Guest post: Louise Riofrio, “Fundamental Values” October 14, 2007Posted by dorigo in astronomy, Blogroll, internet, physics, science.
Louise Riofrio is a researcher in Cosmology. She questions the validity of the standard cosmological model, and she owns a site, http://riofriospacetime.blogspot.com, where she discusses cutting-edge news on the matter, as well as on astrophysics and astronautics. So let us hear it from her.
As scientists we spend much of our time seeking values. These could be the height of plants or the masses of subatomic particles. We have built measuring devices from rulers to giant telescopes and accelerators. Experimental results are then catalogued to end up in books or databases. A large portion of our scientific knowledge is based on fundamental values like the speed of light or the gravitational constant. By measuring the Universe, scientists hope to find what is constant in nature.
Every basic astronomy textbook will list the distance to the Moon. Thanks to laser reflectors left by astronauts, we know that value to the meter. Numbers in the back of the book will be accurate for many centuries, but are not constant. Geologists have known for decades that the Moon is slowly drifting away. Those reflectors on the Moon say that it is receding even faster than geology predicts. If an astronaut returned after a million years she would find the Moon many kilometers more distant from Earth. Though the Moon’s distance is fixed in the astronomy book, it is not constant.
Some values have been nicknamed “constants” even when they are not. The Solar Constant is the amount of sunlight falling per square meter of Earth’s surface when the Sun is directly overhead. This value varies slightly as Earth travels in its elliptical orbit, and to an unknown degree because of variations in the solar interior. These variations are important for study of Earth’s climate, because nothing affects global warming more than the Sun. Though the Solar Constant has allowed life to evolve on Earth’s surface for billions of years, standard models say that when Earth was forming the Sun was only about 75% as bright. Whether the Sun’s luminosity is constant has been an open question.
For much of human history Earth’s location was considered constant. The Sun, planets and stars were seen as circling Earth in epicycles. This can be a reasonable stipulation–for navigating on the planet or even observing stars it is convenient to treat Earth as fixed. Galileo’s discovery of Jupiter’s moons was evidence of objects circling another body. Galileo suffered in part because he lacked a mechanism for holding the planets in place. Defying the complicated mathematics of epicycles, Galileo showed that Earth was not fixed.
Isaac Newton’s gravity provided a mechanism for orbits and a constant. Newton concluded that gravitational force between two objects is dependent upon the product of their masses divided by the square of their distance. To give an answer with the dimensions of force, Newton introduced his gravitational constant G. Though many theories have been proposed about G, at present most measurements say that Newton is truly constant.
The nature of light has long been a subject of wonder. Scientists from Aristotle to Kepler believed that light traveled instantaneously. Galileo tried to time the light of lanterns from distant hilltops, but lacked a good clock. A finite speed of light was finally found using Galileo’s satellites. By timing when the moons appeared to pass in and out of Jupiter’s shadow, Ole Roemer made the first measurements of c. As measurements have become more accurate, many scientists have wondered whether c is constant. While Newton’s Constant and even the “Solar Constant” are part of our vocabulary, a “speed of light constant” is not.
To explain atomic energy levels, a conservative physicist named Max Planck was forced to introduce his own constant. The product hc was key to Planck’s solving the ultraviolet catastrophe of blackbody radiation. Planck called his introduction of h an “act of desperation.” The product hc also appears in Chandrasekhar’s Limit and the fine-structure constant ?. Nature’s subtleties include energies which are constant but whose component values are not. Albert Einstein is quoted as saying, “God is subtle but he is not malicious.”
Though his Relativity incorporated the speed of light, Einstein himself would not state that it was fixed in time. He wrote that fixed c was “neither a supposition nor a hypothesis about the physical nature of light but a stipulation which I can make at my own free discretion.” Though he was careful to include c in his calculations, after Einstein had passed on a branch of Relativity arose that removed the value c.
Einstein introduced his own constant, which he later called his greatest blunder. He realised that enough mass would curve the Universe into a sphere of four dimensions. Such a spherical space would collapse unless it were expanding or supported by a repulsive “cosmological constant.” Edwin Hubble’s observations convinced Einstein to withdraw this hypothetical constant.
Hubble found that recession velocity of a galaxy divided by its distance is constant, indicating an expanding Universe. From the beginning astronomers knew that “Hubble’s Constant” was not constant. It would change over time depending upon whether the Universe’s expansion slowed. Finding the value of this constant was a principle scientific goal of the Hubble Space Telescope.
Though the power source of Type Ia supernovae is not completely understood, astronomers consider their luminosity to be constant. Distant supernovae appear dimmer than expected, making the Hubble expansion appear to accelerate. At first this was seen as return of the cosmological constant. Soon it was realised that a repulsive force would not be constant, but would evolve as a form of “dark energy.” Speculation about this hypothetical energy has expanded to include modified gravity and other additions to Relativity.
Inferences of cosmic acceleration depend on many other values being constant, including luminosity of supernovae. Many values have changed in the billions of years since distant stars exploded. The metal content of ancient stars is known to have been much less than today. Since we cannot time-travel into the past, it is difficult to determine if fundamental values are constant.
In our brief history of measuring the Universe, many values that appeared to be constant have been found to change. We may find that the only constant is change. There is a constant in science, which is the continuing quest for knowledge. New ideas and observations have been introduced, considered, tested and if worthy added to our books. In science, the true fundamental value is a search for truth.