Why light speed?

[Aphile]

First, English is not my first language so, sorry if I use any wrong grammars or words.

 

I am not sure that my question belong here or not because it is my little wonder.

I am not 'Physics' people. I am only interest in some basic knowledges from theory.

I have read books about our universe like 'A Brief History Of Time' by Hawking and a few others of its kind.

 

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They say

'Space and time are relativity'

'Nothing can travel faster than light'

'Light speed is approximately 300,000 km per second' (actually 299,792 km per second).

I understand them all (I mean the basic concepts).

But all of them do not say that 'Why'.

 

 

I mean

'Why this speed is the limit'

 

'Why the speed limit has to be the exactly this rate'

 

'Why the light speed  is not 200,000 km per second or 400,000 km per second'

 

'Light is limited speed by itself or space limit its speed'

(I mean like 'A car engine can go only 100 km per hour or traffic law allow cars to be driven only 100km per hour)

 

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Thanks in advance for the answer and also sorry if my questions are not belong here.

 

[Strange]

13 minutes ago, Aphile said:

But all of them do not say that 'Why'.

I don't think we can say "why" the universe is the way it is. All we can do is produce theories that describe how it works.

It might be that a future theory explains why light travels at the exact speed it does (but it will just leave other questions about why that theory is the way it is). 

Questions about "why" are more in the domain of philosophy or religion than science.

[studiot]

This is a fine place for your equally fine question.

The speed of light is related to two very fundamental constants of free (empty) space.

The electrical permittivity   [math]{{\varepsilon _0}}[/math]  of 8.85 x 10^-12 farads per metre  (capacitance per unit length)

and

The magnetic permeability  [math]{{\mu _0}}[/math]   of   [math]4\pi x{10^{ - 7}}[/math]  Henries per metre (inductance per unit length)

 

When these two constants are substituted into solutions of Maxwell's equations of Electromagnetism EM waves of characteristic speed in free space have this value.

[math]c = \sqrt {\frac{1}{{{\varepsilon _0}{\mu _0}}}} [/math]

This is the speed of light.

 

 

 

 

Edited October 22, 2018 by studiot

[beecee]

14 minutes ago, Aphile said:

First, English is not my first language so, sorry if I use any wrong grammars or words.

 

I am not sure that my question belong here or not because it is my little wonder.

I am not 'Physics' people. I am only interest in some basic knowledges from theory.

I have read books about our universe like 'A Brief History Of Time' by Hawking and a few others of its kind.

 

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

They say

'Space and time are relativity'

'Nothing can travel faster than light'

'Light speed is approximately 300,000 km per second' (actually 299,792 km per second).

I understand them all (I mean the basic concepts).

But all of them do not say that 'Why'.

 

 

I mean

'Why this speed is the limit'

 

'Why the speed limit has to be the exactly this rate'

 

'Why the light speed  is not 200,000 km per second or 400,000 km per second'

 

'Light is limited speed by itself or space limit its speed'

(I mean like 'A car engine can go only 100 km per hour or traffic law allow cars to be driven only 100km per hour)

 

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

Thanks in advance for the answer and also sorry if my questions are not belong here.

 

The speed of light in a vacuum, "c" is simply a universal constant. If there were things that could go faster then light, it would violate causality....eg: you would get this reply before I posted it. This also applies to whether the source of the light is moving or not...eg: If you are travelling in a car at 80kms/hr and shone a torch ahead of you, the light from that torch would not be travelling at 300,000kms/sec plus 80kms/hr, it would still be travelling [leaving the torch at 300,000 kms/sec. It is from those facts that Einstein deduced that it is time and space that are changing. This is known as length contraction and time dilation.

This may explain it all better.....

 

[swansont]

4 minutes ago, beecee said:

The speed of light in a vacuum, "c" is simply a universal constant. If there were things that could go faster then light, it would violate causality....eg: you would get this reply before I posted it.

Yes (sort of. FTL info violating causality requires a slightly more complicated scenario, but it does allow you to do so). There has to be some speed limit to information travel, because causality seems to be something that happens in nature. Light happens to travel at that speed. If you accept that relativity is correct (which means accepting that the speed of information is finite), then you can either have causality or FTL travel, but not both.

 

[Strange]

21 minutes ago, studiot said:

The speed of light is related to two very fundamental constants of free (empty) space.

That just pushes the question back to why do those constants have those values.  

[studiot]

But the OP question (as I understood it) was

Why does light speed have the value it doe?

 

Not what happens if something goes faster or slower.

5 minutes ago, Strange said:

That just pushes the question back to why do those constants have those values.  

I know that but then it depends what you take as fundamental.

Since there are  3 constants involved, only two have to be fundamental.

Relativity was derived using 'light clocks' so light was used there.

And I think that empty space and its properties are more fundamental than light.

 

Edited October 22, 2018 by studiot

[StringJunky]

23 minutes ago, studiot said:

This is a fine place for your equally fine question.

The speed of light is related to two very fundamental constants of free (empty) space.

The electrical permittivity   ε0   of 8.85 x 10^-12 farads per metre  (capacitance per unit length)

and

The magnetic permeability  μ0    of   4πx10−7   Henries per metre (inductance per unit length)

 

When these two constants are substituted into solutions of Maxwell's equations of Electromagnetism EM waves of characteristic speed in free space have this value.

c=1ε0μ0−−−√

This is the speed of light.

 

 

 

 

So, you are saying the SOL, or c, is that because it is set by the limits of the  magnetic and  electrical permittivity of free space?

[Aphile]

5 hours ago, studiot said:

But the OP question (as I understood it) was

Why does light speed have the value it doe?

 

Not what happens if something goes faster or slower.

