THE MANY-WORLDS INTERPRETATION OF QUANTUM MECHANICS
The ‘Multiverse’ – or the idea that there are multiple universes – is an interpretation of quantum mechanics formulated by Hugh Everett III. It is considered a theory of parallel universes, since the interpretation follows that, every time someone makes a decision, the universe branches out to create a parallel universe where the option that wasn’t taken does happen, chosen by another version of them.
This is possible as the interpretation considers the idea that in a quantum world – that of atoms, particles, electrons etc. – anything that can happen, does happen, but applies this to a larger scale.
ATOMS
Everything in the universe which gravity has an influence over has mass and is known as matter – this can be observed on Earth, since it is mostly composed of atoms. Atoms, although small, are not fundamental particles, since they can be further broken down into other particles, such as protons and neutrons – which make up the atom’s nucleus – and electrons. Electrons are fundamental particles, which travel inside areas, known as ‘shells’, which surround the nucleus.
The ‘Multiverse’ – or the idea that there are multiple universes – is an interpretation of quantum mechanics formulated by Hugh Everett III. It is considered a theory of parallel universes, since the interpretation follows that, every time someone makes a decision, the universe branches out to create a parallel universe where the option that wasn’t taken does happen, chosen by another version of them.
This is possible as the interpretation considers the idea that in a quantum world – that of atoms, particles, electrons etc. – anything that can happen, does happen, but applies this to a larger scale.
ATOMS
Everything in the universe which gravity has an influence over has mass and is known as matter – this can be observed on Earth, since it is mostly composed of atoms. Atoms, although small, are not fundamental particles, since they can be further broken down into other particles, such as protons and neutrons – which make up the atom’s nucleus – and electrons. Electrons are fundamental particles, which travel inside areas, known as ‘shells’, which surround the nucleus.
Nonetheless, it has been discovered that the classical laws of physics break down when considering anything smaller than atoms.
For example, within an atom, the electrons aren’t seen to orbit the nucleus in circular paths, but instead appear to move randomly, causing them to be in many places at the same time. This can be observed using the double slit experiment.
THE DOUBLE SLIT EXPERIMENT
The double slit experiment is useful because it can show how light displays both the properties of waves as well as particles. A simple version of this can be done with a laser pointer, whereby the opening is covered with two pieces of electrical tape on either side, and then a small piece of thin wire is also placed across the opening, so that it connects the two pieces of tape.
Nevertheless, the quantum version of this experiment can be conducted using a black box containing a laser which emits single photons individually. Photons are the particles which make light visible, and it has been seen that they act like electrons. The photons from the laser travel through a double slit in the box, and, once they reach the other side of the box, they are then detected by a camera which records their positions. These positions can then be seen on a screen.
For example, within an atom, the electrons aren’t seen to orbit the nucleus in circular paths, but instead appear to move randomly, causing them to be in many places at the same time. This can be observed using the double slit experiment.
THE DOUBLE SLIT EXPERIMENT
The double slit experiment is useful because it can show how light displays both the properties of waves as well as particles. A simple version of this can be done with a laser pointer, whereby the opening is covered with two pieces of electrical tape on either side, and then a small piece of thin wire is also placed across the opening, so that it connects the two pieces of tape.
Nevertheless, the quantum version of this experiment can be conducted using a black box containing a laser which emits single photons individually. Photons are the particles which make light visible, and it has been seen that they act like electrons. The photons from the laser travel through a double slit in the box, and, once they reach the other side of the box, they are then detected by a camera which records their positions. These positions can then be seen on a screen.
It has been argued that logic dictates that the pattern made by all the positions of the photons should be two bars, meaning each photon would have travelled straight through one of the slits. Yet, the pattern formed resembles a line of concentrated blotches.
For this reason, it has been explained that this pattern could only be formed if each photon travelled through both slits at the same time, becoming one again when it reaches the other side of the box. This travelling through both slits at the same time is known as ‘superposition’ as the photons exist in two places at the same time.
For this reason, it has been explained that this pattern could only be formed if each photon travelled through both slits at the same time, becoming one again when it reaches the other side of the box. This travelling through both slits at the same time is known as ‘superposition’ as the photons exist in two places at the same time.
And after conducting the double slit experiment in this way with electrons and atoms, it has been observed that they produce this same pattern.
“We are made up of atoms. So, atoms can be in two places at the same time, why can’t we?”
(Parallel Worlds, Parallel Lives, 2013).
