The Speed of Light, Gravity, and Why it all is what it is.

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SUMMARY

The discussion centers on the relationship between gravity and light, specifically their shared speed of 299,792,458 m/s, as established by Einstein's theory of relativity. Participants clarify that both light and gravity waves are massless, allowing them to travel at this constant speed, denoted as 'c'. The conversation also touches on the philosophical implications of why 'c' has its specific value, concluding that it is a matter of definition rather than an empirical observation. The speed of light is defined based on the distance it travels in a specific time frame, and any changes to its value would necessitate adjustments in other physical constants.

PREREQUISITES
  • Understanding of Einstein's theory of relativity
  • Familiarity with the concept of massless particles
  • Knowledge of physical constants, particularly the speed of light (c)
  • Basic grasp of quantum mechanics and particle physics
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  • Research the implications of massless particles in quantum field theory
  • Explore the concept of gravitational waves and their properties
  • Study the definitions and significance of physical constants in physics
  • Investigate the philosophical questions surrounding the nature of constants in the universe
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Physicists, students of theoretical physics, and anyone interested in the fundamental principles of the universe, particularly those exploring the nature of light and gravity.

  • #31
I should probably expand on my earlier response a bit...

Point 1. It's just as important to describe what you aren't changing as what you are. For instance, c = 1 / sqrt\left(\epsilon_0 \, \mu_0 \right). So, obviously if you're changing 'c', you can't keep both these fundamental constants the same, and you need to specify if you're changing only one, or if you're changing both, how they change. It's also not entirely clear what other physical constants you may or may not be holding constant when you "vary c", the procedure operationally isn't well defined.

Point 2. You might be making a simple "scale change", without even realizing it. For instance, suppose your change of 'c' changes the size of every atom in the Earth uniformly. Maybe what looks like a change will vanish if you define a "new meter" that has the same number of atoms laid end-end as the old meter. This is assuming you are using the old-fashioned meter stick standard rather than the SI definition, which you probably are, because if you were using the modern definition you wouldn't be talking about varying it, because the new definition just assigns 'c' a constant value.
 
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  • #33
tkav1980 said:
Bcrowell, The arXiv paper you linked me to is a bit above, ok i lied, its way above my head. I am quite a few years removed from anything besides basic math and cannot really understand it. I understand that light isn't actually a wave through a medium, I guess my attampt at an analogy failed miserably due mostly to my severe lack of knowledge. However, your explinations in this thread does clear a lot up for me.

Don't let someone elses comment like that discourage your train of thought. Absoulutley electric-magnetic wave forms could be discribed as vibrating.

A quick snap of "No, that's wrong", doesn't add any wieght. Especialy when the responding poster doesn't even read your comment correctly.

You said through a medium. He responded, "No, light is not a vibration of a medium." which may be true, but not even remotely close to what you had said, "light is a vibration through a medium".

So no, your analogy about light being a vibration through a medium is not way off. It is a "vibration" of electro-magnetic waves through a medium.
 
  • #34
pervect said:
I should probably expand on my earlier response a bit...

Point 1. It's just as important to describe what you aren't changing as what you are. For instance, c = 1 / sqrt\left(\epsilon_0 \, \mu_0 \right). So, obviously if you're changing 'c', you can't keep both these fundamental constants the same, and you need to specify if you're changing only one, or if you're changing both, how they change. It's also not entirely clear what other physical constants you may or may not be holding constant when you "vary c", the procedure operationally isn't well defined.

OK, very good. Now then ...

Why are the electric and magnetic constants for vacuum the values they are, versus different values that might lead to (say) 199792458 m/s versus 299792458 m/s ?

What is it about the nature of the very medium such as to produce the electric and magnetic constants for vacuum at the precise tune they exist today?

GrayGhost
 
  • #35
GrayGhost said:
Why are the electric and magnetic constants for vacuum the values they are, versus different values that might lead to (say) 199792458 m/s versus 299792458 m/s ?

This has been answered over and over.
 
  • #36
GrayGhost said:
What is it about the nature of the very medium such as to produce the electric and magnetic constants for vacuum at the precise tune they exist today?
Did you read the links I provided earlier?
 
  • #37
GrayGhost said:
OK, very good. Now then ...

(repeats the original question without explaining anything more about it)

GrayGhost

I'm not quite sure what the problem is. Are you perhaps not having the background to follow the discussions and papers, presented?

Some attempt to provide some clarifications as to the nature and motivation of your question (we're not kidding when we say it's ambiguous as it stands) would be helpful.

I'll assume at the moment that you're looking for something specific, but ignoring everyone's attempt to communicate and repeating the same question in the exact same words isn't going to accomplish anything useful.

In case your question is historical, I can give you a very rough overview of what generally happened, though I don't have any detailed specific knowledge.

Once upon a time the meter used to be defined by a prototype meter in Paris. After a while, using this prototype meter to define length became a problem - comparing different measurements to the prototype became the limiting factor in the reproducibility of experiments. It was time for a change.

