Tag Archives: double slit experiment

Electrons and Double slit experiment

To explain the interference pattern produced by photons, we have proposed the existence ‘photon Ether’ which is nothing but a sea of photons pervading this entire universe. But how do we explain the interference pattern produced by electrons? Do we need to propose now the existence of what may be called as ‘electron Ether’ in addition to the ‘photon Ether’ or ‘lumiferous Ether’ described above? Absolutely not. In fact, not only electrons but many other particles were observed to behave like waves in the double slit experiment and we can explain all of them by the same Ether model.

To understand how electrons and other particles produce the wave like interference pattern in double slit experiment, first we will have to understand the fundamental mechanism by which sensors recognise things and we need to learn about objects and waves from the perspective of the sensors.

1) Objects as energy patterns: We sense our surroundings and know about the existence of various things in this universe via our sense organs. And our sense organs sense things based upon the patterns of energy stimuli they receive from the environment. So it is only based upon the patterns of energy we receive from the environment that we are aware of the existence of various things in this universe. And apart from that specific patterns of energy stimuli, we really don’t have any clues or information about the objects which we presume as truly existing. In other words, as far as we know, objects are nothing but energy patterns. And that is not only the case with human sensors but is true with any sensor. A sensor obviously relies upon the patterns of signals (in other words patterns of energy stimuli) that it receives from the surroundings to sense any object whether it is an electron or a ball.

2) Waves as holograms: A wave is nothing but a true copy of the energy pattern of the object that generated it (vide infra). So, from the perspective of a sensor which judges things only by the energy patterns it receives, a wave and its object (source) are one and the same. And we will also learn soon that a wave is not just a true copy but is a holographic image of its source.

Objects as sensations and energy patterns

We will start this by answering one simple but most fundamental question i.e. how do we actually see and recognise different things in our environment? We know that we see different objects because our eyes (or to be more specific our retina, the photosensitive layer inside our eyes) receive light energy from each of them in different patterns. Ant what is light energy? It is nothing but photons. So it is ultimately photons which collide with and stimulate our retina and cause the various visual sensations that we experience. But if it is the same photon particles that hit our retina, how are we able to see different things? It is obviously by sensing the ‘patterns of hits’ that our sensors (retinas) receive that we (our brains) are able to recognise or see the different objects in our universe.

Similarly we hear different sounds because our ear drums receive different patterns of collisions from the same air particles. It is again recognition of patterns of collisions that help us recognise the different sounds that we hear in our everyday life. And we recognise different objects by touch and again that is because our skin receives specific patterns of impacts or collisions from the same particles that make up the various objects in this world. So it is ultimately recognition of different patterns of the same fundamental stimulus which makes us see/ hear/ feel the different objects in this universe.

We know that every object in this universe is nothing but a conglomeration of the same fundamental particles. So what basically happens when two objects collide or come in contact with each other? The fundamental particles of one object will collide with those of the other. Similarly when a sensor comes in contact with an object, the fundamental particles of the sensor (e.g. our hand) collide with those of the object (e.g. a ball). As all objects are made of the same fundamental particles, how does any sensor differentiate between different objects? Obviously it is only by recognising the patterns of collisions that it receives from each of them.

Going even deeper, what underlies every collision event? Or what basically happens when two particles collide? It is just energy exchange between the particles. And what is energy at the most fundamental level? As far as we know it is impact from a photon particle. So it is ultimately photon particles colliding in specific patterns, which gives us the perception of different things in this universe. That applies to particle detectors as well. A particle detector senses something as an electron because it receives a unique pattern of energy from that particle. Obviously a sensor or a detector doesn’t ‘see’ which particle is actually hitting it, what it feels is just the impact. And only based upon the intensity, pattern, duration, direction etc of the impacts, a sensor ‘identifies’ different particles and judges (‘sees’) its surroundings.

