When the Stars Go Cold: All about the Heat Death Phenomenon!

The universe is a plethora of diverse, gleaming objects - galaxies, stars, and many more. We are very fortunate that today we have the ability to witness these beautiful objects through the powerful telescopes that are at work 24/7, capturing the lights coming from celestial objects. But, what if I tell you that our future generations will never be able to experience these heavenly views, not even with the powerful telescopes we built? This is because our universe has been expanding since its birth (believed to be the Big Bang).

In the vision of Edwin Hubble in 1925, it came to light that all the galaxies are moving away from us (i.e. from our galaxy), and more fascinatingly, the ones that are farther away from us are moving at even faster rates than the closer ones. This could only be explained if we say that it's not the galaxies that are moving in space but the space itself that is dragging them away from us, and hence we can conclude that the universe is expanding as well as accelerating.

So, it means that in the far future, all the celestial objects will have moved so far away that no light from them will ever reach us, leaving us alone in space. More frighteningly, in the far future, our species will not be in existence to experience this horrifying loneliness. That is because at some point, all the processes, including the ones that support life, will cease to work. Nothing but the leftover heat will remain in the universe, with everything else frozen. That is the reason why our end of the universe is also called "The Big Freeze".

Edwin Hubble

Let me elaborate;

There is an inherent rule of the universe that makes sure that no process is finished without giving back to the rest of the universe in the form of heat. In simple words, any process that happens in this universe, no matter how much energy we provide it to work perfectly, will always leave some waste heat energy. A simple example could be - when you use your mobile phone or any electric gadget, you will experience some heat being given off from it, which is nothing but waste.

This brings us to the most fundamental concept that exists and rules physics, which is entropy.

Entropy is a very esoteric topic, that can have many meanings associated with it. One of them is disorder. Basically, in thermodynamics (which is the study of energy and heat transfer in gross bodies), there is a rule that must be followed to apply thermodynamic principles in practical life, which says that entropy must always increase in any process that exists in this universe.

You would never see a hot cup of tea kept on your desk become hotter but would always observe a drop in its temperature, or you would never see broken pieces of glass combining again to form an unbroken glass but would always see the glass getting shattered into pieces.

These examples tell something fundamental about the nature of our universe, or more precisely, about the arrow of time. It seems that our nature loves disorder. It's because for any system to evolve, there are many ways in which it can evolve, but nature selects those ways that have a higher number of possibilities. For example, let us say you have six dice and you roll them.

There is a very small chance that you will get all sixes on every die perfectly ordered since there is only one way to get that, but there are many disordered arrangements of dice possible, and nature tends to favor those disordered arrangements due to having many possible choices. This number of choices is what we refer to as entropy.

Similarly, in any process, there are very few ways to utilise the energy and get 100 percent efficiency, and there are many different possibilities to utilise part of the energy and dissipate the rest in the form of heat or another form of energy. But it seems that if this continues to happen, then there will not be any ordered form left to evolve into a disordered form. In other words, all the evolutionary processes will cease to exist, and only leftover heat energy will be left.

Just as the universe is expanding, its entropy and disorderedness are also increasing, and finally, in the far future (about 10^100 years from now), everything will freeze out. For any process to happen, there should be a flow of energy guided by the entropy principle, but since there will be no ordered form left, no energy transfer will happen and no evolution will happen. This is what is referred to as the "Big Freeze" or "Heat Death of the Universe".

Author: Sayali Sawant

Editor: Sanskriti Nayyar

Illustrator: Sanskar Srivastava