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 Bg1. What is the concept of Time? Do Time and the Universe begin with a dense point called the Big Bang?

There are many definitions of time in mathematics and physics, I will discuss the physical definition of time.  In physics, there is something called the arrow of time which tells about the different notions of time.  The arrow of time is the "one-way direction" or "asymmetry". It was developed in 1927 by British physicist "Arthur Eddington". According to Eddington, this direction could be determined by studying the organization of atoms, molecules, and bodies, and might be drawn upon a four-dimensional relativistic map of the world. A few examples of the arrow of time are as follows

(i). The thermodynamic arrow of time: 

The thermodynamic arrow of time is provided by the second law of thermodynamics, which says that in an isolated system, entropy tends to increase with time. Entropy can be thought of as a measure of microscopic disorder; thus the second law implies that time is asymmetrical with respect to the amount of order in an isolated system: as a system advances through time, it becomes more statistically disordered. This asymmetry can be used empirically to distinguish between the future and past, though measuring entropy does not accurately measure time. Also, in an open system, entropy can decrease with time.  

(ii). Cosmological arrow of time:

If we believe in the theory of the Big Bang then time began just after the Big Bang. The cosmological arrow of time points in the direction of the universe's expansion. It may be linked to the thermodynamic arrow, with the universe heading towards a heat death (Big Chill) as the amount of thermodynamic free energy becomes negligible. Alternatively, it may be an artifact of our place in the universe's evolution, with this arrow reversing as gravity pulls everything back into a Big Crunch. 

(iii). Particle physics (weak) arrow of time:

Certain subatomic interactions involving the weak nuclear force violate the conservation of both parity and charge conjugation, but only very rarely. An example is the kaon decay. According to the CPT theorem, this means they should also be time-irreversible, and so establish an arrow of time. Such processes should be responsible for matter creation in the early universe. 

(iv). Quantum arrow of time:

Quantum evolution is governed by equations of motions that are time-symmetric (such as the Schrödinger equation in the non-relativistic approximation), and by wave function collapse, which is a time-irreversible process, and is either real (by the Copenhagen interpretation of quantum mechanics) or apparent only (by the many-worlds interpretation and relational quantum mechanics interpretation). The theory of quantum decoherence explains why wave function collapse happens in a time-asymmetric fashion due to the second law of thermodynamics, thus deriving the quantum arrow of time from the thermodynamic arrow of time. 

Really Time and Universe begin with Big Bang from a dense dot?

Some people think that the universe begins with the Big Bang. The Big Bang theory was first proposed by mathematician Georges Lemaître in 1927. The “big bang” wasn’t a “bang” at all, at least not in the common definition. It didn’t explode in a scene of shrapnel and fire. The big-bang theory of the universe is derived from Albert Einstein’s general theory of relativity and the idea that the universe expanded from a minuscule dense collection of energy called a singularity. There was no bang, just a vast expansion of extremely condensed material.  

So why describe the theory with such a misleading name? To mock it, perhaps. Sir Fred Hoyle snidely referred to the theory as the “big bang” to reduce it to absurdity, and it stuck. Hoyle believed, contrary to the big-bang theory, that the universe itself did not have a beginning, rather the components inside it did. This is called the steady-state theory, which was developed by Indian scientists Jayant Vishnu Narlikar and Fred Hoyle, and has decreased in popularity in light of the common acceptance of the big-bang theory.

Big Bang theory tells us that all space and time were condensed into very tiny space (almost zero volume) which had infinite density, called a singularity. In physics density is quantified by dividing mass by volume, meaning that the equation to determine the density of a singularity divides by zero. If that doesn’t hurt your brain, this will: Because all of space and time existed within the singularity, the singularity itself did not exist within space or time. 

The universe as we know it (or barely know it) is the result of this singularity expanding and cooling. Since the singularity itself was not in a location on the planes of space or time, there is no center of the universe; everything is expanding from everything else at an equal rate. As for the origins of the singularity, or even what existed before it is not known till now. 

In 1968 and 1970, Roger Penrose, Stephen Hawking, and George F. R. Ellis published papers that showed that mathematical singularities were an inevitable initial condition of relativistic models of the Big Bang. Then, from the 1970s to the 1990s, cosmologists worked on characterizing the features of the Big Bang universe and resolving outstanding problems. In 1981, Alan Guth made a breakthrough in theoretical work on resolving certain outstanding theoretical problems in the Big Bang models with the introduction of an epoch of rapid expansion in the early universe he called "inflation".

But, many people believe that before the Big Bang, there was a big crunch, which tells us that our universe is a bouncing universe and the cycle of the Big Bang to the big crunch will repeat. As we know the age of our universe is 13.7 billion years and it is continuously expanding as confirmed by the CMB (Cosmic Microwave Background) experiment. But, this expansion will reach some peak value and after that, it will start shrinking and approaching the next big crunch. Some of the models suggested that the next big crunch where the universe again will shrink to a dense dot will come 18 billion years from now. So, you can't say the time and our universe began with the Big Bang only. This is again still an open question whether the Big Bang is true or the concept of a bouncing universe is true.

Bg 2. What is the meaning of Time Travel? Is Time Travel possible? What are the possible ways of Time Travel?

 Ans-: Coming soon....

Bg 3. What are the Black Holes, White Hole, and Worm Hole? Why are we not getting information from Black Holes? Is there Information loss inside the Black Hole, if not, how will we get the information stored inside the Black Hole?

Ans-: Coming soon....

Bg 4. What are the Aliens? Do Aliens exist? What do they look like? Can we meet them in the future? Suppose we meet then how will we communicate with them?

Ans-: Coming soon....

Bg 5. Why Coronal (Solar Corona) Heating is Mysterious? Are Thermodynamics laws violating near the Sun's surface? What is Parker's probe and how it will help to study the Solar activity?

Ans-: Coming soon....

Bg 6. Why Quantum Mechanics Have Quantum Measurement Problems? Why Quantization Of Classical Gravity will not give you Quantum Gravity? Why do we need to change the Postulates Of Quantum Mechanics?

Ans-: Coming soon....

Bg 7. Which theory is the best theory to explain Quantum Gravity? Are current theories like String theory and Loop quantum gravity capable of explaining Quantum gravity or do we need a new theory?

Ans-: Coming soon....

Bg 8. Why are we using a Commutator to Quantize the Physical things? What are the real Physical Meanings of Commutators?

Ans-: Coming soon....

 Bg 9. Did an apple ever fall on Newton's head? How true is this story and how did he think of the theory of gravity?

Ans-: Coming soon....