# 186.000 miles a second. Why?

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Light has been measured to move at about 186,000 miles a second. In Einstein's special theory of relativity he explained what would happen if that ultimate speed limit was approached. His theory was proven correct when it was determined that there was an absolute differential between the time registered on atomic clocks on Earth versus the atomic clocks on vehicles orbiting our planet. My question is, does anyone have a theory as to why light maxes out at about 186.000 miles a second. I mean why specifically that speed? I am a part of a think tank that is of just recent trying to answer this very question. Our team is working on the idea that this speed limit has something to do with the speed of how fast the universe itself is moving. Has that question been answered? Does anyone know the speed of how fast the universe is moving?

Edited by Mitch Bass

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Can you define what you mean by 'how fast the universe is moving'?

Are you talking about individual components of the universe? If so, which components and moving relative to what?

Are you talking about the universe as a whole? If so, I don't believe there is anything the universe can be moving 'relative to', and so don't know how you could measure its velocity.

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Asking why the speed of light is 186,000 miles/second is like asking why mass creates gravity. We don't really know, it seems to be an intrinsic property of the universe, like the Planck constant, the mass of a proton, or Newton's constant of gravitation. It may be that these values were set when the universe was created because this combination of values is one of the combinations (or the only combination) that yields a stable universe with solid matter that doesn't collapse in on itself seconds after forming.

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The universe isn't moving. It's expanding, but that is quite different. Since the rate of expansion is given as distance per unit of time per unit of distance, it's not really comparable with a measure of speed.

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Part of the reason for it is our choice of the length of a mile and of a second. Beyond that, it's an unknown, as Greg H. said. Some values of the universe are empirically determined and some have to be defined. Nobody has been able to derive it from first principles.

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I am confused. I thought that it was embedded in Maxwell's equations, specifically this one c 2 = 1/(ε0μ0).

Where ε0 is vaccum permittivity and μ0 is vacuum permeability. c, of course, is the speed of light. I can understand that we may not know why μ0 and ε0 have the values they do, but given those values isn't c automatically determined?

Keep in mind I am a simple minded geologist and it took me years of backbreaking work to get this far, so go gentle with me.

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Part of the reason for it is our choice of the length of a mile and of a second. Beyond that, it's an unknown, as Greg H. said. Some values of the universe are empirically determined and some have to be defined. Nobody has been able to derive it from first principles.

I guess it depends on what 'first principles' you use as a starting point. As Ophilite pointed out, it is an easily derived consequence of the Maxwell equations for the relations of the electric and magnetic fields. It turns out that the speed term in the wave equation derived from the Maxwell equation is dependent on both the permitivity and permiability of free space.

And its value just so happens to be c.

So, the 'why' here is answered by two properties of space. But are those properties fundamental, or is there another turtle down? The answer to that, we don't yet know, as far as I can tell.

I am confused. I thought that it was embedded in Maxwell's equations, specifically this one c 2 = 1/(ε0μ0).

Where ε0 is vaccum permittivity and μ0 is vacuum permeability. c, of course, is the speed of light. I can understand that we may not know why μ0 and ε0 have the values they do, but given those values isn't c automatically determined?

Keep in mind I am a simple minded geologist and it took me years of backbreaking work to get this far, so go gentle with me.

Indeed.

$\bigtriangledown\cdot{E}=\frac{\rho}{\epsilon_0}$

$\bigtriangledown\times{E}=-\frac{\partial{B}}{\partial{t}}$

$\bigtriangledown\cdot{B}=0$

$\bigtriangledown\times{B}={\mu_0}{\epsilon_0}\frac{\partial{E}}{\partial{t}}$

These are the equations that describe how electric fields and magnetic fields interact. Think of $\bigtriangledown\cdot$ as describing whether or not a vector field is pointing inward or outward, think of $\bigtriangledown\times$ as describing which in which direction and how tightly a vector field is curled, and think of $\frac{\partial}{\partial{t}}$ as being the rate of change of the vector field. A vector field is a space where there is a vector at every point. A vector is a mathematical object with both a number and a direction. Having no charges to worry about with light, we can set the charge density equal to zero which makes the equations:

$\bigtriangledown\cdot{E}=0$

$\bigtriangledown\times{E}=-\frac{\partial{B}}{\partial{t}}$

$\bigtriangledown\cdot{B}=0$

$\bigtriangledown\times{B}={\mu_0}{\epsilon_0}\frac{\partial{E}}{\partial{t}}$

Now, let's take the curl of the curl equations and see what happens.

