Why is it that the ultimate speed happens to coincide with the speed of light?

Answer 1

The ultimate speed in Einstein's relativity theory corresponds to the speed at which identically massless particles travel through empty space. It so happens that light ( or, in fact, any electromagnetic radiation such as UV, IR, microwaves, radio waves, x-rays etc) consists of massless particles called photons. There are also other identically massless particles in nature that are not associated with electromagnetism, specifically gluons (associated with the so-called "strong" nuclear force) and gravitons ( associated with gravity). (Gravitons have not yet been observed, though).
Neutrinos have a very tiny mass (much much less than the mass of even an electron) but it is not identically zero. Thus neutrinos can attain speeds arbitrarily close to the "speed of light" but never actually reach it.

The reason this "ultimate speed" acquired the name "speed of light" is just an accident of history, since visible light was known about and its speed experimentally measured fairly early on.

p.s. I don't know much about so-called "superluminal speeds". My understanding is such a thing would not obviously be a direct contradiction of relativity theory, but hypothetical particles travelling at superluminal speeds (called "tachyons") would have bizarre properties (negative or imaginary mass) and lead to bizarre physical effects ( such as the reversal of past and future).

Answer 2

According to relativity, massless particles must always travel at "the ultimate speed". No massless particle can exist at a lower speed since it would have zero energy. Photons just happen to be the most commonly observed massless particle, so the ultimate speed is commonly refered to as the "speed of light"

Answer 3

Hi Graciela

There are two facets to your question:
(i) why does light travel at the ultimate speed
(ii) why do we generally identify this ultimate speed with c "the speed of light"?

First, some background. There is an ultimate speed because of the way space-time is structured. In the absence of complicating factors like gravity, space-time is a special type of geometry called "Minkowski space-time" (after the dude who invented it). This geometry is specially constructed so that the speed of light looks the same to all inertial observers, regardless of their motion.

This is actually quite an unusual property, if you think about it. For example, suppose you can hit a tennis ball at me at about 40 metres/second (a decent serve!). You and I will measure the ball's speed at 40m/s, but someone flying alongside the ball will measure it's speed to be 0m/s and someone flying the other way at the same speed will measure the ball's speed to be about 80m/s. We're intuitively used to this - the speed of an object depends on the observer and the source. However with light it's different, all inertial observers always measure its speed to be c, regardless of their own state of motion or speed. This is the basis of special relativity.

To make this work, we understand that our universe actually works like Minkowski space rather than our more familiar (Euclidean) space. One consequence of the structure of Minkowski space is that it has an ultimate speed of c. Theory dictates that:
* any objects with real non zero mass travelling in Minkowski space are restricted to speeds below c
* any objects with zero mass travelling in Minkowski space are restricted to speeds of exactly c
* any objects with non-real (imaginary or complex) mass travelling in Minkowski space are restricted to speeds above c


So - to answer your questions, light travels at the ultimate speed limit because it is massless. Other massless things (some mentioned above, such as gluons and other bosons) also travel at c.

And the reason that c (the maximum speed) is identified as c (the speed of light) is because at the time that special relativity and minkowski space were put together light was the only thing known to travel at c, and the speed of light is a significant part of Maxwell's theory of electromagnetism which Einstein was driven to fix up.


Hope this helps!
The Chicken

Answer 4

No one can prove that the ultimate speed is the speed of light. It is only a theory. Check out alternate theories.

Answer 5

It doesn't, what you are being taught is merely what is believed by the scientific status-quo, speeds exceeding the speed of light are referred to as superluminous, or spontaneous, and are real. Most people believe that speed exceeding the speed of light cannot be achieved because they are thinking in terms of locomotion, or velocity of a man made object. Spontaneous relocation has been achieved electronically in US gov.experiments, and it has been proven that DNA has a "spontaneous" speed phase when being transferred astrally, like the speed of thought.

Answer 6

We know the distinction between matter and energy.

Matter emits energy and also absorbs energy.

Displacement of matter from one position to another position with respect time, gives the concept of speed.

Energy is also transmitted from one place to another place with out the aid of any matter in between them.

Leaving transmission of gravitational energy, all energy is transmitted only in the form of electro- magnetic radiation. (Light, heat radiation radio transmission and all kinds of energy transmission take place only in the form of EM radiation and this energy is transmitted with a fixed speed in vacuum.) Einstein believed that gravitational energy is also transmitted only with this speed C)

This is nature of electro magnetic radiation and we can say that the law of nature is ‘energy in its pure form is transmitted only with this speed in vacuum.

If we consider energy as bundles of particles, it follows that energy particles must have a speed C.

Now is the question why there is a limit for speed?

Once again, we have matter and energy and nothing else.

We know that speed of material medium depends upon the energy imparted to it.

The energy we do give is manifested by its velocity.

By energy in its pure form with out any matter involved travels with a constant speed C by the law of nature.

Now imagine a matter moving with a velocity greater than the speed of C.

It is equivalent to saying that the kinetic energy possessed by the matter is traveling with a speed more than C. This is contradictory to the law of nature that energy can travel only with a speed of C in vacuum.

Thus matter too at the maximum can travel only with the speed of C. And if it happens the matter will be converted into pure energy.

And if any energy is converted into matter, then the matter may have a speed only less than C.

Answer 7

it is because, we all know that the fastest speed is light's speed...