अपरा विद्या प्रवचन (Apara Vidya Pravachan): Beginning of the Universe

Beginning of the Universe

(Hubble Tension)

Debi Prasad Choudhary

Los Angeles, 03/01/2025

What was there before the universe came to exist? May be nothing, may be not-nothing. How did it come to exist? Who can know? Maybe we can never know. These were the serious discussion by the scholars in ancient India that are recorded in the Nasadiya Sukta of Rigveda about 3000 years ago. Only about 100 years ago, we started exploring this question systematically using both theoretical and experimental tools of modern science.

The General Theory of Relativity by Albert Einstein, proposed around 1917, described the universe as consisting of observable material, unobservable material - the effect of which can be observed and dark energy, the presence of which can be observed. The observable material resides in the stars and galaxies. The unobservable material or dark matter interacts with stars and galaxies that can be measured through the speeding stars in the periphery of galaxies.  The effect of dark energy can be observed through the distribution of galaxies in clusters and other dynamics. The theory predicted that the universe is not statics and does expand as first observed by Edwin Hubble at Mt. Wilson in Los Angeles in 1923. Hubble measured the radial velocity of galaxies and their distance from us. Measurement of radial velocity was performed using doppler effect phenomena in light waves, which changes the pitch (frequency) of the waves depending on the direction of motion of the emitting source. For example, in sound waves when a fire truck moves towards us, we hear higher pitch in contrast to the receding truck. Using the spectra of galaxies, Hubble determined the speed at which galaxies are going away or coming towards us. 

The distances to the stars and galaxies are measured using several methods. Distance to the nearby objects are measured with parallax method, which relates the distance with the angle made as seen from two locations. As the distance to the object increases the angle becomes vanishingly smaller. For the distant objects standard candle method is used. In this method, if we know the true brightness of a light source, the distance can be measured from its apparent brightness since it decreases as the square of the distance. One of the standard candle are a special type of stars called cepheids change their rightness periodically. The changing period directly depend on their peak absolute brightness. So, by measuring the period of brightness change it is possible to estimate their absolute brightness, which can be used to measure the distance. Supernova, which are violent explosions at the end of stars much bigger than our sun, can also be used as standard candles. A special type of supernova called Type Ia has a distinct spectra and attains a specific peak intensity. By identifying them using their spectra it is possible to estimate their peak intensity. If they are detected early as the star bursts, their light curve is another method to estimate their absolute intensity to measure distance. Many galaxies harbour both type of standard candles that can be used to confirm the their true distance from us. Large ground based telescopes and James Webb space telescope are used to precisely measure distances to a large number of distant galaxies.

This collection of 37 images from NASA’s Hubble Space Telescope features galaxies that are all hosts to both Cepheid variables and supernovae. These two celestial phenomena are both crucial tools used by astronomers to determine astronomical distance, and have been used to refine our measurement of the Hubble constant, the expansion rate of the universe. Credit: NASA, ESA, Adam G. Riess (STScI, JHU)

Edwin Hubble's original measurements showed that all galaxies, except few nearby ones, move away from us in such a way that the ones situated at larger distance move faster. These measurements showed that the universe is expanding. Recent measurements of more distant galaxies showed that the expanding rate changes for more distant galaxies that show the acceleration of the expanding universe. The rate at which the universe is expanding is known as Hubble constant, which is a crucial parameter to study the universe.

The discovery of Hubble law was a major foundation of modern cosmology, the understanding of universe. Now, we are in a position to actually answer the questions that are posed in Nasadiya Sukta. It is obvious that the expanding universe must have a beginning, around 13.8 billion years ago, when all matter and energy was concentrated at a tiny region that must be very hot and dense. What was in this tiny region? Very dense energy from which the primordial elements like hydrogen, helium, lithium and beryllium are created. The measurement of these elements confirm to this theoretical proposition. As the universe expanded, it cooled to its present form to about 2.7 degree Kelvin. Measurement of the temperature at locations far from stars and violent neighbourhood show that the temperature of quiet space is indeed 2.7 degree Kelvin. This is confirmed by the temperature determined by using the rotational spectra of molecules in those regions. 

