I teach physics. Am exploring any hidden talent for blogging.
Quantum mechanics is a wonderful theory that explains nature at the very fundamental level. At this level, nature behaves very differently from how we perceive it in our everyday life. A quantum particle can be at many places at the same time. A quantum cat can be simultaneously both alive and dead. A quantum particle with a well-defined position has undefined momentum. A watched pot never boils, and so on.
There is this ever-growing interest that the weird rules of the quantum world may help us resolve the greatest mysteries we are daunted with. Can quantum mechanics explain consciousness? Can quantum indeterminism restore free will in the otherwise deterministic universe? Can the true randomness at the quantum level help settle the debate between intelligent design and natural selection?
In this article, I discuss reality in the quantum world. With few simple examples involving the spin of the electron (we talked about it in the last post), I will show that the objective reality of science is constructed from subjective quantum realities. I will go through several examples to make my argument. I will then briefly talk about some philosophical implications of the quantum notion of reality.
I will take you to a wonderland where the rules of quantum mechanics could be applied to human interactions, beliefs, and value systems. Our most daunting philosophical questions might have very simple answers.
The objective reality of science is constructed from subjective realities at the quantum level.
A spin of an electron
Remember the quantum coin? The spin of the electron that can have only two values labeled as spin-up and spin-down?
Spin is a vector quantity having three components. When we talk about the spin-up electron, we usually mean an electron with a z component of the spin having a value corresponding to the spin-up state. There is nothing special about the z component though. You could, if you want, measure the x or y component of the spin or the component of the spin along any arbitrary direction. However, what you cannot do is measure two different components of the spin at the same time.
Nature does not allow us to know about the two components of the spin of the electron at the same time. These are what we call incompatible observables. They can not be measured simultaneously. Of course, you can measure the second component of the spin after measuring the first component. But the moment you make the second measurement, the result of the previous measurement becomes void. This is not a spin-specific restriction only. We have a number of quantities in the quantum realm that makes sense only if we consider these individually. The moment we start to take them collectively, we run into problems. You must have heard the joke that if you know where you are, you cannot know where you are going.
Some of you must be wondering if this really is a restriction imposed by nature itself? Or it is just an artifact of the mathematical formalism we have employed to explore nature.
This is a profound question, and your humble quantum physicist is unable to address the issue. All I can say is that our best minds have not been able to come up with a better theory in the last one hundred years.
On the other hand, the theory, with all its weirdness, has brought about a technological revolution. We are promised to witness another quantum revolution in information systems in our lifetimes.
The notion of reality becomes a little ambiguous with the rule discussed above. Let’s imagine a scenario where you have an electron (say in a box), and you measure the x component of its spin. Say you get a result corresponding to the spin-up state. So you write in your notebook that the electron in the box has a spin-up x component.
Now you pass the electron to your friend and request him to verify the result. If your friend is careful in setting up the apparatus and aligns it such that he too measures the x component of the spin, then all will be ok. He would have verified your result. But let’s say that by mistake or intention he sets up the apparatus such that he measures the y component of the spin. Now quantum magic has been invoked, and there is no going back. No matter what result he obtains for his measurement, your result has been erased. The electron no longer has a definite spin-up x component. If you perform your measurement again, there is a 50% chance that the x component of the spin will now be down.
This leads us to a natural question: What is the real spin of the electron?
Is it up along the x-axis as you first measured? Or down along the y-axis as your friend might have obtained? Or down along the x-axis according to your second measurement? Which measurement will hold precedence over which? Was the previous measurement along the x-axis more real than the second one you have performed after your friend destroyed your first measurement? Was the measurement by your friend more authentic? Or should we arrange for an unbiased measurement by an independent observer along, say z-axis? These seemingly difficult questions have a simple answer.
But first, let’s look at another example to appreciate better how weird things are.
Suppose you have a ball that can have one of two colors, say blue or red, and the surface of the ball can be either rough or smooth. Assume also that these two traits — color and texture— are incompatible. This means that nature has put the constraint that you cannot touch the ball while you are looking at it. And you can not look at the ball while you are holding it in your hand.
Suppose you look at the ball and you see it is blue. Now you close your eyes and feel the texture of the ball in your hand. You find it rough. Now you remove your hand and open your eyes again. You might find the ball red. Isn’t it surprising? And magical? You keep on repeating your experiments, and the ball will keep on randomly acquiring one of the possible values for the trait you are examining. This is quantum reality. It comes into being after a measurement, and it keeps on changing as you keep on repeating your experiments.
Quantum reality comes into existence after a measurement, and it keeps on changing with repeated measurements.
A Small World Experiment
We have learned enough quantum mechanics to follow the next argument about quantum reality. Consider a small world (an experiment) where we have a source from which identical electrons are emitted. All these electrons have the same (yet unknown) spin state. This is our unknown objective reality in the small world we have created.