Similarly, as already described, we the human sensors feel different objects (e.g. a book or a toy or a particle) in our environment only by the specific patterns of energy we receive from the environment. For example, we may believe that there exists a book in our room because we may have ‘seen’ that with our eyes, or ‘heard’ the sound of the pages turning or may have ‘felt’ it with our hands. But all these signals are nothing but energy patterns we receive from the environment and which our brain interprets as a book. So from our perspective, things in this universe are nothing but energy patterns. So in theory we must be able to describe every object and phenomenon in terms of collisions of photon particles or vibrations of Ether medium.

To conclude, every object we feel is nothing but a sensation and every sensation comes from a specific pattern of energy i.e. specific pattern of collisions from the particles that make up Ether. (May be also that we experience time and space because of the sensations that our brains get from the environment and hence may also be ultimately explained in terms of specific patterns of energy input. But let’s not dive into such deeper issues now.)

A wave as a hologram

We have seen above that objects are nothing but energy patterns. We will now learn that waves are also energy patterns and so from a sensor’s point of view, both waves and objects are one and the same. But there is one important difference between them i.e. while objects behave like ordinary photographs, waves behave like holographs. For those who aren’t familiar, a holograph may be described as a special photograph. The speciality about the photograph is that every part of it will have the data or information about the entire photograph. For example if we take a holographic image of a tree and cut into a number of pieces, each piece will show a miniature image of the whole tree unlike the case with our usual photographs. How is this possible?

When an ordinary picture is cut into pieces, we know that each piece will show only a part of the original picture

When an ordinary picture is cut into pieces, we know that each piece will show only a part of the original picture

When a holographic image is cut into pieces, each piece will show a miniatured version of the entire image.

When a holographic image is cut into pieces, each piece will show a miniature version of the entire image.

Holographic pictures are prepared by making use of the interference property of light waves which means that holography is one of the phenomena of wave motion. So let’s dig into the ‘micro-physiology’ of waves and understand the fundamental basis of holograms in clear terms.

A brief recap on the basics of wave mechanics before we attempt to understand the phenomenon of holography:– In our traditional teaching, a wave is represented as a series of peaks and troughs but this is not correct because this actually represents the cross section of a number of waves and not just one wave. A better understanding of waves can be gained by observing the tides in a sea or ripples in a water tank. Imagine that we have stroked the water surface with a paddle and produced a number of ripples in a large tank of still water. Each ripple in the tank represents a wave. Each wave has nothing to do with the one in front or the one behind. They just happened to be in series simply because the paddle stroked the water surface repeatedly. The attributes of each wave e.g. amplitude, wave length etc depend upon how the paddle strikes the water surface each time and, as just been mentioned, each wave has nothing to do with the one in front or the one behind. Same is the case with sound waves. Each oscillation of a tuning fork produces a wave of compression which travels in the medium independent of the waves produced before or afterwards. So, describing the wave length of a wave as the distance between two consecutive peaks or compressions makes no sense though it often ‘works’. And so is defining the frequency of a wave. Frequency actually applies to the source but not to the wave as such. An individual wave can’t have frequency. Instead of frequency, a better attribute for a wave would be ‘impact time’ or ‘contact time’.

The next important thing to recollect is that though we describe two types of waves traditionally i.e. transverse and longitudinal, in reality all waves are longitudinal waves and there is nothing called a transverse wave. And unlike what we have been taught in physics classes, the particles in a medium always vibrate parallel to the direction of propagation of the wave and never in the ‘transverse’ direction , though they ‘vibrate’ in a spiral fashion near the surface of the medium for reasons explained elsewhere.

By moving a paddle to and fro deep inside a pond, we actually produce longitudinal waves under the water surface. The same thing happens when a tuning fork vibrates under water. As these waves get conducted to water surface, they appear as transverse waves. So what we observe as transverse waves is only a surface manifestation of the underlying longitudinal waves.

trans & longi waves trans & longi waves2

So the ripples or the so called water waves that we observe on the surface of a pond or a sea do not actually represent a complete wave. A wave is better described as a propagating 3 dimensional phenomenon in a medium. A spherical point source produces a wave that looks something like a convex mirror at the beginning. As the wave propagates/ expands, it elongates more along its axis and becomes more like a conical mirror. And on the receding side, the mirror tries to close on itself.

