# Decay in c caused by Universe expansion

• B
I'm currently writing a research paper about the speed of light. I have researched universe expansion, specifically, the quantised redshift spectral index fluctuations of distant galaxies and other structures over time, however, I need to suggest why universe expansion possibly causes a recorded decay in c.

Any help would be very much appreciated!

Kind regards :)

weirdoguy and PeroK

Drakkith
Staff Emeritus
however, I need to suggest why universe expansion possibly causes a recorded decay in c.

What do you mean? Expansion doesn't cause a drop in the speed of light.

pervect
Staff Emeritus
In the SI system of units, "c" is defined as a constant in order to determine the length of the meter.

 The meter, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum c to be 299 792 458 when expressed in the unit m s-1, where the second is defined in terms of ΔνCs.

In general, variation of fundamental constants with units has been criticized as being ambiguous, by authors such as Duff.

There are some references to Duff's arguments in Wiki's article on time variation of fundamental constants, https://en.wikipedia.org/w/index.php?title=Time-variation_of_fundamental_constants&oldid=960689427

wiki said:
It is problematic to discuss the proposed rate of change (or lack thereof) of a single dimensional physical constant in isolation. The reason for this is that the choice of a system of units may arbitrarily select any physical constant as its basis, making the question of which constant is undergoing change an artefact of the choice of units.[5][6][7]

Perhaps you mean to suggest that the fine structure constant, which is dimensoness, varies? There are quite a number of modern papers on that. That said, I don't know enough about your scenario to see why it should vary in your particular case - if you're going to write a paper on it, you should probaly have some idea about why you, or whomever suggested the idea, thinks it should vary.

Dale
Mentor
2020 Award
I need to suggest why universe expansion possibly causes a recorded decay in c.
Any decay in c would be an artifact of your choice of units. In modern SI units the impossibility of a decay in c is tautological.

Instead, you should be looking for evidence of changes in the fine structure constant. However, to my knowledge the best evidence to date does not support such a claim: https://physics.aps.org/articles/v7/117

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Staff Emeritus
Can we please stop saying that people who are asking about a change in c vs. time "really mean" a change in the fine structure constant? First, these are not the same thing, so implying they are is just confusing. Second, we can't read minds, so we can't tell what someone is really thinking about. And third, while c is defined as a constant in the present system of units, one can ask questions that are much closer to the OP's than the fine structure constant, such as "I measured this object to be x meters long yesterday. How long is it today?"

weirdoguy
ZapperZ
Staff Emeritus
I'm currently writing a research paper about the speed of light. I have researched universe expansion, specifically, the quantised redshift spectral index fluctuations of distant galaxies and other structures over time, however, I need to suggest why universe expansion possibly causes a recorded decay in c.

You need to be extremely careful with the words you use here. "decay in c" implies that the value of the speed of light is "decaying", i.e. getting smaller. This is definitely wrong!

The redshift that is observed is NOT due to a "decay in c".. because c remains a constant. It is a result of the "stretching" of the wavelength of light due to the cosmological expansion.

Zz.

Mister T
Gold Member
I need to suggest why universe expansion possibly causes a recorded decay in c.
Why do you need to suggest such a thing?

pervect
Staff Emeritus
Can we please stop saying that people who are asking about a change in c vs. time "really mean" a change in the fine structure constant? First, these are not the same thing, so implying they are is just confusing. Second, we can't read minds, so we can't tell what someone is really thinking about. And third, while c is defined as a constant in the present system of units, one can ask questions that are much closer to the OP's than the fine structure constant, such as "I measured this object to be x meters long yesterday. How long is it today?"

I don't think we can really avoid that, not if we wish to communicate. Though we can certainly make it a suggestion, rather than a statement. For instance, we can say "perhaps you meant to suggest that the fine structure constant varies....." Which is what I did in my reply.

That way, if the person meant to say something that isn't equivalent to the fine structure constant changing, they can say so. And we can respond approprirately.

Also note that if we hold the charge of the electron e, the permitivitty of free space ##\epsilon_0##, and Planck's reduced constant ##\hbar## constant, then a change in the speed of light c implies a change in the dimensionless fine structure constant. In a discussion about fundamental constants varying, it is unfortunately not clear that one is holding these other constants fixed when talking about "the speed of light" changing or decaying.

