friends, last week we saw a VERITAS on the wave function collapse. We saw that an observation of a superposition :
a|+1/2> + b | -1/2> yields 1/2 or -1/2. And that the observation collapses the wavefunction into one of these two states.
One of my very close friends has raised an objection about this. We will call this friend of mine Saki for the rest of this VERITAS. Saki says: ” Thre is nothing very hi-fi about this … This in common man’s language is similar to the “light in the fridge” problem. How do you know if the light is switched off when the door of the fridge is closed? The way to find out is to open the fridge, in which case the fridge is not closed anymore.”
In today’s VERITAS we will examine Saki’s arguments in detail and we will see how our quantum mechanical example differs from this.
take a normal fridge. Open its door. You see a light inside it. Now open the door again, you will see light again. Do this experiment a 1000 times. Evertime you open the fridge you will see light. So you say that “when I open the fridge I see light”. And you are absolutely correct! Saki and I are in agreement here.
Now take a quantum fridge( dont bother where you will find it. This is a thought experiment.. the sort of stuff theoretical Physicists delight in). The quantum fridge has 2 doors. One door on the front and another at the roof. They are both connected to the same light. Now open the front door. You may see light or you may not see light. Open and close the same door 1000 times. And you will see exactly the same thing as you saw the first time. And you can say that there is no mystery here: either the light works or it does not work. But whenever I open the fridge I see what I EXPECT to see. If I saw light once then the future openings will always show me light. If I saw no light then the future observations will also show me no light. We have no right to think there is anything strange here. This is normal. Scientists dont make strange theories when simpler reasons are possible. Here too Saki and I are in agreement.
Now the mysterious : The quantum fridge has 2 doors. Open the front door. You may see light. Now close this and open the top door. You may or may not see light: lets say you do not see light. Now close this and open the front door again: there is NO gurantee that you will see light now! You may not see light. You expected to see light here because your earlier experiment with the front door showed light. But this is against your expectations. Now do this experiment a 1000 times : each time you open the front door, record the obsarvation and close it. Then you open the top door. record, close. After a 1000 observations you will see this : About 500 openings of the front door showed light. And about 500 openings of the top door showed light. THERE IS NO PATTERN HERE! Plot it and you will see NO corelation between the results of the top door and the results of the front door. There is NOTHING in our everyday lives that behaves like this. It is something like this: An observation of the top door destroys the results of the front door. If you open the top door then the results of opening the front door are RANDOM! There is a 50% probability of getting light and 50 % of not getting light.
And the opening of the front door make the results of the top door random. Here Saki’s line of reasoning breaks down.
The fridge is not a concorcted example. This is similar to the electron spin. If you measuse spin in the x direction you may get 1/2 or -1/2. Now if you measure spin along z direction you may get 1/2 or -1/2. Now if you measure spin along x you have a 50% probability of getthing 1/2 and 50% of getting -1/2.
But if you had measured spin along one direction always then you will always have got the SAME result. An observation along one direction COLLAPSES the wave function into a state. But an observation along a orthogonal direction will uncollapse it again into a superposition after which the results of its observation would be a probability.
The probability in Quantum Mechanics is real! And you will never see something like this in your everyday life!!
Friends, Nature is infinitely mysterious. The Universe is a grand game in which even the rules are more mysterious than anything you have seen. Why do you play with little games created by little people with trivial rules???!! Only the mysterious game of nature created by the Infinite Intellect deserves your time and effort. We have a tool called Science to understand this game.
Byron said :
“THERE is a pleasure in the pathless woods,
There is a rapture on the lonely shore,
There is society, where none intrudes,
By the deep sea, and music in its roar:
I love not man the less, but Nature more,
From these our interviews, in which I steal
From all I may be, or have been before,
To mingle with the Universe, and feel
What I can ne’er express, yet cannot all conceal”
Go, wondrous creature! mount where Science guides:
Go, measure earth, weigh air, and state the tides:
Instruct the planets in what orbs to run,
Correct old time and regulate the Sun;