The Big Bang

Big Bang Theory

What is cosmology?

I started this blog to study and try to understand the various aspects of the universe. The name of our blog is thecosmonerds - a place designated for brains with similar interests. A question that still baffles many people as soon as they hear the term cosmology is, what does it mean? Cosmology is the study of the origin and formation of the universe. From the big bang (the theory we are going with and the blog’s topic) to its current state, and the future. It is the study of the large scale properties of the universe as a whole.

Big bang theory is the most acceptable theory when it comes to all the theories surrounding how the Universe originated. The two most important observations that led to the conclusion of an ever-expanding universe that originated from a singularity are namely, the Hubble expansion and the Cosmic Microwave Background Radiation.

Hubble noticed an interesting observation while observing galaxies. He found that the galaxies are moving farther away from us. The farther the galaxy was, the greater was its velocity (now called the Hubble Flow.)  He established the linear relationship,

    v = H * r

where,    v = recession speed

               H = Hubble Constant

               r = radial distance

Finding the exact value of H is a difficult task as it involves measuring the distances of distant galaxies. It has been assigned a value of approximately 21.8 mm/s.ly.

It is natural to conclude, and hence, question; if the galaxies are moving farther apart, there must have been a time they were very close. How close were they? And most importantly, what caused them to move away? The energy released must have been enormous if the galaxies are still receding away from each other despite the gravitational attraction. Was there an explosion? If there was, there might be a factor that is constant throughout the universe.

The last inquiry leads us to the phenomenon called, Cosmic Background Radiation. The cosmic microwave background radiation is the leftover radiation from the Big Bang or the time when the universe began. It is known to be the light that has been in flight across the universe shortly after the universe was born. The light is now so red-shifted that it is in the microwave region of the electromagnetic spectrum. These radiations give the average temperature of the universe, i.e., 2.7 K. The universe had a temperature of 10³² K at the time of big-bang!

So, after briefly discussing the phenomenons that led to the conclusion, we are now brought back to our original topic of discussion, The Big Bang!

The universe began as a singularity, and as we have discussed in previous articles, physics breaks at singularities. So, we can’t exactly talk about the exact time at which the universe formed, say at, T = 0 s. What caused the biggest explosion that would ever happen? What was there before it, if there was a before or is the before even a viable possibility? These questions elude us. But, we can certainly talk about what happened a while later.

T ≈ 10^-43 s. The earliest time at which we could even begin to talk about time. This is the smallest duration of time, called the planck second, the time at which no smaller meaningful length can be validly measured. So, this is the time at which we can say anything meaningful about the development of the universe. It is at this moment that space and time had any physical meaning. The universe was so small that its spatial length was much smaller than that of a proton. It was immensely hot at a temperature of about 10³² K. Quantum fluctuations lay seeds for the universe as we know it.

T ≈ 10^-34 s. The universe had gone under a tremendous expansion increasing in size by a factor of about 10³⁰, The fluctuations have led the universe to become a hot soup of photons, quarks, and leptons at a temperature of 10²⁷ K. Still too hot for protons or neutrons to form.

T ≈ 10^-4 s. Quarks now combine to form protons and neutrons and their antiparticles. The photon is not strong enough to break them. The matter and antimatter particles annihilate and produce energy. For reasons yet unknown, there is a slight excess of matter, and this is the matter that would lead to the formation of galaxies, clusters of galaxies, superclusters of galaxies and us.

T ≈ 1 min. The universe has cooled down enough to allow low mass nuclei ²H, ³He, ⁴He, and ⁷Li. The relative primordial abundance of these light elements is a testimony to our theory. The radiation is present but still can’t move far without colliding with a nucleus. The universe is pretty much opaque at this point.

T ≈ 379000 y. The universe has a temperature of about 2970 K, and electrons can stick to bare nuclei to form atoms. The light is now free to move great distances and thus it begins its never-ending journey. This is what we earlier discussed as the Cosmic Background Radiation. Now, red-shifted enough to be in the microwave range of the electromagnetic spectrum.

T ≈ present. The universe is still expanding at speeds higher than even the speed of light. Leave alone expanding at a constant velocity, it is accelerating! :o Physicists attribute the rate of this expansion to the mysterious form of energy, called dark energy. The general outward motion of galaxies resulting from the expansion of energy is called the Hubble Flow. Apart from this velocity, the galaxies also have been found to have a peculiar velocity that is attributed to some localised attractive forces at work, called the Great Attractor. Calling it as some localised mass would be great injustice because whatever that is it is pulling our galaxy at a rate of 7.78 * 10¹² m/s. Impressive, right?

So, I would conclude this article at this point. It would not have been a difficult thing to notice that many interesting topics diverge from today’s discussion. Be it dark matter, dark energy, quantum fluctuations, or, the great attractor. It surely bores seeds for countless discussions. See you next time.

 Auf Wiedersehen!