The question “Reasons why is the speed of light constant?” is often questioned by those making an effort to comprehend physics. Google has 2760 links to that query. Yet the explanation is so simple that a 10-year-old can understand it, that is, if you accept Quantum Field Theory.
Bring the ten-year-old to a pond and drop a rock in the water. Show her that the waves move through the water at a particular velocity, and explain to her that this speed depends solely on the properties of water. You might release different types of items at varying sites and show her that the waves move at the exact same speed, regardless of the size of the item or location of the water.
Then tell her that sound travels through air with a fixed rate that depends only on the properties of air. You could await a thunderstorm and time the difference between the lightning and the sound. Advise her that a whisper moves as quick as a yell. I believe a ten-year-old can understand the principle that water and air have properties that determine the speed of these waves, regardless of whether she does not understand the formulas.
Anybody who can comprehend this can then understand reasons why the speed of light is constant. You see, in Quantum Field Theory space has properties, exactly as air and water have properties. These properties are knowned as fields.
As Nobel laureate Frank Wilczek wrote, “One of the most basic results of special relativity, that the speed of light is a limiting velocity for the propagation of any physical influence, makes the field concept almost inevitable.”.
As soon as you accept the concept of fields (which admittedly is certainly not an easy one), that is actually all you need to recognize. Light is waves in the electromagnetic field that travel through space (not space-time) at a speed directed by the properties of space. They abide by reasonably simple formulas (not that you have to understand them), just as sound and water waves abide by basic equations. OK, the Quantum Field Theory formulas are a bit more complicated, but quoting Wilczek again, “The move from a particle description to a field description will be especially fruitful if the fields obey simple equations … Evidently, Nature has taken the opportunity to keep things relatively simple by using fields.”.
Nevertheless this inquiry can have a different meaning: “Why is the speed of light independent of motion?” This particular fact was first illustrated by the renowned Michelson-Morley experiment, in which light beams were timed as the earth revolved and rotated. The shocking result was actually that the speed of light was exactly the same despite the earth’s movement.
As I wrote in my book (see quantum-field-theory. net): That the speed of light must be independent of movement was most surprising … It makes no sense for a light beam – or anything, for that matter – to journey at the identical speed no matter the movement of the observer … except if “something funny” is taking place. The “something funny” turned out to be even more astonishing than the M-M result itself. Essentially, objects contract when they move! Even more specifically, they contract in the direction of movement. Think about it. If the path length of Michelson’s device in the forward direction contracted by the exact same amount as the extra distance the light beam would certainly have to travel due to movement, the 2 effects would cancel out. In fact, this is the only way that Michelson’s null result could be explained.
Nevertheless the idea that items contract when in motion was equally as perplexing as the Michelson-Morley outcome. Why should this be? Once more the explanation is provided by Quantum Field Theory. Quoting once more from my book:.
We need to acknowledge that even if the molecular configuration of an object seems stationary, the component fields are constantly interacting with one another. The EM field interacts with the matter fields and vice versa, the strong field interacts with the nucleon fields, etc. These interactions are what holds the object together. Now if the object is moving really quickly, this interaction among fields will become more difficult since the fields, on the average, will need to interact through greater distances. Thus the object in motion ought to in some way adjust itself to ensure that the exact same interaction between fields can occur. How can it do this? The only way is by decreasing the distance the component fields must travel. Since the spacing between atoms and molecules, and hence the dimensions of an object, are determined by the nature and configuration of the force fields that bind them together, the measurements of an item must therefore be impacted by motion.
It is very important to comprehend that it is not just Michelson’s apparatus that contracted, it is anything and everything on earth, including Michelson himself. Even if the earth’s speed and the consequent contraction were a lot greater, we on earth would continue to be unaware of it. As John Bell discussed a moving observer:.
But will she not see that her meter sticks are contracted when laid out in the [direction of motion] – and even decontract when turned in the [other] direction? No, because the retina of her eye will also be contracted, so that just the same cells receive the image of the meter stick as if both stick and observer were at rest. – J. Bell (B2001, p. 68).
In conclusion, for individuals who would like to comprehend physics, I say use Quantum Field Theory and: WAKE UP AND SMELL THE FIELDS.