Though ripples (‘transverse waves’) in a water tank don’t actually represent the waves proper, as long as we keep in mind the above discussion, we can use them to understand wave mechanics and to explain the various phenomena associated with wave motion. With this back ground, we will now move on to the holography.

When we throw an object into a tank of still water, we see it generate a water wave or ripple in the tank. But what actually happens at a more fundamental level is that the particles on the surface of the object collide with those of the water. And each particle on the object acting as a point source generates a wave front of its own. All these individual wave fronts interfere with each other and produce the water wave that we observe. So the ‘water wave as a whole’ represents the sum total of all the individual wave fronts generated by all the point sources on the object. Because each wave front represents the energy of the point source which created it, the energy pattern of all the wave fronts put together (i.e. the water wave) represents the energy pattern of all the point sources put together (i.e. the object as a whole). In other words the ‘water wave as a whole’ represents energy pattern of the ‘object as a whole’. We have discussed above that sensors detect objects only by the energy patterns they receive. So from the perspective of a sensor, both, the object and the wave, are one and the same and without additional clues, it can’t differentiate between the two.

Point no.1: A wave carries the same energy pattern as that of its source. In other words a wave is a true copy its source.

But how do we explain the holography phenomenon? i.e. how every small segment of the wave can possess the energy pattern of the entire source? To understand this, imagine an object as shown below and which is made up of just 3 point particles. When we throw this ‘3-particle’ object onto a sensor, the sensor receives 3 distinct hits and thus recognises the impact as a ‘3-point’ object. Now imagine that we threw this 3-particle body into a pond of still water and placed sensors at multiple locations in the pond. Obviously the 3-particle body generates a water wave which spreads throughout the pond and as it spreads, different portions of the wave hit different sensors. Thus each sensor receives impact from only a small segment of the entire wave. How would the sensor interpret this impact? If the wave is a holographic copy of the 3-particle object, then every small segment of the wave should contain a miniatured copy of the energy pattern of the 3-particle object. So each sensor should feel that it is being hit directly by a 3-particle body though in ‘reality’ it is being hit only by a small portion of the wave generated by that 3-particle body.

Let’s analyse the pattern of impact that each sensor receives in the above scenario.

When we throw the 3-particle object into the pond, what we observe at a ‘macroscopic’ level is that the object generates a water wave which spreads throughout and hits all the sensors as one single wave. But what actually happens at a microscopic level is that each particle of the object strikes the water surface and generates a wave front of its own. So there are going to be 3 wave fronts. These three wave fronts ‘cross’ each other (i.e. interfere with each other) and form specific patterns as they grow bigger and bigger. And though these wave fronts appear to travel as one single unit or one single wave ‘macroscopically’, if we look closely, they remain as separate entities within the wave. For analogy, one may imagine a bundle of curved fibres ‘arranged’ in a regular pattern, while each fibre in the bundle represents a wave front, the bundle as a whole represents the wave. Thus each wave front, despite being part of the wave bundle (or wave as a whole), is actually on its own, and spreads and hits each sensor independently. Thus every sensor receives 3 distinct hits (one from each wave front) at three different points, and this is exactly how our first sensor felt when hit directly by the 3-particle object. So the pattern of the signal received by a sensor will remain the same whether it is hit by an object or by a wave generated by that object.

Point no.2: Every small portion of the wave contains the energy pattern of the entire source. In other words, a wave behaves like a holographic image of its source.

Each particle acts as a point source and produces a wave front that goes and hits each sensor separately. Thus all the sensors receive 3 distinct hits and feel the impact of the 3 point object.

Each particle acts as a point source and produces a wave front that goes and hits each sensor separately. Thus all the sensors receive 3 distinct hits and feel the impact of the 3 point object.

Of course there are going to be some ‘minor’ differences in the energy patterns received by each sensor. For example, while sensor ‘A’ receives the impacts in the order x, y, and z; sensor ‘B’ feels the same impacts in the reverse order. And sensor ‘C’ receives the impact ‘y’ first and then receives the impacts x and z at the same time. Despite these differences, all sensors feel the 3-point energy pattern. In fact, it is these variations that help the sensors ‘know’ the direction of the energy source.

