The word dark is present in both dark matter and dark energy and this creates confusion because many people think this is the same thing They are different, and today we will only talk about Dark Energy. Dark Matter is also important if you want to know about Dark Matter Click Here.
What is Dark Energy
One is the big question present then was what is the future of our universe? We knew this that our universe is expanding but the question was how much is the expansion declaration? There is matter is our universe so we knew it decelerate but what is the speed of its declaration? Just imagine what a big surprise it was for the astronomers then they learnt this that not only the universe is not decelerating on the other hand it is acceleration. This is what astronomers call “dark energy”.
Our Universe Expand or Static
When we talk about the universe we have to start with Einstein’s general theory of relativity. This was published in 1915 and one key factor was that the fabric of our universe is of space time, space 3 dimensions (length breadth and height) and one dimension time.
Now in 1915 scientist thought that our universe is static, it is not changing but Einstein’s general theory said according to its question our universe should expand but Einstein did not like this theory. He said my theory predicts that the universe should expand, but the universe is static. So he added an extra factor in his equation.
This is called lambda and astronomers later named it “Cosmological Constant”. This is one sense an anti gravity force because its theory predicts that our universe should expand, but this lambda factor in the equation is making it static.
Now around 1925 Edwin Hubble, an astronomer (Hubble telescope is named after him) saw the Galaxy in the universe and observed that all the galaxies are moving away from us. One implication of this is that our universe is expanding, and this result was confirmed letter.
If Einstein had not added the cosmological constant or lambda in his equation then this would have been a stunning prediction of the general theory which would have been confirmed by the expansion of the universe. We know that our universe is expanding, and we also know that matter is present in the universe. One prediction is that the expansion must be slowing down. The question was what is the rate of that declaration? I give you an example.
Example: When I throw a ball it upwards when is going up the gravity of earth decelerates its speed when it is going up but because it speed is not much it goes up, stops and start coming back towards Earth. This expansion of the Earth is taking place in the same way as this ball goes up.
In the 1990’s we did not know that this expansion will keep on going forever or it will stop and the universe will collapse which the astronomers called “Big Crunch”. Or this is also possible, if there is not enough matter in our universe that it keeps on expanding forever like this ball if it goes like a rocket more than our escape velocity then it will keep on going and escape from the Earth’s gravity but even then the speed will decelerate because the earth’s gravity is pulling it back. So this was the biggest mystery for astronomers in the 1990s century.
How did the astronomers find out?
For this, you have to find out what is the speed of expansion of the galaxy. Which are very far in our universe and to know this who should know the distance they are from us. For this astronomers use a distance measurement tool called “Type 1A Supernova”. Basically this type Type 1A Supernova is a small star or a core (white dwarf)
Which explodes, and when they explode for a few days, this exploding star becomes bright than all the stars in the galaxy This supernova can be seen by us up to a very far distance, and the supernova is always made from one type of stars. Astronomers team used this supernova and tried to deceleration of our universe. But the surprising thing was when they saw the results they came to know that our universe is not decelerating and not only this but our universe is accelerating. This is just like if I throw this ball, not only this that it does not slow down rather its speed goes on increasing. This was a very surprising and unexpected result.
Now astronomers think that the reserves actually tell us that our universe is expanding. In 2011 the Nobel Prize was given from this discovery.
How many Dark Energy exist
Now we know that if we now see matter energy in our universe, you can use matter energy interchangeably. You and we all electrons, protons, neutrons etc is only 5% of the universe.
Galaxies millions of millions are only 5%. 27% is dark matter which does not interact with the light only with gravity and 68% is dark energy about which we do not know what is it. This is a strange thing when we say that normal normal matter is 5% only. But this is what the results tell us.
General Theory of Relativity
The question now is why is the universe now accelerating?
Remember Einstein’s blunder in which he had added the factor lambda or cosmological constant which is the sort of anti gravity factor. Astronomers have brought it again. It is presumed that when we talk about the general theory of relativity, may be this factor which Einstein had put in one an ad-hoc basis (he did not know then that the universe would be accelerating) But now astronomers use it in the general theory of relativity.
Dark Energy according to theories
One idea is that maybe Dark Energy is a property of our universe, this acceleration is the property of the fabric (spacetime) which is accelerating it. Why is this dark energy property? Maybe its related to quantum physics.
One prediction is that particles and antiparticles are constantly being produced in the empty space because of this production, a vacuum pressure is created due to which our universe is accelerating. Is this really true? We do not know. This is another called “Quintessence” by astronomers.
In which astronomers, which says that maybe there are fields in our universe such as the Higgs field (you must have heard about Higgs Boson), this type of field is probably accelerating it.
Future of our Universe
Leave everything because up till now we do not know what is dark energy and why is our universe accelerating? So what is the future of our universe? It seems that our universe will keep on expanding forever. This idea, which we had before that maybe the universe will stop after expanding and collapse in the big crunch no longer seems valid.
No, it seems our universe will keep on expanding forever. After all this what can we say about dark energy energy?
What we say about dark energy?
Not much, we do not know much about dark energy. But leave aside dark energy. According to me the most fascinating thing is that humans of such small stature on this earth can think of such tests which can tell us about the whole universe and its future. I think it is fascinating.