Natural Sciences

Understanding Natural Phenomena 2: The Big Bang

Editor’s Note: This article is a part of the series Understanding Natural Phenomena.

How and when did our universe begin?

According to the most acceptable scientific model at present, our universe was born ~13.7 billion years ago. A so-called ‘Big Bang’ occurred at the moment of the birth of the universe, and this moment was also the Time Zero for our universe.

But how can something emerge out of nothing? Is that not a violation of the law of conservation of mass and energy? Was there not a Creator involved? No.

A proper explanation requires reference to what is called quantum field theory. But I shall attempt a simple explanation here, just to convey the point that there was no net creation or annihilation of mass/energy involved.

We all know about the force of gravity that the Earth exerts on all objects. If your mass is m, then your weight is mg, where g is ‘acceleration due to gravity’. The mass is a measure of the quantity of matter. The weight is a force; the force the Earth exerts to pull you towards its centre. [Newton’s second law of motion says that force is equal to mass multiplied by acceleration: F = m x a; and a is the same as g in our example.]

Your weight on the Moon would be one-sixth what it is on Earth because the Moon has a lower mass than the Earth, with a correspondingly lower value for its g.

The gravitational force or interaction is one of the four fundamental interactions of Nature. It is an attractive interaction (rather than a repulsive interaction). There is a force of gravitational attraction between any two objects. It is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them. For example, if the distance is doubled, the gravitational force of attraction becomes one-fourth.

Consider an object (say of mass m1) that is so far from everything that there is no gravitational force on it. This is really not possible, but just imagine it as an idealization. We say that it is a ‘free’ object, free from any gravitational force acting on it.

Next, consider another object, of mass m2, at a certain finite distance from the first object. The two attract each other. Physicists speak of this as a negative-energy configuration, because (positive) energy needs to be spent to take the two objects so far away from each other that they are free of each other’s force of attraction. By contrast, a positive–energy configuration would be one in which the two objects repelled each other, rather than attracting.

So, the gravitational interaction makes a negative contribution to the overall energy.

The other big idea I have to introduce here is that mass and energy are inter-convertible. This fact is embodied in the famous Einstein equation: E = mc2. Here c is the speed of light in vacuum. The equation says that if a mass m disappears, an equivalent amount of energy E would be produced or released.

This is how energy is produced in our Sun (by thermonuclear reactions). The mass of five atoms of hydrogen (or rather an atom of ‘deuterium’ (which is twice as heavy as an atom of hydrogen) and an atom of ‘tritium’ (thrice as heavy as an atom of hydrogen)) is a little more than that of an atom of helium and a charge-neutral particle called the ‘neutron’. In the interior of the Sun, conditions are right for the fusing of deuterium and tritium atoms, and the creation of an atom of helium plus a free neutron; the balance mass appears as energy. We receive some of this life-sustaining solar energy on Earth.

Similarly, in a fission-based nuclear reactor we produce energy by losing a little mass of, say, uranium. The nucleus of an atom of uranium captures a neutron to form a ‘compound nucleus’. This then splits (fissions) to two different nuclei the sum total of the masses of which is a little less than the mass of the compound nucleus. The balance mass appears as kinetic energy (same as heat energy) of the particles involved.

What happened at the Big Bang was that there was a simultaneous emergence of the gravitational interaction. There was an explosion of sorts, in which radiation (and, a little latter, matter) emerged. The universe has been expanding ever since then. Expansion means an increase in the distances between the celestial bodies. Such ever-increasing distances mean a build-up of negative energy, which gets compensated by the creation of an equivalent amount of matter.

This is how mass gets created out of ‘nothing’, and there is no violation of the law of mass/energy conservation. This ‘nothing’ is actually a vacuum, which has some remarkable properties which can be described in the language of quantum mechanics only. Further, according to Einstein’s theory of gravitation (to be described in a future post), the existence of a certain ‘cosmological constant’ can endow empty space with mass/energy.

But let us not get into those details yet. For the time being, suffice it to say that our universe emerged out of nothing, and this did not require the intervention of a Creator. The book by Hawking & Mlodinow explains that in some detail.