Whether a sensor interprets some impact as a tiny particle or a large ball depends upon the pattern of the impact it receives from the wave

Whether a sensor interprets some impact as a tiny particle or a large ball depends upon the pattern of the impact it receives from the wave

Of course in reality it is not as simple as that depicted above even for a 3 particle source. Just like how every particle on the leading surface of an object acts as a point source and generates a wave front, every particle on every wave front also acts as a point source and generates a wave front.  So each of the primary wave fronts will generate a huge number of secondary wave fronts and each of the secondary wave fronts will generate a huge number of tertiary wave fronts and so on. Thus, even though our 3 particle object generates only 3 wave fronts to start with, there are going to be ‘infinite’ number of wave fronts in no time. But despite that, the sensors still recognise the original ‘3-point energy pattern’ of our object. The reason is that these secondary and tertiary wave fronts will only cause ‘overtones’ in the three primary wave fronts and so do not alter the source’s primary energy pattern altogether.

While every particle on an object will act as a point source and produce a primary wave front, every particle on each of the primary wave fronts can also acts as a point source and generate a wave front. Thus every primary wave front will lead to a number of secondary wave fronts and every secondary wave front will lead to a number of tertiary wave fronts and so on. But the primary energy pattern will never disappear completely though it gets attenuated as the wave propagates.

While every particle on an object will act as a point source and produce a primary wave front, every particle on each of the primary wave fronts can also acts as a point source and generate a wave front. Thus every primary wave front will lead to a number of secondary wave fronts and every secondary wave front will lead to a number of tertiary wave fronts and so on. But the primary energy pattern will never disappear completely though it gets attenuated as the wave propagates.

So the primary energy pattern of the source never completely disappears, though it gets attenuated as the wave propagates in the medium. And because of this attenuation, a far away located sensor may fail to sense the source’s energy pattern. Obviously sensors can vary in their ‘sensitivity’ or ability to pick up the energy pattern of the source – A highly sensitive detector may sense a source’s energy pattern even after the wave has travelled for miles while a less sensitive detector may fail to do so even when directly hit by the source. (We can discuss a lot more on how sensors sense various aspects like direction of impact, strength of impact, depth and relation between different objects, the phenomenon of motion etc. But we will restrain ourselves to what is relevant to our present task i.e. explain the double slit experiment).

So far we have talked about water waves and explained how a water wave behaves like a holographic image of its source. But in reality water is not the best medium for transfer of images or energy patterns, the reason being that water is much more ‘granular’ compared with the most fundamental energy medium i.e. Ether. So images transferred by water are coarser (due to ‘large pixels’- it is like making a casting of a man using sticky foot-balls rather than fine gravel or mud). Even worse is air medium because energy images transferred by air (eg. sound waves) are not only coarser but will have poor resolution due to less number of pixels (i.e. air particles) per unit area.

As Ether is the most fundamental medium, energy patterns (or ‘energy castings’) of objects get transmitted much better in Ether medium than in any other medium. And for the same reason holographic phenomenon is better experienced with light waves rather than with water waves or air waves. In fact, it is because of the ‘holographic behaviour’ of light waves that all of us are able to see the various things in our world. Let me explain how.