Dale
Hi all :)
Sorry, it's my first time writing on one of these forums.
The assignment is my final year 12 physics research investigation about ambiguous physics claims. Firstly, I got to researching the constancy of the velocity of light, and if there is a possibility that c wasn't always the value it is today. The task is how the investigated research and data is used to suggest the possibility of c-variation.
So I began researching anything to do with c variation.

Firstly, I found this passage:
If the velocity of light has an invariable speed limit, then that means that since the Big Bang it could only have travelled approximately 13.7 billion light-years, the approximate time elapsed since the Big Bang. The distance that light can travel since the Big Bang creates a limit of the visible universe, which is about 47 billion light-years, and although light has only been travelling for 13.7 billion years, this number takes into account the expansion of space that is occurring as light is travelling. However, through methods measuring the cosmic microwave background (the edge of the universe), light has been recorded to reach distances far higher than this value, meaning the universe is too large to have allowed light to travel from one end of the other during its existence with the currently accepted value.

Secondly, many papers attempting to deal with c-variation always referred to the expansion of the universe, so my research in the redshift began. The data and graphs relating to the red-shift of galaxies and other objects fit the task quite well, as data analysis and calculation are a massive part of the criteria.

Further, many of the papers referred to a 'phase-shift' of light early on when the universe initially started expanding, this lead me to a deep hole of uniformity, Hubble's Law, Doppler effect etc.

I don't necessarily believe that the velocity of light is decaying, as a physics student, I have never been taught to doubt the constants used. However, for the purpose of this task, I need to suggest a possible reason why a variation in the velocity of light could occur, and why an expanding universe could influence this.

Thank you very much for your help, from my research I gather that the ambiguity of this concept isn't exactly widely appreciated.

Kindest regards :)

Drakkith
Staff Emeritus
If the velocity of light has an invariable speed limit, then that means that since the Big Bang it could only have travelled approximately 13.7 billion light-years, the approximate time elapsed since the Big Bang. The distance that light can travel since the Big Bang creates a limit of the visible universe, which is about 47 billion light-years, and although light has only been travelling for 13.7 billion years, this number takes into account the expansion of space that is occurring as light is travelling. However, through methods measuring the cosmic microwave background (the edge of the universe), light has been recorded to reach distances far higher than this value, meaning the universe is too large to have allowed light to travel from one end of the other during its existence with the currently accepted value.

I'm not sure where you got your information from, but it is almost certainly incorrect. The CMB is observed to come from a region of space called the surface of last scattering that is roughly 45.7 billion light-years distant, if we account for the expansion of the universe. Since the CMB represents the most extreme distance that EM radiation is able to travel, there is no chance that any light would have been able to travel further than this distance.

I don't necessarily believe that the velocity of light is decaying, as a physics student, I have never been taught to doubt the constants used. However, for the purpose of this task, I need to suggest a possible reason why a variation in the velocity of light could occur, and why an expanding universe could influence this.

That's going to be tough, as the tired light hypothesis, which is the name of what you are researching, has been thoroughly contradicted by evidence as far as I know.

Do you think it would be worth looking into aspects of time dilation? Eg as the universe expands, time runs slower (and the time dilation slowly becomes more pronounced), this is looking into more general relativity. I could then compare supernovae, and how their luminosities decrease as a function of time. Or just compare lightcurves at different redshifts. Do you think I could go on to explain that if time is, in fact, slowing at a relative rate, then the speed of light could slow down?

I've been doing a heavy amount of research on this recently, and feel like I'm just going in circles.

Thank you very much for your help so far, it has been extremely useful :)

PeroK
Homework Helper
Gold Member
2020 Award
Do you think it would be worth looking into aspects of time dilation? Eg as the universe expands, time runs slower (and the time dilation slowly becomes more pronounced), this is looking into more general relativity. I could then compare supernovae, and how their luminosities decrease as a function of time. Or just compare lightcurves at different redshifts. Do you think I could go on to explain that if time is, in fact, slowing at a relative rate, then the speed of light could slow down?

