Can anyone please tell me why "c" is an upper limit to speed. Thinking beyond AE's well known formulae.

What are current thoughts about T=zero; T=minuszero


humble

One way to think about it is like this (and it is due to Lev Landau in his second volume of theoretical physics); let us say that you have a transmitter and receiver, call the T and R respectively.

T gets some information and sends it to R.

The information crosses some distance, d, to get to R.

If there is no upper limit to how fast the information can go, then there is no way to be sure when the information reaches R. It could arrive before, at the exact same time, or after leaving T.

If it arrives before being transmitted then we indeed live in a strange universe where cause and effect mean nothing. You could theoretically go back in time and kill your parents before you were born... No causality is the same as having no ability to predict what is happening next. Since science rests upon the assumption that at some level the universe is predictable, then this rules out the signal arriving before it was transmitted.

If it arrives at the same time then it implies that there is no speed limit to the speed of information. I suspect that if this were true then information would indeed be wonderous; it would spontaneously teleport. Since this does not seem to be happening, I think we can rule out the possibility that the signal arrives at exactly the same instant as it was transmitted.

This leaves the third option, that the signal arrives after it was transmitted. If this is the case then it implies that there is an upper limit of the speed of information transmission.

Having lots of evidence of this last option and no credible evidence of either of the first two, we can conclude that there is a maximum speed of information transmission. This seems to be the speed of light.

George

I have wondered that my self, and probably every other cosmologist out there... no-one knows...

Why is it that the nature of space/time limits c to a certain speed...?
What gives each elementary particle a unique mass?
Why 1/137.06?
why 3.141592653589793236484.....?
Why has time a direction?

All of these are connected, in some way...
there are theories such as m-theory that may point towards an understanding of it. And we are currently looking for the higgs boson (mass particle) , if we find that we can perhaps construct a mechanism that brings about all the constants found in nature...

humble,

Can anyone please tell me why "c" is an upper limit to speed. Thinking beyond AE's well known formulae.

The speed of light in a vacuum is equal to:

c=sqrt(1/e0*u0)

Where e0 is the electric permitivity of empty space, and u0 is the magnetic permeability of empty space.

Although some people on these forums may not agree, it appears that the electric permitivity and magnetic permeability of space limits the speed of light. This should be no surprise since light is electromagnetic radiation.

Tom

Tom:

The equation:

c=sqrt(1/e0*u0)

tells us nothing about why the speed of light is what it is. You are free to choose whatever value of u0 you like. Your choice then defines a system of electromagnetic units. c is fixed prior to this equation, and e0 is determined by your choice of u0.

James,

You are free to choose whatever value of u0 you like. Your choice then defines a system of electromagnetic units. c is fixed prior to this equation, and e0 is determined by your choice of u0.

Aren't e0 and u0 constants that are independent of the speed of light? You seem to be implying that e0 and u0 mean nothing; they are simply used to derive the speed of light. As far as I know, e0 is used in calculating the strengths of electric fields and u0 is used in calculating the strength of magnetic fields. These constants are used in many equations that have nothing to do with the speed of light.

Tom

Tom:

<i>Aren't e0 and u0 constants that are independent of the speed of light?</i>

No. As I said, you can choose u0 to be anything you like. e0 is then fixed by the equation (given that c and u0 are fixed).

In the SI units system, the speed of light c is a <b>defined</b> value, which determines the length of the metre. The second is defined separately. u0 is chosen to be exactly 4pi &times; 10^-7. e0 is then fixed.

Other systems of units make different choices. For example, in "natural" units, c, u0 and e0 are all equal to 1.

In response to the original question:

The speed of light is an upper limit to speed because accelerating any massive object to the speed of light would take an infinite amount of energy, which is obviously unattainable. Einstein's theory of relativity says that an object can go as close to the speed of light as the available energy allows, but it can never reach it.

JamesR got it. The permeativity of free space is the fundamental thing -- if we think of space as a fabric/fluid, then this permeativity can be imagined as the 'viscosity' of free space to changes in its electrical or magnetic characteristics. The magnetic component is orthogonal to the electric component and are thus related; the corresponding ratio of the two leads to the 'speed' that any electromagnetic pulse can travel along the 'fabric'.

The fundamental question isn't why this is the speedlimit -- the fundamental question is why do we exist at all. The world is the mental abstraction of a 'non-existent' thinker, i.e., we are nothing more than a possibility. :eek: :bugeye: :rolleyes: