know one who couldn’t get past the first page.)

And so the choice is yours. You can believe that the electron is a particle, despite the many inconsistencies and absurdities, not to mention questions like how big the particles are and what are they made of. Or you can believe it is a quantum of the electron field. The choice was described this way by Robert Oerter

Wave or particle? The answer: Both, and neither. You could think of the electron or the photon as a particle, but only if you were willing to let particles behave in the bizarre way described by Feynman: appearing again, interfering with each other and cancelling out. You could also think of it as a field, or wave, but you had to remember that the detector always registers one electron, or none – never half an electron, no matter how much the field has been split up or spread out. In the end, is the field just a calculational tool to tell you where the particle will be, or are the particles just calculational tools to tell you what the field values are? Take your pick. – R. Oerter

What Oerter neglected to say is that QFT explains why the detector always registers one electron or none: the field is quantized. The Q in QFT is very important. 

So when you take your pick, dear reader, I hope you won’t choose the picture of nature that doesn’t make sense – that even its proponents call “bizarre”. I hope that, like Schwinger, Weinberg, Wilczek, Hobson (and me), you will choose a reality made of quantum fields – properties of space that are described by the equations of QFT, the most philosophically acceptable picture of nature that I can imagine.

EINSTEIN DIDN’T SAY THAT!

einsteinMany people believe that Einstein’s theory of general relativity states that gravity is caused by curvature in space-time. For example, here’s a recent question posted on Quora: “”Einstein tells us that gravity is motion in curved space-time, so why do scientists still call it a force?”. 

Excuse me for shouting, but this one really makes me mad. EINSTEIN DIDN’T SAY THAT! In his theory of general relativity, developed in 1915, gravity is a force field, not much different from the electromagnetic (EM) field. It is NOT four-dimensional curvature. But first a little history. 

The field concept was introduced into physics in 1845 by Michael Faraday during his studies of electric and magnetic phenomena. When James Maxell supplied equations for Faraday’s field in 1864, the field view of EM forces was generally accepted. However Isaac Newton’s theory of gravity, which involved “action at a distance”, remained unchanged. Newton’s theory was hugely successful, and is still taught in elementary physics classes today, but Newton was not satisfied with the idea of “action-at-a-distance”, saying “That one body may act upon another at a distance, through a vacuum, without the mediation of anything else… is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it.” 

This changed, of course, when Einstein introduced his theory of general relativity in 1915. In Einstein’s words: “As a result of the more careful study of electromagnetic phenomena, we have come to regard action at a distance as a process impossible without the intervention of some intermediary medium… The effects of gravitation also are regarded in an analogous manner… The action of the earth on the stone takes place indirectly. The earth produces in its surroundings a gravitational field, which acts on the stone and produces its motion of fall… [T]he intensity and direction of the field at points farther removed from the body are thence determined by the law which governs the properties in space of the gravitational fields themselves.” 

Note that Einstein said nothing about “curvature”. By developing equations for the gravitational field, as Maxwell had done for EM forces, Einstein answered Newton’s complaint about action-at-a-distance and brought the gravitational field into physics on a par with the EM field.

For those who don’t know what a field is, I offer this simple definition: A field is a property of space. There is no such thing as empty space. You can’t have space without fields. These fields obey laws (i.e., equations) that specify how a change at one point affects the field at adjacent points, and also how one field affects other fields. 

Hermann Minkowski

Hermann Minkowski

It was Hermann Minkowski who introduced the idea of four-dimensional space-time, which Einstein initially called “superfluous erudition”. However he eventually accepted Minkowski’s interpretation as an alternate mathematical interpretation of his equations. That is, Einstein’s equations for the gravitational field are mathematically equivalent to a curvature of spacetime, for those who can picture such a thing. But equivalence doesn’t dictate reality. While the curvature interpretation is useful to physicists, it doesn’t change the fact that physically speaking, gravity is a force field. Nobel laureate Frank Wilczek put it this way: 

“We can describe general relativity using either of two mathematically equivalent ideas: curved space-time or metric field. Mathematicians, mystics, and specialists in general relativity tend to like the geometric view because of its elegance. Physicists trained in the more empirical tradition of high-energy physics and quantum field theory tend to prefer the field view… As you can probably tell, I’m a field man.” 

