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Author Topic: Why Does Light Travel At The Speed It Does ?  (Read 8513 times)

Offline neilep

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Why Does Light Travel At The Speed It Does ?
« on: 05/01/2009 19:48:05 »
Hullo,

I'm sheepy and a part time lamp.



As a lamp I of course bring brightness and joy and a glowing luff into people's lives. I would not be able to achieve this without light though. Light is like, well nice..It's fast too !!...even faster than my cat kneading dough on my tummy !.....faster even than as fast as my treadmills' maximum speed and that is a whopping 10mph !..*le aghast*

There are many questions about the speed of light, I am just wondering as to why it is the speed it is ?...could it just as well be faster ? It's maximum speed is set yes?...not even light can break it's own speed record ?

What is it about light that makes it go the speed it does ?..I don't mean what propels it (we all know it's Light Fairies  ;))..I mean...why does light go at that specific speed ?

Perhaps this is a silly question, would be a novelty for me if it was eh ?


Thanking ewe for your light-speed orientated answers !


Hugs




Neil
Ewe, Light Up My Life !
xxxxxxxxxxxxxxxxxxxxxxx


 

Offline Mr. Scientist

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Why Does Light Travel At The Speed It Does ?
« Reply #1 on: 05/01/2009 19:51:53 »
It's at the speed it is, because it does not contain an invaraint mass. This means, without the inertial drag, it has a non-inertial momentum.
 

Offline LeeE

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Why Does Light Travel At The Speed It Does ?
« Reply #2 on: 05/01/2009 20:37:41 »
The actual value of 'c' appears to be a fundamental constant, if not the most fundamental constant.  The Anthropic Principle would say that 'c' is the value it is because things wouldn't work if it was different, but this is a bit like putting the cart before the horse;  the maths that show that things wouldn't work properly with different value of 'c' is derived from 'c' in the first place, so all it's really saying is that values for 'c' other than 'c' do not equal 'c'.

This is an excellent question because it highlights a vital issue with the analytic process.  If you analyse something from the top down, where you explain things on one level using terms from the level below it, you reach a point where you end up with an abstract concept that says something is the way it is because that's they way it is.  For example: what are the elementary particles such as the electron and quark made out of? (yeah - we all know they must be some form of energy, but what quality/characteristic is it about that energy that it manifests itself as an electron or a quark?)

So just as electrons and quarks are regarded as elementary particles that have no lower substructure, 'c' is regarded as a fundamental constant that is the value that it is because that's what it is.  As it happens, it's quite a good value because it allows quite a high resolution to the universe - work out how fast you'd be going if you traveled a distance of one Planck Length in one Planck Time unit (the first person to point out an interesting problem with this [moving one Planck Length in one Planck Time] gets a 'well done'  ;))
 

Offline lightarrow

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Why Does Light Travel At The Speed It Does ?
« Reply #3 on: 05/01/2009 22:25:52 »
What is it about light that makes it go the speed it does ?..I don't mean what propels it (we all know it's Light Fairies  ;))..I mean...why does light go at that specific speed ?

It's not a silly question, but my answer will probably disappoint you: light's speed is defined to have that value. :)  This because the metre is defined as the space travelled by light in 1/299,792,458 seconds.

Ok, but, you could ask, and before we defined the metre this way?
However, the fact light's speed in the void has a specific numerical value (299,792,458 m/s) it's not so basic, in the sense that it could have any other numerical value depending on the units of measure; infact it has also the value (not exact) of 186,282.397 miles/second, for example. Talking about a dimensional physical quantity, it's not so basic which numerical value it has (it is of course still important because when you make computations you have to know its exact value). It's basic, instead, the fact that light's speed is much greater than ordinary veichles' speed of your life AND the fact it's finite.

It would be more fundamental to investigate why it has these two last properties.
« Last Edit: 05/01/2009 22:35:55 by lightarrow »
 

Offline justaskin

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Why Does Light Travel At The Speed It Does ?
« Reply #4 on: 06/01/2009 10:50:12 »
It's not a silly question, but my answer will probably disappoint you: light's speed is defined to have that value. :)  This because the metre is defined as the space travelled by light in 1/299,792,458 seconds.

This is were I get confused.If a metre is defined as you have said how do you measure a metre
when it has been warped by space time or does the time warp in the same direction as space such
that the speed of light remains constant.I even read the other day,don't know where,that when
space time enters a black hole time and space interchange such that time becomes a measure of distance and space becomes a measure of time.
I mean if you were buying realestate and the agent said of course this three square metres is an acre its just in an area dilation it's really much bigger than it looks.Yea sure. ;)

Cheers
justaskin
 

Offline DoctorBeaver

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Why Does Light Travel At The Speed It Does ?
« Reply #5 on: 06/01/2009 12:19:20 »

I mean if you were buying realestate and the agent said of course this three square metres is an acre its just in an area dilation it's really much bigger than it looks.Yea sure. ;)


 Isn't that what they do anyway?  :D
 

Offline neilep

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Why Does Light Travel At The Speed It Does ?
« Reply #6 on: 06/01/2009 20:43:00 »
THANK EWE all very much for these fascinating comments.

As a avid fan I'm grateful for your valuable contributions and helping me understand the nature of stuff !
 

Offline Bored chemist

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Why Does Light Travel At The Speed It Does ?
« Reply #7 on: 07/01/2009 13:23:09 »
IIRC it's because if you measure the permittivity and permeability of a vacuun, multiply them together, calculate the square root and take the reciprocal you get 3E8 m/s.
You can calculate it from Maxwell's equations.
 

Offline syhprum

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Why Does Light Travel At The Speed It Does ?
« Reply #8 on: 07/01/2009 13:46:41 »
Is it not correct that the planck time is defined as how long it take electomagnetic radiation to travel the planck lenght.
May I claim my brownie point ?
 

Offline lightarrow

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Why Does Light Travel At The Speed It Does ?
« Reply #9 on: 07/01/2009 15:31:33 »
It's not a silly question, but my answer will probably disappoint you: light's speed is defined to have that value. :)  This because the metre is defined as the space travelled by light in 1/299,792,458 seconds.

This is were I get confused.If a metre is defined as you have said how do you measure a metre
when it has been warped by space time or does the time warp in the same direction as space such
that the speed of light remains constant.I even read the other day,don't know where,that when
space time enters a black hole time and space interchange such that time becomes a measure of distance and space becomes a measure of time.
I mean if you were buying realestate and the agent said of course this three square metres is an acre its just in an area dilation it's really much bigger than it looks.Yea sure. [;)
Buy a laser telemetre (less than 100 in a good hardware) and measure the distance with it. The device compute the time delay between emission of the light pulse and coming back of the reflected one. If the time delay multiplied by 299,792,458 is equal to 3, for the lenght, and 1, for the width, then the agent can tell you what he/she wants, but it's still 3 square metres (Even in a warped spacetime).
 

Offline LeeE

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Why Does Light Travel At The Speed It Does ?
« Reply #10 on: 07/01/2009 18:25:16 »
Is it not correct that the planck time is defined as how long it take electomagnetic radiation to travel the planck lenght.
May I claim my brownie point ?

Quite right, but that's not worth a brownie point.

So, if something moves a distance of one Planck Length in one Planck Time period, it is moving at 'c'.  What you'd have got a brownie point for was noticing that any description of movement at rates slower than 'c' requires dealing with sub-Planck Length distances.  And trying to describe accelerations from zero get very interesting.
 

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Why Does Light Travel At The Speed It Does ?
« Reply #10 on: 07/01/2009 18:25:16 »

 

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