Of course, there are other models which compete with the Big Bang model, and the final word has not been said yet. Science is open to all ideas, subject to rational analysis and experimental verification. One such model postulates a cyclical set of events, involving an endless series of Big Bangs and Big Crunches. But then, in such a model, there is no need to argue how matter can emerge out of nothing.

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About the author

Vinod Wadhawan

Dr. Vinod Wadhawan is a scientist, rationalist, author, and blogger. He has written books on ferroic materials, smart structures, complexity science, and symmetry. More information about him is available at his website. Since October 2011 he has been writing at The Vinod Wadhawan Blog, which celebrates the spirit of science and the scientific method.


  • \\You say\\What happened at the Big Bang was that there was a simultaneous emergence of the gravitational interaction\\

    gravitational interaction happened without mass (matter)?
    \\You say\\

    There was an explosion of sorts, in which radiation (and, a little latter, matter) emerged\\

    Without matter, an explosion occured?

    \\You say\\
    This ‘nothing’ is actually a vacuum, which has some remarkable properties\\

    Vaccum by definition means nothing., How can nothing have remarkable properties?.

    A very nice explanation though for us beginners, Thanks for the article.

    • It seems your questions are all semantically based, that is the limitations of language have generated them. Only because we are taught in grade school that gravity acts on mass(es) can we then be surprised to hear that we can have a gravitational interaction without mass – since energy and mass are interchangeable gravity acts on mass and energy both, in fact one of the earliest demonstrations of General Relativity was the observations of light from stars the path of which was deflected by the Sun, gravity acting on pure radiant energy.

      Generally “explosion” is not a term to be used with the Big Bang. Expansion is more accurate, since explosion implies there was something – space – to explode into, which is not correct. Energy/mass, time/space came into existence at the instant of the Big Bang and the expansion has proceeded since.

      “Vacuum” by definition means what physicists define it to mean, and not the grade-school definition we learn. The vacuum has properties and is an active participant in quantum processes – without accounting, for example, for “virtual particles”, which arise from the vacuum according to Heisenberg’s Uncertainty Principle, we could not account for the apparent charge of electrons or their behaviour or for the evaporation of Black Holes (a la Stephen Hawking)

      • @Allan,
        I agree, I am a beginner and also not a science guy.

        My point was, Whatever be the word, Explosion or expansion (where is it expanding into?), How come the gravitational force or interaction happened?

        “Vacuum” by definition means what physicists define it to mean,
        Its ok to say “Vaccum” as per physics is “etc., etc.,
        But Saying ““Vacuum” by definition means what physicists define it to mean” is like saying
        You have to accept vacuum as told by the physicists (not different from a religious propaganda)

        The word itself stems from the Latin adjective vacuus for “empty”. (wikipedia).

        Empty means devoid of anything. Its ok to say as per physics, Vacuum means devoid of matter, so that there might be some other force/pressure acting on it (partial vacuum)

        In my opinion gravity does not act on mass, but also without mass (either as an energy or as a mass), there wont be any gravity (force), but only pure Vacuum.

        • Arguing by definitions has its pitfalls.

          And no. You don’t have to take the physicists at their word. What you can do is, learn the necessary math and physics and see for yourself. Unlike religion, which makes every excuse possible for its baseless assumptions (like the need of a guru), learning science in the age of the Internet isn’t that hard. Knowledge is just a google away.

  • Here the ‘nothing’ of classical physics is not the same as the ‘nothing’ of quantum mechanics. Classical mechanics fails to describe vacuum properly. All laws of Nature are quantum mechanical. Vacuum does not, by definition, mean nothing.

  • A response to your post.

    The only way you can bring objects that are in a state of chaos and disorder into order, is through a power or force that is great than the those objects that are in that chaotic state.

    An abstract example would be…if a satellite blows up in outer space, the debris from that satellite will continue in that state of chaos and disarray seemly forever. However, what if we found this debris in a specific type of order. For example all aluminum parts would be together, all copper together, etc. From that order we would understand that something (a force greater than these objects in a state of chaos and disarray) has put these parts in a specific kind of order.

    Likewise, if the universe started with a chaotic event(big bang) than the order that we have now,(creation) is a result of a force or power that was great enough to take matter out of a state of chaos and disorder and put them in a specific kind of order.

    From this order we can get form a clear understanding of the force, power or God that is behind it.