The beginning of the universe created space and time immersed with matter and energy. As the universe expanded it cooled, became less dense and matter became clumpier due to gravitational force. We observe the clumpiness of the material distribution in galaxy clusters. Using the Einstein's equation describing the shape of time, space with matter and energy distribution, we can understand the structure of early, baby universe and its subsequent evolution. These components are now very well measured from ground and space. The measurement of expansion rate or Hubble Constant at the early universe that created the clumpiness in radiation distribution in early universe and material distribution in forms of present galaxy distribution is now determined to be different that can not take into account of the measurement errors. 

So, the Hubble constant derived from the measurement of recession galaxy speed (Distance Ladder) and cosmic microwave background radiation (CMB) are not the same. This is profound as perhaps Nasadiya Sukta states. Who knows what happened? But, unlike 3000 years ago, we have the tools now and one day not in distant future, we shall know what exactly happened 13.8 billion years ago. Before that? Who knows. May be no one!

Measurement of Hubble Constant over years. The most recent measurements show that value of Hubble Constant measured using Distance Leader and Cosmic Microwave Background differs significantly.

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 नासदीय सूक्त

(Nāsadīya Sūkta of Rigveda)

नासदासीन्नो सदासीत्तदानीं नासीद्रजो नो व्योमा परो यत् | किमावरीवः कुह कस्य शर्मन्नम्भः किमासीद्गहनं गभीरम् ॥ १॥

न मृत्युरासीदमृतं न तर्हि न रात्र्या अह्न आसीत्प्रकेतः | आनीदवातं स्वधया तदेकं तस्माद्धान्यन्न परः किञ्चनास ॥२॥

तम आसीत्तमसा गूहळमग्रे प्रकेतं सलिलं सर्वाऽइदम् | तुच्छ्येनाभ्वपिहितं यदासीत्तपसस्तन्महिनाजायतैकम् ॥३॥

कामस्तदग्रे समवर्तताधि मनसो रेतः प्रथमं यदासीत् | सतो बन्धुमसति निरविन्दन्हृदि प्रतीष्या कवयो मनीषा ॥४॥

तिरश्चीनो विततो रश्मिरेषामधः स्विदासीदुपरि स्विदासीत् | रेतोधा आसन्महिमान आसन्त्स्वधा अवस्तात्प्रयतिः परस्तात् ॥५॥

को अद्धा वेद क इह प्र वोचत्कुत आजाता कुत इयं विसृष्टिः | अर्वाग्देवा अस्य विसर्जनेनाथा को वेद यत आबभूव ॥६॥

इयं विसृष्टिर्यत आबभूव यदि वा दधे यदि वा न | यो अस्याध्यक्षः परमे व्योमन्त्सो अङ्ग वेद यदि वा न वेद ॥७॥

Translation (Basham 1954) The wonder that was India

1. Then even non-existence was not there, nor existence,There was no air then, nor the space beyond it. What covered it? Where was it? In whose keeping? Was there then cosmic fluid, in depths unfathomed?

2. Then there was neither death nor immortality nor was there then the torch of night and day.

The One breathed windlessly and self-sustaining. There was that One then, and there was no other.

3. At first there was only darkness wrapped in darkness. All this was only unillumined cosmic water. That One which came to be, enclosed in nothing, arose at last, born of the power of knowledge.

4. In the beginning desire descended on it - that was the primal seed, born of the mind. The sages who have searched their hearts with wisdom know that which is, is kin to that which is not.

5. And they have stretched their cord across the void, and know what was above, and what below. Seminal powers made fertile mighty forces. Below was strength, and over it was impulse.

6. But, after all, who knows, and who can say Whence it all came, and how creation happened the gods themselves are later than creation, so who knows truly whence it has arisen?

7. Whence all creation had its origin, the creator, whether he fashioned it or whether he did not, the creator, who surveys it all from highest heaven, he knows — or maybe even he does not know.