I know that but then it depends what you take as fundamental.

Since there are  3 constants involved, only two have to be fundamental.

Relativity was derived using 'light clocks' so light was used there.

And I think that empty space and its properties are more fundamental than light.

 

Yeah, you got me.

 

My question is why light speed or fastest speed that anything can travel is that limited rate.

The answer that will satisfy me is the same like the explanation of 'pi' value that we (human) can explain.

[studiot]

5 hours ago, Aphile said:

My question is why light speed or fastest speed that anything can travel is that limited rate.

So what was wrong with my explanation?

[StringJunky]

19 minutes ago, studiot said:

So what was wrong with my explanation?

Probably too technical that the  OP can't see it.

Edited October 23, 2018 by StringJunky

[Strange]

5 hours ago, Aphile said:

The answer that will satisfy me is the same like the explanation of 'pi' value that we (human) can explain.

Then you are going to remain unsatisfied. 

[StringJunky]

6 hours ago, Aphile said:

Yeah, you got me.

 

My question is why light speed or fastest speed that anything can travel is that limited rate.

The answer that will satisfy me is the same like the explanation of 'pi' value that we (human) can explain.

It's best to just accept it as an axiom and that it is the way nature behaves.

[geordief]

Was watching Brian  Cox on BBC  who opined that the fundamental constants such as the speed of light  could vary from one multiverse (!!!) to another.

 

So not that fundamental after all according to his musings(?)

Edited October 23, 2018 by geordief
@@@@**** autocomplete

[studiot]

5 minutes ago, geordief said:

Was watching Brian  Cox on BBC  who opined that the fundamental constants such as the speed of light  could vary from one multimeter to another.

 

So not that fundamental after all according to his musings(?)

Professor Cox is quite a prolific showman,

so how about a more detailed reference to what he was talking about?

 

I am particularly interested in a multimeter than can measure the speed of light.

 

Edited October 23, 2018 by studiot

[geordief]

I know it is not what you are asking but I think it was his latest series(called something  like "Being Human " from memory)

I think I described it fairly accurately.

Often what he says is surprising ,which is why I wondered if he was openly "musing

I am ,without foundation attracted to this infinite multiverses idea but accept that it may be unscientific if it is entirely unverifiable (not that I am in a position to claim even that)

 

Edited October 23, 2018 by geordief

[Strange]

21 minutes ago, studiot said:

I am particularly interested in a multimeter than can measure the speed of light.

You can measure the speed of light with a microwave oven and a large bar of chocolate.

26 minutes ago, geordief said:

Was watching Brian  Cox on BBC  who opined that the fundamental constants such as the speed of light  could vary from one multimeter to another.

 

So not that fundamental after all according to his musings(?)

Depends on how you define "fundamental". As studiot points out, it can be defined in terms of other (more?) fundamental constants.

In another universe, these other constants could be different. Or perhaps the way in which they relate to the speed of light could be different. Or maybe one day we will find a theory that explains why there can only ever be a universe with the exact set of physical constants that we see (although I doubt that).

Edited October 23, 2018 by Strange

[geordief]

Oh dear .Thanks autocomplete....."multimeter" should  have been "multiverse"  in my post

[Endy0816]

7 hours ago, Aphile said:

Yeah, you got me.

 

My question is why light speed or fastest speed that anything can travel is that limited rate.

The answer that will satisfy me is the same like the explanation of 'pi' value that we (human) can explain.

Its similar to absolute zero in Farenheit and Celcius. They end up with essentially arbitrary values for their lower limits due to how the scales were set up in the first place.

You see length contracting towards zero as you approach c.

Again a zero and a corresponding limit.

[Strange]

Just now, Endy0816 said:

Its similar to absolute zero in Farenheit and Celcius. They end up with essentially arbitrary values for their lower limits due to how the scales were set up in the first place.

In other words, if you choose the right units of measurement, light speed = 1 and thus the question "why does it have that value" seems less significant.

Or, to put it another way, the answer to the question "why is the speed of light actually 299,792 km per second?" is: "because we measure it arbitrary units called km and seconds."

 

[geordief]

@ strange

Is that  like replacing fundamental constant values with fundamental ratios?

Edited October 23, 2018 by geordief

[Strange]

9 minutes ago, geordief said:

@ strange

Is that  like replacing fundamental constant values with fundamental ratios?

I suppose you can think of it that way. Speed (of light or anything else) is a ratio between two units: distance and time. The numerical value of a particular speed depends on the units you use (50 mph vs 80 km/h).

So, there are several questions in the OP, all of which have been answered I think:

1. Why is the speed of light constant
2. Why is the speed of light invariant
3. Why is the speed of light equal to 1.8x10¹² furlongs per fortnight and not some other value

The answer to (1) and (2) can only be "because that is the way the universe is" (which one can blame on a god, if desired).

And the answer to three is "because we are human"

[geordief]

Referring back to Brian Cox's "musings "would it be conceivable for a fundamental ratio like that between distance and time to be different in another universe?

[Silvestru]

8 minutes ago, geordief said:

Referring back to Brian Cox's "musings "would it be conceivable for a fundamental ratio like that between distance and time to be different in another universe?

That "universe" would function very differently from ours. Even this slight change in c would have drastic effects on all particles.

I mean if c was 1 mm/s faster/slower.

[Strange]

11 minutes ago, geordief said:

Referring back to Brian Cox's "musings "would it be conceivable for a fundamental ratio like that between distance and time to be different in another universe?

I don't think there is anything fundamental about the ratio itself; speed is just a thing we have invented because it is useful. (Although, seeing Silvestru's answer, I may have misunderstood the question!)

Edited October 23, 2018 by Strange