John Marburger III

Einstein and his Legacy

June / July 2005 By: John Marburger III Volume 3 Number 3

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Einstein's reputation can be daunting, but his work was truly practical and pervades nearly all modern science and technology.

Einstein did not work in a vacuum. Basic phenomena of mechanics, electromagnetism, and gravity had been captured in mathematical "laws" as he began his work early in the 20th century. Einstein assumed these laws were telling us something deeper than the collection of experiments that led to them.
He wondered what it was about nature that makes the laws look as they do and tried to reduce them to their simplest forms. The point of this was that, as they stood then, the laws were not consistent with each other, and ironing out the inconsistencies meant modifying their formulas. Since the old formulas worked, the new ones had to reduce them under the conditions of the old experiments. Under new conditions, the new formulas would predict new phenomena that experimenters could look for. This kind of work is difficult because no approach is guaranteed to find a framework that ties everything together.
Einstein thought deeply about how to proceed and often wrote about the philosophical and aesthetic principles that guided him.

You can see how such investigations would have broad impact. The old laws we are talking about are Newton's "force equals mass times acceleration" and "gravitational force is proportional to the product of the attracting masses and the inverse square of the distance between them" and the equally famous equations of Maxwell for electromagnetism that you sometimes see on engineering students' tee-shirts. Engineers use these "laws" for designing machinery and plotting the paths of spacecraft. But Newton's laws apply to moving particles, and Maxwell's apply to continuous "fields" of force. Where the two come together, such as in the radiation of light by oscillating charges, incompatibilities emerge. Einstein's work transformed or led to the transformation of all these laws.

I want to be clear about what these laws are for. They do not tell how matter appears in all its glorious manifestations from galaxies to little girls. We have to look out at the world to get that information. The laws do tell us how all the things we observe will change under their mutual influences. They are specifically about how things move from one state to another in time. Of course the laws must account for all the forces that cause change, so they contain implicitly an inventory of forces and the things they grab. Most of this inventory is contained today in the so-called Standard Model of particle physics, which lists quarks and leptons and their forces (but not yet gravity).

Einstein believed such laws of motion should be much simpler than the more or less accidental clumps of matter that make things what they are. He looked for properties like energy that remained the same during the motions, and even wished later he had called his most famous discovery the theory of invariants rather than the theory of relativity. So when the old Maxwell equations produced a speed for light without telling what stationary platform you should stand on to measure it, Einstein said it didn't matter: Just fix up all the other old laws to be consistent with light-speed being the same from any uniformly moving platform. The principle was simple, but the changes needed to fix up Newton's F = ma implied that the world should look very strange to an observer moving near the speed of light. The symbols that represented durations (and lengths) in the old laws had to be re-interpreted to allow them to stretch (and shrink) in the new laws for moving objects. Since light moves at 186,000 miles per second the corrections are negligible at normal speeds, unless you are making very accurate measurements. Today's global positioning technology requires measurements of time so accurate that Einstein's corrected laws of motion are essential to describe the motion of the GPS satellites.
Incidentally, the formula for energy derived from the corrected F = ma contains a new term, the famous E = mc2, where m is mass and c the speed of light.

The special condition of measuring from a "uniformly moving platform" troubled Einstein who saw no reason why the most fundamental laws of motion should look any different for a non-uniform (i.e., accelerated) motion. Because acceleration is tied to force by Newton's law, making accelerated motions of observers irrelevant required a radical new way of representing the presence of a force. In Einstein's general theory of relativity, the gravitational force is represented by intrinsic distortions of the new concepts of space and time that had to be introduced in the special theory. The distortions are caused by concentrations of matter and energy in a new formula replacing the old law of gravity. The new picture enabled Einstein's followers to envision a dynamic universe whose very geometry continues to expand from a cataclysmic Big Bang that seems to have occurred about 13.5 billion years ago.

These altered concepts of space, time, energy and gravity came from changing Newton's laws to fit consistently with Maxwell's and with the notion that the laws should not depend on how the observer moves. Einstein rocked the entire framework by showing that a formula invented by Max Planck to account for the color spectrum of heat radiation implies that the energy light carries acts like independent particles, contrary to a century of teaching that light must come in waves. From this "heuristic viewpoint" Einstein inferred a new law describing how light knocks electrons out of metal surfaces, the so-called photo-electric effect. It won Einstein his Nobel prize in 1920, but the weird new laws of nature that others eventually found to accommodate his photons violated Einstein's philosophical instinct. In later years he followed his own lonely path apart from the new immensely fruitful quantum theory of nature.

Einstein brightened other parts of physics, but it was in laying entirely new foundations for its fundamental laws that he made the greatest impact.

John H. Marburger III is science advisor to President Bush and director of the Office of Science and Technology Policy. He was previously director of the Brookhaven National Laboratory and president of the State University of New York at Stony Brook. He had been a professor of physics and co-founder of the Center of Laser Studies at the University of California. He received his Ph.D. in physics from Stanford University.