As discussed before, we are able to see and recognise different objects because our sensors (retina) receive specific patterns of energy from each of them. And conversely, for objects to be seen or to be sensed, they must release energy i.e. they must emit photons in specific patterns. (Foot note: If an object doesn’t release any energy at all, we really can’t see that or it may be ‘seen’ as a ‘black spot’ in the background). Every object releases energy by two mechanisms i.e. reflection and radiation. When a beam of light is shone upon a body, part of that gets absorbed and part of that gets reflected by the body. And it is because of this reflected light that we are able to see most objects in our everyday life. Even in the absence of external light beam, energy (i.e. light photons) does get emitted from every object (radiant energy), but in most cases this radiant energy is not strong enough to be sensed by human retina. (Those objects which emit strong enough radiation to be seen by human eyes are considered as self-luminescent but in reality self-luminescence is a relative phenomenon). Whether it is by radiation or reflection, each photon that gets emitted from every point of an object initiates a wave front in the Ether medium. Thus from every object, numerous wave fronts get generated at any instant and because each wave front represents the energy of a point source on the body, all the wave fronts together represent the energy of all the point sources on the body, in other words the energy of the body as a whole. So, just like how the water wave carried the energy pattern of its source; the light wave or pulse which represents the sum of all the wave fronts from an object carries the energy pattern of its source. We have discussed previously that a sensor judges its surroundings only from the patterns of energy it receives from the surroundings. Because a light impulse from an object carries the same energy pattern as that of the object, a sensor would feel the same impact whether it is hit by the light impulse or the object.

As mentioned earlier our visual world is merely a manifestation of the holographic phenomenon. For example, imagine that a ball is lying on a table in front of a group of students (we may also join them for better experience) and imagine that 3 red dots are marked on the ball as shown in the picture.

ball 3 dots

Obviously each student in the group will be able to see the 3 dot pattern on the ball and that is because the retina (the sensor) of each eye receives three distinct hits. And we can explain this by the same holographic mechanism discussed above. We know that each dot emits energy in the form of photons and each photon (or shower of photons) that gets emitted generates a wave front in the Ether medium which pervades this entire Universe. Each wave front then spreads (or gets scattered) in all directions and hits all the sensors (retinas). Thus each retina gets three separate hits and recognises the 3 dot pattern on the ball. Of course not only our retinas but every inch of our skin also receives the same 3 dot energy pattern. And interestingly this is the same energy pattern that our skin receives when hit by a 3-point object. So logically speaking, we must all feel being bombarded by 3-point objects whenever we stand in the vicinity of a 3-dot object. But why isn’t that we experience this odd phenomenon? The reason is that our skin is not sensitive enough to pick up these subtle light energy patterns unlike our retina.

So our brain recognises the 3-dot pattern on the ball because our retina receives 3 distinct impacts from the 3 dots on the ball. But how does our brain recognise the ball as a whole? Obviously that must be because our retina receives distinct hits from all the points on the ball. Thus all of us receive specific patterns of impacts from all the objects around us. But, only our eyes are sensitive enough to sense these patterns while our skin is not. Only when ‘objects’ are in ‘direct contact’, that our skin will receive strong enough energy inputs and will be able to sense the energy patterns of the objects. Even if our skin is sensitive enough to feel the impact of the light waves from an object, this ‘indirect impact’ from the object will be millions of times weaker than the direct impact received from the object, so our skin will only feel some ill defined heat sensation and not the object as such.

In summary, we can describe a wave as a propagating holographic image of its source (or the source’s energy pattern, to be more accurate). And just like how every small portion of a holographic picture contains a miniatured image of the original picture, each portion of the wave also contains the energy pattern of the source and behaves like a miniatured copy of the source.

Now coming to the double slit experiment- Imagine that we throw a tiny stone into a large tank of still water. As the stone impinges upon the water surface, it transmits its energy pattern to the water molecules and generates a wave in the water tank. From the discussion above, we can consider the water wave as a growing holographic image of the stone’s energy pattern. Sensors placed at different locations in the tank will be able feel the impact of the stone as the ‘stone wave’ goes and hits the sensors. We have noted above that sensors recognise things only by the pattern of impacts they receive from the environment. Each of the sensors receives the same kind of impact and hence interprets the signal as if they were hit by the stone itself. (The only difference is in the intensity – sensors that are situated far away receive a weaker impact than the ones ahead of them. And, depending upon their relative position, some sensors receive ‘head on’ impacts while others receive ‘side’ impacts). Of course it is ‘actually’ a group of water molecules which impinge upon the sensors and not the stone itself but still the sensors may identify the impact as that of a stone. As long as the sensor receives the same pattern of impact, the sensor doesn’t know whether it is hit by a stone or by a mass of water molecules.

