Does dark matter exist?

Hello everyone. I recently read about the search for dark matter and it has fascinated me. So I went ahead and did some digging on the subject and here is what I have to share about it.

What is dark matter?

Fun fact: Just two days ago on October 31, the world celebrated the first dark matter day!

Before we learn if dark matter exists or not, we need to know what dark matter actually is.

Wikipedia defines dark matter as:

In standard cosmology, matter is anything whose energy density scales with the inverse cube of the scale factor, i.e. ρ ∝ a^−3. This is in contrast to radiation, which scales to the inverse fourth power of the scale factor ρ ∝ a^−4, and dark energy, which is unaffected ρ ∝ a^0. This can be understood intuitively: for an ordinary particle in a square box, doubling the length of the sides of the box decreases the density (and hence energy density) by a factor of eight. For radiation, the decrease in energy density is greater, because an increase in spatial distance also causes a redshift. Dark energy, as an intrinsic property of space, has a constant energy density regardless of the volume under consideration.
Dark matter is that component of the universe which is not ordinary matter, but still obeys ρ ∝ a^−3

In layman's terms, dark matter is the type of matter which acts completely different from the type of matter we know today(lets call it normal matter for simplicity).

Sounds crazy right?

Well, its not.

Dark matter is unique in the fact that it does not interact with electromagnetic radiation of any wavelength which means we can not see it; not through any kind of telescope and definitely not through our naked eye. It does not reflect, refract or emit light i.e. its literally invisible.

Which is why it is so difficult to find.

The idea behind dark matter

You may ask "How can you say there is something like dark matter when we can't even see it?"

Dark matter map. Source

The gravitational force(which is not exactly 'just' a force but that is up for discussion in another post) is one of the four fundamental forces of physics. It is actually the weakest among them.

Source

It is responsible for the existence of the universe as we know it. It is what holds everything in the vast space together.

It is the reason why galaxies, stars, planets and their satellites, and all other celestial bodies interact in the way they do.

Gravitational force is the force between two bodies which have mass. So, for there to be gravity there has to be mass.

The universe is so vast that the gravitational force which is not very strong would be able to hold the universe together unless it is filled with matter.

But the gravitational force due to mass of all the galaxies alone is not enough to hold them together. So scientists thought that there must be something else at play here.

One possibility is that gravitational force is stronger at the galactic level which contradicts the inverse square law.

Another possibility is that there must be some form of invisible matter which amounts for the gravity thats holding the strings of the universe which also seems logical. Hence the idea of dark matter was born.

But does it really exist?

We are now back to our initial question.

As dark matter is invisible, it can only be detected by its effects on the gravitational field in cosmos.

Various scientific phenomenon hints towards the possibility that dark matter indeed exists. Phenomenon like the motions of baryonic(normal) matter, gravitational lensing, formation of galaxies, cannot be explained without the possibility of existence of dark matter.

Source

Gravitational lensing is quite interesting.

Dark matter acts like a giant magnifying glass which distorts the light coming from distant stars in the same way as a magnifying glass distorts a drawing on a piece of paper.

@muphy elaborated it further in the comments as

Gravitational lenses originate from the deformation of spacetime due to a large mass: light travels in a straight line, so if space is bent, the path of light bends too, like it does in a lense.
The light of a bright distant object (for example a quasar) will be bent by a massive object. If such massive object is between the emitter (The Quasar) and the observer (Planet Earth), light will be focused and amplified into a very bright point if we are at the focal distance (very very improbable). If we are not at the focal distance, it will appear as a disk (rare), and if in addition we are not well aligned as an arc (most common case).
From the intensity of the arc one can calculate the mass of the body creating the deformation of space time and the bending of the light. We compare it with the luminosity of the massive body, and deduce that 90% of the mass is not visible.

NASA in 2006 had witnessed a collision which further strengthens the hypothesis that dark matter exists in this article.

So does it exist?
I highly think so. What do you think about it?

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Thanks for reading. Please upvote and resteem this article if you liked it.

If I'm wrong somewhere please correct me in the comment section below.

References:

1. Technologyrewiew
2. Wikipedia

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