Rodney A. Brooks > Quotes

“In the field picture there is no such thing as empty space. Fields pervade space; they are a condition or property of space; you can't have space without fields. Fields obey laws that specify how a change at one point affects the field at adjacent points, and thus how that change is propagated through space.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Relativistic twins? When one looks at the paths that Newton and Einstein followed while pursuing their theories of gravity, one is struck by the many similarities: the unexplained data on orbits, the sudden insight about falling objects, the need for a new mathematics, the calculational difficulties, the retroactive agreements, the controversy, the problem-plagued expeditions, and the final triumph and acclaim.. Both men had worked in the same eccentric and lonely way, divorced from other scientists, armed with a great feeling of self-reliance while struggling with new concepts and difficult mathematics, and both produced earth-shaking results. One can't help but wonder if these two greatest of scientists, born 237 years apart, were "relativistically related", conceived as twins in some ethereal plane in a far-off galaxy and sent to earth to solve a matter of some gravity.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Whether it is a falling man or an orbiting satellite, the effect of inertia is to create an apparent upward force that depends on the mass of the object. It is the same force we feel when riding in a car that goes around a tight curve. This inertial effect is equal and opposite to gravity and therefore cancels the pull of gravity. In physicist language, the "gravitational mass" and "inertial mass" are equal. This is not a tautology, as Ambrose Bierce thought, but a recognition that the pull of gravity is proportional to the inertia of the object being pulled. Einstein called this the "Principle of Equivalence", and it became the basis for his new theory of gravity that he called the general theory of relativity.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“I believe that common sense is choosing, wherever possible, the simplest, most intuitively-satisfying explanation that is consistent with observations.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Enigmas answered. Not only is QFT the answer to Einstein's search, it also answers or resolves his Enigmas, and in a way that can be understood by the man (or woman) on the street. In Appendix A you will see how the paradoxes of special relativity become natural and understandable consequences of the way fields behave. In Appendix B you will see that the problematic curvature of space-time in general relativity is gone; in QFT gravity is just another force field and space and time are the same space and time we intuitively believe in. Finally, in Appendix C you will see how the infamous wave-particle duality of QM is eliminated because there are no particles - only fields - and hence there is no duality. However abandoning the familiar picture of solid particles and replacing it with intangible fields is not easy. It will require a leap of imagination greater than did the atomic picture that Eddington struggled with.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“I once read that for every equation, you lose a thousand readers.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“The job of science is to look beyond our intuition, to find out by any means possible what's really going on, and to give up old ways of thinking when the evidence requires it.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Force fields are directional. The gravitational field is a force field and forces are directional. In the case of gravity, the direction of the force is toward the object that created the field. What, you may then ask, happens when there are several gravitational fields set up by several objects? For example, the gravitational field at the surface of the earth also contains component fields arising from the moon and the sun. The answer is that the various fields combine to give a net gravitational field, but they don't add numerically; each field has its own direction, and the directions must be taken into account. Thus there is a point between the earth and the moon where the two gravitational fields, being in opposite directions, cancel each other out. When a moon rocket is fired, it must have enough power to reach that point or else it will fall back to the earth. Beyond that point it will be pulled toward the moon. This compounding of forces also causes the tides as the water in oceans and seas is pulled toward the sun and moon. Even though those tugs are imperceptible to us, they create a variety of tides, such as neap and ebb tides, depending on the positions of the sun and moon.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Propagation speed. An important feature of fields is that changes in their intensity do not propagate through space instantaneously but proceed, point by point, with a speed that is limited by a number in the equations. This number is about 300,000 km/sec (186,000 miles/sec) and, since light itself is a field, it's no coincidence that this number is the speed of light. If we imagine that an object suddenly appears in space, the gravitational field generated by that object will first appear near the object and then rapidly extend outward until all of space has acquired, to some extent, the attractive property created by that field. Similarly, if the object were suddenly to disappear, the field would continue to exist for some time afterward. If the earth were suddenly to disappear, the moon would continue in its orbit for another second and a half before the gravitational field in its vicinity vanished. If the sun were suddenly to disappear, earth would continue in its orbit for eight and a half minutes before heading off into space.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“That the physics community has so ignored the only understandable, paradox-free picture of nature that we have boggles my mind. Maybe physicists like being seen as "high priests" who are entrusted with mysteries that mere mortals cannot hope to comprehend.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Feynman converts! According to Frank Wilczek, Feynman eventually lost confidence in his particles-only view of nature:

