The diffence between expanding universe and light slowing?

In summary, the conversation discusses the possibility of the slowing of light over time and its potential impact on the perceived expansion of the universe. It also considers the role of the permittivity and permeability of space, but ultimately concludes that there is no evidence to support a decrease in the speed of light. The conversation also touches on the relationship between the speed of light and the alpha constant, noting that there is no noticeable change in this constant over billions of years. Overall, there is no concrete evidence to suggest that the speed of light has decreased since the Big Bang.
  • #1
Edward Solomo
72
1
I am under the impression that the slowing of light over time would make the universe appear to be expanding. Is it possible that the permittivity or permeability of space has been decreasing over time giving the illusion of an expanding universe?

Is there any way to test the differences and rule out the slowing of light. In fact, if we were to assume that the speed of light was decreasing (in a vacuum), would it even be possible to detect a decreasing speed of light, given our instruments, metrics and clocks would all slow down proportionally?
 
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  • #2
Edward Solomo said:
I am under the impression that the slowing of light over time would make the universe appear to be expanding. Is it possible that the permittivity or permeability of space has been decreasing over time giving the illusion of an expanding universe?

Is there any way to test the differences and rule out the slowing of light. In fact, if we were to assume that the speed of light was decreasing (in a vacuum), would it even be possible to detect a decreasing speed of light, given our instruments, metrics and clocks would all slow down proportionally?
The difficulty here is that the speed of light is intimately related to the relative strength of the electric and magnetic forces which hold matter together. So if you change the speed of light, you also change the structure of atoms and molecules. The structure of atoms appears to be nearly identical across the entire observable universe. There may be some tiny changes for really far-away galaxies, but those are so far using rather error-prone measurements that have yet to be independently confirmed. And regardless, the changes in the structure of atoms are so tiny that they wouldn't result in any noticeable change in the speed of light.
 
  • #3
I think he means that the specific light traveling to us through deep space is being slowed, creating an impression of expansion, rather than suggesting the maximum speed of light in general has decreased since the big bang.

I'm only making a guess, but I don't think light with a lowered top-speed would, by itself, account for the observed red shifting. Also, a decrease in the permittivity of space would most likely require an increase in its density, leading to the opposite effect of expansion which would blue shift the light.
 
  • #4
salvestrom said:
I think he means that the specific light traveling to us through deep space is being slowed, creating an impression of expansion, rather than suggesting the maximum speed of light in general has decreased since the big bang.

I'm only making a guess, but I don't think light with a lowered top-speed would, by itself, account for the observed red shifting. Also, a decrease in the permittivity of space would most likely require an increase in its density, leading to the opposite effect of expansion which would blue shift the light.
There's also the point that space is far, far too transparent to be filled with any sort of medium that would allow any sort of change in the speed of light due to a change in permittivity.
 
  • #5
I thought Light red-shifted because of a change in frequency as it passes through expanding space, not that photons slow down.
 
  • #6
Correct shifty, OP is just saying what if...
 
  • #7
The speed of light is intimately tied to the alpha [fine structure] constant, as noted by Chalnoth. The alpha constant is vital to stellar fusion and even a modest change could disrupt synthesis of elements like carbon, or even prohibit stellar fusion in the first place. We also know from spectral lines of quasars that alpha has not changed to any noticeable extent for about 10 billion years. So we have good reason to believe c has been fairly constant throughout most of the history of the universe.
 

What is the difference between an expanding universe and light slowing?

An expanding universe refers to the idea that the space between galaxies and other celestial bodies is growing larger over time. This is supported by observations that show galaxies are moving away from each other at increasing speeds. On the other hand, light slowing refers to the concept that the speed of light may not be constant and could potentially decrease over time.

How do we know that the universe is expanding?

The expansion of the universe was first proposed by astronomer Edwin Hubble in the 1920s, based on his observations of distant galaxies. Today, this theory is supported by various lines of evidence, including the redshift of light from distant objects, the cosmic microwave background radiation, and the distribution of galaxies in the universe.

What is the role of dark energy in the expansion of the universe?

Dark energy is a theoretical form of energy that is thought to be responsible for the accelerating expansion of the universe. It is believed to make up about 70% of the total mass-energy of the universe, but its exact nature and properties are still not fully understood.

How does light slowing impact our understanding of the universe?

If light slowing were to occur, it could have significant implications for our understanding of the universe. It could mean that the universe is not expanding at an accelerating rate, as currently believed, and that our measurements of distance and time in the universe may need to be revised. It could also provide clues about the nature of dark energy and the fundamental laws of physics.

Are there any experiments or observations that could confirm or disprove the idea of light slowing?

There are ongoing experiments and observations aimed at testing the idea of light slowing, such as the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Hubble Space Telescope. These experiments and observations may provide evidence for or against light slowing, but the concept is still highly debated among scientists.

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