Similarly when an electron is fired, it initiates a wave in the Ether medium and its energy pattern dissipates throughout the space. Detectors placed at different locations in space sense the wave as if they were hit by a ‘real’ electron and register the impact as that from an electron. So it is the energy pattern of the electron which travels in space in all directions simultaneously but not the electron itself.

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Understanding the Quantum Delusions: Part 2

So what exactly is energy? Does it have any physical form or existence? If it has physical existence, it becomes nothing but a kind of matter again. If so, then what differentiates this energy stuff from the non-energy stuff? On the other hand, if energy has no physical existence, how does it exist? And how does it influence matter?

For most of us energy is still a mysterious stuff in Nature. The one thing we are certain of energy is that it moves matter particles. Of late scientists realised that energy at the most fundamental level exists as electromagnetic radiation. They also came to know that light is a form of electromagnetic radiation. But what is electromagnetic radiation? Scientists first thought that electromagnetic radiation behaves like waves without any physical existence but later they realised that it has particle or matter properties too. Now scientists are totally confused: energy exists as both waves and particles at the same time, the result of which is quantum mechanics!

That takes us to the first and the foremost difference between classical mechanics and quantum mechanics: According to classical mechanics, waves and particles are totally different things i.e. waves can’t behave like particles and particles can’t behave like waves. But quantum mechanics teaches exactly the opposite: Waves and particles are actually one and the same. Depending upon how we see it, the same thing will appear as a particle at one time and a wave at another time. So it all depends upon how we see something.

Classical rules

First let’s learn about particles and waves from the perspective of classical mechanics. A particle is nothing but a physical entity that has definite mass. We may call the same as a ‘body’ or an ‘object when it is big enough. Apart from mass, there are other features that we can describe for any physical body or particle. They are size, shape, density, position or location and whether it is at rest or moving with respect to us, and if it is moving its velocity, direction etc. Using the principles of classical mechanics, we can exactly predict an object’s position, velocity and its trajectory if we know the object’s mass and the various forces acting upon it.

Waves are not the same as particles or bodies in our classical understanding of physics. A wave is a physical phenomenon by which energy gets transferred in a medium without transfer of the medium’s particles. The attributes of a wave include wavelength, frequency, amplitude etc. The product of wavelength and frequency apparently gives the velocity of a wave (v=ƛf). (Of course this is not true – we will realise this later when we discuss in depth about wave mechanics and wave particle duality)

A wave is not a localised physical entity like a particle but is something like an ill-defined energy cloud, the spatial distribution of which is given by its wavelength and amplitude. And there is nothing called ‘mass’ for a wave. There are some ‘epiphenomena’ specific to waves:- interference, diffraction, scattering etc. Of these, interference is the most important and is said to be the most fundamental of these. When waves from two different sources traveling in a medium come together, the amplitude of the resultant wave will be more at points where the peaks of both waves meet and it will be less at points where the peaks of one wave meet with the troughs of the other. That is waves get cancelled at some points (destructive interference) and get amplified at some points (constructive interference) depending upon their ‘phase difference’ at the point of meeting.

The weird rules of the quantum mechanics

In contrast to what we have discussed above, quantum mechanics teaches that waves and particles are not two different entities but are just one and the same. What we imagine as a wave can behave like a particle and similarly what we imagine as a particle can behave like a wave depending upon how we observe. So what behaves like what depends entirely upon how we observe the same. But what made physicists come to this weird conclusion? Well, it was their observations on light or electromagnetic radiation. Let’s learn about those observations which twisted the scientific minds and squeezed the logical sense out of them.

The first one is Young’s double slit experiment which proved the wave like nature of light by demonstrating interference between two light rays/ photons emitting from two slits in a screen. It is very important that we learn in detail about this simple experiment because it is this experiment that every quantum physicist swears upon to support the weird notion of wave particle duality. But before we talk about light photons in double slit experiment, let’s first learn how bullets (particles) and water waves (waves) would behave in a similar setting.

