What is Dark Energy?

DEFINITION

Dark energy is a form of energy in physical cosmology, astronomy, astrophysics, and celestial mechanics that is supposed to continually expand the universe and push galaxies apart.

According to the known laws of physics, an object that moves in any way either stops by decreasing its speed over time or continues its movement at the same speed if there is no energy loss. For example, the velocity of an object launched on Earth decreases and stops after a while. This is because on Earth it loses energy due to friction and gravity. If we throw the same object in an environment (in space) where there is no gravity and air, it will move until an obstacle appears in front of it. On the scale of the universe, this obstacle is the force of mass gravity. The universe itself, contrary to the aforementioned laws of physics, has been expanding since the Big Bang and the rate of expansion of the universe is increasing over time.

When scientists discovered this, they decided that there must be an energy that increases this speed. This putative energy has been called dark energy. In 1980, Alan Guth and Alexei Starobinsky suggested that a negative pressure field similar to dark energy triggered the sudden expansion of the universe after the Big Bang. In 1998, Saul Perlmutter and Brian Schmidt stated that, as a result of their observations, the expansion rate of the universe increased and that it was dark energy, which we can call a kind of internal tension of space. Research on dark energy, which cannot be fully resolved, is still ongoing.

OBSERVATIONAL EVIDENCE

Evidence for dark energy is indirect but mainly comes from three independent sources:

Distance measurements showing that the expansion of the universe is greater in the second half of its life and their relationship to redshift.

Theoretical need for a form of energy other than matter and dark matter (absence of any spherical inclination) to create an observably flat universe.

Measures of large-scale wave patterns of mass density in the universe.

Estimated distribution of matter and energy in the universe. The top chart shows today, and the bottom chart shows 380,000 years after the Big Bang.

dark matter and dark energy

The word dark in these two concepts means that; This is due to the fact that they do not interact in any way, let alone with matter, even with light. Light is the key to seeing, but these two concepts are invisible because they do not interact with light. After the big bang, the gravitational force of dark matter was probably the dominant of the universe for the first 5 billion years, after which dark energy became the absolute ruler of the universe. Material laws as we know them relate to only roughly 5 percent of the known universe. The remaining 95% is still a puzzle to us. As a result of recent observations, it is thought that 23% of the universe consists of dark matter and 72% of it consists of dark energy.

In fact, the concept of dark energy was first introduced by Albert Einstein. Using his formulas according to the theory of relativity he found, he calculated that the universe could never remain at a constant volume, would expand and/or collapse. However, Hubble called this new energy absurd energy, which he found by proving that the universe is always expanding, and he did not care about the dark energy he actually proved with his formulas.

HOW DOES DARK ENERGY EXPAND THE UNIVERSE?

Looking at distant galaxies with the Hubble space telescope, astrophysicists found that the universe has been expanding at an accelerating rate over the past 5 billion years. This is caused by dark energy called the energy of the void. However, the amount of dark energy in the universe is constant. So how does fixed energy accelerate the expansion of the universe? Will the universe, overblown by dark energy, be torn apart someday in the future? Let's see together.

Cosmic Face Lift

In fact, dark energy and dark matter are very similar in some negative ways. For example, we cannot detect or measure dark energy, and we cannot touch this mysterious energy field. However, we see how it affects the universe.

For example, while dark matter affects the universe at every scale with the additional gravity it creates; Dark energy begins to affect space only from a distance of 3 million 260 thousand light years. Here's a much weirder situation than dark matter, and let's explain it right away:

Dark matter is sparsely dispersed in space and interacts weakly with gravity. Therefore, dark matter's gravity is also too weak to be considered at small scales. Dark matter only attracts massive objects such as globular star clusters and giant gas clouds 72 light-years across.

PAINS OF CREATION

Dark Matter attracted huge clouds of gas and dust that would give birth to the first stars in the universe. As a matter of fact, if it didn't, the gases would be sparsely dispersed into space, and the first stars would not have formed when the universe was 180 million years old.

The first stars, on the other hand, formed when gas gathered into one spot by dark matter collapsed under its own weight and into small balls of gas.

In short, dark matter did not directly initiate star formation. The gravitational pull of normal matter primarily caused the collapse of individual stars to ignite. However, dark energy is only released on large scales and in this respect shows very different properties from dark matter:

Imagine a space where there is no such thing as dark energy at a distance of 10, 100, 1000, or even 1 million light years. Let the dark energy be so weak that it is negligible at these distances, there is no active dark energy at these short (!) distances! Let the dark energy cause the universe to expand at an accelerating rate from a distance of just 3.26 million light years.

WHAT EXACTLY IS DARK ENERGY?

Since dark energy is the energy of empty space, it only appears if there is enough empty space in the universe. In this respect, it is not like electromagnetic energy, that is, it does not spread into space like a force field. On the other hand, it affects the whole space and causes its expansion.