To address this problem, a standards convention was called. I'd have to look up the exact name, but the standards they created are now known as the SI standards.

By this time, ample data had been collected on measuring the speed of light (using the old prototype meter standard), showing that it was constant, and as to what it's value was. There was still some margin of error, of course, but it was low.

The best values experimental values at the time were chosen to make the "new" definition of the meter operationally equivalent to the old, within the experimental margin of error.

Similar adjustments were made in the values of the various electrostatic and permeability constants, to make the new units equivalent to the old units up to the experimental accuracy of the time.

This solution would make the old experimental results compatible with the new ones within the existing margin of error, and allow for new, more precise, results to be obtained in the future that wouldn't be limited by the process of comparing to the standard meter.
 
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  • #38
Phyzwizz:

It was mentioned that through Einstein we learned that Gravity travels at the same speed of light. What relationship exists between Gravity and Light that makes them travel at the same speed?

Also besides the speed of light relationships between light and gravity, are there any other forces of nature that exist at this same speed? What aspect do all these things possess.

Nobody knows the exact relationship between gravity and the other three forces. The effort to understand that relationship is called "grand unification" and stumped Einstein for most of his life. Quantum gravity is one current area trying to unify theories.

What we think we know is that all the forces popped out of a "big bang" of some sort...along with space, time, mass, energy...So it seems a unified "something" underwent spongtaneious symmetery breaking...and out popped all these apparently different entities.

There is a lot we don't know...like why the mass of an electron is what it is, why the electromagnetic force has the strength it does, etc, etc. Why do we have the particles we observe? Maybe we'll get there eventually.
 
  • #39
nitsuj said:
So no, your analogy about light being a vibration through a medium is not way off. It is a "vibration" of electro-magnetic waves through a medium.

It can be a vibration of EM waves through a medium. No medium is required. In fact mediums get in the way. All that absorption and re-emission. It's like getting somewhere by running and getting in and out of one stalled taxi after another.
 
  • #40
DaleSpam said:
Did you read the links I provided earlier?

No, looking at them now, and boning up a bit.

GrayGhost
 
  • #41
pervect said:
In case your question is historical, I can give you a very rough overview of what generally happened, though I don't have any detailed specific knowledge. Once upon a time ...

Thanks anyway, but no, history has nothing to do with my question.

My question was as to why c is the precise value it is, versus a different precise value ... given (say) we use only meters and seconds. DaleSpam's reference to a post of a summary of his prior work suggests that the value of c cannot change if the fine structure constant does not change. Sounds analogous to LET theory whereby c remains 300k km/s simply because the ruler contracts to ensure such. I'm still looking at it, but I'm wondering why the fine structure constant should remain unchanged if the speed of light is assumed to change? While it does look interesting, I'm not so sure yet that the conclusion is valid in a physical sense. Mathematically, yes. I'll need to look at it further.

GrayGhost
 
  • #42
GrayGhost said:
I'm wondering why the fine structure constant should remain unchanged if the speed of light is assumed to change?
The fine structure constant also depends on other things besides just the speed of light. It is how you vary all of those terms together that determines if or how much the fine structure constant changes.
 
  • #43
danR said:
It can be a vibration of EM waves through a medium. No medium is required. In fact mediums get in the way. All that absorption and re-emission. It's like getting somewhere by running and getting in and out of one stalled taxi after another.

Ooh, great analogy -- I've got to use that one in the future!
 
  • #44
I could be wrong, but I humbly suggest that the problem with the discussion here is that we're consistently using arbitrary definitions (or, even worse, definitions derived from c) for time and length. People keep asking "Yes, but why does light have to travel at [X arbitrary length units] per [arbitrary time unit] ?", and bcrowell keeps exasperatedly answering: "Because we defined the units that way!"

So, here's my small attempt to ask a meaningful version of the question: let's define units based on unchanging physical constants that seem completely unrelated to c.

Overriding the biblical definition, let's define 1 cubit to be the average length of the sigma bond in a molecule of hydrogen at the temperature halfway between absolute zero and the temperature at which the hydrogen dissociates into plasma.

Again overriding the more common definition, let's define 1 epoch to be the time it takes a hydrogen molecule to make a complete orbit around a mass of an avogadro's number of lead atoms (pick an isotope, if you must) at a radius of an avogadro's number of cubits.

Neither of these units seem to have anything to do with c. So the question "why does light travel at X cubits per epoch, as opposed to some other value?" should, I think, be meaningful. Perhaps there is an answer, somehow relating c to the length of the sigma bond in the molecule of hydrogen, or some other relation. Perhaps there is not, in which case different values of c (in these units) would have drastically different effects. For example, there would be values of c for which the hydrogen orbiting the mass of lead might intercept its own light somewhere else along its orbit.
 
