The War begins
Did you know that Friedmann was a pilot? 1st of August 1914, the first world war had begun following the assassination of Archduke Francis Ferdinand of Austria by Serbia. Russia came in support of Serbia while Germany supported Austria, preparations for war started, and many people volunteered to fight for their country. Among all of these, a graduate student from Russia also volunteered to participate in the ongoing war.
He worked with the aviation department and was involved in bombing raids in Austria, he even survived deadly attacks, and his bravery got him a George Cross medal. He used his knowledge of physics in modelling bombing targets and helped other pilots with his acquired knowledge of aeronautics as it was his primary interest back then. This young guy was none other than Alexander Friedmann. Later, Russia had to pull out of WW1 due to the ongoing civil war in their own country.
A New Beginning
Friedmann partly regretted his decision to go to the war and decided to stay away from the civil war to focus back on physics. He had various teaching positions at different institutions and moved from city to city due to the ongoing civil war. Then around 1920, Friedmann came across Einstein’s General Theory of relativity which was published back in 1915 but reached late in Russia due to the war. Friedmann took a keen interest in this theoretical work and began to work out Einstein’s equations.
The work of Friedmann
During the time, Einstein and many other scientists believed that our Universe was static(Steady-state theory), and the solutions of his equations also showed that. However, he had made a small error in the calculation that led him to this conclusion. This error of his went unnoticed due to the bias of steady-state theory. When Friedmann highlighted this in a letter to Einstein, he initially rejected it but acknowledged it later. Friedmann’s corrections led to predictions that were contrary to the ongoing conception of our Universe, suggesting that our Universe is expanding!
Friedmann proposed two assumptions, based on which he put forward the solution to Einstein’s equations.
The assumptions were-
- The Universe must be Homogenous
- The Universe must be Isotropic
The famous Friedmann’s equations are foundations of modern cosmology; his equations implied that our Universe has three possibilities for its structure,
- Our Universe is closed
- Our Universe is flat
- Our Universe is open
Our Universe being any one of these, depends on the balance between the rate of expansion and the gravitational pull of the matter present. In simple terms, if the gravitational pull of our universe is less the expansion will overcome it and tear us apart, if the gravitational pull is stronger than the expansion we will get squeezed and in the third case if both are equal the Universe will be stable.
Friedmann’s equations not only told us that the Universe is expanding but also indicated that its rate of expansion is increasing. He predicted this a few years before Hubble observed the redshift of nearby galaxies, confirming the expansion of the Universe. It left the steady-state theory believers astounded.
Friedmann’s work wasn’t known to the west for a long time. But as it gained popularity, scientists researched the density of our Universe, eventually leading to the prediction of ‘Dark matter.’ This also helped in the formation of the ‘Big Bang theory.’
Want to know about the theories apart from the Big Bang which hypothesize the beginning of time? Check out: Big Bang Theory and 4 alternatives to it
A Lucky Accident
Around 40 odd years had passed after Friedmann’s equation and Hubble’s discovery. The Steady-state lost interest, and the idea of an expanding Universe and the big bang theory had become the standard.
In 1964, two guys Arno Penzias and Robert Wilson, worked for Bell telecommunications, using a radio telescope to detect possible sources of interference that would interrupt the planned satellite communication systems. While at work, they got some constant background noise, which they could not trace back to a source. After many system checks, they were still not able to find its origin and had to accept that the noise was from a source uniform all over the space.
Coincidentally, very close to that location, at Princeton University, two cosmologists Dicke and Peebles were in search of the remnant of the Big Bang. When they came to know that Penzias and Wilson discovered the noise, they wondered if this could be what they were looking for. Penzias and Wilson published their discovery and got the Nobel prize in 1978 (hard luck for Dicke and Peebles) But what was the noise? What was so important about it that gave strong proof for the Big Bang?
These guys accidentally discovered the noise we now call Cosmic microwave background radiation; it is uniform throughout space. The radiation has a very distinct spectrum, called the Black body spectrum. Before getting into it let’s take a quick glimpse around the terms ‘spectrum’, ‘Black body.’ Every object at any given time emits as well as absorbs heat energy while doing so only a bunch of wavelengths are involved.
Although, in theory, there is the term ‘Black body’ which refers to a body that absorbs and emits all radiation regardless of its frequency and wavelength. This is theoretical, Surprisingly CMB’s graph is very close to an ideal black body. And after calculations, its temperature was found out to be 2.7 K (pretty cold).
What exactly is this noise? Let’s go a little back in time.
Around 400,000 years after the big bang, the universe was still very hot and Plasma was present everywhere. Due to the high temperature, the electrons could not bind with the proton and neutron to form an atom. Hence the light emitted by the Plasma bounced from one electron to another making a visually opaque environment.
Eventually, when the temperature dropped due to expansion, at around 3000 Kelvin, the conditions were adequate for atoms to form. The light that was trapped bouncing off electrons, was free to wander around making the Universe transparent. The Universe’s stretching changed the light’s colour from orange to red and from red to infra-red. And it is still present, but not visible to us. This old age remnant was accidentally detected by Penzias and Wilson that day.
An excerpt from the book ‘The Clues to the Cosmos’ by Sohini Ghose- experience the big bang for yourselves,
‘Find an old television or radio- not a digital one, but one with rabbit-ear antennae that you may remember from your grandmother’s home. Tune in to a TV channel that has nothing but static, or to a radio station that only hisses with noise. A tiny bit of that noise comes from the background radiation of the big bang that Penzias and Wilson first observed. Take a few minutes to immerse yourselves in the signal-a fourteen-billion-year-old hidden message about our origins. No other TV or radio show will ever be as interesting.’
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