That's why it's so different from dark matter; because dark matter creates a gravitational field that spans all space.

Don't be surprised, though, that while dark energy isn't a force field, it affects all of space, causing it to expand. I will explain this seemingly contradictory situation. But at least now that we understand that dark energy is the energy of empty space, we can also tell at what distance it arises.

3 SHAPES OF SPACE 

Closed Space: The universe will stop expanding and collapse on itself, turning into a black hole and disappearing.

Horse Saddle Hyperbolic Space: The universe will expand forever at an ever-increasing rate.

Flat Space: Our universe. The universe will expand forever at an exponentially increasing rate with a constant multiplier, that is, at a constant rate of acceleration. This is provided by "Dark Energy".

From a distance of about 3 million 260 thousand light years (1 megaparsec), dark energy causes space to expand at a speed of 70 km per second.

In fact, dark energy appears at shorter distances. However, the average speed of stars in a galaxy is 60 km per second, and the average speed of galaxies reaches 220 to 600 km per second. For this reason, we realize that dark energy causes the expansion of space only at long distances.

To put it more precisely: Dark energy is only noticeable at a distance of 1 megaparsec, and only at a distance of 60 million light-years defeats the gravity of matter and dark matter in the universe. That's why the universe is constantly expanding.

The expansion of space will never stop; because 26 percent of the universe is made up of matter and dark matter, and 74 percent is dark energy. Although dark matter is 5 times more than normal matter, the combined mass of these two is not enough to prevent the expansion of the universe.

There's more; If you look at the pictures, you'll see that there are three possible forms of outer space, encompassing the observable universe 90 billion light-years across. globe shape, saddle shape and plain paper.

I know you envision the observable universe as a sphere. For this reason, you will say, “Sir, how can the surface of a sphere be in the form of a sphere, horse saddle or flat copy paper? Shouldn't the surface of the sphere be round like an apple peel?" This is because the universe is actually 4 dimensional:

The universe could be a 4-dimensional hypersphere. We are three-dimensional creatures. It is very difficult for us to imagine and draw a 4D sphere. But something like this.

SPACE-TIME IS 4 DIMENSIONAL

The universe is made up of space and time. Therefore, there are 3 space and 1 time dimensions in the universe. In this case, the true shape of our universe could also be a 4-dimensional hypersphere. However, when we say the shape of the observable universe, we only take into account the 3 space dimensions and do not count the time dimension.

However, do not try to visualize 4D objects in vain, the human brain cannot perceive it. For now, just focus on dark energy and that space is as flat as copy paper fresh out of the package. I will give you an example:

The area called flat space is actually the 3-dimensional surface of our 4-dimensional hypersphere-shaped universe. Think of it this way: Our world is round, but from the ground it looks flat to us. That the Earth is round is only evident after the horizon or when you go out into space.

SO IS SPACE REALLY FLAT?

Straight as far as we can measure. For this reason, we can say that what we call the observable universe is the 3-dimensional circle on the surface of a 4-dimensional hypersphere. A circle about 90 billion light-years across. But the actual shape of the universe, including time, is the 4-dimensional hypersphere. Because the observable universe is a tiny fraction of this sphere, it looks flat, like Earth.

Since space is flat, the observable universe could also be the 3D surface of a 4D hypersphere. More things fit on the 3D surface of the hypersphere than the 2D surface of the normal sphere.

SO WHERE DID THE DARK ENERGY COME FROM?

That's exactly how it came out: When Einstein developed his general theory of relativity in 1915, he saw that the universe was unstable: Space would either expand or collapse on itself. This did not fit the divine and perfect static universe design in Einstein's mind. So he made up a number called the cosmological constant and added it to the equation of the universe to get a static universe.

Einstein later called the cosmological constant the biggest mistake of my life! The reason for this was Edwin Hubble. In 1929, the American astronomer Hubble found that all galaxies far enough away from Earth (60-70 million light-years) are moving away from us.

This showed that the universe was expanding, and moreover, all matter and energy in the universe had been gathered in a single point in the past. In short, Hubble had found the big bang! The universe was born out of nothing with the big bang and continues to expand today.

ALL THANKS TO THE DARK ENERGY

Dark energy makes the universe heavier by doing what matter and energy cannot. For this reason, it prevents the expansion rate from increasing exponentially over time. Only space and the galaxies in it are moving away from us at an exponentially increasing, but constant multiplier, rate.

For this reason, we can say that we live in a very lucky age. We discovered the big bang theory and that the universe is expanding because we can see galaxies moving away from us. However, if we lived 10 billion years from now, galaxies outside the local galaxy group would be too far away for us to see.

Thank you for reading. I returned to the blog with this post. More articles will follow. stay well!

Resources:

Khosan

Wikipedia

Euronews