When Quantum Field Theory was perfected by Julian Schwinger in the 1950’s, the gravitational field found a natural place alongside the other force fields (EM, strong, and weak). In QFT even matter is made of fields. As my good friend Prof. Edward Finn asked, why would God chose fields for everything else and not gravity? Nobel laureate Steven Weinberg put it this way: 

“In learning general relativity, and then in teaching it to classes at Berkeley and MIT, I became dissatisfied with what seemed to be the usual approach to the subject. I found that in most textbooks geometric ideas were given a starring role, so that a student… would come away with an impression that this had something to do with the fact that space-time is a Riemannian [curved] manifold… But now the passage of time has taught us not to expect that the strong, weak, and electromagnetic interactions can be understood in geometrical terms, and too great an emphasis on geometry can only obscure the deep connections between gravitation and the rest of phys¬ics… In my view, it is much more useful to regard general relativity above all as a theory of gravita¬tion, whose connection with geometry arises from the peculiar empirical properties of gravitation.” 

This doesn’t mean that the four-dimensional curvature interpretation is not useful. It is a convenient way of handling the mathematical relationships in Einstein’s equations. But I say shame on those who try to foist four-dimensional curvature onto the public as essential to the understanding of relativity theory. Unfortunately this view has been around for 100 years and has become the “accepted truth”. I think it’s time to WAKE UP AND SMELL THE FIELDS.

 

The Principle of Relativity – The Easy Way

In the entire history of physics there is no equation more famous than e = mc2. This relationship between mass (m) and energy (e) was derived in 1905 by Albert Einstein from his Principle of Relativity. The derivation wasn’t easy and merited a paper on its own, called “Does the inertia of a body depend upon its energy content?”. The equation continues to bewilder and mystify lay people, because in the usual particle picture of nature, it is hard to see why there is an equivalence between mass and energy. 

emc2

In the meantime, a new theory called Quantum Field Theory was developed. QFT was perfected in the 1950’s by Julian Schwinger in five papers called “Theory of Quantized Fields”. In QFT there are no particles, there are only fields – quantized fields. Schwinger succeeded in placing matter fields (leptons and hadrons) on an equal footing with force fields (gravity, electromagnetic, strong and weak), despite the obvious differences between them. Further, Schwinger developed the theory from fundamental axioms, as opposed to Richard Feynman’s particle picture, which he justified because “it works”. Unfortunately it was Feynman who won the battle, and today Schwinger’s approach (and Schwinger himself) are mostly forgotten. 

Yet QFT has many advantages. It has a firmer basis than the particle picture. It explains many things that the particle picture does not, including the many paradoxes associated with Relativity Theory and Quantum Mechanics, that have confused so many people. Philosophically, many people can accept fields as basic properties of space, as opposed to particles, whose composition is unknow. Or if there visualized as point particles, one can only ask “points of what?” And most of all, QFT provides an easy derivation and understanding of e = mc2, as follows. 

Mass. In classical physics, mass is a measure of the inertia of a body. In QFT some of the field equations contain a mass term that affects the speed at which quanta of these fields evolve and propagate, slowing it down. Thus mass plays the same inertial role in QFT that it does in classical physics. But this is not all it does; this same term causes the fields to oscillate, and the greater the mass, the higher the frequency of oscillation. The result, if you’re picturing these fields as a color in space (as in my book “Fields of Color”), is a kind of shimmer, and the greater the mass, the faster the shimmer. It may seem strange that the same term that slows the spatial evolution of a field also causes it to oscillate, but it is actually straightforward mathematics to show from the field equations that the frequency of oscillation is given by f = mc2/h, where h is Planck’s constant. 