$\bigtriangledown\times\bigtriangledown\times{E}=-\frac{\partial}{\partial{t}}\bigtriangledown\times{B}=-{\mu_0}{\epsilon_0}\frac{\partial^2{E}}{\partial{t^2}}$

$\bigtriangledown\times\bigtriangledown\times{B}={\mu_0}{\epsilon_0}\frac{\partial}{\partial{t}}\bigtriangledown\times{E}=-{\mu_0}{\epsilon_0}\frac{\partial^2{B}}{\partial{t^2}}$

Since $\bigtriangledown\times(\bigtriangledown\times{V})=\bigtriangledown(\bigtriangledown\cdot{V})-\bigtriangledown^2{V}$ for any vector field V, we can write:

$-{\mu_0}{\epsilon_0}\frac{\partial^2{E}}{\partial{t^2}}=-\bigtriangledown^2{E}$

$-{\mu_0}{\epsilon_0}\frac{\partial^2{B}}{\partial{t^2}}=-\bigtriangledown^2{B}$

which we rearrange to get:

$\frac{\partial^2{E}}{\partial{t^2}}-\frac{1}{{\mu_0}{\epsilon_0}}\cdot\bigtriangledown^2{E}=0$

$\frac{\partial^2{B}}{\partial{t^2}}-\frac{1}{{\mu_0}{\epsilon_0}}\cdot\bigtriangledown^2{B}=0$

which are the electromagnetic wave equations. The speed term is $\frac{1}{\sqrt{{\mu_0}{\epsilon_0}}}$.

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I am confused. I thought that it was embedded in Maxwell's equations, specifically this one c 2 = 1/(ε0μ0).

I guess it depends on what 'first principles' you use as a starting point. As Ophilite pointed out, it is an easily derived consequence of the Maxwell equations for the relations of the electric and magnetic fields.

The question was "why specifically that speed?" The values of the constants are experimentally determined; there's nothing in the theory that sets the values.

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Those values of epsilon and mu, along with the fact that in free space the electric wave is in phase with the magnetic wave also lead to the impedance of free space being 377 ohms.

We could equally well ask why this value.

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If you flip things around, you can consider it as your "zero" in terms of time experienced.

|--------------------|----

c us

To my own thinking it feels less arbitrary that way.

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The question was "why specifically that speed?" The values of the constants are experimentally determined; there's nothing in the theory that sets the values.

IIRC one of them is defined by the definition of the amp. The other is experimentally measured (Or, it was until they redefined time in terms of the speed of light.).

However, that's still a reasonable explanation.

The speed of waves traveling along a spring depends on the tension and the mass per unit length of the string.

In a vaguely similar way, the speed of em waves travelling through a medium depends on ε and μ.

I don't need to explain why the string has a particular tension and lineal density to say why the wave velocity is the value it is.

I can just say it's sqrt (t.(m/l))

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The question was "why specifically that speed?" The values of the constants are experimentally determined; there's nothing in the theory that sets the values.

Which is why I said:

But are those properties fundamental, or is there another turtle down? The answer to that, we don't yet know, as far as I can tell.

At some point, you run into brute facts and there is no explanation other than "That's the way it is". The speed of light is not a brute fact. If space behaved differently with electromagnetic fields, c would be different and we could calculate it with these experimental values.

So, the question of "Why c?" does have an answer. The questions of "Why $\mu_0$?" and "Why $\epsilon_0$?" may or may not have their own answers. They are, though, distinct from the question of "Why c?".

At some point, there is a bottom turtle. Are permitivity and permeability of free space that bottom turtle? I don't know, but that doesn't mean it doesn't answer the question.

However, that's still a reasonable explanation.

The speed of waves traveling along a spring depends on the tension and the mass per unit length of the string.

