Speed of light may have changed over time
Recent results (New Scientist, American Institute of Physics,…,) have indicated that fine structure constant may not be a constant, meaning that speed of light may not be a constant also and may have changed over time !
The fine-structure constant, α (dimensionless number, α = e2/4πε0hc = 1/137.03599) is the ratio of the quantum unit of electromagnetic force to the electron-based quantum unit of inertial force. This number determines the strength of the electromagnetic force. More accurately, it governs how strongly a charged particle will interact with that force (i.e. absorb or emit photons). The size of alpha determines how well atoms hold together and what types of light atoms will emit when heated up. And just as the elastic band keeping a swimsuit snug will gradually relax with time, so it is reasonable to ask whether an atoms' elasticity (or alpha) might also vary with time.
The idea that the constants might evolve over time is an old one. Paul Dirac first took these constants and combined them together to form dimensionless numbers. One example is the magnitude of the ratio of the universe's age and the time it takes light to travel across an electron, is very similar to the magnitude of the electrostatic and gravitational forces present in the hydrogen atom. (1040 compared to 1039) As the universe has of course got older, to keep this relationship constant, the values of the fundamental forces would have to change over time.
A recent investigations of numerous group of scientists test this proposition by sampling ancient light emitted by ancient atoms, and comparing them to modern light from modern atoms. In particular they looked at the relative spacing of doublets of absorption lines in the spectra of several types of atoms in distant gas clouds lying in front of still more distant quasars. The fine-structure constant is so called because it is related to the fine-structure apparent in atomic spectra. These spectral lines are due to the transitions of electrons between available energy levels.
This is one of the primary physical constants that determines the nature of the Universe. If it were a different value, electrons wouldn't orbit atomic nuclei in quite the same way, if at all.
If it were larger, you wouldn't be able to tell the difference between matter and radiation.
If it were smaller, particles might as well ignore the electromagnetic interaction.
Another reason having the fine-structure constant change over time is that it allows one to postulate the speed of light might not be constant. This would explain the flatness, horizon and monopole problems in cosmology.
Recent work has shown the universe is expanding at an ever faster rate, and there may well be a non-zero cosmological constant after all. (Einstein said his inclusion of the constant to balance the books was his "worst mistake".) There is a lot of theories where the speed of light is determined by a scalar field (the force making the cosmos expand, the cosmological constant) that couples to the gravitional effect of pressure. Changes in the speed of light convert the energy density of this field into energy. The basic upshot being when the universe was very young and hot during the radiation epoch, this prevented the scalar field dominating the universe, as the universe expands pressureless matter dominates, variations in c decrease (and therefore alpha becomes fixed and stable) and the scalar field begins to dominate, driving a faster expansion of the universe.
Well, the jury is still out on this one, there is quite simply not enough evidence to prove the fine-structure or any other fundamental constant changes with time.
If the constants can be proven to change however, it could possibly validate new theories of physics, and help confirm other hypothesis such as the existence of dark energy and quintessence; scalar fields involved in a varying cosmological constant.
Scientific American recently published an article that suggests that perhaps the fine structure constant isn't, in fact, constant. More specifically, astronomers have found observational evidence that seems to indicate that the fine structure constant was weaker by one part in a thousand around 5 billion years ago. One the one hand, this seems almost irrelevant. A difference of one part in a thousand, 5 billion years ago, doesn't affect us directly in any way. On the other hand, it makes all the difference; if one of the so-called constants of the Universe is changing, this pokes holes in all sorts of current theories in physics.
Anyhow, fact that fine structure constant was weaker in the past imply that light velocity (c = e2/4πε0hα) should have (with same: e, π, ε0 and h) a larger value !!!
Current experimental value for light velicity is cexp= 299792458 m/s and “one part in a thousand” difference is 299792458/1000 = 299792,458 m/s. Considering that fact we obtain:
299792458 m/s + 299792,458 m/s = 300092250.458 m/s
what is very, very close to ours “Maxwell’s EMW theoretical value” !!! Moreover, basic matter–radiation relationship “mechanism” is very close to our suppositions !
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