Invisibility in Plain Sight: Dark Matter and Dark Energy

 Here's a mind-bender for you:

The Universe is everything that exists, right? And, scientists are saying that the Universe is expanding. So, if the Universe itself is everything, what is it expanding into?

This question randomly came into my mind one day and I have been pondering over it ever since. I looked for the answer all over the web and even asked ChatGPT but I still am not satisfied with the answers. Why don't you readers also give your opinion about what the universe is expanding into? (I shall be waiting for your opinions!🙂)

Now, onto the topic of this post-

What is Dark Matter?

The answer to this question, is 'Nobody knows!'. Actually, I'm going to amend that to 'No human knows!'. There might be a set of Aliens living in the Andromeda Galaxy or the Pinwheel Galaxy, or maybe even on the opposite side of the Milky Way, who know what exactly this cosmic mystery is.

Until now, scientists and astrophysicists have not been able to locate or detect dark matter and consider it as a hypothetical type of matter.

Astrophysicists believe that dark matter is made up of particles that don't interfere or interact with light or electromagnetic fields. Basically dark matter is thought to be made up of particles that do not absorb, emit, or reflect light. Hence, it is extremely hard to find signs of dark matter.

Fig. 1- The estimation of the distribution of matter and energy in the universe.
Image credit:Wikipedia

Scientists speculate that this elusive nature of dark matter could be because of the structure of its particles. Now, normal matter is made up of atoms. These atoms are made up of even smaller units called protons, electrons and neutrons. Speculations suggest that dark matter might be made up of other particles of matter that are not protons, electrons or neutrons.

How do we know that Dark Matter Exists?

After reading the Mahabharat that I have written about dark matter, you might be wondering how we know that it exists.

The answer is that we know that something invisible exists that is acting upon the gravity of the objects that are present around it. Since it is invisible, and has to have some mass to act upon gravity, scientists have termed it as dark matter.

What is Dark Energy?

Now, onto another topic about which the information that we don't know is more than that we know!

See, in the 1990s, before the launch of the Hubble Space Telescope, scientists believed that the amount of gravity in the universe was enough to at least slow down, if not stop the expansion of the universe.

However, Hubble changed this belief in an instant after observing some distant galaxies. According to the calculations, the universe was expanding at an even quicker pace than during the big bang! Talk about mind blowing 🤯!

Fig. 2- A diagram representing the accelerated expansion of the Universe.
Image credit: Wikipedia

But how could this happen?

So, scientists put their brains to work and came up with two main theories to justify this increased pace of expansion-

The first suggested that the theory of relativity given by Einstein was wrong and that a new such theory had to be formulated.

The second and more widely accepted theory (because of which I am writing this) suggested the presence of some anti-gravity energy in the Universe, which pushes things away from each other.

Basically, this is what dark energy is thought to be: An evil arch nemesis of gravity.

How was this theory formed?

The theory of dark matter was formed when two two teams of scientists working independently were surveying Type 1a supernovas, that occur when enormous stars die and produce light so uniformly that they are excellent for measuring distances in space.

Due to Doppler shift, the light from such supernovae that exploded about a few billion years after the big bang has shifted into infrared light.

What these scientists found out was that more distant supernovas that had exploded when the universe was much younger, were fainter than expected. This meant these supernovas were further away than they were thought to be, hence suggesting that the expansion of the universe was actually speeding up rather than slowing down.

This further led to all the drama, as a result of which, dark energy was theorised.

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In brief (ahem, cough), I think that my post would have explained quite well about these two topics (at least as much as we know about them). Even if you still have any queries or suggestions (which is quite expected with this topic), please don't hesitate to contact me using the contact form or just drop a comment below.

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Cloudless nights,
Aarav Iyer

Thumbnail credit: EasthSky