**Is a photon always moving at the speed of light?**

**Photons **are said to be** the quantum (***new-Indian-term: प्र-भागी*

**)**that

**carries the energy**of

**unified electromagnetic fields.**

*An unified field is an advance treatment of electric and magnetic fields that are treated “same” *because of a **great idea** of Einstein’s* special theory of relativity.* Like the

**equivalence of space-distance and time-intervals**,

*electric field and magnetic fields are the manifestation of the same “gauge” fields.*This is necessary

**if one observes the electric and magnetic phenomena from a space-point**(

*or frame of reference*) which is

**moving so fast with respect to the highest speeds attainable in our Universe**that if

*something moves even at 1/20th the speed of light*

**differences****start to show up in our calculation**from so-called classical

*understanding.*

**A classical understanding is something that you readily see in a day-to-day world**, *eg rotating a magnet piece very fast*, **say**; *like a manual-pedal bicycle wheel*, so that **electric current is produced** from it. A **“gauge” is the idea that** *the mathematical functions that describe*** the electric currents**, **the space around electric****currents and charges**, **the space around magnets**, when they are still or moving **are not unique**. Rather **one can add constants** and **specially chosen functions** and we still describe the original behavior of electric and magnetic phenomena. These are **specially chosen** so that **we do not violate the already observed behavior.**

In other words if we experimentally observe certain behaviors **no matter what “gauge” function we chose** to describe our phenomena **we must see the same effect under the same circumstances**. *This is called a “symmetry under transformation”* of physical laws.

**Symmetry refers to conservation of the same form of phenomena**or same behavior while

**transformation refers to the ability to see the phenomena from**

*a different perspective, a different frame of reference or a different situation*.

The** gauge functions** are basically **not** in terms of** an electric field (E)**, (*space around an electric matter or energy*) or a **magnetic field (B),** (*space around a magnetic matter or energy*); these latter functions (** gauge functions**) are still

**vector or scalar quantities**like the E, B field.

**Theory of Relativity**(the special kind) as opposed to the general kind called

**Theory of Relativity: General,**is formulated in terms of these

**gauge functions as a fundamental field**,

*more fundamental than the E, B field*.

The **gauge scalar function** is denoted as** Greek letter PHI** and** gauge vector function** is denoted as **Roman letter A.** In this formulation** E** (*as well as*** B**) are **functions of PHI and A**. *Specially* **Theory of Relativity** says *there are sets of laws that treats these gauge functions, PHI and A with equal importance*; that is these two functions can be dealt **in the same frame of reference** so that the **“set of laws”** *are valid without inconsistency*. **These laws** *in terms of B, E* are

**not**

*self-consistent*. In other words

**B, E are not**the

**fundamental fields**but

*are special cases*of

**PHI and A**

*when the speed of various constituents that describe the phenomena is quite quite large*to what we see on a day-to-day affair.

**B, E are valid only when the speed is quite less compared to the speed of light**.

**A photon** is a **particle** that *constitutes of functions of these PHI (scalar) and A (vector) functions*. **A photon is a function** or more correctly a **wave-function** so that *it satisfies the Schrödinger’s equation.* It has **both vector and scalar properties therefore**, eg its **spin 1** which says** it’s a vector particle**, but the fact that you can talk about** number of photons **means its a **scalar properties of the particle.** *The catch is if you want to add photon numbers you can not directly do so without violating fundamental laws of nature;* namely** quantum mechanics or Schrödinger’s equation**. So more correctly **a photon is a vector** which is **added like a scalar only when the number of photon is so large** that *the essential error you make in adding the photons is not practically a problem*.

A **photon** for the same reason **must not be connected to the E and B field directly** unless *the E and B field are perhaps so large that the number of photons is proportionately colossal*. **When the field are small we better be careful,** *its the amplitudes we are adding and not the number of photons*. If you remember this from basic physics (*Quantum field theory*) a “**photon**” is an energy value of **creation/annihilation operators**, more appropriately *the difference between the n’th and its penultimate state*.

Now that we are careful how to deal with the photon, we can safely say when we rotate the magnets or electrically charged conductors we produce the photons. **The larger the field value of electric and magnetic fields the larger the number of photons we produce**. It is only in that situation that a **photon has enough energy to be produced** and move **at its will** which is** c=3×10^8 meters/sec**. *When the magnets and currents are small, as small as we observe in our day-to-day affairs it is difficult to say how many photons were produced without first calculating the entire complex configuration.*

What happens is the **electrons are the only freely available electric charge** *(in atoms)* hence they carry away the energy available to them from the fields. **A photon will carry the energy only if it is produced**. *Its a misunderstanding that photons are necessarily produced when we rotate a magnet. *(*I am not saying its not, but no one has calculated the exact laws*)

**The photons once produced all its energy is kinetic energy and it moves at the speed of light. **(*a photon is by definition one that moves at speed of light to make the associated laws Lorentz invariant*)

If its not produced there are other free charges such as electrons that carry away this energy. Electrons having “**large**” masses (*not compared to the other particles but compared to how it will eat up the available energy*) **they can not move at a fast pace**, *as fast as photons*. **The lightning is an example that involves production of photons in some cases and no production in some cases (***no production of photons is possible***),** but there are **plenty of other charges** *not just the electrons* that **carry away the PHI and A fields.**

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