String theory

String theory and the hidden structure of space and time.

So very briefly and very quickly, I will take you from the time of Galileo to Newton, to Maxwell, to Einstein, and to the present day work in string theory. 

Galileo

Galileo discovered a new law of nature which still holds. You all know about the experiment from the leaning tower of Pisa, where he took two objects, one very heavy one and one very light one, and both of them actually under good condition of weather, basically hit the ground at the same time.

So they fall in the same way, independent of their mass. That's a great law of nature that is still valid.

Issac Newton

There is his famous law of gravitation that how two objects interact with each other. You will notice that this force is actually very weak because if we are standing nearby any person or thing, we are not attracted towards it. But when the distance between object become very small, you see that this force is huge and uncontrolled. It is also very large when the masses are very huge.

Important thing is that this force cannot be screened like the force of electromagnetism because charges come indifferent signs. I put plus charge, minus charge together; so it becomes neutral, no force outside. But gravity cannot be screened and this is the reason why it is really dominant force of nature that shapes large-scaled structure of universe.

Maxwell

Maxwell completed the theory of electromagnetism, and he unified it with what used to be called optics. He showed that light is actually a form of electromagnetic wave which travels at a fixed but very high speed. The important thing is that it's speed is not infinite. It's finite, but it's very large. That is way most of our daily lives, we feel that things happen instantaneously.

This great discovery of Maxwell in the 19th century had a profound impact on postulation of great theory of relativity in 1905.

 Albert Einstein

 Albert Einstein gave the special theory of relativity in 1905. What is theory of relativity? I will explain you in one line that, That it actually overthrew the idea of simultaneity. What does that mean? It means that if I have, for example some rod here with two light bulbs, I switch them - they are connected, so the bulb will go on together, right?

This is simultaneous event for me. However, if you are actually moving with respect to me, at very high speed nearly to the speed of light, It wont be simultaneous for you.  So, simultaneity is not universal. That means what is simultaneous for me or instantaneous is not instantaneous for somebody who's moving with respect to me, and you will detect it experimentally only if your speed is very very high. So, simultaneity overthrown.

 

String theory

If you see water it is a smooth object we cannot say without a microscope that it is made up of molecules. Gravitational law and the general relativity theory when we study the microscopic level of  anything. So this granularity we are after of this space-time. I think it is a great achievements of the subject of string theory, which is going on from the last three decades now, that it has succeeded in at least, in theory, telling you about what are the atoms of space-time, what is the granular structure below this very smooth space-time that we all experience.

The clue lies in the study of black holes in string theory. So now, what is a black hole? A Black hole a solution of Einstein's equations, so it's consistent to Einstein's equations. It is also known today that they exist in nature, so the theory of general relativity had the prediction and can explain objects in the sky, so what better a laboratory than to understand the granular structure of space-time in terms of black holes? A black hole has a very peculiar feature that is it surface called the horizon. It's a one way gate. If you fall in, you can't get out. If light falls in it cannot get out.

Something very very important happened in a the early part of the 20th century. A new mechanics was discovered. It's called quantum mechanics. While it is true that general theory of relativity very few practical applications except setting your GPS very accurately. That's a only application I can tell you about. Quantum mechanics has applications which are totally ubiquitous, I mean every thing that is working in your room, all the electronics, all the computers, everything works on quantum mechanics. Laws of nature are different when we approach the system to be very very small like atoms, electrons, molecules. But when lots of them come together then you can apply classical mechanics of newton.

String theory is basically that the smallest thing the universe made up of is not atom but it is a string. Inside the atom there is a nucleus and electrons, Inside the nucleus there are protons and neutrons, Inside the neutrons there are Quarks, and inside the quarks there is a thread like structure which is known as String.  

The whole universe is made up of strings. All the strings vibrate at different frequencies by which an object is formed. Different frequency posses a different object.

According to the string theory the string is the only thing in the universe which has zero dimension.