All that we see today, from soil to metals and from humans to the screen that you are currently looking at, are made up of atoms. An atom is known as the smallest unit of every matter that makes a chemical element.
According to Indians, the concept of Atom or Parmanu was first given by Maharishi Kanad, while the Greeks believe that it came from a Greek philosopher Democritus – who first used the word atom, to signify something that’s indivisible and the basis of everything.
And then in 1808 the English meteorologist John Dalton gave the first modern theory of atoms. But it wasn’t until 1897 when JJ Thompson discovered the negatively charged electrons in the atom and Rutherford discovered the proton – that the “atoms” were proved to be divisible.
And even after that – for a long – long time it was believed that everything in this universe is made up of atoms.
But not any longer!
Today, it is known that atoms only make up a very small part of this universe. All the things that we see around us from the giant galaxies, stars and planets to the smallest microscopic organisms on a slide – form only 5% of the total universe. And only this 5% of universe which is visible to us is made up of atoms.
Then one might ask, what about the rest 95% of the universe? Which is neither visible to us nor understandable.
Well according to the physicists, that unknown and invisible part of universe is “Dark Universe.” Made up of dark matter and dark energy.
How do we know that Dark Matter exists?
Now, to answer this – first we must answer which things are visible to us and how? So, the things which are made up of atoms are visible to us under light. The electromagnetic wave of light when strikes to an object and reflects back to our eyes, we are able to form an image of it.
So, in 1933 when in a series of experiments, a Swiss American astronomer Fritz Zwicky determined the mass of all the stars in the Coma cluster of galaxies. He realized that he could account for only 1% of the total mass needed to hold these galaxies together. That there wasn’t enough visible stuff to provide the gravitational force to hold them together within the cluster.
In 1970s the American astronomers Vera Rubin and W.Kent Ford confirmed the same puzzling result when they measured the motions of individual galaxies and the mass contained in them and realized that the total mass required by the galaxy to hold all the stars and planets within it’s gravitational pull couldn’t be visualized. So, the planets and the stars ought to fly apart and yet, they aren’t! Which meant that the unaccountable mass must be in a form that we can’t visualize.
And this simple understanding led to the conclusion : that the rest of the mass, providing that gravitational force is a non- luminous material, defined as the dark matter.
Evidence:
The first and the foremost evidence is of course, that the galaxies, stars and planets wouldn’t be existing or moving the way that they are, if they didn’t contain the large amount of unseen matter.
The other two prime evidences given in support of black matter are –
- Gravitational lensing
- Cosmic microwave background.
Gravitational lensing is a phenomena best explained by General relativity. It states that large objects like cluster of galaxies between an observer and a far distant light source – acts as a lens and bends the light coming from this light source before it reaches the observer.
So, the Hubble Space Telescope has been used to observe the strong gravitational lensing in Abell 1689 (one of the largest cluster of galaxies in Virgo constellation) and using the measurements of the distorted geometry and the bending of light due to that strong gravitational lensing, scientists have been allowed to calculate the mass present in the intervening space between them which can’t be visualised, i.e., the amount of dark matter present.
What is dark matter made up of ?
Answer is – The super symmetric particles
Dark matter is believed to be composed of non-baryonic matter, or in another word – the matter that doesn’t contain baryons (protons or neutrons). So, one of the best known theories to explain dark mater is ‘The theory of super symmetry.’
Super symmetry or susy for short, predicts a whole new range of particles, some of which like WIMPS could make up dark matter.
WIMPS (Weakly Interacting Massive Particles) according to many can be the major constituent of dark matter, which shows very weak interactions with ‘normal matter’ and make it difficult to be detected.
Another faction of scientists believe, sterile neutrinos to be the particle that makes up the dark matter. A stream of neutrinos come out of the sun and pass through our earth and through us, without us ableing detect it, since neutrinos do not interact with normal matter.
There are 3 types of neutrinos, already known to us. A new – 4th type of sterile neutrinos have been proposed to explain dark matter. These sterile neutrinos are thought to interact with baryonic or normal matter only through gravity.
Creation of dark matter:
Dark matter is something that doesn’t interact with any kind of electromagnetic force. And since light is itself an electromagnetic wave – dark matter could neither absorb, nor reflect light and thus, couldn’t be seen.
But scientists theorized that we could create dark matter, even though we can’t see them (yet). Using the 27 KM long large hadron collider(LHC), in Geneva Switzerland which is also known as the most powerful particle collider in the world.
Within the LHC – two protons beams moves in a circular path, in opposite directions, which are accelerated to almost the speed of light. In this circular path, there are 4 collision points where protons smash into each other within every few seconds.
We already know that protons are made up of even smaller particles – the quarks and gluons. In most collisions the two protons pass through each other without creating any significant difference. However, 1 in a million collision two components of the protons hit each other so violently that most of the collision energy is set free. And thus, producing thousands of new particles. It is only through these collisions that the particles thought to create the dark matter can be produced.
The LHC also constitutes around a 100 million sensors surrounding these four collision points along with huge 3D cameras which measure the newly produced particle’s characteristics like their trajectory, electrical charge and energy. Data from these sensors allows scientists to computerize what each of these new particle is.
But the production of any such particle is extremely rare. For example the production of a Higgs bosons particle in LHC is about 1 out of 3 million, and the particle only exists for a tiny fraction of a second. So, if the LHC could indeed produce the particles that make up the dark matter then it would be an even rarer occurrence that the production of a Higgs Boson particles and make take billions and billions of collisions and years of time to even start looking for dark matter that could reshape our understanding of the universe.
Conclusion:
When in an unpleasant situation, we are often told to, ‘look at the bigger picture’. And this, I suppose is the biggest picture one can get of the universe, which comes with an enormous realization that we, our world and all our problems and the things that we see and feel, only makes up a minuscule fraction of the universe. But that realization should not make us feel small or insignificant because as far as we know, we are the member of the only species known in this universe who had begun grasp even a little about it’s deep mysteries.