Quantum Entanglement explained in simple words

Quantum physics is the branch of physics that describes the behavior of particles at the smallest possible scales. In the quantum realm, quantum mechanical effects become significant and particles can no longer be described using classical physics.

Quantum entanglement is a phenomenon observed at the quantum scale where entangled particles stay connected (in some sense) so that the actions performed on one of the particles affects the other, no matter the distance between two particles. Difficult to understand? It won’t be anymore. Keep reading the article.

Before understanding what quantum entanglement is, let us first have a look at the Double-slit experiment.

Double-slit experiment

Double-slit experiment, first performed by Thomas Young in 1801 showed that when light passes through the double-slit assembly, it behaves exactly like a wave. The experiment which was initially a part of classical physics and aimed at demonstrating the wave nature of light later proved to be a revolutionary experiment in the field of quantum physics.

Two_sources_interference
Water waves (Source: Wikimedia commons)

The adjacent image is a simulation of two waves created on the surface of water. It can be seen that when the two waves interfere, at regions where the crests (or elevations) of one wave falls on the crests of the other wave, the amplitudes add up and the resultant amplitude at those regions is maximum. On the other hand, when the crests of one wave falls on the troughs (or depressions) of the other wave, the amplitudes cancel out and the resultant amplitude at those regions is zero. Thus we can see alternate regions of maxima and minima formed in the image.

Exactly the same happens with light. When light passes through two slits, alternate regions of maximum and minimum amplitude are recorded on the screen. The double-slit assembly and the interference pattern developed using light is depicted below:

DSE
Set up of the Double-slit experiment

As one can see, the light from the light source is made to pass through the double-slit and the resultant interference pattern is recorded on the screen (which consists of alternate maxima and minima).

Wave-particle duality:

In the later versions of the double-slit experiment, when light was replaced by an electron beam, the interference pattern recorded on the screen was found to be wave-like. Not only electrons but even atoms and molecules were seen to behave like waves. Thus, it was found that at the quantum scale, objects can show characteristics of both particles and waves. The wave-particle duality hypothesis originally put forward by De Broglie was confirmed by physicists Davisson and Germer through their famous Davisson–Germer experiment.

Therefore, in the quantum world, particles like electrons can show wave-like characteristics. We can imagine this wave to be a wave of probabilities- the probability of finding the electron at a certain position. This is the same reason why electrons do not orbit the nucleus of an atom in the form of fixed orbits. Instead there is a probability of finding the electron in any specific region around the nucleus.

The probability of finding the electron can be expressed using a wave function. When the electron is not being observed, it behaves like a wave and produces a wave-like interference pattern on the screen but when a detector is located near one of the slits to observe the electron, the wave-function collapses and the electron behaves like a particle. Thus, when the electron is being observed, no (wave-like) interference pattern is produced on the screen.

Sounds weird? Well, what else can you expect? It is quantum physics!

Quantum entanglement

Now, lets get back to the main reason why we are here: What is ‘Quantum entanglement?’

Inside an atom, when a photon (particle of light) interacts with the strong electric field around the nucleus, it is transformed into two particles (This is not the only way to create entangled particles). Since the photon has a zero charge and a zero spin, it is obvious that the two particles created in this process must have charges and spins in such a manner that the total charge and spin for the system is zero. (Since they must be conserved.)

The process mentioned above results into production of an electron (- charge) and a positron (+ charge) both having opposite charges (E = mc²). So the net charge of the system is zero. But what about their spins? Both electrons and positrons can have two types of spins: spin-up or spin-down. Since the resultant spin of the system must be zero, if one of the particles is spin-up, the other particle must be spin-down.

Thus the two possible states are:

  • Electron (up) and positron (down)
  • Electron (down) and position (up)

When the system of electron-positron is not being observed, the system can exist in both possible states at the same time (as seen previously for the electron). Thus the two particles act as if they’re one and exist in multiple superposition states at the same time. Such particles are said to be entangled. But as soon as one of the particles is observed, the wave function collapses and if the measured spin of electron is up, then the spin of the positron automatically takes a down value.

Even if you keep one of the particles (say positron) at the edge of the universe, as soon as you measure the spin of the other particle (electron), the spin of the particle at the edge of the universe becomes defined. This gives an impression that the information between the two entangled particles is transmitted instantaneously or faster than light. But this is not true. Quantum entanglement does not violate relativity because no actual information is passed when the entangled particles affect each other.

Note that this is the simplest explanation that can be given to a phenomenon as complex as quantum entanglement. If you still have queries, feel free to ask them in the comments.

28 thoughts on “Quantum Entanglement explained in simple words

    1. As the two particles are created they have both probable states. As we measure state of one particle state of other particle becomes defined. This only means that there is one super observer who is observing both particles and gives states accordingly. Kind of confirms a creator?