Feynman told me that when he realized that his theory of photons and electrons is mathematically equivalent to the usual theory, it crushed his deepest hopes...He gave up when, as he worked out the mathematics of his version of quantum electrodynamics, he found the fields, introduced for convenience, taking on a life of their own. He told me he lost confidence in his program of emptying space...(see quote in Chap. 2, "The Gravitational Field")-F. Wilczek (W2008, p. 84. 89)

However this "conversion" is not generally known. Most physicists today routinely use Feynman graphs while promulgating and perpetuating the particle picture of nature, puzzling and paradoxical as that picture may be.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“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 determined by nature and configuration of the force fields that bind them together, the dimensions of an object must therefore be affected by motion.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“We assert that the atom in reality is merely the...phenomena 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. I have, however, already mentioned that we have yet really observed such particle paths [see, for example, Fig. 6-6]...We find it confoundedly difficult to interpret the traces we see as nothing more than narrow bundles of equally possible paths.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“The uncertainty principle. The uncertainty principle, introduced by Heisenberg in 1927, states that the position of a particle cannot be determined, but provides a mathematical formula relating its uncertainty to the uncertainty of the particle's momentum. Now in QFT what we call particles are really fields, and since fields spread out, there is no precise "position". However there is a property of fields in general, known as Fourier's theorem, that relates the spatial spread of any field to the spread of its wavelengths. In QFT, the wavelength of a quantum is related to its momentum, and I still remember my moment of insight when I realized that Heisenberg's relation between the uncertainties of position and momentum is simply Fourier's theorem.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“I understand," says Schwinger, "and I admit that QFT has not solved the causality problem. But at least it has localized the probability aspect to a single event called field collapse-an event that is not covered by the equations of QFT. That is to say (Schwinger's favorite expression), QFT itself is causal, but it only takes us so far. At some point a discontinuous event takes place that is not covered by the theory. It is possible that at some time a theory will be developed for field collapse and it may turn out to be causal after all. On the other hand, it may be that it is a truly probabilistic process, and perhaps God does play dice with the world. Either way, it doesn't detract from what QFT has accomplished.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Fields of color. A special feature of this book is the use of color to depict fields that in themselves are unpicturable. Just as the color blue permeates the sky, so you will be asked to picture space as permeated with colors, with different colors representing different fields. Color is an appropriate tool for this job because color is something that does not exist in itself; it exists only as a property of something else. By using colors to represent physical fields, we remind ourselves that fields are a property of space, not a separate substance in space.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“The weak interaction is unique in that it can change the nature of a particle, for example transforming a neutron into a proton or vice versa. Such transformations are crucial for the sun and it is the weakness of the interaction which leads to the very slow burning of the nuclear fuel of the sun and thus creates the conditions on earth which can support life.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Non-locality. One of the most troubling aspects of field collapse is that it is instantaneous and occurs at the same time at widely separated points. Physicists call this non-locality. This is especially bothersome when the sudden change involves two entangled field quanta. Einstein argued vehemently against the idea of non-locality, claiming that it violated a result of his Principle of Relativity - that nothing can be transmitted faster than the speed of light. Now Einstein's postulate (which we must remember was only a guess) is indeed valid in relation to the evolution and propagation of fields as described by the field equations. However field collapse is not described by the field equations, so there is no reason to expect or to insist that it falls in the domain of Einstein's postulate. Non-locality is a fact; it has been experimentally documented. Nor does it lead to any paradoxes or inconsistencies. Even those who believe in particles as the ultimate reality acknowledge that something happens non-locally. Just as we said, "So the earth is round, not flat; that's surprising but I can live with it", so we can say, "Fields suddenly collapse. It's not what I expected but I can live with it." There are no logical contradictions involved.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“My mission soon turned into a labor of love, with emphasis on labor. I had not anticipated the breadth and depth of the subject, or the drama as our greatest minds waged what I think is our greatest battle: to understand the world we find ourselves in (a far more worthy battle than the wars we are so good at waging against each other). By drama I mean not only the philosophic struggle to wrest nature's secrets from their most hidden recesses with only the flimsiest of evidence; I also mean the human side of the story - stories that are sometimes tragic, sometimes nettlesome, but always fascinating.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Because quanta are fields, they do not have sharp edges and can spread over large distances, but no matter how spread out they are, each quantum maintains its own identity. If it is absorbed or changes its spin state, it does so as a unit. Because of this all-or-nothing behavior, quanta in many ways mimic the behavior of particles.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“The number of matter quanta in a given region or state is limited by the Exclusion Principle.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Mass is not weight.....Weight is the pull of gravity -the downward force exerted by the earth. If there is no gravity there is no weight, but there is still inertia. In ordinary speech the two concepts are often blurred, as in "a heavy object is harder to push". Nevertheless, weight is the pull of gravity and mass is inertia, and they are different concepts.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“general spin is an abstract mathematical concept that is related to the number of field components and how they change when viewed from different angles. The more field components, the higher the”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Note about youth. Before ending this chapter, I'd like to say something about youth. It was a popular edict in the 1960's to never trust anyone over 30. Whether or not this is true in general, it has great validity in theoretical physics. When Einstein discovered his theory of relativity he was 25. Bohr was 28 when he developed his atomic theory. De Broglie was 28 when he had his ephiphany. Pauli was 25 when he announced his exclusion principle. Heisenberg was 26 when he presented his uncertainty principle (although the exact date is uncertain). Dirac was 26 when he discovered his relativistic equation. Newton was 23 when he worked out his gravitational theory. Even Schwinger and Feynman (but not Tomonaga), despite the interruption of WWII, found the renormalization solution before the age of 30. It seems that the ability to "think outside the box" is strongest in the young!”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“SUMMARY