COPENHAGEN INTERPRETATION
Nonetheless, the nature of photons, electrons, and particles to be in several positions at once can be countered by the Copenhagen Interpretation, which states that when one of these particles is observed, it exists only in that state within which it is being observed. This was developed by Niels Bohr, who believed the universe should be classified into big stuff, which followed the traditional laws of physics, and small stuff – such as atoms – which followed the laws of quantum mechanics.
This became an accepted theory within the scientific community. Although, not every physicist agreed, including Everett, and Erwin Schrödinger.
SCHRÖDINGER’S CAT
Schrödinger developed a thought experiment considering quantum ideas at a larger, human scale, called Schrödinger’s Cat.
Within this experiment, a cat is locked in a box, inside which it is impossible to see. With the cat inside the box is a Geiger counter – a device which will detect radiation – a radioactive substance, of which there is a 50/50 chance that one of its atoms will decay, and thus emit radiation, along with a hammer, which is linked to the Geiger counter, and a bottle of poison. Therefore, if the radioactive substance decays, this will be picked up by the Geiger counter, triggering the hammer, which will smash the bottle and poison the cat.
Nonetheless, the nature of photons, electrons, and particles to be in several positions at once can be countered by the Copenhagen Interpretation, which states that when one of these particles is observed, it exists only in that state within which it is being observed. This was developed by Niels Bohr, who believed the universe should be classified into big stuff, which followed the traditional laws of physics, and small stuff – such as atoms – which followed the laws of quantum mechanics.
This became an accepted theory within the scientific community. Although, not every physicist agreed, including Everett, and Erwin Schrödinger.
SCHRÖDINGER’S CAT
Schrödinger developed a thought experiment considering quantum ideas at a larger, human scale, called Schrödinger’s Cat.
Within this experiment, a cat is locked in a box, inside which it is impossible to see. With the cat inside the box is a Geiger counter – a device which will detect radiation – a radioactive substance, of which there is a 50/50 chance that one of its atoms will decay, and thus emit radiation, along with a hammer, which is linked to the Geiger counter, and a bottle of poison. Therefore, if the radioactive substance decays, this will be picked up by the Geiger counter, triggering the hammer, which will smash the bottle and poison the cat.
However, it is impossible to see inside the box, so whether the cat is alive or dead at a certain point in time cannot be observed.
Due to this, following the Copenhagen Interpretation, if the cat remains unobserved, it is possible it is both dead and alive at the same time. It will not take on only one state until the box is opened, and it can be observed.
Yet, Schrödinger couldn’t believe this paradox, along with Everett.
Due to this, following the Copenhagen Interpretation, if the cat remains unobserved, it is possible it is both dead and alive at the same time. It will not take on only one state until the box is opened, and it can be observed.
Yet, Schrödinger couldn’t believe this paradox, along with Everett.
“But when you opened the box, when the collapse occurred and the live cat jumped out, where did the possibilities you did not see go? Since it must have been real at some stage, where did the dead cat go? That is the mystery”
(Galfard, 2016:320).
WAVE FUNCTION & SPLITTING
As seen from Schrödinger’s cat, both Schrödinger and Everett believed that the laws of quantum mechanics could be applied on a large scale. This is what led to Everett’s many-worlds interpretation of quantum mechanics.
However, parallel universes are only consequences of this interpretation. Everett’s theory changed physics by being independent of the observer, in contrast to the Copenhagen Interpretation.
Rather, Everett’s interpretation considers the wavefunction of the universe – the mathematical description of the quantum state of a certain area, which could contain any number of particles, atoms etc. – as never collapsing.
Nonetheless, this is one of the reasons why parallel universes are not observable from this universe, since superposition (as shown by the double slit experiment and Schrödinger’s cat) can only be detected if it is not directly observed – a sensation called ‘decoherence’.
From this, it can be seen how parallel universes are a consequence of Everett’s theory. To replace the observer, Everett instead proposed ‘splitting’, which happens when events in the quantum world (such as radioactive decay) happen, leading to parallel universes. Thus, this took the paradox out of Schrödinger’s cat. Now, the paradox could be explained as the branching out of the universe to create another, causing one cat to be alive in one universe, and one to be dead in another. Two cats in different states in different universes, with both outcomes, both choices, happening.
This is Everett’s many-worlds interpretation of quantum mechanics. It has been said that this can neither be proved nor disproved, as our universe appears to be curved, like a goldfish bowl, and thus we cannot see what could be outside of it.
As seen from Schrödinger’s cat, both Schrödinger and Everett believed that the laws of quantum mechanics could be applied on a large scale. This is what led to Everett’s many-worlds interpretation of quantum mechanics.
