M-Theory | how to test string theory | dark matter | dark energy | Wormhole

In the last post on “string theory” we discussed many things like the super symmetry, higher dimensions, strings, need for the theory of everything, different versions of string theory and many more. I request you to first read the previous post and then read this because this is the continuation of it. 

There are many different string theories and that’s a big problem. We need only one theory that can explain everything in the universe. Today we will discuss such an attempt named M-Theory. We will also discuss how string theory explains blackhole, dark matter, dark energy, wormholes, etc. How to test the string theory? And many more things…

But before that we need to know…

What are branes? 

String theory takes into account the 1-Dimensional strings but the M-theory takes branes into consideration. Branes are the fundamental basis of nature but with higher dimensions than strings. Branes can be any dimensional starting from 0 to 9 dimensions. 

Branes can have electrical charge as well as tension (force experienced when you stretch the rubber band). Presence of electrical charge means that the branes can interact with each other using the Electromagnetic force. Branes can move from one place to another. These properties, instead of simplifying, made the theory more complicated. This also introduced more objects into the theory.

You can imagine branes as the surface of trampoline. The surface of trampoline needs to be perfectly adjusted to give you fun. If it is too loose, you can’t jump high and may hit the ground. If it is too tight, you can get hurt by hard hitting. The same is true for branes, branes need to have right amount of tension. 

The introduction of branes and duality played a crucial role in combining the theories together into 1. 

Duality 

Duality is actually a mathematical technique to combine 2 different theories or equations into one. In simple words, when you look at the same phenomena in 2 distinct ways it is physical interpretation of duality. Let me give you some examples to take a feel of the term: -

• Electricity and magnetism were seen completely different from one another. James clerk Maxwell combined them into one electromagnetic theory by 4 equations. That’s duality. 

• Algebra and geometry look completely different. But geometrical figures can be represented with algebraic equations and algebraic equations can be represented geometrically. That’s again duality. 

When closely observed the different versions of string theories were seen to be representing same thing when some parameters were changed. The theories were mathematically equivalent but physically different.

The M-Theory 

Physicist Mike Duff suggested that introducing 11th dimension can combine all the theories. All the theories actually represent the different manifestation of same thing. The “M” here can be anything-matrix, mother, membrane, etc. Scientists have not yet prepared the full complete version of the theory. The theory is in progress. 

The theory takes into account the branes as the fundamental unit of nature. There is a requirement of 11 dimension of space. The super symmetry is also the key feature of the theory. Mostly all the concepts included in string theory are also included here. The 2 new concepts are duality and branes. 

How are particles formed from strings?

The strings basically vibrate all the time. Many strings combine to form a particle. The atom is made from electrons, protons and neutrons. The protons in turn are made up of 3 quarks. While the quarks are made up of 3 quark strings. 

More vibration of string implies more energy and more energy means more mass. hence the vibration of strings is responsible for the mass of particles. Strings are the bundle of waves. This confirms the postulate of quantum field theory which states that every matter is made up of wave packets.

 

The different modes of vibrations lead to different particles. This can be visualized as the vibrating strings of the musical instruments. The different vibration generates different musical node, likewise 

different vibration of fundamental strings generates different particles. This explains why we have found so many fundamental particles. 

How can we test the string Theory?

Testing string theory is very difficult as we are not technologically so advanced. Still physicists have found some ways to test the theory, I will discuss them below in short and crisp manner. 

1. Testing Strings 

These are the basis of the string theory, if it is verified experimentally then theory will gain some scientific importance. The string is very small that it appears point like, of the order of Plank’s length (10^-35 meter). We cannot see it directly. To verify its existence, we need high amount of energy. (particle accelerators may help)

2. Super symmetry

The key to test super symmetry is to search for super partner. Some theories suggest that these super partners are 1000 times heavier than proton. This implies that the super partner must be unstable and must have decayed into low energy particles. 

High energy particle accelerators like the Large Hadron Collider (LHC) can help in the quest of these super partners. The particles need to be accelerated, when they gain high energy they collide. If the energy is missing during collision it can mean: -

• Collision created a new super partner which is actually a dark matter and don’t interact with normal matter. The dark matter is responsible for the difference in energy (confirming super symmetry)

• The missing energy somehow passed to higher dimension and not to 4D space-time (confirming higher dimensions)

Just after the big bang, universe started expanding and cooled down eventually. As a result, the super partners decayed and collapsed to low energy particles that we see today. The universe has broken super symmetry, that’s why it is not yet verified. 

There are many theoretical models prepared to verify super symmetry but not yet verified experimentally. Unless verified experimentally, it can’t be considered fully scientific. One of the models suggest that the dark matter may be the missing super partner. 

3. Higher dimensions

Extra dimensions are also the most important block upon which the theory is built. There is a method to verify the existence of higher dimensions and find them.

The gravity needs to be tested in higher dimensions. If there is violation of inverse square law (the effect of gravity decreases with the increase in square of distance of separation in our 4D world), it can account for higher dimensions. The string theory predicts the gravitational waves in the cosmic microwave background radiation, if we detect these waves it can also verify the higher dimensions. (the detailed explanation is beyond the scope of this post). 

The string theory tells that the higher dimensions are compactified. To verify this, physicists have tested the gravitational force up to 1 millimeter, the results are negative. So, if any compactified higher dimension is present, it is smaller than 1 millimeter. 

String theory agrees with general relativity in case of wormholes and gravitational waves. 

What do string theory say about dark matter and dark energy?

Dark matter is the unseen matter that holds the stars in the galaxy together. String theorists suggest that the dark matter is the gravitational interaction between the branes. Some also say that dark matter is actually the missing super partners. These particles are predicted by string theory but nor yet found. Some computer simulations by physicists say that if we detect some Gama rays from the dark matter, we can verify it. 

Dark energy is the unseen vacuum energy that pushes the galaxies apart. This is the positive energy responsible for the expansion of the universe. it is the dominant part of the universe but string theory don’t explain it completely. In fact, the dark energy left the string theorists puzzled and forced them to make some changes in the theory in order to include dark energy. But all went in vain. 

String theorists on wormhole

Wormholes are the shortcuts in the fabric of space-time that are predicted by General theory of relativity. The string theory also predicts wormholes but the analogy is different. 

String theory states that the world is made up of branes. This branes touch and get connected with each other. When these branes overlap, we can travel from space of 1 brane to the other. This can also lead to exchange of matter and energy from one brane to another.

There are more that 10^500 solutions of string theory. This is hard to verify. Yet the string theory is able to explain many things theoretically. So, string theory can be called a theory only and not the picture of reality unless verified experimentally.

This is was the brief introduction and idea about the string theory. It was a bit technical, I tried to make it as simple as possible. hope u like it. Let me know your views.