# Why does light have invarient speed?

• Xeinstein
In summary, the invariant speed of light is a requirement of special relativity, which states that the speed of light is the same no matter what the physical properties of the space in which it is traveling are.
Xeinstein
What is the physics answer to the question of why light has an invariant speed
to anyone and everyone, other than this is what light is? There must be a
reason why light behaves this way (or perhaps not necessarily this way
always). I'd think something must have happened external to the light to give
it this peculiar property. Put it in another way, what's wrong with the
classical physics where velocity would follow the law of vector arithmetics,
when applied to light?

Why is a difficult question for much of science. The speed of light is constant is one of the requirements of special relativity, which, as I am sure you well know, has been experimentally verified for around a hundred years. Ordinary classical physics for the addition of velocity doesn't work for anything approaching the speed of light, not just light.

The parameter c was important to classical physics before it was known to be the speed of light. It is the ratio between the natural unit of charge for electric and for magnetic forces. It appears as a necessary constant in Maxwell's equations. "Ordinary classical physics" would be inconsistent if c were not constant. All of classical electromagnetism would be wrong if c were not an invariant constant. It also just happens to follow from Maxwell's equations that c is the speed at which light travels. The electrodynamics of moving objects requires the constant c (or epsilonnaughtmunaught) in order to include electric and magnetic forces in the same equation. Understanding all of this was why Einstein titled his relativity paper "The Electrodynamics of Moving Bodies" and not "The Speed of Light".

Xeinstein said:
What is the physics answer to the question of why light has an invariant speed
to anyone and everyone, other than this is what light is? There must be a
reason why light behaves this way (or perhaps not necessarily this way
always). I'd think something must have happened external to the light to give
it this peculiar property. Put it in another way, what's wrong with the
classical physics where velocity would follow the law of vector arithmetics,
when applied to light?

c = 1/sqr(Uo*Ep)... where Uo is the permeability and Ep is the permittivity for free space.

This relationship holds true because the speed of light (and of all electromagnetic phenomena) is determined at the aether level. It remains constant in all frames because it is not dependent on a coordinate system like matter with mass is. Since ratios like permeability and permittivity are determined at the aether level and the aether is immaterial and not bound by spacetime laws, 'c' can be frame independent.

The speed of light is frame independent, but it is dependent on the physical properties of free space, and free space is immaterial, with no landmarks, therefore, not subject to the laws of Relativity, like objects in spacetime are. That's why the speed of light is a constant unaffected by the speed of the observer or the observed.

The speed of light sets the scales. For fields to continue to work regardless of spacetime conditions there must be time and space distortions between the observer and the observed when dealing with relativistic speeds. This is where the principles of relativity and equivalency come from. Because a field's speed must not change regardless of relative motion, and because energy is finite, for reality to work, all parameters must be adjusted around the speed of light. This is why we get time dilation and length contraction.

Since the speed of light, hence, the propagation speed of fields, must remain constant for all the other fundamental constants to continue to be proportionally the same, process (mass) has to increase in order to keep up... to a point, once we go over the speed limit and fields can't keep up, matter disintegrates. When we reach the speed of light, wavelength and frequency drop to zero, waves become flat, devoid of any information, and we are back to being immaterial empty space.

Time and length contractions are real. They need to be in order for the Equivalency Principle and the laws of Thermodynamics to hold. Spacetime, or material space, is a product, not a fundamental or primary component of reality, and that is precisely what is claimed by Relativity. In spacetime, space-like separation is relative. If spacetime were primary then spatial extension wouldn't be variable or dynamic, but it is, it shrinks and expands, just like clocks run slower or faster, depending on energy usage vs. energy available.

Since the speed of light is constant and closely related to the Compton wavelength and the Schwarzschild radius, the universe is the same everywhere, independently from existing spacetime conditions. This means that matter will always have the same properties and behave the same way everywhere, regardless of the existing spacetime conditions, that a carbon atom will look and behave like a carbon atom anywhere in the universe.
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"...quantum field theory says that associated with any mass m there is a length called its Compton wavelength, lc, such that determining the position of a particle of mass m to within one Compton wavelength requires enough energy to create another particle of that mass. Particle creation is a quintessentially quantum-field-theoretic phenomenon. Thus, we may say that the Compton wavelength sets the distance scale at which quantum field theory becomes crucial for understanding the behaviour of a particle of a given mass. On the other hand, general relativity says that associated to any mass m there is a length called the Schwarzschild radius, ls, such that compressing an object of mass m to a size smaller than this results in the formation of a black hole. The Schwarzschild radius is roughly the distance scale at which general relativity becomes crucial for understanding the behaviour of a given mass. Now, ignoring some numerical factors, we have:

lc = hbar/mc

and

ls = Gm/c^2

These two lengths become equal when m is the Planck mass. And when this happens, they both equal the Planck length!"

------ John C. Baez (from "Higher-dimensional algebra and Planck scale physics", as it appeared on the book "Physics Meets Philosophy at the Planck Scale" by Craig Callender and Nick Hugget)

## 1. Why is the speed of light considered invariant?

The speed of light is considered invariant because it remains constant regardless of the observer's frame of reference. This means that no matter how fast an observer is moving, the speed of light will always appear to be the same. This was first demonstrated by the famous Michelson-Morley experiment in 1887.

## 2. How is the speed of light related to the laws of physics?

The speed of light is a fundamental constant in the laws of physics and plays a crucial role in many theories, including Einstein's theory of relativity. It is the fastest possible speed at which energy, information, and matter can travel in the universe. It is also used as the basis for defining distance and time in the theory of relativity.

## 3. What does it mean for light to have an invariant speed?

An invariant speed means that the speed of light is the same for all observers, regardless of their relative motion. This is in contrast to other types of speeds, such as the speed of sound, which can vary depending on the observer's frame of reference. The concept of an invariant speed is a fundamental principle in the theory of relativity.

## 4. How was the speed of light first measured?

The speed of light was first accurately measured by Ole Rømer in 1676 using observations of the moons of Jupiter. However, it was not until the late 19th century that the speed of light was determined with high precision through experiments like the Michelson-Morley experiment and the Fizeau experiment. Today, the speed of light is defined as exactly 299,792,458 meters per second by the International System of Units (SI).

## 5. Are there any exceptions to the invariance of the speed of light?

While the speed of light is considered invariant in a vacuum, it can be slowed down when passing through certain materials, such as water or glass. This is due to the fact that light travels at different speeds in different mediums. However, the speed of light in a vacuum is always constant and is the fastest possible speed in the universe.

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