Energy. In classical physics, energy means the ability to do work, which is defined as exerting a force over a distance. This definition, however, doesn’t provide much of a picture, so in classical physics, energy is a rather abstract concept. In QFT, on the other hand, the energy of a quantum is determined by the oscillations in the field that makes up the quantum. In fact, Planck’s famous relationship e = hf, where h is Planck’s constant and f is frequency, found in the centennial year of 1900, follows directly from the equations of QFT. 

wilczek_frankWell, since both mass and energy are associated with oscillations in the field, it doesn’t take an Einstein to see that there must be a relationship between the two. In fact, any schoolboy can combine the two equations and find (big drum roll, please) e = mc2. Not only does the equation tumble right out of QFT, its meaning can be visualized in the oscillation or “shimmer” of the fields. Nobel laureate Frank Wilczek calls these oscillations “a marvelous bit of poetry” that create a “Music of the Grid” (Wilczek’s term for space seen as a lattice of points): 

“Rather than plucking a string, blowing through a reed, banging on a drum­head, or clanging a gong, we play the instrument that is empty space by plunking down different combinations of quarks, gluons, electrons, photons,… and let them settle until they reach equilibrium with the sponta­neous activity of Grid… These vibrations represent particles of different mass m… The masses of particles sound the Music of the Grid.” 

This QFT derivation of e = mc2 is not generally known. In fact, I have never seen it in the books I’ve read. And yet I consider it one of the great achievements of QFT.

Space-Time Curvature and Relativity

General Relativity is the name given to Einstein’s theory of gravity that described in Chapter 2. As the theory is usually presented, it describes gravity as a curvature in four-dimensional space-time. Now this is a concept far beyond the reach of ordinary folks.. Just the idea of four-dimensional space-time causes most of us to shudder… The answer in Quantum Field Theory is simple: Space is space and time is time, and there is no curvature. In QFT gravity is a quantum field in ordinary three-dimensional space, just like the other three force fields (EM, strong and weak).

curved-space

This does not mean that four-dimensional notation is not useful. It is a convenient way of handling the mathematical relationship between space and time that is required by special relativity. One might almost say that physicists couldn’t live without it. Nevertheless, spatial and temporal evolution are fundamentally different, and I say shame on those who try to foist and force the four-dimensional concept onto the public as essential to the understanding of relativity theory.

The idea of space-time curvature also had its origin in mathematics. When searching for a mathematical method that could embody his Principle of Equivalence, Einstein was led to the equations of Riemannian geometry. And yes, these equations describe four-dimensional curvature, for those who can visualize it. You see, mathematicians are not limited by physical constraints; equations that have a physical meaning in three dimensions can be generalized algebraically to any number of dimensions. But when you do this, you are really dealing with algebra (equations), not geometry (spatial configurations).

By stretching our minds, some of us can even form a vague mental image of what four-dimensional curvature would be like if it did exist. Nevertheless, saying that the gravitational field equations are equivalent to curvature is not the same as saying that there is curvature. In QFT, the gravitational field is just another force field, like the EM, strong and weak fields, albeit with a greater complexity that is reflected in its higher spin value of 2.

While QFT resolves these paradoxical statements, I don’t want to leave you with the impression that the theory of quantum gravity is problem-free. While computational problems involving the EM field were overcome by the process known as renormalization, similar problems involving the quantum gravitational field have not been overcome. Fortunately they do not interfere with macroscopic calculations, for which the QFT equations become identical to Einstein’s.