I've been doing a heavy amount of research on this recently, and feel like I'm just going in circles.

Thank you very much for your help so far, it has been extremely useful :)
This subject is tough to research without the necessary background in relativity and cosmology. As @Drakkith says, there is a well-known and thoroughly debunked "tired light" theory. Unfortunately, a number of pseudo-scientists still promote this, so you will find a lot online about it - including material that looks like genuine scientific material from respected sources.

The debunking of the tired light theory ultimately rests on the specific cosmological data, which fits a universal expansion, but not tired light.

As far as mainstream science is concerned the speed of light is now a defined constant and, along with the definition of the second, defines the metre. Also, it's a postulate of relativity that light travels at an invariant speed ##c##. Any analysis to the contrary must, in 2020, be an analysis of theories at odds with mainstream relativity and cosmology.

Given that we at PF focus on mainstream science, we probably can't help you much, I'm sorry to say. Also, as @Dale said, any revision of mainstream theories would not result in a change to the speed of light, which is simply a conversion factor between units. Instead, it would focus on the fine structure constant, which is a dimensionless constant.

In summary, I think you need to be careful with this task, as you could easily be led astray into controversial preudo-science, some of which (I'm afraid) you've already picked up.

lomidrevo
Dale
Mentor
2020 Award
one can ask questions that are much closer to the OP's than the fine structure constant, such as "I measured this object to be x meters long yesterday. How long is it today?"
I think that would also reflect a change in the fine structure constant. The size of an object is based on the diameter of the atoms and molecules, and the Bohr radius depends on the fine structure constant.

pervect
jbriggs444
Homework Helper
time runs slower
What would that even mean? Suppose that today, right now, "time is running slower". How could we tell?

We might look down at our wristwatch expecting that it will appear to be ticking more slowly. But our heartbeat, the impulses in our neurons, the pace of our daily workout would also have slowed. We would look at the wristwatch with our slowed perception and see nothing amiss.

Perhaps we could look at signals generated yesterday and received today. Since we are now running slow (and yesterday less so) we would naively expect such signals to look abnormally fast. But we actually see the opposite -- red shift, not blue.

ZapperZ
Staff Emeritus
Do you think it would be worth looking into aspects of time dilation? Eg as the universe expands, time runs slower (and the time dilation slowly becomes more pronounced), this is looking into more general relativity.

You can't have it both ways!

The concept of time dilation comes directly from Special Relativity, and in there, it is explicitly stated as a starting point that the speed of light is a constant in all inertial reference frame! So using that as a postulate, you get many consequences, and one of them is the effect of time dilation.

So what you are trying to do is to use time dilation to show that c is "decaying"? Don't you see the absurdity in that?

BTW, why do you think this is an issue that qualifies as an "ambiguous topic" for your research project? Ambiguous to whom?

Zz.

Nugatory
Mentor
The assignment is my final year 12 physics research investigation about ambiguous physics claims.
If you really mean “ambiguous”, then the various forms of the claim that the speed of light is changing are a pretty good example - restating such a claim as an unambiguous and falsifiable proposition free of ambiguity is often both difficult and illuminating. (Yes, I did that on purpose)

PeterDonis
Mentor
2020 Award
I found this passage

phinds
Gold Member
Do you think it would be worth looking into aspects of time dilation? Eg as the universe expands, time runs slower (and the time dilation slowly becomes more pronounced) ...
You misunderstand time dilation. Time does NOT "run slower" in something you see as time dilated, you just SEE it as running slower. In the reference frame of the object the time runs perfectly normally, one second per second just as it does for you. From the reference frame of the object, YOUR time is "running slower".

pervect
Staff Emeritus
I think that would also reflect a change in the fine structure constant. The size of an object is based on the diameter of the atoms and molecules, and the Bohr radius depends on the fine structure constant.

I concur. One of the physical interpretations of the fine structure constant is :

wiki said:
The ratio of the velocity of the electron in the first circular orbit of the Bohr model of the atom, which is 1/4πε0 e2/ħ, to the speed of light in vacuum, c.

