I was once involved in an unsuccessful attempt to measure the variance of the fundamental constants. Thanks to this experience, I have always been interested in these measurements, so a new document describing an alternative way of detecting changes in fundamental constants caught me in the eye.
The main constants – the speed of light, Planck's constant, the charge of the electron, and so on. – are considered to be fixed in value. But there is no theory to explain the main constants, nor is there a reason for them to be permanent. They may have been different in the past and may be different in the future. Spectroscopic measurements of stars and galaxies on ever-increasing distances tell us that if the main constants are different, there is not much. We now know that the relative alpha boundary is 10-17 per year.
Which constants should we measure?
When it comes to these measurements, physicists and astronomers usually focus on alpha and his. Alpha, also known as a permanent fine structure, is a combination of electric charge, velocity of light and the constant of Planka. It describes the power of the connecting energy between negatively charged electrons and the positively charged nucleus of the atom. Therefore, it can be measured directly in the light emitted by hydrogen in distant stars.
However, alpha measurements like this have two potential problems. If excited, a lone hydrogen atom will radiate a fairly wide spectrum of light – or at least "broad" compared to the magnitude of the change we are trying to measure. In addition, the hydrogen pressure and temperature in a star expand further.
Mu is the ratio of the mass of the electron and the mass of the proton. This changes the energy of electron binding to the nucleus, but also affects how atoms in the molecule vibrate (alpha also changes this). In the cosmos where molecules do not collide very often and are rather cold, the color of light they swallow to set them to vibrate is very well defined. Therefore, potentially smaller changes can be measured. Unfortunately, our absorption measurements are simply not accurate enough to detect any changes.
New approach to his and alpha
A group of theorists notes that the merging of technological development may allow a new approach to the measurement of mu and alpha. They offer a measurement of the lengths of a block of material. The idea is alpha and its to change the length of the bonds between the atoms. If alpha and its change are, the lengths of the links. Since the length of the connection changes, it is also the volume of the material in the block (until the number of atoms changes).
The question then is how much are the lengths of the bonds changed? In order to get a score, the researchers used a combination of techniques to calculate the diatomic binding lengths of several materials (for example, the copper-copper molecule). They were compared with experimental data to ensure that the calculations are reasonably accurate. Researchers found that for diatoms, their calculations were accurate at a level of about 1%. Further calculations have shown that alpha and alpha change the length of the link between one part of ten and one part in one million. Taking into account current experimental uncertainties, the researchers believe that these relative changes are accurate to about 5%.
When weighed to solids, the accuracy drops to about 20% (because the lengths of volumetric crystal bonds are less known for many materials). The relative magnitude of changes in the length of the link due to alpha and mu changes, however, remains approximately the same or even slightly larger.
So it seems pretty sure if fundamental constants are changed, changes will occur when measuring the length of the link.
How do we measure this?
On the other hand, the development of high precision interferometers enables us to measure relative length changes with an accuracy of 10-18Using light, interferometers measure a relative change in the distance between two mirrors. This is the basis of gravitational wave observatories that have a relative sensitivity 10-22If alpha changes with the maximum speed, we should be able to see it very quickly in an interferometer with the same sensitivity as the gravitational wave observatory. Even when using a highly accurate interferometer, measurements should detect alpha changes within a reasonably short time (they are called one year).
At first I was rather skeptical about this idea. I think the biggest problem will be to prevent erosion or oxidation of the block during the measurement. Other problems such as temperature or residual gas pollution in a vacuum system are addressed in other measurement systems so they need to be resolved. However, the stability of the selected material will be critical and this is not an easy to solve problem.
Still, I hope the researchers will get him to work and create a magnificent interferometer to perform the measurements.
Physical Review Letters, 2019, DOI: 10.1103 / PhysRevLett.122.160801 (for DOI)