Your choice. Once again you the reader have a choice, as you did in regard to the two approaches to special relativity. The choice is not about the equations, it is about their interpretation. Einstein’s equations can be interpreted as indicating a curvature of space-time, unpicturable as it may be, or as describing a quantum field in three-dimensional space, similar to the other quantum force fields. To the physicist, it really doesn’t make much difference. Physicists are more concerned with solving their equations than with interpreting them. If you will allow me one more Weinberg quote:

weinberg“The important thing is to be able to make predictions about images on the astronomers photographic plates, frequencies of spectral lines, and so on, and it simply doesn’t matter whether we ascribe these predictions to the physical effects of gravitational fields on the motion of planets and photons or to a curvature of space and time.” (The reader should be warned that these views are heterodox and would meet with objections from many general relativists.) – Steven Weinberg

So if you want, you can believe that gravitational effects are due to a curvature of space-time (even if you can’t picture it). Or, like Weinberg (and me), you can view gravity as a force field that, like the other force fields in QFT, exists in three-dimensional space and evolves in time according to the field equations.

 

TOP-DOWN vs. BOTTOM-UP

Albert-Einstein

 

Most physicists today are Einsteinian “top-downers”. They regard the various relativistic effects as consequences of the Principle of Relativity and that’s the way they present relativity to the public. They believe that deriving these effects as consequences of the way fields behave is somehow illegitimate.

“Look what you’ve done to our beautiful theory,” they say. “You’ve reduced it to mere physical effects. The F-L contraction is not a physical process that occurs because field configurations are affected by motion; it is something that is built into the nature of space. And this time dilation – it’s not that processes happen more slowly, it is a property of time itself.”

While the above is my paraphrasing, note how Einstein’s biographer, Abraham Pais, applied the condescending word “corrected” to the bottom-up explanations given by FitzGerald and Lorentz:

FitzGerald and Lorentz had already seen that the explanation of the Michelson-Morley experiment demanded the introduction of a new postulate, the contraction hypothesis. Their belief that this contraction is a dynamic effect (molecular forces in a rod in uniform motion differ from the forces in a rod at rest) was corrected by Einstein; the contraction of rods is a necessary consequence of his two postulates and is for the first time given its proper observational meaning in the June paper.

The fact is, either approach is correct and one does not preclude the other. Yes, the Principle of Relativity is elegant and the top-down approach is easier to use; physicists love it for that reason. But the field equations are also elegant and they not only contain the Principle of Relativity within them, they also provide a physical explanation for effects that otherwise are paradoxical. We can never know if God started with the Principle of Relativity and derived the field equations or started with the field equations from which follows the Principle. If She started with the principle that the laws of nature should be the same in all moving systems, then She also provided mechanisms to make it happen. And if the mechanisms are there, why not use them? They are real and understandable, and they should not be ignored.

 

Why Time “Dilates”

Quantum Field TheoryTime dilation is probably the best-known of the relativity effects because of the twin paradox. Here is the scenario: An astronaut leaves on a rocket ship traveling at close to the speed of light. After whizzing around the galaxy she returns to find that her (non-identical) twin brother on Earth is an old man with a long beard while she herself is still young. Now this is certainly mind-boggling. Why should time pass more slowly just because you’re moving? What physical explanation can we find for that?

Intuitive explanation. The explanation is again based on the field nature of matter, described by the field equations. Consider two atoms in a rocket ship (or in its contents). Suppose that one atom creates a field disturbance and when that disturbance reaches the second atom something happens. (It is the interaction among atoms, after all, that causes everything to happen.) Now if the rocket ship is moving, the second atom will have moved farther ahead, so the disturbance must travel a greater distance to get there, even after taking the F-L contraction into account. Since fields travel at a fixed rate, it will therefore take longer for the disturbance to reach the second atom. (Disturbances that propagate in the backward direction have a shorter distance to travel, but this effect turns out to be not as great.) In short, things happen more slowly when you’re moving because the fields have to travel a greater distance.

An analogy. Consider two men on a raft who exchange information by calling back and forth to each other. Suppose further that this exchange of information determines the evolution of events on the raft. That is, when B receives information from A he makes certain things happen, and when B calls back to A, other things happen. The problem is, it takes time for the sound waves to travel from A to B and by the time the sound reaches B, he will have moved to a new position B’. Therefore the sound must travel through a greater distance and the communication will take longer than if the raft were at rest.