So, going with the modern system of units where c is defined as constant, a change in the fine structure constant would imply that the velocity of the electron in the Bohr model of the atom was varying. One needs to further assume that the period of the orbit remains constant to conclude that the circumference of the orbit, and by implication the length of the bar, must be shrinking, however. This is equivalent to assuming that the SI second is not "varying".

Because it is independent of the details of unit choices, talking about the dimensionless fine structure constant avoids a lot of interpretational issues. Since there are papers in the literature discussing the issue (see in particular Duff, who is strongly critical about any claims about a dimensionfull constant varying with time), and other papers talking about experimental limits on variation of the fine structure constant, I'd really suggest strongly that any analysis of "the speed of light" changing have at least a mention of what happens to the fine structure constant.

Dale
Hi all,

{unacceptable reference deleted}

My teacher told me to analyse and evaluate the graphs from the paper to meet the research investigations criteria, but I want to find out why a 'slowly expanding universe' has a 'speed of light that falls overtime'. It covers concepts such as Hubble's Law, VSL, dark energy and so on, but has there been an explanation as to why some people have previously hypothesised this? Does the literature mean that the two apects (universe expansion and SoL) are separate from each other, and not one is a causation of the other?

Further, the claim that I was given is that 'c is not the speed limit of the universe'. Does anyone know another branch/ concept of physics that could support this claim using data and graphs? As you can tell I've led myself down some pretty controversial (and frankly incorrect) holes, and I'd greatly and warmly appreciate if anyone could give me any possible ideas.

Thank you for your help again :)

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Dale
Mentor
2020 Award
Hi all,
...
Unfortunately SCIRP is a known predatory publisher.

https://web.archive.org/web/20170111172306/https://scholarlyoa.com/publishers/

Such publishers are very unethical and doubly deceptive. They deceive unwary or new researchers into believing that they are publishing in a peer reviewed journal and they deceive unwary or new readers into believing that they are reading a peer reviewed paper. The truth is that they publish anything as long as the author pays their fee. The papers found in such journals are no more credible than blogs.

The paper you cited is so bad that we will not discuss it in detail. From the first sentence it is opposed to the scientific literature

Further, the claim that I was given is that 'c is not the speed limit of the universe'. Does anyone know another branch/ concept of physics that could support this claim using data and graphs?
The claim is false and is not supported in the professional scientific literature.

Here is a decent online textbook explaining what I think is the most convincing aspect of c as the universal speed limit. See especially figure 2.

https://opentextbc.ca/universityphysicsv3openstax/chapter/relativistic-energy/

Here is a page that summarizes the experimental evidence. It references many original scientific papers with the original data and graphs.

http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

You will want to pay particular attention to section 6.

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PeroK
ZapperZ
Staff Emeritus
Hi all,

...

My teacher told me to analyse and evaluate the graphs from the paper to meet the research investigations criteria, but I want to find out why a 'slowly expanding universe' has a 'speed of light that falls overtime'. It covers concepts such as Hubble's Law, VSL, dark energy and so on, but has there been an explanation as to why some people have previously hypothesised this? Does the literature mean that the two apects (universe expansion and SoL) are separate from each other, and not one is a causation of the other?

Further, the claim that I was given is that 'c is not the speed limit of the universe'. Does anyone know another branch/ concept of physics that could support this claim using data and graphs? As you can tell I've led myself down some pretty controversial (and frankly incorrect) holes, and I'd greatly and warmly appreciate if anyone could give me any possible ideas.

Thank you for your help again :)

I can find PAPERS in more prestigious and important journals that will contradict this guy's claim:

Couldn't you show that to your teacher to show that the paper you were given isn't valid, or at the very least, dubious?

I can't believe that this is the type of assignment that you are given at your level.

Zz.

vanhees71, Dale, PeroK and 1 other person
jedishrfu
Mentor
It seems this is a good time to close this thread since the OP's questions have been answered on physics and on a dubious peer-reviewed article from a questionable source.

Thank you all for contributing here with special thanks to @Dale for pointing out:
There are ethical vs unethical publishing practices. The generally poor quality [of SCIRP] is a symptom of the unethical practices of predatory publishers.

Thank you,

Jedi

vanhees71