Death of the Universe || Part 1 || The Big Crunch

Before talking about the ways the universe is gonna die, we should know how it all started. The Big Bang is scientifically proven and the evidence is pretty convincing. Let me explain how it is true,

I guess everyone learnt "The Relativistic Doppler Effect" (Doppler effect in light) in their secondary education already. For those who didn't, here is a brief explanation, Let us suppose that you are standing on the side of a road and a car passes by. When the car is approaching you from a distant point, you will experience a significant amount of increase in sound. Also, when it is going away, you will experience decreasing volume. It means, by knowing whether the sound is increasing or decreasing, you can tell the object is approaching towards you or is moving away from you This is "Doppler effect in sound". Coming to the Doppler effect in light, "If a body emitting light is moving away from you, It's light will shift towards the red side of the visible spectrum i.e, it'll undergo a Redshift. If a body is moving towards you, it'll undergo a Blueshift. What does all of this have to do with the Big Bang right?

Yeah, this guy called Edwin Hubble, an American Astronomer, discovered that the galaxies are apparently moving away from the milky way galaxy and, the farther away they are, the faster they are moving away. The ratio of how fast the galaxy is moving away(speed) to how far the galaxy is(distance) is always constant and is called the Hubble Constant. So, now from the observations, we know that the everything in the universe is moving away from us i.e, The universe is expanding. It means, All the other stars and galaxies were closer to you yesterday than they are today and they will be tomorrow. So, If we go back in time, the universe is closer and closer and closer. According to the calculations made by the astronomers, ~(13.798±0.037) Billion years ago every galaxy, every star, every planet, every atom was at the same point. At this point, time was wibbly wobbly the physics as we know it made no sense. All the forces, i.e, Gravitational, Strong nuclear force, Weak nuclear force, ElectroMagnetic force were indifferentiable. As the pressure is very high, the temperatures were very high which was ~(10^30  Degree Celsius). For unknown reasons, The forces split accompanied by an enormous release of energy and rapid increase in space. Which is called The Big Bang. This is how the universe as we know it exists.

Now we know that the universe is expanding. But, Is the expansion speeding up? or slowing down? or moving at a constant speed? Let's get into that too. When you look into a telescope and point it towards any galaxy, the light coming from the galaxy tells you two things,  it's position in the spectrum tells you how fast the galaxy is moving away from you and it's brightness tells you how far away it is from you. If you look at a single galaxy and note down its speed every day,  It would take a million years for you to know the expansion is speeding up or slowing down. Also, when you look at a galaxy you not looking at it as it is now. Light takes time to travel. You are actually looking back in time. So, this implies that "Looking at different galaxies at different distance is a rough proxy of looking at the same galaxy at different times" and with the observations made if you plot a graph between, time and speed of a galaxy there are three likely possibilities, One, you'll get a straight line which means the universe is expanding at a constant speed or an increasing speed curve or a decreasing speed curve. For a long time, Astronomers thought that the expansion of the universe is slowing down. But to their surprise, after doing the calculations and plotting the graph they discovered that the expansion of the universe is accelerating! Astrophysicists say that the reason behind the acceleration of the expanding universe is "Dark Energy" which is yet to be studied and no one knows what it actually is.

Let's revise what all we know till now,

We know that The universe as we know it started with a Big Bang, The universe is expanding, The expansion of the universe is accelerating. The question that might arise in all of your heads is "Will the universe ever slow down or not?" Well, it depends. If the density of the universe is greater than the critical density(Critical density is the density at which the universe is at balance and stops expanding), then the gravity takes over whatever the force accompanies the expansion of the universe. And when I say gravity takes over, I mean, the stars and galaxies will come back closer and closer and collapse into a single point again. i.e, THE BIG CRUNCH. What if this keeps on repeating? after collapse another Big Bang? and another Big Crunch? there is a name for it, "The Big Bounce"

Oh! you came this far? Damn! that's a lot of patience. Thank you!. This is Anirudh Dasari Signing off.