Physicists have a bad habit or good habit, depending on your point of view, of ignoring things they don't understand.
They always begin a problem with what they do understand and go from there.
In the case of the development of quantum mechanics they were very lucky. They were lucky because they ignored gravity but successfully developed a theory which got the right answers in agreement with experiment, despite ignoring the most fundamental force of gravity. To anyone who studies physics, this is the most perplexing development in physics.
Here is an example to illustrate what happened: Consider the hydrogen atom consisting, in the usual simplistic model, of a heavy positive electric charged object called the proton with a relatively small or light electron moving about it and having an opposite negative electric charge. The usual calculation, now performed in junior level undergraduate classes, is to use the classical version of Coulomb's Law, along with the Schroedinger Equation. Solving this equation leads to an infininte sequence of "stationary" states with discrete energy levels. There exists a lowest energy state.
When the electron is in one of these stationary states, it does not emit radiation. This is how the catastrophy of the collapse of matter with the old theory, as mentioned by Dr. Witten, is avoided. But in order to move the election from a lower to a higher energy state, it is necessary to add light or radiation of a particular wavelength or frequency.
The frequency of the radiation is proportional to the difference between the energy of any two states. The constant of proportionality is called Planck's constant, often abbreviated as h, actually the inverse of this number. This is now considered a fundamental constant of nature like the speed of light or electric charge on an electron or mass of an electron etc. One gets agreement with the measured spectral lines with this model which ignored the effects of gravity. Isn't this amazing?
So far as we know, all objects which possess the property of mass, possess the property of gravitational attraction. Gravity is only found to attract, never to repel, unlike electrical charges which can repel with likes (two positives or two negatives) or attract with opposites (a negative and a positive). Evidently gravity is a very fundamental property of matter, so why can one ignore in this problem and still get the right answer for the spectral lines?
The answer usually given by most physicists is that gravity is a small effect. They seek to prove this by using the classical formula for gravity of the universal gravitational constant times the product of the two masses divided by the square of the distance between them. This is Newton's Law of gravitation.
When one does this, one finds that this term is much smaller than the electrical term from Coulomb's law.
But there is a caveat. The equations we used implicitly contained a mysterious number or parameter called Planck's Constant which was put in externally and assumed implicitly.
Moreover, the assumed force for the gravitational effect was based on that known for large distances, but not proved for small distances inside an atom directly. There is no reason a priori, to think the same classical gravitational force law would apply inside an atom.
But as Dr.Witten said, we don't know how to quantize the gravitational laws of general relativity, so we don't know how to correctly construct the correct quantum law of gravity inside an atom, let alone at smaller distances inside a nucleus or an elementary particle or inside an electron itself. If it is ever discovered, it likely is related to the mysterious number Planck's Constant. Who knows?
Physicists are a very lucky group because they were able to develop the whole theory of quantum mechanics without knowing how to quantize gravity. They simply ignored gravity completely. I think this is an amazing story.
One might also make this observation. When I first took physics classes over 50 years ago, the author of our textbook Professor Francis W. Sears, distinguished professor of physics at MIT, whose book was used by generations of physicists and engineers and scientists world wide at the time, stated that the microscopic causes or underlying reasons for gravity were not understood then. That was about 3.5 centuries from the discoveries of Tycho Brahe, Johannes Kepler and Issac Newton on the motions of the planets about our Sun. Today we are about 4 centuries from those discoveries and, as Dr. Witten stated in the lecture, we still don't understand the microscopic causes of gravity as we understand those of electricity and magnetism a la Feynman, et al. We may never understand the microscopic causes of gravity.
But fortunately for us, we can avoid being struck by a falling brick, or fly airplanes around the world or space shuttles to outer space or construct high skyscrapers,etc., without that knowledge. We and the physicists are very lucky indeed.
Winfield J. Abbe, Ph.D., Physics
Posted by: Winfield J. Abbe |
Posted by: Winfield J. Abbe | May 22, 2011 2:40:02 PM
Witten is weird because he has a high voice?
Re: the quotation of Winfield Abbe, I don't find it surprising at all that we don't need to understand the microscopic causes of things to get things done.
Beer; pregnancy; cuisine; the idea to sew clothing tightly around us instead of draping it over us; most of the magnificent things in our culture, electronics and the microbe theory of disease aside, were invented without sophisticated scientific knowledge.
Even scientists today (let's say biochemists) probably know a bit about the foundations microscopic to their domain -- but QCD for example doesn't have any impact on the microbiological scale.
The magnificent things in our culture were invented using the sophisticated knowledge of the time...and relying on an intense desire to know. For example, the Newcomen and Watt steam engines were primitive by modern standards, but were revolutionary in terms of the demands they put on manufacturing. The desire to develop more efficient engines gave birth to the discipline of Thermodynamics (which, in turn, led to the development of Quantum Mechanics, etc.)
To say we don't need to understand microscopic reasons for physical phenomena is shortsighted. Maybe for most applications, this is true. However, better understanding means trying to come up with better models for physical processes. As an example, consider turbulent flows. Turbulence defies easy explanation because it is a multiscale phenomenon that is extremely difficult to model. It must be modeled simultaneously microscopically and macroscopically over many orders of magnitude of length. This is generally impossible given present computational methods. Yet, turbulence has many practical effects that would benefit from better understanding of its behavior on all length scales. For this reason it is one of the great unsolved problems of classical continuum mechanics.
"I couldn't tear myself
away from 3 Quarks Daily, to the point of neglecting my work. Congratulations on
this superb site."—Steven
Pinker, Johnstone Professor of Psychology, Harvard University.
"I have placed 3 Quarks Daily at the head of my list of web bookmarks."—Richard
Dawkins, Charles Simonyi Professor of the Public Understanding of Science at Oxford University.