  • Vacuum is not the ‘nothing’! Well, then how and where is that something going to be attached to this ‘vacuum’? Of course it can be only in terms of ‘quantum field theory. Don’t you think this something which is going to make the ‘vacuum’ different from ‘nothing’ is far more important than the secret of creation of this universe? Can any light be shed on this ‘something’ accruing to this vacuum? Without this problem will be as difficult as at the beginning itself, I think.

  • Good overview.. need more details….more pro’s and con’s of the theory.. more detail on origin of the theory and proponents of it…wat are the possibilities that if Einstein’s equation goes wrong.. wat might emerge.. role or string theory..

    • The sole purpose of this article was to introduce the idea that the gravitational potential is attractive, and therefore makes a negative contribution to the total energy. And this feature carries over even into the quantum field theory. For everything else, please wait till I introduce the basics of quantum field theory and relativity. This series is addressed to lay persons, and not to experts. Of course, the experts are always welcome to join the discussion with insightful comments.

  • Hello Prakar

    Where does gravity come from? The best ideas that I have heard suggest that the forces of nature are exactly what one would expect in order to preserve symmetry in nature, that is the uniformity of the laws of nature through time, and space and so forth.

    Vacuum had a meaning for the Greeks but now it has a technical meaning in physics and certain properties (for example the vacuum energy which, if it exists, is what is pushing the expansion of the universe at greater and greater rates). In order to understand what is meant by “vacuum” we need to know the mathematics of quantum mechanics and cosmology, which is beyond most of us. Certainly gravity is defined to operate on mass-energy (any entity with mass-energy, which is all of them, as far as I know, interacts gravitationally with other entities) – not only defined to work thus, but observed to work thus in countless experiments, which trump opinion and personal definitions. As I think about it “vacuum” may be superfluous; perhaps we only need to consider the properties of space as it expands

    Hello Satish

    We agree I think – the definitions I speak of are the mathematical, technical definitions of physics, which are all that matter in the discussion. The nebulous definitions of philosophy won’t get us anywhere, but as a I mentioned above, I think the math is beyond most of us, and so we have to take the descriptive definitions put forth by physicists and hope they are reasonable if we wish to understand.

  • According to the most acceptable scientific model at present, our universe was born ~13.7 billion years ago////////
    Yes..We have a lot of scientific evidences which prove that our universe is so old than we expect. But, according to the ‘Book of Genesis’ ; god created this universe , 23 October 4004 BC Sunday(James Usher).
    It sounds so funny that most people disbelieve in ‘Big bang’ theory blindly believe in ‘Intelligent design’ of god!!!!!!

    • The Big Bang Theory (BBT) is not only opposed by irrational religious people. The BBT has been criticized by well known astro-physicists like late Sir Fred Hoyle, Geoffrey Burbidge, Chip Arp, Lerner and our own Professor Emeritus J.V. Narlikar being amongst the most famous names. If one goes deeper into the BBT, one finds that it has itself acquired a status of a religious cult. Though the proponents of the theory may be donning the cloak of science, there are a lot of variables that lie or exist within the imagination of these scientists. Dark matter, dark energy, black holes etc which exist only in their mathematical calculations and for which no empirical evidence has been found. Just because something can be proven by rigid mathematical calculations, does not mean it exists in nature, like for example, white holes? Why do I think BBT is a religion in scientific cloak because the first red flag that comes up is that it was proposed by Lemaitre,a Belgian catholic priest, who wanted to prove the origins of the Cosmos to fit the biblical version of the Universe. The chance discovery of galactic red shift by Edwin Hubble. Even though Edwin Hubble explicitly stated that “red shift” of the distant stellar objects should not be taken as an evidence for expansion as the light might get red shifted due to variety of other reasons.

      Furthermore, Lemaitre never suggested a relic of the BB, now popularly known as “Cosmic Microwave Background Radiation” would be found. Gamov and other scientists predicted the relic radiation and calculated the temperature of its thermal radiation from 5K to 50K. Whereas, the Arthur Eddington, a proponent of Steady State calculated that space heated by relic radiation should have a black body temperature of 3K, which is remarkably closer to the actual computed temperature of the CMBR at 2.7K, which also explains the uniformity of the radiation in whichever direction we see.

