Why Then is the Speed of Light Constant?

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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 John Bell, Quantum Field Theory, Quantum Physics, Speed of Light, Fields of Colorcontinue 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.


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In June, 2014, I lectured at the Physics Department of the Czech Technical University in Prague. I started by asking the question “Just what does the electron look like?”, and I showed 2 images. The first was the familiar Rutherford image of particles orbiting a nucleus, and the second was a (very simplified) image of the electron as a field in the area around the nucleus.

Then I asked for a vote. Rather remarkably just four people in the audience chose the field image, and no one selected the particle picture. In other words, THEY DID N’T KNOW. So here we are, 117 years after the electron was discovered, and this highly educated bunch of physicists had zero idea what it looks like.

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Naturally when the electron was discovered by J. J. Thomson, it was naturally pictured as a particle. After all, particles are easy to visualize, while the field concept, let alone a quantized field, is not an easy one to grasp. But this picture soon ran into problems that led Niels Bohr in 1913 to propose that the particles in orbit picture must be replaced by something new: undefined electron states that satisfy the following two postulates:

1. [They] possess a peculiarly, mechanically unexplainable [emphasis added] stability.

2. In contradiction to the classical EM theory, no radiation occurs from the atom in the stationary states themselves, [however] a process of transition among two stationary conditions can be accompanied by the emission of EM radiation.

This led Louis de Broglie to propose that the electron has wave characteristics. There then followed a type of struggle, with Paul Dirac leading the “particle side” and Erwin Schrodinger the “wave side”:.

We insist that the atom in truth is merely the … phenomenon of an electron wave caught, as it were, by the nucleus of the atom … From the point of view of wave mechanics, the [particle picture] would be merely fictitious.– E. Schrodinger.

Nevertheless the fact that a free electron acts like a particle could not be solved, and so Schrodinger gave in and Quantum Mechanics became a theory of particles that are described by probabilities.

A second struggle occurred in 1948, when Richard Feynman and Julian Schwinger (along with Hideki Tomanaga) established numerous techniques to the “renormalization” issue that afflicted physics. Once again the particle view espoused by Feynman won out, in huge part because his particle diagrams proved easier to work with than Schwinger’s field equations. And so two generations of physicists have been brought up on Feynman diagrams and led to think that nature is made from particles.

In the meantime, the theory of quantized fields was perfected by Julian Schwinger:.

My retreat started at Brookhaven National Laboratory in the summer of 1949 … Like the silicon chip of more recent years, the Feynman design was bringing computing to the masses … But eventually one must bring it all together again, and after that the piecemeal strategy loses some of its appeal … Quantum field theory must work with [force] fields and [matter] fields on a completely equal footing … Here was my obstacle.– J. Schwinger.

Schwinger’s last version of the theory was published between 1951 and 1954 in a collection of five papers entitled “The Theory of Quantized Fields”. In his words:.

It was to be the purpose of further advancements of quantum mechanics that these two distinctive classical principles [particles and fields] are merged and become transcended in something that has no classical counterpart– the quantized field that is a fresh conception of its own, an oneness that replaces the classical duality.– J. Schwinger.

I believe that the primary reason these masterpieces have been disregarded is that lots of physicists considered them too difficult to comprehend. (I know one who could not get past the initial page.).

And so the choice is all yours. You can think that the electron is a particle, despite the many inconsistencies and absurdities, in addition to questions like how significant the particles are and what are they made of. Or you can conclude it is a quantum of the electron field. The choice was described in this manner by Robert Oerter:.

Wave or particle? The answer: Both, and neither. You could think of the electron or the photon as a particle, but only if you were willing to allow particles act in the unusual way described by Feynman: showing up again, interfering with one another and cancelling out. You can also think of it as a field, or wave, but you should keep in mind that the detector always registers one electron, or none– certainly never half an electron, no matter how much the field has been broken up or spread out. Ultimately, is the field just a calculational instrument to inform you where the particle will be, or are the particles just calculational tools to tell you what the field values are? Take your pick.– R. Oerter.

What Oerter neglected to say is that QFT describes why the detector constantly registers one electron or none: the field is quantized. The Q in QFT is very important.

So when you choose, dear reader, I really hope you will not choose the image of nature that doesn’t make sense– that even its proponents call “bizarre”. I wish that, like Schwinger, Weinberg, Wilczek, Hobson (and me), you will select a reality made of quantum fields– properties of space that are illustrated by the equations of QFT, the highest philosophically appropriate image of nature that I can think of.

Find out more on the Fields of Color blog.