LorentzIf the line between the two men is transverse to the motion (upper sketch) the calculation is not hard to do. The result, as it happens, is exactly the same as Lorentz’s result from Maxwell’s equations. The result is the same if the men are aligned in the direction of motion (lower sketch), although the calculation is harder because the time for forward communication is different from the time for backward communication.

NASA routinely observes time dilation in orbiting satellites and corrections are applied to keep atomic clocks on the GPS satellites in sync with clocks on earth. Time dilation has also been seen in particle accelerators. At the CERN accelerator radioactive particles traveling at 99.9% the speed of light are observed to decay 30 times more slowly than they do at rest (S1986, p. 57).

Another analogy. The idea of length contraction and time dilation may be easier to accept when you consider that objects contract and processes slow down when cooled. The only difference between the effect of temperature and the effect of motion is the mechanism: In a cooler chest it is the slowing down of atomic motion that affects rates and interatomic distances, while in moving objects it is the extra distance through which fields must propagate. Would we think it paradoxical if a twin was placed in a cold chamber for 50 years and then emerged to find that her brother was old and she was young? No, we would not; in fact there are firms that offer to preserve people by freezing them. Why then should we not accept that motion can have a similar effect on chemical and physical processes? As Lorentz himself said,

We may, I think, even go so far as to say that… the conclusion is no less legitimate than the inferences concerning the dilatation by heat. – H. Lorentz (L1916, p. 196)

 

Why Lengths Contract With Motion

George_Francis_FitzGeraldThe idea of contraction was first suggested by a relatively unknown Irish physicist, George Francis FitzGerald. FitzGerald expressed his idea in a short communication to the American journal Science in 1891, ten years after Michelson’s first reported result, and he also suggested a reason.

I would suggest that almost the only hypothesis that can reconcile this [conflict] is that the length of material bodies changes, according as they are moving through the ether or across it, by an amount depending on the square of the ratio of their velocities to that of light. We know that electric forces are affected by the motion of the electrified bodies relative to the ether, and it seems a not improbable supposition that the molecular forces are affected by the motion, and that the size of a body alters consequently.

While FitzGerald referred to the ether, which was believed to be the carrier for light waves at the time, the reasoning holds with or without the ether. Somewhat later his rather timid suggestion that molecular forces are affected by motion was repeated and refined by the most famous physicist of the time.

While FitzGerald was little known outside Ireland, the Dutch scientist Hendrik Lorentz was recognized as the greatest physicist since Maxwell. In 1902 he and Pieter Zeeman received the second Nobel Prize ever awarded for discovering the “Zeeman effect” that led to the discovery of electron spin (Chapter 6). Einstein called Lorentz “the most well-rounded and harmonious personality he had met in his entire life” (P1982, p. 169). Upon Lorentz’s death, Europe’s greatest physicists attended his funeral and three minutes of silence were observed throughout Holland.

Lorentz had not seen FitzGerald’s paper, but he too realized that Michelson’s strange result would make sense if the apparatus contracted along the direction of motion. However he went further than FitzGerald; he did the calculation (not an easy one) using Maxwell’s equations. When he found that the theoretical contraction exactly compensated for the extra travel distance, this was surely one of the great “Eureka” moments in physics, comparable to those of Newton and Einstein.

When Lorentz learned of FitzGerald’s work, he wrote to him to be sure he was not usurping credit,… and thereafter Lorentz was careful to acknowledge FitzGerald’s priority. The contraction is sometimes called the FitzGerald contraction, some¬times the Lorentz contraction, and sometimes the FitzGerald-Lorentz (F-L) contraction. Fig. A-3 shows a modern version of Lorentz’s calcu¬lation done by John Bell with the aid of a computer.

