The many, many dimensions of String Theories and the Multiverse constitute the extremes of fairytale physics brought about by the continuous cobbling-together of more and more fantastical, fictional forces, effects and invented particles in attempts to make sense of the puzzles inherent in the empirical evidence of experiments such as Young's double-slit phenomenon.

But even the photon, the point-particle of light, does not bear close examination. A while ago, I was having a discussion with an Open University student when I called the photon a massless particle. He looked at me with disdainful suspicion and asked how can a particle that carries energy, be massless?

It takes the undoctrinated to ask such glaringly obvious questions, when practicing physicists accept this kind of nonsensical description without question. Quantum physicists are too fond of suggesting that the quantum world with its "purely quantum effects" just cannot be related to the macro world in which we live.

The definition of the photon makes no sense - not to common sense. But it should!

This Blog offers a simple, common-sense description of the photon, and of every particle: from this, and directly from this, applying the same logical explanation, I am able to desribe all quantum effects and processes in four-dimensional spacetime, with no extra dimensions, no alternative universes - and far, far fewer particles.

Young's Double-Slit Experiment

The Double Slit Experiment - The Questions

This is the very famous and well-studied experiment that illustrates the wave/particle duality of protons and electrons. Appreciation of what this experiment shows is essential for the understanding of Unified Absolute Relativity.

The double-slit experiment, or sometimes called Young's interference experiment, is a simple set-up of light source shining through two slits onto a receptor screen as illustrated below.
What happens is that the two streams of light on the receptor side of the double-slit set-up cause a pattern on the screen of lighter and darker bands. This is because the light is coming in waves: so picture two wave sources in water, two separate, waggling fingers for example. The water waves will interfere with each other, with some parts forming troughs and cancelling each other out, some parts combining to form peaks, as illustrated below, which, you can imagine, would lead to an interference pattern on a screen:

This shows the wave nature of light; in fact, coloured light is measured in its wavelength, or wave-frequency. Blue light is of shorter wavelength, changing more frequently, while red light is of longer wavelength, changing less frequently. The rapidity of change also denotes the energy of the light, whereas the intensity is the amount of light. Blue light is therefore more energetic than red light.

So, light is a wave.

But when the intensity of the light source is turned down low enough, just one “piece” of light goes through the system at a time, which instigates a single response at the screen. One piece of light, one quanta, is the photon, the single particle of light. Which suggests that light is actually a particle, not a wave. And the particles appear on the screen randomly; no matter how the responses are analysed, there is no predicting the next response position, no telling where the photon is likely to land on the screen.

The strange thing is, though, that if the system is left on like this, with single particles landing randomly on the screen, the pattern they make will eventually build back into the interference pattern, exactly as before.

So how do the random particles “know” where they should and should not go? Somehow, they are aware of where the other photons have landed, and are able to arrange themselves to finally build the interference pattern back again. How?

And then, perhaps even stranger, is what happens when physicists attempt to find out through which of the two slits the photon has passed. By placing just one detector into the system, at one slit or the other, so that the particle can be detected there or not, whenever a photon makes it to the screen physicists can tell if it has either passed through the slit with the detector or the other slit. The detector doesn't stop the particle – the photon still gets to the screen. But, guess what? The interference pattern has disappeared. The pattern appears as two separated light patches directly behind the two slits on the screen, as if light was not a wave at all.

Even if the detector is positioned in the system after the slits, the photons seem to “know” they are being examined and change their behaviour. In fact, it is possible to leave the detector in place but stop taking readings and the interference pattern returns. Examine the system and the pattern disappears again.

The system will simply not allow itself to be examined. The American physicist Richard P. Feynman called it "a phenomenon which is impossible ... to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery (of quantum mechanics)". And he was fond of saying that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment.

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The implications of the double-slit experiment have been thought through many times and there have been many interpretations of what exactly is happening within this system. The most important and famous of which is:

The Copenhagen Interpretation

The Copenhagen Interpretation, first posed by physicist Danish physicist Niels Bohr in 1920, suggests that a quantum particle (photon or electron, perhaps) doesn't exist in one state or another, but in all its possible states at once. It's only when we observe its state that a quantum particle is forced to choose one probability, and that's the state that we observe.

This state of existing in all possible states at once is called an object's coherent superposition, or simply superposition of states. The total of all possible states in which an object can exist makes up the object's wave function (wave functions are discussed a bit later in this section). When we observe an object, the superposition collapses and the object is forced into only one of its states.

So the Copenhagen Interpretation determines that the photon (or electron) exists everywhere until we decide to measure it. Therefore, it reasons, it must be the observer who is responsible for the actual positioning of the photon. In other words, the photon behaves as it does because we are examining it.

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As a result of the Copenhagen Interpretation, Viennese physicist Erwin Schrödinger in 1935, devised a famous thought experiment, ever since called Schrödinger's Cat; not to show how the quantum micro world relates to the macro world, but to illustrate the apparent impossibility of relating the standard model of quantum mechanics to the real world in which we live.

There are many versions if this experiment, but essentially it goes like this:

An unfortunate cat has to be locked in a box which has two connected compartments. The cat is trapped in one compartment and a gun is pointed at its head (just a thought experiment, remember). The gun is triggered by a device that will detect the presence of a single photon that is released into the system – just the one photon in the whole sealed box. Now, if the photon is in the compartment with the cat and the gun, the detector will sense it and the cat will die. If the photon is in the other compartment, the cat lives. But the photon will be in a superposition of states until we open the box and attempt to examine it.

So, is the cat dead or alive? If the photon is in a superposition of states, then the detector has detected the photon and it has not detected the photon, and the gun has and has not been fired. If the photon is in a superposition of states, then so is the cat. It is neither dead nor alive, or it is both, choose whichever one you fancy.

I'm sure you will agree, this thought experiment certainly does manage to show that the standard model of quantum mechanics disallows a simple and logical connection between the micro and the macro worlds.

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Going a huge step further into implausibility, the Many-Worlds Theory suggests that as the photon exists everywhere until it is observed, it is fixed into a single position here only; but all the other infinite possibilities are still realised in an infinite number of parallel universes. In other words, every time a photon is positioned here, an infinite number of alternative photons are positioned individually in an infinite number of instantaneously-created alternative, parallel universes.

A significant number of scientists have taken up such far-flung suggestions as the Many-Worlds Theory amongst others – others which include String Theory and its sister M Theory. These theories depend upon other dimensions, sometimes many of them, even possible links through membrane-like parallel universes. But the questions asked in this way will always be far, far out of the reach of conclusive answers. All we should do, all we can do is to show why such suggestions and their attendant paradoxical questions are totally and irrefutably irrelevant.

The Double Slit Experiment - The Solutions

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