Rodney A. Brooks Quotes

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.

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.

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.

MASS INCREASES

The final paradox of relativity is the increase in mass due to motion. Mass increase has been observed experimentally in particle accelerators, with increases as great as 3000% for particles traveling at over 99.9% the speed of light. How can the mass of an object get bigger just because it's moving?

Intuitive explanation. As we saw in Chapter 2, mass means inertia - i.e., resistance to acceleration. If you push something and it doesn't respond much, then by definition it has a large mass or inertia. Now we just saw that pushing on something that is traveling at close to the speed of light has little effect on its speed because the underlying fields are already moving almost as fast as they can. Thus its resistance to acceleration has become greater and this means its mass has increased. Mass increase is just another way of saying that fields can't propagate faster than c.