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  • #45
cephron said:
Neither of these units seem to have anything to do with c. So the question "why does light travel at X cubits per epoch, as opposed to some other value?" should, I think, be meaningful. Perhaps there is an answer, somehow relating c to the length of the sigma bond in the molecule of hydrogen, or some other relation. Perhaps there is not, in which case different values of c (in these units) would have drastically different effects. For example, there would be values of c for which the hydrogen orbiting the mass of lead might intercept its own light somewhere else along its orbit.

You've reinvented pervect's #24. As pervect pointed out in that post, the result is that you end up defining how to measure the fine structure constant, not c.
 
  • #46
c has a particular value because its a relational holistic bridge - it should not be thought of as simply the speed of light - in that example it is saying something about electromagnetics and space - in the conversion of matter it appears as the bridge between energy and mass.. it ties apparently unrelated factors to one another .. attesting to the interconnectedness of all things - changing the units from meters/sec to furlongs per fortnight doesn't change the connectedness
 
  • #47
bcrowell said:
You've reinvented pervect's #24. As pervect pointed out in that post, the result is that you end up defining how to measure the fine structure constant, not c.

You're right, I skimmed through that post a little fast because there were unit-issue posts right after it. Seems like his post answers what the OP was trying to ask.

Cool, so the fine structure constant has a relationship to c... *runs off to wikipedia*
 
  • #48
yogi said:
c has a particular value because its a relational holistic bridge - it should not be thought of as simply the speed of light - in that example it is saying something about electromagnetics and space - in the conversion of matter it appears as the bridge between energy and mass.. it ties apparently unrelated factors to one another .. attesting to the interconnectedness of all things - changing the units from meters/sec to furlongs per fortnight doesn't change the connectedness

Dude, I want some of what you're smoking.
 
  • #49
bcrowell said:
Dude, I want some of what you're smoking.

Dude Smoke This:

e = mc^2.
The fine structure constant alpha.
The Robert Dickie relationship (GM/R) = c^2
The Wienberg constant
Planck units
The black hole radius


c appears throughout physics in many different relationships - some have no direct bearing on the use of the constant in the context of light velocity
 
  • #50
danR said:
It can be a vibration of EM waves through a medium. No medium is required. In fact mediums get in the way. All that absorption and re-emission. It's like getting somewhere by running and getting in and out of one stalled taxi after another.

Interesting thought, but isn't it rather the reverse of the case? It's QED that requires you to think in terms of absorption and re-emission since fields consist only of particles. Basing EM (or weak or strong force interactions) on a continuum of some type of medium allows you to escape from the necessity of requiring absorption and re-emission. And generally problems of refraction and dispersion are enormously simpler with a continuum.
 
  • #51
yogi said:
Dude Smoke This:

e = mc^2.
The fine structure constant alpha.
The Robert Dickie relationship (GM/R) = c^2
The Wienberg constant
Planck units
The black hole radius


c appears throughout physics in many different relationships - some have no direct bearing on the use of the constant in the context of light velocity

Sure, that's fine, but I don't think that has anything to do with the things you said in #46 about "the interconnectedness of all things," etc. In appropriate units, c=1. I could then say that 1 attests to the interconnectedness of all things, and I guess that would be true, too, because 1 sure does show up in a lot of equations.
 
  • #52
Phyzwizz said:
Is it even known why light travels at the speed that it does?
You mean why does it take light to go from the Earth to the Moon about 1.26 seconds and not for instance 1 second or 2 seconds?

Nobody knows.
 
  • #53
Passionflower said:
You mean why does it take light to go from the Earth to the Moon about 1.26 seconds and not for instance 1 second or 2 seconds?

Nobody knows.

I know this thread is extremely long now, so it may be time-consuming to go back through it all, but we had a long discussion of this earlier, and as argued there, I disagree with the "nobody knows" answer.
 
  • #54
bcrowell said:
Sure, that's fine, but I don't think that has anything to do with the things you said in #46 about "the interconnectedness of all things," etc. In appropriate units, c=1. I could then say that 1 attests to the interconnectedness of all things, and I guess that would be true, too, because 1 sure does show up in a lot of equations.

You have given a good example of what is wrong with modern physics - let c = 1 and G = 1 and whatever else = 1... then try to find the physics - first you denude the factor of its units (which are often useful in finding relationships) - then compound the sin by disregarding the numerical value - so with the physics stripped and the value obliterated - you hope to find some physical meaning in these factors -

Its no wonder your blind to any significance revealed by the fact that c shows up in so many relationships - cosmological and quantum
 
  • #55
yogi said:
You have given a good example of what is wrong with modern physics - let c = 1 and G = 1 and whatever else = 1... then try to find the physics - first you denude the factor of its units (which are often useful in finding relationships) - then compound the sin by disregarding the numerical value
Neither of these assertions are correct. We use units where the numerical value is 1. E.g. Years and light years, or ~feet and nanoseconds, or Planck lengths and Planck times.

Do you think that physics may only be done in SI units?
 
  • #56
This thread is done.

Zz.
 

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