"Just wanted you to know I’m one of many who reads and enjoys 3 Quarks....almost daily."—David Byrne, musician, former lead-singer of the Talking Heads, artist, intellectual.
Comments
Physicists have a bad habit or good habit, depending on your point of view, of ignoring things they don't understand.
They always begin a problem with what they do understand and go from there.
In the case of the development of quantum mechanics they were very lucky. They were lucky because they ignored gravity but successfully developed a theory which got the right answers in agreement with experiment, despite ignoring the most fundamental force of gravity. To anyone who studies physics, this is the most perplexing development in physics.
Here is an example to illustrate what happened: Consider the hydrogen atom consisting, in the usual simplistic model, of a heavy positive electric charged object called the proton with a relatively small or light electron moving about it and having an opposite negative electric charge. The usual calculation, now performed in junior level undergraduate classes, is to use the classical version of Coulomb's Law, along with the Schroedinger Equation. Solving this equation leads to an infininte sequence of "stationary" states with discrete energy levels. There exists a lowest energy state.
When the electron is in one of these stationary states, it does not emit radiation. This is how the catastrophy of the collapse of matter with the old theory, as mentioned by Dr. Witten, is avoided. But in order to move the election from a lower to a higher energy state, it is necessary to add light or radiation of a particular wavelength or frequency.
The frequency of the radiation is proportional to the difference between the energy of any two states. The constant of proportionality is called Planck's constant, often abbreviated as h, actually the inverse of this number. This is now considered a fundamental constant of nature like the speed of light or electric charge on an electron or mass of an electron etc. One gets agreement with the measured spectral lines with this model which ignored the effects of gravity. Isn't this amazing?
So far as we know, all objects which possess the property of mass, possess the property of gravitational attraction. Gravity is only found to attract, never to repel, unlike electrical charges which can repel with likes (two positives or two negatives) or attract with opposites (a negative and a positive). Evidently gravity is a very fundamental property of matter, so why can one ignore in this problem and still get the right answer for the spectral lines?
The answer usually given by most physicists is that gravity is a small effect. They seek to prove this by using the classical formula for gravity of the universal gravitational constant times the product of the two masses divided by the square of the distance between them. This is Newton's Law of gravitation.
When one does this, one finds that this term is much smaller than the electrical term from Coulomb's law.
But there is a caveat. The equations we used implicitly contained a mysterious number or parameter called Planck's Constant which was put in externally and assumed implicitly.
Moreover, the assumed force for the gravitational effect was based on that known for large distances, but not proved for small distances inside an atom directly. There is no reason a priori, to think the same classical gravitational force law would apply inside an atom.
But as Dr.Witten said, we don't know how to quantize the gravitational laws of general relativity, so we don't know how to correctly construct the correct quantum law of gravity inside an atom, let alone at smaller distances inside a nucleus or an elementary particle or inside an electron itself. If it is ever discovered, it likely is related to the mysterious number Planck's Constant. Who knows?
Physicists are a very lucky group because they were able to develop the whole theory of quantum mechanics without knowing how to quantize gravity. They simply ignored gravity completely. I think this is an amazing story.
One might also make this observation. When I first took physics classes over 50 years ago, the author of our textbook Professor Francis W. Sears, distinguished professor of physics at MIT, whose book was used by generations of physicists and engineers and scientists world wide at the time, stated that the microscopic causes or underlying reasons for gravity were not understood then. That was about 3.5 centuries from the discoveries of Tycho Brahe, Johannes Kepler and Issac Newton on the motions of the planets about our Sun. Today we are about 4 centuries from those discoveries and, as Dr. Witten stated in the lecture, we still don't understand the microscopic causes of gravity as we understand those of electricity and magnetism a la Feynman, et al. We may never understand the microscopic causes of gravity.
But fortunately for us, we can avoid being struck by a falling brick, or fly airplanes around the world or space shuttles to outer space or construct high skyscrapers,etc., without that knowledge. We and the physicists are very lucky indeed.
Winfield J. Abbe, Ph.D., Physics
Posted by: Winfield J. Abbe |
Posted by: Winfield J. Abbe | May 22, 2011 2:40:02 PM
Witten is weird because he has a high voice?
Re: the quotation of Winfield Abbe, I don't find it surprising at all that we don't need to understand the microscopic causes of things to get things done.
Beer; pregnancy; cuisine; the idea to sew clothing tightly around us instead of draping it over us; most of the magnificent things in our culture, electronics and the microbe theory of disease aside, were invented without sophisticated scientific knowledge.
Even scientists today (let's say biochemists) probably know a bit about the foundations microscopic to their domain -- but QCD for example doesn't have any impact on the microbiological scale.
Posted by: isomorphisms | May 11, 2012 3:37:38 PM
The magnificent things in our culture were invented using the sophisticated knowledge of the time...and relying on an intense desire to know. For example, the Newcomen and Watt steam engines were primitive by modern standards, but were revolutionary in terms of the demands they put on manufacturing. The desire to develop more efficient engines gave birth to the discipline of Thermodynamics (which, in turn, led to the development of Quantum Mechanics, etc.)
To say we don't need to understand microscopic reasons for physical phenomena is shortsighted. Maybe for most applications, this is true. However, better understanding means trying to come up with better models for physical processes. As an example, consider turbulent flows. Turbulence defies easy explanation because it is a multiscale phenomenon that is extremely difficult to model. It must be modeled simultaneously microscopically and macroscopically over many orders of magnitude of length. This is generally impossible given present computational methods. Yet, turbulence has many practical effects that would benefit from better understanding of its behavior on all length scales. For this reason it is one of the great unsolved problems of classical continuum mechanics.
Posted by: Bill | May 11, 2012 5:03:45 PM
Post a comment