Light Again

[Bazile]

Why does light -. well - travel at the speed of light ? - if you follow me

Is this a silly question , because it just does ?

[mibn2cweus]

Because light is energy without a home and in search of a place to be so that it can do what energy does, excite atoms. Matter is light confined to sublight velocity by the mass of the particle created by the coalescence of two or more photons. Its lonely out in space. Perhaps that's why the universe came into being; to satisfy the need presented by loneliness . . . or to find relief from the crowd.

I'm not sure there is a complete answer to your first question but in seeking answers we find new meaning in and understanding of the universe we are priviledged to be the eyes and mind of. It's certainly not silly for the universe to want to have some awareness, knowledge, understanding and appreciation for its own existence. Is it?

[Bazile]

Should I have asked - what gives light it's velocity ?

thanks mibn2cweus - i'll digest your answer later - got to pop out .

[Bazile]

I can see that my question can be interpreted in two ways

for example - a man is walking at a speed of 10 mph

Am I asking him :-
1. why he is walking at 10mph
or
2. why he is able to walk at 10mph

My question was meant to be number 2 , however mibn2cweus answer ( very thought provoking ) was probably based on number 1 interpretation of the question - equally interesting question - yes?

[fo3nix]

Light is made up of particles (actually, everything has a wave-particle duality). These particles that you can think of are called photons. They have zero mass.

Using zero mass in the equations of relativity, leads you to the conclusion that they travel at a fixed speed, that of the speed of light.

Their velocity is very definitely not fixed. But that's another story.

[ryepie]

I don't think any physicist would use a definition of matter as 'light confined to sublight velocity'. Matter & light are merely two possible manifestations of energy.

[jake-the-peg]

Light travels at the speed of light because it has mo mass. Anything with no mass travels at that speed.

We believe that neutrinos have no mass (at least nobody has ever been able to measure it ) and travel at the speed of light.

But it may be that c has actually changed over time
See varying c in time time here: http://en.wikipedia.org/wiki/Variable_speed_of _light

What actually sets the speed of light to the value we see is something at the forefront of ideas right now. People are very very interested in trying to understand how all of the fundamental constants are what they are.

However consider that physical space and time is quantised - you cannot have a distance smaller than the planck length, similarly there is the planck time the smallest meaningful period of time. One Planck length per Planck time is - you've guessed it c.

Now this is a very oversimplified idea neglecting all sorts of quantum mechanical issues such as tunnelling, virtual photons and Heisenberg but there's an underlying idea in there.

You may of course cry "foul" and ask OK then what sets the Planck length and time to be what they are and that we have really little idea of.

Maybe there are trillions of universes each with different quantum sizes and ours are set that way by chance or perhaps its set from a deeper underlying mechanism - right now we really don't know

[Bazile]

So , anything with zero mass cannot be still , but has got to move - and move at 184k approx miles per second , i.e . the speed of light - yes ?

[jake-the-peg]

That's pretty much it!