Speed of Light - Why is it a constant?

Question

A mess of questions to indicate my mess of understanding.

Why is the speed of light a constant?

Does this exact figure correspond to mass requiring an infinite amount of energy at that given point, can't it actuall happen ever so slightly before or after this speed?


Is the speed of light an arbitrary marker used by physicists?

Is there an inhibiting factor to non-rest particles beyond this speed? Why this particular speed? It just seems so arbitrary.

I just div'nae understand.

Answer 1

I have often wondered the same thing; why is the speed of light constant? I'm not sure that anyone really knows otherwise it would be mentioned by physicists quite prominently. One way to look at it is that Einstein's equation E = mc2 (Energy equals mass times the speed of light, c, squared) is known by lab tests to work. Therefore, the equation can be used to dertermine how much energy will be produced if a known quantity of mass (matter) is converted to energy. To reverse-engineer the process, if you know how much energy was produced by converting a known amount of mass, you can solve the equation for c2 and take the square root to calculate c. It turns out that c is always the constant speed of light. An area of one square inch can be represented by an infinite series of rectangles where S1 x S2 = A (one square inch). Why is A a constant? S1, S2 and A are merely descriptions of the nature of that particular figure. If more energy was created by conversion of a gram of mass (than presently observed) it follows that the speed of light would be different (using Einstein's equation). Remember that the energy being created is in the form of photons (released perhaps by electrons orbiting an atom that change energy states) and they in fact travel at the constant speed of light and vary in the amount of energy carried by exhibiting different wavelengths. Short wavelengths are increasingly more energetic and penetrating than longer wavelengths. Ultraviolet is stronger than infrared, gamma waves are stronger than x-rays, etc. Your interesting question seems to evoke a circular argument like the moon is made of green cheese; because the moon is made of green cheese. It took a moon landing to disprove that theory, right?

Answer 2

To the current state of physics knowledge, and my knowledge from univ. physics:

The speed of light is NOT arbitrary. The value (~3.00*10^8) comes out of maxwell's equations for electromagnetism (4 equations) when calculated for a vacuum. The actual calculations require much higher level math. The speed of light is maximum in a vacuum, and slower in other media (e.g. water). But even in media in which light is not v=3.00*10^8, light's speed in the media is the limiting speed. There have been no experiments that've proven otherwise.

Yes, to accelerate a particle to the speed of light (c), the amount of energy needed is infinite (oo). An example below:

D = greek letter delta = "change in"
Y = greek letter gamma
i = initial
f = final

These equations come out of Einstein's theory of relativity.
Eo = rest mass energy = mc^2
E = total energy = Ymc^2
Y = v^2/c^2

vi = 0
vf = c
DE = Ef - Ei
= Ef - Eo (use Eo instead of E for Ei because particle's vi = 0)
= Yfmc^2 - mc^2
= mc^2 / (1- v^2/c^2)^0.5 - mc^2
as v --> c, mc^2 / (1- v^2/c^2)^0.5 --> oo
( do you see this?
as v --> c, v^2/c^2 --> 1, (1- v^2/c^2) --> 0 )

The speed of light is the speed at which electromagnetic waves travel, or if you want the speed at which photons (carriers of the fundamental force electromagnetism) travel. Their mass = 0.

The only things I know travel at v = c & have m=0, are the carriers of the 4 fundamental forces ( http://en.wikipedia.org/wiki/Force_carrier ) -- strong, weak, electromagnetic, and gravitational forces. The graviton is only hypothesithized at this point. This doesn't change the fact that anything with mass cannot travel at c.

Hope this helps.

P.S.
From my 3rd source:
If anything can travel faster than c, then causality will be violated. Causality says that for an event A that causes an event B, event A must happen before B.

Answer 3

the speed of light is constant because it is.

this figure isn't "exact". We only know an approximation of the speed of light. precision is always a bother. So, it's not exact.
we know the speed of light is a bit less than 300.000km/s (we know a lot of significant figures, but I only remember that rought approximation)
Maybe you should rephrase that particular question, too... the energy to get a specific mass to the speed of light is enormous, but not infinite. And the mass would transform into energy. In the end, the mass you force to go to the speed of light would lose all its mass, transformed into energy through e=mc².

the speed of light appears naturally in a lot of equations.


what the hell are you talking about? for your other questions, read the THEORY of relativity by einstein.


PS: you obviously don't even understand the questions you're asking. My advice is therefore:
1) for the moment, only remember that the speed of light is the speed of light (about 300.000km/s)
2) nothing can go faster
3) humans can only send very small mass CLOSE TO the speed of light (using cyclotrons)
4) go to school, and go through quantic physics and relativistic physics classes to learn more.

Answer 4

No idea. I've read about 4 years back other scientific theories that some scientists actually 'measured' the speed of light in certain parts of the universe and concluded that the speed of light has been decreasing very insignificantly over the history of the universe. It was said that the speed of light at 'Big Bang' was much faster relatively when you compare to that now.

Maybe it has something to do with the fourth dimension space-time. Take this with a pinch of salt.
The source came out from a relatively reputable magazine though

Answer 5

Is it a constant? I only ask because the different colours which make up 'white' light, i.e., the spectral colours, travel at different speeds through different media. That's why prisms can separate the colours from a point source.
Personally I believe the idea of it's constancy is simply a convenience which helps explain the laws of universal physics - not to understand them.
I also don't see why light speed is considered the ultimate. Just because we don't know how, yet, doesn't mean we never will travel at super-light velocity.

Answer 6

There is sifnificant evidence that the spped of light is not constant, but is decreasing - knwon as CDK (c decay).

South Australian scientist Barry Setterfield has been publishing on the matter for some years.
It is not a popular idea because it challenges evolutionary ideas, and some people don't like potential truth to get in the way of their philosophy :)

Interestingly the earliest measurements of c were higher than the current measurements - but they were less accurate.
It is possible that c has now decayed to a level where it is constant as far as we can tell with the accuracy of our measurements.

Answer 7

George,
I don't think the speed of light is constant. What gave you that impression?
I think that your speed of light is the one in a vacuum which is constant. The speed of light through other mediums, like the lenses in you glasses and the liquid inside you eyes (and the air inside your head) is slower.
Our old mate Albert predicted that as a particle approaches the speed of light, its mass would get bigger and bigger (tend towards infinite mass). His theory has been subsequently proven in particle accelerators.
I think that modern theories predict time travel via worm holes but a speeds greater than the speed of light inside the worm hole (black hole) but thats way above my head.
So the speed of light (in a vacuum) is a constant but more a limitation: I've never been able to get even near it.

Answer 8

well every equation requires a constant, so we maintain that light speed is constant. if we can travel faster, than time concpet becomes obslete. also the ffecr of gravity on the speed of light cannot be neglected

Answer 9

DO NOT CONSIDER THE LIGHT CREATED BY HUMAN BEINGS ,THE SPEED WE ARE RELATING TO THE SPED OF LIGHT ISTHAT FROM SON OR MOON OR STARS .YOU MUST BE HAVING AN IDEA ALREADY .THE SPEED IS VERY VERY HIGH AND EVEN IF THERE IS A SLIGHT DEVIATION OUR NAKED EYE CAN NOT VISUALISE .BUT FOR ALL PURPOSES IT IS STATIC AS FAR WE ARE CONCERNED

Answer 10

i was explained by einestien by the special theory of relativity.If you want a brief explanation read "great ideas in physics"by alan lightman