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      1. Thank you for your reply. I try to look for patterns to guide me around things which mystify and send us down many wrong paths. I wonder if you agree with me when I say emotions driven by neural activity have the same ambiguous pattern? Dreams are a good example of this, the subconscious has the same misleading information. I understand the incompatibility of relativity and quantum, but I can’t get rid of the feeling that this is telling us something important and maybe a marriage of the two. We are driven by purpose and this arrangement is perfect for distributing a need, without need an intelligent species could not exist.
        Good to hear from you, thanks again.

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  1. Can we measure the spin of two entangled particles simultaneously? Won’t that lead to a conclusion about this phenomenon?

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    1. Quantum particles only diverse into wave complexity when not being observed, and only change when being observed by an artificial detector. This is the only way to detect this surreal happening.
      After studying the subconscious for many years and the pattern that it portrays, which is as close to the behaviour of these particles as one can get; my question is – could the conscious and subconscious be working in the same way? If so, we would have to go back to the beginning and start all over again; everything we have thought about evolution would be wrong.
      For example; Darwin’s diversity of finches was not down to what kind of food they ate, but by the particles coming from the subconscious brain.

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  2. It seems like particles, down to the smallest, have a kind of intelligence since they seem to act differently when observed. I’ve never studied this so I am new and just curious. What is the theory about why they act differently when observed.

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    1. I also find this fascinating. Evidence points to a dormant life-form being our heritage and from this dormancy comes all the diversity we see today, but there is still that one connection – the dormancy. The subconscious is an equivocal world of cul-de-sacs, but is it a trait from the very beginning? If the dormancy still prevails after billions of years, we must not dismiss it lightly. Consciousness works 16/7, but the subconscious works 24/7 never stopping. In the greater scheme of things, the subconscious appears to be the most important. What could observe these quantum particles more thoroughly?
      I have no scientific background and what I write may not stand up to scrutiny, but I will finish with the pattern which comes over so clearly to me, it is the pattern of entanglement and the pattern of our subconscious. (Dormancy) Perhaps we have to go back to square one and place entanglement and the dormancy together; then start all over again. When I think of the diversity of life with all its mutations, I hunger for the loss of what might have been if the fruits of life had been more benevolent.

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  3. If we are keeping one particle at one edge of our universe and 2nd particle at other egde can we calculate distance between them ?

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  4. Answer asap please.

    What do you call that process in which a photon interacts with the strong magnetic field of nucleus and breaks in two particles ( electron and positron ) ?
    Is this process in theory only or is there any experiment which produces such partilces from photon when it interacts with field of nucleus?

    Department of Physics, IITR

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  5. If no actual information is passed between the particles when they are affected, how does the particle at the edge of the universe know that the local particle was observed, and thus, its spin defined?

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  6. How do we know that they will share information when we put them at the edge of the universe? Who put them on the edge of the universe…
    Maybe my question will look stupid for someone but it is logical for me therefore asking..

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  7. There are neural charges in the brain which are not only influenced by our consciousness, but are influenced on a much bigger scale when coming from our subconsciousness.. This is because the subconscious works 24/7 and the consciousness only 16/7. Could this observant mass be affected by an observant subconsciousness instantaneously with the subconscious of unparalleled distance?

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    1. Thank you for replying, and you must forgive my lack of scientific knowledge. I have so much bending towards Einstein’s box theory and can understand why this would not be ideal for sending information. My interest is mainly in the pattern of a one energy system, which whether it’s biological or not, the same rules apply and so does the same pattern; of course this can vary according to the size of the one energy system. A star for instance, it converts hydrogen into helium, creating a nuclear pressure which stops the star from collapsing. This is also kept stable by letting the explosions occur which we call solar flares. These ‘solar flares’ belonging to a smaller and different one energy system could be mistaken for other things, if that energy system is driven by another source.
      Our subconscious works 24/7 world-wide, never stopping and subjective to all life. It has all the ingredients that go into making a one energy system if all life was connected.
      Dr Donald Hoffman discovered that all life cannot see accurately, which puts all life in the same boat and if all life is in the same boat then why hasn’t all life reached the same level of intellect? If all life had reached the same level of intelligence, that would have destroyed intelligent life as we know it, because it would have destroyed purpose to some extent. (Like the star intelligent life would collapse).
      The wave being one of the properties of quantum, allows the growth of plant life and though this does not explain evolution perhaps the secret may lie with quantum entanglement, because it is driven by intelligence – life. (Activity in the brain). Quantum and relativity are presumed not compatible, but this can’t be true.
      When we observe evolution as different pockets of energy, are we, like Dr Hoffman discovered, not seeing accurately? Is what we are really seeing, a one energy system with all its kinetic energies converting to sustain its function?