      The only point I wish to drive home is that scientists are human beings like us and it is but natural to assume that they are not entirely de-sensitized of the religious and theological leanings. Bias plays a big role in our life, in the decisions that we make and majority of the scientists are no exceptions to the rule.

      The scientific community has to start seriously tackling with other competing theories in cosmology and just not put all attention to the BBT.

      • Let the best theory win. People are welcome to come up with a better theory. It is unimportant how a person conjures up a hypothesis or a model. The final test is experimental evidence. At present there is overwhelmingly more evidence in favour of the Big Bang theory than for any alternative theory.

        • Tomorrow if a different theory better explains the data, the Big Bang theory would be abandoned. That is how science works. My information is that religions do not work like that. Your information seems to be different.

          Scientists have human failings, but science has self-correcting mechanisms. This is not the case with religions.

          • Dear Professor Wadhawan,

            The alternative thoery would come into existence if the present scientific establishment casts aside its romance with BBT and allocates human, financial resources and equipment time for the study of alternatives. Also I think particle physics is doing more harm than good to the study of Cosmology. While, particle physics should complement astro-physics but it must not be in the driver’s seat. There are astrophysicists that have impeccable reputations that do not agree with the current ruling theory.

            The attitude of the establishment to ignore dissident voices and say that those theories do not hold water is just as unscientific in attitude and approach as it can get. One more thing I wish to add here that researches in cosmology are being conducted in the West, where Christianity and Biblical thought is dominant and it could be possible that establishment (both government and academic) only support those ideas that conform to a certain religious belief.

            You had promised me, a while ago, that you will discuss the contentious issues of BBT like “Horizon problem”, “Flatness Problem”, “Monopole problem” etc here. May be I missed them, could you please provide a link to those articles?

          • What you’re saying is a conspiracy theory at best. BBT is a severe blow to Christianity and it takes a certain stretch of imagination to think that a 13.7 billion year old Universe is somehow consonant with the Biblical worldview.

        • I agree that the best theory wins. I am not against any theory, I am just against the prejudiced, biased and one dimensional approach, the current scientific establishment has towards BBT, while ignoring other alternative competing theories. Like I said earlier, when new observations are found, which contradict the present theory (BBT), the theory is modified to fit the current observations and new variables are introduced. Like a little over ten years ago, astrophysicists claimed the expansion of the Universe was slowing down and now they claim the contrary and have devised a new variable “dark energy”, something that was not originally predicted BBT theory. Non baryonic dark matter is another “hypothetical” element, which has not been detected through any known means, yet the academics just take it as something that has been proven beyond reasonable doubt. Repeated experiments at CERN have come to a nought. Does anybody remember “aether”, which was supposed to fill up cosmos, that scientists thought acted as a medium for light to travel. It was only later proved that light can travel in a vacuum.

          Wide acceptability of theory, concept, idea does not mean that it is correct. Many scientists in the past centuries thought of the Universe as centred around the Earth. Tycho Brahe, mentor of Johannes Kepler believed in Geo-centric model of the Universe just like his other contemporaries did.

          • Satish,

            What I said is not something of my own making but it is in fact the opinion of those within the academic circles who have faced discrimination and denial of equipment usage time by the by the higher ups. BBT was devised by Georges LeMaitre, a Belgian catholic priest turned astro-physicist who wanted (not explicitly) to prove that Universe was “created”, as in Biblical sense. When he explained the BBT to Einstein, Einstein reportedly told LeMaitre that his calculations were ok but his physics was abominable. For an astro-physicist, no greater insult can hurled at him/her than saying that his/her physics is worthy of contempt.

          • Newton was also a staunch Christian who wanted to unravel the workings of The Maker. That should tell you something about how science works and where your prejudices lie.

          • This just got in:



            “A team using the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory, along with other telescopes, has mapped the motions of more than 400 stars up to 13 000 light-years from the Sun. From this new data they have calculated the mass of material in the vicinity of the Sun, in a volume four times larger than ever considered before.

            “The amount of mass that we derive matches very well with what we see — stars, dust and gas — in the region around the Sun,” says team leader Christian Moni Bidin (Departamento de Astronomia, Universidad de Concepcion, Chile). “But this leaves no room for the extra material — dark matter — that we were expecting. Our calculations show that it should have shown up very clearly in our measurements. But it was just not there!””

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