Thursday, November 25, 2004

Pondering Einstein

Bravo! Your special Einstein issue [September] is excellent! By focusing many writers on one topic, you’ve reminded us of two important lessons. First, that physics is like any other human endeavor: It and its practitioners are subject to as many interpretations as there are interpreters. Second, a dose of humility is still good medicine, even for a pantheon of modern physicists, because when a Newton or an Einstein does come along, his or her greatness is always defined by the trampling of majority-accepted “truths.”


Sammamish, Washington

I can think of dozens of scientists whose work was more important than Einstein’s. His work was mostly theoretical and has been of little use to humanity. I rate Watson and Crick, Newton, Bernoulli, Faraday, Clausius, and dozens of others as being more important scientists than Einstein.


Wimberley, Texas

As I was reading the summaries of Einstein’s theories of relativity [“Einstein in a Nutshell”], a few questions came up about the accepted Einsteinian view of time and space. First, what happened to the commonsense conceptualization of space as nothingness—the nothingness between objects or matter that fills the empty intervals between events that we call time? How can nothingness suddenly become a fabric that can exert force upon objects? The idea that nothingness exerts force or has a shape that is not determined by forces or material limits seems about as substantial as the idea of an ether, and no more logical than the idea that objects pull with gravity. Also, how can light be considered a constant if the terms that light is measured with—space and time—are not constant?


Vancouver, Washington

Part of the reason Einstein’s ideas sound so strange is that we are using linguistic metaphors to describe his theories rather than the mathematical equations that describe them much more accurately. At any rate, common sense is an unreliable guide in evaluating how the universe behaves on scales that lie far outside human experience. Scientists abandoned the notion of an ether because they could find no evidence to support it, even though it appealed to their common sense about how light travels through a vacuum. Scientists now accept Einstein’s relativity because they find an impressive match between theory and observation, even though concepts such as curved space-time run counter to human intuition. One of these observations is that the speed of light in a vacuum always appears the same. Einstein concluded that the constancy of light reveals a deep cosmic truth: The laws of physics appear the same to all observers, regardless of their state of motion. This constancy is possible only if each observer is perceiving the universe relative to his or her local definition of time and space.

The editors

Theoretical physicist Michio Kaku’s four-dimensional inflating balloon is a wonderful device for describing a cosmic positive curvature of space-time [“Einstein in a Nutshell”]. But the balloon need not be expanding. If, as is stated elsewhere in the article, positive curvature causes light frequencies to stretch, thereby shifting them toward the red end of the spectrum, then space-time need not expand in order for us to observe the redshift. As necessitated by relativity, we would see more positive curvature from the bottom of Earth’s or the solar system’s gravitational trough than we would see in open space. I suggest that space-time could be better described as expansive than expanding.


Laguna Beach, California

It is the stretching of space, rather than the curvature of space (which is quite small), that can account for the redshift of the distant galaxies, which is why scientists have concluded that the universe is expanding. An expanding universe can have either positive or negative curvature. Think of a plastic balloon (with positive curvature) or the surface of a trumpet or a saddle (with negative curvature) made of plastic. In either case, it’s possible to stretch the plastic, expanding the distance between any two points on the surface, thereby creating a redshift. Scientists have recently confirmed (using satellites such as the Wilkinson Microwave Anisotropy Probe, along with other experiments) that the curvature of the universe is neither positive nor negative but actually close to zero. (This still leaves open the possibility that our visible universe is a tiny, flat surface in a much bigger universe with positive or negative curvature.) So the universe is both expanding and expansive.

Michio Kaku

Thanks for a wonderfully informative issue! One comment: In “Plucking the Strings of Relativity,” Michael S. Turner says “the singularity at the center of a black hole . . . could be a wormhole, or shortcut, to another place in our universe or even to another universe entirely.” But the effects of relativity mean that it takes an infinite amount of time for an object to fall into a black hole, so the wormhole is effectively closed from the standpoint of anyone external to the event horizon. From the perspective of the person falling in, the wormhole seems to be a one-way trip to an infinitely distant future. Does a wormhole that cannot be used in a finite amount of time exist in any real sense? It’s certainly not a “shortcut”!


Madison, Alabama

Theorists have yet to resolve whether Einstein’s theory even permits wormholes. Current indications are that the required space-time tunnels cannot persist long enough to be traversed, but for the sake of argument we will assume that usable wormholes exist. The journey to the center of a black hole and back out takes infinitely long only as viewed from the outside. From the perspective of the person falling in, the trip happens in a finite period. Depending upon where and when the traveler emerges, the passage through a black hole could be a fabulous shortcut, allowing him to travel across the universe in a short time. The trip through a black hole could even take the traveler back to a place and time in his own past. Of course, traveling back in time to the same place raises questions about the relationship between cause and effect (for example, intervening in an event crucial to your own existence). In the language of relativity theory, doing so would involve the existence of “closed timelike curves,” loops in time that curve in on themselves. Some exotic solutions to Einstein’s equations allow such curves; however, Stephen Hawking’s chronology protection conjecture states that in mathematically sensible solutions of Einstein’s theory, closed timelike curves cannot exist. But who knows? Hawking recently lost a bet about black holes and information—maybe he is wrong here too!

