BY: Arjit Mishra
Today our whole Scientific Community agree to the fact that the Quantum World is intensely mysterious and weird because in this stuffs don't work according to our thinking.
when Quantum Theory was new, It has bothered number of scientists back then which includes Albert Einstein too.
Actually Albert Einstein was not able to swallow the Theory beyond his throat because predictions of Quantum Theory were literally weird. So to prove this Theory wrong, he though described a Thought Experiment with his two colleagues, which he named EPR Paradox. and this thought Experiment birth an unique phenomenon which is still a topic for research due to its weird behaviour. This phenomenon is called Quantum Entanglement. Einstein and his colleagues just created the base of EPR Paradox to defy the concept of Quantum Theory but happened contrary. Actually when Einstein and his colleagues discussed about EPR Paradox ,then there were no required instruments to go for experimentation that's why it has been treated as a Thought Experiment, because of which any conclusion can't be made.
But after some years when they have required instruments, they Experimented it and found that Einstein and his colleagues were wrong, not the Quantum Theory because the results of the performed experiment were same as predicted by the Quantum Theory.
As Quantum Theory and it's weird predictions were true, It has completely changed our visionary perspective for the REALITY. Today Scientists agree to the fact leaving no room for debate that
the Real Nature of this UNIVERSE can only be explained by the Quantum Theory.
In 1920s Nature of Reality was the biggest Topic of Debate between Einstein and Neil Bohr.
Einstein believed that our reality is always fixed that's why there is no difference in it's format, if we observe it or not. He said Moon is always present at it's position whether we observe it or not, In fact our whole classical physics is based on this notion and we blindly believe that entities present near us that we are observing are present in same nature and position at the time when we are not observing them.but Quantum Theory doesn't agree to this notion and believe in fuzzy nature of Reality.
Neil Bohr believed that In the Quantum World and in absence of observations and measurements our Reality do not exist, In case of Quantum particles till when we don't observe or measure them we can't tell anything about their characteristics because before observation and measurement they are actually not in a well defined form instead they exist in all the possible states of themselves together which we call Superposition state and till this time physical nature of Reality doesn't make sense at all because till then there is no physical form of these Quantum Particles and the Reality form of this time can only be represented by Wave Function which itself describe the superposition state but as we observe and measure these Quantum Particles their wave function collapses and because of this, A single possible state is chosen from all the possible states it could ever have and in the end this state is obtained; After our observation and measurement we only get a single possible state and because of this we come to a conclusion that this state only is the Reality of that Quantum particle but actually amongst all those possible states any one could be obtained and this means it is not fixed that after observation or measurement which possible state would be obtained. thus in the absence of observation and measurement our Reality doesn't makes sense.
The Copenhagen Interpretation is based on this theory which is believed to be true in the Quantum Mechanics.(I will make a separate Blog on this concept later. )
Anyway, Einstein can't swallow Neil Bohr's theory beyond his throat. He thought everything is Real always and doesn't rely on our observation and measurement.About the Weird predictions of Quantum Theory Einstein said that the Quantum Theory is still incomplete and lacks some Local hidden variable which can be used to predict everything accurately so that we don't need the concepts of superposition state and wave function. Einstein with Boris Podolsky and Nathan Rosen designed the base of EPR paradox to prove Neil Bohr's theory wrong, which itself was the good example of Quantum Entanglement. Actually at that time required equipments were not present which could test Neil Bohr's Theory that's why EPR paradox is considered as a Thought Experiment at that time.
In EPR paradox, paradox word is used because in this experiment the information between the two particles is travelling more than the speed of light which is violating the rule of Einstein which states-"Spread of Any information in this UNIVERSE can achieve maximum to the speed of Light ."
To understand Quantum Entanglement we should firstly understand these two concepts:-
1- Superposition State: As I have already described, in absence of observation and measurement Quantum particles do not exist in their single possible state instead they exist in their all the possible states.
for example-
There is a intrinsic property of subatomic particles like electrons which we call 'spin'.
[NOTE- don't confuse spin to be something like electrons are spinning on their axis, no please not I will describe spin in later Blogs]
now the electron has two possibilities in aspect of spin, 'up spin' and 'down spin'. According to superposition principle the electron is not present in one of the single possibilities mentioned above, but occur in both possibilities together, means the existence of 'up spin electron' and 'down spin electron' together.
2- Measurement Rule: It states that till when we don't observe Quantum particle it occurs in superposition state but as we observe or measure the Quantum particle it's wave function collapses and in the end a single possible state is obtained which becomes our Reality.
