The farthest known galaxy is GNz11, which currently resides at a distance of 32 billion light years from Earth. But wait, how could there be a galaxy "older" than the existence of our cosmos? In this video, we'll explore the mystery of this topic.

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Table of content:
0:00 Opening
0:54 The clues from the past
3:05 Why we are expanding
6:31 The idea of the universe without end
9:26 The inevitable fate of the universe

Script:
The expansion of the early universe is adequately explained by the Big Bang theory. That the explosion started it all, from a single point of singularity until everything that now exists. Because of this Big Bang, it is thought that the expansion of the universe will eventually slow down, owing to the "attracting" aspect of gravity. Namely, the gravitational attractions from the stars and galaxies.

So until recently, all evidence supported this accelerated expansion without any exceptions. Observations such as the CMBR and the redshift of galaxies supported this theory.

However, in 1998, two research groups from the Berkeley Lab and the Supernova Cosmology Project found something strange. As expansion can't be observed directly, they look for other effects caused by expansion and deduce the expansion speed based on these observations. By using reliable data from all over the skies, both teams independently discovered that distant supernovae seem to be dimmer than expected. The researchers claimed that when they look at these objects, they look further into the past, to about 79 billion years ago.

This finding shattered the previous theories of sloweddown expansion. Which would mean that the universe expansion is accelerating instead of slowing down. And just recently in May 2018, a research team from The Dark Energy Survey has released the largest map so far. Their findings continue to support this expansion rate change, with a pretty surprising twist—these changes are accelerating over time. Yes, it was all happening regardless of the effect of gravity we talked about before.

To answer why the universe is expanding, it's critical to first understand what caused the expansion. The scientific consensus so far is due to the mysterious #Dark #energy that permeates nearly all of space. Of course, the term "Dark" doesn't really imply that it's dark at all. It's just called dark energy because nobody knows what it is or where it comes from. We can't even see it directly since light can't travel through such a dense and pervasive field, unlike normal matter. It just doesn't behave as anything physicists know about.

Also, the name implies this as energy, like gravity or radiation. But in reality, there isn't any physical evidence for this. When you really dig deep into the theories, there is no way how Dark Energy can interact with matter or radiation. It just operates in a completely different manner. That's why some researchers are calling it "Phantom Energy".

The expansion of Dark Energy is constant, but mainly not uniform in nature. There are regions where expansion happens much faster than others. Take for example a constellation named Hydra. In the relatively far future, due to a faster rate of expansion there, all galaxies in the Hydra constellation will be outside our cosmic horizon. It's not that all of it will be gone immediately, but it's going to be pushed away from our view, beyond our visible universe. All information they contain about their existence will be lost forever.

Imagine if this were to happen today on nearby objects from our planet, say the planets on our solar system. If they began to move away from us faster than the universe's current rate of expansion, eventually all information about the solar system would disappear beyond the horizon. Our future grandchildren wouldn't know that there were something called Jupiter and Saturn. This may be the most disheartening thing you hear today.

When expansion seems to be much higher than expected for a given gravity and density of the object, we call this effect "Gravity Enhancement". The phenomenon was first discovered by Nobel laureate Saul Perlmutter, astrophysicist Adam Riess and the Supernova Cosmology Project. They found out that expansion was much faster than it should be if Dark Energy expansion is constant everywhere.

One popular speculation is that expansion happens due to a mechanism called "Vacuum Metastability". It is an idea that expansion might be due to the universe being in a "quantum fluctuation from nothing". Or in other words, an expansion might simply be a result of our universe spontaneously popping out from nothingness. After all, perhaps expansion is an inherent result of expansion itself. The rate grows exponentially due to a feedback loop that feeds on dark energy tension.