Particles in double slit experiment: Imagine that we fire a stream of bullets towards a wall with two slit-like openings in it. Most of them will get stopped by the wall but few of them pass to the other side of the wall through the slits to hit the second wall. If the second wall senses and registers every bullet impact that it receives, we would obviously note the following patterns of impacts on the second wall.

Particles- slit1 open

Particles- 1st slit open

Particles- only 2nd slit open

Particles- 2nd slit open

Particles- both slits open

Particles- both slits open

Waves in double slit experiment: Now imagine a series of water waves instead of bullets in the same scenario. As each water wave hits the first wall, part of the wave passes to the other side via each slit. So for each wave that strikes the first wall, two wave fronts emerge on the other side. These wave fronts get scattered and interfere with each other and result in a specific interference pattern on the second wall. At points where the peaks of the two waves come together, the amplitude of the resulting wave gets doubled and at points where the peaks and troughs come together, the amplitude gets nullified and elsewhere it is in between. Let’s look at the patterns of impacts that would be produced by waves in different scenarios of the double slit experiment.

Water waves - only 1st slit open

Water waves – only 1st slit open

Water waves- only 2nd slit open

Water waves- only 2nd slit open

Water waves with both slits open

Water waves with both slits open

So obviously waves and particles produce different patterns of impacts on the second wall. But how do light rays behave in the same scenario?

In 1803, Thomas Young had shown that light behaved exactly like water waves and produced wave like interference patterns on the second wall as shown below.

Light- only 1st slit open

Light- only 1st slit open

pattern of hits produced (only 1st slit open)

pattern of hits produced (only 1st slit open)

Light- only 2nd slit open

Light- only 2nd slit open

pattern of hits produced (only 2nd slit open)

pattern of hits produced (only 2nd slit open)

Light with both slits open

Light with both slits open

Pattern of hits produced by light when both slits are open

Pattern of hits produced by light when both slits are open

Compare the above with the pattern of hits produced by particles when both slits are open-

Particles- both slits open

Particles- both slits open

pattern of hits produced by particles when both slits are open

pattern of hits produced by particles when both slits are open

This observation had actually overthrown the corpuscular or particle theory of light that was put forward by Newton and dominated the scientific society for more than two centuries.

But then in 1901, Max Planck, from his observations on black body radiation, suggested that electromagnetic radiation comes in discreet bits or quanta just like how matter particles would exist. And later Einstein in 1905 confirmed the particle like behaviour of light from his work on photoelectric effect. As a matter of interest, Einstein had actually received Noble prize not for his theory of relativity which made him so popular but for his work on photoelectric effect which demonstrated the particle like behaviour of light rays.

Photoelectric effect: When light rays were made to fall upon a metal plate, scientists found that they ejected electrons from the metal plate and produced electric current. When scientists analysed the velocity and the number of electrons ejected from the metal plate, it became clear that light rays actually behaved like showers of particles while knocking down the electrons from the atoms of the metal plate. And scientists couldn’t explain the observed patterns of photoelectric current if they imagined light rays as waves. That is to say, wave model of light failed to explain the photoelectric effect.

So while the double slit experiment demonstrated the wave like behaviour of light, photoelectric effect suggested that light behaved like particles. Astonished by this ‘bizarre’ behaviour of light, de Broglie put forward a highly logical argument i.e. if electromagnetic waves can behave like particles, then why not matter particles behave like waves? In the years to come, electrons were shown to behave like waves by various experiments as predicted by de Broglie and and wave particle duality of matter became an accepted ‘reality’.

Then came the main problem for the physicists to solve. If light is composed of particles, how could one explain the interference patterns produced by the same in the double slit experiment? Even when light photons were emitted one at a time rather than in streams or showers, the same interference pattern was observed on the photosensitive screen after a sufficient number of photons got fired. This implied that each particle went through both the slits simultaneously, emerged on the other side and interfered with itself. How could any particle go through two paths at the same time? How could a particle interfere with itself? This happened not only with photons, but scientists observed the same phenomenon with electrons and other particles.

This combined with many other counterintuitive observations and the need to explain the wave like behaviour of particles forced the physicists to formulate the weird rules of the quantum world:

1) Feynman’s multiple histories: An electron or a photon during its flight from point A to point B travels simultaneously in infinite number of paths and apparently what we see or observe is the average of all these paths.