In a vaguely similar way, the speed of em waves travelling through a medium depends on ε and μ.

I don't need to explain why the string has a particular tension and lineal density to say why the wave velocity is the value it is.

Indeed, you don't need to reach the bottom turtle (or even know where it is) to answer a question.

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Which is why I said:

At some point, you run into brute facts and there is no explanation other than "That's the way it is". The speed of light is not a brute fact. If space behaved differently with electromagnetic fields, c would be different and we could calculate it with these experimental values.

So, the question of "Why c?" does have an answer. The questions of "Why $\mu_0$?" and "Why $\epsilon_0$?" may or may not have their own answers. They are, though, distinct from the question of "Why c?".

At some point, there is a bottom turtle. Are permitivity and permeability of free space that bottom turtle? I don't know, but that doesn't mean it doesn't answer the question.

I think you're answering a different question, and in a sense your position is backward, based on how we've chosen to do things. We define c, and the values of $\mu_0$ and $\epsilon_0$ depend on it rather than the other way around. But that's arbitrary. The point is that none of the values ultimately come from theory, they come from experiment.

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I think you're answering a different question, and in a sense your position is backward, based on how we've chosen to do things. We define c, and the values of $\mu_0$ and $\epsilon_0$ depend on it rather than the other way around.

Now, that's true. But it wasn't always. As you go on to state, the values for $\mu_0$ and $\epsilon_0$ were originally experimentally determined values, not defined values. It is the very fact that the speed of light is determined by these properties of space and the fact that the speed of light in a vacuum is constant that allow for us to go in after the fact and define them in terms of c.

The point is that none of the values ultimately come from theory, they come from experiment.

Indeed. They are the brute facts (maybe brute, maybe turn out to have another turtle beneath them about which we don't yet know) which explain why the speed of light in a value is the way it is. The speed of propagation in the electromagnetic field is explained by how well empty space can hold a field. What numbers we assign to these properties are of no importance, as we are talking about the properties themselves.

My question is, does anyone have a theory as to why light maxes out at about 186.000 miles a second. I mean why specifically that speed?

As I said above, light goes as fast as it does in empty space because of how well empty space holds an electromagnetic field. Whether or not there is a "Why?" for how well empty space holds an electromagnetic field is unknown.

Our team is working on the idea that this speed limit has something to do with the speed of how fast the universe itself is moving. Has that question been answered? Does anyone know the speed of how fast the universe is moving?

That question is, to put it bluntly, meaningless. It's like asking what color eπ is. The universe simply isn't something that it is meaningful to talk about moving.

Motion is defined in terms of time and space. Motion is, after all, an object's rate of change of distance traveled with respect to duration. So, motion is a relational quantity. So, however, are space and time. One can't answer "How far from Chicago?", but one can answer "How far from Chicago is New York?". To answer questions about distance, you need at least two points in space to compare. The same thing applies with time. But the universe is all of space and time. So, it has all of the places and times contained within it. It can't go from one place to another, because all places are within it. And it can't go from one time to another, because all times are within it.

The motion of the universe is undefined.

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The universe isn't moving. It's expanding, but that is quite different. Since the rate of expansion is given as distance per unit of time per unit of distance, it's not really comparable with a measure of speed.

I wish I had checked in earlier after posting my initial response. There is a lot for me to react to in terms of what has been written since I started this post. I will start with the the above quote about the "universe isn't moving".

I did some prelliminary research in response to the words of Delta1212 and found the following:

"our whole solar system orbits around the center of the Milky Way Galaxy. We are moving at an average velocity of 828,000 km/hr."-Does the Sun move around the Milky Way??

Delta1212 and/or to whomever else I would appreciatevely get a response from, I now ask this: How is it that our solar system moving at 828,000 km/hr around the Milky Way is as Delta1212 writes "not really comparable with a measure of speed" because "the universe isn't moving. It's expanding."? Delta1212 writes "since the rate of expansion is given as distace per unit of time per unit of distance"…within these words is there an answer I am not comprehending.

I am just now guessing that Delta1212 would respond to my response to his response in a way which would suggest that just because our Soloar Sysem is moving doesn't mean the univserse is moving because our Solar Sytem is not the universe.

