Stellar Parallax A nearby star's apparent movement against the background of more distant stars as the Earth revolves around the Sun is referred to as stellar parallax. This exaggerated view shows how we can see the movement of nearby stars relative to the background of much more distant stars and use that movement to calculate the distance to the nearby star. The parallax can be used to measure the distance to the few stars which are close enough to the Sun to show a measurable parallax. The distance to the star is inversely proportional to the parallax. The distance to the star in parsecs is given by The nearest star is proxima centauri, which exhibits a parallax of 0.762 arcsec, and therefore is 1.31 parsecs away. Some well-known examples of distance measurement by parallax are 61 Cygni at 1/3 of an arcsec, distance 3 parsecs, and Barnard's Star at 1.8 parsecs = 5.9 light years.   1 Parsec = 3.26163344 light year

SCHRÖDINGER'S CAT

Schrödinger's cat is a famous illustration of the principle in quantum theory of superposition , proposed by Erwin Schrödinger in 1935. Schrödinger's cat serves to demonstrate the apparent conflict between what quantum theory tells us is true about the nature and behavior of matter on the microscopic level and what we observe to be true about the nature and behavior of matter on the macroscopic level -- everything visible to the unaided human eye.
Here's  (theoretical) Schrödinger's experiment: We place a living cat into a steel chamber, along with a device containing a vial of hydrocyanic acid. There is, in the chamber, a very small amount of hydrocyanic acid, a radioactive substance. If even a single atom of the substance decays during the test period, a relay mechanism will trip a hammer, which will, in turn, break the vial and kill the cat. 
The observer cannot know whether or not an atom of the substance has decayed, and consequently, cannot know whether the vial has been broken, the hydrocyanic acid released, and the cat killed. Since we cannot know, according to quantum  law, the cat is both dead and alive, in what is called a superposition  of states. It is only when we break open the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive). This situation is sometimes called quantum indeterminacy or the observer's paradox: the observation or measurement itself affects an outcome, so that the outcome as such does not exist unless the measurement is made. (That is, there is no single outcome unless it is observed.)
We know that superposition actually occurs at the subatomic level, because there are observable effects of  interference , in which a single particle is demonstrated  to be in multiple locations simultaneously. What that fact implies about the nature of reality on the observable level (cats, for example, as opposed to electrons ) is one of the stickiest areas of quantum physics. Schrödinger himself is rumored to have said, later in life, that he wished he had never met that cat.

BIRTH OF THE UNIVERSE

 Physics of the early Universe is at the boundary of astronomy and philosophy since we do not currently have a complete theory that unifies all the fundamental forces of Nature at the moment of Creation.  Our physics can explain most of the evolution of the Universe after the Planck time (approximately 10^-43 seconds after the Big Bang). Events before the Planck time are undefined in our current science and, in particular, we have no solid understanding of the origin of the Universe (i.e. what started or ‘caused’ the Big Bang).

Cosmic Singularity: 

One thing is clear in our framing of questions such as ‘How did the Universe get started?’ is that the Universe was self-creating. This is not a statement on a ‘cause’ behind the origin of the Universe, nor is it a statement on a lack of purpose or destiny. It is simply a statement that the Universe was emergent, that it probably derived from an indeterminate sea of potentiality that we call the quantum vacuum, whose properties may always remain beyond our current understanding. Extrapolation from the present to the moment of Creation implies an origin of infinite density and infinite temperature (all the Universe's mass and energy pushed to a point of zero volume). Such a point is called the cosmic singularity. But the next level of inquiry is what is the origin of the emergent properties of the Universe, the properties that become the mass of the Universe, its age, its physical constants, etc. The answer appears to be that these properties have their origin as the fluctuations of the quantum vacuum. The properties of the Universe come from ‘nothing’, where nothing is the quantum vacuum, which is a very different kind of nothing. If we examine a piece of ‘empty’ space we see it is not truly empty, it is filled with spacetime, for example. Spacetime has curvature and structure, and obeys the laws of quantum physics. Thus, it is filled with potential particles, pairs of virtual matter and anti-matter units, and potential properties at the quantum level. The Universe is not filled by the quantum vacuum, rather it is ‘written on’ it, the substratum of all existence.

(also black holes are considered singularities)

Zeno’s Paradox of Achilles and the Tortoise

Zeno of Elea (circa 450 b.c.) is credited with creating several famous paradoxes, but by far the best known is the paradox of the Tortoise and Achilles. (Achilles was the great Greek hero of Homer's The Iliad.) It has inspired many writers and thinkers through the ages, notably Lewis Carroll and Douglas Hofstadter, who also wrote dialogues involving the Tortoise and Achilles.
The original goes something like this:

            The Tortoise challenged Achilles to a race, claiming that he would win as long as Achilles gave him a small head start. Achilles laughed at this, for of course he was a mighty warrior and swift of foot, whereas the Tortoise was heavy and slow.
            “How big a head start do you need?” he asked the Tortoise with a smile.
            “Ten meters,” the latter replied.
Achilles laughed louder than ever. “You will surely lose, my friend, in that case,” he told the Tortoise, “but let us race, if you wish it.”
            “On the contrary,” said the Tortoise, “I will win, and I can prove it to you by a simple argument.”
            “Go on then,” Achilles replied, with less confidence than he felt before. He knew he was the superior athlete, but he also knew the Tortoise had the sharper wits, and he had lost many a bewildering argument with him before this.
            “Suppose,” began the Tortoise, “that you give me a 10-meter head start. Would you say that you could cover that 10 meters between us very quickly?”
            “Very quickly,” Achilles affirmed.
            “And in that time, how far should I have gone, do you think?”
            “Perhaps a meter – no more,” said Achilles after a moment's thought.
            “Very well,” replied the Tortoise, “so now there is a meter between us. And you would catch up that distance very quickly?”
            “Very quickly indeed!”
            “And yet, in that time I shall have gone a little way farther, so that now you must catch that distance up, yes?”

            “Ye-es,” said Achilles slowly.
            “And while you are doing so, I shall have gone a little way farther, so that you must then catch up the new distance,” the Tortoise continued smoothly.
Achilles said nothing.
            “And so you see, in each moment you must be catching up the distance between us, and yet I – at the same time – will be adding a new distance, however small, for you to catch up again.”
            “Indeed, it must be so,” said Achilles wearily.
            “And so you can never catch up,” the Tortoise concluded sympathetically.
            “You are right, as always,” said Achilles sadly – and conceded the race.

Time Line of the Universe 2008

The expansion of the universe over most of its history has been relatively gradual. The
notion that a rapid period "inflation" preceded the Big Bang expansion was first put forth 25
years ago by Alan Guth. The new WMAP observations favor specific inflation scenarios over
other long held ideas. (Image courtesy of NASA/WMAP Science Team)

COBE All-Sky Map 1992

The Cosmic Background Explorer (COBE) satellite was launched in 1989, twenty five
years after the discovery of the microwave background radiation in 1964. In 1992, the COBE
team announced that they had discovered “ripples at the edge of the universe”, that is, the first
sign of primordial fluctuations at 380,000 years after the Big Bang. These are the imprint of the
seeds of galaxy formation. These appear as temperature variations on the full sky map that
COBE obtained (shown above). Red areas represent areas with slightly higher temperatures
and blue areas a slightly lower temperature than the mean.