However, parallel universes are only consequences of this interpretation. Everett’s theory changed physics by being independent of the observer, in contrast to the Copenhagen Interpretation.
Rather, Everett’s interpretation considers the wavefunction of the universe – the mathematical description of the quantum state of a certain area, which could contain any number of particles, atoms etc. – as never collapsing.
Nonetheless, this is one of the reasons why parallel universes are not observable from this universe, since superposition (as shown by the double slit experiment and Schrödinger’s cat) can only be detected if it is not directly observed – a sensation called ‘decoherence’.
From this, it can be seen how parallel universes are a consequence of Everett’s theory. To replace the observer, Everett instead proposed ‘splitting’, which happens when events in the quantum world (such as radioactive decay) happen, leading to parallel universes. Thus, this took the paradox out of Schrödinger’s cat. Now, the paradox could be explained as the branching out of the universe to create another, causing one cat to be alive in one universe, and one to be dead in another. Two cats in different states in different universes, with both outcomes, both choices, happening.
This is Everett’s many-worlds interpretation of quantum mechanics. It has been said that this can neither be proved nor disproved, as our universe appears to be curved, like a goldfish bowl, and thus we cannot see what could be outside of it.
REFERENCES
Francis, M. (2011) ‘What Does the New Double-Slit Experiment Actually Show?’ In: Scientific American 7/6/11. At: https://blogs.scientificamerican.com/guest-blog/what-does-the-new-double-slit-experiment-actually-show/#(Accessed on 16 November 2019).
Galfard, C. (2015) The Universe In Your Hand. London: Pan Macmillan.
Howell, E. (2018) ‘Parallel Universes: Theories and Evidence.’ In: space.com 10/5/18. At: https://www.space.com/32728-parallel-universes.html (Accessed on 16 November 2019).
How To Make Your Own Double Slit Experiment (Young's) - Easy At-Home Science (2013) [Online Video] At: https://www.youtube.com/watch?v=kKdaRJ3vAmA&list=PLc9QYgv46S0PqaESmTLhM9Cji18I9PpR1&index=8&t=0s (Accessed on 17 November 2019).
Parallel Worlds, Parallel Lives (2013) [TV Documentary] At: vimeo.com/58603054 (Accessed on 17 November 2019).
Rees, M. (ed.) (2011) Illustrated Encyclopaedia of The Universe. (3rd ed.) London: DK Publishing. p.28.
Siegel, E. (2018) ‘What Is (And Isn’t) Scientific About The Multiverse.’ In: Forbes 17/7/18. At: https://www.forbes.com/sites/startswithabang/2018/07/17/what-is-and-isnt-scientific-about-the-multiverse/#6f776b8c25c4 (Accessed on 16 November 2019).
Tegmark, M. (2007) ‘Many lives in many words.’ In: Nature 448 pp.23-4. At: https://space.mit.edu/home/tegmark/PDF/everett2.pdf (Accessed on 16 November 2019).
Francis, M. (2011) ‘What Does the New Double-Slit Experiment Actually Show?’ In: Scientific American 7/6/11. At: https://blogs.scientificamerican.com/guest-blog/what-does-the-new-double-slit-experiment-actually-show/#(Accessed on 16 November 2019).
Galfard, C. (2015) The Universe In Your Hand. London: Pan Macmillan.
Howell, E. (2018) ‘Parallel Universes: Theories and Evidence.’ In: space.com 10/5/18. At: https://www.space.com/32728-parallel-universes.html (Accessed on 16 November 2019).
How To Make Your Own Double Slit Experiment (Young's) - Easy At-Home Science (2013) [Online Video] At: https://www.youtube.com/watch?v=kKdaRJ3vAmA&list=PLc9QYgv46S0PqaESmTLhM9Cji18I9PpR1&index=8&t=0s (Accessed on 17 November 2019).
Parallel Worlds, Parallel Lives (2013) [TV Documentary] At: vimeo.com/58603054 (Accessed on 17 November 2019).
Rees, M. (ed.) (2011) Illustrated Encyclopaedia of The Universe. (3rd ed.) London: DK Publishing. p.28.
Siegel, E. (2018) ‘What Is (And Isn’t) Scientific About The Multiverse.’ In: Forbes 17/7/18. At: https://www.forbes.com/sites/startswithabang/2018/07/17/what-is-and-isnt-scientific-about-the-multiverse/#6f776b8c25c4 (Accessed on 16 November 2019).
Tegmark, M. (2007) ‘Many lives in many words.’ In: Nature 448 pp.23-4. At: https://space.mit.edu/home/tegmark/PDF/everett2.pdf (Accessed on 16 November 2019).