Darn, even as I am editng the first response to my intial post it is has been indicated that someone has added to this post….maybe to what I wrote but wanted to edit. I should check what has been written before I delve further into this subject matter/

Edited by Mitch Bass
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Movement within the universe is not the same as the universe itself moving.

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ACG52 wrote what he wrote

Movement within the universe is not the same as the universe itself moving.

before I finished reediting my post. which ended up incuding me writing

I am just now guessing that Delta1212 would respond to my response to his response in a way which would suggest that just because our Soloar Sysem is moving doesn't mean the univserse is moving because our Solar Sytem is not the universe.

However, could it be that the movement within the universe is a result of the movement of the universe?

Or as Delta1212 wrote

The universe isn't moving. It's expanding, but that is quite different. Since the rate of expansion is given as distance per unit of time per unit of distance, it's not really comparable with a measure of speed.

Is the movement within the universe, the velocities at which things travel around each other, a result of what Delta1212 is saying is not movement but expansion, which he Delta1212 is saying is different than movement since "the rate of expansion is given as a distance per unit of time per unit of distance" which I am not quite comprehending. If no one cares to clarify what this means I would understand and will do my best to either research for an answer or deconstuct what has been written and make sense of it in a way which becomes a logical understanding. Regardless, I am brand new to this forum however I am quite postive to get personal in these posts is not proper, and I promise this will be the one and only time I will do so hoping not to get a penatly, but I do want to write I am both impressed and appreciative by the amount of energy and effort people have put into responding to the words with which I started this post. Thank you greatly.

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I am just now guessing that Delta1212 would respond to my response to his response in a way which would suggest that just because our Soloar Sysem is moving doesn't mean the univserse is moving because our Solar Sytem is not the universe.

You would be correct. Just because I'm moving when I climb into the back seat doesn't mean that the car isn't in park.

ACG52 wrote what he wrote

before I finished reediting my post. which ended up incuding me writing

However, could it be that the movement within the universe is a result of the movement of the universe?

Or as Delta1212 wrote

Is the movement within the universe, the velocities at which things travel around each other, a result of what Delta1212 is saying is not movement but expansion, which he Delta1212 is saying is different than movement since "the rate of expansion is given as a distance per unit of time per unit of distance" which I am not quite comprehending. If no one cares to clarify what this means I would understand and will do my best to either research for an answer or deconstuct what has been written and make sense of it in a way which becomes a logical understanding. Regardless, I am brand new to this forum however I am quite postive to get personal in these posts is not proper, and I promise this will be the one and only time I will do so hoping not to get a penatly, but I do want to write I am both impressed and appreciative by the amount of energy and effort people have put into responding to the words with which I started this post. Thank you greatly.

Things move around within the universe. This is not the same thing as the universe itself moving (with respect to what?) nor is it the same thing as the metric expansion of space.

As far as what that means: space is expanding. That is, the distance between objects is increasing even though those objects are not moving (this is only noticeable at very, very large distances as anything closer enough to be even in the same group of galaxies is close enough for gravity to overcome the expansion).

The rate of this expansion is generally given as kilometers per seconds per megaparsec. To visualize what this means, imagine that you have a ruler that is a foot long. Every second, that ruler grows by one inch. You put it down in front of you and after one second, the end of the ruler is now one foot and one inch away.

Now imagine that instead of one ruler, you placed 12 of these rulers end to end. Now, as each expands, it pushes the next one further away, so after one second, the end of the row of rulers is now 13 feet away instead of 12, an extra in for each ruler.

So you can say that the end is receding from you at a rate of one inch per second per foot.

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Delta1212 so here comes the question to the very idea of whether or not the universe is truly expanding reversing the idea behind the metaphor you just wrote

You would be correct. Just because I'm moving when I climb into the back seat doesn't mean that the car isn't in park.

It is not true that people think the universe is expanding because objects such as stars are moving further away from each other?

So my metaphor that asks if the univerese is expanding is as follows: Just because a person decides to alter the format of a room and move the furniture further from each other, does it mean the room itself is getting bigger?