Next, let’s introduce a few subjects in the world. A few experimentalists whose task is to measure the spin state of the electrons, i.e., to work out the objective reality. The electrons from the source are distributed among these observers. Each observer has his separate apparatus and is allowed to set the apparatus independently.
When the experiment is run, each observer will have an independent result for the spin state of the electron he has measured. God will play dice each time a measurement is performed, and a different reality will be invoked after each measurement.
Some observer will get spin up along a direction say a, someone else will get spin down along some other direction say b, and so on. In fact, it is possible that some two observers may have accidentally aligned their measurement apparatus and are, in fact, measuring the spin of their electron along the same direction. But in this case, too, it is quite possible that they get opposite results— spin up for the observer one and spin down for the other.
God does play dice in the quantum world.
The spin state of the electron in this experiment (so far) is thus a subjective reality. Every observer has his own random result for the spin of his electron. This is despite the fact that all electrons were initially in the same spin state. We can now make some interesting observations regarding the outcomes of the small world experiment just discussed above.
- All measurement results are correct. This is true even if any two observers obtain contradictory results. For example, the two observers may accidentally align their instruments with measuring the x-component of the spin. The result obtained by the first observer maybe spin up. The result obtained by the second may be spin down. Both these results are simultaneously true. This is astonishing but true. Quantum mechanics allows having cats that are both alive and dead at the same time.
- It is impossible to get the wrong result. Say that the actual spin of the electron coming from the source — objective reality — was spin up along the x-axis. If it were the case, then no observer can get the spin value down along the x-axis. The only way to obtain the wrong result is either the observer is too careless in performing the experiment or is dishonest in communicating his result.
- All subjective experiences hold an element of truth as all of these have some overlap with the true objective reality.
All subjective experiences hold an element of truth.
The message up to this part is that science at the level of few quantum events is subjective. No two observers can see the same photon. No single quantum particle can be detected by two detectors. There are stars out there beyond the ones we can see with our most powerful telescopes whose existence can not be objectively ascertained. Not because they do not exist. Simply because very few photons from those distant stars reach us, even if we develop the technology to isolate single photons coming from the distant stars, we will still not see those stars as objective reality.
Some of you must have started wondering if anything I am saying is true. Science would not have come so far as an established domain of knowledge if it were just toying with subjective realities. The world we see and perceive around us is an objective reality. How does this fit with the subjective chaotic dance happening at the quantum level? The answer to this question is simple— repetition.
The objective reality from subjective experiences
The objective world we see all around us results from a mind-boggling number of subjective quantum events. The repetition of the experiments brings order in the chaotic quantum dance. Let’s go back to our experiment where identical electrons were distributed among several observers, and each observer measured a separate spin state of the electron. The observers can reach the true objective spin state of the electron if they keep on repeating their experiments and then combine all their results. This is the lesson we can learn from the quantum world.
All our subjective experiences combined together may constitute the objective truth.
Even a single observer who keeps on repeating the experiment can vary the measurement apparatus in a clever way to make it align with the objective spin state of the incoming electrons. At this point, all subsequent measurements with his apparatus will give consistent results. This might very well be nature‘s way to find the truth. We might be required to keep on changing our views and our beliefs until we get rid of all contradictions in our philosophy of life.
There are other examples where we see objective reality coming out of subjective experiences. For example, consider yourself in a well-lit room with a number of other observers. You, along with all the observers, can agree on the objective reality all around you. This reality is again the result of an enormous number of quantum events. If the room is lit with five hundred watt electric bulbs, then in one second, roughly a billion trillion photons are being emitted from the light bulbs that scatter from all the objects present in the room and reach your eyes. If you could squeeze these many observers in the room, you will lose the objective reality.
Alternatively, if you could slow things down to individual quantum events or reduce the intensity of light to the level that only a handful of photons are available in a given time, again you will start experiencing a reality that will be different from the ones experienced by other observers in the room.
For example, you may observe a photon scattered from the painting on the right wall, but your friend sitting next to you may experience a spark from the photon scattered off the showpiece on the left table. At this time, you two have different subjective realities. But if you wait long enough, you will get few photons from the showpiece and your friend from the painting. If you two keep track of all your observations, you will eventually agree upon the same objective reality.
A philosophical wonderland?
What I’ve discussed above is backed by science.
What if this also holds true for our everyday life?
What if the lessons learned from the quantum world could be generalized to the different philosophies of life?
Nature may hold answers to the philosophical questions we are facing.
We all have different value systems, different beliefs, and different religions. What if all these subjective experiences are simultaneously true? What if all these hold an element of truth? Both believers and non-believers are right at the same time? What if the ultimate absolute reality does exist? What if it consists of all our subject experiences combined together? What if the purpose of life is to make as many subjective experiences as possible to realize the absolute reality?
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