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      1. Hi Derek – I am new to this site and find these concepts interesting, especially your comment above that “My interest is mainly in the pattern of a one energy system, which whether it’s biological or not, the same rules apply and so does the same pattern”. I am a counsellor, not a physicist, but I am also searching for a connection between natural laws as we currently understand them and the human experience. I also see reality as far more complex than we currently understand it to be and wonder how entanglement theory applies to human consciousness, how humans are also both particles and waves. Interested in your thoughts if you have any insight you’d like to share.

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      2. Hello Janet,
        I have been researching for many years in my layman’s capacity, which may be limited to some unscientific theories. A virus is a one energy system, and so is the universe and all that it contains. A star is a good example of this one energy system. Its hydrogen converts into helium to form a thermal pressure, which keeps the star from collapsing. During its fluctuation to keep stable, it allows its excess to escape – they are explosions that we call flares. A one energy system, plus the sum of all its kinetic energy, is proportional to its function. this includes an ant, a dog, a human being or the universe. If we take evolution as a one energy system with a dichotomy of variants (Subconscious and consciousness) its pattern becomes more attractive. This balance like in the star, could be the reason that intelligent life does not collapse.
        Dr Donald Hoffman discovered while researching the decline of Australia’s jewel beetle, that all life cannot see accurately; this includes our species. This brings forth the biggest question and that is, if all life is in the same boat, then why hasn’t all life reached the same level of intelligence? If all life reached the same level of intellect, it would destroy purpose to such an extent that life as we know it could not exist. It was only by looking at life, not as a biological diversity, but as a one energy system that I started to see more clearly. I went on to research some of the supernatural in the hope of being able to modify and place it in the natural world.
        Quantum entanglement works best when being observed and when we consider that the consciousness works 16/7 but the subconscious works 24/7 never stopping; the latter appears to be the most important in the greater scheme of things. I repeat, quantum entanglement works best when being observed – the subconscious resembles the one energy system and would observe constantly.
        Good to hear from you.

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  8. I’m n old grandma with no scientific background. This info has caused me to get seriously interested in quantum physics. It has a striking resemblance to many concepts in the Bible.
    God has been saying this stuff since the beginning of time.
    So excitingly thank you for your definitions.

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    1. I agree up to a point, but what is mistaken for a divine influence is what most of us call physics. How you see things is dependant on your outlook. I always think of it this way – why should I believe in something that is not demonstrable to something that is. It is only with time, will entanglement be explained, because the laws of nature dictate this.

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  9. I am fascinated by quantum entanglement – it is a mind boggling phenomenon.

    Just a suggestion – if we are living in a multidimensional universe and the limitations of our senses only allow us to detect 4 dimensions (3 spatial and time). Could it be that the actual universe is multi-dimensional and when the creation of a particle and an anti-particle occurs, the two particles are separated in our space and time, but they are still connected in one or many of the other dimensions that are undetectable by us. This way they would appear to be separate in terms of our senses, but still adjacent/connected to one another in these other dimensions.

    Just extending this idea a bit. Maybe dark matter only exists in these other dimensions but is connected to “our” universe by gravitational attraction (which may be all pervasive) and so manifests itself in our dimensions as hidden mass. As we cannot interact with these “other dimension”, investigation of these phenomena will be challenging.

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  10. Electrons have wave-like characteristics. We can imagine this wave as a wave of the possibilities for an electron to be in a specific position…to what? To the double slit? To the screen? I get lost over that imagination. This seems arbitrary and unjustified to me.

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    1. i understand that two particles reacting to each other as one over any distance cannot communicate. Because of this lack of interaction, is it possible that Einstein’s box theory is the most credible?
      Has science any other theory for this long distance spooky event?

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    2. I am not a scientist, but may I humbly put forward a theory for the uses of entanglement.
      Mass + space = 0 – all is energy. The universe is a one energy system, a star is a one energy system and we are all individual one energy systems.
      If we consider evolution as a one energy system; the energy it contains keeps evolution stable. (The balance in nature). Does entanglement keep evolution and the universe in symmetrical comfort? Though entangled particles appear to be unable individually to communicate; this would produce a different picture if these particles were active within a one energy system. The information possessed by the up spin would be the same as in the down spin, but spread instantaneously. Though life is a biological energy it would still have to adhere to the laws of nature and the pattern is unmistakable when taking in the amount of diversity needed to keep a balance. A diversity that is needed for any one energy system for it to serve its function, but this would take us back to square one when taking into account the works of Darwin.
      I often wonder if entanglement might solve the mystery of dark matter too?

      Like

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