Misconception #1. Some writers claim that the F-L contraction was an ad hoc explanation offered without any theoretical basis. In fact it was based on a deep understanding of how fields behave when in motion and how this behavior affects the molecular configurations.

Surprising as this hypothesis may appear at first sight, yet we shall have to admit that it is by no means far-fetched as soon as we assume that molecular forces are also transmitted through the ether, like the electric and magnetic forces of which we are able at the present time to make this assertion definitely. If they are so transmitted, the translation will very probably affect this action between two molecules or atoms in a manner resembling the attraction or repulsion between charged particles. Now, since the form and dimensions of a solid body are ultimately conditioned by the intensity of molecular actions, there cannot fail to be a change of dimensions as well. – H. A. Lorentz (E1923, p. 5-6)

Intuitive explanation. While I hope you can accept, as did FitzGerald and Lorentz, that length contraction happens because the field equations require it, it would be nice to have some intuitive insight into the phenomenon. We must recognize that even if the molecular configuration of an object appears to be static, the component fields are always interacting with each other. The EM field interacts with the matter fields and vice versa, the strong field interacts with the nucleon fields, etc. These interactions are what holds the object together. Now if the object is moving very fast, this communication among fields will become more difficult because the fields, on the average, will have to interact through greater distances. Thus the object in motion must somehow adjust itself so that the same interaction among fields can occur. How can it do this? The only way is by reducing the distance the component fields must travel. Since the spacing between atoms and molecules, and hence the dimensions of an object, are deter¬mined by the nature and configuration of the force fields that bind them together, the dimensions of an object must therefore be affected by motion.

 

Why I Wrote “Fields of Color”

Rodney BrooksThis book started from a chapter in a book I once intended to write, called “Can Robots Have Orgasms?” Here is how that title came about. In my earlier years if I thought about consciousness at all, I probably believed that the mind operates according to the laws of physics and chemistry, like any other organ of the body. But then one day I thought about pain – that strong searing sensation that can make one scream and yell. Pain, I thought, surely cannot be explained by fields or particles or relativity or quantum mechanics or even quantum field theory. It is something that is quite apart, quite different from what happens in a computer or in any other machine. Then I thought about all the other things that computers can’t feel, one of which is the intense pleasure of an orgasm.

Then one day we had a visitor – a bright young computer hot shot. I asked him as we were sitting down for dinner “Do you think a computer can ever experience a sexual orgasm?” Well this young fellow began to tell me how you could create an orgasm by putting the right 0’s and 1’s into the right memory banks. Of course this was ridiculous nonsense, so I told him he had flunked the test and couldn’t have any dinner.

I didn’t really. We fed him, but he did give me the idea for the title: “Can Robots Have Orgasms?” As it happened, I eventually abandoned the book because I figured that a book that boiled down to just one word (“No”) wouldn’t sell. However I had already written or sketched chapters that I called “dead ends” about three explanations that have been proposed for consciousness: Artificial Intelligence, Religion, and Quantum Mechanics. To my way of thinking these all fail to provide an answer, or any hope of an answer. However, as I worked on the chapter entitled “Quantum Mechanics”, I realized that all the quantum mechanical explanations ignored Quantum Field Theory. And then I realized that QFT is ignored everywhere, as if it never existed. And that’s why I wrote the book that I wrote…

Why Quantum Field Theory is Ignored

Given all its successes, you must surely wonder why QFT has remained an unwanted child. For one thing, there is no physical evidence to compel us to believe in fields, or for that matter, to believe in anything. Philosophers tell us that we can’t prove what is real, or even that there is a reality. I cannot prove that my entire life has not been a dream in the mind of some alien being. All that we can do is try to find a theory that explains our observations; and then, if we choose – and only if we choose, – we can believe that the theory represents reality.

So the choice is yours. You can believe that reality consists of particles – tiny spheres or point particles – despite the many inconsistencies and absurdities, not to mention questions like how big the particles are and what are they made of. Or you may choose to believe in wave-particle duality, which is neither fish nor fowl. Or you may want to join those physicists, like Steven Hawking, who don’t worry about reality.