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Delta1212 so here comes the question to the very idea of whether or not the universe is truly expanding reversing the idea behind the metaphor you just wrote

It is not true that people think the universe is expanding because objects such as stars are moving further away from each other?

So my metaphor that asks if the univerese is expanding is as follows: Just because a person decides to alter the format of a room and move the furniture further from each other, does it mean the room itself is getting bigger?

If everything in the room is moving away from you with the furniture farthest from you moving away the fastest and this includes the walls, then the room is probably expanding.
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Delta1212 so here comes the question to the very idea of whether or not the universe is truly expanding reversing the idea behind the metaphor you just wrote

It is not true that people think the universe is expanding because objects such as stars are moving further away from each other?

So my metaphor that asks if the univerese is expanding is as follows: Just because a person decides to alter the format of a room and move the furniture further from each other, does it mean the room itself is getting bigger?

If everything in the room is moving away from you with the furniture farthest from you moving away the fastest and this includes the walls, then the room is probably expanding.

I never wrote everything is moving including the walls as you wrote I wrote. I wrote only that the furniture is moving.

The point of the me starting this post was that my think tank team is trying to figure out whether the speed of the unviverse is the reason for the speed of light. Responses to this have had to do with the universe not moving but rather expanding. Why should anyone think the universe is expanding if all scientists have to go on is the observeable objects that are moving within the universe. The metaphor of the furniture moving away from each other, you have accurately suggested that the further the furniture is the faster it is moving. But since light takes 186,000 miles a second to move, that furniture observed at the furthest points might no longer be moving any faster than the furniture you are observing closer?

Edited by Mitch Bass
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I never wrote everything is moving including the walls as you wrote I wrote. I wrote only that the furniture is moving.

Well unless the walls move too, sooner or later the furniture is going to run into them.

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I never wrote everything is moving including the walls as you wrote I wrote. I wrote only that the furniture is moving.

The point of the me starting this post was that my think tank team is trying to figure out whether the speed of the unviverse is the reason for the speed of light. Responses to this have had to do with the universe not moving but rather expanding. Why should anyone think the universe is expanding if all scientists have to go on is the observeable objects that are moving within the universe. The metaphor of the furniture moving away from each other, you have accurately suggested that the further the furniture is the faster it is moving. But since light takes 186,000 miles a second to move, that furniture observed at the furthest points might no longer be moving any faster than the furniture you are observing closer?

Two points, while you didn't say that everything in the room is moving away, that is what we observe in the actual universe, at least everything that isn't close enough to be gravitationally bound. So yes, if stuff was just randomly moving about, using that as evidence for the universe expanding would be silly. That isn't what is happening though, and using an analogy that ignores what we actually observe isn't going to allow you to draw any conclusions (really no analogy should be used to draw conclusions, but a bad one is that much worse).

Second, objects at the edge of the observable universe are all receding and objects significantly closer (though still far away) are receding. Unless you thing that the universe was expanding for 13 billion years and then suddenly stopped around the time the dinosaurs walked the Earth and we just haven't noticed because the light hasn't reached us yet, what you're proposing doesn't match what we see.

Additionally, when we compare the rate of expansion over a given distance between the closer and farther objects, there is a discrepancy that implies that the rate of expansion in the past was actually slower and that the expansion is accelerating, not slowing down.

Finally, setting aside the question of universal expansion for a moment, if you think the speed of light is related to the movement of the universe, I have to ask: What do you think the universe is moving with respect to?

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Well unless the walls move too, sooner or later the furniture is going to run into them.

(I did some editing of the post you responded to not knowing you had already given a response to what I had orginally written. This is the second time I did this and even though I am new to this entire forum I apoligize.)

Finally, setting aside the question of universal expansion for a moment, if you think the speed of light is related to the movement of the universe, I have to ask: What do you think the universe is moving with respect to?

Is it possible for you to clarify what you mean when you ask: What do I think the universe is moving in respect to?

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(I did some editing of the post you responded to not knowing you had already given a response to what I had orginally written. This is the second time I did this and even though I am new to this entire forum I apoligize.)

Is it possible for you to clarify what you mean when you ask: What do I think the universe is moving in respect to?

All motion is relative to something else. What is the universe moving relative to?

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