In Quantum Entanglement Entangled particles are used, let us understand what are Entangled particles and how they are formed:
Imagine we have a energetic Photon, and this energy can be converted to mass using Einstein's mass-energy equivalence. for example we can make other different particles using photon but our UNIVERSE has laws which decides how and what would be the nature of these particles, as photon has no electrical charge that's why the electric charges of produced particles must add up to zero.
which means if a photon produce a electron then it should produce a positron to maintain the electrical neutrality. along with this there is a property which is called as conservation of spin-
photons have no spin but electrons and positrons have their spins, it can be 'up' or 'down' and one of them must have 'up' spin and other one must have 'down' spin because then only they add up to zero spin(which correspond to photon) but we can't specify that which one would have which spin. if we take the perspective of superposition state, till when we don't observe and measure them they occur in 'up state' and 'down state' together. now if we talk about Entangled state, it is the state in which two particles are linked in such a way that they exist only in combined state which means without knowing the states of both the particles we can't define the state of a single particle. if you didn't get it yet understand with an example- we have an electron and a positron, there spins could be 'up' or 'down'. which particle have which spin that we don't know. In superposition state it can be represented as:
here electron and positron are in 'up-down' and 'up-down' spins together. which means without knowing the state of one we can't tell the state of the other and in conclusion we can say that in Entanglement, particles can only be described through joined states.
According to EPR paradox or Quantum Entanglement if we have two Entangled particles and if we somehow get the state of one particle then we can surely tell the state of other particle irrespective of their distance. for example- after measuring if we get the spin of one particle to be 'up' then we can tell that other particle would have it's spin 'down' and vice-versa. Quantum Theory explain it through this way- As we have two Entangled particles, there properties are linked in such a way that both can exist only in combined state. Before measuring both particles are present in superposition state, which means electron and positron have their spins 'up-down','up-down' together. it can be represented as:
but as we measure any one of them, their wave function collapses and amongst their two possible states only one would be selected .
if we get spin of first particle to be 'up' then second one would have 'down' spin.
or if we get spin of first particle to be 'down' then second one would have 'up' spin.
As Entangled particles exist in combined state only, it doesn't makes sense that these two particles are kept at which distance from one-another. the effect is instantaneous and is independent of distance.
which means if we keep one particle in first end of the UNIVERSE and other one in the second end of the UNIVERSE, then also spin state observed in the first particle changes the spin of other particle and would be instantaneous. As the state of Entangled particles depend on the measurement and observance of one of the particle present in Entangled pair, it can be seen that these particles inform their states to each other with speed more than Light. but Einstein's special theory of Relativity states that-"Spread of Any information in this UNIVERSE can achieve maximum to the speed of Light ."
then how it is possible that Entangled particles present in two different ends of this UNIVERSE effect each other instantaneously because if the exchange of information is taking place with the speed of light then also information should take much Time that's why Einstein called it a paradox.
Einstein agree to the fact that if two particles are away from each other and if we know the state of one particle, state of other one could be found but he didn't agreed that information between them can travel with the speed more than the speed of light. He believed if we have local hidden variables and if we somehow able to know the state of one particle then state of other particle could be obtained at that time only, information doesn't need to travel with the speed more than light.
Quantum Entanglement was firstly experimented by John Steward Bell and this experiment has proved the Quantum Entanglement Theory to be true, and it has been tested many times till now.
But it is still a mystery for us that two Entangled particles create which type of medium between themselves that enable them to share the information with the speed more than Light.
In 1920s Nature of Reality was the biggest Topic of Debate between Einstein and Neil Bohr.
Einstein believed that our reality is always fixed that's why there is no difference in it's format, if we observe it or not. He said Moon is always present at it's position whether we observe it or not, In fact our whole classical physics is based on this notion and we blindly believe that entities present near us that we are observing are present in same nature and position at the time when we are not observing them.but Quantum Theory doesn't agree to this notion and believe in fuzzy nature of Reality.
Neil Bohr believed that In the Quantum World and in absence of observations and measurements our Reality do not exist, In case of Quantum particles till when we don't observe or measure them we can't tell anything about their characteristics because before observation and measurement they are actually not in a well defined form instead they exist in all the possible states of themselves together which we call Superposition state and till this time physical nature of Reality doesn't make sense at all because till then there is no physical form of these Quantum Particles and the Reality form of this time can only be represented by Wave Function which itself describe the superposition state but as we observe and measure these Quantum Particles their wave function collapses and because of this, A single possible state is chosen from all the possible states it could ever have and in the end this state is obtained; After our observation and measurement we only get a single possible state and because of this we come to a conclusion that this state only is the Reality of that Quantum particle but actually amongst all those possible states any one could be obtained and this means it is not fixed that after observation or measurement which possible state would be obtained. thus in the absence of observation and measurement our Reality doesn't makes sense.
The Copenhagen Interpretation is based on this theory which is believed to be true in the Quantum Mechanics.(I will make a separate Blog on this concept later. )
Anyway, Einstein can't swallow Neil Bohr's theory beyond his throat. He thought everything is Real always and doesn't rely on our observation and measurement.About the Weird predictions of Quantum Theory Einstein said that the Quantum Theory is still incomplete and lacks some Local hidden variable which can be used to predict everything accurately so that we don't need the concepts of superposition state and wave function. Einstein with Boris Podolsky and Nathan Rosen designed the base of EPR paradox to prove Neil Bohr's theory wrong, which itself was the good example of Quantum Entanglement. Actually at that time required equipments were not present which could test Neil Bohr's Theory that's why EPR paradox is considered as a Thought Experiment at that time.
