Future

The truth about predicting the future revealed

ARYAN BANERJEE
Aug. 8, 2021

We can see regularities in the behavior of nature. These regularities are obvious in the motion of planets and other heavenly bodies. These regularities have helped scientists to make more fundamental laws about the universe in which, first to discover was Newton's theory of gravity.

Can we successfully predict the future?

The idea that the state of the universe at one time determines the state at all other times has been a central principle of science ever since Laplace’s time. It implies that we predict the future in principle at least. In practice, our ability to predict the future is very limited by the complexity of the equations.

Ask those, who have seen Jurassic Park, will know this means a tiny disturbance in one place can cause a major change in another. For example, a butterfly flapping its wings in Australia can disrupt a marriage ceremony in Central Park, New York by bringing a Storm. This is known as the Butterfly effect! The problem is that it is not repeatable. The next time butterfly flaps its wings a bunch of other things will be different, which will influence the weather.

Another Disaster!

Despite these practical difficulties, scientific determinism remained the official dogma throughout the nineteenth century. However, in the twentieth century, there were two developments that show that Laplace’s vision, of a complete prediction of the future, cannot be realized. The first of those developments was what's called quantum physics.

This was suggested in 1900 by the German physicist Planck as a billboard hoc hypothesis, to unravel an impressive paradox. According to the classical nineteenth-century ideas dating back to Laplace, a hot body, sort of a piece of red-hot metal, should give off radiation. It would lose energy in radio waves, the infra-red, light, ultra-violet, X-rays, and gamma rays, all at an equivalent rate. This would mean not only that we would all die of skin cancer, but also that everything in the universe would be at the same temperature, which clearly it is not!

An elegant solution

However, Planck showed one could avoid this disaster if one gave up the thought that the quantity of radiation could have just any value, and said instead that radiation came only in packets or quanta of a particular size. It is a bit like saying that you can’t buy sugar lose in the supermarket, it has to be in kilogram bags. The energy within the packets or quanta is higher for ultra-violet and X-rays than for infra-red or light . It means unless a body is extremely hot, just like the Sun, it'll not have enough energy to offer off even one quantum of ultra-violet or X-rays. That is why we don’t get sunburn from a cup of coffee!

It was not until 1927, that Werner Heisenberg another German physicist pointed out that one could not measure simultaneously both the position and velocity of a particle exactly! To see where a particle is one has to shine a light on it. But by Planck’s work, one can't use an arbitrarily small amount of light. One has to use at least one quantum (also called quanta; Plural of quantum) of light.

This will disturb particles and change their speed in a way that can't be predicted. To measure the positions of the particles more accurately you’ll have to use the light of short wavelengths, like the ultraviolet, X-rays, and Gamma rays. But, again by Planck’s work, quanta of light will have higher energies than those of visible light. So, they will disturb the particles more. It is a kinda No-Win Situation: the more accurately you try to measure the positions of the particles, the less accurately you measure the velocity of the particle and vice-versa.

Heisenberg’s Uncertainty principle

This is summed up in the uncertainty principle that Heisenberg formulated: The uncertainty in the position of particle times the uncertainty in its speed is always greater than the quantity called Planck’s constant, divided by twice the mass of the particle.

Einstein was not happy about this apparent randomness in nature. He summed up his views in his famous phrase “God doesn’t play dice”

So the question remains can we predict the future?

Erwin Schrödinger (another badass) from Austria and British physicist Paul Dirac put a new theory, in which particles don’t have well-defined positions and speed. Instead, they are represented by what is called a “Wave function”. This is a number at each point of space and the size of the wave function gives the probability that the particle will be found in that position. The rate at which the wave function varies from point to point gives the speed of the Particle. The wave function is all one can know about a particle, the combination of its position and its speed.

If you know the wave function at one time then its values at other times are determined by what is called the Schrödinger equation. Instead of being able to predict the positions and speed of particles all we can predict is the wave function, nothing more. However, it is still possible to predict a combination of position and speed, but perhaps even this limited predictability might disappear if monsters of the Universe, black holes, are taken into account!

Share this with someone to let them know about the true beauty of physics! Thank you for reading this far!