The choice was described this way by Robert Oerter:

Wave or particle? The answer: Both, and neither. You could think of the electron or the photon as a particle, but only if you were willing to let particles behave in the bizarre way described by Feynman: appearing again, interfering with each other and cancelling out. You could also think of it as a field, or wave, but you had to remember that the detector always registers one electron, or none – never half an electron, no matter how much the field has been split up or spread out. In the end, is the field just a calculational tool to tell you where the particle will be, or are the particles just calculational tools to tell you what the field values are? Take your pick.

And when you take your pick, dear reader, I hope you won’t choose the picture of nature that doesn’t make sense – that even its proponents call “bizarre”. I hope that, like Schwinger, Weinberg, Wilczek (and me), you will choose to believe in a reality made of quantum fields – properties of space that are described by the equations of QFT. This is a picture that resolves all three of Einstein’s enigmas (see Appendices), a picture that solves the action-at-a-distance problem that even Newton found unacceptable, a picture based on simple and elegant equations (take my word for that), a picture that explains or is consistent with all the data known to date. And on top of that, QFT provides the most philosophically acceptable picture of nature that I can imagine…. The choice is now up to you.

Choose Quantum Field Theory.

Speed of Light – Why Nothing Can Go Faster

Of course the idea that there is an ultimate speed limit seems absurd. While the speed of light is very high by earthly standards, the magnitude is not the point; any kind of speed limit in nature doesn’t make sense. Suppose, for example, that a spaceship is traveling at almost the speed of light. Why can’t you fire the engine again and make it go faster – or if necessary, build another ship with a more powerful engine? Or if a proton is whirling around in a cyclotron at close to the speed of light, why can’t you give it additional energy boosts and make it go faster?

Speed-of-Light

Intuitive explanation. When we think of the spaceship and the proton as made of fields, not as solid objects, the idea is no longer ridiculous.  Fields can’t move infinitely fast. Changes in a field propagate in a “laborious” manner, with a change in intensity at one point causing a change at nearby points, in accord­ance with the field equations. Consider the wave created when you drop a stone in water: The stone generates a disturbance that moves outward as the water level at one point affects the level at another point, and there is nothing we can do to speed it up. Or consider a sound wave traveling through air: The disturb­ance in air pressure propagates as the pressure at one point affects the pressure at an adjacent point, and we can’t do anything to speed it up. In both cases the speed of travel is determined by properties of he transmitting medium – air and water, and there are mathematical equations that describe those properties.

wilczek_frankFields are also described by mathematical equations, based on the properties of space. It is the constant c in those equations that determines the maximum speed of propagation. If the field has mass, there is also a mass term that slows down the propagation speed further. Since everything is made of fields – including protons and rocketships – it is clear that nothing can go faster than light. As Frank Wilczek wrote,

One of the most basic results of special relativity, that the speed of light is a limiting velocity for the propagation of any physical influence, makes the field concept almost inevitable. – F. Wilczek (“The persistence of Ether”, p. 11, Physics Today, Jan. 1999)

David Bodanis tried to make this point in the following way:

Light will always be a quick leapfrogging of electricity out from magnetism, and then of magnetism leaping out from electricity, all swiftly shooting away from anything trying to catch up to it. That’s why its speed can be an upper limit. – D. Bodanis

However Bodanis only told part of the story. It is only when we recognize that everything, not just light, is made of fields that we can conclude that there is a universal speed limit. 

Now let’s take another look at that proton whirling around in an accelerator, using our colored glasses to visualize the fields. We see the proton as a blob of redness “oozing” (I prefer that term to “leapfrogging”) ahead, as the amount of redness at one point affects the redness at a neighboring point. The process is very fast by our usual norms, but it is not instantaneous. The proton can’t move any faster because the field equations put a limit on how fast the redness can ooze.