speed of light?

Question

why is there a speed limit to light and also if a particle has always traveled faster than light then would it be detectable?

Answer 1

The speed of light is just a natural property of the universe. it just 'is' there is no 'why'.

a particle cannot travel faster than the speed of light. Nothing can. Ever.

Answer 2

Remember that light is also a wave (as well as a mass-less particle). Why is the speed of sound (in air) what it is? Because it takes some time for a gas (air) molecule (pick one, H2, N2, Co2) to accelerate and transfer momentum to the next and so on in a wave. Similarly, NOT identically, it is so with light.

Specifically, light is an electromagnetic propagation. More specifically, it is an electric field propagation in one plane and this induces an magnetic field in another (90º to the first) and then the magnetic field induces an electric field and so on. Instead of acceleration and momentum transfer, there is a property of free space called permittivity. It takes some time for the one field to induce the other and vice versa. That is why light is that speed. Why is the permittivity what it is? Why is any constant what it is?

Actually you can exceed the speed of light in a specific medium besides vacuum. Radiation around nuclear reactors does it all the time resulting in Cherenkov radiation. But nothing is faster than the speed of light in a vacuum or C.

Answer 3

All observers, irregardless of their relative velocities, will measure the speed of light exactly the same. This apparent contradiction is due to time and distance differences relative to the observer. Because of this phenomenon, the speed of light is considered the Universal Constant (hence the C as used in E=MC2)

Since energy and mass are interchangeable, an object that gains kinetic energy also gains mass - and this is why an object will never achieve the speed of light. As an object approaches the speed of light, its mass increases dramatically - and at the speed of light, its mass would be infinite and the energy required to accelerate it would also have to be infinite - obviously, an impossibility.

The increase in mass at high velocities has been validated experimentally and is no longer considered a theory - it is a fact. The same is true for the slowing of time with increased acceleration, increased gravity or high velocity.

It appears that Albert was indeed a genius!

Answer 4

There is not a speed limit, the speed of light is just the speed that light has been observed moving at. Your second question is intriguing, though. In theory, objects with any sort of mass cannot travel faster than the speed of light. But even if they could, how would we detect them? Curious.

Answer 5

I just HAVE to point out an inconsistancy in another's post. A photon of light must have mass.

E = m * c * c (m = mass, c = speed of light)
E = h * nu (h = Planck's constant, nu = frequency of light)

Ergo

m * c * c = h * nu

m = nu * h / (c * c)

As h & c are physical constants, the only way for m to equal 0 is if nu = 0. All light has a frequency nu that does NOT equal zero, so therefore all light must have some (very small but real) mass.

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Note:
For the post about "showing thinking", indeed it does show thinking. It is the simplest derivation, and most accessible to the untrained in quantum mechanics.

I do not contest the following statement: "E=mc^2 is only applicable to particles with mass." This of course is absolutely true, because all particles, by definition, have mass.

It is a fallicy to state the following:"E=h nu is only applicable to massless particles,"

You, a macroscopic object, with a very large mass, have a wavelength (known as your deBroglie wavelength). There are very small objects for which the deBroglie wavelength is physically observable yet are clearly macroscopic.

Unless of course you mean to contest the collected work of deBroglie, Einstein, Compton, Born, and Planck.
When it is stated that the photon is "massless", one is referring to the "at rest" mass; but the photon does not exist "at rest", so this definition is meaningless to any real world existence of the photon. All photons are in motion, therefore they have mass. The full-fledged particle nature (something that has mass!) was mathematically proven by Einstein and later experimentally by Compton.

The entire Theory of Quantum Electordynamics relies on the photon having tiny, but real mass for two reasons.
(1) if m(photon) = 0 , you will lose gauge invariance and thus renormalizability.
(2) charge conservation will no longer be guaranteed.

Since Quantum Electrodynamics works (that is, all predictions made by the theory have been borne out in experiment, and no experiments have contradicted it), one must accept that although photons have infinitisimal mass, it is real.

Moreover, the Heisenberg Uncertainty Principle is observably maintained by photons, which arises out of the noncommutability of the momentum and position operators.

On the other hand, is impossible to prove a 0 mass for a photon whether one uses either a nonrelativistic or relativistic approach; instead, consistent with the probabilistic nature of matter and light, the best that can be done is to place upper bounds on its mass.

It is convenient, then, to assign a mass of "0" to a photon, which is what is general practice in physics, but this is not technically correct.

Answer 6

The limit of the speed of light is that no particle with mass can accellerate to the speed of light. Some people have theorized about a particle called a tachyon, which always moves faster than light. Just like other particles, as you put energy in and it approaches the speed of light the mass grows, but in its case the speed decellerates to the speed of light, as energy is removed it accellerates towards infinity. Tachyons can never go slower than the speed of light.

You can read more about them here http://scienceworld.wolfram.com/physics/Tachyon.html, or on wikipedia

Answer 7

There is a speed to light because light energy does not simply exist. It must move in order for us to see it. Technically speaking, nothing can ever move faster than the speed of light. Though if something was able to do this, it wou;d probably be able to be detected by some means, though it woudl be impossible to see.

Answer 8

Hi
I must commend the person whom took the trouble to combine equations to alledgely illustrate that photons has mass.

It shows thinking.

I must unfortunately point out that ceratin equations are applicable only in certain circumstances.

E=mc^2 is only applicable to particles with mass
E=h nu is only applicable to massless particles,

Thus teh equations can not be combined since the underlying assumptions in thier derivation would be violated.

However I point out again, it shows thinking to try to combine them

Cudos

Answer 9

Only God knows why. Scientists never answer why questions

Answer 10

it is E=mc2