The theory of Special Relativity as formulated by Einstein in 1905 was based on the postulate that the laws of physics are the same regardless of the state of motion of the observer, so long as it is uniform. This is known as the Principle of Relativity, from which there follow many strange effects. While these behaviors seem paradoxical, they make perfectly good sense when seen as a result of the way fields behave:

Objects contract when moving because motion affects the interaction of fields that hold the object together. Space itself contracts because space is made of fields.

Things happen more slowly in a moving system because the interacting fields must travel a greater distance (despite the contraction).

Nothing can go faster than light because everything is made of fields that propagate at a finite rate determined by the field equations.

Mass increases with speed because mass means resistance to acceleration and acceleration beyond the speed of light is impossible.

I call this the bottom-up approach. Although most physicists prefer to start with the Principle of Relativity (top-down approach), the bottom-up method provides insight into why these strange things happen. Even the Principle of Relativity follows from the bottom-up approach.

Either way, one must cope with a Rashomon reality in which observers in differently-moving systems see the same reality in different ways.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“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 that the frequency of oscillation is given by f=mc^2/h, where h is Planck's constant.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Misconception #3. Some physicists claim that length contraction and time dilation are not real and that the physical explanations of Fitzgerald, Larmor and Lorentz are not to be taken seriously. This is not true. As N. David Mermin points out in his popular book on relativity "It's About Time":

Moving clocks really do run slowly and moving sticks really do shrink, if the concept of a clock or the length of a stick has any meaning at all...It is necessary for clocks and sticks really so to behave if the while subject is to fit coherently together, and not collapse into a mass of self-contradiction. - N.D. Mermin

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.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“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.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“The Higgs mechanism was actually suggested earlier by Schwinger, in the same paper where he introduced the V and A equation. Like the V-A discovery, this contribution by Schwinger is also largely forgotten.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein

“Occam's Razor. I'm tempted to add another principle, but it's really more of a wish than a rule. I'm referring to Occam's razor, which states in essence, "All things being equal, the simplest explanation is best." Einstein put it somewhat differently: "A physical theory should be as simple as possible, but no simpler." The last phrase is important because, as Schwinger said, "nature does not always select what we, in our ignorance, would judge to be the most symmetrical and harmonious possibility". If the theory were as simple as possible, there would be just one field (or perhaps none!), and the world would be very uninteresting-not to mention uninhabitable. I think it can be said that the equations of QFT are indeed about as simple as possible, but no simpler.”
― Rodney A. Brooks, Fields of Color: The theory that escaped Einstein