In EPR paradox, paradox word is used because in this experiment the information between the two particles is travelling more than the speed of light which is violating the rule of Einstein which states-"Spread of Any information in this UNIVERSE can achieve maximum to the speed of Light ."
Let us now understand Quantum Entanglement :
To understand Quantum Entanglement we should firstly understand these two concepts:-
1- Superposition State: As I have already described, in absence of observation and measurement Quantum particles do not exist in their single possible state instead they exist in their all the possible states.
for example-
[NOTE- don't confuse spin to be something like electrons are spinning on their axis, no please not I will describe spin in later Blogs]
now the electron has two possibilities in aspect of spin, 'up spin' and 'down spin'. According to superposition principle the electron is not present in one of the single possibilities mentioned above, but occur in both possibilities together, means the existence of 'up spin electron' and 'down spin electron' together.
2- Measurement Rule: It states that till when we don't observe Quantum particle it occurs in superposition state but as we observe or measure the Quantum particle it's wave function collapses and in the end a single possible state is obtained which becomes our Reality.
In Quantum Entanglement Entangled particles are used, let us understand what are Entangled particles and how they are formed:
Imagine we have a energetic Photon, and this energy can be converted to mass using Einstein's mass-energy equivalence. for example we can make other different particles using photon but our UNIVERSE has laws which decides how and what would be the nature of these particles, as photon has no electrical charge that's why the electric charges of produced particles must add up to zero.
which means if a photon produce a electron then it should produce a positron to maintain the electrical neutrality. along with this there is a property which is called as conservation of spin-
photons have no spin but electrons and positrons have their spins, it can be 'up' or 'down' and one of them must have 'up' spin and other one must have 'down' spin because then only they add up to zero spin(which correspond to photon) but we can't specify that which one would have which spin. if we take the perspective of superposition state, till when we don't observe and measure them they occur in 'up state' and 'down state' together. now if we talk about Entangled state, it is the state in which two particles are linked in such a way that they exist only in combined state which means without knowing the states of both the particles we can't define the state of a single particle. if you didn't get it yet understand with an example- we have an electron and a positron, there spins could be 'up' or 'down'. which particle have which spin that we don't know. In superposition state it can be represented as:
here electron and positron are in 'up-down' and 'up-down' spins together. which means without knowing the state of one we can't tell the state of the other and in conclusion we can say that in Entanglement, particles can only be described through joined states.
According to EPR paradox or Quantum Entanglement if we have two Entangled particles and if we somehow get the state of one particle then we can surely tell the state of other particle irrespective of their distance. for example- after measuring if we get the spin of one particle to be 'up' then we can tell that other particle would have it's spin 'down' and vice-versa. Quantum Theory explain it through this way- As we have two Entangled particles, there properties are linked in such a way that both can exist only in combined state. Before measuring both particles are present in superposition state, which means electron and positron have their spins 'up-down','up-down' together. it can be represented as:
but as we measure any one of them, their wave function collapses and amongst their two possible states only one would be selected .
if we get spin of first particle to be 'up' then second one would have 'down' spin.
or if we get spin of first particle to be 'down' then second one would have 'up' spin.
As Entangled particles exist in combined state only, it doesn't makes sense that these two particles are kept at which distance from one-another. the effect is instantaneous and is independent of distance.
which means if we keep one particle in first end of the UNIVERSE and other one in the second end of the UNIVERSE, then also spin state observed in the first particle changes the spin of other particle and would be instantaneous. As the state of Entangled particles depend on the measurement and observance of one of the particle present in Entangled pair, it can be seen that these particles inform their states to each other with speed more than Light. but Einstein's special theory of Relativity states that-"Spread of Any information in this UNIVERSE can achieve maximum to the speed of Light ."
then how it is possible that Entangled particles present in two different ends of this UNIVERSE effect each other instantaneously because if the exchange of information is taking place with the speed of light then also information should take much Time that's why Einstein called it a paradox.
Einstein agree to the fact that if two particles are away from each other and if we know the state of one particle, state of other one could be found but he didn't agreed that information between them can travel with the speed more than the speed of light. He believed if we have local hidden variables and if we somehow able to know the state of one particle then state of other particle could be obtained at that time only, information doesn't need to travel with the speed more than light.
Quantum Entanglement was firstly experimented by John Steward Bell and this experiment has proved the Quantum Entanglement Theory to be true, and it has been tested many times till now.
But it is still a mystery for us that two Entangled particles create which type of medium between themselves that enable them to share the information with the speed more than Light.
“Life is a field of cosmic consciousness, expressing itself in million ways in space-time through quantum entanglement.”