Michael S. Turner

In Tim Folger’s article, “Einstein’s Grand Quest for a Unified Theory,” I was pleased to see his comment that Einstein “believed, emphatically, in a universe that exists completely independent of human observation.” I have long had problems with the often-stated interpretation that a human observer is required for the universe to exist, just because the results of experiments like the double slit are indeterminate until a measurement is made, at which time either a wave or a particle manifests. I contend that the same quantum mechanical “choices” occur all the time just because the wave or particle interacts with something, whether or not they take place in an experimental setup observed by a human.


Mountain View, California

I’m enjoying your special issue about Einstein, whom I’ve studied off and on for 30 years. I’m pleased to report that I’m learning things from your issue. However, the graphic explanation of the twin paradox by Michio Kaku and Nigel Holmes [“Einstein in a Nutshell”] contains an error. The twin who travels does not become younger. Both twins age, but the traveling twin ages much more slowly. So when he returns to Earth, he is only a little older, while his brother is considerably older.


Dallas, Texas

Sharp eye! You have spotted erroneous mustaches and wrinkles on the twins right before one of them begins his journey. Perhaps the spacefaring twin bribed the artist to make him seem more youthful when he returned. Or (as some of us here suggested when we, too, spotted this mistake) he may have shaved and used wrinkle cream to help pass the time during his long flight. We do apologize for the error.

The editors

I enjoyed your special Einstein issue, but for many years now I have not been able to accept either the special or general theory of relativity as logical because both are based on a false premise: that the speed of light is absolute and not relative. I do not believe that rejecting the idea of an absolute speed of anything means accepting the notion of any unproven “ether.” But we have to question anything that does not make sense, even if the person who developed the theory is highly revered. Einstein has been deified, and whoever questions him commits heresy. But, as in the familiar children’s story, someone has to be brave enough to say that the emperor is naked.


Montgomery, Alabama

There is a common misperception that scientists believe Einstein’s theories of relativity because he is so revered. This is an exact inversion of history: Einstein is revered because scientists became convinced that his theories are the best, most complete descriptions of physical law ever devised. And physicists were won over not just by the logical beauty of the theories but also because of startling and increasingly abundant experimental and observational verification. Even so, researchers continue to put relativity to the test and to seek alternative and more all-encompassing theories of physics. In April 2003 Discover ran a feature on João Magueijo, a researcher who is developing a theory that the speed of light can vary. Many people doubt his ideas are correct, but he has hardly been ostracized for raising them. String theory, one of the most high-profile areas of theoretical physics, is predicated on the notion that general relativity is incomplete. We tried to convey this sense of ongoing development and debate in our Einstein issue. Einstein’s theories, no matter how impressive, are certainly not the last word. Whatever replaces them, however, will have to do a better job of describing the physical world than relativity does.

The editors

Brad Lemley states in “A Tangled Life” that “as a pacifist and Zionist, [Albert Einstein] garnered a 1,427-page FBI file and was invited in 1952 to be Israel’s second president, which he declined.” Mr. Lemley does not explain why Dr. Einstein declined, and his characterization of Einstein as “Zionist” is somewhat misleading. In fact, Einstein was ardently opposed to the establishment of a Jewish state in Palestine. In his 1950 book, Out of My Later Years, he said, “I should much rather see a reasonable agreement with the Arabs on the basis of living together than the creation of a Jewish state. Apart from practical considerations, my awareness of the essential nature of Judaism resists the idea of a Jewish state with borders, an army, and a measure of temporal power no matter how modest. I am afraid of the inner damage Judaism will sustain.” Einstein’s courage in upholding this unpopular position is one more reason to honor him.


Sacramento, California

Einstein had complicated, conflicting feelings about a Jewish state, but he strongly supported the right of Jews to settle in Palestine and was widely regarded as a Zionist, if a somewhat unconventional one. As the American Museum of Natural History stated in its Einstein exhibit: “In 1919, Einstein joined the Zionist movement and supported the establishment of a Jewish homeland in the Middle East. At the same time, he stressed the need for cooperation between Jews and Arabs.” The American Institute of Physics similarly states, “Einstein had been a strong supporter of the Zionist movement since the 1920s, and was one of the main figures behind the creation of the Hebrew University atop Mount Scopus in Jerusalem.”

Brad Lemley

When I saw your September cover of Einstein with a screwdriver in one hand and a clock in the other, I immediately thought you were illustrating my favorite among Einstein’s remarks, made in yet another reference book, The Evolution of Physics, written in 1938: “Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world. In our endeavor to understand reality we are somewhat like a man trying to understand the mechanism of a closed watch. He sees the face and moving hands, even hears its ticking, but he has no means of opening the case. If he is ingenious he may form some picture of a mechanism which could be responsible for all the things he observes, but he may never be quite sure his picture is the only one which could explain his observations.” Einstein was modifying theologian William Paley’s famous “intelligent design” proof of a designer so as to argue just the opposite: that the universe is like a sealed watch, the study of which can provide no more than reasonable speculation even as to its workings. As Einstein knew, however, the joy of such speculation is what nature (or perhaps God) assuredly gives us.


King of Prussia, Pennsylvania 

I was struck by the simple drawings of Einstein as a child in “Einstein’s Gift for Simplicity” by Thomas Levenson, who asks, “If others like [Einstein] ever come along, how will we know them? By a remarkable ability to ask the right questions clearly and cleanly.” Einstein had the time as a child to ask simple questions with childlike wonder. Are today’s children being given enough free time for imagination? Are they being taught critical-thinking skills? Others like Einstein will come along, but they may never have a moment to question and think for themselves.


San Luis Obispo, California

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