A—————x————–y————z—————–B

Amongst the infinite number of paths that a particle takes simultaneously as it travels from point A to point B, could include a trip to the moon or even to the other side of the universe before the particle reaches point B. Even weird is that, the particle can apparently be observed at any of the x, y, z points between A to B if we decide to observe it, but if we don’t ‘look’ at it, it can be wandering anywhere in the universe. It is as if the particle knows where and when someone is going to watch its behaviour. We have to believe in this odd behaviour of tiny particles because they appear to pass through both the slits simultaneously in the ‘double slit experiment’. So the reality we perceive (i.e. the observed path from A to B) is apparently just one of the several probabilities/ histories/ realities.

2) Quantum uncertainty- The position and the velocity of a particle can’t be accurately known simultaneously. Moreover, a particle doesn’t exist at just one position but exists simultaneously in a number of positions.

3) A particle or body can be in multiple states simultaneously as long as we don’t ‘look’ at them. For example a radioactive atom can be in both decayed and not yet decayed state, a cat can be both dead and alive, a door can be in both closed and not closed (and partially closed) positions at the same time, a table can be both present and yet not present in our room and so on. But why we don’t experience such funny things in our daily life? The reason is that things exist in multiple states only when we don’t observe them. The moment we observe them, they quickly ‘settle’ to one state. Imagine that we have just seen a cat inside a wooden cage in the centre of a room. We may think that they continue to remain so even when we turn our eyes away or walk out of the room. But apparently we can’t be certain of their state when we don’t look at them- It may be that the cat lies outside the cage, it may be that the cat is dead and the cage doesn’t exist in the room but is in the forest being made. Or the cage may be sitting on the head of the cat or it may be that while the cage goes on a trip to the moon, the cat is dancing behind you. That is, they could be in any of the infinite number of possible states. But the moment we look back, the cat and the cage may be seen just as before as if nothing had happened.

4) In our classical world we can predict the ‘fate’ of any individual object if we know all the forces acting upon it, but apparently the same is not possible in the quantum world. For example despite knowing everything about a radioactive atom, we cannot exactly predict what will happen to it after some time, whether it decays or not and if it decays when it is going to decay. Apparently we can only know the probability of an event happening in a given time. For example we may be able say ‘there is 50% chance of a particular atom getting decayed in 24hrs’. Or we may be able say ‘50% of the atoms of a given radioactive substance get decayed in 20years’. But we can’t say exactly which atoms decay and at what point of time they decay.

Of course, even in our everyday world we cannot accurately predict the outcomes of individual events in many scenarios and we may only be able to ‘guess’ the probabilities of a particular outcome. For example, when we toss a coin, we can’t exactly say which way it will land. We can only say that there is a 50% chance for landing head on and 50% for tail on. But why are we unable to exactly predict the outcome of every coin tossing? The reason is that we can’t / don’t have all the information about all the forces acting upon the coin. In other words, the uncertainty of our macroscopic world is to do with our inability and ignorance. But apparently this is not the case with the uncertainty of the quantum world. The reason why our physicists are unable to predict individual events of quantum world is apparently because the Nature itself doesn’t know for sure. So physicists know as much as Nature knows about things in the quantum world despite their vast ignorance in the easily accessible macroscopic world!

Luckily for the scientists, despite all its weird rules, quantum mechanics has been highly successful in explaining various phenomena in Nature both at microscopic and macroscopic levels. And it has helped scientists invent many gadgets of modern society. Does it mean that quantum physics is correct? While most scientists believe that our world is really weird and swear by what the quantum mechanics preaches, there are some who remain sceptical. Apparently the mathematics of quantum mechanics and that of general relativity are not compatible with one another. It implies that the mere success of a mathematical model in explaining certain things in Nature doesn’t automatically mean that the model is correct.

And why should the basic physical principles or the laws of Nature be different in the microscopic and macroscopic worlds? We will explore the truth in other chapters.