Alpha Variation vs Cosmological Expansion: Basics Explained

In summary, The conversation discusses the differences between the effects of a variable fine-structure constant and the expansion of space on spectral measurements. The higher powers of alpha are crucial in distinguishing between the two, and spectroscopy allows for measuring both simultaneously and setting upper limits on the possible shift of the fine-structure constant. The conversation also highlights the difficulty of finding this basic information in popular science sources and thanks the expert for their help.
  • #1
fhenryco
63
5
hello,

My question will be quite naive for experts and reflects the fact that I'm new to the subject of varying the fine structure constant alpha and mainly need an introductory reference ... so if someone has a good one to advice ...thanks a lot

i just don't understand the basics: how people can distinguish pure expansion effects (that should shift absorption ray wavelengths, let say Lambda1 and Lambda2 by the same factor so also the difference Lambda1-Lambda2 by the same factor ) from time variations of the fine structure constant alpha that also modifies Lambda1-Lambda2 ?

It's because i don't understand how the modification of alpha could modify Lambda1-Lambda2 by some factor F without modifying also Lambda1 and Lambda2 individually by the same factor F , which would make it indistinguishable from a pure expansion effect...i guess (?)

thanks in advance
 
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  • #2
A variable fine-structure constant would change ##\lambda_1 / \lambda_2## (via the fine-structure, which depends on higher powers of ##\alpha##), the expansion of space does not. Spectroscopy therefore allows to measure both at the same time, and there are good upper limits on any possible shift of the fine-structure constant.
 
  • #3
mfb said:
A variable fine-structure constant would change ##\lambda_1 / \lambda_2## (via the fine-structure, which depends on higher powers of ##\alpha##), the expansion of space does not. Spectroscopy therefore allows to measure both at the same time, and there are good upper limits on any possible shift of the fine-structure constant.

Thank you very much ! i suspected something like "higher powers of alpha" involved ! this is much more clear now ! it's very difficult to find such a basic crucial information in vulgarisation sites while in scientific publications it is often buried in the formalism. so thank you again for helping me save my time.
 

1. What is the difference between alpha variation and cosmological expansion?

Alpha variation refers to changes in the fine structure constant, which is a measure of the strength of the electromagnetic force. This constant has been observed to vary over time, while cosmological expansion refers to the overall expansion of the universe, which can also affect the properties of physical constants.

2. How does alpha variation affect cosmological expansion?

The strength of the electromagnetic force, as represented by the fine structure constant, plays a role in determining the expansion rate of the universe. Therefore, changes in alpha variation can impact the overall rate of cosmological expansion.

3. What evidence do we have for alpha variation and cosmological expansion?

Observations of distant quasars and their absorption spectra have shown that the fine structure constant has varied over time. Additionally, measurements of the cosmic microwave background radiation and the expansion rate of the universe also support the existence of both alpha variation and cosmological expansion.

4. How do scientists study alpha variation and cosmological expansion?

Scientists use a variety of techniques, including spectroscopy and observations of distant objects, to measure the fine structure constant and the expansion rate of the universe. They also use mathematical models and simulations to understand the underlying processes and potential causes of these phenomena.

5. What implications does alpha variation and cosmological expansion have for our understanding of the universe?

The existence of both alpha variation and cosmological expansion challenges our current understanding of the laws of physics and the fundamental constants that govern our universe. It also has implications for theories of the early universe and potential connections between different physical phenomena.

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